Greenland has massive lakes beneath the ice, repeatedly filling and draining away

In April 2014, researchers flew over a site in southwest Greenland to find that a sub-glacial lake had drained away. This photo shows the crater left behind, as well as a deep crack in the ice.  Credit: Photo by Stephen Price, Los Alamos National Laboratory, courtesy of The Ohio State University. [Click to enlarge image]

Researchers who are building the highest-resolution map of the Greenland Ice Sheet to date have made a surprising discovery: two lakes of meltwater that pooled beneath the ice and rapidly drained away.

One lake once held billions of gallons of water and emptied to form a mile-wide crater in just a few weeks. The other lake has filled and emptied twice in the last two years.

Researchers at Ohio State University published findings on each lake separately: the first in the open-access journal The Cryosphere and the second in the journal Nature.

Ian Howat, associate professor of earth sciences at Ohio State, leads the team that discovered the cratered lake described in The Cryosphere. To him, the find adds to a growing body of evidence that meltwater has started overflowing the ice sheet's natural plumbing system and is causing "blowouts" that simply drain lakes away.

"The fact that our lake appears to have been stable for at least several decades, and then drained in a matter of weeks -- or less -- after a few very hot summers, may signal a fundamental change happening in the ice sheet," Howat said.

The two-mile-wide lake described in Nature was discovered by a team led by researcher Michael Willis of Cornell University. Michael Bevis, Ohio Eminent Scholar in Geodynamics and professor of earth sciences at Ohio State, is a co-author of the Nature paper, and he said that the repeated filling of that lake is worrisome.

Each time the lake fills, the meltwater carries stored heat, called latent heat, along with it, reducing the stiffness of the surrounding ice and making it more likely to flow out to sea, he said.

Bevis explained the long-term implications.

"If enough water is pouring down into the Greenland Ice Sheet for us to see the same sub-glacial lake empty and re-fill itself over and over, then there must be so much latent heat being released under the ice that we'd have to expect it to change the large-scale behavior of the ice sheet," he said.

Howat's team was first to detect the cratered lake described in The Cryosphere, on a spot about 50 kilometers (31 miles) inland from the southwest Greenland coast earlier in 2014. There, previous aerial and satellite imagery indicates that a sub-glacial lake pooled for more than 40 years. More recent images suggest that the lake likely emptied through a meltwater tunnel beneath the ice sheet some time in 2011.

The crater measures 2 kilometers (1.2 miles) across and around 70 meters (230 feet) deep. Researchers calculated that the lake that formed it likely contained some 6.7 billion gallons of water.

That's not a large lake by most reckoning, but it's roughly the same size as the combined reservoirs that supply water to the Columbus, Ohio, metropolitan area's 1.9 million residents. And it disappeared in a single season -- remarkably quickly by geologic standards. Howat characterized the sudden drainage as "catastrophic."

Researchers suspect that, as more meltwater reaches the base of the ice sheet, natural drainage tunnels along the Greenland coast are cutting further inland, Howat explained. The tunnels carry heat and water to areas that were once frozen to the bedrock, potentially causing the ice to melt faster.

"Some independent work says that the drainage system has recently expanded to about 50 kilometers inland of the ice edge, which is exactly where this lake is," he added.

It's possible that the lake was tapped by one of the invading tunnels. It's also possible that thousands of such lakes dot the Greenland coast. They are hard to detect with radar, and researchers don't know enough about why and how they form. In contrast to Antarctica, researchers know much less about what's happening under the ice in Greenland.

"Until we get a good map of the bed topography where this lake was, we have no idea whatsoever how many lakes could be out there," Howat said. "There may be something really weird in the bed in this particular spot that caused water to accumulate. But, if all you need is a bumpy surface a bit inland from the coast, then there could be thousands of little lakes."

Howat and his team flew over the site in southwest Greenland in April 2014, after they realized that detection of the crater, nestled in the midst of a flat ice expanse, was not just an error in the high-resolution surface data they've been collecting. Using DigitalGlobe Inc.'s Worldview satellites, they're assembling a Greenland ice map with 2-meter (approximately 6.5-feet) resolution.

