Massive chunk of Larsen C ice shelf breaks off
One of the biggest icebergs in recorded history just broke loose from Antarctica
The Washington Post, July12, 2017
Scientists announced Wednesday that a much anticipated break at the Larsen C ice shelf in Antarctica has occurred, unleashing a massive iceberg that is more than 2,200 square miles in area and weighs a trillion tons.
In other words, the iceberg — among the largest in recorded history to splinter off the Antarctic continent — is close to the size of Delaware and consists of almost four times as much ice as the fast melting ice sheet of Greenland loses in a year. It is expected to be given the name “A68” soon, scientists said.
“Its volume is twice that of Lake Erie, one of the Great Lakes,” wrote researchers with Project MIDAS, a research group at Swansea and Aberystwyth Universities in Wales that has been monitoring the situation closely by satellite.
The break was detected by one NASA satellite instrument, MODIS on the Aqua satellite, and confirmed by a second, they said. The European Space Agency has also confirmed the break.
The iceberg contains so much mass that if all of it were added anew to the ocean, it would drive almost 3 millimeters of global sea level rise. In this case though, the ice was already afloat so there won’t be a substantial sea level change.
The Project MIDAS group said that the effect of the break is to shrink the size of the floating Larsen C ice shelf by 12 percent. While they can’t be certain, they’re concerned that this could have a destabilizing effect on the remainder of the shelf, which is among Antarctica’s largest.
“The iceberg is one of the largest recorded and its future progress is difficult to predict,” said Adrian Luckman, the lead MIDAS researcher and an Antarctic scientist at Swansea University, in a statement. “It may remain in one piece but is more likely to break into fragments. Some of the ice may remain in the area for decades, while parts of the iceberg may drift north into warmer waters.”
There is no expected immediate effect on shipping, Luckman said by email.
“Icebergs from this region occasionally make it out beyond the tip of the Antarctic Peninsula, but it will take a while for that to happen to this iceberg or its fragments, and there is not a lot of shipping in the area that I am aware of,” he explained.
The change is large enough that it will trigger a redrawing of the Antarctic coastline, according to Ted Scambos, senior research scientist with the National Snow and Ice Data Center.
Indeed, it means that the Larsen C ice shelf, previously the fourth largest of its kind in Antarctica, is now probably only the fifth or sixth largest, Scambos said.
Even larger icebergs than this have broken off of Antarctica in the past, however, including an over 4,000 square mile berg, famously dubbed B15, in 2000. That was almost twice the size of this one and broke off the Ross Ice Shelf, Antarctica’s largest floating ice body. It was the biggest iceberg ever recorded.
Larsen C also lost an even larger piece in 1986, Scambos said, but that occurred in considerably different circumstances. It came after the shelf had grown considerably and extended much farther out into the Weddell Sea than it does now.
“This calving is a little bit different, because it makes the ice shelf so much smaller,” Scambos said.
Indeed, the front of Larsen C ice shelf has retracted back farther than ever previously observed, according to Eric Rignot, a glaciologist with NASA and the University of California, Irvine.
“The ice front is now almost 40 km farther back,” said Rignot by email. “A similar evolution was seen on Larsen A and B before they collapsed in 1995 and 2002 respectively,” he added, referring to Larsen C’s now missing northern cousins.
Scientists will now proceed to track the iceberg using satellite imagery, and should be able to get a chance at regular glimpses even in Antarctic night, due to the use of radar and thermal imaging.
The iceberg’s progress is expected to be northward in the direction of South America. First, it will be swept up in the Weddell Sea Gyre, an elongated circuit of ocean flow, and then should pass to the west of South Georgia and the South Sandwich Islands, according to Helen Amanda Fricker, an Antarctic expert at the Scripps Institution of Oceanography.
Then the iceberg, or its pieces, will become swept up in the Antarctic Circumpolar Current, which encircles the entire continent, flowing in a west-to-east direction.
Before the break, a rift across the Larsen C ice shelf had extended more than 100 miles in length, and just a few miles of remaining ice connected the nascent iceberg to the shelf. The break began several years ago but had quickened its advance in the last year, increasingly convincing scientists that the iceberg detachment was inevitable, despite the fact that it is actually winter in Antarctica right now.
There is a debate over whether this event can be attributed in any way to climate change. Scientists don’t have all the data to show what is happening in the environment of the floating Larsen C ice shelf, which is affected not only but air temperatures above it but also ocean temperatures below it.
Antarctica’s ice shelves do calve large pieces regularly, a natural process. But at the same time, Larsen C is the next ice shelf in line in a southward progression that has previously seen the collapse of the Larsen A and Larsen B ice shelves, making this occurrence at least suspicious.
“I think we’re all scratching our heads as to just what combination of changes in the ice, air, and ocean caused this,” said Scambos. “It’s unclear if this is a new trend for this area of Antarctica. The case for a climate-related cause is not nearly as good as for other areas of Antarctica.”
But Eric Rignot, the NASA and University of California, Irvine researcher, is convinced of a climate role.
“For me, there is no doubt that this event is not part of a natural cycle,” he said by email. “The Larsen C ice shelf will not collapse for another few decades, most likely, but this calving is unique in the history of the ice shelf since first seen by human eyes by the Norwegian explorer Carl Anton Larsen in 1893.” Rignot observed that Larsen C’s northern cousin Larsen B, which collapsed in 2002, is believed to have previously held its position for over 10,000 years and something similar is probably true of Larsen C.
The Antarctic continent is ringed by ice shelves, which are large, thick, floating extensions of glaciers that have extended from the land, where they have built up due to snowfall over vast time periods, into the sea. These shelves are now vulnerable to warming air temperatures and ocean waters, which can cause them to thin, break off pieces at an unusual rate, and even collapse. And when they do so, the ice behind them is liberated to flow more rapidly into the ocean, raising seas.
Scientists stress, however, that because the trillion ton iceberg is already afloat in the Weddell Sea, its detachment does not raise the globe’s sea level. Their fear, however, is that its loss could speed up the outward ice flow of the remainder of the Larsen C ice shelf, which would indeed increase sea level — but glaciers in this region only have the potential to raise seas by about a centimeter.
The greater fear is the loss of ice shelves, and glaciers, farther southward in Antarctica, where the sea level rise potential begins to be measured in feet.