antarctica, – Hybrid Learning

an iceberg the size of delaware just broke away from ice rises are islands that are overridden by the ice shelf.

Batoota — Fri, 21 May 2021 18:47:24 +0000

A crack more than 120 miles long had developed over several years in a floating ice shelf called Larsen C, and scientists who have been monitoring it confirmed on Wednesday that the huge iceberg had finally broken free.

There is no scientific consensus over whether global warming is to blame. But the landscape of the Antarctic Peninsula has been fundamentally changed, according to Project Midas, a research team from Swansea University and Aberystwyth University in Britain that had been monitoring the rift since 2014.

“The remaining shelf will be at its smallest ever known size,” said Adrian Luckman, a lead researcher for Project Midas. “This is a big change. Maps will need to be redrawn.”

Larsen C, like two smaller ice shelves that collapsed before it, was holding back relatively little land ice, and it is not expected to contribute much to the rise of the sea. But in other parts of Antarctica, similar shelves are holding back enormous amounts of ice, and scientists fear that their future collapse could dump enough ice into the ocean to raise the sea level by many feet. How fast this could happen is unclear.

In the late 20th century, the Antarctic Peninsula, which juts out from the main body of Antarctica and points toward South America, was one of the fastest-warming places in the world. That warming had slowed or perhaps reversed slightly in the 21st century, but scientists believe the ice is still catching up to the higher temperatures.

Some climate scientists believe the warming in the region was at least in part a consequence of human-caused climate change, while others have disputed that, seeing a large role for natural variability — and noting that icebergs have been breaking away from ice shelves for many millions of years. But the two camps agree that the breakup of ice shelves in the peninsula region may be a preview of what is in store for the main part of Antarctica as the world continues heating up as a result of human activity.

“While it might not be caused by global warming, it’s at least a natural laboratory to study how breakups will occur at other ice shelves to improve the theoretical basis for our projections of future sea level rise,” said Thomas P. Wagner, who leads NASA’s efforts to study the polar regions.

The time-lapse image below shows the rift gradually widening from late 2014 to January of this year.

In frigid regions, ice shelves form as the long rivers of ice called glaciers flow from land into the sea. The result is a bit like a clog in a drain pipe, slowing the flow of the glaciers feeding them. When an ice shelf collapses, the glaciers behind it can accelerate, as though the drain pipe had suddenly cleared.

At the remaining part of Larsen C, the edge is now much closer to a line that scientists call the compressive arch, which is critical for structural support. If the front retreats past that line, the northernmost part of the shelf could collapse within months.

“At that point in time, the glaciers will react,” said Eric Rignot, a climate scientist at the University of California, Irvine, who has done extensive research on polar ice. “If the ice shelf breaks apart, it will remove a buttressing force on the glaciers that flow into it. The glaciers will feel less resistance to flow, effectively removing a cork in front of them.”

Scientists also fear that two crucial anchor points will be lost.

According to Dr. Rignot, the stability of the whole ice shelf is threatened, as the shelf front thins.

“You have these two anchors on the side of Larsen C that play a critical role in holding the ice shelf where it is,” he said. “If the shelf is getting thinner, it will be more breakable, and it will lose contact with the ice rises.”

Ice rises are islands that are overridden by the ice shelf, allowing them to shoulder more of the weight of the shelf. Scientists have yet to determine the extent of thinning around the Bawden and Gipps ice rises, though Dr. Rignot noted that the Bawden ice rise was more vulnerable.

“We’re not even sure how it’s hanging on there,” he said. “But if you take away Bawden, the whole shelf will feel it.”

The Antarctic Peninsula may be a canary in a coal mine.

The collapse of the peninsula’s ice shelves can be interpreted as fulfilling a prophecy made in 1978 by a renowned geologist named John H. Mercer of Ohio State University. In a classic paper, Dr. Mercer warned that the western part of Antarctica was so vulnerable to human-induced climate warming as to pose a “threat of disaster” from rising seas.

He said that humanity would know the calamity had begun when ice shelves started breaking up along the peninsula, with the breakups moving progressively southward.

