Melting and refreezing of deep Greenland ice speeds flow to sea, study says

Jun 15, 2014
The flat topography seen from a plane over Greenland is in sharp contrast to the jagged features found to be underlying much of the ice sheet. Credit: Kirsty Tinto

Beneath the barren whiteness of Greenland, a mysterious world has popped into view. Using ice-penetrating radar, researchers have discovered ragged blocks of ice as tall as city skyscrapers and as wide as the island of Manhattan at the very bottom of the ice sheet, apparently formed as water beneath the ice refreezes and warps the surrounding ice upwards.

The newly revealed forms may help scientists understand more about how sheets behave and how they will respond to a warming climate. The results are published in the latest issue of Nature Geoscience.

"We see more of these features where the starts to go fast," said the study's lead author, Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory. "We think the refreezing process uplifts, distorts and warms the ice above, making it softer and easier to flow."

The structures cover about a tenth of northern Greenland, the researchers estimate, becoming bigger and more common as the ice sheet narrows into ice streams, or glaciers, headed for the sea. As meltwater at the bottom refreezes over hundreds to thousands of years, the researchers believe it radiates heat into the surrounding ice sheet, making it pick up its pace as the ice becomes softer and flows more easily.

Since the 1970s, and as recently as 1998, researchers flying over the region mistook radar images of these structures for hills. Newer instruments flown during NASA's IceBridge campaign to map ice loss at both poles found the hills to be made of ice instead of rock. Bell, who had discovered similar ice features at the base of the East Antarctic ice sheet, recognized them immediately.

Melting and refreezing at the bottom of ice sheets warps the layer-cake structure above, as seen in this radar image from Greenland. Credit: Mike Wolovick

While mapping Antarctica's ice-covered Gamburtsev Mountains in 2008 and 2009, Bell and colleagues discovered extensive melting and refreezing along ridges and steep valley walls of the range. Though researchers had long known that pressure and friction can melt the bottom of ice sheets, no one knew that refreezing water could deform the layer-cake structure above. In a 2011 study in Science, Bell and colleagues proposed that ice sheets can grow from the bottom up, not just from the top-down accumulation of falling snow.

The current study builds on the findings from Antarctica by linking the bottom features to faster ice sheet flow. The researchers looked at Petermann Glacier in the north of Greenland, which made headlines in 2010 when a 100-square mile chunk of ice slipped into the sea. They discovered that Petermann Glacier is sweeping a dozen large features with it toward the coast as it funnels off the ice sheet; one feature sits where satellite data has shown part of the glacier racing twice as fast as nearby ice. The researchers suggest that the refreeze process is influencing the glacier's advance hundreds of miles from where Petermann floats onto the sea.

"Overall, these observations suggest that basal freeze-on is a key control on the large-scale flow of Petermann Glacier, a possibility that has not been explored previously," writes University of Texas researcher Joseph MacGregor in the same issue of Nature Geoscience.

Greenland's glaciers appear to be moving more rapidly toward the sea as climate warms but it remains unclear how the refreeze process will influence this trend, the researchers said.

Uplifted and deformed ice sheet in the fast flowing Petermann Glacier as seen in this radar image from Greenland. Credit: Mike Wolovick

They expected to find bottom features in the ice sheet's interior, as they did in Antarctica, but did not expect to see features at the edges, where lakes form and rivers flow over the surface, they said. Water from those lakes and rivers appears to fall through crevasses and other holes in the ice to reach the base of the ice sheet, where some of it apparently refreezes. Their discovery indicates that refreezing and deformation at the base of the ice sheet may be far more widespread than previously thought. Bell and her colleagues believe that similar features may come to light as other parts of Greenland and Antarctica are studied in closer detail.

Flying over northern Greenland during the 2011 Ice Bridge season, Kirsty Tinto, a geophysicist at Lamont-Doherty, sat up straight when the radar images began to reveal a deformed layer-cake structure. "When you're flying over this flat, white landscape people almost fall asleep it's so boring—layer cake, layer cake, layer cake," said Tinto, a study coauthor. "But then suddenly these things appear on the screen. It's very exciting. You get a sense of these invisible processes happening underneath."

