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

Abstract

Abstract. 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 Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariæ Isstrøm. 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 Isbræ 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 estimate the duration of speedup periods (80–95 days) and to demonstrate a strong relationship between ice front position and ice flow at Jakobshavn Isbræ, 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 % (2015) and 18 % (2016) at Petermann Glacier and Zachariæ Isstrøm, 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.

Resolving Seasonal Ice Velocity of 45 Greenlandic Glaciers With Very High Temporal Details

“…Our dense observations also enabled us to classify Alison Glacier (16), Upernavik Isstrøm − III (26), and Helheim Glacier (28) as type 1 (Figures S16, S26, S28, S36, and Table 1). For instance, changes in ice front positions at Helheim Glacier (28) and Jakobshavn Isbrae (not measured in this study), two of Greenland's highest discharge glaciers, greatly influence their seasonal velocity variations Kehrl et al, 2017;Lemos et al, 2018). For instance, changes in ice front positions at Helheim Glacier (28) and Jakobshavn Isbrae (not measured in this study), two of Greenland's highest discharge glaciers, greatly influence their seasonal velocity variations Kehrl et al, 2017;Lemos et al, 2018).…”

A decade of variability on Jakobshavn Isbræ: ocean temperatures pace speed through influence on mélange rigidity

“…Ocean temperatures are expected to rise over the next century (Stocker et al, 2013), which will likely produce further retreat of Jakobshavn Isbrae. Superimposed on any trend for the last century, however, there is substantial multi-decadal scale variability of ocean temperatures in Disko Bay that correlates well with the Atlantic Multidecadal Oscillation (AMO) index, which has been linked to past changes on Jakobshavn Isbrae (Lloyd et al, 2011). Thus, whether Jakobshavn Isbrae can stabilize, at least temporarily, likely depends on whether a cycle similar to that of the last century produces an extended period (several more years to decades) of cooler waters in Disko Bay.…”

Greenland Ice Mapping Project: ice flow velocity variation at sub-monthly to decadal timescales

“…In particular, many glaciers in Greenland have sped up substantially over the last two decades (e.g. Joughin et al, 2010;Moon et al, 2012;Rignot and Kanagaratnam, 2006), including several of Greenland's largest glaciers (Howat et al, 2005;Joughin et al, 2004;Luckman et al, 2006). In addition to the ice sheet's outlet glaciers, slowflowing areas near its margin speed up and slow down seasonally (e.g.…”