Land-facing, southwest Greenland Ice Sheet movement decreasing

October 28, 2015 by Samson Reiny
Meltwater streams and rivers flow on the surface of the western area of the Greenland Ice Sheet. Credit: Andrew Sole, University of Sheffield

In the face of decades of increasing temperatures and surface melting, the movement of the southwest portion of the Greenland Ice Sheet that terminates on land has been slowing down, according to a new study being published by the journal Nature on Oct. 29.

Researchers derived their results by tracking ice sheet movement through Landsat satellite images taken from 1985 to 2014 across a roughly 3,088-square-mile (8000-square-kilometer) region in southwest Greenland. They found that, between 2007 and 2014, ice movement slowed in 84 percent of the study area, during a period of high surface melt, compared to the years between 1985 and 1994. The average slowdown was 12 percent, or 32.8 feet (10 meters) per year.

The finding is contrary to the widely held view that a greater amount of surface melting will result in faster-moving ice sheets, as the movement of both ocean- and land-terminating ice sheets is caused in part by surface meltwater, which makes its way to the bedrock through openings in the ice and acts as a lubricant. The amount of meltwater draining from the ice sheet in four out of the five years between 2007 and 2012 has been the most substantial of the last 50 years.

Researchers found that while the larger summertime meltwater volume of recent years has led to greater lubrication of the ice sheet base, speeding up its flow as expected, by the end of summer the meltwater has also established channels at the base that act as efficient drainage systems to lessen the water under the ice sheet, slowing it down by winter.

"This suggests that further increases in melting will not cause these land-terminating margins of the ice sheet to speed up," said lead author Andrew Tedstone, a glaciologist at the University of Edinburgh, Scotland.

"Nevertheless, it is unclear how much more slowdown we will see under the current and future melting conditions," said co-author Noel Gourmelen, University of Edinburgh. "More research and observation are needed to determine this."

While these results may be viewed as good news for the Greenland ice sheet, they are offset by the fact that it is not the change in movement of the land- but rather the ocean-terminating portion of the ice sheet that is contributing to .

"The ongoing acceleration of both glacier surface melt volumes and the ice motion of ocean-terminating glaciers ensures that Greenland's contribution to sea level rise will likely increase in our warming world," said co-author Peter Nienow, University of Edinburgh.

A river flows in the western region of the Greenland Ice Sheet. Credit: Credits: Andrew Sole, University of Sheffield

The Greenland Ice Sheet is the second largest mass of ice on Earth, containing enough water that if it all melted, ocean levels would rise by about 20 feet. Greenland has shed on average 303 gigatons of ice per year since 2004, and with every successive year the loss has increased by 31 gigatons. (Each gigaton equals one billion metric tons.) Recent estimates suggest that surface melting is responsible for 60 percent of Greenland's ice sheet losses, while the remainder is caused by discharge into the ocean.

Thomas Neumann, a cryospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland who was not involved in the study, said the finding highlights the importance of having access to a long time series of remote sensing data, such as the Landsat record. "By analyzing velocity estimates extracted from 30 years of Landsat data, this study highlights the complex, and sometimes counterintuitive, interplay between surface meltwater and ice motion."

NASA and the United States Geological Survey have already begun work on Landsat 9 to help continue this record.

Explore further: Study shows increased summer melting not increasing annual movement of Greenland ice sheet

More information: Decadal slowdown of a land-terminating sector of the Greenland Ice Sheet despite warming, Nature, DOI: 10.1038/nature15722

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14 comments

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Returners
2.1 / 5 (7) Oct 28, 2015
"More research and observation are needed to determine this."


Always.
Maggnus
4.6 / 5 (10) Oct 28, 2015
Always.


They have a name for it too. It's called "science".
jeffensley
1.7 / 5 (6) Oct 29, 2015
Always.


They have a name for it too. It's called "science".


Unfortunately for some, science is concrete, inflexible, and infallible.
Maggnus
4.1 / 5 (9) Oct 29, 2015
Unfortunately for some, science is concrete, inflexible, and infallible.


