Antarc­tica looses a huge ice­berg

Shelf’s break prom­ises clues on how oceans lev­els will rise

Northwest Arkansas Democrat-Gazette - - NEWS - JUGAL K. PA­TEL AND JUSTIN GILLIS In­for­ma­tion for this ar­ti­cle was con­trib­uted by An­jali Singhvi of The New York Times.

A Delaware-sized chunk of float­ing ice that weighs more than a tril­lion met­ric tons broke away from the Antarc­tic Penin­sula, pro­duc­ing one of the largest ice­bergs ever recorded.

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 Wed­nes­day that the huge ice­berg had fi­nally bro­ken free.

There is no sci­en­tific con­sen­sus on whether cli­mate change 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 col­lapse could dump enough ice into the ocean to raise the sea level by sev­eral feet.

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 that the ice is still catch­ing up to the higher tem­per­a­tures.

Some cli­mate sci­en­tists be­lieve that 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 re­gion may be a preview of what is in store for the rest 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 Wag­ner, who leads NASA’s ef­forts to study the po­lar re­gions.

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 if 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 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 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 col­lapse of the penin­sula’s ice shelves were pre­dicted in 1978 by John Mercer, a ge­ol­o­gist at Ohio State Univer­sity. In a pa­per, Mercer warned that the west­ern part of Antarc­tica was so vul­ner­a­ble to hu­man-in­duced cli­mate warm­ing that it posed a “threat of dis­as­ter” from ris­ing seas.

He said 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 col­lapsed 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,” 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.”

Bri­tish Antarc­tic Sur­vey

The break­away part of the Larsen C ice shelf is shown in this aerial photo taken in Fe­bru­ary and re­leased Wed­nes­day.

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