Antarctic scientists have made a startling new discovery: liquid water locked deep under the Antarctic ice sheet regularly thaws and refreezes to the bottom, contributing more than half the thickness of the ice sheet in places and actively modifying its structure.

This newly discovered process, occurring far below the ice surface, could reshape our understanding of how the ice sheet expands and moves and how it might react to a warming climate.

Ice sheets are known to grow from the top as snow falls and builds up annual layers over thousands of years. But until now scientists have known little about the processes going on far below.

The discovery was made after an intensive field expedition in 2008–09, as part of the International Polar Year, known as Antarctica’s Gamburtsev Province Project (AGAP). The expedition involved scientists, engineers, pilots and support staff from the UK, USA, Australia, Germany, Japan and China, working out of two field camps in the Gamburtsev subglacial mountain range — AGAP South, operated by the United States, and AGAP North, run by the Australian Antarctic Division. From these bases Twin Otter aircraft carrying geophysical instruments flew 120 000 linear kilometres of survey lines to create 3-D images of the buried mountain range. The expedition also made detailed images of the overlying ice and subglacial water.

While the mountains lie beneath as much as three kilometres of ice in places, the scientists were able to detect refrozen structures that looked like beehives at the base of the ice sheet.

“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,” said project co-leader Robin Bell, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory.

“We did not think that water moving through ancient river valleys beneath more than one mile of ice would change the basic structure of the ice sheet.”

Dr Fausto Ferraccioli of the British Antarctic Survey, who worked out of the AGAP North camp, said the discovery provides a unique view on the interactions between subglacial water and ice sheet structure in East Antarctica.

‘Understanding these interactions is critical for the search for the oldest ice and also to better comprehend subglacial environments and ice sheet dynamics,’ he said.

‘Incorporating these processes into models will enable more accurate predictions of ice sheet response to global warming and its impact on future sea level rise.’

The research was published online on 3 March in the journal Science.