Antarctica has a Huge Mantle Plume Beneath it, Which Might Explain Why its Ice Sheet is so Unstable

Beneath the Antarctic ice sheet, there lies a continent that is covered by rivers and lakes, the largest of which is the size of Lake Erie. Over the course of a regular year, the ice sheet melts and refreezes, causing the lakes and rivers to periodically fill and drain rapidly from the melt water. This process makes it easier for Antarctica’s frozen surface to slide around, and to rise and fall in some places by as much as 6 meters (20 feet).

According to a new study led by researchers from NASA’s Jet Propulsion Laboratory, there may be a mantle plume beneath the area known as Marie Byrd Land. The presence of this geothermal heat source could explain some of the melting that takes place beneath the sheet and why it is unstable today. It could also help explain how the sheet collapsed rapidly in the past during previous periods of climate change.

The study, titled “Influence of a West Antarctic mantle plume on ice sheet basal conditions“, recently appeared in the Journal of Geophysical Research: Solid Earth. The research team was led by Helene Seroussi of the Jet Propulsion Laboratory, with support from researchers from the Department of Earth and Planetary Sciences at Washington University and the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research in Germany.

Glaciers seen during NASA’s Operation IceBridge research flight to West Antarctica on Oct. 29, 2014. Credit: NASA/Michael Studinger

The motion of Antarctica’s ice sheet over time has always been a source of interest to Earth scientists. By measuring the rate at which the ice sheet rises and falls, scientists are able to estimate where and how much water is melting at the base. It is because of these measurements that scientists first began to speculate about the presence of heat sources beneath Antarctica’s frozen surface.

The proposal that a mantle plume exists under Marie Byrd Land was first made 30 years ago by Wesley E. LeMasurier, a scientist from the University of Colorado Denver. According to the research he conducted, this constituted a possible explanation for regional volcanic activity and a topographic dome feature. But it was only more recently that seismic imaging surveys offered supporting evidence for this mantle plume.

However, direct measurements of the region beneath Marie Byrd Land is not currently possible. Hence why Seroussi and Erik Ivins of the JPL relied on the Ice Sheet System Model (ISSM) to confirm the existence of the plume. This model is essentially a numerical depiction of the physics of the ice sheet, which was developed by scientists at the JPL and the University of California, Irvine.

To ensure that the model was realistic, Seroussi and her team drew on observations of changes in altitude of the ice sheet made over the course of many years. These were conducted by NASA’s Ice, Clouds, and Land Elevation Satellite (ICESat) and their airborne Operation IceBridge campaign. These missions have been measuring the Antarctic ice sheet for years, which have led tot he creation of very accurate three-dimensional elevation maps.

A view of mountains and glaciers in Antarctica’s Marie Byrd Land seen during the Nov. 2nd, 2014, IceBridge survey flight. Credit: NASA / Michael Studinger

Seroussi also enhanced the ISSM to include natural sources of heating and heat transport that result in freezing, melting, liquid water, friction, and other processes. This combined data placed powerful constrains on the allowable melt rates in Antarctica, and allowed the team to run dozens of simulations and test a wide range of possible locations for the mantle plume.

What they found was that the heat flux caused by the mantle plume would not exceed more than 150 milliwatts per square meter. By comparison, regions where there is no volcanic activity typically experience a feat flux of between 40 and 60 milliwatts, whereas geothermal hotspots – like the one under Yellowstone National Park – experience an average of about 200 milliwatts per square meter.

Where they conducted simulations that exceeded 150 millwatts per square meter, the melt rate was too high compared to the space-based data. Except in one location, which was an area inland of the Ross Sea, which is known to experience intense flows of water. This region required a heat flow of at least 150 to 180 milliwatts per square meter to align with its observed melt rates.

In this region, seismic imaging has also shown that heating might reach the ice sheet through a rift in the Earth’s mantle. This too is consistent with a mantle plume, which are thought to be narrow streams of hot magma rising through the Earth’s mantle and spreading out under the crust. This viscous magma then balloons under the crust and causes it to bulge upward.

Temperature changes in the Antarctic ice sheet over the last 50 years, measured in degrees Celsius. Credit: NASA/GSFC Scientific Visualization Studio

Where ice lies over top of the plume, this process transfers heat into the ice sheet, triggering significant melting and runoff. In the end, Seroussi and her colleagues provide compelling evidence – based on a combination of surface and seismic data – for a surface plume beneath the ice sheet of West Antarctica. They also estimate that this mantle plume formed roughly 50 to 110 million years ago, long before the West Antarctic ice sheet came into existence.

