南極冰下湖泊入海 加速海面上升

Scientists unveiled on Sunday the first direct evidence that massive floods deep below Antarctica's ice cover are accelerating the flow of glaciers into the sea.

How quickly these huge bodies of ice slide off the Antarctic and Greenland land masses into the ocean help determine the speed at which sea levels rise.

The stakes are enormous: An increase measured in tens of centimeters could wreak havoc for hundreds of millions of people living in low-lying deltas and island nations around the world.

Researchers discovered only recently that inaccessible subglacial lakes in Antarctica periodically shed huge quantities of water.

Data collected by a satellite launched in 2003 - the Ice, Cloud and Land Elevation Satellite, or ICESat - revealed a complex network of subglacial plumbing in which water periodically cascades from one hidden reservoir to another.

But the new study, published online in the journal Nature Geoscience, is the first to measure the potential impact of this invisible flooding on sea-bound glaciers.

A trio of scientists led by Leigh Stearns of the Climate Change Institute at the University of Maine matched ICESat data against a nearly 50-year record of how fast the Byrd Glacier in East Antarctica has moved toward the sea.

They discovered that during the same 14-month period that 1.7 cubic km of water cascaded through subglacial waterways, the 75-km long glacier downstream pick up speed, moving about 10 percent faster.

"Our findings provide direct evidence that an active lake drainage system can cause large and rapid changes in glacier dynamics," the researchers concluded.

"Water acts as a lubricant, reducing friction at the base of the ice and making ice flow faster," explained Helen Fricker of the Scripps Institution of Oceanography of California in a commentary, also in Nature Geoscience.

The study adds to growing scientific concern about the pace at which glaciers are melting into the seas

科學家於上週日首次公佈資料，證明南極冰層下的大規模水流正加速冰川流向海洋。

這些體積龐大的冰川正從南極大陸和格陵蘭島漂向海洋，它們漂移的速度直接決定了海平面升高的速度。

這導致的後果將觸目驚心：海平面升高幾十釐米就足以威脅居住在地勢較低的三角洲及島國地區的億萬人民的生存。

研究人員最近發現，南極冰層下隱祕的湖泊會發生週期性的傾瀉。

美國宇航局2003年發射的“冰雲和地面高度衛星”（ICESat）收集的數據顯示，南極冰層下有一個複雜的湖泊排水網絡，湖水會週期性地從一個隱祕的湖泊流向另一個湖泊。

而這項最新研究則首次估量了海洋冰川下隱祕水流的潛在影響。該研究成果在《自然地學》期刊的網絡版上發表。

以美國緬因州大學氣候變化學院的斯特恩斯爲首的三位科學家將衛星數據與南極東部的伯德冰川在過去近50年中移向海洋的速度進行了對比。

通過比較，研究人員發現，在14個月的時間中，冰層下湖泊溢出了1.7立方千米的水，75公里長的伯德冰川的移動速度加快了10%。

研究人員由此得出結論：“活躍的湖泊排水系統會導致冰川運動出現大規模、快速的變化，我們的研究結果爲此提供了直接證據。”

加州斯克裏普斯海洋學研究所的海倫•弗裏克在一篇科學評論中解釋說：“水可起到潤滑劑的作用，減少了冰層底部的摩擦，所以加速了冰川的流動。”她的這篇文章也在《自然地學》期刊上發表。

該研究進一步加劇了科學家對冰川融化速度的擔憂。