A valley underneath East Antarctica's most rapidly-changing glacier delivers warm water to the base of the ice, causing significant melting.
The intrusion of warm ocean water is accelerating melting and thinning of Totten Glacier, which drains enough ice to raise global sea levels by 3.5 metres. The glacier is one of the major outlets for the East Antarctic Ice Sheet, which is the largest mass of ice on Earth and covers 98 percent of the continent.
Climate change is raising the temperature of the oceans, and sea levels are predicted to rise about one metre per century. Totten Glacier could represent a major component of this change.
The research is published today in Nature Geoscience by scientists from Imperial College London and institutions in the US, Australia and France.
"It's only one glacier, but it's changing now and it is significant for sea levels globally," said study co-author Professor Martin Siegert, Co-Director of the Grantham Institute at Imperial College London. "The 3.5 metre rise may take several centuries to complete, but now the process has started it is likely irreversible. This is another example of how human-induced climate change could be triggering major changes with knock-on impacts that will be felt globally."
The East Antarctic Ice Sheet was previously thought to be surrounded by colder water and so relatively stable compared to the smaller West Antarctic Ice Sheet, which is losing more than 150 cubic kilometres of ice each year. However, satellite data have shown that the Totten Glacier has also been thinning considerably. To investigate why, the team of researchers surveyed the area.
Using radar and other geophysical techniques, they obtained a map of the topographical landscape underlying the glacier where it met the sea. Their results revealed a 5 km-wide valley running underneath the glacier capable of letting warm ocean water reach the ice base.
On thin ice
Thin ice at the margins of ice sheets can float on the ocean, but the ice inland is 'grounded' and in contact with the bedrock. The newly-discovered valley allows warm ocean water to flow underneath a region of floating ice, exposing the grounded edge of the ice sheet to the warmth and leading to glacier melting.
Destabilisation of the Totten Glacier could leave more ice inland vulnerable to change, said Professor Siegert: "Once a certain region starts to change, the implications for the connected ice are potentially significant. We are using computer modelling to understand whether changes in Totten Glacier could lead to changes in both adjacent and more distant places in Antarctica. While this work needs to be undertaken, the change at Totten Glacier itself is significant and concerning."
There are still many unknown landscapes beneath the Antarctic ice, and Professor Siegert and his colleagues are planning to map even more remote regions in an effort to understand the dynamics of the continent. These include two 'poles of ignorance' -- spots on Antarctica where you can stand and be at least 200km from the nearest data point relating to the continent beneath the ice.
The research was supported in the UK by NERC, and by the US NSF, the Australian Antarctic Division, as well as NASA's Operation IceBridge and the G. Unger Vetlesen Foundation.
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