Sentinels track Greenland’s summer speed-up

ESA’s Sentinel-1 mission has revealed exactly how fast Greenland’s glaciers are flowing into the Arctic Ocean.

The research, published in The Cryosphere, used Sentinel-1 data to show that Greenland’s largest glacier has actually slowed down by 10% since 2012, but that flow is seasonal, with summer ice speeds increasing by up to 25% on some parts of the ice sheet.

The study used Sentinel-1 to track Greenland’s four main glaciers, Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariæ Isstrøm, between 2014 and 2017.

With these glaciers alone containing enough water to increase global sea levels by 1.8 m, monitoring their flow is vital to understanding the overall ice sheet dynamics.

The fastest flowing glacier, Jakobshavn Isbræ, had reached a peak of 17 km per year in 2013, the result of an unusually warm summer.  But the Sentinel-1 data showed that, on average, it had actually slowed down by 10% between 2012 and 2017, to 12.5 km per year.

This was overlaid by a seasonal pattern, with the glacier accelerating by up to 14% over a three-month summer period, before slowing down again in winter.

Jakobshavn Isbrae ice flow

Lead author and CPOM research student Adriano Lemos explained: “We saw this summer speed-up at all four glaciers, reaching 25% at Petermann Glacier.  This means that speed needs to be monitored throughout the year to fully understand how the glaciers are moving.”

Until recently it was difficult to closely observe exactly how fast the glaciers were flowing, because they are remote, vast, and can change so rapidly. But the launch of the Sentinel-1 constellation (1A in 2014, followed by 1B in 2016), with its global coverage and short revisit times, means that small, weekly changes can be spotted.

Lemos added: “Sentinel-1 has real advantages for studying these glaciers.  We get more data, more often, so we can see the finer detail in even the most inaccessible and fast moving areas.”

The data also showed a relationship between glacier speed and the location of the calving front –where icebergs are born – and grounding line, where the ice leaves the bedrock and begins to float on the ocean.

Lemos said: “This shows how flow is influenced not only by the glacier’s surrounding environment, but also the nature of the ice itself.”

Co-author Dr Anna Hogg added: “Acquiring all this valuable radar data needed international coordination between multiple space agencies (ESA and DLR, the German Aerospace Centre).  This paper shows how our efforts are being rewarded through improving our understanding of environmental change in Greenland.”

Near real time ice velocity measurements for Greenland, as well as the Antarctic Ice Sheet, can be accessed via the CPOM data portal.

CPOM Director Andy Shepherd summarised: “We have shown how the new generation of radar satellites can give us important details on ice velocity across the Greenland Ice Sheet.

“Next, we will use Sentinel-1 to investigate the patterns seen here, further improving our understanding of how these glaciers will respond to a changing climate.”

The full reference is: Lemos, A. et al. (2018) Ice velocity of Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariæ Isstrøm, 2015–2017, from Sentinel 1-A/B SAR imagery, The Cryosphere doi:10.5194/tc-12-2087-2018