Ice-loss moves the Earth 250 miles down

At the surface, Antarctica is a motionless and frozen landscape. Yet hundreds of miles down the Earth is moving at a rapid rate, new research has shown.

The study, led by Newcastle University, UK, and published this week in Earth and Planetary Science Letters, explains for the first time why the upward motion of the Earth’s crust in the Northern Antarctic Peninsula is currently taking place so quickly.

Previous studies have shown the earth is ‘rebounding’ due to the overlying ice sheet shrinking in response to climate change. This movement of the land was understood to be due to an instantaneous, elastic response followed by a very slow uplift over thousands of years.

But GPS data collected by the international research team, involving experts from Newcastle University, UK; Durham University; DTU, Denmark; University of Tasmania, Australia; Hamilton College, New York; the University of Colorado and the University of Toulouse, France, has revealed that the land in this region is actually rising at a phenomenal rate of 15mm a year – much greater than can be accounted for by the present-day elastic response alone.

And they have shown for the first time how the mantle below the Earth’s crust in the Antarctic Peninsula is flowing much faster than expected, probably due to subtle changes in temperature or chemical composition. This means it can flow more easily and so responds much more quickly to the lightening load hundreds of miles above it, changing the shape of the land.

Lead researcher, PhD student Grace Nield, based in the School of Civil Engineering and Geosciences at Newcastle University, explains: “You would expect this rebound to happen over thousands of years and instead we have been able to measure it in just over a decade. You can almost see it happening which is just incredible.

“Because the mantle is ‘runnier’ below the Northern Antarctic Peninsula it responds much more quickly to what’s happening on the surface. So as the glaciers thin and the load in that localised area reduces, the mantle pushes up the crust.

“At the moment we have only studied the vertical deformation so the next step is to look at horizontal motion caused by the ice unloading to get more of a 3-D picture of how the Earth is deforming, and to use other geophysical data to understand the mechanism of the flow.”

Since 1995 several ice shelves in the Northern Antarctic Peninsula have collapsed and triggered ice-mass unloading, causing the solid Earth to ‘bounce back’.

“Think of it a bit like a stretched piece of elastic,” says Nield, whose project is funded by the Natural Environment Research Council (NERC). “The ice is pressing down on the Earth and as this weight reduces the crust bounces back. But what we found when we compared the ice loss to the uplift was that they didn’t tally – something else had to be happening to be pushing the solid Earth up at such a phenomenal rate.”

Collating data from seven GPS stations situated across the Northern Peninsula, the team found the rebound was so fast that the upper mantle viscosity – or resistance to flow – had to be at least ten times lower than previously thought for the region and much lower than the rest of Antarctica.

Professor Peter Clarke, Professor of Geophysical Geodesy at Newcastle University and one of the authors of the paper, adds: “Seeing this sort of deformation of the earth at such a rate is unprecedented in Antarctica. What is particularly interesting here is that we can actually see the impact that glacier thinning is having on the rocks 250 miles down.”

Underlying ocean melts ice shelf, speeds up glacier movement

This is a researcher's remote field camp on Pine Island Glacier. -  Kiya Riverman, Penn State
This is a researcher’s remote field camp on Pine Island Glacier. – Kiya Riverman, Penn State

Warm ocean water, not warm air, is melting the Pine Island Glacier’s floating ice shelf in Antarctica and may be the culprit for increased melting of other ice shelves, according to an international team of researchers.

“We’ve been dumping heat into the atmosphere for years and the oceans have been doing their job, taking it out of the air and into the ocean,” said Sridhar Anandakrishnan, professor of geosciences, Penn State. “Eventually, with all that atmospheric heat, the oceans will heat up.”

The researchers looked at the remote Pine Island Glacier, a major outlet of the West Antarctic Ice Sheet because it has rapidly thinned and accelerated in the recent past.

“It has taken years and years to do the logistics because it is so remote from established permanent bases,” said Anandakrishnan.

