Vast iceberg poised to crack off Antarctica ice shelf

An enormous rift in one of Antarctica's largest ice shelves grew dramatically over the past several weeks, and a chunk nearly the size of Delaware could break away within months, British scientists reported this week.

If this happens, it could accelerate a further breakup of the ice shelf, essentially removing a massive cork of ice that keeps some of Antarctica's glaciers from flowing into the ocean. The long term result, scientists project, could be to noticeably raise global sea levels by 10 centimeters, or almost four inches.

It's the latest sign of major ice loss in the fast warming Antarctic Peninsula, which has already seen the breakup of two other shelves in the same region. These events have been widely attributed to climate change.

The crack in the ice shelf, known as Larsen C, been growing at an accelerating rate. Since the beginning of December, it has grown about 11 miles in length, after extending 13 miles earlier in 2016. The rift has grown about 50 miles since 2011, to a length of almost 100 miles in total, and has widened to well over 1,000 feet. Now, only 12 miles of ice continue to connect the chunk with the rest of the ice shelf.

When it breaks away, the loss would be of nearly 2,000 square miles of ice, say the researchers with Project MIDAS, a British government-funded collaboration based at Swansea and Aberystwyth universities in Wales. That's larger than Rhode Island and almost as big as Delaware.

[This stunning Antarctic lake is buried in ice. And that could be bad news.]

The consequences of the break could be dramatic.

"When it calves, the Larsen C Ice Shelf will lose more than 10% of its area to leave the ice front at its most retreated position ever recorded; this event will fundamentally change the landscape of the Antarctic Peninsula," said the researchers in a statement about the rift.

"We have previously shown that the new configuration will be less stable than it was prior to the rift, and that Larsen C may eventually follow the example of its neighbour Larsen B, which disintegrated in 2002 following a similar rift-induced calving event."

The British Antarctic Survey also released a statement on the growing rift, saying a huge iceberg is "set to calve" from Larsen C.

"Because of the uncertainty surrounding the stability of the Larsen C ice shelf, we chose not to camp on the ice this season," said David Vaughan, the survey's director of science, in the statement.

The floating ice shelf is fed by the flow of ice glaciers that sit above sea level on the Antarctic Peninsula. As the shelf shrinks, these glaciers could flow more quickly – which would contribute to rising sea levels. Losses from the ice shelf alone, however dramatic, would not have that effect, because the shelf is already floating on water, just like an ice cube in a glass of water.

Fortunately, the Antarctic Peninsula does not contain nearly as much ice as other, thicker parts of Antarctica, such as the West and East Antarctic ice sheets. The potential sea level rise if Larsen C is lost would be measured in centimeters; the sea level from these ice sheets could be measured in feet.

Still, it would subtract a major, enduring geographic feature from the planet, and add to already dramatic changes that have been seen in the Antarctic Peninsula, the portion of the icy continent that extends northward towards South America.

Two smaller ice shelves near Larsen C – Larsen A, and Larsen B – have already largely disintegrated. Larsen B has a remnant, but scientists have determined that this ice, too, could vanish before too long. They have also documented that following the collapse of much of the Larsen B ice shelf in 2002, the glaciers behind it sped up their flow toward the sea. Now, the fear is the same process could be unleashed on the larger Larsen C shelf.

The Larsen C ice shelf is more than 1,000 feet thick, and in spatial extent, nearly the size of Scotland. It is the fourth-largest ice shelf in Antarctica, although much smaller than the two largest, the Ross and Filchner-Ronne ice shelves.

The Antarctic continent is ringed with ice shelves, which are the ocean-front portions of larger glaciers. But as the climate changes, these features have been thinning and in some cases breaking apart dramatically.

Previous research has also documented that the Larsen C ice shelf is becoming less thick, and so floating lower in the water, and this appears tied to the warming of the Antarctic Peninsula in recent decades. Warmer seas could also be playing a role.

Now, the wait for the anticipated break begins.

Swansea University's Adrian Luckman, who heads up Project MIDAS, told the BBC that "If it doesn't go in the next few months, I'll be amazed."

Daniela Jansen, a researcher with the Alfred Wegener Institute in Germany who collaborates with the Project MIDAS team, largely agreed in an email to The Washington Post.

"I think the iceberg will calve soon," she said. "The jumps of the rift tip occurred in shorter time intervals the longer the rift got. This is probably due to the longer 'lever' for the forces acting to advance the rift, such as the up and down of the tides or strong winds towards the sea. Whether it will be months or maybe next year, I don't know."