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VOA慢速英语新闻:南极洲冰架正在缩小

Lily85 于2013-08-13发布 l 已有人浏览
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科学家在研究地球最寒冷地方—南极洲的新情况,比如,南极洲的冰架正在缩小。一项新研究发现,南极洲部分地区夏季冰的损失达到1000年来的最高水平。
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Scientists are learning new things about Antarctica, the coldest place on Earth. For example, the Antarctic ice sheet is shrinking. A new study found that summer ice loss in parts of Antarctica was at its highest level in 1,000 years. The study showed that Antarctic ice was melting mostly from below ice shelves, where the water is warmer than the ice.

Ice shelves are the floating edges of the ice sheet – the ice cover - that extend over ocean waters. The study is the first complete look at all of the continent's ice shelves.

Eric Rignot is an earth system expert at the University of California, Irvine. He also works for the American space agency, NASA. There he serves as senior research scientist at NASA's Jet Propulsion Laboratory, also in California.

He says ice melting from below is responsible for 55 percent of the shelf loss from 2003 to 2008. That is a much higher rate than scientists thought earlier.

"We find that the melting of the underside of the ice shelves is even larger than the production of icebergs. So it is the dominant process of mass removal in the Antarctic."

Professor Rignot and his team used satellite observations, radar and computer models to measure features above the ice to learn what was going on below.

"That includes the velocity of the ice, the thickness of the ice, how fast the freeboard (height of ice above sea level) of the ice shelf is changing with time and also how much snowfall there is on the top of the ice shelves."

The measurements show differences from one area to the next around the continent. The major ice shelves are called Ross, Filchner and Ronne. They make up two-thirds of Antarctica's ice shelves. But they are responsible for only 15 percent of the melting ice.

At the same time, about ten smaller ice shelves produced half the total water from ice melting during the same period. The smaller ones are found along the edges of comparatively warm water. Professor Rignot describes the importance of the information.

"That means that during warming of the climate where the properties of the Southern Ocean are changing, they may be changing faster than other oceans in the world. We may be in a situation where the coastline of Antarctica may be changing at a faster pace than we thought in the past."

The professor says even small changes, like changes in ocean flow driven by wind, can make a huge difference in the melting of the ice shelf.

"If the wind regime changes in the Southern Ocean, it is going to change the way the ocean heat is distributed on the coast. And that's going to affect glaciers."

Sixty percent of the Earth's fresh water is held in the huge Antarctic ice sheet. Professor Rignot says the study will help experts predict how the continent reacts to warmer ocean waters and helps to cause rising sea levels around the world. The study was published in the journal Science.

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