Pine Island Glacier or PIG lies far from McMurdo base, the usual location of American research in Antarctica. Work done in the southern hemisphere’s summer, December through January 2012-13, included drilling holes in the ice to place a variety of instruments and using radar to map the underside of the ice shelf and the bottom of the ocean. Penn State researchers did the geophysics for the project and the research team’s results are reported today (Sept. 13) in Science.

The ice shelf is melting more rapidly from below for a number of reasons. The oceans are warmer than they have been in the past and water can transfer more heat than air. More importantly, the terrain beneath the ice shelf is a series of channels. The floating ice in the channel has ample room beneath it for ocean water to flow in. The water melts some of the ice beneath and cools. If the water remained in the channel, the water would eventually cool to a point where it was not melting much ice, but the channels allow the water to flow out to the open ocean and warmer water to flow in, again melting the ice shelf from beneath.

“The way the ocean water is melting the ice shelf is a deeply non-uniform way,” said Anandakrishnan. “That’s going to be more effective in breaking these ice shelves apart.”

The breaking apart of the ice shelf in the channels is similar to removing an ice jam from a river. The shelf was plugging the channel, but once it is gone, the glacier moves more rapidly toward the sea, forming more ice shelf, but removing large amounts of ice from the glacier.

The melting of floating ice shelves does not contribute to sea level rise because once they are in the water, the ice shelves have already contributed to sea level rise. However, most of the Antarctic glaciers are on land, and rapidly adding new ice shelf material to the floating mass will increase sea level rise.

“Antarctica is relatively stable, but that won’t last forever, said Anandakrishnan. “This is a harbinger of what will happen.”

The researchers believe that the interaction of the ocean beneath the ice shelf and melting of the ice shelf is an important variable that should be incorporated into the sea level rise models of global warming. Other recent research shows that without the channelized underbelly of the ice shelf and glacier, melting would be even more rapid.

“The Antarctic has been relatively quiet as a contributor to sea rise,” said Anandakrishnan. “What this work shows is that we have been blind to a huge phenomenon, something that will be as big a player in sea level rise in the next century as any other contributor.”

Sea level rise: New iceberg theory points to areas at risk of rapid disintegration

In events that could exacerbate sea level rise over the coming decades, stretches of ice on the coasts of Antarctica and Greenland are at risk of rapidly cracking apart and falling into the ocean, according to new iceberg calving simulations from the University of Michigan.

“If this starts to happen and we’re right, we might be closer to the higher end of sea level rise estimates for the next 100 years,” said Jeremy Bassis, assistant professor of atmospheric, oceanic and space sciences at the U-M College of Engineering, and first author of a paper on the new model published in the current issue of Nature Geoscience.

Iceberg calving, or the formation of icebergs, occurs when ice chunks break off larger shelves or glaciers and float away, eventually melting in warmer waters. Although iceberg calving accounts for roughly half of the mass lost from ice sheets, it isn’t reflected in any models of how climate change affects the ice sheets and could lead to additional sea level rise, Bassis said.

“Fifty percent of the total mass loss from the ice sheets, we just don’t understand. We essentially haven’t been able to predict that, so events such as rapid disintegration aren’t included in those estimates,” Bassis said. “Our new model helps us understand the different parameters, and that gives us hope that we can better predict how things will change in the future.”

The researchers have found the physics at the heart of iceberg calving, and their model is the first that can simulate the different processes that occur on both ends of the Earth. It can show why in northern latitudes-where glaciers rest on solid ground-icebergs tend to form in relatively small, vertical slivers that rotate onto their sides as they dislodge. It can also illustrate why in the southernmost places-where vast ice shelves float in the Antarctic Ocean-icebergs form in larger, more horizontal plank shapes.

The model treats ice sheets-both floating shelves and grounded glaciers-like loosely cemented collections of boulders. Such a description reflects how scientists in the field have described what iceberg calving actually looks like. The model allows those loose bonds to break when the boulders are pulled apart or rub against one another.

The simulations showed that calving is a two-step process driven primarily by the thickness of the ice.

“Essentially, everything is driven by gravity,” Bassis said. “We identified a critical threshold of one kilometer where it seems like everything should break up. You can think of it in terms of a kid building a tower. The taller the tower is, the more unstable it gets.”

