A hunk of ice the size of Delaware broke off from the Antarctic Peninsula.
Sometime in the last few days, scientists say an iceberg weighing roughly a trillion metric tons separated from the Larsen C Ice Shelf and began its long, slow drift northward through the Weddell Sea.
The 2,400 square-mile mass of ice won’t immediately raise sea levels, but its loss has probably altered the profile of the continent’s western peninsula for decades to come.
The Larsen Ice Shelf consists of a series of many floating ice chunks. It is named for Norwegian explorer Capt. Carl Anton Larsen, who discovered it in 1893.
By the time it was first photographed in the 1960s, the fateful crack was already visible, according to NASA.
But in 2014, the crack began to grow — and fast. It eventually expanded into a 124-mile-wide semicircular rift, with the iceberg holding on to the peninsula by a thread of ice less than 3 miles wide a month before it broke away.
The release of this iceberg has reduced Larsen C, the largest ice shelf in the Larsen formation and the fourth-largest on the continent, by more than 12%. Scientists says the remaining ice shelf could now be less stable, which could pave the way for a more severe event: disintegration.
Here’s what you need to know about the break:
What’s an ice shelf anyway?
Ice shelves are thick platforms of ice that float on the surface of the ocean.
As ice sheets on land accumulate heavy packs of snow, these formations flow downhill to the sea, forming a “shelf.”
Ice shelves naturally shed weight in the form of icebergs through a process called calving, or via melting on the bottom.
“That’s just the way Antarctica works,” said Helen Fricker, a glaciologist at the Scripps Institution of Oceanography who studies the Larsen C and other ice shelves.
One way to know if a shelf is healthy is to see if it’s gaining as much ice as it’s losing. If a large enough iceberg calves off, the entire shelf could collapse. That’s what happened with Larsen A in 1995 and Larsen B in 2002.
The iceberg that formed from Larsen C wasn’t abnormally large, Fricker said. It was only about half the size of one that calved from the Ross Ice Shelf in 2000: a 4,200-square-mile hunk of ice the size of Jamaica.
What’s worrisome about Larsen C’s calving is the possibility that it will lead to the collapse of the entire shelf, but scientists think that’s probably decades away. In the coming months and years, scientists will watch the area for signs of regrowth or more calving events, said Adrian Luckman, project leader for Project MIDAS and a glaciologist at Swansea University.
The iceberg itself probably will break into pieces, with some remaining in the vicinity and others drifting north into warmer waters.
Rignot isn’t optimistic that the ice shelf will recover. He noted that it has now retreated further than it has in the last 100 years.
“More bergs will detach, it will become weaker and eventually fall apart in a domino effect,” he said.
Does this mean sea level will rise?
The calving of this particular iceberg will not directly cause sea levels to rise.
In fact, the ice shelf already raised sea levels centuries ago when it first flowed from the continent into the ocean.
But Larsen C, which is nearly half a mile thick at its largest point, is holding back piles of ice and glaciers on land behind it, Rignot said.
“It’s like uncorking a bottle,” Rignot said. “These ice shelves are really plugs for future sea level rise.”
Scientists with Project MIDAS warn that if the ice shelf loses much more area, it could allow more glaciers to flow into the ocean, impacting sea levels at a “modest rate,” they said in a statement.
Larsen A and Larsen B held back relatively little land ice, Rignot said. However, if all the glacial ice behind Larsen C melted away, it would be equal to almost half an inch of sea level rise.
Farther south on the peninsula, unplugging larger ice shelves would have more severe impacts on sea level rise. For example, the George VI Ice Shelf on the peninsula’s south side holds back 11 inches of equivalent sea level rise.
Is climate change to blame?
Scientists do not agree on whether the calving of Larsen C can be linked to climate change.
Martin O’Leary, a glaciologist at Swansea and Project MIDAS, said in the statement that the calving was a natural event.
“We’re not aware of any link to human-induced climate change,” he said.
However, Dan McGrath, a glaciologist at Colorado State University, said the rapid warming of the Antarctic Peninsula helped fuel the collapse of the Larsen A and B ice shelves. While scientists haven’t made a direct connection between the rift on Larsen C and climate change, it’s not out of the question, he said in a NASA statement.
“There are definitely mechanisms by which this rift could be linked to climate change, most notably through warmer ocean waters eating away at the base of the shelf,” he said.
Rignot said the latest calving event, which took a 25-mile-wide bite out of the ice shelf, shows how the climate interacts with Antarctica.
“This is a proxy for what is looming ahead as climate keeps warming up,” he said. “This is not a natural cycle. This is a process of disintegration of ice around the Antarctic.”
Between 1990 and 2009, Larsen C was growing thinner, but in recent years the shelf has almost returned to its previous thickness, according to an analysis by Fricker. The problem is that reliable data go back only about 25 years, but the iceberg calving process occurs over a 50-year period, scientists estimate.
“We’re looking at things that have long time scales that we have been only observing for a short length of time,” she said. The latest calving event may turn out to be “a precursor to a collapse. We’re just not going to know that until time goes on.”
Scientists will learn more in the coming months as they observe how the shelf’s thickness and velocity change post-iceberg.
“It’s still winter down there,” Fricker said. “For the next six months, the ice shelf is going to be completely fine.”
MORE IN SCIENCE