Antarctica Melts.

Scientist want to know why Earth's frozen continent is vanishing.

Imagine sailing through dark, frigid Antarctic waters. In the distance you spot an iceberg, a floating chunk of ice, creeping toward you. Only this monster is the size of Rhode Island--24 miles long by 48 miles wide and 200 feet high, with a total area of 3,000 square kilometers (1,150 square miles). It's a chiller that makes the Titanic-sinker seem like an ice cube.

One such mammoth ice island, which trackers call B-10A, broke or calved off Antarctica, Earth's most southerly continent, in 1986. But by August 1999, B-10A spelled imminent danger as it drifted into busy shipping lanes between Antarctica and South America. For every foot of B-10A above sea level, three to five feet of ice jut below sea level--and "icebergs cut through a steel ship like a knife into a stick of butter," says Jeff Andrews, an analyst at the National Ice Center in Washington, D.C.

What's more, last year glaciologists, scientists who study glaciers (moving bodies of ice), made an alarming discovery. Nearly 3,000 sq km of the Antarctic Peninsula's Larsen and Wilkins ice shelves, continental ice masses that extend over the sea, vanished into the oceans in one year (see map, above). The massive thaw only fuels scientists' worst fear: Antarctica may be headed for a gradual meltdown.

ANTARCTICA HEAT-UP

In the past 50 years, average daily Antarctic temperatures have risen 3 [degrees] C (5.4 [degrees] F), a rate of heating that is faster than anywhere else on Earth--and faster than any time in recorded history. Since 99 percent of Antarctica is blanketed in ice, scientists worry that even partial melting could swell the world's oceans by 5 m (17 ft) and submerge many coastal cities!

A substantial Antarctic meltdown isn't probable in the foreseeable future. Yet, "if this trend continues, there'll certainly be reason for great concern," says Richard Moritz, a climatologist (climate scientist) at the University of Washington in Seattle.

Now researchers are scrambling to get a handle on the potential crisis. Last September, NASA and the Canadian Space Agency (CSA) launched Radarsat, an Earth-sensing satellite that uses radar (radio waves) to create the most detailed map ever made of Antarctica. Over the next year, mapmakers will stitch together more than 8,000 images collected by Radarsat--images so detailed they can detect buried snow-tractor tracks made 40 years ago! Researchers will use the new map to study how quickly Antarctica is shrinking.

BOTTOM OF THE WORLD

Antarctica, the coldest, windiest continent on Earth, boasts summer temperatures of -30 [degrees] C (-22 [degrees] F); frigid winds rage at 400 km (250 mi) per hour. Antarctica is also the planet's largest desert, or dry region (either hot or cold) that supports little vegetation. It gets less than 5 cm (2 in.) of snow or rain a year.

But Antarctica wasn't always a frozen wasteland. Scientists first found clues to a far warmer continent in 1982, when paleontologists (scientists who study fossils) unearthed the world's oldest marsupial (mammals that carry babies in pouches) fossil in the Antarctic Peninsula. The mammal never could have survived today's frigid Antarctic temperatures. How did the marsupial get there? Another clue: Antarctic sedimentary (formed by erosion) rocks' age, structure, and composition closely match those of rocks in South America and Australia--two far warmer continents.

Two hundred million years ago, scientists now deduce, the continents of South America, Africa, Australia, and Antarctica formed a single "super-continent," Gondwana; fossil evidence suggests it was once a tropical, dino-roamed landmass.

Over the course of 100 million years, plate tectonics--the movement of continental plates (chunks of Earth's crust)--split Antarctica from the vast continent and caused it to drift to the South Pole. There, hardly any direct sunlight reached the new continent and months elapsed without a sunrise. Earth's tilt keeps the South pole away from the sun during the northern summer. Even during Antarctic summers, most sunlight reflects off snow instead of melting it.

