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Media captionDr Kelly Hogan: "Thwaites is the plug holding back much of the West Antarctic Ice Sheet"

The US icebreaker Nathaniel B Palmer leaves Punta Arenas in Chile on Tuesday to begin an expedition to Antarctica's Thwaites Glacier.

The huge ice stream in West Antarctica is currently melting, and scientists are looking to their future future contribution to sea-level rise.

If all of Thwaites' frozen bulk were to give way, it would add 80cm to the height of the world's oceans.

"How much, how fast? That's our mantra," said Dr. Robert Larter.

"These are the questions we're asking about Thwaites," the British Antarctic Survey scientist told BBC News before leaving Chile.

Dr Larter wants to be operating on the Palmer when it gets on site.

What is the purpose of the expedition?

The Palmer's 52-day cruise is just one part of a five-year, joint US-UK research program to investigate the glacier.

Data is being collected in front of, and on the top of the ice stream. Instruments wants to be even under its floating front, or shelf.

It's hoped that by capturing Thwaites' every behaviour, computer modellers can predict how much they will respond to a warming world.

Image copyright
A.L.GORDON / NSF

What sort of experiments are planned?

One of the Palmer is a seal-tagging exercise.

Marine mammals wants to be captured on islands near the glacier and fitted with sensors.

When they are released to Thwaites, they'll report back on seawater conditions.

Dr Lars Boehme from St Andrews University. "Weddell and Elephant seals like hanging out near the ice.

"The sensors record details about the seals' immediate physical environment, which gives a clear picture of the current oceanic conditions in these remote and inaccessible places."

Image copyright
L.Boehme / St Andrews University

Image caption

The tags gather valuable data before falling off when the seal moults

Why is there such interest in Thwaites?

Thwaites, which is comparable in size to Britain, is what's termed a marine-terminating glacier. Snows fall inland and these are compacted into ice then flows out to sea.

When the snow hits the ice at the front of the icebergs. But Thwaites is out of balance.

It has been flying at 4km per year. It's also about 40cm a year.

Satellite data suggests Thwaites alone accounts for around 4% of global sea-level rise – an amount that has been doubled since the mid-1990s.

What is 'marine ice sheet instability'?

Thwaites' ice shelves and eroding the grounding – the point at which the ice stream becomes buoyant.

The problem for the glacier is its geometry. A large portion of it sits below sea level, with the rock bed sloping back towards the continent.

This creates what scientists refer to as "marine ice sheet instability" – an inherently unstable architecture, which, once knocked, can go into an irreversible decline.

Some scientists have argued that Thwaites is already in this state. The joint US-UK program aims to test all assumptions.

"We have had fantastic measurements over the past 25 years from satellites and research vessels that have visited the region," he explained. Dr Kelly Hogan.

"I think we are seeing anthropogenic (human-driven) change, but we do not have any links in the chain to say that definitively."

Image caption

Sediment cores wants to reveal the past history of Thwaites Glacier

Dr Hogan wants to be sediment cores in front of Thwaites.

The fossil contents and chemistry of these muds can be used to deduce the past position of the glacier and the ocean conditions.

US collaborator Dr Rebecca Totten Minzoni, from the University of Alabama, said: "By discovering the history of Thwaite's Glacier under past climate and ocean conditions, we can assess the stability of the glacier today.

"With the majority of the global population living on the coast, including important cultural and industrial centers like my hometown of New Orleans, we want to contribute to sea-level rise over the coming decades."

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