P re c i se in te rpo la rpha s ingo fab rup tc l ima te changedu r ingthe la s t iceage Au tho rs : WA ISD iv ideP ro jec t Membe rs Th i si sapo s tp r in to fana r t i c letha to r ig ina l l y appea r edinNa tu re onAp r i l2015 . WA ISD i v ideP ro je c t Membe r s ."P re c i sein te rpo la rpha s ingo fab rup tc l ima techangedu r ingthe la s ti ceage . "Na tu re520 ,no .7549(Ap r i l2015 ) :661 -665 . DO I :10 .1038 /na tu re14401 Madeava i lab leth roughMon tanaS ta teUn i ve rs i t y ’ sS cho la rWo r ks s cho la rw o rks .mon tana .edu P r e c i s ein t e rpo l a rph a s in go fab rup tc l im a t ech an g e du r in gth el a s ti c ea g e WA ISD iv ideP ro j ec t Membe r s* *L i s t so fpa r t i c ipan t sandthe i ra f f i l ia t ion sappea ra ttheendo fthepape r . Th el a s tg l a c i a lp e r iode xh ib i t edab rup tD an s g a a rd–O e s ch g e rc l i m a t i co s c i l l a t ion s ,e v id en c eo fwh i chi sp r e s e r v edinav a r i e t yo f No r th e rnH em i sph e r ep a l a eo c l im a t ea r ch i v e s1.I c eco r e sshowth a t An t a r c t i c acoo l ed du r in gth ew a rm ph a s e so fth eG r e en l and g g e s t in ganin t e r D an s g a a rd–O e s ch g e rc y c l eandv i c ev e r s a2,3,su h em i sph e r i cr ed i s t r ibu t iono fh e a tth rou gham e ch an i smc a l l edth e b ipo l a rs e e s aw4–6.V a r i a t ion sinth eA t l an t i cm e r id ion a lo v e r tu rn in gc i r cu l a t ion(AMOC )s t r en g tha r ethou gh ttoh a v eb e en impo r t an t ,bu t mu chun c e r t a in t yr em a in sr e g a rd in gth ed yn am i c sand 7 – 9 t r i g g e ro fth e s eab rup te v en t s .K e yin fo rm a t ioni scon t a in edin th er e l a t i v eph a s in go fh em i sph e r i cc l im a t ev a r i a t ion s ,y e tth e l a r g e ,poo r l ycon s t r a in edd i f f e r en c eb e tw e eng a sa g eandi c ea g e andth er e l a t i v e l ylow r e so lu t ion o f m e th an er e co rd sf rom An t a r c t i c i c eco r e sh a v esof a rp r e c lud ed m e th an e -b a s eds yn ch ron 2 , 3 , 1 0 i z a t iona tth er equ i r edsub c en t enn i a lp r e c i s ion .H e r ew eu s ea r e c en t l yd r i l l edh i gh a c cumu l a t ionAn t a r c t i ci c eco r etoshowth a t , ona v e r a g e ,ab rup tG r e en l and w a rm in gl e ad sth eco r r e spond in g rD an s g a a rd– An t a r c t i ccoo l in gon s e tb y218692y e a r s(2s)fo O e s ch g e re v en t s ,in c lud in gth eBø l l in ge v en t ;G r e en l andcoo l in g l e ad s th e co r r e spond in g on s e to f An t a r c t i c w a rm in g b y 20869 6y e a r s . Ou rr e su l t sd emon s t r a t eano r th to sou thd i r e c t ion a l i t yo fth eab rup tc l im a t i cs i gn a l ,wh i chi sp rop a g a t edtoth e Sou th e rnH em i sph e r eh i ghl a t i tud e sb yo c e an i cr a th e rth ana tmo sph e r i cp ro c e s s e s .Th es im i l a rin t e rpo l a rph a s in go fw a rm in gand coo l in gt r an s i t ion ssu g g e s t sth a tth et r an s f e rt im eo fth ec l im a t i c s i gn a li sind ep end en to fth eAMOCb a ck g rounds t a t e . Ou rf ind in g scon f i rmac en t r a lro l efo ro c e anc i r cu l a t ioninth eb ipo l a r s e e s awandp ro v id ec l e a rc r i t e r i afo ra s s e s s in gh ypo th e s e sand mod e ls imu l a t ion so fD an s g a a rd–O e s ch g e rd yn am i c s . N e th e a tt r an sp o r tb yth eA t l an t i cb r an cho fth eg lo b a lo c e ano v e r tu rn in gc i r cu l a t i on i sn o r thw a rd sa ta l l l a t i tud e s ,r e su l t in g inah e a t f lu x f r omth eS ou th e rn H em i sph e r e( SH )toth e No r th e rn H em i sph e r e 4 .V a r i a t i on sinth i sf lu xa c ttor ed i s t r ibu t eh e a tb e tw e enth e (NH ) h em i sph e r e s ,a m e ch an i smcommon l yin vo k edtoe xp l a inab rup t sub o r b i t a lc l im a t i cv a r i ab i l i t yandth ea s yn ch r on ou scoup l in go f G r e en l andandAn t a r c t i c t emp e r a tu r ev a r i a t i on son th e s e t im e s c a l e s2,6. M i l l enn i a l s c a l eAMOCv a r i ab i l i t yi sco r rob o r a t edb yNo r thA t l an t i c p r o x i e sf o rd e ep -w a t e rv en t i l a t i onand p ro v en an c eth a tsu g g e s t d e c r e a s ed N o r th A t l an t i cd e ep w a t e rp rodu c t i onandth ein t ru s i on o fsou th e rn s ou r c ed w a t e rm a s s e s du r in gs t ad i a l( th a ti s , No r th A t l an t i cc o ld )p e r i od s11,12.Th eo c e an i cin s t ab i l i t i e sa r ea c c omp an i ed b ysh i f t in ga tm o sph e r i ct r an spo r tp a t t e rn s .P ro x yd a t aandc l im a t e mod e l sc on s i s t en t l yind i c a t eno r thw a rdandsou thw a rd m i g r a t ion s o f th e in t e r t r op i c a lc on v e r g en c ezon e inr e spon s e toab rup tNHw a rm 1 3 , 1 4 in gandc o o l in g ,r e sp e c t i v e l y .Ab rup tNHe v en t sm a ya l s oindu c e ch an g e s in th es t r en g thandpo s i t i ono f th eSHm id l a t i tud ew e s t e r l i e s . S t r en g th en edand / o rs ou thw a rd sh i f t edw e s t e r l i e sdu r in gNHs t ad i a l s h a v eth ep o t en t i a lt ow a rmth eSou th e rn O c e anand An t a r c t i c ab y enh an c in gth ew ind -d r i v enupw e l l in go fr e l a t i v e l yw a rmc i r cumpo l a r d e epw a t e r s ,p r o v id in gad i r e c ta tmo sph e r i cp a thw a yfo rth eb ipo l a r 1 5 s e e s awt oop e r a t e .C l im a t e mod e ls imu l a t ion sfu r th e rsu g g e s tth a t a tm o sph e r i cr e ad ju s tm en tinr e spon s etod e c r e a s ed No r th A t l an t i c d e ep w a t e rfo rm a t ion c anindu c einhomo g en e ou st emp e r a tu r e 1 6 , 1 7 , po s s i b l yb ym e an so f ch an g e so v e rth e An t a r c t i ccon t in en t w ind -d r i v ench an g e sins e a i c ed i s t r i bu t ion8. A tmo sph e r i ct e l e c onn e c t i on sop e r a t eons e a son a ltod e c ad a lt im e 8 , 1 8 , 1 9 .B y s c a l e sb e c au s eo fth ef a s tr e spon s et im eo fth ea tm o sph e r e con t r a s t ,o c e an i ct e l e c onn e c t i on sc anop e r a t eonaw id er an g eo f t im e s c a l e sf r omd e c ad a lto mu l t i -m i l l enn i a l ,d ep end in gonth ep r o c e s s e s 1 9 – 2 1 .C l im a t i cs i gn a l sc anb er ap id l yp r op a ando c e anb a s in s in vo l v ed 5 , g a t ed f romth eNo r thA t l an t i c toth eSou thA t l an t i cv i aK e l v inw a v e s bu tmod e l ssu g g e s tamo r eg r adu a l( c en t enn i a l t im e s c a l e )p r op a g a t i on f romth eSou th A t l an t i ctoth eSHh i ghl a t i tud e sa sar e su l to fth e ab s en c eo fazon a ltopo g r aph i cbound a r ya tth el a t i tud e so fth e et im e s c a l eon wh i ch An t a r c t i cc i r cumpo l a rcu r r en t(ACC )19,21. Th n ew l yfo rm edNo r thA t l an t i cd e epw a t e ri se xpo r t edtoth eS ou th e rn eb ipo l a rs e e s awr e l a O c e an i ss im i l a r l ya r ounds e v e r a lc en tu r i e s22.Th t ion sh ipob s e r v edb e tw e eni c eco r er e c o rd s po t en t i a l l yb e a r sth e imp r in to fbo tha tmo sph e r i cando c e an i c t e l e c onn e c t i on s ;p r e c i s ec on s t r a in t sonth ein t e rh em i sph e r i cph a s in gc anh e lpd i s t in gu i shwh i ch mod edom in a t e s ,andc ana l s oid en t i f yl e ad sandl a g s10,19,21. Comp l e t ed inD e c emb e r2 0 1 1 , th eW e s tAn t a r c t i cI c eSh e e t(WA I S ) a sd r i l l edandr e c o v e r edtoad ep tho f D i v id ei c eco r e(WDC )17 w 3 , 4 0 5m .H e r ew ep r e s en tr e su l t sf r omth ed e epp a r to fth ec o r e . (F i g .1 ) ,e x t end in gb a c kto6 8k y rb e f o r e1 9 5 0(b e fo r ep r e s en t ;BP) Th e WDCc l im a t i cr e c o rd sshownos t r a t i g r aph i cd i s tu r b an c e s( su ch a sl a r g e s c a l efo ld s )th a ta r ecommon l yen c oun t e r edn e a rth eb a s eo f i c eco r e s ,a f a c tw ea t t r i bu t e tob a s a lm e l t in ga t th es i t e th a tr em o v e so ld i c eb e f o r esu chd i s tu r b an c e sc and e v e lopandth a td e c r e a s e ssh e a r s t r e s sb ylub r i c a t in gth eb ed .Th eG r e en l and NGR IPc o r es im i l a r l y h a ss t r on gb a s a lm e l t in gandanund i s tu rb eds t r a t i g r aph y1. WDC 1 8 f i c e ,ap ro x yfo r lo c a lcond en s a t i ont emp e r a tu r e ,e xh i b i t sc l e a r d Oo m i l l enn i a l s c a l ev a r i ab i l i t ya sob s e r v eda c r o s sth eAn t a r c t i cc on t in en t (F i g .1 c ,d ) .W ee v a lu a t eth eph a s in go f WDC m i l l enn i a lv a r i a b i l i t y 1 8 Oo fth eG r e en l and NGR IPco r e(F i g .1 a ) .F o re a ch r e l a t i v etod G r e en l andD an s g a a rd–O e s ch g e r(DO )e v en tw ec an id en t i f yac o r r e s l th ou ghA IM9 pond in gAn t a r c t i cI s o top i cM a x imum(A IM )e v en t3,a i son l yv e r yw e a k l ye xp r e s s ed in WDC(w eadop tth en am in gc on v en t ionwh e r eb yA IM xi scon com i t an tw i thDO x ) . To in v e s t i g a t eth eph a s in go fth eb ipo l a rs e e s aw ,w eh a v es yn ch r o n i z ed WDCtoth eG r e en l andNGR IPco r eb ym e an so fg l o b a l l yw e l l 2 , 2 3 i g .1b ) . WDCa l l ow s CH m i x eda tmo sph e r i cm e th an e(CH4;F 4 s yn ch ron i z a t iona t unp r e c ed en t ed ,sub c en t enn i a lp r e c i s i ona sa r e su l to fth esm a l ld i f f e r en c eb e tw e eng a sa g eandi c ea g e( Da g e ) e co rd(E x t end ed andcon t inuou s ,c en t im e t r e s c a l er e so lu t ionCH 4r D a t aF i g s1and2 ) .B e c au s eun c e r t a in t i e sinth er e l a t i v eph a s in go f 2 4 r e en l andc l im a t e a r esm a l l e rth an un c e r t a in t i e sin CH4 and G i r e c t l yt o NGR IP G r e en l and Da g e ,w es yn ch ron i z e WDC CH 4d 2 3 r a th e rth antoNGR IPCH4) . d18O( t r on gan t i c o r r e l a t i one x i s t s A spo in t edou tb ys e v e r a lau tho r s6,21,as 1 8 er a t eo fch an g e( th a t i s ,th ef i r s tt im e b e tw e enG r e en l andd Oandth 1 8 O .Th i sr e l a t i on sh ipi scon s i s t en tw i tha d e r i v a t i v e )o f An t a r c t i cd s imp l e th e rm od yn am i cmod e lo f th eb ipo l a rs e e s aw inwh i chAn t a r c t i c t emp e r a tu r ev a r i a t i on sa r emod e r a t edb y th e l a r g e th e rm a lm a s so f th e 60 55 50 45 40 35 30 25 –38 a –40 –42 –44 600 –46 550 500 b 450 −36 400 −38 350 ATSΔT( °C ) –4 –6 c –40 18O WDC δ (‰ ) .p .b . ) WDCCH4(p 650 18O NGR IPδ (‰ ) 65 –42 d –8 –10 DO : 18 M IS4 65 1716 60 15 14 55 13 50 12 11 10 9 M IS3 45 40 8 7 35 65 .2 5 .1 4 3 30 2 M IS2 25 WD2014age(kyrBP) F i gu r e1|R e co rd so fg l a c i a lab rup tm i l l enn i a l s c a l ec l im a t i cv a r i ab i l i t y . 1 8 Or e c o rd1onG ICC 0 531 . 0 0 6 3ch r on o l o g y a ,G r e en l andNGR IP d e c o rdon th e WD 2 0 1 4ch r on o l o g y ,wh i ch i s (M e th od s ) .b, WDCd i s c r e t eCH 4r yn ch r on i z a t i ont oNGR IP b a s edon l a y e rcoun t in g( 0– 3 1 . 2k y r )andCH 4s 1 8 2 3 3 0 ( 3 1 . 2 – 6 8k y r ) . c , WDC d Or e c o rd .d,An t a r c t i c t emp e r a tu r es t a c k(AT S ) in d e g r e e sC e l s iu sr e l a t i v etoth ep r e s en td a yonA ICC 1 231 . 0 0 6 3ch r on o l o g y . DO /A IMe v en t sa r eind i c a t edw i tho r an g ev e r t i c a lb a r s ,num b e r eda tth e bo t tomo fth ef i gu r e . 