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Home* Antarctic News → Does the Lar­sen C ice shelf in the Wed­dell Sea col­lap­se?

Does the Lar­sen C ice shelf in the Wed­dell Sea col­lap­se?

In the begin­ning of Janu­a­ry, Bri­tish rese­ar­chers noti­fied on the cur­rent situa­ti­on of the Lar­sen C Ice Shelf. This ice shelf is loca­ted on the East side of the Ant­arc­tic Pen­in­su­la. A well known and obser­ved crack has grown quick­ly lar­ger during 2016. The Ger­man Alfred Wege­ner Insti­tu­te repor­ted about that topic during the last few mon­ths on its Ice Blog. Bet­ween May and August 2016 the sci­en­tists obser­ved an exten­si­on of a crack by 25 km. In Decem­ber this crack expan­ded ano­t­her 18 km. The ante­rior part of the Ice Shelf is now only con­nec­ted to the remai­ning Shelf by a 20 km wide “bridge”.

The Bri­tish Ant­arc­tic Sur­vey experts sup­po­se a pos­si­ble break-off sce­n­a­rio of the appro­xi­mate­ly 50,000 km² shelf ice area alrea­dy later this year. In recent years, rese­ar­chers have given spe­cial atten­ti­on to the “Lar­sen C” ice shelf. The ear­lier col­lap­ses of the Lar­sen A (1995) and Lar­sen B (2002) Ice Shel­ves had clear­ly shown one effect: The floa­ting ice acts as a bar­ri­er and slows down land based gla­ciers behind. The loss of such a bar­ri­er results in the acce­le­ra­ti­on of gla­ciers behind it. Lar­sen C covers an area about 15 times lar­ger than the 2002 lost ice of Lar­sen B. Thus it also holds back lar­ger gla­ciers mas­ses. Two ques­ti­ons are inte­res­ting in that con­text: What cau­ses the break-off of the ice shelf? And what are the con­se­quen­ces of the ice loss?

Sci­en­tists have gai­ned a lot of new know­ledge about the under­lay­ing pro­ces­ses of the loss of shelf ice during the last years. The col­lap­se of Lar­sen B was most likely the result of the incre­a­sed annu­al tem­pe­ra­tures on the pen­in­su­la over the past 50 years. During that peri­od of time the rese­ar­chers have shown an average incre­a­se of 2.5 degrees. As a con­se­quence of the war­ming, the snow lay­er and the firn lay­er on the ice shelf vanis­hed more rapidly during sum­mer. Thus melt water ponds evol­ved more fre­quent­ly. The­se lakes fro­ze during win­ter. Ice of this ori­gin is war­mer and sof­ter than the sur­roun­ding ice, which has been for­med by the trans­for­ma­ti­on of snow to firn to gla­cier ice. The melt water zones in the gla­cial ice chan­ge the struc­tu­re of the ent­i­re ice shelf. The fol­lowing sum­mer the­se zones will start to melt ear­lier. This effect cau­sed the sud­den col­lap­se in Lar­sen B in 2002.

For the detach­ment of Lar­sen C this effect is not the only rea­son. The results of the BAS stu­dies show a decli­ning firn lay­er and a decre­a­sing thic­kness of the snow lay­er, due to an incre­a­sed annu­al air tem­pe­ra­tu­re of the area. Fur­ther ice loss occurs at the bot­tom of the ice shelf by war­mer water cur­r­ents. The war­ming of the earth’s atmo­s­phe­re and the Ant­arc­tic ozone hole streng­t­hen the West wind cur­r­ents and thus the cir­cum­po­lar cur­rent. This gives enough ener­gy to swa­sh up war­mer and sal­tier water mas­ses from the oce­an depths to the con­ti­nen­tal shelf. The sci­en­tists cal­cu­la­ted the thin­ning of the ice to 4 meters, in the peri­od of 1998 and 2012.

What would be the con­se­quen­ces, when Lar­sen C will disap­pe­ar? The shelf ice its­elf has no impact on the sea-level, sin­ce shelf ice is floa­ting ice. Howe­ver, the­re would not be any other bar­ri­er for the land based gla­ciers behind. They will incre­a­se their speed. In the case of Lar­sen B the sur­roun­ding land based gla­ciers acce­le­ra­ted five times their pre­vious velo­ci­ty. The­se gla­ciers lost a lot of ice, cra­cked, thin­ned, and retrea­ted. Meltwa­ter ponds on top of the gla­ciers, drai­ned into the new cracks and wea­ke­ned the gla­cier ice. In a simi­lar sce­n­a­rio for Lar­sen C, the rese­ar­chers pre­dict a con­tri­bu­ti­on to the glo­bal sea level rise of 50 cm until the year 2100, which will be a chal­len­ge for many coas­tal cities.

Crack in the Lar­sen C ice shelf. Pho­to © John Sonn­tag, NASA.

Bruch im Larsen C Schelfeis

http://www.nature.com/articles/ncomms11897

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last modification: 2017-01-20 · copyright: Rolf Stange
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