Researchers: Northeast Greenland ice loss accelerating

All margins of ice sheet now unstable -- and contributing to sea level rise

2014-03-16

(Press-News.org) COLUMBUS, Ohio—An international team of scientists has discovered that the last remaining stable portion of the Greenland ice sheet is stable no more.

The finding, which will likely boost estimates of expected global sea level rise in the future, appears in the March 16 issue of the journal Nature Climate Change [DOI:10.1038/NCLIMATE2161].

The new result focuses on ice loss due to a major retreat of an outlet glacier connected to a long "river" of ice - known as an ice stream - that drains ice from the interior of the ice sheet. The Zachariae ice stream retreated about 20 kilometers (12.4 miles) over the last decade, the researchers concluded. For comparison, one of the fastest moving glaciers, the Jakobshavn ice stream in southwest Greenland, has retreated 35 kilometers (21.7 miles) over the last 150 years.

Ice streams drain ice basins, the same way the Amazon River drains the very large Amazon water basin. Zachariae is the largest ice stream in a drainage basin that covers 16 percent of the Greenland ice sheet—an area twice as large as the one drained by Jakobshavn.

This paper represents the latest finding from GNET, the GPS network in Greenland that measures ice loss by weighing the ice sheet as it presses down on the bedrock.

"Northeast Greenland is very cold. It used to be considered the last stable part of the Greenland ice sheet," explained GNET lead investigator Michael Bevis of The Ohio State University. "This study shows that ice loss in the northeast is now accelerating. So, now it seems that all of the margins of the Greenland ice sheet are unstable."

Historically, Zachariae drained slowly, since it had to fight its way through a bay choked with floating ice debris. Now that the ice is retreating, the ice barrier in the bay is reduced, allowing the glacier to speed up—and draw down the ice mass from the entire basin.

"This suggests a possible positive feedback mechanism whereby retreat of the outlet glacier, in part due to warming of the air and in part due to glacier dynamics, leads to increased dynamic loss of ice upstream. This suggests that Greenland's contribution to global sea level rise may be even higher in the future," said Bevis, who is also the Ohio Eminent Scholar in Geodynamics and professor of earth sciences at Ohio State.

Study leader Shfaqat Abbas Khan, a senior researcher at the National Space Institute at the Technical University of Denmark, said that the finding is cause for concern.

"The fact that the mass loss of the Greenland Ice Sheet has generally increased over the last decades is well known," Khan said, "but the increasing contribution from the northeastern part of the ice sheet is new and very surprising."

GNET, short for "Greenland GPS Network," uses the earth's natural elasticity to measure the mass of the ice sheet. As previous Ohio State studies revealed, ice weighs down bedrock, and when the ice melts away, the bedrock rises measurably in response. More than 50 GNET stations along Greenland's coast weigh the ice sheet like a giant bathroom scale.

Khan and his colleagues combined GNET data with ice thickness measurements taken by four different satellites: the Airborne Topographic Mapper (ATM), the Ice, Cloud and Land Elevation Satellite (ICESat), and the Land, Vegetation and Ice Sensor (LVIS) from NASA; and the Environmental Satellite (ENVISAT) from the European Space Agency.

They found that the northeast Greenland ice sheet lost about 10 billion tons of ice per year from April 2003 to April 2012.

According to previous measurements and aerial photographs, the northeast Greenland ice sheet margin appeared to be stable for 25 years—until 2003. Around that time, a string of especially warm summers triggered increased melting and calving events, which have continued to the present day.

A large calving event at the Zachariae glacier made the news in May 2013, and Khan and his team witnessed and filmed a similar event in July.

Increased ice flow in this region is particularly troubling, Khan said, because the northeast ice stream stretches more than 600 kilometers (about 373 miles) into the center of the ice sheet, where it connects with the heart of Greenland's ice reservoir.

"This implies that changes at the margin can affect the mass balance deep in the center of the ice sheet. Furthermore, due to the huge size of the northeast Greenland ice stream, it has the potential of significantly changing the total mass balance of the ice sheet in the near future," he added.

Bevis agreed: "The fact that this ice loss is associated with a major ice stream that channels ice from deep in the interior of the ice sheet does add some additional concern about what might happen."

The Greenland ice sheet is thought to be one of the largest contributors to global sea level rise over the past 20 years, accounting for 0.5 millimeters of the current total of 3.2 millimeters of sea level rise per year.

INFORMATION: Coauthors on the paper hailed from the University of Copenhagen; University of Bristol; University of Colorado, Boulder; University of Kansas; Utrecht University; The Chinese University of Hong Kong; and Aarhus University.

This research was supported by the Danish Research Council, the Danish National Research Foundation and the Villum Foundation. GNET is a collaboration of Ohio State University, the National Space Institute at the Technical University of Denmark, and the University of Luxembourg, and it receives technical support from UNAVCO Inc. and logistical support from CH2M HILL Polar Services. The American component of GNET was funded by the US National Science Foundation.

Contacts: Michael Bevis, (614) 247-5071; Bevis.6@osu.edu Shfaqat Abbas Khan, +45-45-25-97-75; abbas@space.dtu.dk

Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu

Editor's note: Images and video are available from Pam Frost Gorder.

