New clues to the icy Antarctic continent revealed

December 12, 1999

With new tools and technology, scientists are getting a first look at strange features and puzzling behaviors on the frozen Antarctic continent. Icy tributaries feed giant, frozen streams that churn icebergs into the sea. Rows of long, sinuous snow dunes on the East Antarctic plateau are blown by fierce, constant winds, but appear to stay frozen in place for decades. Hundreds of meters below ice ridges, warped ice layers record the dynamic history of some ice streams, and the quiet stability of others.

These latest findings by Antarctic researchers will be reported at the Fall American Geophysical Union meeting in San Francisco. The press briefing will be held on Dec. 13, 1999 at 3 p.m. PST (6 p.m. EST) in Room 112 of the Moscone Convention Center.

In unraveling the ancient history of the continent, scientists hope to be able to tell its future. Dr. Robert Bindschadler, a NASA Goddard Space Flight Center (Greenbelt, Md.) glaciologist, studies the way that the West Antarctic ice sheet flows along massive rivers of ice into the sea. "We have to understand the ice streams in order to predict the future and to know what their contribution will be to sea level change," he said, adding that if the entire West Antarctic ice sheet were to flow into the ocean, global sea level could rise as much as 20 feet (six meters).

Scientists have been aware of ice streams since Antarctic exploration in the mid-1970s. Vast streams of ice flow for hundreds of miles from the West Antarctic ice sheet into the sea, acting as giant conveyer belts dumping the continent's accumulated snow cover.

For a long time, scientists were mystified because the ice streams appeared to start from a near standstill and then flow hundreds of feet per year faster than the surrounding ice sheet.

The point where ice streams begin to flow rapidly is marked by deep crevasses in the ice between the fast flowing ice streams and the slower moving ice sheet. But upstream, there isn't anything on the surface to tip scientists off to where the ice streams are coming from, said Bindschadler.

Now, data taken by the Canadian Radarsat satellite in 1997 during NASA and the Canadian Space Agency's Antarctic Mapping Mission, has allowed researchers to see that the vast rivers of ice were actually the product of smaller tributaries flowing from further into the continent's interior.

"It's a huge amount of information that would have taken decades to collect, and we never would have the resources to make this stunning discovery without Radarsat," said Bindschadler. "What we see is that there are tributaries - well-defined regions of flowing ice that are feeding the ice streams." Bindschadler said that the tributaries flow more slowly than the larger ice streams and therefore aren't marked by gaping crevasses along their borders.

Another interesting discovery, said Bindschadler, is that the tributaries flow within valleys on the continent's rocky surface, a factor that could be causing the ice to pick up speed. Ice funneled into the valleys becomes thicker than the surrounding ice, causing the base to become warmer and flow more easily. Then, two or more tributaries join and feed into the larger and faster-flowing ice streams, quickly moving the continent's accumulated ice to sea.

The Radarsat Antarctic Mapping Mission allowed Byrd Polar Research Center glaciologist Dr. Kenneth Jezek and colleagues to produce the first, high-resolution radar map of the entire Antarctic continent. The map is so clear, it can pick out features as small as a research bungalow but still outline with great precision the entire Antarctic coastline to help researchers see how the ice sheet ebbs and flows over time.

Jezek's team also identified areas of fast flowing ice on the ice sheet. Jezek said that the map shows the complexity of ice streams feeding the ice shelves in East and West Antarctica and small, fast-flowing glaciers scattered around the entire continent's perimeter.

Because of the rapid movement of ice streams, the surface of the ice only records their movement for a hundred years or so. To look further back in time, Nadine Nereson, a glaciologist from the University of Washington, studies the slow moving ridges between the ice streams that contain a record of ice flow for thousands of years.

"The important questions are," said Nereson, "have the ice streams always been where they are now, and how did they look in the past?" Nereson said that the ice ridges contain a record of their flow history, and the challenge is to interpret the record using ice flow models to discover how the fast moving ice streams that borders the ridges have changed over time.

By dragging ice-penetrating radar behind a snowmobile, Nereson and colleagues can see all the way through the 3,000-foot (1,000-meter) -thick ice to the rock below. The radar picks out different layers in the ice that deform in response to the movement of the neighboring ice streams.

Nereson said that a ridge bounded by two ice streams that flow very stably for thousands of years will show a very symmetrical bulge in the ice layers beneath the ridge divide, and analyzing the shape of the bulge can reveal past changes in ice stream elevations. In ridges bounded by rapidly changing ice streams, the bulge is skewed or warped. "The exciting part is that we could previously detect changes of only a 100 years or so," said Nereson, adding that the new method can tell what the ice streams have been doing over the last 1,000 to 5,000 years.

Across the continent, on the East Antarctic plateau, glaciologists Mark Fahnestock, from the University of Maryland, and Ted Scambos, from the University of Colorado, discovered from a satellite view something impossible to see from the ground. Three massive fields of snow dunes,-together covering an area larger than the state of California-dot the plateau. "The dunes represent a very extreme environment on the surface of the ice sheet caused by very stable winds," said Fahnestock.

Using data from National Oceanic and Atmospheric Administration satellites and declassified military satellite images, Fahnestock found that the dunes have crests that are up to 60 miles (100 kilometers) long, lie 1.2 miles (two kilometers) apart and are only 10 feet (three meters) high from base to crest. Explorers have crossed the dunes by foot, but they were never identified because their faces are far less steep than more familiar sand dunes.

Fahnestock said that the dunes may be formed by recrystalization of snow caused by warm winds rather than snow drifting, but like many things about the mysterious continent, the dunes are something scientists are just beginning to understand.
Lynn Chandler, GSFC, Greenbelt, Md.
(Phone: 301-614-5562)

Earl Holland, Byrd Polar Research Center, Columbus, Ohio
(Phone: 614-292-8384)

Vince Stricherz, University of Washington, Seattle, Wash.
(Phone: 206-543-2580)

Lee Tune, University of Maryland, College Park, Md.
(Phone: 301-405-4679)

NASA/Goddard Space Flight Center

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