6 Sou th e rn O c e an .Ine v a lu a t in gth i sr e l a t i on sh ipa t WA I SD i v id e (F i g .2 a ,b lu ecu r v e ) ,w ef indth es t r on g e s tan t i co r r e l a t iona ta NH l e ado fa b ou t1 7 0y e a r s ( b lu edo t inF i g .2 a ) .Th i s t im in g i sd i s t in c t f r om th ez e r o y e a r l e adc omm on l ya s sum ed inm a th em a t i c a ld e s c r ip t ion so f th eb ip o l a rs e e s aw .Th ean a l y s i si sr ep e a t edu s in ganen s emb l eo f 3 431 0 a l t e rn a t i v e WDCch r ono l o g i e s(M e thod s ) ,show in gth a tth e c en t enn i a l s c a l et im in gi saro bu s tr e su l t(F i g .2d )w i thane s t im a t ed un c e r t a in t yo f6 9y e a r s( 2sun c e r t a in t ybound sa r eu s edth rou ghou t th i sw o r k ) .E v a lu a t i ono fth ec ro s s co r r e l a t i on su s in g WDC CH 4 1 8 in s t e ado f NGR IPd Og i v e sa lm o s tid en t i c a lr e su l t s(F i g .2 a ,g r e en cu r v e ) , in l in ew i thth en o t ionth a tCH sagoodp ro x y fo rG r e en l and 4i 2 c l im a t e . N e x tw ean a l y s eth eDO –A IMcoup l in g in mo r ed e t a i l .Th eb ipo l a r s e e s awth e o r ysu g g e s t sth a tdu r in gG r e en l ands t ad i a lp e r iod sh e a t a c cumu l a t e s in th eSH ,c au s in gg r adu a lw a rm in go fAn t a r c t i c a ;du r in g in t e r s t ad i a lp e r i od sAn t a r c t i c a i scoo l in g .Th eab rup ts t ad i a l– in t e r s t a d i a lt r an s i t i on sinG r e en l anda r ea c c omp an i edb yab r e a kpo in tinth e 1 8 WDC d Or e c o rd , wh e r eth ew a rm in gt r endch an g e stoacoo l in g t r end .A l th ou ghth et im in go fab rup tt r an s i t i on sc anb ee s t ab l i sh ed 1 8 un amb i gu ou s l y inb o thCH4andG r e en l andd Or e c o rd s ,th esm a l l e r 1 8 s i gn a l t o -n o i s er a t i oo fAn t a r c t i cd Ot im es e r i e scomp l i c a t e sb r e a k p o in t id en t i f i c a t i onf o r ind i v idu a lA IMe v en t s .Too v e r com eth i s l im i t a t ion ,w es t a c kanda v e r a g eth eA IMe v en t stod e t e c tth e i rsh a r ed c l im a t i cs i gn a l(M e th od sandE x t end edD a t aF i g s3and4 ) .W ea l i gn WDCr e c o rd sa tth em idp o in to fth eDOCH4t r an s i t ion s ,wh i ch i ss e t 1 8 2 4 tol a gth em idp o in tinth eNGR IPd Ot r an s i t i onb y5 663 8y e a r s . 1 8 Th er e l a t i v e t im in go f th e WDCd OandCH4cu r v e s i sd e t e rm in edb y Da g e ,wh i chi sth el a r g e s tsou r c eo fun c e r t a in t y(M e thod s ) . W ef indth a t An t a r c t i ccoo l in gi sd e l a y edr e l a t i v etoab rup t NH 2y e a r s on a v e r a g e(F i g . 2b ,e ) ;s im i l a r l y , w a rm in gb y2 1 869 An t a r c t i cw a rm in gl a g s NHcoo l in gb y2 0 869 6y e a r s(F i g .2 c ,f ) . Th er o bu s tn e s so fth i sr e su l ti sd em on s t r a t ed w i tha Mon t eC a r lo an a l y s i sinwh i chw er andom l yp e r tu rbth er e l a t i v ea l i gnm en to fth e 3 ind i v idu a lA IMe v en t s ,incom b in a t ionw i thanen s emb l eo f4 31 0 1 8 a l t e rn a t i v e WDCch r ono l o g i e s .Th et im in go fth e WDCd Ob r e a k po in t(o r an g edo t s inF i g .2b ,c ) i sd e t e rm in edb yu s in ganau t om a t ed f i t t in ga l go r i thm(M e thod sandE x t end edD a t aF i g .5 ) .P e r f o rm in g th e an a l y s i ss ep a r a t e l yonas t a c ko fon l yth em a j o rA IMe v en t s(A IM4 ,8 , 1 2 ,1 4and1 7 ) ,on l y th em ino rA IMe v en t so rs t a c k so fe i gh tr and om l y s e l e c t edA IMe v en t sg i v e sn e a r l y id en t i c a lph a s in g(E x t end edD a t aF i g . 6 ) ,e x c lud in gth epo s s ib i l i t yth a tth er e su l t i sdom in a t edb yth et im in g o faf ewp rom in en te v en t s .W er ep e a tth es t a c k in gp ro c edu r ef o rth e WDCs e a s a l tsod iumr e co rd(E x t end edD a t aF i g .7 ) ,and f ind th a t th i s 2 5 t r a c e r ,wh i chh a sb e en in t e rp r e t eda sap ro x yfo rs e a i c ep r odu c t i on , 1 8 ch an g e sa lmo s ts yn ch r on ou s l yw i th WDCd O—p o s s i b l yr e f l e c t in ga 6 commonfo r c in gb ySou th e rnO c e ant emp e r a tu r e s . A t th eon s e to f th eNHBø l l in gw a rmp e r i od(DO1 ;1 4 . 6k y r )w e f ind ano r th– sou thph a s in gcomp a r ab l etoth a to fth eg l a c i a lp e r i od ,w i tha 1 8 2 5 661 3 3 y e a rl a go fth e An t a r c t i cd Or e spon s e(F i g . 3and E x t end ed D a t aT ab l e1 ) .Th ein t e rpo l a rph a s in ga tth eon s e tand t e rm in a t iono fth eYoun g e rD r y a ss t ad i a li samb i gu ou sinou rr e c o rd (E x t end ed D a t aT ab l e1 ) , mo s t l yb e c au s eo fth er e l a t i v e l yg r adu a l n a tu r eo fth e Youn g e rD r y a son s e tandth ep r e s en c eo ftw ol o c a l 1 8 m a x im ainth e WA I S -D d Or e c o rda r oundth eYoun g e rD r y a s – Ho l o c en et r an s i t i on(p o s s i b l yr e f l e c t in gr e g ion a lc l im a t e ) . Ar e c en t s tud yu s in gaCH s yn ch ron i z eds t a c ko ff i v en e a r co a s t a lAn t a r c t i c 4 co r e ssp ann in gth ed e g l a c i a t ionsu g g e s t eda n e a rs yn ch r on yo f An t a r c t i cb r e a kpo in t sand G r e en l andt r an s i t ion sw i th ina d a t in g un c e r t a in t yo f2 0 0y e a r s10. Ou rr e su l to v e r l ap sw i thth i sr an g e . How e v e r ,th e mu chsm a l l e rd a t in gun c e r t a in t ya t WDCandou ru s e o f th e fu l ls equ en c eo fg l a c i a lA IMe v en t sshow s th a tac en t enn i a l s c a l e An t a r c t i c l a g i sas y s t em a t i cf e a tu r eo fDO –A IMcoup l in gth r ou gh ou t th eg l a c i a lp e r iod . Th el e ado f NHc l im a t er e v e a l eda t WDC(F i g .2 )p ro v id e sc lu e s abou t DOc l im a t ed yn am i c s .Th es imp l e s tin t e rp r e t a t i oni sth a tth e ab rup tph a s e so fth eDOc y c l ea r ein i t i a t edinth eNH ,p r e sum a b l yin th e No r th A t l an t i c . Th i si scon s i s t en tw i ths e v e r a lp rop o s ed DO m e ch an i sm s ,su cha s No r th A t l an t i cs e a i c ed yn am i c s9,f r e shw a t e r a b 0 .2 SHleads NHleads No rma l i zeds igna l Co r re la t ion 0 –0 .2 –0 .4 –0 .6 –0 .8 –500 –250 c 2 .0 1 .5 1 .0 0 .5 0 0 –500 –250 250 500 750 0 600 d 169± 69 400 200 0 0 50 100 150 200 250 300 NHleadt ime(yea rs ) F requency(×103) F requency Lag(yea rs ) 40 e 30 20 10 0 0 100 250 500 750 –250 T ime(yea rs ) 0 250 500 750 218± 92 f 200 208± 96 300 0 100 NHleadt ime(yea rs ) 200 300 400 F i gu r e2|In t e rh em i sph e r i cph a s in go fth eb ipo l a rs e e s aw .a ,L a g g ed 1 8 1 8 Oand WDCd (d O ) /dt( b lu e ) ,andb e tw e en c o r r e l a t i onb e tw e enNGR IPd 1 8 ( d O ) /dt( g r e en ) .M i l l enn i a l s c a l ev a r i a b i l i t yi si so l a t edb y WDCCH4andd u s in gafou r th -o rd e rBu t t e rw o r thb andp a s sf i l t e r( 5 0 0– 1 0 , 0 0 0 y e a rw indow ) ; s yn ch ron i z edp a r to fth er e c o rd si su s ed( 3 1 . 2– 6 8k y r ) .b,DO3– 1 8 th eCH 4 1 8 1 8 O(b lu e ) , WDCCH4( g r e en )and WDCd O( o r an g ew i th s t a c ko fNGR IPd cu r v ef i t ) ,a l i gn eda tth em idp o in to fth eDOw a rm in gs i gn a l .E v en t sa r e a v e r a g edw i thth e i ro r i g in a lamp l i tud e sandn o rm a l i z eda f t e rs t a c k in gfo r con v en i en c eo fv i su a l i z a t i on .c ,A s in b,bu t fo rNHab rup tcoo l in ge v en t s( th a t i s ,th ein t e r s t ad i a lt e rm in a t i on s ) .d– f ,H i s to g r am so fNH l e adt im ea s s o c i a t ed – c ,r e sp e c t i v e l y ,g en e r a t edb yb inn in gso lu t i on sf romth es en s i t i v i t y w i tha 3 5 s tud y .Th eto t a lnum b e ro fso lu t i on s i s431 0 ind,and4 31 0 ineand f .D i s t r i bu t ionm e anand2 sp r ob a b i l i t ybound sa r e l i s t ed in th ep an e l s .Sh ad ed v e r t i c a ly e l lowb a r s(upp e rp an e l s )showNH l e ad t im e ; th ee r r o rb a rr ep r e s en t s sa sd e f in edfo rth elow e rp an e l s . 2 8 7 fo r c in g o ri c esh e l fc o l l ap s e .W ea c know l ed g e ,how e v e r ,th a tth e ab rup tN o r thA t l an t i ce v en t scou ldb e th er e spon s e toar emo t ep ro c e s s no tv i s i b l e in th e i c ec o r er e c o rd s ; th e r e f o r e ,a l thou ghw ec anno ta s c e r t a inth el o c a t i ono fth ee lu s i v eDO ‘ t r i g g e r ’( i fsu chacon c ep ti se v en m e an in g fu l inah i gh l yc oup l edd yn am i c a ls y s t em ) ,ou rr e su l t sc l e a r l y ind i c a t ean o r th t o s ou thd i r e c t ion a l i t yo fth eab rup tph a s e so fth e b ip o l a rs e e s aws i gn a l . Th ec en t enn i a lt im e s c a l eo fth e NHl e add em on s t r a t e sth edom in an c eo fo c e an i cp r o c e s s e s inp rop a g a t in gNH t emp e r a tu r eanom a l i e s toth eSHh i ghl a t i tud e s .An ya tm o sph e r i ct e l e conn e c t ionwou ldb e m an i f e s t edw i th ina tm o s taf ewd e c ad e sa f t e rth eab rup tNHe v en t18; 1 8 on th i s t im e s c a l e th e WDCd Os t a c k s(F i g .2b ,c )shownod i s c e rn ib l e t emp e r a tu r er e sp on s eabo v eth eno i s e .W ee s t im a t eth eno i s el e v e lb y 1 8 su b t r a c t in g th e f i t t edcu r v e s f rom th ed Os t a c k s ; th er em a in in gs i gn a l h a sa2sv a r i a b i l i t yo f0 . 1 4 %,o rab ou t0 . 1 8 u Ca s sum in gani s o top e s en s i t i v i t yo f0 . 8 % K21. W eth e r e f o r ee s t im a t eanupp e rboundo f 0 . 1 8u Conana tm o sph e r i c a l l yindu c ed An t a r c t i ct emp e r a tu r er e s p on s e( f o rc omp a r i s on ,m i l l enn i a l An t a r c t i ct emp e r a tu r ev a r i a t i on s a r eonth eo rd e ro f1– 2u C ) .Ar e ad ju s tm en to fa tm o sph e r i ct r an sp o r t m a yindu c esp a t i a l l yinhomo g en e ou st emp e r a tu r ech an g e s8,16 th a t m a yb e(p a r t l y )r e sp on s i b l efo rth eh e t e ro g en e i t yine xp r e s s ion ,o r 3 sh ap e ,o fA IMe v en t sa c r o s sAn t a r c t i c a . W e f ind th a tona v e r a g e th eDOcoo l in gs i gn a l i s t r an sm i t t eda s f a s t toAn t a r c t i c aa sth eDOw a rm in gs i gn a li s(ou rs en s i t i v i t ys tud ysu g g e s t sad i f f e r en c einp r op a g a t i ont im eo f1 068 9y e a r s ) .Th i simp l i e s th a t th en o r th t o s ou thp rop a g a t i on t im e i s ind ep end en to f th eAMOC b a c k g r ounds t a t e ; th a t i s , i t i s ind ep end en to fwh e th e rth eAMOC i s in th ew e a ko rs t r on go v e r tu rn in gs t a t e . Mod e l l in gwo r ksu g g e s t s th a t th e m e r id i on a lp r op a g a t i ont im ea c r o s sth eACC l a t i tud e sd ep end sp r im 2 1 a r i l yonACCs t r en g th ;ou rin f e r en c eo fs im i l a rp rop a g a t i ont im e s m a ythu sr e f l e c tas t a b i l i t yo fth eACConm i l l enn i a lt im e s c a l e s .Th e r e i sa l s oac on sp i cu ou ss yn ch r on i c i t yb e tw e en th eph a s in go f th eb ipo l a r s e e s awandth edu r a t i ono fth eab rup tin c r e a s einCO t1 4 . 6k y r 2a (F i g .3d ) ; i fth ef o rm e rdo e s ind e edr e f l e c tth et im e s c a l eo fth eo c e an i c r e spon s e ,th i sm a yh o ldc lu e sabou tth e(un id en t i f i ed )sou r c eo fth i s CO2( r e f .2 6 ) . P ro x yr e co rd so f No r th A t l an t i cv en t i l a t ion and o v e r tu rn in g s t r en g thdu r in gM a r in eI s o top eS t a g e3 t yp i c a l l yshow th em o s tp r om 1 1 , 1 2 in en te x cu r s ion sdu r in gH e in r i chs t ad i a l s ,p e r iod so fe x t r em e co ldinth e No r th A t l an t i ca s so c i a t ed w i thl a y e r so fi c e r a f t ed d eb r i sino c e ans ed im en t sth a tr ep r e s en tt im e so fm a s s i v ed e l i v e r yo f 15 14 13 12 11 –40 700 –42 –44 –34 18O WDC δ (‰ ) 800 a 600 b 500 400 –35 –36 WDCCH4(p .p .b . ) –38 c 270 –37 260 –38 250 –39 240 d WDCCO2(p .p .m . ) 18O NGR IPδ (‰ ) –36 230 OD 15 B−A/ACR 14 YD 13 Ho loc . 