Bevis and his colleagues discovered the lake described in Nature under similar circumstances in March 2013. They were gathering data to supplement their long-standing efforts to weigh the Greenland Ice Sheet with GPS and spotted the mitten-shaped lake by accident.

Using data from Worldview and NASA's Operation IceBridge, the Cornell-led team calculated that the lake filled and emptied twice since 2012, at one point experiencing a sub-surface blowout that drove water from the lake at a volume of 215 cubic meters (nearly 57,000 gallons -- close to the volume of a 30-foot-by-50-foot backyard swimming pool) every second.

Though researchers have long known of the existence of sub-glacial lakes, never before have they witnessed any draining away. The sudden discovery of two -- one of which seems to be refilling and draining repeatedly -- signals to Bevis that Greenland ice loss has likely reached a milestone.

"It's pretty telling that these two lakes were discovered back to back," he said. "We can actually see the meltwater pour down into these holes. We can actually watch these lakes drain out and fill up again in real time. With melting like that, even the deep interior of the ice sheet is going to change."

Coauthors on the paper in The Cryosphere include Myoung-Jong Noh, a postdoctoral researcher, and Seongsu Jeong, a doctoral student, both of earth sciences at Ohio State; Claire Porter of the Polar Geospatial Center at the University of Minnesota; and Ben Smith of the Polar Science Center of the University of Washington.

Coauthors on the paper in Nature include Bradley Herried of the University of Minnesota and Robin Bell of Columbia University. Willis holds a joint appointment at the University of North Carolina, Chapel Hill.

These projects were funded by NASA and the National Science Foundation.

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Story Source

The above story is based on materials provided by Ohio State University. The original article was written by Pam Frost Gorder. Note: Materials may be edited for content and length.

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Journal References

1. Michael J. Willis, Bradley G. Herried, Michael G. Bevis, Robin E. Bell. Recharge of a subglacial lake by surface meltwater in northeast Greenland. Nature, 2015; DOI: 10.1038/nature14116
2. I. M. Howat, C. Porter, M. J. Noh, B. E. Smith, S. Jeong. Brief Communication: Sudden drainage of a subglacial lake beneath the Greenland Ice Sheet. The Cryosphere, 2015; 9 (1): 103 DOI: 10.5194/tc-9-103-2015.

http://www.sciencedaily.com/releases/2015/01/150121135156.htm

Scientists find evidence of vast “storage tanks” of water deep below the melting Greenland ice sheet that could have a major effect on sea level rise

by Tim Radford, Climate News Network, January 5, 2015

LONDON − One small mystery that surrounds Greenland’s melting ice is a little closer to being solved as scientists in the US confirm that surface meltwater can drain all the way down to fill concealed lakes under the ice.

This means that atmospheric warming can reach thousands of metres below the ice sheet − warming the glacial base and potentially increasing its rate of flow.

One group, led by geologist Michael Willis, of Cornell University, and another team led by glaciologist Ian Howat, of Ohio State University, report in two different journals on separate but related studies of Greenland’s plumbing system: what happens to meltwater.

The ice sheet of Greenland adds up to about four-fifths of the mass of the vast frozen island, and there is evidence that, as a consequence of global warming, the rate of melting has begun to accelerate.

Measurable difference

This has already begun to make a measurable difference to global sea levels, and were the entire island to shed its burden of ice – a process that would take a considerable time − then sea levels would rise by 7 metres or more.

So what exactly happens to the water that forms on the surface and collects in lakes each summer, and how much of it gets into the sea, has become an important but perplexing problem. Surface lakes are now appearing much further inland, and at higher altitudes, than recorded in the past.

Dr Howat and his colleagues report in The Cryosphere that they measured a 2-km-wide depression 70 metres deep in the icecap of southwest Greenland, which they then identified as “the first direct evidence for concentrated long-term storage and sudden release of meltwater at the bed.”

The slumped crater suggested a holding capacity of more than 30 million cubic metres of water, which had suddenly drained away.