During the next 100 million years, the continent froze and melted several times, until ice eventually amassed to a thickness of 5 km (3 mi) in some regions. As Antarctica iced up, it became unlivable for most animals and plants. Today only insects and tiny organisms called microbes (see sidebar, left) inhabit the continent year-round. Seals and penguins migrate or travel to Antarctica during its warmer months from November to March. So, if Antarctica was warmer millions of years ago, is the present thaw part of Earth's natural periodic warming/ cooling cycle?

SEARCHING FOR ANSWERS

Many scientists think a warming Antarctic climate is induced by human activity. Factories, cars, and deforestation (destruction of forests) are among factors that increase atmospheric levels of greenhouse gases--heat-trapping gases like carbon dioxide and methane. Scientists link increasing greenhouse gases in the atmosphere to Antarctica's rising temperatures.

A different type of gas, chlorofluorocarbons (CFCs), produced by spray cans and refrigeration systems, for example, may also trigger Antarctica's shrinking ozone layer, or layer of heat-blocking gas in the atmosphere.

Already, satellite data from Radarsat are yielding vital clues. "Radar images of the Antarctic taken in 1997 show a different picture from satellite pictures snapped in the 1980s," says Kenneth Jezek, a geophysicist (scientist who studies Earth's physical aspects) at the Byrd Polar Research Center in Columbus, Ohio. "In some cases, ice shelves seem to be advancing into the ocean--in others they aren't."

Radarsat maps also reveal how ice shelves, moving through riverlike ice streams, reach the ocean and splinter into icebergs. And when icebergs the size of Rhode Island break off and float away, scientists take quick notice.

First at the Pole

In 1911, driven by a team of Dogs, Norwegian explorer Roald Amundsen reached the South Pole.

MELTDOWN

The white ice of Antarctica reflects most of the sun's light and heat. This is called the albedo effect. Do other colors of ice reflect light and heat as well?

YOU NEED:

plastic ice-cube tray * three shades of food coloring * wax paper * freezer * desk lamp or sunny window

TO DO:

1. Fill the tray with water. Use three food colorings to color some cubes, but leave a few clear ones. Place the tray in the freezer.

2. After the cubes are frozen, remove one of each color and replace the rest.

3. Place the cubes on a piece of wax paper about 5 cm (2 in) apart. Place the paper on a sunny windowsill or under the lamp.

4. Compare the cubes as they melt.

5. Try it again.

CONCLUSIONS

Which colors melt faster? Why? Do your results help explain the albedo effect?

How Glaciers Melt

A glacier (moving body of ice) drains into the ocean like a river. Due to the pressure of its own weight, ice underneath its surface becomes water and carries the glacier downhill. As the glacier flows, it collects debris, anything from particles to boulders. Once the river of ice reaches the snout (point where it meets the sea), it breaks apart into icebergs. Like ice cubes in a glass of water, icebergs melt. Larger icebergs often take years before they completely thaw.

Life Grows On!

Talk about extremes. In Antarctica's underground Lake Vostock, scientists just discovered microbes, or tiny organisms, living in total darkness under 5 km (3 mi) of ice. The critters thrive in average temperatures of-89 [degrees] C (-129 [degrees] F) --some of the coldest temperatures on Earth. Brrrr!

In 1996, using ice-piercing radar, scientists first discovered the nearly frozen lake --about the size of Lake Ontario--buried directly underneath the Russian research station at Vostock in East Antarctica. The hidden lake is home to microbes that have survived in apparent isolation from all other forms of life for more than one million years.

Like an igloo, ice protects the lake's microbes from frigid Antarctic air temperatures, while the planet's hot core warms the lake bottom. The weight of protective ice also increases the lake's surface pressure, speeding up water molecules, causing the lake to remain liquid in sub-zero temperatures.

Scientists hope the critters will answer questions about climate patterns and evolution on Earth and other planets. They're also mapping the microbes' genetic code, or hereditary material, to see if the microbes have relatives anywhere else on Earth.