12 11 WD2014age(kyrBP) 1 8 F i gu r e3|T im in go fth el a s td e g l a c i a t ion .a,NGR IP d OonG ICC 0 5 1 8 1 . b, WDCCH . c , W D C d O w i t h b r e a k p o i n t s a so r an g ed o t sand ch ron o lo g y 4 e r r o rb a r sshow in gth e2 sun c e r t a in t ybound s(E x t end edD a t aT a b l e1 ) . a t a(do t s )w i thsp l in e f i t( so l id l in e )26.P e r iodabb r e v i a t i on s :OD , d, WDCCO 2d O ld e s tD r y a s ;B–A ,Bø l l in g–A l l e rød ;ACR ,An t a r c t i cCo ldR e v e r s a l ;YD , Youn g e rD r y a s ;Ho lo c . ,Ho l o c en e .V e r t i c a lo r an g el in e sco r r e sp ondt oth e m idpo in t so fth e WDCCH4t r an s i t i on s .NGR IPand WDCch r on o l o g i e sa r e bo thb a s edonannu a l l a y e rcoun t in g ,anda r efu l l yind ep end en t . d e b r i s l ad eni c e b e r g s(H e in r i che v en t s ) .Th i ssu g g e s t sth a tth e r em a y b ead i f f e r en c eb e tw e enc l im a t ed yn am i c sdu r in gH e in r i chandnon H e in r i chs t ad i a l s .W e f indnoan om a lou sNH l e ad t im e fo rDO t r an s i t ion sd i r e c t l ya f t e ro rb e f o r eH e in r i chs t ad i a l s(E x t end edD a t aF i g .6 ) , andthu sn oe v id en c eth a tH e in r i chs t ad i a l sa r eunu su a lf romth e p e r sp e c t i v eo fth eo c e an i ct e l e c onn e c t i on sth a tdom in a t eth eb ipo l a r s e e s aw .S im i l a r l y ,p r e v i ou s wo r kh a sshownth a tanin c r e a s ein An t a r c t i c t emp e r a tu r e i s l in e a r l yr e l a t ed toG r e en l ands t ad i a ldu r a t ion , 3 . i r r e sp e c t i v eo f th eo c cu r r en c eo fH e in r i che v en t sdu r in g th e s es t ad i a l s R e c en ts tud i e ssu g g e s tth a td e c r e a s e sinAMOCs t r en g thp r e c ed eth e H e in r i che v en t s ,a l l ow in gth epo s s i b i l i t yth a tth e l a t t e ra r ear e spon s e 2 7 , 2 8 .Th em a in in f lu en c eo f t oAMOCv a r i a t i on sr a th e r th an th e i rc au s e H e in r i che v en t sonth eb ip o l a rs e e s aw m a ythu sb etol en g th enth e s t ad i a lp e r i od sdu r in gwh i chth e yo c cu rb ysupp r e s s in gth eAMOCb y m e an so f i c e b e r g -d e l i v e r ed f r e shw a t e r ,a l l ow in g l a r g eamoun t so fh e a t t obu i ldupinth eS ou th e rnO c e an . 1 9 , 2 1 e mod e l s su g g e s taf a s tt emp e r A l th ou ghb o thth ed a t a5andth a tu r er e sp on s e in th eS ou thA t l an t i c(d e c ad a l s c a l e inmod e l s ) , th e r e i s cu r r en t l yn oc on s en su sine x i s t in g mod e ls tud i e sonth eph y s i c a l m e ch an i sm sandt im e s c a l e so fth ep ro c e s s e sth a tp rop a g a t et emp e r a tu r es i gn a l sb e tw e enth eSou th A t l an t i candth eSou th e rn O c e an ; c omp l i c a t in gf a c t o r st oc on s id e rin c lud eth e l a c ko fazon a lbound a r y 2 1 ,th e l a r g eth e rm a l in e r t i a t osupp o r tth ep r op a g a t i ono fK e l v inw a v e s 6 ,th ecomp l e x i t yo fedd yh e a tt r an sp o r ta c r o s s o fth eS ou th e rnO c e an th e An t a r c t i cc i r cump o l a rcu r r en t ,andth ecoup l in gb e tw e enth e 2 9 .Inth i s e x t en to fAn t a r c t i cs e ai c eandth eo v e r tu rn in gc i r cu l a t i on con t e x t ,ou rp r e c i s eph a s in gob s e r v a t i on sp ro v id ean ewcon s t r a in t w i th wh i cht ot e s tfu tu r e mod e ls imu l a t ion ss e e k in gtoc ap tu r eth e d yn am i c so fm i l l enn i a l s c a l ec l im a t ev a r i ab i l i t y . On l ineCon ten tMe thod s ,a longw i than yadd i t iona lE x tendedDa tad i sp layi tem s andSou r ceDa ta ,a rea va i lab le in theon l ineve r s iono f thepape r ;re fe ren ce sun ique tothe sese c t ion sappea ron lyintheon l inepape r . Rece ived11Sep tembe r2014 ;accep ted3 Ma rch2015 . 1 . NGR IPP ro jec t Membe r s .H igh reso lu t ionreco rdo fNo r the rnHem isphe rec l ima te ex tend ingin tothela s tin te rg lac ia lpe r iod .Na tu re431 ,147–151(2004 ) . 2 . B lun ie r ,T .&B rook ,E .J .T im ingo fm i l lenn ia l -sca lec l ima techangeinAn ta rc t ica andG reen landdu r ingthelas tg lac ia lpe r iod .Sc ience291 ,109–112(2001 ) . 3 . EP ICACommun i ty Membe rs .One to -onecoup l ingo fg lac ia lc l ima teva r iab i l i tyin G reen landandAn ta rc t ica .Na tu re444 ,195–198(2006 ) . 4 . C row ley ,T .J .No r thA t lan t icDeep Wa te rcoo l sthesou the rnhem isphe re . Pa leoceanog raph y7 ,489–497(1992 ) . 5 . Ba rke r ,S .e ta l .In te rhem isphe r icA t lan t icseesawresponsedu r ingthelas t deg lac ia t ion .Na tu re457 ,1097–1102(2009 ) . 6 . S tocke r ,T .F .&John sen ,S .J .A m in imumthe rmodynam ic mode lfo rtheb ipo la r seesaw .Pa leoceanog raph y18 ,1087(2003 ) . 7 . Pe te rsen ,S .V . ,Sch rag ,D .P .&C la rk ,P .U .Anew mechan ismfo rDansgaa rd– Oe schge rcyc les .Pa leoceanog raph y28 ,24–30(2013 ) . 8 . R ind ,D .e ta l .E f fec tso fg lac ia l me l twa te rintheG ISScoup leda tmo sphe re–ocean mode l .2 .Ab ipo la rseesawinA t lan t icDeep Wa te rp roduc t ion .J .Geoph y s .Re s . 106(D21 )27355–27365(2001 ) . 9 . Dokken ,T .M . ,N i sanc iog lu ,K .H . ,L i ,C . ,Ba t t is t i ,D .S .&K i sse l ,C .Dansgaa rd– Oe schge rcyc les :in te rac t ionsbe tweenoceanandseaicein t r in s ictotheNo rd ic seas .Pa leoceanog raph y28 ,491–502(2013 ) . ta l .Thela s tdeg lac ia t ion :t im ingtheb ipo la rseesaw .C l im .Pa s t .7 , 10 . Ped ro ,J .B .e 671–683(2011 ) . 11 .P io t rowsk i ,A .M . ,Go lds te in ,S .L . ,Hemm ing ,S .R . ,Fa i rbanks ,R .G .&Zy lbe rbe rg ,D . R .Osc i l la t ingg lac ia lno r the rnandsou the rndeepwa te rfo rma t ionf rom comb inedneodym iumandca rboniso topes .Ea r thP lane t .Sc i .Le t t .272 , 394–405(2008 ) . 12 . Ma r t ra t ,B .e ta l .Fou rc l ima tecyc leso frecu r r ingdeepandsu r facewa te r des tab i l iza t ionsontheIbe r ian ma rg in .Sc ience317 ,502–507(2007 ) . 13 . Pe te rson ,L .C . ,Haug ,G .H . ,Hughen ,K .A .&Röh l ,U .Rap idchanges in thehyd ro log ic cyc leo fthet rop ica lA t lan t icdu r ingthela s tg lac ia l .Sc ience290 ,1947–1951 (2000 ) . 14 . Ch iang ,J .C .H .&B i tz ,C .M .In f luenceo fh ighla t i tudeiceco ve ronthe ma r ine l im .D yn .25 ,477–496(2005 ) . In te r t rop ica lCon ve rgenceZone .C 15 . Toggwe i le r ,J .R .&Lea ,D .W .Tempe ra tu red i f fe rence sbe tweenthehem isphe res andiceagec l ima teva r iab i l i ty .Pa leoceanog raph y25 ,PA2212(2010 ) . 16 .T imme rmann ,A .e ta l .Towa rdsaquan t i ta t iveunde r s tand ingo fm i l lenn ia l sca le An ta rc t icwa rm ingeven ts .Qua t .Sc i .Re v .29 ,74–85(2010 ) . 17 . WA ISD i v ideP ro jec t Membe r s .On se to fdeg lac ia lwa rm ingin We s tAn ta rc t ica d r ivenbyloca lo rb i ta lfo rc ing .Na tu re500 ,440–444(2013 ) . 18 . Ve l l inga ,M .& Wood ,R .A .G loba lc l ima t icimpac t so faco l lap seo ftheA t lan t ic the rmoha l inec i rcu la t ion .C l im .Change54 ,251–267(2002 ) . ,Z .Y .&A lexande r ,M .A tmo sphe r icb r idge ,ocean ictunne l ,andg loba lc l ima t ic 19 .L iu te leconnec t ions .Re v .Geoph y s .45 ,RG2005(2007 ) . 20 . Ma suda ,S .e ta l .S imu la tedrap idwa rm ingo fabys sa lNo r thPac i f icwa te rs .Sc ience 329 ,319–322(2010 ) . 21 . Schm i t tne r ,A . ,Saenko ,O .A .& Weave r ,A .J .Coup l ingo fthehem isphe resin ob se rva t ionsands imu la t ion so fg lac ia lc l ima techange .Qua t .Sc i .Re v .22 , 659–671(2003 ) . 22 . Eng land ,M .H .Theageo fwa te randven t i la t iont imesca les inag loba locean mode l . J .Ph y s .Oceanog r .25 ,2756–2777(1995 ) . ta l .The WA ISD i v idedeepiceco re WD2014ch rono logy .Pa r t1 . 23 . Bu i ze r t ,C .e Me thanesynch ron iza t ion(68–31kaBP )andthega sage– iceaged i f fe rence .C l im . Pa s t .11 ,153–173(2015 ) . 24 . Baumga r tne r ,M .e ta l .NGR IPCH4concen t ra t ionf rom120to10ky rbe fo re p resen tandi t sre la t iontoad15Ntempe ra tu rerecons t ruc t ionf romthesameice co re .C l im .Pa s t10 ,903–920(2014 ) . 25 . Wo l f f ,E .W . ,Rank in ,A .M .&Röth l i sbe rge r ,R .Aniceco reind ica to ro fAn ta rc t icsea icep roduc t ion ?Geoph y s .Re s .Le t t .30 ,2158(2003 ) . 26 . Ma rco t t ,S .A .e ta l .Cen tenn ia l -sca lechanges intheg loba lca rboncyc ledu r ingthe la s tdeg lac ia t ion .Na tu re514 ,616–619(2014 ) . 27 . Gu t jah r ,M .&L ippo ld ,J .Ea r lya r r i va lo fSou the rnSou rce Wa te rinthedeepNo r th A t lan t icp r io rtoHe in r icheven t2 .Pa leoceanog raph y26 ,PA2101(2011 ) . 28 . Ma rco t t ,S .A .e ta l .Ice -she l fco l lapsef romsubsu r facewa rm ingasat r igge rfo r He in r icheven ts .P roc .Na t lAcad .Sc i .USA108 ,13415–13419(2011 ) . 29 . Fe r ra r i ,R .e ta l .An ta rc t icsea icecon t ro lonoceanc i rcu la t ion inp resen tandg lac ia l roc .Na t lAcad .Sc i .USA111 ,8753–8758(2014 ) . c l ima tes .P ta rc t ic 30 . Pa r ren in ,F .e ta l .Synch ronou schangeo fa tmo sphe r icCO2andAn tempe ra tu redu r ingthe las tdeg lac ia lwa rm ing .Sc ience339 ,1060–1063(2013 ) . Supp lemen ta ryIn fo rma t ionisava i lab leintheon l ineve rs iono fthepape r . Acknow ledgemen tsWethankthe WA ISD i v ideD r i l l ingTeam(2006–2013 )(E . Mo r ton , P .Ca ss idy ,M .Jay red ,J .Rob inson ,S .Po l i sh in sk i ,J .Koeh le r ,L .A lbe r sha rd t ,J .Goe tz , B .G ros s ,R .Ku l in ,S .Haman ,W .Neume i s te r ,C .Zande r ,J .Kyne ,L .Augus t in ,B .Fo lme r , S .B .Han sen ,E .A lexande randJ .Fow le r )andthedozenso fco rehand le rswho p roces sedtheiceco reinthef ie ldanda ttheNa t iona lIceCo reLabo ra to ry(N ICL ) .Th i s wo rk is fundedth roughtheUSNa t iona lSc ience founda t iong ran t s0944078 ,0841308 ( to M .A . ) ,1043528( toR .B .A . ,D .E .V .andJ .M .F . ) ,1142173( toR .B . ) ,1204172 ,1142041 , 1043518( toE . J .B . ) ,0839066( toJ .C . -D . ) ,0087345 ,0944191( toH .C .andE .D .W . ) , 0539232 ,0537661( toK .M .C . ) ,1142069 ,1142115( toN .W .D . ) ,0841135( toIDDO ) , 0839093 ,1142166( toJ .R .M . ) ,0440819 ,1142164( toK .C .M . ) ,1142178( toP .B .P . ) , 0538657( toJ .P .S . ) ,1043500 ,0944584( toT .A .S . ) ,1043313( to M .K .S ) ,0537930 , 1043092( toE . J .S . ) ,0230149 ,0230396 ,0440817 ,0440819 ,0944191 ,0944348( to K .C .T . ) ,0944266( to M .S .T . ) ,0839137( toK .C .W .andK .N . ) ,0537593and1043167( to J .W .C .W . ) ;theUSGSC l ima teandLandUseChangeP rog ram( toG .D .C .andJ . J .F . ) ;the NOAAC l ima teandG loba lChangeFe l lowsh ipP rog ram ,adm in is te redbytheUn ive r s i ty Co rpo ra t ionfo rA tmosphe r icResea rch( toC .B . ) ;theV i l lumFounda t ion( to M .W . ) ;the Jo in t In s t i tu tefo rtheS tudyo ftheA tmo sphe reandOcean( toJ .B .P . ,J ISAOcon t r ibu t ion no .2343 ) ;andtheKo reaPo la rResea rch In s t i tu te ,g ran tPE15010( toJ .A . ) .TheNa t iona l Sc ienceFounda t ionO f f iceo fPo la rP rog ramsa lsofundedthe WA ISD i v ideSc ience Coo rd ina t ionO f f icea ttheDe se r tResea rchIn s t i tu teo fNevadaandUn i ve rs i tyo fNew Hamp sh i refo rtheco l lec t ionandd i s t r ibu t iono fthe WA ISD i v ideiceco reandre la ted ta sk s ;theIceD r i l l ingP rog ramO f f iceandIceD r i l l ingDe s ignandOpe ra t ionsg roupfo r co r ingac t i v i t ies ;theN ICLfo rcu ra t iono ftheco re ;Ray theonPo la rSe r v ice sfo r log i s t ic s suppo r tinAn ta rc t ica ;andthe109 thNewYo rkA i rNa t iona lGua rdfo ra i r l i f tin An ta rc t ica . Au tho rCon t r ibu t ionsDa taana ly s i sandDage mode l l ingwe repe r fo rmedbyC .B . ; annua l laye rcoun t ing(da t ing )o fuppe r2 ,850 mby M .S . ,T . J .F . ,M .W . ,K .C .T .andK .C .M . ; CH4synch ron iza t ion(da t ing )o f lowe r555 mbyC .B . ,K .M .C . ,J .P .S .andT . J .F . ;agesca le va l ida t ionbyN .W .D . ,N . I . ,K .C .W . ,K .N .andT .E .W . ;d i sc re tewa te riso topeana lys i sby E . J .S . ,A . J .Sc .andS .W .S . ;con t inuouswa te riso topeana lys i sbyJ .W .C .W . ,T .R . J . ,B .H .V . andV .G . ;d i sc re teCH4ana ly s i sbyT .A .S . ,L .E .M . ,J .E .L . ,J .S .E . ,J .L .R .andE . J .B . ;con t inuous CH4ana lys i sbyR .H .R . ,E . J .B .andJ .R .M . ;CO2ana ly s i sbyS .A .M . ,M .L .K . ,T .K .B . ,J .A .and E . J .B . ;d15No fN2ana lys i sbyD .B . ,C .B . ,A . J .O .andJ .P .S . ;con t inuou s f lowchem ica l ana ly s i sby M .S . ,O . J .M . ,N . J .C . ,D .R .P .andJ .R .M . ;d i sc re techem ica lana ly s i sbyJ .C . -D . , D .G .F . ,B .G .K . ,K .K .andG . J .W . ; iceco rephys ica lp rope r t iesbyR .B .A . ,J .M .F . ,D .E .V . ,M .K .S . andJ . J .F . ;bo reho le logg ingbyR .C .B .andG .D .C . ;b io log ica ls tud iesbyJ .C .P .andP .B .P . ; tempe ra tu rerecons t ruc t ion sbyK .M .C .andG .D .C . ;teph roch rono logybyN .W .D .and N . I . ; f i rns tud iesbyM .A . ,T .A .S .andS .G . ;10Beana ly s i sbyK .C .W .andT .E .W . ; f ie ldsc ience ove r s igh t ,D .E .V .andB .H .V . ;s i tese lec t ionbyH .C . ,E .D .W .andE .C .P . ;sc ience managemen tandsamp led i s t r ibu t ionby M .S .T .andJ .M .S . ; log i s t ic ssuppo r t ,p lann ing and managemen tby M . J .K . ;d r i l l ing managemen tbyA . J .Sh . ,C .R .B . ,D .A .L . ,andA .W .W . ; deepd r i l ldes ignbyA . J .Sh . ,J .A . J . ,N .B .M .andC . J .G . ;d r i l l ingf ie ld managemen tbyJ .A . J . , K .R .S .andN .B .M . ;samp leco l lec t ionandd r i l lope ra t ionsbyC . J .G . ,J . J .G . ,T .W .K .and P . J .S .Thef ie ldsamp lehand l ingleade r swe reA . J .O . ,B .G .K . ,P .D .N .andG . J .W . ;samp le cu ra t ion ,p roce ss ingandd i s t r ibu t ionwa spe r fo rmedbyG .M .H . ,B .A . ,R .M .N . ,E .C .and B .B .B . ;theove ra l l WA ISD i v ideP ro jec tdes ignand managemen t ,Ch ie fSc ien t is tand f ie ldleade rwasK .C .T .The manu sc r ip twa sw r i t tenbyC .B . ,E . J .S .andJ .B .P .w i th as s i s tancef romJ .P .S . ,B .R .M . ,E . J .B .andK .C .T ;a l lau tho rsd i scus sedthere su l t sand con t r ibu tedto imp rov ingthef ina l manu sc r ip t .Anyuseo ft rade ,p roduc t ,o r f i rmnames isfo rdesc r ip t i vepu rposeson lyanddoesno timp lyendo rsemen tbytheUS Go ve rnmen t . Au tho rIn fo rma t ionRep r in tsandpe rm i ss ion sin fo rma t ionisava i lab lea t www .na tu re .com / rep r in t s .Theau tho rsdec la renocompe t ingf inanc ia lin te re s ts . Reade rsa rewe lcometocommen tontheon l ineve rs iono fthepape r .Co r respondence andreques tsfo r ma te r ia l sshou ldbeadd re ssedtoC .B .