Roughly 11,000 years ago, when the last ice age ended, the ice sheet experienced a period of rapid, sustained ice loss. As global weather patterns and rising sea levels began to change, warm water was pushed closer to the ice sheet. Seroussi and Irvins study suggests that the mantle plume could be facilitating this kind of rapid loss today, much as it did during the last onset of an inter-glacial period.

Understanding the sources of ice sheet loss under West Antarctica is important as far as estimating the rate at which ice may be lost there, which is essentially to predicting the effects of climate change. Given that Earth is once again going through global temperature changes  – this time, due to human activity – it is essential to creating accurate climate models that will let us know how rapidly polar ice will melt and sea levels will rise.

It also informs our understanding of how our planet’s history and climate shifts are linked, and what effect these had on its geological evolution.

Further Reading: NASA, Journal of Geophysical Research

NASA West Antarctic Ice Sheet Findings: Glacier Loss Appears Unstoppable

It’s a key piece of the climate change puzzle. For years, researchers have been eyeing the stability of the Western Antarctic Ice Sheet as global temperatures rise. Melting of the ice sheet could have dire consequences for sea level rise.

And though not unexpected, news from today’s NASA press conference delivered by Tom Wagner, a cryosphere program scientist with the Earth Science Division of NASA’s Science Mission Directorate in Washington D.C., Sridhar Anandakrishnan, a professor of geosciences at Pennsylvania University, and Eric Rignot, JPL glaciologist and professor of Earth system science at the University of California Irvine was certainly troubling.

Credit: NASA
The key region targeted in the study (arrowed) Credit: NASA

The Western Antarctic Ice Sheet is a marine-based ice sheet below sea level that is bounded by the Ronne and Ross Ice Shelf and contains glaciers that drain into the Amundsen Sea. The study announced today incorporates 40 years of data citing multiple lines of observational evidence measuring movement and thickness of Antarctic ice sheets. A key factor to this loss is a thinning along the grounding line of the glaciers from underneath. The grounding line for an ice sheet is the crucial boundary where ice becomes detached from ground underneath and stretches out to become free floating. A slow degradation of the Western Antarctic Ice Sheet has been observed, one that can be attributed to increased stratospheric circulation along with the advection of ocean heat coupled with anthropogenic global warming.

Credit: Eric Rignot
A closeup of the region: red indicates regions where flow speeds have accelerated in the past 40 years. Credit: Eric Rignot

“This sector will be a major contributor to sea level rise in the decades and centuries to come,” Rignot said in today’s press release. “A conservative estimate is it would take several centuries for all of the ice to flow into the sea.”

Thickness contributes to the driving stress of a glacier. Accelerating flow speeds stretch these glaciers out, reducing their weight and lifting them off of the bedrock below in a continuous feedback process.

A key concern for years has been the possible collapse of western Antarctica’s glaciers, leading to a drastic acceleration in sea-level rise worldwide. Such a catastrophic glacial retreat would dump millions of tons of ice into the sea over a relatively short span of time. And while it’s true that ice calves off of the Western Antarctic ice sheet every summer, the annual overall rate is increasing.

The study is backed up by satellite, airborne and ground observations looking at thickness of ice layers over decades.

Researchers stated that the Amundsen Sea Embayment sector alone contains enough ice to increase global sea level by 1.2 metres.  A strengthening of wind circulation around the South Pole region since the 1980s has accelerated this process, along with the loss of ozone. This circulation also makes the process more complex than similar types of ice loss seen in Greenland in the Arctic.

The research paper, titled Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011 has been accepted for publication in the American Geophysical Union’s journal Geophysical Research Letters. The American Association for the Advancement of Science will also be releasing a related study on the instability of the West Antarctic ice sheet today in the journal Science.

The most spectacular retreat referenced in the study was seen occurring at the Smith/Kohler glaciers, which migrated about 35 kilometres and became ungrounded over a 500 kilometre square region during the span of 1992 to 2011.

Another telling factor cited in the study was the large scale synchronous ungrounding of several glaciers, suggesting a common trigger mechanism — such as ocean heat flux — is at play.

On the ice shelf proper, the key points that anchor or pin the glaciers to the bedrock below are swiftly vanishing, further destabilizing the ice in the region.

Assets that were used in the study included interferometry data from the Earth Remote Sensing (ERS-1/2) satellites’ InSAR (Interferormetry Synthetic Aperture Radar) instruments, ground team observations and data collected from NASA’s Operation IceBridge overflights of the Antarctic. IceBridge uses a converted U.S. Navy P-3 Orion submarine hunting aircraft equipped with radar experiment packages used to take measurements of the thickness of the ice sheet.

