Tril­lion tons of ice

One of the big­gest ice­bergs in recorded his­tory just broke loose

The Denver Post - - NEWS - By Chris Mooney

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 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 Wed­nes­day 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 fourth­largest 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.

If you add to­gether all the ice lost from the var­i­ous Larsen ice shelves since the 1970s, it is around 7,350 square miles, ac­cord­ing to fig­ures pro­vided by Rig­not. That is a lit­tle bit smaller than the state of New Jer­sey.

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.

Bri­tish Antarc­tic Sur­vey via The As­so­ci­ated Press

This is how the grow­ing chasm in the Larsen C ice shelf looked in Fe­bru­ary. The sheet of ice, al­most the size of Delaware, has bro­ken away and be­come a mas­sive ice­berg, scientists said Wed­nes­day.

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