The Indian Express (Delhi Edition)
As Antarctic rift quickens, giant iceberg is poised to break away
Chunk the size of one-and-a-half Goas hanging on by just 20 km of ice; shelf collapses allow glaciers to flow faster out to sea, raising ocean levels globally
NEW SATELLITE images show that a longwatched rift in the Larsen C ice shelf in Antarctica rapidly grew about 18 km in the secondhalfofdecember2016.theriftisnowjust 20 km from reaching the end of the shelf; once that happens, an iceberg the size of the US state of Delaware — a little smaller than oneand-a-half times the size of Goa — and one of the 10 largest ever, will break and float away.
This, University of Colorado scientist Ted Scambos said, could happen as early as in March, and would “cut deeper to the bone” of the ice shelf, changing its shape.
“If it doesn’t go in the next few months, I’ll be amazed,” Prof Adrian Luckman, leader of Project MIDAS, a UK government-funded research project investigating the effects of a warming climate on the Larsen C ice shelf, told BBC News. “It’s so close to calving that I think it’s inevitable,” Prof Luckman said.
Ice shelves — sheets of floating ice — wrap around three-quarters of the South Pole’s coastline. NASA describes them as “the gatekeepers” for glaciers flowing from Antarctica towards the ocean. Without them, glacial ice would enter the ocean faster and accelerate the pace of global sea level rise.
The Larsen ice shelf — named after Norwegian explorer Carl Anton Larsen who sailed close to it nearly 125 years ago — fringes the Weddell Sea to the northwest of the Antarctic Peninsula. The shelf originally had three parts, called, from north to south, Larsen A, Larsen B, and Larsen C. Larsen A, the smallest, disintegrated in 1995; and a large part of Larsen B, which had been stable for at least 10,000 years, collapsed in a matter of just 6 weeks in early 2002. It is expected to disappear altogether by 2020.
Larsen C is the largest of the three and, with an area of 50,000 sq km, the fourth largest ice shelf in all of Antarctica. While the breaking of the shelf along the lengthening fault will weaken Larsen C, it is unlikely to lead to “a runaway disintegration”, according to Prof Scambos.
NASA glaciologist Dr Jay Zwally said there is no rapid melting with ponds of water on top of the ice this time, as had been the case when Larsen B disintegrated. “By itself this calving is not a cause for alarm,” he said.
Large icebergs periodically break off from Antarctica, Zwally said. “But”, he added, “the ice shelf has been thinning as other ice shelves havebeenthinningintheantarcticpeninsula.”
NASA clarified that cracks and calving of ice from the front of an ice shelf are “normal”. Shelves are fed by glaciers and ice streams coming from the interior of the Antarctic continent. They advance into the ocean until a calving event takes place. The shelf front retreats and then advances again. The whole cycle can occur over the span of a few decades.
But calving that happens faster than a shelf can re-advance can mean trouble for an ice shelf. For example, large and frequent calving events at Larsen B preceded that shelf’s final, spectacular disintegration. Whether Larsen C will go the same way remains to be seen, NASA said, but that’s one reason why its scientists plan to make observations before and after the next calving event.
Ice shelves float, so they do not directly contribute to sea level rise. They are important, however, because they buttress land ice and keep it inland. If a shelf disintegrates, glaciers that feed it can flow more quickly out to sea — a process that directly increases sea level. Theoretically, if all the ice that Larsen C currently holds back entered the sea, global waters would rise by about 10 cm.
Prof Luckman said that although there is no evidence specifically linking this particular cleavage to climate change, it does fit the overall warming picture of global warming. COMPILED FROM AGENCIES
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