The Larsen A ice shelf broke up over several years starting in 1995; the Larsen B underwent a dramatic collapse in 2002; and now, scientists fear, the calving of the giant iceberg could be the first stage in the breakup of Larsen C.

“As climate warming progresses farther south,” Dr. Rignot said, “it will affect larger and larger ice shelves, holding back bigger and bigger glaciers, so that their collapse will contribute more to sea-level rise.”

Iceberg Splits From Antarctica, Becoming World’s Largest

Batoota — Fri, 21 May 2021 18:31:48 +0000

An iceberg nearly half the size of Puerto Rico that broke off the edge of Antarctica last week is now the world’s largest, researchers said.

The iceberg, known as A76, following a naming convention established by the National Ice Center, naturally split from Antarctica’s Ronne Ice Shelf into the Weddell Sea through a process known as calving, the center said.

It measures about 1,668 square miles (4,320 square kilometers), making it larger than A23a, an iceberg that formed in 1986 and had a total area of more than 1,500 square miles (4,000 square kilometers) in January.

Researchers sought to put the formation of A76 in context, saying that the forces that severed it from the Ronne Ice Shelf were part of the shelf’s normal life span and may not be directly related to climate change.The iceberg will not add to sea level rise as it melts; as floating ice, it is already displacing the same volume of water it will add as it melts.

“There is really essentially no sign that this is an unusual event with climate significance,” Dr. Shuman said.

The formation of the iceberg does, however, bring renewed attention to the broader issue of ice loss, in both the Antarctic and Greenland, said M Jackson, a glaciologist and an explorer with the National Geographic Society. Although the Weddell Sea is not warming as quickly as other parts of the Antarctic, she said, the impact of climate change in the region cannot be discounted, and it is hard to disconnect what happened with the Ronne Ice Shelf from the larger problem.

“I am concerned with any ice loss today, because any ice loss is part of our greater global ice loss and to me it’s terrifying,” Dr. Jackson said. “Globally, we’ve got a glacier problem; we’re losing a lot of ice.”

The largest iceberg on record, B15, broke off from the Ross Ice Shelf in March 2000 measuring more than 4,200 square miles (11,000 square kilometers). Despite being more than twice the size of A76, Dr. Shuman said, B15 did not destabilize the Ross Ice Shelf. B15 has since fractured into several icebergs, all but one of which have melted away.

According to Dr. Shuman, the last significant calving event on the Ronne shelf was in May 2000.

By studying the new iceberg, researchers hope to better understand the overall state of Antarctica’s ice shelves, said David Long, who runs the Antarctic Iceberg Tracking Database at Brigham Young University.

“Understanding when the ice sheets calve helps us understand whether some of these other more unstable ice sheets could break up or disintegrate,” he said. “And that would be important because as these more unstable ice sheets break up they can release the flow of glaciers that are held in place by the ice shelves.”

While ice shelves are floating on the water, the glaciers behind them are on land. So if they are released into the sea and melt, that would add to sea levels, he said.

The National Ice Center names and tracks Antarctic icebergs that are at least 10 nautical miles long or 20 square nautical miles large. The center, which is operated by the Navy, the Coast Guard and the National Oceanic and Atmospheric Administration, is currently tracking 42 named icebergs.

The question with A76 is what will happen next.

An iceberg about 100 miles long and 30 miles wide that had broken off from the Antarctic Peninsula in 2017 raised alarm in November when it appeared to be on a collision course with the British island territory of South Georgia. That iceberg, A68a, ended up grounding off the island’s coast. If A76 hits a similar current, it could reach the Antarctic Peninsula within months and could interfere with shipping lanes there, said Christopher Readinger, the Ice Center’s Antarctica team lead.

As A76 makes its journey, Dr. Jackson said, climatologists will be watching closely — even if much of the public isn’t. Dr. Jackson cited A68a, the iceberg that briefly threatened South Georgia.“The whole world was going crazy about that and then everyone forgot it, right?” she said. “This one’s going to be in the imagination until the next big one, and the next big one and the next big one. And it’s part of the larger global problem. We’re losing our world’s ice, and I frankly don’t want to live in a world without ice.”