Explore further: Image: Southwestern coast of Greenland captured from orbit

More information: Nature Geoscience DOI: 10.1038/ngeo2179

add to favorites email to friend print save as pdf

Related Stories

Lakes discovered beneath Greenland ice sheet

Nov 27, 2013

The study, published in Geophysical Research Letters, discovered two subglacial lakes 800 metres below the Greenland Ice Sheet. The two lakes are each roughly 8-10 km2, and at one point may have been up to t ...

Antarctica's Whillans Ice Plain ice flows are highly variable

May 06, 2014

The Whillans Ice Plain (WIP) is a roughly 20,000-square-kilometer (772-square-mile) region of the West Antarctic Ice Sheet that acts as a massive conveyor, driving glacier ice into the Ross Ice Shelf. As the climate changes, ...

Giant channels discovered beneath Antarctic ice shelf

Oct 06, 2013

Scientists have discovered huge ice channels beneath a floating ice shelf in Antarctica. At 250 metres high, the channels are almost as tall as the Eiffel tower and stretch hundreds of kilometres along the ...

Groundwater could fuel life under glaciers

May 22, 2014

Subglacial lakes in Antarctica might have nutrient-rich groundwater flowing into them, say scientists investigating the origin of the water in ice streams.

Recommended for you

Tropical Storm Dolly forms, threatens Mexico

1 hour ago

Tropical Storm Dolly formed off Mexico's northeastern coast on Tuesday and headed toward landfall in Tamaulipas state, threatening to spark floods and mudslides, forecasters said.

Giant garbage patches help redefine ocean boundaries

3 hours ago

The Great Pacific Garbage Patch is an area of environmental concern between Hawaii and California where the ocean surface is marred by scattered pieces of plastic, which outweigh plankton in that part of ...

New satellite maps out Napa Valley earthquake

5 hours ago

Scientists have used a new Earth-observation satellite called Sentinel-1A to map the ground movements caused by the earthquake that shook up California's wine-producing Napa Valley on 24 August 2014.

Rainfall monitoring with mobile phones

5 hours ago

Agriculture, water resource management, drought and flood warnings, etc.: rainfall monitoring is vital in many areas. But the observation networks remain insufficient. This is not the case for antennas for ...

Seismic hazards reassessed in the Andes

5 hours ago

Although being able to predict the date on which the next big earthquake will occur is still some way off becoming a reality, it is now possible to identify the areas where they will occur. IRD researchers ...

User comments : 10

Adjust slider to filter visible comments by rank

Display comments: newest first

mauro48it
1.8 / 5 (5) Jun 16, 2014
Part_1
I suspect that all or a wall of energy which is related to the melting of ice may come from changes in Earth's magnetic field, caused by the solar wind, which induce electrical currents in the sub-glacial water.
Among other things, this system is self-regulating, since the conductivity of the water should decrease with the amount of ice melted and increase with decreasing energy causing reformation of ice but the increase of salinity.
Probably the areas subject to the phenomenon of heating are areas where the intensity of the magnetic field is increased.
There could also be contributing factors as geothermal activity where there was there would probably be more magnetic material in the magma.
To be continued.
mauro48it
1 / 5 (4) Jun 16, 2014
Part_2
Another clue could be the aforementioned uniformity of energy distribution.
Following other considerations.
I think there is a chance to capture the magnetic energy associated with changes in Earth's magnetic field determined from solar storms or even from the normal variations in the solar wind.
I know that changes in the Earth's magnetic field have been analyzed and are so small that it does not seem possible to use, at least on a small scale. From the information on the article "Getting Ready for the Next Big Solar Storm" (NASA) about the effects on power lines with long route, staggers me this certainty.
I believe that the variations of the magnetic field can be maximum in proximity with the magnetic poles, and in particular there may be areas in which the field thickens significantly.
To be continued.
mauro48it
1 / 5 (4) Jun 16, 2014
Part_3
My hope an fantasy is that with the construction of a large wire loop around the above particular areas of the poles , in which the earth's magnetic field is more intense, it is possible to extract a considerable amount of electrical energy.
Following this hypothesis , I then ventured into a search for data on specific abnormalities may be present at the poles, and I think I found something suspicious.
The two particular sites, near the magnetic pole, are the buried Lake Vostok in Antarctica and a buried lake near the town of Qaanaaq in northwestern Greenland.
These two lakes have a deep liquid phase that appears to be derived from a geothermal energy.
I suppose it is appropriate to investigate carefully whether this is due to the heat dissipated by the currents induced in the salt water.
End.