Possible follow up studies targeting the region are upcoming, including five Earth science and observation missions scheduled to be launched this year, which include the Soil Moisture and Passive (SMAP) mission, The Orbiting Carbon Observatory (OCO-2) and the Global Precipitation Measurement (GPM) Core Observatory, launched this past February.

Along with these future NASA missions, there are also two missions — RapidScat and the Cloud-Aerosol Transport System or CATS — slated to study climate headed for the International Space Station this year.

This comes as recent United Nations and United States reports have also announced the reality of climate change and anthropogenic global warming.

“The collapse of this sector of West Antarctica appears to be unstoppable,” Rignot said. “The fact that the retreat is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating sections of the glaciers.”

Of course, the solar cycle, volcanic activity, global dimming (via changes in reflectivity, known as albedo) and human activity all play a role in the riddle that is climate change. The bad news is, taking only natural factors into account, we should be in a cooling period right now.

And yes, reflective ice cover also plays a role in the albedo of the Earth, but researchers told Universe Today that no significant overall seasonal variations in the extent of surface layer of ice will change, as the key loss comes from the ungrounding of ice from below. Thus, this ice loss does not present a significant contribution to changes in overall global albedo, though of course, much of this additional moisture will eventually be available for circulation in the atmosphere. And the same was noted in the press conference for those pinning their hopes on the 2014 ice extent being greater than previous years, a season that was a mere blip on the overall trend. The change and retreat in the grounding line below seen in the study was irrespective of the ice extent above.

NASA’s Operation IceBridge will continue to monitor the ice flow when the next Antarctic deployment cycle resumes in October of this year.

And in the meantime, the true discussion is turning to the challenges of living with a warmer planet. Insurance companies, the Department of Defense and residents of low-lying coastal regions such as Miami’s South Beach already know that the reality of global warming and sea level rise is here. Perhaps the very fact that naysayers have at least backed up their positions a bit in recent years from “global warming isn’t happening” to “Its happening, but there are natural cycles” can at least give us a starting point for true intelligent science-based dialogue  to begin.

– Social media questions from today’s conference can be reviewed at the #AskNASA hastag.

 

Study Shows More Antarctic Ice Loss

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Increasing amounts of ice mass have been lost from West Antarctica and the Antarctic peninsula over the past ten years, according to a 10-year study from the University of Bristol, England. But at the same time, however, the ice mass in East Antarctica has been roughly stable, with neither loss nor accumulation over the past decade.

Professor Jonathan Bamber at the University of Bristol and colleagues estimated a loss of 132 billion tons of ice in 2006 from West Antarctica “up from about 83 billion tons in 1996” and a loss of about 60 billion tons in 2006 from the Antarctic Peninsula.

“To put these figures into perspective,” Bamber said, “four billion tons of ice is enough to provide drinking water for the whole of the UK population for one year.”

The data comes from satellite imagery that cover 85% of Antarctica’s coastline, which the researchers compared with simulations of snow accumulation over the same period, using a regional climate model.

“Over the 10 year time period of the survey, the ice sheet as a whole was certainly losing mass,” said Bamber, “and the mass loss increased by 75% during this time. Most of the mass loss is from the Amundsen Sea sector of West Antarctica and the northern tip of the Peninsula where it is driven by ongoing, pronounced glacier acceleration.”

In East Antarctica, the mass balance, which accounts for addition to the ice sheet due to snowfall and the subtraction of ice due to changes in the glacier, is near zero. But the thinning of its potentially vulnerable marine sectors suggests this may change in the near future.

As to the differences in the West and East Antarctic ice sheets, Bamber said, “The West Antarctic Ice Sheet is a “marine based” ice sheet resting on bedrock below sea level with bed slopes inclined downward inland. It has been suggested that this makes the WAIS more susceptible to change caused by the ocean than the East Antarctic Ice Sheet.”

The study conclude that the Antarctic ice sheet mass budget is more complex than indicated by the evolution of its surface mass balance or climate-driven predictions.

Changes in glacier dynamics are significant and may in fact dominate the ice sheet mass budget. This conclusion is contrary to model simulations of the response of the ice sheet to future climate change, which conclude that it will grow due to increased snowfall.

Satellite data was obtained from ERS-1, ERS-2, RADARSAT and ALOS.

Original News Source: University of Bristol Press Release