“For global sea-level change in the next century, this Thwaites Glacier is almost the entire story” — David Holland, a geoscientist at New York University

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The largest U.S.-British Antarctic collaboration in seven decades officially launched at an event in Cambridge on Monday, as the two countries pooled dollars and scientific resources for missions to West Antarctica’s Thwaites Glacier, a Florida-size ice body that, scientists fear, could flood the world’s coastlines in our lifetimes.

“For global sea-level change in the next century, this Thwaites Glacier is almost the entire story,” said David Holland, a geoscientist at New York University, who will pair with British Antarctic Survey researcher Keith Nicholls to lead one of the six scientific field missions.

Thwaites is wide and deep and flows out of the heart of West Antarctica, a marine ice sheet that could contribute about 10 feet of global sea-level rise. Thwaites is losing ice rapidly, with its 50 billion tons a year currently driving 4 percent of global sea-level rise, and sits perched in 2,600-foot-deep waters atop a seafloor “bump” that scientists fear is the last thing holding it in place.

Past the bump, the ocean gets deeper still, and if Thwaites retreats down that hill, there could be no stopping it. Its contribution to sea-level rise could increase dramatically, bumping up the current global rate of 3.2 millimeters (about 0.12 inch) per year.

“The thinking is that if it goes inland, there are no bumps to hold it, and it will go faster and faster and retreat effectively to the South Pole,” Holland said.

Thwaites is a key part of the reason that recent computer-modeling studies have predicted that the Antarctic could double the previously projected rate of sea-level rise during this century. But it is in an extremely remote area, and the critical region that will determine how fast the glacier retreats — the “grounding line” where ocean, ice and bedrock meet at 2,600-foot depths — remains little studied.

It’s among the most difficult places on Earth for humans to explore.

The six field missions that the U.S. National Science Foundation and the British Natural Environment Research Council (NERC) will deploy to Thwaites in the next several years will be backed by two computer-modeling projects to process data from those missions and calculate what it means for the world’s coastlines.

One celebrity will be participating: “Boaty McBoatface,” an underwater research vehicle whose name stems from an online vote in Britain. After NERC gently ignored a popular vote and declined to award that name to a new icebreaker, as the online voters wanted, it went to the research vehicle.

The cost: $25 million for the research itself and possibly $25 million more for logistical support, which will mean transporting scientists to the remote Thwaites via planes, icebreakers, tractors, helicopters and other vehicles, and supporting them in the harsh environment. About 100 scientists are involved in the project in various capacities.

“Thwaites is exactly in the worst position in West Antarctica,” said Sridhar Anandakrishnan, a Pennsylvania State University geoscientist who will lead a Thwaites mission with Andy Smith of the British Antarctic Survey. “It’s just about as far from anywhere as you can get. It makes it really, really important to have this kind of integrated push of logistics.”

Anandakrishnan’s team will be doing seismic surveys — detonating small explosives within Thwaites to measure the echo as the sound waves from the blast bounce off the seabed beneath the thick ice and return. That will allow for measurement of what kind of substance Thwaites is flowing over, whose makeup could determine the glacier’s rate of retreat.

“If you have a soft bed, the bed deforms readily, the ice at the grounding line melts because of the ocean, it gets steep there, it wants to accelerate, and it wants to pull in ice from the interior,” Anandakrishnan said. “And the bed says, ‘Yep, that’s fine, here you go.’ ”

Holland’s project, meanwhile, will involve setting up atop the ice over the grounding line, drilling down as much as 2,600 feet, and releasing undersea vehicles and installing measuring devices in the ocean below in pitch black and at extreme pressures.

“We are going to drill at the grounding zone, put in a remotely operated vehicle and explore that area that’s never before been seen,” Holland said. “That’s very exciting.”

This research will help determine the melt rate beneath Thwaites Glacier and the ocean dynamics that are driving that.

The entire Amundsen Sea region, where Thwaites lies, has been losing ice rapidly, and scientists think this is being caused by warm ocean waters, which are climbing onto continental shelves from farther offshore and melting the glaciers from below.

In the Antarctic, a cold surface layer of ocean water lies above a warmer, deeper layer. While not much above freezing, the salty waters, acting at high pressures because of the depths involved, can rapidly melt ice.

Moreover, recent research suggests that in the Amundsen Sea region, the ongoing losses of ice from Thwaites and other glaciers are freshening the surface ocean, blocking a process in which surface waters sink and form so-called Antarctic Bottom Water — and, along the way, inhibit warm offshore waters from melting Thwaites and other glaciers.

This could be a “feedback” process in which more ice loss from Thwaites leads, via the ocean, to more ice loss from Thwaites.

The thickness of the glacier is another concern. As Thwaites retreats backward into a deep ocean canyon — even deeper than the current 2,600 feet — the entire glacier front will get thicker and thicker, and more than 300 feet of ice could eventually protrude above sea level. But it’s not clear whether ice cliffs this tall are able to be sustained above the water level, meaning that the cliffs could continually collapse, driving faster retreat.

The Thwaites mission is designed to gather large volumes of data on all of these processes that, once fed into computer models, will give more accurate projections of the rate and volume of sea-level rise during the current century — and help determine whether Thwaites will indeed play an outsize role.

“We still don’t know enough to put the proper error bounds on what that risk is,” Anandakrishnan said.