Antarctic ice sheet built from the bottom up

Some of the Antarctic ice sheet is formed by water re-freezing from below not just by snow falling on top as was traditionally thought, a study claims.

Scientists, who unveiled their findings on March 3, believe their research will help them project the effects of climate change.

Experts are seeking to understand the frozen continent since even a small thaw could swamp low-lying coastal areas and cities.

Antarctica contains enough ice to raise world sea levels by about 57meters if it ever all melted.

A six-nation study of the jagged mountain range as high as the Alps that is buried under ice in East Antarctica found that almost a quarter of the ice sheet in the area was formed by a thaw and re-freeze of water from underneath.

Deep below the surface, ice flowing into narrow, submerged valleys often melted because of high pressure and heat from the earth below and re-froze when it was forced up again.

The findings, published in the journal Science, confound a traditional view that ice sheets are almost solely formed by snow that lands on top, gets compressed into ice and flows slowly towards the oceans because of gravity.

'We usually think of ice sheets like cakes - one layer at a time added from the top. This is like someone injected a layer of frosting at the bottom - a really thick layer,' Robin Bell, lead author at Columbia University in New York, said.

The scientists said that about 24 per cent of the ice in an area around Dome A, a 13,800ft high plateau the size of California that forms the top of East Antarctica, was formed by re-frozen ice.

'In some places up to half the ice thickness has been added from below,' they wrote of ice above the invisible Gamburtsev Mountain range.

The finding could help understand flows of Antarctic and Greenland ice sheets, and possible responses to global warming.

The British Antarctic Survey (BAS), which took part, said it gave 'new understanding about ice sheet growth and movement that is essential for predicting how the ice sheet may change as Earth's climate warms'.

Radars spotted unexpected bulges deep in the ice - one was 0.6miles high from the bottom of the ice sheet.

'We almost thought the equipment was broken,' co-author Tom Jordan of BAS said.

The UN panel of climate scientists projected in a 2007 report that world sea levels may rise by 18cm to 59 cm in the 21st century, or by more if a thaw of Greenland or Antarctica picks up.

The thaw and re-freeze might also affect chances of finding unknown life in sub-glacial lakes in Antarctica such as Vostok, where Russian scientists have been drilling. These lakes may have been isolated for a shorter time than previously believed.

Antarctica's ice sheet formed about 32million years ago but Jordan said that experts now believed the oldest ice was only 1.4million years old.

‘남극 빙판, 아래서 만들어져 올라와’

남극 대륙의 빙판 일부는 지금까지 생각한 것처럼 단지 눈이 내려서가 아니라 아래에서 물이 다시 얼어 만들어 진 것이라고 과학자들이 지난 3월 3일 한 연구논문에서 밝혔다.

이 과학자들은 자신들의 연구결과가 기후변화의 영향을 계산하는 데 도움이 될 것으로 믿고 있다.

조금만 해빙이 돼도 저지대의 해안과 도시를 넘쳐나기 때문에 얼어붙은 대륙을 이해할 수 있다.

남극대륙은 얼음을 많이 품고 있어 만약 전부 녹으면 세계 해수면이 약 57미터 올라가게 된다.

동 남극대륙에 얼음으로 묻혀 있는 알프스만큼 높은 뾰족뾰족한 산등성이인데 대해 6개국이 참여한 연구결과로 이 지역 빙판 거의 1/4이 아래에서 해빙과 물의 재빙에 의해 형성됐다는 것을 알아냈다.

표면 밑 깊숙이 좁고 침수된 계곡을 흘러 다니는 얼음이 지하의 고압과 열로 녹기도 하고 위로 올라오면 다시 얼었다.

잡지 “과학”에 발표된 이 같은 발견은 빙판이 거의 하늘에서 내린 눈으로만 형성되며 얼음으로 압축돼 중력으로 서서히 대양으로 떠내려간다는 전통적인 견해가 틀렸음을 입증해주고 있다.

뉴욕 콜럼비아대 수석 연구원인 로빈 벨은 “우리는 보통 빙판을 케이크처럼 생겼다고 생각한다. 즉 위에서부터 한번에 한 층씩 쌓인 것이다. 이는 누군가가 정말로 두꺼운 층인 바닥에 서리층을 불어넣은 것 같다.

돔A 주위 지역에 있는 얼음의 약 24%는 재차 얼은 얼음으로 돼있다. 돔A는 동 남극대륙 정상에 형성된 캘리포니아 주 크기의 1만 3,800피트의 고원이다.