Icebergs do have a tendency to form before that threshold though, Bassis suspects, due to cracks that are already there-either formed when capsizing bergs crash into the water and send shockwaves through the surrounding ice, or when melted water on the surface cuts through. The former is believed to have led to the Helheim Glacier collapse in 2003. The glacier had begun to retreat slowly in 2002, but suddenly gave way the following year when the thinner ice had broken away, exposing a thicker ice coast.

The latter-melted water pools-are occurring more frequently due to climate change, and they’re believed to have played a role in the rapid disintegration of the Antarctica’s Larsen B ice shelf, which crumbled over about six weeks in 2002.

When the researchers added random cracks to their model, it could mirror both Helheim and Larsen B.

A third feature is also required for the most dramatic ice collapses to occur. Icebergs can’t float away and make room for more icebergs to break off the main sheet unless the system has access to open water. So areas that border deep, unobstructed ocean rather than fjords or other waterways are at greater risk of rapid ice loss. The researchers point to the Thwaites and Pine Island glaciers in Antarctica and the Jakobshavn Glacier in Greenland, which is already retreating rapidly, as places vulnerable to “catastrophic disintegration” because they have all three components.

“The ice in those places gets thicker as you go back. If our threshold is right, then if these places start to retreat as you expose the thicker calving font, they’re susceptible to catastrophic breakup,” Bassis said.

Retreat of the current ice coasts in these places areas could occur via melting or iceberg calving.

Ancient glacial melting process similar to existing concerns about Antarctica, Greenland

An analysis of prehistoric “Heinrich events” that happened many thousands of years ago, creating mass discharges of icebergs into the North Atlantic Ocean, make it clear that very small amounts of subsurface warming of water can trigger a rapid collapse of ice shelves.

The findings, to be published this week in Proceedings of the National Academy of Sciences, provide historical evidence that warming of water by 3-4 degrees was enough to trigger these huge, episodic discharges of ice from the Laurentide Ice Sheet in what is now Canada.

The results are important, researchers say, due to concerns that warmer water could cause a comparatively fast collapse of ice shelves in Antarctica or Greenland, increasing the flow of ice into the ocean and raising sea levels. One of the most vulnerable areas, the West Antarctic Ice Sheet, would raise global sea level by about 11 feet if it were all to melt.

“We don’t know whether or not water will warm enough to cause this type of phenomenon,” said Shaun Marcott, a postdoctoral researcher at Oregon State University and lead author of the report. “But it would be a serious concern if it did, and this demonstrates that melting of this type has occurred before.”

If water were to warm by about 2 degrees under the ice shelves that are found along the edges of much of the West Antarctic Ice Sheet, Marcott said, it might greatly increase the rate of melting to more than 30 feet a year. This could cause many of the ice shelves to melt in less than a century, he said, and is probably the most likely mechanism that could create such rapid changes of the ice sheet.

To find previous examples of such events, scientists reconstructed past ocean temperatures and used computer simulations to re-create what probably happened at various times during Heinrich events of the distant past. It had been known for some time that such events were associated with major climate changes, but less clear whether the events were a reaction to climate change or helped to cause them.

“There is now better evidence that the climate was getting colder prior to the Heinrich events, causing surface ocean waters to cool but actually causing warmer water in the subsurface,” Marcott said. “We tried to demonstrate how this warmer water, at depth, caused the base of the ice shelf to warm and collapse, triggering the Heinrich events.”

A present-day concern, Marcott said, is that ocean currents could shift and change direction even before overall ocean water had warmed a significant amount. If currents shifted and warmer water was directed toward ice shelves, more rapid melting might begin, he said.

This study was done by scientists from OSU, the University of Wisconsin, National Center for Atmospheric Research, and the Nanjing University of Information Science and Technology. The lead author was Shaun Marcott, a postdoctoral researcher at OSU. The studies were supported by the National Science Foundation, NASA and other agencies.