(bu ize r tc@sc ience . o regons ta te .edu ) . WA ISD iv ideP ro jec t Membe rs 2 3 4 5 Ch r is toBu ize r t1,Be t tyAd r ian ,J inhoAhn , Ma ryA lbe r t ,R icha rdB .A l ley ,Dan ie l 1 7 2 Baggens tos6,ThomasK .Bauska ,RyanC .Bay ,B r ianB .Benc ivengo ,Cha r lesR . 8 1 9 10 11 Ben t ley ,Edwa rdJ .B rook,Na thanJ .Che l lman,Ga ryD .C low ,J ihongCo le -Da i, 13 14 15 Howa rdConway12,E r icC ravens ,Ku r tM .Cu f fey ,Ne l ia W .Dunba r ,JonS . 1 5 11 16 12 Edwa rds,John M .Fegy ve re s i,Da veG .Fe r r is ,JoanJ .F i tzpa t r ick ,T .J .Fudge , 17 ,18 8 4 Ch r isJ .G ibson8,Vas i le iosGk in is ,JoshuaJ .Goe tz ,S tephan ieG rego ry , 2 15 8 17 Geo f f rey M .Ha rg reaves ,Ne lsIve rson ,JayA .Johnson,Ty le rR .Jones , M ichae l 1 19 20 21 8 L .Ka lk , Ma t thewJ .K ippenhan ,BessG .Ko f fman ,Ka r lK reu tz ,Tanne rW .Kuh l , 8 1 1 ,22 12 Dona ldA .Leba r ,JamesE .Lee,ShaunA . Ma rco t t ,B rad leyR . Ma rk le ,O l iv iaJ . 9 9 9 1 Mase l l i ,JosephR . McConne l l,Kenne thC . McGw i re,LoganE .M i tche l l,N ico la iB . 23 24 2 Mo r tensen8,Pe te rD .Ne f f ,Kun ih iko N ish i izum i ,R icha rd M . Nunn ,Ana isJ . 6 ,25 9 18 ,26 27 7 O rs i ,Dan ie lR .Pas te r is,Joe lB .Ped ro ,E r inC .Pe t t i t ,P .Bu fo rdP r ice,John 1 1 12 C .P r iscu28,Rachae lH .Rhodes ,Ju l iaL .Rosen ,And rewJ .Schaue r ,Sp ruce W . 12 8 6 Schoenemann ,Pau lJ .Sende lbach,Je f f reyP .Seve r inghaus,A lexande rJ . 8 9 8 29 Sh tu rmakov , M ichae lS ig l,K r is t inaR .S lawny,Joseph M .Souney ,ToddA . 30 12 9 29 Sowe rs5, Ma t thewK .Spence r ,E r icJ .S te ig ,Kend r ickC .Tay lo r ,Ma rkS .Tw ick le r , 17 5 12 24 B ruceH .Vaughn ,Dona ldE .Vo ig t,Edw inD . Wadd ing ton ,KeesC . We l ten , 8 17 12 ,18 31 An thony W . Wend r icks ,James W .C . Wh i te , Ma iW ins t rup ,G i f fo rdJ . Wong & Thoma sE . Wood ru f f32 1 Co l legeo fEa r th ,Ocean icandA tmo sphe r icSc iences ,O regonS ta teUn ive rs i ty ,Co rva l l i s , log ica lSu rveyNa t iona lIceCo reLabo ra to ry ,Den ve r , O regon97331 ,USA .2USGeo lo fEa r thandEnv i ronmen ta lSc ience ,Seou lNa t iona l Co lo rado80225 ,USA .3Schoo rSchoo lo fEng inee r ing ,Da r tmou thCo l lege , Un ive r s i ty ,Seou l151 -742 ,Ko rea .4Thaye r tmen to fGeosc iences ,Penn sy lvan iaS ta te Hano ve r ,NewHamp sh i re03755 ,USA .5Depa r ippsIn s t i tu t iono f Un ive r s i ty ,Un ive r s i tyPa rk ,Penn sy lvan ia16802 ,USA .6Sc Oceanog raphy ,Un ive r s i tyo fCa l i fo rn iaa tSanD iego ,LaJo l la ,Ca l i fo rn ia92093 ,USA . 7 Depa r tmen to fPhy s ic s ,Un ive r s i tyo fCa l i fo rn iaa tBe rke ley ,Be rke ley ,Ca l i fo rn ia94720 , r i l l ingDes ignandOpe ra t ions ,Un ive rs i tyo fW i scon s in -Mad ison , Mad i son , USA .8IceD W i scon s in53706 ,USA . 9De se r tRe sea rchIn s t i tu te ,Ne vadaSy s temo fH ighe rEduca t ion , 10 Reno ,Ne vada89512 ,USA . USGeo log ica lSu rvey ,Bou lde r ,Co lo rado80309 ,USA . 11 Depa r tmen to fChem i s t ryandB iochem i s t ry ,Sou thDako taS ta teUn ive rs i ty ,B rook ing s , Sou thDako ta57007 ,USA .12Depa r tmen to fEa r thandSpaceSc ience s ,Un ive rs i tyo f 13 Wa sh ing ton ,Sea t t le , Wa sh ing ton98195 -1310 ,USA . ADC Managemen tSe rv ices , Lakewood ,Co lo rado80226 ,USA .14Depa r tmen to fGeog raphy ,Un ive r s i tyo fCa l i fo rn iaa t Be rke ley ,Be rke ley ,Ca l i fo rn ia94709 ,USA .15Ea r thandEnv i ronmen ta lSc ience Depa r tmen t ,New Me x icoTech ,Soco r ro ,New Me x ico87801 ,USA .16USGeo log ica l Su rvey ,Denve r ,Co lo rado80225 ,USA .17In s t i tu teo fA rc t icandA lp ineResea rch , Un ive r s i tyo fCo lo rado ,Bou lde r ,Co lo rado80309 -0450 ,USA .18Cen t re fo r iceandc l ima te , Un ive r s i tyo fCopenhagen ,DK -2100CopenhagenØ ,Denma rk .19An ta rc t icSuppo r t Con t rac t ,Lockheed Ma r t in USAn ta rc t ic P rog ram , Cen tenn ia l , Co lo rado80112 , USA . 20 Lamon t -Dohe r tyEa r th Ob se rva to ry , Co lumb ia Un ive rs i ty ,Pa l i sades , NewYo rk 10964 , USA .21C l ima te ChangeIn s t i tu teandSchoo lo fEa r thand C l ima teSc ience s , Un ive r s i tyo f Ma ine ,O rono , Ma ine04469 , USA . 22Un ive r s i tyo fW i scon s in -Mad ison , 23 Mad i son ,W i scon s in ,W i scon s in53706 USA . An ta rc t ic Resea rch Cen t re ,V ic to r ia Un ive r s i tyo f We l l ing ton , We l l ing ton6012 , NewZea land .24SpaceSc iencesLabo ra to ry , 25 Un ive r s i tyo fCa l i fo rn iaa tBe rke ley ,Be rke ley ,Ca l i fo rn ia94720 ,USA . Labo ra to i rede s Sc ience sdu C l ima te tdel ’En v i ronnemen t ,In s t i tu tP ie r reS imonLap lace ,91191 26 G i f -Su r -Y ve t te ,F rance . Jo in tIn s t i tu tefo rtheS tudyo ftheA tmo sphe reand Ocean , Un ive r s i tyo f Wa sh ing ton ,Sea t t le , Wa sh ing ton98195 , USA . 27Depa r tmen to f Geosc iences , Un ive rs i tyo fA laskaFa i rbank s ,Fa i rbank s ,A laska99775 , USA . 28 Depa r tmen to fLand Re sou rce sandEnv i ronmen ta lSc iences , Mon tanaS ta te 29 Un ive r s i ty , Bozeman , Mon tana59717 , USA . In s t i tu tefo rtheS tudyo fEa r th , Oceans andSpace , Un ive r s i tyo f New Hamp sh i re , Du rham , New Hamp sh i re03824 , USA . 30 Schoo lo fPhys ica lSc iences ,LakeSupe r io rS ta te Un ive rs i ty ,Sau l tSa in te Ma r ie , 31 M ich igan49783 , USA . Depa r tmen to fEa r thSc iences , Da r tmou th Co l lege , Hanove r , New Hamp sh i re03755 , USA . 32PR IMELabo ra to ry ,Pu rdue Un ive rs i ty , We s tLa faye t te , Ind iana47907 , USA . METHODS Co r er e co v e r yand p ro c e s s in g . Th el o c a t i ono fth e WA I SD i v id ei c ec o r e ( 7 9 . 4 8 uS ,1 1 2 . 1 1 uW )w a ss e l e c t edt op r o v id eth eh i gh e s tp o s s i b l et im e r e s o lu t i on r e c o rdo fAn t a r c t i cc l im a t edu r in gth ep a s t5 0k y ro rm o r e ,andt oen su r eth a tth e r e c o rd f rom th e l a s td e g l a c i a t i onw ou ldn o tb e in i c e f r om th e l ow e r qu a l i t yb r i t t l e 21 1 7 i c ez on e .Th es i t eh a sap r e s en t -d a yi c ea c cumu l a t i onr a t eo f2 2cmy r ,d i v id e f l owandan i c e th i c kn e s so f3 , 4 6 0m( J .P ad en ,p e r s on a lc ommun i c a t i on2 0 1 1 ) .N o s t r a t i g r aph i ci r r e gu l a r i t i e sw e r ed e t e c t e dinth ec o r eu s in gv i su a lo b s e r v a t i on , mu l t i t r a c ke l e c t r i c a lcondu c t i v i t ym e a su r em en t so rg a ss t r a t i g r aph y .C o r in gw a s s t o pp ed5 0mabo v eth eb edt op r e v en tc on t am in a t i ono fth eun f r o z enb a s a l en v i r onm en t .D r i l l in go fth em a inc o r e(WDC 0 6A )s t a r t e ddu r in gth e2 0 0 6 / 2 0 0 7 f i e lds e a sonand f in i sh eddu r in g th e2 0 1 1 / 2 0 1 2 f i e lds e a s on ,a t th e f in a ld ep th o f3 , 4 0 5m .D r i l l in gw a sdon ew i thth eU SD e epI c eSh e e tC o r in g(D I SC )d r i l l ,a n ewd r i l ld e s i gn edandop e r a t edb yth eI c eD r i l l in gD e s i gnandOp e r a t i on sg r ou p ( en g in e e r in gt e ama t Un i v e r s i t yo fW i s c on s in ,M ad i s on ) .C o r eh and l in gand d i s t r i bu t i ono fi c es amp l e sw e r ep e r f o rm edb yth eN a t i on a lI c eC o r eL a b o r a t o r y (U SG e o lo g i c a lSu r v e y )andth eS c i en c eC o o rd in a t i onO f f i c e(Un i v e r s i t yo fN ew H amp sh i r eandD e s e r tR e s e a r chIn s t i tu t e ) .Th ed r i l landc o r eh and l in gm e th od s h ad m an yinn o v a t i on sth a timp r o v e dc o r equ a l i t y ,e sp e c i a l l yinth eb r i t t l ei c e . Th e s ein c lud edimp ro v e dm e ch an i c a lch a r a c t e r i s t i c so fth ed r i l l ,b e t t e rc on t r o l o fth ed r i l l in gop e r a t ion ,co r eh and l in gp r o c edu r e sth a tm in im i z edth e rm a land m e ch an i c a lsho c ktoco r e ,n e t t in gt oc on t a inth eb r i t t l ei c e ,andt emp e r a tu r e t r a c k in go fa l l i c es amp l e sf r omth ed r i l lt oth el a b o r a t o r i e s . 1 8 D a t ad e s c r ip t ion .W a t e r 18O /16Oc om p o s i t i on(d O )w a sm e a su r eda tI s oL a b , Un i v e r s i t yo fW a sh in g ton ,S e a t t l e ,W a sh in g t on .M e a su r em en tp r o c edu r e sf o r WDCh a v eb e end e s c r i b ede l s ewh e r e17,31.Insh o r t ,m e a su r em en t sw e r em ad ea t 0 . 5md ep tha v e r a g edr e s o lu t i on ,u s in g l a s e rsp e c t r o s c op y(P i c a r r oL 2 1 2 0 iw a t e r 1 8 i s o t op ean a l y s e r ) .d Od a t aa r er ep o r t edr e l a t i v et oth eV SMOW(V i enn a S t and a rd M e an O c e anw a t e r )s t and a r d ,andn o rm a l i z edt oth eV SMOW SLAP ( S t and a rdL i gh tAn t a r c t i cP r e c ip i t a t i on )s c a l e . Tw os ep a r a t ed a t as e t so fa tm o sph e r i cm e th an ee x i s t f o r WDC .Th e f i r s t i sb a s ed ond i s c r e t es amp l in go fth eco r e ; i tw a sm e a su r ed j o in t l ya tP ennS t a t eUn i v e r s i t y ( 0– 6 8k y r ,0 . 5– 2mr e s o lu t i on )anda tO r e g onS t a t e Un i v e r s i t y( 1 1 . 4– 2 4 . 8k y r , 1– 2mr e s o lu t ion ) .Fo rth i sr e c o rdth ea i rw a se x t r a c t edu s in ga m e l t– r e f r e e z e t e chn iqu ef rom,5 0gi c es am p l e s ,andan a l y s e donag a sch r om a t o g r aphw i tha 3 2 f l am ei on i z a t i ond e t e c t o r .C o r r e c t i on sf o rg a ss o lu b i l i t y ,b l an kandg r a v i t a t i on a len r i chm en tfo rth eO r e g onS t a t e Un i v e r s i t yd a t aw e r ep e r f o rm edin a c c o rd an c ew i thr e f .3 3 ;co r r e c t i on s t o th eP ennS t a t eUn i v e r s i t yd a t aa r ed e s c r i b ed inr e f .1 7 .As e c ondd a t as e t(R .H .Rh od e s ,E . J .B r o o k ,J .C .H .Ch i an g ,T .B lun i e r , O . J .M a s e l l i ,J .R .M cConn e l l ,D .R om an in iandJ .P .S e v e r in gh au s ,unpu b l i sh ed o b s e r v a t i on s )i sb a s edoncon t inu ou sf l owan a l y s i s(CFA )inc om b in a t i onw i th 3 4 , 3 5 l a s e rsp e c t ro s cop y .Th i sd a t as e t ,wh i chi so fh i gh e rt emp o r a lr e s o lu t i on ,w a s u s e d t od e t e rm in e th e t im in go f th ea b rup tDO t r an s i t i on s(E x t end edD a t aF i g .2 ) . A l lCH4d a t aa r er ep o r t edonth eNOAA 0 4s c a l e36. WDC N acon c en t r a t ion sw e r e m e a su r eda tth eU l t r aT r a c e Ch em i s t r y L a b o r a t o r ya tth eD e s e r tR e s e a r chIn s t i tu t e ,R en o ,N e v ad a ,b ym e an so fCFA . S t i c k so f i c ew e r em e l t edcon t inu ou s l yonah e a t edp l a t e .P o t en t i a l l yc on t am in a t ed m e l tw a t e rf romth eou t e rp a r to fth ei c es t i c kw a sd i s c a rd ed .Tw oindu c t i v e l y c ou p l edp l a sm am a s ssp e c t r om e t e r sw e r eu s edt oan a l y s eth es t r e amo fm e l t w a t e r37.Th e CFAch em i s t r yandCH a t aw e r em e a su r e ds imu l t an e ou s l yon 4d th es am ei c es amp l e s ,anda l lm e a su r em en t sa r ec o r e g i s t e r edind ep th . A g es c a l eandDa g e .Fo r WDCw eu s e th e WD 2 0 1 4ch r on o l o g y ,wh i ch i sb a s edon ,andons t r a t i g r aph i cm a t ch annu a l l a y e rcoun t in gdown t o2 , 8 5 0m( 3 1 . 