Greenland ice flow likely to speed up

August 16, 2017
The researchers carried out seismic surveys at a surface lake like this. Credit: C F Dow

Flow of the Greenland Ice Sheet is likely to speed up in the future, despite a recent slowdown, because its outlet glaciers slide over wet sediment, not hard rock, new research based on seismic surveys has confirmed. This sediment will become weaker and more slippery as global temperatures rise and meltwater supply becomes more variable.

The findings challenge the view that the recent slowdowns in ice flow would continue in the long term.

The research, published in Science Advances, was led by Professor Bernd Kulessa, a glaciologist at Swansea University, and involved experts from the UK, Canada, Sweden and Norway.

Previous research has identified two possible mechanisms for controlling the speed of the ice flow. The first is self-regulation, which proposes that slow down at the end of the summer because large networks of channels drain water away at the base, increasing frictional resistance to ice flow. The second is to do with the soft sediments that recent research has shown underlie glaciers; in this model, changing patterns of water flow alternately weaken or strengthen the sediment, making it more or less slippery, and thus enhancing or decreasing the speed of ice flow.

The team's aim was to test the sediment theory for the first time using measurements on the .

They carried out seismic surveys at a surface lake on the Greenland Ice Sheet, where the ice is around 1.2 km thick. This involves using a series of controlled explosions to send acoustic waves through the glacier, which then bounce back to a series of geophones -small microphones - set up on the glacier. The data are then analysed to delineate and characterise the physical properties of the sediment underneath the ice.

Their seismic observations confirmed that:

The researchers use controlled explosions to send acoustic waves through the ice, with microphones to track the data, which allows them to analyse the sediment under the ice. Credit: A D Booth

  • sediment played the key role in controlling ice sheet flow;
  • variability in meltwater supply controls sediment's slipperiness;
  • weakening of subglacial sediment leads to accelerated ice flow.

They conclude that:

  • The future response of the ice sheet to climate warming will be more complex than a simple case of the flow slowing down due to self-regulation
  • Understanding how widespread sediments are and how their properties change with meltwater supply is essential if we are to build up an accurate picture of future patterns of ice flow

Professor Bernd Kulessa of the College of Science at Swansea University, lead researcher on the project, said:

"Greenland's margin has many that act as fast conveyor belts of ice. Thousands of surface lakes act as taps that deliver meltwater to the ice base, turning it into a slippery bathtub.

Because it is difficult to see beneath them we surmised until recently that the glaciers slip over hard rock, but we realise now that they often slip over sloppy wet sediments instead.

In a warming Arctic climate more ice will melt and make the sediments even sloppier and more slippery, so that fast ice can occur long into the future.

This discovery leaves us concerned because we have so far accepted the exact opposite - that Greenland's icy conveyor would slow down."

Explore further: Ice loss accelerating in Greenland's coastal glaciers, study finds

More information: B. Kulessa el al., "Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow," Science Advances (2017). advances.sciencemag.org/content/3/8/e1603071

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6 comments

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aksdad
1 / 5 (9) Aug 17, 2017
In other words, the previous research that said the slowdown may continue could be wrong based on the latest hypothesis, even though there appears to be no evidence of accelerating ice flow. Should be fun to see who's right. Pass the popcorn.
HeloMenelo
5 / 5 (8) Aug 17, 2017
Easy, the outcome always proves you wrong, being an antigoracle/waterprophet sockpuppet we expect no more. Yet.. again you are grasping at short straws ;)
J Doug
1 / 5 (1) Aug 18, 2017
This information should be of interest to anyone who has an interest in the Greenland ice sheet.
In 1942, eight U.S. WWII aircraft (2 bombers, 6 fighter planes) emergency-landed on the Southwestern coast of Greenland after encountering severe weather. The crews were rescued and the planes ultimately had to be abandoned at the landing site. So there the planes sat on the Greenland ice sheet, undetected, for more than 4 decades. The active search for the WWII planes had been ongoing since 1981, but it wasn't until 1988 that a group of artifact enthusiasts (Greenland Expedition Society) were able to finally locate the planes. The primary reason why it was so excruciatingly difficult to find the planes is that the explorers had originally assumed the planes were buried under ice that was relatively close to the ice sheet's surface. They weren't.
J Doug
1 / 5 (1) Aug 18, 2017
When the planes were finally found in 1988, 46 years after crash-landing on the Greenland ice sheet, they were buried under 260 feet (79 meters) of ice. In other words, between 1942 and 1988, the Greenland ice sheet gained mass at a rate of 57 feet (17 meters) per decade at that location. In 1992, the planes were impressively pulled out of the ice part-by -part. In that 4-year span between 1988 (discovery) and 1992 (recovery), the Greenland ice sheet had advanced with another 8 feet of ice, as the planes were 268 feet beneath the ice sheet surface when they were rescued.
It should come as no surprise that the Greenland ice sheet gained so many billion tons of ice during the 50 years from 1942 to 1992.
http://notrickszo...ose-600/
J Doug
1 / 5 (1) Aug 18, 2017
Greenland ice sheet mass balance reconstruction. Part I: net snow accumulation (1600-2009)
Journal of Climate 2012;

''We find a 12% or 86 Gt y-1 increase in ice sheet accumulation rate from the end of the Little Ice Age in ~1840 to the last decade of the reconstruction. This 1840-1996 trend is 30% higher than that of 1600-2009, suggesting an accelerating accumulation rate. The correlation of Ât(G) with the average surface air temperature in the Northern.''
J Doug
1 / 5 (1) Aug 18, 2017

We should all understand that before the Ice sheet melts or runs off to the sea, the temperature needs to get above 32 °F.
Summit Camp, Greenland
11:58 PM -02 on August 18, 2017 (GMT -0200)
Summit Camp | Change Station
Overcast
-1 °F
Feels Like -1 °F
https://www.wunde...45000076

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