First map of ground beneath Thwaites Glacier revealed by British Antarctic Survey

Research that has effectively turned back the geological click 100 million years - to a time when New Zealand was ripped away from Antarctica - has led to new understanding of how Thwaites Glacier is being affected by climate change.

The British Antarctic Survey has created the first map of the ground beneath what is Antarctica’s most vulnerable glacier.

And the analysis shows there is less sedimentary rock than expected, which could affect how the ice slides and melts in decades to come.

Dr Tom Jordan, the BAS geophysicist who the led study published in Science Advances, explained: “Sediments allow faster flow, like sliding on mud.

“Now we have a map of where the slippery sediments are, we can better predict how the glacier will behave in future as it retreats.”

The glacier is about the size of Great Britain, or the US state of Florida, and is one of the fastest-changing ice-ocean systems in Antarctica.

Much of the ice sheet is below sea level and susceptible to rapid, irreversible ice loss that could raise the global sea level by more than half a metre within centuries.

Thwaites glacier’s grounding zone — the point where it meets the seafloor — has retreated 14km since the late 1990s.

To study the distribution of sedimentary rocks beneath the glacier, researchers used airborne surveys using aircraft equipped with radar that can see through the ice to the rocks below, and sensors that can map minute variations in gravity and magnetism hundreds to thousands of metres below the ground and seabed on which the glacier rests.

These multiple data sources were combined into a a 3D picture of features, including the type and extent of different rocks.

Dr Jordan said: “The integrated nature of the airborne surveys was one of the keys to this research. Each sensor on the aircraft provided an important but incomplete part of the picture, but by bringing them all together we could provide the detailed map of the underlying geology”.

It gives a picture of what happened long before the Thwaites glacier was formed.

And it surprised researchers. As the base of glacier lies far below sea level, they had expected thick sediments to have been deposited over millions of years, as similar analysis has found on some other Antarctic glaciers.

But the data suggests only about a fifth of the ground below the glacier is sedimentary rock, which is found in a series of basins between 80 and 200km long and about 30km wide.

The rest comprises other geological bodies, including granite peaks and other hard rocks.

The BAS team believe the sedimentary basins were once much larger, but have been ground down to the bedrock by the glacier’s movement.

Despite the new understanding of the subglacial geology, it is not yet clear how this will affect estimates of ice flow and loss from Thwaites or other glaciers. But the study shows the geological landscape has a direct control on the basal shear stress, and this influences how fast ice can flow into the ocean.

Further study of these processes is now planned, while modellers may use the data to make more reliable projections of future ice loss.

Dr Jordan added: “We hope that by showing the detailed geology, and how it correlates with the basal friction, future models of glacial retreat will have lower uncertainty, as the controls of the basal processes will be better understood.

“No single scientific study could ever match the scale and challenge of climate change. But it is the incremental building of all the individual scientific studies like this that allows us to understand and tackle that challenge.”

Glaciologist Dr Sarah Thompson, a co-author on the paper, said: "The integrated approach used in this study has significant potential for successful application elsewhere in Antarctica, enabling us to explore other potentially vulnerable regions where current knowledge is sparse."A