2k y rBP) in gb ym e an so fg lo b a l l yw e l l -m i x e dm e th an ef o rth ed e e p e s tp a r to fth ec o r e 2 3 ( 2 , 8 5 0 – 3 , 4 0 5m ) .Th ed e eps e c t i ono fth e WD 2 0 1 4ch r on o l o g yh a sb e ens yn ch r on i z edtoal in e a r l ys c a l edv e r s i ono fth el a y e r c oun t ed G r e en l andi c ec o r e ch r on o l o g y(G ICC 0 5 ) . Mu l t ip l y in gth eG ICC 0 5ch r on o l o g yb y1 . 0 0 6 3b r in g s th ea g e so fab rup tDOe v en t sa so b s e r v ed inG r e en l and i c ec o r er e c o rd s ina g r e e m en tw i thth ea g e so fth e s ee v en t so b s e r v edinth eU /Th -d a t ed Hu luC a v esp e 2 3 l e o th emr e c o rd(wh i chp r o v id e sb e t t e ra b s o lu t ea g ec on t r o l ) .Th eNGR IPd a t a in F i g .1 ah a v es im i l a r l yb e enp l a c edon th e1 . 0 0 6 33G ICC 0 5a g es c a l e ;NGR IPd a t a inF i g .3 aa r ep l o t t edonth eo r i g in a lG ICC 0 5ch r on o l o g y . WDCp e rm i t sp r e c i s e in t e rh em i sph e r i cs yn ch r on i z a t i onf o rtw or e a s on s .F i r s t , a sar e su l to fth eh i gha c cum u l a t i onr a t e s ,Da g er em a in sr e l a t i v e l ysm a l l . WDC Da g ei sabo u tano rd e ro fm a gn i tud esm a l l e rth anDa g einc o r e sf r omth eE a s t An t a r c t i cP l a t e au ,andabo u ton e th i rdo fDa g ea to th e rc o a s t a ls i t e s th a tc o v e r th e 2 3 l a s tg l a c i a lp e r iod(E x t end edD a t aF i g .1 a ) .A sth eun c e r t a in t yinDa g ei sp r o p o r t i on a l toDa g e i t s e l f , th i s l e a d s t osm a l l e rd a t in gun c e r t a in t i e sa t WDC .S e c ond , r e c en tt e chn o lo g i c a ld e v e lopm en t sinc oup l in gl a s e rsp e c t r om e t e r sw i thi c ec o r e 3 4 c on t inu ou s f lowan a l y s i s h a v er e su l t edina WDCCH4r e c o rdw i thth eh i gh e s t t emp o r a lr e s o lu t i ono fa l lAn t a r c t i ci c ec o r e ss of a r .E x t end edD a t aF i g .2 cc om p a r e sth e WDCCH4r e c o rd( g r e y ,,2 y e a rs am p l in gr e s o lu t i on )w i thth eEDML CH4r e c o rd( o r an g e ,,1 0 0 y e a rs am p l in gr e s o lu t i on ) .Th ee s t im a t edun c e r t a in t y in WDCDa g e( r e f .2 3 )i ssh owninE x t end edD a t aF i g .1 b– e . s yn ch ron i z ed N o t eth a tth et r an s i t i onb e tw e enth el a y e r c oun t edand CH4s e c t i on so fth e WD 2 0 1 4ch r on o l o g ya t3 1 . 2k y rd o e sn o tin f lu en c eou ran a l y s i s o fth eb ip o l a rs e e s awph a s in g .Inth es t a c k in gp r o c edu r ew ea l i gne a cho fth e ind i v idu a lAn t a r c t i ce v en t sa tth em id p o in to fth ea s s o c i a t edDOCH r an s i t ion . 4t 1 8 Ind o in gs o ,w ee f f e c t i v e l ys yn ch r on i z ea l lth e WDCe v en t st oNGR IPd O ,no t ju s tth ee v en t sb e tw e en6 8and3 1 . 2k y r .Inp e r f o rm in gth ec r o s s co r r e l a t ion b e tw e enNGR IPand WDC(F i g .2 a ) ,w eon l yan a l y s eth eCH s yn ch ron i z edp a r t 4 o fth er e c o rd . su s e dt oc a l cu l a t eth e Ad yn am i c a lv e r s i ono fth ef i rnd en s i f i c a t i on m od e l23,38i 2 3 Da g eo fth e WD 2 0 1 4ch r on o l o g y .W efu r th e rm o r ec a l cu l a t ed WDC Da g eu s in g 2 3 , 3 9 , 4 0 ana l t e rn a t i v ef i rnd en s i f i c a t i on m od e l (E x t en d edD a t aF i g .1 b ,b lu ecu r v e ) . U s in g th i sa l t e rn a t i v eDa g es c en a r i og i v e saNH l e adt im eo f2 4 2and2 4 7y e a r s fo r a b r up tDOw a rm in gandDOc o o l in g ,r e s p e c t i v e l y , ing o oda g r e em en t(w i th in th e sun c e r t a in t yb ound )w i thr e s u l t sp r e s en t edinth et e x t . 1 Id en t i f i c a t iono fab rup t DOt r an s i t ion s .W eu s eth em id p o in to fth eab r up t t r an s i t i on sa st im em a r k e r s t oa l i gn ind i v idu a le v en t s .Th em e th od f o rf ind in g th e m id p o in t i s id en t i c a l t o th a tu s e d inr e f .2 3 ,wh e r e fu r th e rd e t a i l sc anb e found .Th e m e th od i ssh own inE x t end edD a t aF i g .2 a ,bf o rDO1 7and1 6(w eu s ear e c en t l y 4 1 p r op o s edDOn om en c l a tu r e ) .F o re a ch t r an s i t i onw ed e f in eap r e t r an s i t ion l e v e l andap o s t t r an s i t i on l e v e l(h o r i z on t a lo r an g em a r k e r s ) ,andu s e l in e a r in t e rp o l a 1 8 t i ont o f indth ed ep tha twh i chth et r a c e ro f in t e r e s t( d Oo rCH4)h a scom p l e t ed 2 5% ,5 0%and7 5%o fth et r an s i t i onf r omth ep r e t r an s i t i on a lt op o s t t r an s i t ion a l v a lu e .Th e5 0%d ep th ( r edd o t s ) i su s ed t od e f in e th e t im in go f th ea b r up te v en t ; th e 2 3 2 5%and7 5%d ep th s( b lu ed o t s )p r o v id eanun c e r t a in t yr an g eonth em idpo in t . yn ch r on i z a t i oni scom p l i I th a sb e ensu g g e s t edth a tin t e rh em i sph e r i cCH 4s c a t edb yth ef a c tth a tg a sbu b b l e sini c ec o r e sh a v eag a sa g ed i s t r i bu t ion ,r a th e r 4 2 th anas in g l ea g e .T o in v e s t i g a t eth i se f f e c ta t WDC ,w ec on s t ru c tah ypo th e t i c a l g a sa g ed i s t r i bu t i on(E x t en d ed D a t aF i g .2d ) ,u s in ga( t run c a t ed )lo g -n o rm a l d i s t r i bu t i ona ssu g g e s t ede l s ewh e r e42,43,in wh i ch w ec on s e r v a t i v e l ys e ts51 4 4 andm5ln ( 5 0 ) .Th esp e c t r a lw id th( o rs e c ond m om en t )o fth i sa g ed i s t r i bu t ion i s2 4 . 3y e a r s ; f o rc om p a r i s on , th eg a s a g esp e c t r a lw id th f o rp r e s en t -d a y WDC f i rn 4 5 i son l y4 . 8y e a r s .App l y in gth i sf i l t e rt oana tm o sph e r i cr am p inCH E x t end ed 4( D a t aF i g .2 e )sh i f t sth em id p o in to fth et r an s i t i on( a sr e c o rd edinth ei c eco r e ) f o rw a r d sb y5y e a r s .B e c au s ew eh a v ec on s e r v a t i v e l ych o s en th ea g ed i s t r i bu t i on to b ev e r yw id e , th i s5 y e a rsh i f tsh o u ldb ec on s id e r edanupp e rb ound .Th e in f lu en c e o f th eg a sa g ed i s t r i bu t i onon th e t r an s i t i onm idp o in t id en t i f i c a t i on i sv e r ysm a l l in c om p a r i s onw i tho th e rs ou r c e so fun c e r t a in t y ,and i sn e g l e c t ed in th er em a ind e ro f th em anu s c r ip t . S t a ck in gp ro c edu r e .W ed e f in ea t im ev e c t o r tth a trun s f r om t im e t 521 , 2 0 0 to t 51 , 2 0 0in1 y e a rin c r em en t s .N e x t ,f o re a cho fth eDO /A IMe v en t s ,w es e tth e 1 8 m id p o in to fth eNGR IPd Ot r an s i t i ont ot 50 ,andu s el in e a rin t e rp o l a t ionto s am p l eth ed i f f e r en tr e c o rd son t ot im ev e c t o rt .F o re a chind i v idu a l DO /A IM e v en tth i sr e su l t sinar e c o rdth a tsp an sf r om21 , 2 0 0t o11 , 2 0 0y e a r sr e l a t i v eto th ea b r up tt r an s i t i on ,a tannu a lt im es t ep s ;w esh a l lr e f e rt oth e s ea sth econ t r i b u t o r yr e c o rd s .T oa l i gnth e WDCr e c o rd sw es e tth em id p o in tinth e WDCCH4 t r an s i t i ont ot 55 6y e a r s ,u s in gth eo b s e r v a t i onth a tth eCH r an s i t ions l i gh t l y 4t 1 8 , 4 7 l a g s th eG r e en l and d Os i gn a l23,24,46 ( th eun c e r t a in t y in th i s t im e l a g i se v a lu a t ed inth es en s i t i v i t ys tud y ) . W i tha l lth eind i v idu a le v en t ss yn ch r on i z edand r e s amp l edt oid en t i c a lt im esp a c in g ,w ec ana v e r a g eth emt oo b t a inth es t a c k ed r e c o rd . Th esp a c in gb e tw e enDOe v en t sv a r i e sw id e l yo v e rt im e ,r an g in gf r oms e v e r a l th ou s and so fy e a r st oon l yhun d r ed so fy e a r s .Th i sm e an sth a t ins e v e r a lc a s e sth e 2 , 4 0 0 y e a rw in d oww eu s ec on t a in sm o r eth anas in g l ee v en t .W ec ropth econ t r i bu t o r yr e c o rd swh en e v e ranad j a c en te v en to c cu r sw i th inth es am p l in gw indow (E x t end edD a t aF i g .3 ) .F o rw id e l ysp a c ed( th a ti s , l on g -du r a t i on )e v en t ssu cha s DO /A IM1 2 ,n oad j a c en te v en t sf a l lw i th inth et im ew in d ow ,andn oc ropp in gi s r equ i r ed(E x t end edD a t aF i g .3 a ) .F o rc l o s e l ysp a c ede v en t s ,su cha sDO /A IM1 7 . 1 , w en e e dt oc r opn e i gh b ou r in ge v en t s(E x t end edD a t aF i g .3 b ) .Th ec ro pp edp a r t s o f th ec on t r i bu t o r yr e c o rd sa r er ep l a c edw i thc on s t an tv a lu e s th a tequ a l th ebound a r yv a l u e s( 5 0 y e a ra v e r a g e s )o fth eun c r opp edp a r to fth er e c o rd .Th enum b e ro f c on t r i bu t o r yr e c o rd sa v a i l a b l ea safun c t i ono ft im e i ssh own in th ebo t tomh a l fo f E x t end ed D a t aF i g .4 .Th esh o r t e s tc on t r i bu t o r yr e c o rdi sth eA IM1 7 . 1r e c o rd , wh i chi s7 0 0y e a r sl on g . 1 8 D e t e rm in in gth eb r e akpo in tinth e WDC d Os t a ck .W eu s eanau t om a t ed 4 8 r ou t in eth a ti ss im i l a rt oth eBREAKF ITa l g o r i thm ,th em a ind i f f e r en c eb e in g th eu s eo fas e c ond o rd e rp o l yn om i a l( r a th e rth anal in e a r )f i tt oth ed a t a ,to 1 8 a c c oun tf o rth ef a c tth a tth e WDCd Os t a c ki scu r v edr a th e rth anl in e a r .Th e a l g o r i thmf ind sth eb r e a kp o in tth a tm in im i z e sth er o o tm e ansqu a r ed e v i a t ion ( r .m . s .d . )b e tw e enth es t a c k( th a t i s ,th ed a t a )andth ep o l yn om i a lf i t inth e26 0 0 t o17 0 0y e a r st im ein t e r v a l(E x t end ed D a t aF i g .4 ) ;th ein t e r v a lw a sch o s en a s ymm e t r i c a l l ya roundz e r ot oa c c oun tf o rth ef a c tth a tth eb r e a kp o in ti sa lw a y s f ounda tpo s i t i v ev a l u e s .Th er ou t in eop e r a t e sa sf o l l ow s . F i r s t ,th eu s e rs e l e c t sth er an g e inwh i chth ea l g o r i thm i st o l o o kf o rth eb r e a k p o in t ,a sw e l la sat im es t ep .F o re x am p l e ,i fth eu s e rs e l e c t s0– 4 0 0y e a r sa ta1 0 0 y e a rt im es t e p ,th ea l g o r i thmw i l lt e s tth ep o s s i b i l i t i e st 50 ,1 0 0 ,2 0 0 ,3 0 0and 4 0 0y e a r s .W esh a l lr e f e rtoth i son e -d im en s i on a la r r a yo fv a l u e sa sth einpu t v e c t o r . 