Submarine to explore why Antarctic glacier is melting so quickly

An international team of scientists has reached the Thwaites glacier in Antarctica and is preparing to drill through more than half a kilometre of ice into the dark waters beneath.

The 600-metre deep borehole will allow researchers to lower down a torpedo-shaped robotic submarine that will explore the underside of the ice shelf to better understand why it is melting so fast.

Thwaites glacier, which is part of the west Antarctic ice sheet, has lost an estimated 540bn tonnes of ice since the 1980s. But recent measurements show that the melting of the glacier is speeding up, sending even more ice into the Amundsen Sea.

“There are several glaciers in Antarctica that are doing similar things, but this is the one we are most worried about,” said David Vaughan, the director of science at the British Antarctic Survey, who has travelled south with the UK-US drilling team.

Thwaites glacier is one of the most remote and inhospitable places on Earth. It has taken the researchers weeks to get themselves and their equipment to the drilling site, a spot on the ice shelf about 1,500km (932 miles) from both the British Antarctic Survey’s Rothera research station and the American McMurdo station.

In brutal conditions, where the temperature can fall below -20C, the researchers will have only a few days to drill through the ice shelf, deploy the “icefin” submarine and retrieve it, and set a suite of monitoring instruments into the ice before the hole freezes over. “The aim is to do it as rapidly as possible. All of this will happen in three to four days. They really can’t afford to muck about,” said Vaughan.

The expedition to the Florida-sized glacier became more pressing this year when Nasa scientists used ground-penetrating radar to reveal a massive cavity in its base. The cavern, two-thirds the size of Manhattan and 300 metres tall, was formed as 13bn tonnes of ice melted away over the past three years. The enormous cavity allows water to get under the glacier and melt it from beneath.

Earlier this week, scientists on the team hauled radar-equipped sledges over the ice to map the thickness of the shelf near the “grounding line” where the glacier leaves land and extends over the sea. The map will help them pinpoint where to drill the borehole. During the site assessment, they came across a crevasse that plunged deep into the ice shelf.

The warming of the Southern Ocean is resulting in glaciers sliding into the sea increasingly rapidly.

Once they get the green light, the scientists will use a hot water drill to bore a 30cm-wide hole through the ice shelf. The equipment can melt a hole at about 1.5 metres per minute, meaning it will take more than six hours of nonstop drilling to get all the way through. Small teams who sleep overnight in tents on the ice will work in rotation around the clock to drill the hole, deploy the submarine, and set other instruments into the borehole for long-term monitoring.

“Nobody has ever been able to drill through the ice close to where it starts to float and that is the critical point,” Vaughan told the Guardian. “If everything goes to plan, they will drill the hole and then ream it out until it’s about 50cm across, and then lower in the autonomous underwater vehicle. That will actually go into the cavity and send back images in real time so they can navigate it right up to the point where the ice starts to float.”

The 3.5 metre-long icefin carries high definition cameras, sonar, and instruments for monitoring water flow, salinity, oxygen and temperature. These can determine how much fresh water is flowing out from under the ice shelf. The robotic sub will also sample the gritty sediment shed into the water as the glacier grinds over the slab of rock it sits on. The data will feed into computer models to refine predictions about the fate of the glacier and the magnitude of sea level rise its melting will produce.

Thwaites glacier is already responsible for about 4% of the global sea level rise, as the ice slips off the land and into the sea. But because the ice shelf is melting and thinning, the glacier is speeding up. Thwaites itself contains enough ice to raise global sea levels by more than 2 feet (61cm), but it holds back other inland glaciers that contain far more ice, enough to raise global sea levels by more than 2 metres.

“If Thwaites glacier melts, on its own, we will see a rise in sea level around our own coast,” said Vaughan. “We are not saying that it’s going to happen in the next 100 years or so, but it could certainly begin in that time period.”

“We’ll look at the flow of the ice and see how it’s affected, for instance, by tidal changes. All of those things tell us about the sensitivity of the system to small perturbations, which in future might be large perturbations as the ice shelf melts,” he added. “This is all about sea level rise. That is why we are here.”

The fieldwork, part of the International Thwaites Glacier Collaboration, will run until March 2020.