New threat to Antarctic ice shelf emerges | Environment| All topics from climate change to conservation | DW | 14.05.2012
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New threat to Antarctic ice shelf emerges

German researchers have found evidence that areas in Antarctica, previously thought relatively safe from the direct influence of climate change, are melting rapidly.

Melting ice east of Greenland

Scientists fear that melting Antarctic ice could drastically raise sea levels

An Antarctic area previously thought stable is at risk of melting rapidly within the next century, new research suggests.

In a study published earlier this month, a team from the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany says the now-intact Filchner-Ronne ice shelf in the peripheral Weddell Sea could disintegrate, pushing parts of the West Antarctic Ice Sheet into retreat.

The German researchers found that rising temperatures could thin the ice on the Weddell Sea, sending warm ocean currents under the frozen Filcher-Ronne ice shelf and accelerate melting.

Karte der Antarktis mit den Kennzeichnungen Weddell-Meer, Filchner-Ronne-Schelfeis und Ammundsensee --- DW-Grafik: Peter Steinmetz

The frozen Filchner-Ronne ice shelf lies in the Weddell Sea

"We found a mechanism which drives warm water towards the coast with an enormous impact on the Filchner-Ronne Ice Shelf in the coming decades,” Hartmut Hellmer, the study’s co-author, said in a statement.

Ice shelves like Ronne-Filchner sit on water, and thus their disintegration can't raise sea levels directly. But they also hold back ice sheets that sit atop land - and those would start to drain into the sea if shelves weren't there to block them.

The research is at odds with previous studies that indicated that global warming was thawing ice primarily along Antarctica’s west coast, but seemed to have little impact on other regions . The Weddell Sea lies at the southern most point of the Atlantic Ocean, near the tip of South America.

Ice Feeds Ice

Antarctica spans the land and the seas around the South Pole. The Arctic Circle delineates its borders. The continent’s landscape rises and plummets across daunting ice-covered mountains and valleys.

The ice that reaches past Antarctica’s coastlines covers its bays. Glaciers connect these ice shelves to the land, allowing them to lie on solid ground and simultaneously float in the sea.

The largest sheets of ice are the Ross Ice Shelf and the Filchner Ronne Ice Shelf.
The Filchner Ronne Ice Shelf spans an area of 450.000 square kilometers, larger than Germany. The ice pack extends out 1000 km into the ocean. Ice that gradually migrates from the land toward the coast “feeds” the ice shelves.

Climate change affects the Weddell Sea

Until now, researchers believed that mainly the ice in the Amundsen Sea off Antarctica’s west coast was melting.

"The Weddell Sea as not really on the screen because we all thought that, unlike the Amundsen Sea, its warm waters would not be able to reach the ice shelves," Hartmut Hellmer said in a statement.

Hellmer’s team used computer models to simulate the effects of rising temperatures in the Weddell Sea. They found it melted sea ice, redirecting warm currents under the Filchner-Ronne Ice Shelf. They projected average thinning of 4 meters a year by the end of the century, with a portion melting by as much as 50 meters a year near the point that the shelf is grounded.

ATA, 2003 : Koenigspinguin (Aptenodytes patagonicus), Gruppe. [en] King Penguin (Aptenodytes patagonicus), group. | ATA, 2003: King Penguin (Aptenodytes patagonicus), group.

The Antarctic is home to penguins

“Earlier publications said that this region was protected because the water masses under the ice shelf were supposed to decrease in a warmer climate,” said Hellmer. The newest calculations by the researchers in Bremerhaven shows that the Weddel Sea is also subject to fluctuations in the climate.

Predicting the worst

Hellmer and his team predict that increasing air temperatures over the southeastern Weddell Sea will set off a chain reaction within the next 60 years.

First, the warm air will make the ice that’s floating in the sea thinner and more fragile. This will lead to a fracture in the area that has been keeping the warm water from melting the ice shelves under water.

“According to our calculations, this protective barrier will dissolve by the end of the century,” said Hellmer.

**FILE** In this July 29, 2008 file photo large pieces of ice are seen drifting off after separating from the Ward Hunt Ice Shelf. A chunk of ice shelf nearly the size of Manhattan has broken away from Ellesmere Island in Canada's northern Arctic, another dramatic indication of how warmer temperatures are changing the polar frontier, scientists said Wednesday, Sept. 3, 2008. (AP Photo/Sam Soja, The Canadian Press)

Ice shelfs hold back ice sheets that could melt into the sea

Ice shelves act like corks in a bottle. They hold the ice away from the ocean that migrates to the coast from the land. If the ice shelf thins, then the ice it’s holding back on land can begin to migrate toward the sea, the researchers reported.

“If it hits the ocean, then it doesn’t even need to melt to increase sea levels greatly. It displaces a lot of water on its own,” said Hellmer.

According to these calculations, this process could lead to a sea level increase of 4.4 mm per year.

“That’s, of course, the worst case scenario,” said Hartmut Hellmer. “The system will probably even out to the lesser value at some point.”

Researchers need more on site data

The latest data is based only on computer models. The question is how well these types of calculations can reflect reality. Hellmer’s team also ran the same analysis for 20th century data in order to test the reliability of their predictions for the future. According to the researchers, their tests were very consistent with the real life outcomes.

Hellmer pointed out that the scientific community lacks measurements from this region of the Antarctic. The sea ice is so dense there that even the best ice-measuring equipment can’t cut through it.

“The few measurements that we and other researchers have does confirm this and also that there’s a current of warm water directly at the edge of the ice shelf. However, it still hasn’t given us the temperatures that our model has shown,” he said.

International support for latest findings

Other researchers have been making similar predictions. Martin Siegert and his research colleagues at the University of Edinburgh have been reporting that the Weddell Sea will be much warmer by the end of the 21st century. They also predict that this would affect the ice coverage.

Siegert’s colleagues also used computer analysis. Siegert said this region of Antarctica will be changing, “but it’s impossible to predict what effects these changes will have.”

At this point, no one knows enough about this region of Antarctica.

Author: Brigitte Osterath/
Editor: Judith Hartl

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