1 8 Os t a c k i ssp l i t in t otw o S e c ond ,a te a cho fth ev a l u e s inth e inpu tv e c t o r , th ed p i e c e s ,andas e c ond o rd e rp o l yn om i a lcu r v ei sf i t t edt od a t aone a chs id es ep a r a t e l y .Th etwof i t t in gcu r v e sa r em e r g eda tth e i rp o in to fin t e r s e c t i on .N o t eth a t th ep o in to f in t e r s e c t ionc and i f f e r f r om th ep o in twh e r e th ed a t as e r i e sw e r esp l i t in tw o . Th i rd ,fo re a chf i tthu so b t a in ed ,w ec a l cu l a t eth er .m . s .d .t oth es t a c k edd a t a o v e rth e26 0 0to17 0 0y e a r st im e in t e r v a l ,andw es e l e c tth eb e s tf i t .Th ep o in to f in t e r s e c t iono f th e twocu r v e s ,r a th e r th an th ep o in twh e r e th ed a t as e r i e sw e r esp l i t in t o two( th a t i s , th ev a l u e s in th e inpu tv e c t o r ) , i sc on s id e r ed th eb r e a kp o in t in th e 1 8 Os t a c k . d F o rmo s to f th er e su l t s in th i sw o r kw e l e t th ea l g o r i thms e a r ch in th e0– 4 0 0 y e a r r an g e ,a ta2 y e a rt im es t ep .Th ee x c ep t i oni sth es t a c k so fr and om l ys e l e c t e dDO e v en t s(E x t end ed D a t aF i g .6 ) ,f o r wh i ch w eu s e da w id e rr an g e( 21 0 0t o 15 0 0y e a r s )toa c coun tfo rth el a r g e rsp r e adins o lu t i on s .N o t eth a tth ee f f e c t i v e r an g eo fb r e a kp o in td e t e c t i on i sw id e rth anth e inpu tr an g e ,b e c au s eth ep o in to f in t e r s e c t iono fth ef i t t in gcu r v e si sp e rm i t t edt o l i eou t s id eth er an g esp e c i f i edb y th e inpu tv e c to r .Th ef i t t in gcu r v e sg en e r a t edb yth ea l g o r i thma r ep l o t t ed ind a r k o r an g e l in e s inF i g .2b ,candE x t end edD a t aF i g s4 a ,b ,6 a–dand7 b ,c ;th eb r e a k p o in t i s ind i c a t edw i thano r an g ed o t .Th e MATLABc od e imp l em en t in g th e f i t t in g p r o c edu r ei sp r o v id edinSupp l em en t a r yIn f o rm a t i on . Th er e a sonfo ru s in gaqu ad r a t i cr a th e rth anal in e a rf i t t in gp r o c edu r ei sth a t An t a r c t i ct emp e r a tu r e sdon o tch an g e ina l in e a rf a sh i one i th e rb e f o r eo ra f t e rth e 1 8 Os t a c k a b r up t t r an s i t i on s .A sa t e s t ,w eapp l you r f i t t in gp r o c edu r e t o th e WDCd (F i g .2 b ) ,u s in ge i th e r l in e a ro rqu a d r a t i c f i t t in g fun c t i on s , inwh i chw ech an g e th e s i z eo fth ed a t aw indowf r om3 0 0y e a r st o1 , 6 0 0y e a r s .Th ew ind owi sapp l i ed s ymm e t r i c a l l y ,m e an in gth a tequ a lnum b e r so fy e a r sa r eu s edb e f o r eanda f t e r th ed e t e c t edb r e a kp o in t( 8 0 0y e a r sone a chs id ef o ra1 , 6 0 0 y e a rw ind ow ) .D a t a f a l l in gou t s id eth i sw indowa r ei gn o r edinth ef i t t in gp r o c edu r e . W ef indth a tth ep e r fo rm an c eo fth equ ad r a t i cf i t t in gp r o c edu r ei ssup e r i o rin tw oimp o r t an ta sp e c t s(E x t end edD a t aF i g .5 ) .F i r s t ,b yu s in gaqu ad r a t i cf i t ,th e b r e a kpo in tw ed e t e c t i s ind ep end en to fth ew ind ows i z e ,wh i ch i sn o tt ru ef o rth e l in e a rf i t .S e c ond ,th equ a d r a t i cm e th odp r o v id e sab e t t e rapp r o x im a t i ont oth e d a t a ,a se xp r e s s edb yth er .m . s .d .b e tw e enth ed a t aandth ef i t t in gcu r v e .A tsm a l l w in d ows i z e so f,7 0 0y e a r s ,b o thm e th od sa g r e ev e r yw e l l ,and th e f i t t o th ed a t a i s c om p a r a b l e in t e rm so f th er .m . s .d .Th i s i sdu e t o th e f a c t th a ta tsm a l lw ind ows i z e s th ecu r v a tu r eo f th e t im es e r i e s i sn o tv e r yp r on oun c edand i sw e l lapp r o x im a t edb y 4 8 ,wh i chu s e sa l in e a r f i t a l in e a r t r end .W eh a v ea l s o t e s t ed th eBREAKF ITr ou t in e onb o ths id e so fth eb r e a kp o in t .W ef indav e r yg o o da g r e em en tb e tw e enth e b r e a kpo in t s id en t i f i e du s in g th eBREAKF ITr ou t in eandou r l in e a r f i t t in gr ou t in e , w i tham e and i f f e r en c eo f0 . 2y e a r sb e tw e en th em .U s in gam o v in gb l o c kb o o t s t r ap 4 8 ,th eBREAKF ITa l g o r i thmsu g g e s t sa2 sun c e r t a in t yo f5 0 . 8y e a r sin an a l y s i s b r e a kpo in tid en t i f i c a t ion . Mon t eC a r los en s i t i v i t ys tud y .T oa s s e s sh owth ed i f f e r en tun c e r t a in t i e sinou r m e th oda f f e c tou rcon c lu s ion s ,w ep e r f o rma M on t eC a r l os en s i t i v i t ys tud y .Th e l a r g e s tsou r c eo fun c e r t a in t y i s th ed i f f e r en c eb e tw e eng a sa g eand i c ea g e ,o r Da g e 1 8 ndd Or e c o rd s , ( r e f .4 9 ) .Da g ed e t e rm in e sth er e l a t i v et im in go fth e WDCCH 4a andth e r e b yth eph a s in gw ein f e rf o r WDCA IMe v en t sr e l a t i v et oG r e en l and 2 , 3 , 5 0 .In c r e a s in gDa g esh i f t s WDCi c ea g e st ow a rd so ld e ra g e s ,th e r e b y c l im a t e d e c r e a s in gth eNHl e a dt im eth a tw ein f e r ;v i c ev e r s a ,d e c r e a s in gDa g ew i l lsh i f t th e i c ea g e syoun g e r , in c r e a s in g th eo b s e r v edNH l e ad t im e .Th eDa g er e c on s t ru c 4 0 , 4 7 , 5 1 – 5 4 t i onw eu s eh e r ei sob t a in edf r omad yn am i c a lf i rn -d en s i f i c a t i on m od e l 1 5 c on s t r a in edb yd N -N2d a t a ,ap r o x yf o rp a s tf i rn c o lumnth i c kn e s s55.Th ef i rn 2 3 w i thth ea l t e rn a t i v eDd ep th d en s i f i c a t ion mod e lr e su l t sa r eing o o da g r e em en t o rou rcu r r en tpu rp o s ew eu s eanen s em b l eo f1 , 0 0 0 m e th odd e v e lo p edr e c en t l y56.F Da g eh i s to r i e s(E x t end ed D a t aF i g .1 b– e )g en e r a t edb yv a r y in gasu i t eo finpu t efu r th e rm o r eu s ef ou rd i f f e r en t p a r am e t e r so fth ef i rn -d en s i f i c a t i on m od e l23. W r o v id in gat o t a lo f1 , 0 0 0 3454 , 0 0 0 d ep th– a g ein t e rp o l a t ions t r a t e g i e s23,57,p a l t e rn a t i v e WDCch r ono lo g i e s . F o re a cho fth e s e4 , 0 0 0p o t en t i a l WDCch r on o l o g i e sw efu r th e rp e r f o rma M on t eC a r los imu l a t i on( 1 0 0r e a l i z a t i on s )inwh i chw ep e r tu r bth ea l i gnm en to f th ec on t r i bu to r yr e c o rd s .Th er a t i on a l eb eh ind th eM on t eC a r l os tud y i s th a t th e r e i sanun c e r t a in t y inth es yn ch r on i z a t i ono fth ec on t r i bu t o r yr e c o rd s ,andw ew an t t oa s s e s show th i sun c e r t a in t y imp a c t sou rc on c lu s i on s .Inth eM on t eC a r l os tud y , ar and om t im in ge r r o r i sa s s i gn ed t oe a cho f th ec on t r i bu t o r yr e c o rd s ,and th e r e b y th e ya r ee f f e c t i v e l ysh i f t edr e l a t i v e t oon ean o th e r in t im e .W ed i s t in gu i shb e tw e en s y s t em a t i candnon s y s t em a t i ce r r o r s , inwh i ch th e f o rm e ra r ec o r r e l a t edb e tw e en th ed i f f e r en tA IMe v en t s ,andth el a t t e ra r en o t .S en s i t i v i t yt e s t sw i thth ef i rn d en s i f i c a t i onm od e lsh ow th a tDa g e i sas y s t em a t i ce r r o r ; i fw eh a v eo v e r e s t im a t ed g l a c i a lDa g eb y , f o re x amp l e ,5 0y e a r s ,th i sw i l lp r o b a b l yb et ru ef o ra l lo fth eA IM e v en t s .W ec on s id e rf i v eind ep end en ts ou r c e so fun c e r t a in t yinth es yn ch ron i z a t i onp r o c edu r e . 1 8 Ot r an s i t i on sh a san F i r s t ,th em id p o in td e t e c t i oninth ea b rup t NGR IPd un c e r t a in t y ;w esh i f tth er e c o rdb yav a lu ed r awnf r omaG au s s i and i s t r i bu t i on o fz e r om e anandaw id thth a tequ a l sth em idp o in tun c e r t a in t ya sd e f in edabo v e . Th i se r r o ri sn on s y s t em a t i c . S e c ond ,a s in th e f i r s tp o in ta b o v e ,bu t f o r th em id p o in t in th ea b rup t WDCCH 4 t r an s i t i on . Th i rd ,a l th ou gha l lf ou rin t e rp o l a t i ons t r a t e g i e ss yn ch r on i z eth eab r up t NH w a rm in ge v en t sb e tw e en NGR IPand WDC ,on l ytw oo fth ems yn ch r on i z eth e o rs t a c k so fNHc o o l in gw eadd edanadd i t i on a lun c e r t a in t y NHc o o l in ge v en t s23.F d r awnf r omaG au s s i and i s t r i bu t i ono fz e r om e anandaw id thc o r r e spond in gto 1 8 Oand WDC th ea g ed i f f e r en c eb e tw e en th ec o o l in ge v en ta sd e t e c t e d inNGR IP d i se r r o ri sn on s y s t em a t i c . CH4.Th 1 8 F ou r th ,ar e c en te x t en s i v ean a l y s i ssu g g e s t sa l a go fCH4b eh indG r e en l andd O 2 4 .Th e r ea r etw ot yp e so fun c e r t a in t yt oc on s id e r :f i r s t ,th e o f5 663 8y e a r s( 2 s) a gc and i f f e rb e tw e enind i v idu a l DOe v en t s(n on s y s t em a t i ce r r o r ) ,and CH4l s e c ond ,th ec en t r a le s t im a t eo f5 6y e a r sh a saninh e r en tun c e r t a in t y( s y s t em a t i c e r r o r ) .W eh e r ea s sum eth a tb o tha r eequ a l l y l a r g e ,and inth es t a c k in gp ro c edu r e w ea s s i gnb o tha2 7 y e a rs y s t em a t i ce r r o randa2 7 y e a rn on s y s t em a t i ce r r o r to th e a gt im e .B o tha r ed r awnind ep end en t l yf r omaG au s s i and i s t r i bu t i on ,and CH4l 2 21 12 7 )/253 8y e a r s( th a ti s ,th e2 s th e i rc om b in edun c e r t a in t yi sth e r e f o r e( 2 7 . un c e r t a in t yb oun d24) F i f th , th eb r e a kp o in t f i t t in gp r o c edu r eh a san in t r in s i cun c e r t a in t y .W ee s t im a t e 4 8 th i sb yu s in gth em o v in g b l o c kb o o t s t r apan a l y s i so fth eBREAKF ITa l g o r i thm , wh i chsu g g e s t sa1sun c e r t a in t yo f2 5 . 4y e a r s(E x t end edD a t aF i g .5 a ) .W eth e r e f o r eapp l ya5 0 . 8 y e a r( 2 s)s y s t em a t i cun c e r t a in t y( s y s t em a t i cb e c au s e i tapp l i e s to 1 8 Os t a c kr a th e rth ant oind i v idu a le v en t s ) . th efu l ld E a chc on t r i bu t o r yr e c o rd i sth en ind i v idu a l l ysh i f t edb yanam o un tth a tco r r e sp ond st oth esumo fth er and om l ya s s i gn edn on s y s t em a t i ce r r o r s .A f t e rr e a l i gn in g th ec on t r i bu t o r yr e c o rd s in th i sm ann e r , th een t i r es t a c k i ssh i f t ed in t im eb yan am o un tth a tc o r r e s p ond st oth esumo fr and om l ya s s i gn eds y s t em a t i ce r r o r s .W e d e t e c tth eb r e a kp o in tb yu s in gth ef i t t in ga l g o r i thm .F o re a cho fth e4 , 0 0 0ch r o n o l o g i e sw e t e s t1 0 0r e a l i z a t i on so f th eM on t eC a r l or e a l i gnm en t ,thu sob t a in in ga 5 1 8 ( 1 , 0 0 0 3431 0 0 )e s t im a t e so fth e WDCd Ob r e a kpo in t . No t o t a lo f4 31 0 s t a t i s t i c a lm e th od sw e r eu s edt op r ed e t e rm in eth es amp l es i z eu s edinth e M on t eC a r l oan a l y s i s .Th eou t c om eo fth es en s i t i v i t ys tud yi sp r e s en t edinth e h i s t o g r am so fF i g .2 e ,fandE x t end edD a t aF i g .6 e–h . Th en on s y s t em a t i ce r r o r s ,b e c au s eth e ya r eind e p end en to fe a cho th e r ,a c cu mu l a t es l ow l ywh enadd ed inqu ad r a t u r e .Th es y s t em a t i ce r r o r s( su cha sth eDa g e un c e r t a in t yo rth eb r e a kp o in tf i t t in gp r o c edu r e )th e r e f o r ed om in a t eth ef in a l un c e r t a in t ye s t im a t e .Runn in gth eM on t eC a r l oe xp e r im en tw i thDa g eun c e r t a in t i e sw i thh e ldg i v e sa2 sun c e r t a in t yb oun donth ein t e rp o l a rph a s in go f6 0and 6 8y e a r sf o rth e DOon s e tand DOt e rm in a t i ons t a c k s ,r e s p e c t i v e l y ;u s in gon l y Da g eun c e r t a in t i e sg i v e sa2 sun c e r t a in t yb oundo f6 9y e a r s .Th eDa g eun c e r t a in t y i sth e r e f o r ea simp o r t an ta sa l lo th e rs ou r c e so fun c e r t a in t yc om b in ed . Cod ea v a i l ab i l i t y .Th e MATLABc od eu s e dt os t a c kth er e c o rd sandp e r fo rmth e M on t eC a r l oan a l y s i sa r ep r o v id edinSupp l em en t a r yIn f o rm a t i on . 1 8 Os t a c k A l t e rn a t i v es t a ck s .T oe x c lud eth ep o s s i b i l i t yth a tt im in go fth e WDCd i sd om in a t edb yaf ewp r om in en tA IMe v en t sw ep e r f o rmth ef o l low in gt e s t s . F i r s t ,w ed i s t in gu i shb e tw e en m a j o rA IMe v en t sth a ta r ev e r yp rom in en t inth e r e c o rd ,andm in o re v en t s .Th em a j o rA IMe v en t sa r eA IM1 7 ,1 4 ,1 2 ,8and4 ;a l lo f th e s ea r ep r e c ed edb y NH H e in r i che v en t s .Th e s el a r g ee v en t sh a v eh i s to r i c a l l y b e enc a l l edA e v en t s ,anda r ec l e a r l yv i s i b l ee v en in l ow r e s o lu t i onAn t a r c t i cco r e s (A IM8 ,1 2 ,1 4and1 7h a v eb e enr e f e r r edt oine a r l i e rw o r ka sA 1 ,2 ,3and4 , 2 , 3 .Th em in o re v en t sa r eth er em a in in gon e s(A IM3 ,5 . 1 ,5 . 