Scientists have discovered huge ice channels beneath a floating ice shelf in Antarctica.

At 250 metres high, the channels are almost as tall as the Eiffel tower and stretch hundreds of kilometres along the ice shelf. The channels are likely to influence the stability of the ice shelf and their discovery will help researchers understand how the ice will respond to changing environmental conditions.

Researchers from Newcastle University, the universities of Exeter, Bristol, Edinburgh, York and the British Antarctic Survey, used satellite images and airborne radar measurements to reveal the channels under the ice shelf.  The channels can be seen on the surface of the ice shelf, as well as underneath, because the ice floats at a different height depending on its thickness. 

The researchers also predicted the path of meltwater flowing under the part of the ice in contact with the land – known as the ice sheet. They discovered that the predicted flow paths lined up with the channels under the ice shelf at the point where the ice starts to float. 

The match-up indicates that the water flow beneath the grounded ice sheet is responsible for the formation of the channels beneath the floating ice shelf.  When the meltwater flowing under the ice sheet enters the ocean beneath the ice shelf, it causes a plume of ocean water to form, which then melts out the vast channels under the ice shelf. 

Previously, it was thought that water flowed in a thin layer beneath the ice sheet, but the evidence from this study suggests it flows in a more focussed manner much like rivers of water.  The way in which water flows beneath the ice sheet strongly influences the speed of ice flow, however, the implications for the future of the ice sheet are yet to be determined.

Dr Neil Ross, a lecturer in physical geography at Newcastle University, who is one of the study’s authors, said: "Discovering these huge ice shelf channels has dramatically changed our perception of the way in which the Antarctic ice sheet interacts with its surrounding ocean.

“We have established that in some parts of Antarctica, water, melted out from the bottom of the ice sheet, reaches the ocean in defined river-like channels flowing up to 1 km below sea level. This discovery has significant implications for how we measure, monitor and predict ocean water-driven ice melt, thought to be the primary process driving present-day ice sheet change.

“Our discovery suggests that melt rates along the ice front could be highly variable, dependent on where, and how, water from beneath the ice sheet enters the ocean."

Dr Anne Le Brocq from the University of Exeter, who led the study, said: “If we are to understand the behaviour of the ice sheet, and its contribution to changes in sea level, we need to fully understand the role of water at the base of the ice sheet. The information gained from these newly discovered channels will enable us to understand more fully how the water system works and, hence, how the ice sheet will behave in the future.”

Channels of this magnitude have been observed before elsewhere, but their formation has been attributed to purely oceanic processes rather than meltwater exiting the grounded ice sheet.  Now, with the connection to the meltwater system established, readily obtainable observations from the channels have the potential to shed light on how meltwater flows at the base of an inaccessible kilometre-thick ice sheet. The study received funding from Natural Environment Research Council (NERC) and the European Space Agency (ESA).

ENDS

Notes to editors

• The paper, Evidence from ice shelves for channelized meltwater flow beneath the Antarctic Ice Sheet,   is published in Nature Geoscience.

published on: 6 October 2013