An­cient tree ex­poses cause of hike in Arc­tic tem­per­a­ture

Weekend Mirror - - CHILDREN’S CORNER - By Amy Wal­lace

A re­cent study shows that an an­cient kauri tree may hold the key to spikes in Arc­tic tem­per­a­tures. Photo courtesy www.an­cien­tkau­ripro­ject.com

Sci­en­tists from the Univer­sity of New South Wales have found an an­cient kauri tree in New Zealand that holds the key to the cause of ris­ing Arc­tic tem­per­a­tures.

The 30,000- year- old kauri tree in a peat swamp in New Zealand showed a new mech­a­nism that could ex­plain how tem­per­a­tures in the North­ern Hemi­sphere spiked sev­eral de­grees centi­grade within a few decades dur­ing the last global ice age.

Sig­nif­i­cant, rapid warm­ing spikes dur­ing glacial pe­ri­ods are known as Dans­gaard-Oeschger events and are linked to a phe­nom­e­non known as bipo­lar see­saw where in­creas­ing tem­per­a­tures in the Arc­tic si­mul­ta­ne­ously oc­cur as cool­ing oc­curs over the Antarc­tic and con­versely.

Pre­vi­ously, it was thought the di­ver­gences in tem­per­a­ture at op­po­site poles were driven by changes in the North At­lantic caus­ing deep ocean cur­rents -- re­ferred to as the ocean con­veyor belt -- to shut down lead­ing to warm­ing in the North­ern Hemi­sphere and cool­ing in the South­ern Hemi­sphere.

The study, pub­lished Tues­day in Na­ture Com­mu­ni­ca­tions, used a de­tailed se­quence of ra­dio­car­bon dates from an an­cient New Zealand kauri tree to pre­cisely align ice, ma­rine and sed­i­ment records over a pe­riod of great cli­mate change.

"In­trigu­ingly, we found that the spike in tem­per­a­ture pre­served in the Green­land ice core cor­re­sponded with a 400-year-long sur­face cool­ing pe­riod in the South­ern Ocean and a ma­jor re­treat of Antarc­tic ice," pro­fes­sor Chris Tur­ney, UNSW sci­en­tist, said in a press re­lease.

"As we l ooked more closely for the cause of this op­po­site re­sponse we found that there were no changes to the global ocean cir­cu­la­tion dur­ing the Antarc­tic cool­ing event that could ex­plain the warm­ing in the North At­lantic. There had to be an­other cause."

Re­searchers turned to ex­am­in­ing lake sed­i­ments from the Ather­ton Table­land in Queens­land and found sed­i­ments ex­hibit­ing a si­mul­ta­ne­ous col­lapse of rain-bear­ing trade winds over trop­i­cal north­east Aus­tralia.

They then an­a­lyzed cli- mate mod­els show­ing the re­lease of large vol­umes of fresh­wa­ter into the South­ern Ocean and found there was cool­ing in the South­ern Ocean but no change in the global ocean cir­cu­la­tion.

Re­searchers also found that the fresh­wa­ter pulse caused rapid warm­ing in the trop­i­cal Pa­cific, which led to changes to the at­mo­spheric cir­cu­la­tion that trig­gered sharply higher tem­per­a­tures over the North At­lantic and the col­lapse of rain-bear­ing winds over trop­i­cal Aus­tralia.

"Our study shows just how im­por­tant Antarc­tica's ice is to the cli­mate of the rest of the world and re­veals how rapid melt­ing of the ice here can af­fect us all. This is some­thing we need to be acutely aware of in a warm­ing world," Tur­ney said.

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