Ice shelves disappearing on Antarctic Peninsula

This image shows ice-front retreat in part of the southern Antarctic Peninsula from 1947 to 2009. USGS scientists are studying coastal and glacier change along the entire Antarctic coastline. The southern portion of the Antarctic Peninsula is one area studied as part of this project, and is summarized in the USGS report, “Coastal-Change and Glaciological Map of the Palmer Land Area, Antarctica: 1947—2009” (map I—2600—C).
This image shows ice-front retreat in part of the southern Antarctic Peninsula from 1947 to 2009. USGS scientists are studying coastal and glacier change along the entire Antarctic coastline. The southern portion of the Antarctic Peninsula is one area studied as part of this project, and is summarized in the USGS report, “Coastal-Change and Glaciological Map of the Palmer Land Area, Antarctica: 1947—2009” (map I—2600—C).

Ice shelves are retreating in the southern section of the Antarctic Peninsula due to climate change. This could result in glacier retreat and sea-level rise if warming continues, threatening coastal communities and low-lying islands worldwide.

Research by the U.S. Geological Survey is the first to document that every ice front in the southern part of the Antarctic Peninsula has been retreating overall from 1947 to 2009, with the most dramatic changes occurring since 1990. The USGS previously documented that the majority of ice fronts on the entire Peninsula have also retreated during the late 20th century and into the early 21st century.

The ice shelves are attached to the continent and already floating, holding in place the Antarctic ice sheet that covers about 98 percent of the Antarctic continent. As the ice shelves break off, it is easier for outlet glaciers and ice streams from the ice sheet to flow into the sea. The transition of that ice from land to the ocean is what raises sea level.

“This research is part of a larger ongoing USGS project that is for the first time studying the entire Antarctic coastline in detail, and this is important because the Antarctic ice sheet contains 91 percent of Earth’s glacier ice,” said USGS scientist Jane Ferrigno. “The loss of ice shelves is evidence of the effects of global warming. We need to be alert and continually understand and observe how our climate system is changing.”

The Peninsula is one of Antarctica’s most rapidly changing areas because it is farthest away from the South Pole, and its ice shelf loss may be a forecast of changes in other parts of Antarctica and the world if warming continues.

Retreat along the southern part of the Peninsula is of particular interest because that area has the Peninsula’s coolest temperatures, demonstrating that global warming is affecting the entire length of the Peninsula.

The Antarctic Peninsula’s southern section as described in this study contains five major ice shelves: Wilkins, George VI, Bach, Stange and the southern portion of Larsen Ice Shelf. The ice lost since 1998 from the Wilkins Ice Shelf alone totals more than 4,000 square kilometers, an area larger than the state of Rhode Island.

The USGS is working collaboratively on this project with the British Antarctic Survey, with the assistance of the Scott Polar Research Institute and Germany’s Bundesamt fűr Kartographie und Geodäsie. The research is also part of the USGS Glacier Studies Project, which is monitoring and describing glacier extent and change over the whole planet using satellite imagery.

$32 Million Contract From NASA To Manage Snow And Ice Data System

The University of Colorado at Boulder has been awarded a five-year, $32 million contract from NASA to manage and operate a sophisticated data system charting global phenomena like sea ice, ice shelves, ice sheets, glaciers and snow cover.

The five-year contract means CU-Boulder’s National Snow and Ice Data Center will manage the Distributed Active Archive Center, or DAAC, for NASA through at least 2013. The DAAC — the largest data management and research activity at the NSIDC — has been operated at the CU-Boulder center for NASA since 1993.

Employees at DAAC process, archive, validate and distribute snow and ice data products generated from a variety of Earth-orbiting satellites and research ground stations. NSIDC maintains data on a wide variety of phenomena in cold regions of the planet, including snow cover, glaciers, avalanches, ice sheets, freshwater ice, sea ice, ground ice, permafrost, atmospheric ice and ice cores.

Researchers at NSIDC use the DAAC data to study ongoing declines in sea ice, glaciers and ice caps, including events like record extent lows of Arctic sea ice and ice-shelf breakups. When Antarctica’s Wilkins Ice Shelf began to rapidly disintegrate in March 2008, NSIDC scientists first spotted the events using DAAC satellite data.

