US-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 want to understand its likely 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 will be directing operations 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 programme to investigate the glacier. Data is to be gathered in front of, and on top of the ice stream. Instruments will even be sent under its floating front, or shelf.  It's hoped that by capturing Thwaites' every behaviour, computer modellers can then better predict how its mass will respond to a warming world. What sorts of experiments are planned? One of the studies to be conducted off the Palmer is a seal-tagging exercise. Marine mammals will be captured on islands near the glacier and fitted with sensors. When seals are released to dive in the vicinity of Thwaites, they'll report back on seawater conditions.

"Weddell and Elephant seals like hanging out near the ice front or under ice shelves, places we as humans can't go," explained Dr Lars Boehme from St Andrews University. "The sensors record details about the seals' immediate physical environment, which gives us a clearer picture of the current oceanic conditions in these remote and inaccessible places."