“The fact that our lake appears to have been stable for at least several decades, and then drained in a matter of weeks – or less – after a few very hot summers, may signal a fundamental change happening to the ice sheet,” Dr Howat said.

The Cornell team worked in northeast Greenland, and in 2011 found a collapsed basin 70 metres deep. Dr Willis and colleagues report in the journal Nature that between 2011 and 2014 they watched as summer meltwater made its way down fissures in the depression and refilled a lake basin at the base of the icecap. When this in turn emptied, the researchers calculated that the flow from the subglacial lake was at a rate of 215 cubic metres per second.

“We’re seeing surface meltwater make its way to the base of the ice where it can get trapped and stored at the boundary between the bedrock beneath the ice sheet and the ice itself,” they say.

“As the lake beneath the ice fills with surface meltwater, the heat released by this trapped meltwater can soften surrounding ice, which may eventually cause an increase in ice flow.”

Glacial flow

The researchers do not yet know whether the draining water is increasing glacial flow, and nor can they be sure how many such depressions in the Greenland ice mask buried meltwater storage tanks.

But melting of glacial ice is likely to accelerate anyway, according to new research in the journal Climate Dynamics.

Earth scientist Patrick Applegate, of Penn State University, reports that computer models confirm that the more temperatures increase, the faster the ice will melt.

Were all Greenland’s ice to melt, sea levels would rise catastrophically. At least one billion people live on coasts and estuaries vulnerable to a mere one metre rise.

The Arctic is already the fastest warming place in the northern hemisphere, and the Penn State scientists wanted to see how present warming could play back into future warming. Engineers call this positive feedback.

“If we are going to do something to mitigate sea level rise, we need to do it earlier rather than later,” Dr Applegate said. “The longer we wait, the more rapidly the changes will take place and the more difficult it will be to change.”

Ian Howat: 2 Greenland glaciers (Jakobshavn Isbrae and Kangerdlugssuaq) lose enough ice to fill Lake Erie

2 Greenland glaciers lose enough ice to fill Lake Erie

esciencenews, published May 24, 2011, in Earth & Climate

A new study aimed at refining the way scientists measure ice loss in Greenland is providing a "high-definition picture" of climate-caused changes on the island. And the picture isn't pretty.

In the last decade, two of the largest three glaciers draining that frozen landscape have lost enough ice that, if melted, could have filled Lake Erie.

The three glaciers – Helheim, Kangerdlugssuaq and Jakobshavn Isbrae – are responsible for as much as one-fifth of the ice flowing out from Greenland into the ocean.

"Jakobshavn alone drains somewhere between 15 and 20 percent of all the ice flowing outward from inland to the sea," explained Ian Howat, an assistant professor of earth sciences at Ohio State University. His study appears in the current issue of the journal Geophysical Research Letters.

As the second largest holder of ice on the planet, and the site of hundreds of glaciers, Greenland is a natural laboratory for studying how climate change has affected these ice fields.

Researchers focus on the "mass balance" of glaciers, the rate of new ice being formed as snow falls versus the flow of ice out into the sea.

The new study suggests that, in the last decade, Jakobshavn Isbrae has lost enough ice to equal 11 years' worth of normal snow accumulation, approximately 300 gigatons (300 billion tons) of ice.

"Kangerdlugssuaq would have to stop flowing and accumulate snowfall for seven years to regain the ice it has lost," said Howat, also a member of the Byrd Polar Research Center at Ohio State.

Surprisingly, the researchers found that the third glacier, Helheim, had actually gained a small amount of mass over the same period. It gained approximately one-fifteenth of what Jakobshavn had lost, Howat said.

The real value of the research, however, is the confirmation that the new techniques Howat and his colleagues developed will provide scientists a more accurate idea of exactly how much ice is being lost.

"These glaciers change pretty quickly. They speed up and then slow down. There's a pulsing in the flow of ice," Howat said. "There's variability, a seasonal cycle and lots of different changes in the rate that ice is flowing through these glaciers."