“We’re seeing unprecedented changes in the ice cover of the Earth,” said CU-Boulder researcher Ted Scambos, lead scientist at NSIDC. “These changes are happening so fast, and are so widespread, that the only way to monitor them and understand them is with satellite data.

“NSIDC’s NASA data archive at the DAAC provides scientists all over the world with ready access to this data, past, present and future, into the next decade,” said Scambos. “That’s how you study climate change — with long-term data sets.”

NSIDC is a major source of data and information for journalists and the public regarding snow and ice research. As Arctic sea ice approached its all-time record low extent in September 2007, NSIDC posted satellite imagery and ongoing scientific analysis of sea ice conditions on the Internet. NSIDC staff responded to a deluge of requests from reporters worldwide for images, interviews and information, helping the public obtain accurate data and scientific information regarding the declining sea ice and the role of global climate change.

The NSIDC activity supports NASA’s mission to understand the Earth and its response to natural and human-induced change using the NASA Earth Observing System Data and Information System. To date, the DAAC team has distributed more than 125 terabytes of data to researchers and other users. DAAC holdings are six times the volume of the digital collections at the Library of Congress.

NSIDC is part of the Cooperative Institute for Research in Environmental Sciences, a joint institute of CU-Boulder and the National Oceanic and Atmospheric Administration. The center supports research into Earth’s frozen regions, offering more than 500 products, primarily data and information from Earth observation satellites to researchers, commercial users, educators, and others worldwide.

Antarctic ice shelf collapse explained

When the Larsen B Ice Shelf in Antarctica collapsed in 2002, the event appeared to be a sudden response to climate change, and this long, fringing ice shelf in the north west part of the Weddell Sea was assumed to be the latest in a long line of victims of Antarctic summer heat waves linked to Global Warming.

However in a paper published in the Journal of Glaciology, Prof. Neil Glasser of Aberystwyth University, working as a Fulbright Scholar in the US, and Dr Ted Scambos of University of Colorado’s National Snow and Ice Data Centre now say that the shelf was already teetering on collapse before the final summer.

“Ice shelf collapse is not as simple as we first thought,” said Professor Glasser, lead author of the paper. “Because large amounts of meltwater appeared on the ice shelf just before it collapsed, we had always assumed that air temperature increases were to blame. But our new study shows that ice-shelf break up is not controlled simply by climate. A number of other atmospheric, oceanic and glaciological factors are involved. For example, the location and spacing of fractures on the ice shelf such as crevasses and rifts are very important too because they determine how strong or weak the ice shelf is”.

The study is important because ice shelf collapse contributes to global sea level rise, albeit indirectly. “Ice shelves themselves do not contribute directly to sea level rise because they are floating on the ocean and they already displace the same volume of water. But when the ice shelves collapse the glaciers that feed them speed up and get thinner, so they supply more ice to the oceans,” Prof. Glasser explained.

Professor Glasser acknowledges that global warming had a major part to play in the collapse, but emphasises that it is only one in a number of contributory factors, and despite the dramatic nature of the break-up in 2002, both observations by glaciologists and numerical modeling by other scientists at NASA and CPOM (Centre of Polar Observation and Modeling) had pointed to an ice shelf in distress for decades previously. “It’s likely that melting from higher ocean temperatures, or even a gradual decline in the ice mass of the Peninsula over the centuries, was pushing the Larsen to the brink”, said co-author Ted Scambos of University of Colorado’s National Snow and Ice Data Centre.

The focus of further study is now moving to the Larsen C shelf, a much thicker and apparently more stable area, and while there are at present no signs that this shelf is likely to collapse, Professor Glasser’s paper will play an important role in informing future study. The keen interest expressed in the paper has also been a boost to Professor Glasser’s hopes of raising funds to travel to Antarctica this year to conduct some of his research in the field.

The Journal of Glaciology is one of the most influential journals in the field, and as a sign of its esteem for the research conducted by Professor Glasser and the team, the journal decided to ‘fast-track’ the paper through the publication process and give it prominence as lead article in the first edition in 2008.