thermodynamics
5 / 5 (5) Jun 16, 2014
mauro48it: Have you run any of the numbers? Do you understand how diffuse the field is, even near the magnetic poles? You would also be dependent on the motion of the field because I don't see how you would move a large enough coil through the field. It would have to be the field that is moving. I would be interested in any numbers you have that indicate how this would work out.
mauro48it
3 / 5 (2) Jun 16, 2014
No, I do not have the numbers, and I can not have them since I'm not a scientist, and I do not have the culture and the means to find them, my main goal is just to stimulate those who have expertise in the field. But did you read this article "Getting Ready for the Next Big Solar Storm" (NASA)? The effects on power lines are catastrophic and probably in some area of the magnetic poles, the variations of field strength are larger, but there is still the possibility of having a negative effect of average (lines of force which open, but at the same time other reconnect can reduce the variation of a large section).
thermodynamics
5 / 5 (3) Jun 16, 2014
No, I do not have the numbers, and I can not have them since I'm not a scientist, and I do not have the culture and the means to find them, my main goal is just to stimulate those who have expertise in the field. But did you read this article "Getting Ready for the Next Big Solar Storm" (NASA)? The effects on power lines are catastrophic and probably in some area of the magnetic poles, the variations of field strength are larger, but there is still the possibility of having a negative effect of average (lines of force which open, but at the same time other reconnect can reduce the variation of a large section).


If you are interested in feedback, let me start by pointing out a few sites:

http://www.ngdc.n...ld.shtml

http://www.ngdc.n...#igrfwmm

When I looked up the magnetic field at my house today it was about 53 nT (nano Tesla). This is an interesting number because nano is small and Tesla is large. Continued
thermodynamics
5 / 5 (3) Jun 16, 2014
Continued: To put this in perspective you can get fields near 1 T from rare earth permanent magnets by ganging them and adding iron yokes.

I have purchased my rare earth magnets from:

http://www.kjmagnetics.com/

They are amazing.

If you want more power you need to go to electromagnets. The beam steering magnets at CERN are about 8 T. Experimental facilities go to about 50 T for long pulses and 100 T for nanosecond pulses (where everything blows apart).

In a typical generator you will normally run at about 0.1 T.

There is no generation of electricity unless lines of force are broken by a conductor. The interaction of the moving conductor and stationary field or moving field and stationary conductor causes a voltage gradient across the conductor and when the ends are connected current flows.

The issue of capturing the energy in the magnetic field of the earth is that with a field as small as 50 nT you need huge equipment to harvest any of the energy. Continued
thermodynamics
5 / 5 (3) Jun 16, 2014
Continued: This the same kind of trade off you will find with any diffuse energy source. You add equipment costs to mitigate fuel costs.

The reason the Carrington event was as significant a it was is due to the telegraph lines that spanned the world. They acted as a huge antenna and the event had enormous power. We have not been hit by another one since 1859. In the mean time we have been hit by significant events since then, but not huge ones. If you built a capture system that would capture solar storm energy you would have sporadic supply and large equipment.

Can it be done? Yes.

Is it worth doing? Probably not.

Would it be fun? Definitely.

If the various sites I pointed you at are not clear and my message was not clear, feel free to add followup questions.
mauro48it
not rated yet Jun 17, 2014
Thank you very much for your explanations, but the fact that these phenomena are sporadic but extraordinary stimulates my curiosity, and since the lines of force pass largely from the magnetic poles, I wonder what it would cost to run a cable form a large coil and monitor short-term changes in the field, it would be useful to study these phenomena, although it did not have the same precision, resolution, and cost of sending satellites to study the reconnection of magnetic lines of force? It would however be integrative.
I do not know if the short field variations have been carefully studied as it has been studied the stationary magnetic field.
The captured energy not only depends on the intensity of the change, but also the rate of change.
How does the phenomenon of the aurora borealis on the magnetic field?
The variations in brightness and shape, causing changes in the magnetic field?
mauro48it
not rated yet Jun 17, 2014
Another imaginative consideration:
A coil of wire, with big section, around a large area of the magnetic poles would be a good defense against catastrophic solar storms, it could absorb a large part in the energy, which otherwise would discharge the electricity grids around the world.
Does it seem like a good idea for a science fiction novel?