Past estimates, he said, have been merely snapshots of what was going on at these glaciers in terms of mass loss. "We really need to sample them very frequently or else we won't really know how much change has occurred.

"This new research pumps up the resolution and gives us a kind of high-definition picture of ice loss," he said.

To get this longer-timeframe image, Howat and colleagues drew on data sets provided by at least seven orbiting satellites and airplanes, as well as other sources.

"To get a good picture of what's going on, we need different tools and each one of these satellites plays an important role and adds more information," Howat said.

The next step is to look at the next-largest glaciers in Greenland and work their way down through smaller and smaller ice flows.

"Currently, the missing piece is ice thickness data for all of the glaciers, but a NASA aircraft is up there getting it. When that's available, we'll be able to apply this technique to the entire Greenland ice sheet and get a monthly total mass balance for the last 10 years or so," he said.

http://esciencenews.com/articles/2011/05/24/2.greenland.glaciers.lose.enough.ice.fill.lake.erie

Jakobshavn Glacier northern feeding branch retreats a mile in one night

Giant Greenland Glacier Cracks Open Overnight

The Arctic's biggest iceberg factory just hit overdrive

by Larry O'Hanlon , DiscoveryNews, July 13, 2010

• Greenland's monster Jakonbshavn glacier is spotted losing a mile of ice in one night.
• The warm winter and no sea ice may have led to the record retreat of the glacier.
• Such huge loses were once missed because of lack of daily satellite images.

enlarge

The record retreat of Jakonbshavn may have been helped by an exceptionally warm winter, which prevented sea ice from forming in front of the glacier. Click to enlarge this image.
Ian Joughin

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It used to be that when a glacier had a bad night it was like that proverbial tree falling in the forest.

Now ice researchers using several satellites to monitor Greenland's most active glaciers almost daily have caught the north limb of the mother-of-all-Greenland glaciers, Jakonbshavn, retreating a mile in a night.

"A few nights ago a crack opened up," said Tom Wagner, cryospheric program scientist at NASA. "Two nights later (July 6, 2010) the whole (gosh darned) thing breaks off and flows away." The lost portion has been described as about an eighth the size of Manhattan Island and set a new record for the retreat of that glacier.

But that's not all. On July 12 there was a new large crack discovered in the glacier's southern limb as well. Whether that means another gigantic release of ice or not remains to be seen.
Jakonbshavn is already well known for being a major exit route for 10 percent of the ice that leaves Greenland for the sea. The river of ice fills a vast valley which, if emptied, would rival the Grand Canyon in scale.
It appears that the record retreat of Jakonbshavn may have been helped by an exceptionally warm winter, which prevented sea ice from forming in front of the glacier, said Ian Joughin of the Polar Science Center Applied Physics Lab at the University of Washington.

There's usually about four miles of sea ice floating in front of the glacier, keeping the water nice and chilly near the calving front of the glacier -- and less prone to calving off icebergs.

Normally the glacier retreats in the summer, then regains ground in winter as it surges towards the sea with the help of sea ice. The lack of sea ice appears to have changed that, say researchers.

"This year it started (calving) where it left off last summer," said Ian Howat of the Byrd Polar Research Center at Ohio State University.

In the past, satellite images could be months or years apart. Over such periods glaciers can advance and retreat many times, making the few snapshots only useful for determining long-term trends. For a more detailed study of just how glaciers behave, a better time-resolution was needed.

"It's exciting because there's a lot we don't understand," said Joughin. Getting higher time-resolution images like those that caught Jakonbshavn retreating so quickly finally lets researchers begin to study the basic principles of glacier behavior.

The satellites the researchers are using to keep almost daily tabs on the giant Jakonbshavn, Kangerlugssuaq, and Helheim glaciers, and weekly checks on smaller outlet glaciers include DigitalGlobe's WorldView 2, which takes optical (visible light) images.

When clouds get in the way, radar images can be used from a German satellite that can penetrate the cloud cover. Data is also being used from Landsat, Terra, and Aqua satellites.

Link:  http://news.discovery.com/earth/greenland-glacier-warming.html