2 ,6 ,7 ,9 , r e sp e c t i v e l y ) 1 0 ,1 1 ,1 3 ,1 5 ,1 6and1 8 ) . Wh enw ec om p a r eas t a c kc on s i s t in go fon l yth em a jo r A IMe v en t sw i thas t a c ko fon l yth em in o rA IMe v en t s ,w ef indnos t a t i s t i c a l l y s i gn i f i c an td i f f e r en c e in th e i r t im in g(E x t end edD a t aF i g .6 a ,b ) .Th eNH l e ad t im e f o rth em a j o rand m in o rA IMs t a c k s i s2 3 0 69 3and2 1 169 4y e a r s ,r e sp e c t i v e l y (E x t end ed D a t aF i g .6 e ,f ) ;th et im in go fth efu l ls t a c k( 2 1 869 2y e a r s )i sin t e r m ed i a t et oth e s ev a l u e s ,a se xp e c t ed(F i g .2 b ) . Inas e c onde xp e r im en tw er and om l ys e l e c t ede i gh t DO /A IMe v en t sinth e 5 r e a l i z a t i on so fth eM on t eC a r loe xp e r i s t a c k in gp r o c edu r ef o re a cho fth e431 0 m en t ;on esu chr e a l i z a t i oni ssh owninE x t end e dD a t aF i g .6 c ,dfo rab r up t NHw a rm in gandc o o l in g ,r e s p e c t i v e l y .Th eNH l e a dt im ew ef indinth i se xp e r i m en ti s2 1 061 1 3y e a r sand2 0 861 0 8y e a r sf o ra b rup t NH w a rm in gand c o o l in g ,r e sp e c t i v e l y(E x t end ed D a t aF i g .6 g ,h ) .Th e s em e anv a l u e sd i f f e rb y 1 8 Os t a c k(F i g .2 ) .No t eth a t on l yaf ewy e a r s f r omth o s e f oundf o rth efu l l WDCd th ed i s t r i bu t i on w id tho f NHl e a dt im e sinth i se xp e r im en ti sw id e rth anth e 1 8 d i s t r i bu t i on w id thfoundfo rth efu l ld Os t a c k s .Th er e a s onf o rth i sm a yb e th r e e f o ld :f i r s t ,as t a c kw i thf ew e rc on t r i bu t o r yr e c o rd sh a sasm a l l e rs i gn a l t o n o i s er a t io ,m a k in gth eb r e a kp o in td e t e c t i onl e s sc e r t a in ;s e c ond ,i fth eNHl e ad t im ed i f f e r ss l i gh t l yb e tw e enth eA IMe v en t s ,th ea v e r a g et im in go far and om l y s e l e c t e dsub s e tm a yd i f f e rf romth ea v e r a g et im in go fth efu l ls e t ;andth i rd , inth e M on t eC a r lop ro c edu r eth econ t r i bu t i ono fn on s y s t em a t i cun c e r t a in t i e ss c a l e s r ou gh l y inp r opo r t i on to! N ,a g a insu g g e s t in gan a r r ow e rd i s t r i bu t i on f o rh i gh e rN ( th enum b e ro fe v en t sinth es t a c k ) .Th ew id e rd i s t r i bu t i onf oundond e c r e a s in g th enumb e ro fe v en t sinth es t a c kth e r e f o r ed o e sn o tr ep r e s en ta m o r er e a l i s t i c un c e r t a in t yboundonth eph a s in go fth eb ip o l a rs e e s aw . S t a ck in gth e WDCN ar e co rd .L a s t ,w e in v e s t i g a t eth eph a s in go fth e WDCs e a s a l tN a( s sN a )r e c o rdr e l a t i v et oG r e en l andandAn t a r c t i cc l im a t e .Th es e a i c e su r f a c e i sam a j o rsou r c eo fs e a s a l ta e r o s o l s t o th ea tm o sph e r ea r oundAn t a r c t i c a , andc on s equ en t l ys sN ah a sb e enin t e rp r e t eda sap r o x yf o rth ep r odu c t i onand 2 5 , 5 8 , 5 9 .S e a s a l tN ai ss t r on g l yan t i c o r r e l a t ed w i th e x t en to fr e g ion a ls e ai c e An t a r c t i cc l im a t eonbo tho r b i t a land m i l l enn i a lt im e s c a l e s58,60. M e a su r eds sN acon c en t r a t i on sc anb ec on v e r t edt oas sN af lu xb y mu l t ip l y in g w i th th ea c cumu l a t ionr a t e sa t th es i t e .On th eE a s tAn t a r c t i cp l a t e au , th eN a f lu x i s e xp e c t edtop ro v id eab e t t e rm e t r i cf o ra tm o sph e r i cc on c en t r a t i on s ,b e c au s ed r y d ep o s i t i on dom in a t e sa s ar e s u l to fth ev e r yl ow a c cum u l a t i on r a t e s58. A c cumu l a t i onr a t e sa r e mu chh i gh e ra t WA I SD i v id e ,h ow e v e r ,andG r e en l and i c ec o r e sp ro v id eab e t t e ran a l o gu eth an th o s eon th eE a s tAn t a r c t i cp l a t e au .I th a s 6 1 th a ts e a s a l tc on c en t r a t i on sinth ei c er e f l e c t b e ensh owna tG r e en l andSumm i t th ea tm o sph e r i cv a r i a t ion sw i th in5% ,wh e r e a s th es e a s a l t f lu xund e r e s t im a t e s th e a tm o sph e r i cv a r i a t i on sb yabo u t5 0% .Thu s , th eo b s e r v edv a r i a t i on s in WDCs sN a c on c en t r a t i on ssho u ldtof i r s to rd e rr e f l e c tv a r i a t i on s inth ea tm o sph e r i c l o a d in g . W e in v e s t i g a t e th er e l a t i v e t im in go f th es sN ar e c o rdw i th th es am e t o o l sa s th o s e 1 8 Or e c o rd .Ane v a lu a t i ono fth e l a g g edc o r r e l a t i on th a tw eapp l i edtoth e WDCd 1 8 et im ed e r i v a t i v eo fth ev a r i ou s WDCr e c o rd si s b e tw e en NGR IPd Oandth sh owninE x t end edD a t aF i g .7 a .F o rs sN aw eo b t a inac en t enn i a l s c a l eNHl e ad 1 8 .S t a c k in go f th e WDC impu r i t y t im e ,c om p a r ab l e to th a tob s e r v ed f o r WDC dO r e c o rd sy i e ld sth es am ep i c tu r e(E x t end edD a t aF i g .7 b ,c ) ;th eb r e a kp o in tinth e 1 8 Os t a c k ,andl a g sth e s sN as t a c k sco in c id e sw i thth eb r e a kp o in tinth e WDCd 1 8 Oands sN a a b r up tNHt r an s i t i onb yrou gh l ytw oc en tu r i e s .N o t eth a tb e c au s ed a r eb o thm e a su r ed in th e i c eph a s e , th eun c e r t a in t y th a tw ee s t im a t e f o r th e t im in g 1 8 Ob r e a kpo in t( 2so fa b ou t9 0y e a r s )a l s oh o l d sf o rth e impu r i t yr e c o rd s . o fth ed 1 8 Ov a r i a t i on ssu g g e s t sth a tAn t a r c t i c Th es yn ch ron i c i t yo f WDCs sN aandd c l im a t eands e a i c ee x t en ta r ec l o s e l yl in k edonc en t enn i a l ,o rp e rh ap se v ensu b c en t enn i a lt im e s c a l e s .Th i sm a yr e f l e c tac omm onf o r c in gand / o raf e ed b a c k b e tw e enSou th e rn O c e ansu r f a c et emp e r a tu r e sands e a i c ee x t en t .Th es e a i c e e x t en tm a yfu r th e rm o r eb eimp o r t an tinf o r c in g An t a r c t i ct emp e r a t u r e s( and 1 8 6 O ),62,p a r t i cu l a r l ya tth e WA I SD i v id es i t e , wh e r eth em a r in ein f lu en c ei s d 1 7 . s t r on g e rth anonth eE a s tAn t a r c t i cp l a t e au 31 .S te ig ,E .J .e ta l .Recen tc l ima teand ice shee tchanges in We s tAn ta rc t icacompa red w i ththepa s t2 ,000yea r s .Na tu reGeo sc i .6 ,372–375(2013 ) . 32 . Sowe rs ,T .e ta l .Anin te r labo ra to rycompa r isono ftechn iquesfo rex t rac t ingand ana lyz ingt rappedga se s in iceco re s .J .Geoph y s .Re s .102 ,26527–26538(1997 ) . 33 . M i tche l l ,L .E . ,B rook ,E .J . ,Sowe r s ,T . , McConne l l ,J .R .&Tay lo r ,K . Mu l t idecada l va r iab i l i tyo fa tmo sphe r ic me thane ,1000–1800C .E .J .Geoph y s .Re s .116 ,G02007 (2011 ) . 34 .S towa sse r ,C .e ta l .Con t inuous mea su remen t so f me thane m ix ingra t iosf romice co re s .A tmo s . Mea s .Tech .5 ,999–1013(2012 ) . 35 . Rhodes ,R .H .e ta l .Con t inuou s me thane measu remen tsf romala teHo locene G reen landiceco re :a tmo sphe r icandin -s i tus igna l s .Ea r thP lane t .Sc i .Le t t .368 , 9–19(2013 ) . 36 .D lugokencky ,E .e ta l .Conve r s iono fNOAAa tmo sphe r icd rya i rCH4mo lef rac t ions toag rav ime t r ica l lyp repa reds tanda rdsca le .J .Geoph y s .Re s .110 ,D18306 (2005 ) . 37 .S ig l ,M .e ta l .Anewb ipo la riceco rereco rdo fvo lcan ismf rom WA ISD i v ideand NEEMandimp l ica t ionsfo rc l ima tefo rc ingo fthela s t2000yea r s .J .Geoph y s .Re s . A tmo s .118 ,1151–1169(2013 ) . 38 . He r ron ,M .M .&Langway ,C .C .F i rndens i f ica t ion :anemp i r ica l mode l .J .G lac io l .25 , 373–385(1980 ) . 39 .A rnaud ,L . ,Ba rno la ,J .M .&Du va l ,P . inPh y s ic so f IceCo reReco rd s(ed .Hondoh ,T . ) 285–305(Hokka idoUn i v .P res s ,2000 ) . 40 . Gou jon ,C . ,Ba rno la ,J .M .&R i tz ,C .Mode l ingtheden s i f ica t iono fpo la r f i rn inc lud ing hea td i f fus ion :app l ica t iontoc lose -o f fcha rac te r is t icsandga siso top ic f rac t iona t ionfo rAn ta rc t icaandG reen lands i te s .J .Geoph y s .Re s .108(D24 ) ,4792 (2003 ) . 41 . Ra smus sen ,S .O .e ta l .As t ra t ig raph icf ramewo rkfo rab rup tc l ima t icchanges du r ingtheLa s tG lac ia lpe r iodba sedonth reesynch ron izedG reen landice -co re reco rd s :re f in ingandex tend ingtheINT IMATEeven ts t ra t ig raphy .Qua t .Sc i .Re v . 106 ,14–28(2014 ) . 42 . Köh le r ,P .Rap idchangesiniceco rega sreco rds .Pa r t1 .Ontheaccu racyo f me thanesynch ron isa t iono ficeco re s .C l im .Pa s tD i scu s s .6 ,1453–1471(2010 ) . 13 43 . Köh le r ,P . ,F i sche r ,H .&Schm i t t ,J .A tmo sphe r icd CO2andi t sre la t iontopCO2 13 anddeepoceand Cdu r ingthela teP le is tocene .Pa leoceanog raph y25 ,PA1213 (2010 ) . 44 .T rud inge r ,C .M .e ta l .Recon s t ruc t inga tmo sphe r ich i s to r iesf rom measu remen t s .Geoph y s .Re s .107(D24 )4780(2002 ) . o fa i rcompos i t ioninf i rn .J 45 . Ba t t le ,M .O .e ta l .Con t ro l sonthe mo vemen tandcompos i t iono f f i rna i ra tthe We s t tmo s .Chem .Ph y s .11 ,11007–11021(2011 ) . An ta rc t icIceShee tD i v ide .A 46 . Hube r ,C .e ta l .Iso topeca l ib ra tedG reen landtempe ra tu rereco rdove r Ma r ine Iso topeS tage3and i t sre la t iontoCH Ea r thP lane t .Sc i .Le t t .243 ,504–519(2006 ) . 4. 47 . Ra smus sen ,S .O .e ta l .Af i rs tch rono logyfo rtheNo r thG reen landEem ianIce D r i l l ing(NEEM )iceco re .C l im .Pa s t9 ,2713–2730(2013 ) . r .Ph y s .J .Spec .Top .174 ,49–63(2009 ) . 48 . Mude l see ,M .B reak func t ionreg res s ion .Eu 49 . Schwande r ,J .&S tau f fe r ,B .Aged i f fe rencebe tweenpo la r iceand thea i rt rapped in i t sbubb le s .Na tu re311 ,45–47(1984 ) . 50 . Cap ron ,E .e ta l .Synch ron is ingEDMLandNo r thGR IPiceco re sus ingd18Oo f 18 a tmo sphe r icoxygen(d Oatm)andCH easu remen t sove rM IS5(80–123ky r ) . 4m Qua t .Sc i .Re v .29 ,222–234(2010 ) . 51 . Ba rno la ,J .M . ,P im ien ta ,P . ,Raynaud ,D .&Ko ro tke v ich ,Y .S .CO2–c l ima te re la t ion sh ipasdeducedf romtheVo s tok iceco re :are -e xam ina t ionba sedonnew measu remen tsandonare -e va lua t iono fthea i rda t ing . Te l lu s43 ,83–90(1991 ) . 52 . Schwande r ,J .e ta l .Agesca leo fthea i rinthesumm i tice :imp l ica t ionfo rg lac ia l– in te rg lac ia ltempe ra tu rechange .J .Geoph y s .Re s .102 ,19483–19493(1997 ) . 53 . Se ie rs tad , I .e ta l .Cons i s ten t lyda tedreco rdsf romtheG reen landGR IP ,G ISP2and NGR IPiceco re sfo rthepa s t104kare vea lreg iona lm i l lenn ia l sca leiso tope g rad ien t sw i thpos s ib leHe in r ichEven t imp r in t .Qua t .Sc i .Re v .106 ,29–46(2014 ) . 54 . Bu i ze r t ,C .e ta l .G reen landtempe ra tu rere sponsetoc l ima tefo rc ingdu r ingthe la s t deg lac ia t ion .Sc ience345 ,1177–1180(2014 ) . 55 . Sowe rs ,T . ,Bende r ,M . ,Raynaud ,D .&Ko ro tkev ich ,Y .S .d15No fN2ina i rt rapped in po la rice :at race ro fga st ranspo r t inthef i rnandapo ss ib lecons t ra in ton iceage– ga saged i f fe rence s .J .Geoph y s .Re s .97 ,15683–15697(1992 ) . 56 . Pa r ren in ,F .e ta l .Onthega s– icedep thd i f fe rence(Ddep th )a longtheEP ICADome Ciceco re .C l im .Pa s t8 ,1239–1255(2012 ) . 57 . Fudge ,T .J . , Wadd ing ton ,E .D . ,Conway ,H . ,Lund in ,J .M .D .&Tay lo r ,K . In te rpo la t ion me thodsfo rAn ta rc t icice -co ret ime sca le s :app l ica t iontoBy rd ,S ip leDomeand LawDomeiceco re s .C l im .Pa s tD i scu s s .10 ,65–104(2014 ) . 58 .F ische r ,H . ,S iggaa rd -Ande r sen ,M . -L . ,Ru th ,U . ,Röth l isbe rge r ,R .& Wo l f f ,E .G lac ia l / in te rg lac ia lchangesin m ine ra ldu s tandsea sa l treco rdsinpo la riceco re s : sou rces ,t ranspo r t ,anddepo s i t ion .Re v .Geoph y s .45 ,RG1002(2007 ) . 59 . deVe rna l ,A . ,Ge r sonde ,R . ,Goosse ,H . ,Se idenk ran tz ,M . -S .& Wo l f f ,E .W .Sea ice in thepa leoc l ima tesy s tem :thecha l lengeo frecons t ruc t ingsea icef romp rox ies—an in t roduc t ion .Qua t .Sc i .Re v .79 ,1–8(2013 ) . 60 . Wo l f f ,E .W .e ta l .Sou the rnOceansea iceex ten t ,p roduc t iv i tyand i ronf lu xove rthe pa s te igh tg lac ia lcyc les .Na tu re440 ,491–496(2006 ) . 