Here’s what’s below an unstable glacier


Antarctic robot gathers information at the all-important grounding line.


Scientists have made the first visit to the grounding line of Antarctica’s Thwaites Glacier.
CREDIT: Icefin / Georgia Tech / Schmidt lab / ITGC

By Nick Carne

Scientists have taken a close-up look at the foundations of one of the most unstable glaciers in Antarctica.

Using a robotic underwater vehicle called Icefin, they captured the first images of the grounding line below the Thwaites Glacier – the line between where the glacier rests on the ocean bed and where it floats over water.

The farther back the grounding line recedes, the faster the ice can flow into the sea, pushing up the sea level.

"Visiting the grounding line is one of the reasons work like this is important because we can drive right up to it and actually measure where it is," says Britney Schmidt, from Georgia Institute of Technology, US.

"It's the first time anyone has done that or has ever even seen the grounding zone of a major glacier under the water, and that's the place where the greatest degree of melting and destabilisation can occur."

Thwaites already accounts for about 4% of global sea-level rise, researchers say, and there are concerns that a tipping point in the stability at its foundations could result in a run-away collapse of the glacier and boost sea levels by as much as 60 centimetres.

So great is the concern that the International Thwaites Glacier Collaboration (ITGC) was established just to keep an eye on a block of ice the size of Britain.

For the latest project, researchers from the US and the British Antarctic Survey (BAS) spent December and January on the glacier and used a hot-water drill to melt a 590-metre hole in the ice to provide access to the ocean cavity.

"Icefin swam over 15 kilometres round trip during five missions,” says Schmidt. “This included two passes up to the grounding zone, including one where we got as close as we physically could to the place where the seafloor meets the ice.

"We saw amazing ice interactions driven by sediments at the line and from the rapid melting from warm ocean water."

The scientists also took seismic and radar measurements and collected cores of sediment from the seafloor and under parts of the glacier grounded on the bed to examine the quality of the foothold that it offers.

"We know that warmer ocean waters are eroding many of west Antarctica's glaciers, but we're particularly concerned about Thwaites,” says Keith Nicholls, a BAS oceanographer.

“This new data will provide a new perspective of the processes taking place, so we can predict future change with more certainty."

Schmidt says the amount of ice flowing to the sea from Thwaites and neighbouring glaciers has nearly doubled. In the past three decades

"While Greenland's contribution to sea level has already reached an alarming rate, Antarctica is just now picking up its contributions to sea level," he says.

"It has the largest body of ice on Earth and will contribute more and more of sea level rise over the next 100 years and beyond. It's a massive source of uncertainty in the climate system."

  1. https://thwaitesglacier.org/
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