Why the ice­berg broke away

Calv­ing is a nat­u­ral event, and sci­en­tists had pre­dicted the break.

The Star Malaysia - Star2 - - Science - By ALEXAN­DRA ZAVIS and SEAN GREENE

SOME­TIME last week, a block of ice the size of Delaware broke away from Antarc­tica and is now float­ing freely in the Wed­dell Sea.

The ice­berg, which at around 1 tril­lion tonnes is one of the largest on record, poses no im­me­di­ate threat to sea lev­els. But sci­en­tists say the break may have al­tered the pro­file of the con­ti­nent’s western penin­sula for decades to come and could of­fer a pre­view of what global warm­ing might do to mar­itime ice shelves.

Sci­en­tists at Project Mi­das, a re­search team from Swansea Uni­ver­sity and Aberys­t­wyth Uni­ver­sity in Bri­tain, first con­firmed the break last Wed­nes­day us­ing data from Nasa satel­lites.

They said they had been mon­i­tor­ing a rift in an ice shelf called Larsen C for years be­fore it started to grow rapidly in Jan­uary, in­creas­ing in length to about 193km (120mi) and leav­ing the ice­berg hang­ing by a thread of ice less than 4.8km (3mi) wide.

“We have been an­tic­i­pat­ing this event for months, and have been sur­prised how long it took for the rift to break through the fi­nal few kilo­me­tres of ice,” said Adrian Luck­man of Swansea Uni­ver­sity, the project’s lead in­ves­ti­ga­tor.

What hap­pens next to the ice­berg is dif­fi­cult to pre­dict. “It may re­main in one piece but is more likely to break into frag­ments,” Luck­man said in a state­ment. “Some of the ice may re­main in the area for decades, while parts of the ice­berg may drift north into warmer wa­ters.”

There is still de­bate about whether man-made global warm­ing played a role.

Martin O’Leary, a glaciol­o­gist at Project Mi­das, said that the process known as calv­ing is a nat­u­ral event.

“We’re not aware of any link to hu­man-in­duced cli­mate change,” he said. But sci­en­tists say the break has re­duced Larsen C by more than 12 per­cent, which some worry could have a desta­bil­is­ing ef­fect on the re­main­der of the shelf, among Antarc­tica’s largest.

Larsen C, which is nearly half a mile thick at its largest point, floats on the ocean at the edge of the Antarc­tic Penin­sula, hold­ing back a flow of glaciers that feed into it.

“As cli­mate warm­ing ad­vances far­ther south, it will af­fect larger and larger ice shelves that cur­rently hold back big­ger and big­ger glaciers, so their col­lapse will con­trib­ute more to sea level rise,” said Eric Rig­not, a Uni­ver­sity of Cal­i­for­nia, Irvine glaciol­o­gist and re­search sci­en­tist at Nasa’s Jet Propul­sion Lab­o­ra­tory.

Named­forthe­man­who dis­cov­ered it in 1893, the Nor­we­gian ex­plorer Carl An­ton Larsen, the Larsen Ice Shelf is ac­tu­ally a se­ries of many float­ing chunks of ice. Larsen C, the largest, was first pho­tographed in the 1960s. Even then, the fate­ful crack was al­ready vis­i­ble, ac­cord­ing to Nasa.

Ice shelves are thick plat­forms of ice float­ing on the sur­face of the ocean. They form as ice sheets – large ac­cu­mu­la­tions of snow on top of a land­mass – flow down­hill to the ocean.

Ice shelves nat­u­rally shed weight in the form of ice­bergs, the process called calv­ing, or through melt­ing on the bot­tom. One way to know if a sheet is healthy is to see if it’s gain­ing as much ice as it is los­ing.

Ice sheets grow as snow ac­cu­mu­lates and freezes on the sur­face, and lose ice through melt­ing and calv­ing of their shelves.

If a large enough ice­berg calves off, an ice shelf could col­lapse.

That’s what hap­pened to Larsen C’s neigh­bors, Larsen A and Larsen B, in 1995 and 2002 re­spec­tively.

“That’s just the way Antarc­tica works,” said Helen Fricker, a glaciol­o­gist at the Scripps In­sti­tu­tion of Oceanog­ra­phy who stud­ies the Larsen C ice sheet.

A col­lapse of Larsen C is prob­a­bly decades away, Rig­not said. But the ice shelf has now re­treated far­ther back than it has in the last 125 years.

“More bergs will de­tach; it will be­come weaker and even­tu­ally fall apart in a domino ef­fect,” he said. – Tri­bune News Ser­vice

Af­ter months of dan­gling on by a miles-thin thread of ice, an ice­berg calved off Antarc­tica’s Larsen C ice shelf.

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