61 .A l ley ,R .e ta l .Changes incon t inen ta landsea sa l ta tmo sphe r ic load ings incen t ra l G reen landdu r ingthe mo s trecen tdeg lac ia t ion : mode l -ba sedes t ima te s .J .G lac io l . 41 ,503–514(1995 ) . 62 . Noone ,D .&S immonds ,I .Seaicecon t ro lo fwa te riso topet ranspo r ttoAn ta rc t ica and imp l ica t ionsfo r iceco re in te rp re ta t ion .J .Geoph y s .Re s .109 ,D07105(2004 ) . 63 . Ve re s ,D .e ta l .TheAn ta rc t iciceco rech rono logy(A ICC2012 ) :anop t im ized mu l t i l im . pa rame te rand mu l t i s i teda t ingapp roachfo rthelas t120thousandyea r s .C Pa s t9 ,1733–1748(2013 ) . 64 . Baz in ,L .e ta l .Anop t im ized mu l t i -p ro xy , mu l t i s i teAn ta rc t iciceandga so rb i ta l ch rono logy(A ICC2012 ) :120–800ka .C l im .Pa s t9 ,1715–1731(2013 ) . 65 . Kawamu ra ,K .e ta l .No r the rnHem isphe refo rc ingo fc l ima t iccyc lesinAn ta rc t ica ove rthepa s t360 ,000yea r s .Na tu re448 ,912–916(2007 ) . 66 . Sch i l t ,A .e ta l .A tmo sphe r icn i t rousox idedu r ingthela s t140 ,000yea r s .Ea r th P lane t .Sc i .Le t t .300 ,33–43(2010 ) . 67 . Köh le r ,P . ,Kno r r ,G . ,Bu i ron ,D . ,Lou ran tou ,A .&Chappe l laz ,J .Ab rup tr i sein a tmo sphe r icCO2a ttheon se to ftheBø l l ing /A l le rød :in -s i tuiceco reda tave rsus t ruea tmo sphe r ics igna ls .C l im .Pa s t7 ,473–486(2011 ) . 68 . Ro sen ,J .L .e ta l .An iceco rereco rdo fnea r -synch ronou sg loba lc l ima techangesa t theBø l l ingt rans i t ion .Na tu reGeo sc i .7 ,459–463(2014 ) . 69 . Köh le r ,P . ,Kno r r ,G .&Ba rd ,E .Pe rma f ros tthaw ingasapo ss ib lesou rceo fab rup t ca rbonre leasea ttheon se to ftheBø l l ing /A l le rød .Na tu reComm5 ,5520(2014 ) . 6000 5000 60 50 40 30 20 10 0 Vo s to k 4000 2000 EDC DomeFu j i 20kaBP : 521±120yea r 150 100 50 EDML 400 1000 800 700 600 500 d 200 TALD ICE F requen c y Δage(yea rs ) 3000 c 200 F requency 70 a 7000 400 300 200 WDC A l l ±2 σ ±1 σ 600 e F requen c y Δage( yea r s ) 600 700 40kaBP : 351±73yea r 150 100 50 250 300 350 400 450 b 800 400 200 0 70 500 Δage( yea r ) 60 50 40 30 20 WD2014Age( kaBP ) E x t end edD a t aF i gu r e1|D i f f e r en c eb e tw e eng a sa g eandi c ea g e(Da g e )a t WA I SD i v id e .a,Comp a r i s ono f WDC Da g ew i tho th e rAn t a r c t i cco r e s .I c e c o r ea bb r e v i a t i on s :EDC ,EP ICAD om eC on c o rd i a ;EDML ,EP ICAD ronn in g M audL and ;TALD ICE ,T a l o sD om e ; WDC , WA I SD i v id e . Da g ev a l u e sa r e t a k enf romr e f s2 3 ,6 3– 6 5 .Th ev e r t i c a la x i si sonal o g a r i thm i cs c a l e .b, Da g e g e un c e r t a in t ybound sob t a in edf r omanen s em b l eo f1 , 0 0 0a l t e rn a t i v eDa 10 0 Δage( yea r ) 200 60kaBP : 262±50yea r 150 100 50 0 200 250 300 Δage( yea r ) 350 s c en a r io s ;d e t a i l sa r eg i v ene l s ewh e r e.A Da g es c en a r ioob t a in edw i than a l t e rn a t i v ed en s i f i c a t ion mod e l( r e f .3 9in s t e ado fr e f .3 8 )i sshowninb lu e . c ) ,4 0k y rBP c –e ,H i s to g r am so fth e1 , 0 0 0 Da g es c en a r io sa t2 0k y rBP( ( d)and6 0k y rBP( e ) ;s t a t edv a lu e sg i v eth ed i s t r i bu t ion m e an 6th e2 s s t and a rdd e v i a t ion . 2 3 59 58 .5 a d −1 −40 −42 −44 600 58 Dens i ty(yea rs ) −38 59 .5 b 500 600 0 .01 e 750 450 700 c 550 500 Ga saged i s t r ibu t ion 0 .02 0 −50 550 CH4(ppb ) 18 EDMLCH4(ppb ) WDCCH4(ppb ) NGR IP δ O(‰ ) 60 0 60 59 .5 59 Age( kaBP ) 58 .5 E x t end edD a t aF i gu r e2|D e t e rm in in gth et im in go fth eab rup tDO 4 1 )a s t r an s i t ion s .a , b,DO1 7 . 2 ,1 7 . 1 ,1 6 . 2and1 6 . 1( f r omo ld e s tt oy oun g e s t 1 8 )and WDCCH ( b ) . H o r i z o n t a l o r a n g e b a r s d e n o t e r e c o rd ed inNGR IPd O(a 4 p r e t r an s i t ionandpo s t t r an s i t i on l e v e l s ; th e t r an s i t i onm idp o in t( 5 0%o fs i gn a l amp l i tud e ) i s ind i c a t edb yar edd o t ; th e2 5%and7 5%s i gn a lamp l i tud em a r k e r s 58 100 150 A tmo sphe re I ceco re( f i l te red ) 650 600 m idpo in tsh i f ted b y−5yea r s 550 500 450 50 Ga sAge 450 −40 −20 0 20 40 60 80 100 120 T ime( yea r s ) a r eind i c a t edw i thb lu edo t s .c ,Comp a r i sono f WDCCH g r e y )w i thEDML 4( 3 , 5 0 , 6 6 r an g e ) . d,H yp o th e t i c a lg a s a g ed i s t r i bu t ionfo r WDCdu et of i rn CH4(o d en s i f i c a t ionandg r adu a lbub b l ec lo su r e ,u s in gat run c a t ed lo g -n o rm a l e ,Sh i f tint r an s i t i on m idpo in tindu c edb yf i l t e r in go fth e d i s t r ibu t ion67. a tm o sph e r i cr e c o rdinth ef i rnco lumn . DO /A IM17 .1 DO /A IM12 a 18 NGR IPδ O(‰ ) −38 −40 −42 b −40 −42 −44 −38 −37 −39 −38 18 WDC δ O(‰ ) −44 −38 18 WDC δ O(‰ ) 18 NGR IPδ O(‰ ) −36 −40 −2000 −1000 0 1000 T ime( yea r ) −41 2000 −39 −2000 −1000 0 1000 T ime( yea r ) 2000 E x t end edD a t aF i gu r e3|C ropp in go find i v idu a lr e co rd sinth es t a ckto p lo t t edinb lu eando r an g efo rNGR IPand WDC ,r e sp e c t i v e l y .Th ey e l l ow p r e v en to v e r l apo fe v en t s .a,DO /A IM1 2 ,wh e r en oc r opp in gi sn e ed ed . v e r t i c a lsh ad in gb a rinb a c k g r oundshow sth eNH l e adt im e( 2 0 0y e a r s ) ;th e b,DO /A IM1 7 . 1 ,wh e r e th em o s tc r opp in g i sn e ed ed .Fu l l t im es e r i e sw i th f i v e - pu rp l er e c t an g l eg i v e sth e21 , 2 0 0to11 , 2 0 0t im ew indow . p o in trunn in ga v e r a g ea r ep l o t t eding r e y ,andth ec on t r i bu t o r yr e c o rd sa r e −1000 −500 0 500 1000 −39 −1000 b −39 −500 0 500 1000 −39 .5 18 δ O(‰ ) 18 δ O(‰ ) a −39 .5 −40 −1000 −500 0 500 T ime( yea r s ) 1000 E x t end edD a t aF i gu r e4|Numb e ro fr e co rd sandf i t t in gp ro c edu r e . 1 8 Os t a c k sf o ra b rup tNH Num b e ro fcon t r i bu t o r yr e c o rd st oth e WDCd w a rm in g( in t e r s t ad i a lon s e t )(a )andf o ra b rup tNHc o o l in g( in t e r s t ad i a l 20 N r .A IMreco rds 20 N r .A IMreco rds −40 15 15 10 10 5 5 0 −1000 −500 0 500 T ime( yea r s ) 1000 0 t e rm in a t ion )( b) .B lu er e c t an g l e sind i c a t eth et im ew indowo v e rwh i chth e f i t t in gp r o c edu r ee v a lu a t e sth ef i ttoth ed a t a( 26 0 0to17 0 0y e a r s ) ;sh ad ed v e r t i c a ly e l lowb a r ssh owNH l e adt im e . NHleadt ime(yea rs ) a 220 400 600 800 1000 1200 1400 1600 200 180 160 140 120 L inea rb rea k f i t Quad ra t i cb rea k f i t Mude l see(2009 )b rea k f i t 100 80 b RMSD(‰ ) 0 .08 0 .07 0 .06 400 600 800 1000 1200 1400 1600 W indows i ze( yea r s ) E x t end edD a t aF i gu r e5|E v a lu a t in gth ep e r fo rm an c eo fth eb r e a kpo in t d e t e c t iona l go r i thm .a,B r e a kp o in td e t e c t i ona sa fun c t i ono fd a t aw indows i z e u s in gbo thl in e a r(b lu e )andqu ad r a t i c( o r an g e )fun c t i on s ,c omp a r edw i thth e g r e yd o t sw i th1 se r r o rb a r s ) .Th ed a t aw indowi s BREAKF ITa l g o r i thm48( app l i eds ymm e t r i c a l l y ,m e an in gth a tequ a lnum b e r so fy e a r s(h a l fth ew ind ow s i z e )a r eu s edb e f o r eanda f t e r th ed e t e c t edb r e a kp o in t .D a t a f a l l in gou t s id e th i s w indowa r ei gn o r edinth ef i t t in gp r o c edu r e .b,Roo tm e ansqu a r ed e v i a t i on 1 8 b e tw e enth e WDCd Os t a c kandth ef i t t in gcu r v e . No rma l i zeds igna l 2 Ma jo rA IMeven ts M ino rA IMe ven t s a b RandomA IMe ven t s RandomA IMe ven ts 1 .5 1 0 .5 0 c d −500−250 0 250 500 750 −250 0 250 500 750 −250 0 250 500 750 −250 0 250 500 750 F requenc y T ime( yea r s ) 60 k e T ime( yea rs ) 230± 93 f T ime(yea rs ) 211± 94 g T ime(yea rs ) 210± 113 h 208± 108 40 k 20 k 0 0 100 200 300 NH lead( yea r s ) 0 100 200 300 NH lead( yea rs ) E x t end edD a t aF i gu r e6|A l t e rn a t i v es t a ck in go fA IMe v en t s .a,S t a c ko f 1 8 1 8 O(b lu e ) , WDCCH4( g r e en )and WDCd O( o r an g ew i thf i t )fo r NGR IPd ju s tth em a jo rA IMe v en t s( 4 ,8 ,1 2 ,1 4and1 7 ) ,a l i gn eda tth ea b rup tNH w a rm in g .b,A s in a ,bu t fo ron l y th em in o rA IMe v en t s( 3 ,5 . 1 ,5 . 2 ,6 ,7 ,9 ,1 0 ,1 1 , ,A s in a ,bu tf o re i gh tr and om l ys e l e c t edDO /A IMe v en t s . 1 3 ,1 5 ,1 6and1 8 ) .c d,A s in c ,bu ta l i gn e da tth ea b rup tNHc o o l in g .E v en t sa r ea v e r a g edw i thth e i r 0 100 200 300 NH lead(yea rs ) 0 100 200 300 400 NH lead(yea rs ) o r i g in a lamp l i tud e sandno rm a l i z eda f t e rs t a c k in gfo rcon v en i en c eo f v i su a l i z a t ion .e –h,H i s to g r am so fNH l e adt im ea s s o c i a t edw i th 5 so lu t ion sf romth e a –d,r e sp e c t i v e l y ,g en e r a t edb yb inn in gth e4 31 0 s en s i t i v i t ys tud y .Th ed i s t r i bu t i onm e anand2 sun c e r t a in t ybound sa r e l i s t ed in th ep an e l s .Sh ad edv e r t i c a ly e l lowb a r s(upp e rp an e l s )showNH l e adt im e . 0 .6 SH lead s Co r re la t ion 0 .2 a b s sNa 0 −0 .2 −0 .4 18 δO −0 .6 No rma l i zeds igna l 0 .4 2 NHlead s c 1 0 −1 −0 .8 −750−500−250 0 250 500 750 Lag( yea r s ) −500 −250 E x t end edD a t aF i gu r e7|T im in go fs e a s a l tsod ium .a,L a g g edco r r e l a t i on 1 8 1 8 Oandth et im ed e r i v a t i v eo f WDCd O( o r an g e ) ,and b e tw e enNGR IPd 1 8 Oandth et im ed e r i v a t i v eo f WDCs sN a( g r e y ) .Th edo t s b e tw e enNGR IPd ind i c a t e th em a x imum( an t i ) c o r r e l a t i ona t1 6 7 y e a rand2 2 9 y e a rNH l e ad fo r 1 8 WDC d Oands sN a ,r e sp e c t i v e l y .Af ou r th o rd e rBu t t e rw o r thb andp a s s f i l t e r w i tha5 0 0 – 1 0 , 0 0 0 y e a rw ind owi sapp l i edt oth et im es e r i e st oi s o l a t eth e 1 8 O( b lu e ) , WDCCH4 m i l l enn i a l s c a l ev a r i ab i l i t y .b,DO 3 – 1 8s t a c ko fNGR IP d 0 250 500 750 −250 T ime(yea rs ) 0 250 500 750 T ime(yea rs ) 1 8 ( g r e en ) , WDCd O(o r an g e )and WDCs sN a( g r e y ) ,a l i gn eda t th em idp o in to f th eDOw a rm in gs i gn a l .Th ee s t im a t edb r e a kp o in t in th es t a c k s(d o t s )o c cu r sa t 1 8 Oands sN a ,r e sp e c t i v e l y .c ,A s in b,bu t f o r t 52 1 8and1 9 5y e a r sfo r WDCd th eab rup tNHcoo l in ge v en t s ,w i thth ee s t im a t edb r e a kpo in ta tt 52 0 8and 1 8 1 9 9y e a r sfo r WDCd Oands sN a ,r e sp e c t i v e l y .Sh ad edv e r t i c a ly e l l owb a r s showNH l e adt im e s . E x tendedDa taTab le1| Pha s ingo ftheb ipo la rsee sawdu r ingthela s tdeg la c ia t ion 24 ,46 Fo rthedeg lac ia t ionweu seaG reen land -CH4pha s ingtha t i sthea ve rageo fthe56638 -yea rCH4lagob se r ved fo rtheg lac ia lpe r iod ,andthenea r synch ronou spha s ing(4 .5 624 -yea rCH4lag )ob se r ved fo rthe 18 l ls ta tede r ro r srep re sen t2 sunce r ta in tybound s ;unce r ta in ty inthe WDCd Ob reakpo in t i sde te rm inedu s ingtheBREAKF ITa lgo r i thm48;unce r ta in ty intheCH ran s i t ion i sde f ineda sthe Bø l l ingt ran s i t ion68.A 4t 23 ran s i t ion(E x tendedDa taF ig .2 ) ;Dageunce r ta in ty i sfoundbyu s ingaf i rnden s i f ica t ion mode lsen s i t i v i tys tudy (E x tendedDa taF ig .1 ) ;unce r ta in ty intheG reen land -CH ha s ingi s 25 –75%rangeo ftheCH4t 4p 24 ,68 takentobetheroo t meansqua reo ftheunce r ta in t ie s inthec i teds tud ie s ;theunce r ta in ty intheNHc l ima te i stheroo tsumsqua reo ftheunce r ta in t ie s inthep reced ingco lumn s .Thepo ten t ia lro leo fCO n 2i de lay ingAn ta rc t iccoo l inga ttheBø l l ingon se ti sd i scu s sedinre f .69 . te rm in ingthepha s ing . {Th i se s t ima teu se stheon se t ,ra the rthanthe m idpo in t ,o ftheBø l l ing –A l le rødtoYounge rD rya st ran s i t ionin WDCCH4inde 18 Oa tabou tth i st imetha t mayre f lec t loca lc l ima te ,a swe l la saun iqueandp ronouncedaccumu la t ionanoma lys ta r t inga tabou t11 .9ky rBP. {Th i se s t ima te maybeun re l iab lebecau seo fadoub lepeak in WDCd