Usually the religious or the US conservative right, but only went it supports their pre-determined views.

There are some fools who think that science is subject to their opinion as well.
jeffensley
2.3 / 5 (6) Oct 30, 2015
Usually the religious or the US conservative right, but only went it supports their pre-determined views.

There are some fools who think that science is subject to their opinion as well.


Just like people are supposed to be subject to your opinion? From my experience, the far left is the most guilty of seeing science as God-like and infallible. Human's want something to believe in... if you shun religion then odds are you put your faith in the human intellect to understand and solve all problems. For those who put too much faith in it, the mistakes and flaws of science are hard to bear and instead of simply acknowledging its inherent flaws, they lash out at those who dare question it.
gkam
1.5 / 5 (8) Oct 30, 2015
"For those who put too much faith in it, the mistakes and flaws of science are hard to bear and instead of simply acknowledging its inherent flaws, they lash out at those who dare question it."
-------------------------------

Really? Do they torture them ? Put them on the Rack and break them? Tie them to posts and slowly burn them alive in front of everybody else??

That is religion, Toots, not science.
jeffensley
2.3 / 5 (6) Oct 30, 2015
Really? Do they torture them ? Put them on the Rack and break them? Tie them to posts and slowly burn them alive in front of everybody else??


Thankfully not, though I'm sure some would love to. Mostly they do what you do and attempt to shame people via insults and labels like "deniers" in an effort to check what you apparently feel is threatening dissent against the status quo. Truly Science has become a religion for some.
gkam
1.7 / 5 (6) Oct 30, 2015
"Truly Science has become a religion for some."
-------------------------------------

I am open to change. Give me evidence.

It ain't easy to change important opinions - I once volunteered for Vietnam. I learned a lot by that one.
Maggnus
5 / 5 (6) Oct 30, 2015
Just like people are supposed to be subject to your opinion?
Hilarious! You talk about lashing out - do you understand what "hypocrisy" means?

From my experience, the far left is the most guilty of seeing science as God-like and infallible. Human's want something to believe in... if you shun religion then odds are you put your faith in the human intellect to understand and solve all problems. For those who put too much faith in it, the mistakes and flaws of science are hard to bear and instead of simply acknowledging its inherent flaws, they lash out at those who dare question it.
A lot of assumptions, and a clear insight into your belief. You should look in a mirror.
jeffensley
1 / 5 (2) Oct 31, 2015
My statements are true of many of the commenters on this site, especially in regards to the climate change issue. Each study (at least any with apocalyptic projections) is treated as a concrete truth that must be reacted to IMMEDIATELY. Oddly these same people are pretty silent when other studies show that climate change is slower than believed, or nature adapts to it better than we thought, or there are actual benefits to a warmer Earth, etc... It's basically partisanship brought to an issue that isn't political. I take a firm stance in saying I don't think we know as much as we think we know and maybe we shouldn't make rash decisions based on amazingly incomplete data and fantasy-like projections. That's not all that unreasonable.
gkam
2 / 5 (4) Oct 31, 2015
Gosh, Jeff,we were just wondering why those folk who needed no proof at all to mass-murder 200,000 Iraqi civilians who had done nothing to us, now need absolute proof to save the Earth.

Why is that?
jeffensley
1 / 5 (2) Oct 31, 2015
Gosh, Jeff,we were just wondering why those folk who needed no proof at all to mass-murder 200,000 Iraqi civilians who had done nothing to us, now need absolute proof to save the Earth.

Why is that?


You're really reaching buddy. The Earth doesn't need saving but it's in our best interested to protect its resources. We don't need dire predictions of doom or a fledgling, mostly statistical-based science to tell us that.
gkam
2 / 5 (4) Oct 31, 2015
How about a thermometer?
Nik_2213
5 / 5 (2) Nov 02, 2015
So, the gradient is such the SW dry-foot glaciers are thawing in place rather than sliding off ?

Interesting. Still leaves the NE mega-valley glaciers with wet feet...

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