ELSE PRESS RELEASES FROM THIS DATE:

Mercury's contraction much greater than thought

2014-03-16

Washington, D.C.—New global imaging and topographic data from MESSENGER* show that the innermost planet has contracted far more than previous estimates. The results are based on a global study of more than 5,900 geological landforms, such as curving cliff-like scarps and wrinkle ridges, that have resulted from the planet's contraction as Mercury cooled. The findings, published online March 16, 2014, in Nature Geoscience, are key to understanding the planet's thermal, tectonic, and volcanic history, and the structure of its unusually large metallic core. Unlike Earth, ...

Thermal vision: Graphene light detector first to span infrared spectrum

2014-03-16

ANN ARBOR—The first room-temperature light detector that can sense the full infrared spectrum has the potential to put heat vision technology into a contact lens. Unlike comparable mid- and far-infrared detectors currently on the market, the detector developed by University of Michigan engineering researchers doesn't need bulky cooling equipment to work. "We can make the entire design super-thin," said Zhaohui Zhong, assistant professor of electrical engineering and computer science. "It can be stacked on a contact lens or integrated with a cell phone." Infrared ...

Southern Ocean iron cycle gives new insight into climate change

2014-03-16

An international team of researchers analysed the available data taken from all previous studies of the Southern Ocean, together with satellite images taken of the area, to quantify the amount of iron supplied to the surface waters of the Southern Ocean. They found that deep winter mixing, a seasonal process which carries colder and deeper, nutrient-rich water to the surface, plays the most important role in transporting iron to the surface. The iron is then able to stimulate phytoplankton growth which supports the ocean's carbon cycle and the aquatic food chain They ...

Regional warming triggers sustained mass loss in Northeast Greenland ice sheet

2014-03-16

Northeast Greenland, where the glacier is found, is of particular interest as numerical model predictions have suggested there is no significant mass loss for this sector, leading to a probable underestimation of future global sea-level rise from the region. An international team of scientists, including Professor Jonathan Bamber from the University of Bristol, studied the Northeast Greenland Ice Stream which extends more than 600 km into the interior of the ice sheet: much further than any other in Greenland. Professor Bamber said: "The Greenland ice sheet has contributed ...

Cancer therapy may be too targeted

2014-03-16

Researchers have identified two novel cancer genes that are associated with the development of a rare, highly aggressive, cancer of blood vessels. These genes may now act as markers for future treatments and explain why narrowly targeted therapies that are directed at just one target fail. Angiosarcoma is a rare cancer of blood vessels. It occurs either spontaneously or can appear after radiotherapy treatment. Although quite rare, with approximately 100 people diagnosed with the cancer in the UK each year, the survival outcomes for the cancer are poorer than many other ...

Mercury contracted more than prior estimates, evidence shows

2014-03-16

New evidence gathered by NASA's MESSENGER spacecraft at Mercury indicates the planet closest to the sun has shrunk up to 7 kilometers in radius over the past 4 billion years, much more than earlier estimates. The new finding, published in the journal Nature Geoscience Sunday, March 16, solves an apparent enigma about Mercury's evolution. Older images of surface features indicated that, despite cooling over its lifetime, the rocky planet had barely shrunk at all. But modeling of the planet's formation and aging could not explain that finding. Now, Paul K. Byrne and ...

Newly identified small-RNA pathway defends genome against the enemy within

2014-03-16

Cold Spring Harbor, NY – Reproductive cells, such as an egg and sperm, join to form stem cells that can mature into any tissue type. But how do reproductive cells arise? We humans are born with all of the reproductive cells that we will ever produce. But in plants things are very different. They first generate mature, adult cells and only later "reprogram" some of them to produce eggs and sperm. For a plant to create reproductive cells, it must first erase a key code, a series of tags attached to DNA across the genome known as epigenetic marks. These marks distinguish ...

Novel gene-finding approach yields a new gene linked to key heart attack risk factor

2014-03-16

ANN ARBOR, Mich. — Scientists have discovered a previously unrecognized gene variation that makes humans have healthier blood lipid levels and reduced risk of heart attacks -- a finding that opens the door to using this knowledge in testing or treatment of high cholesterol and other lipid disorders. But even more significant is how they found the gene, which had been hiding in plain sight in previous hunts for genes that influence cardiovascular risk. This region of DNA where it was found had been implicated as being important in controlling blood lipid levels in ...

Climate change will reduce crop yields sooner than we thought

2014-03-16

A study led by the University of Leeds has shown that global warming of only 2°C will be detrimental to crops in temperate and tropical regions, with reduced yields from the 2030s onwards. Professor Andy Challinor, from the School of Earth and Environment at the University of Leeds and lead author of the study, said: "Our research shows that crop yields will be negatively affected by climate change much earlier than expected." "Furthermore, the impact of climate change on crops will vary both from year-to-year and from place-to-place – with the variability becoming ...

Novel membrane reveals water molecules will bounce off a liquid surface

2014-03-16

Consider the nearest water surface: a half-full glass on your desk, a puddle outside your window, or a lake across town. All of these surfaces represent liquid-vapor interfaces, where liquid meets air. Molecules of water vapor constantly collide with these liquid surfaces: Some make it through the surface and condense, while others simply bounce off. The probability that a vapor molecule will bounce, or reflect, off a liquid surface is a fundamental property of water, much like its boiling point. And yet, in the last century, there has been little agreement on the likelihood ...

Researchers: Northeast Greenland ice loss accelerating

ELSE PRESS RELEASES FROM THIS DATE:

LAST 30 PRESS RELEASES: