POSITION ANALYSIS AC E. Anta rc tic Se a Ic e a nd Clima te Cha ng e Clima te Sc ie nc e fo r Austra lia s Future

Transcription

1 POSITION ANALYSIS Anta rc tic Se a Ic e a nd Clima te Cha ng e 2014 AC E C RC ANTARC TIC C LIMATE & EC O SYSTEMS C RC Clima te Sc ie nc e fo r Austra lia s Future 1

2 POSITION ANALYSIS: Anta rc tic Se a Ic e And Clima te Cha ng e 2014 PA ISBN CONTACTS Dr Ja n L. Lie se r Ma rine Gla c iolog ist E: Ja n.lie se r@ a c e c rc.o rg.a u Profe ssor Ma rc us Ha wa rd Polic y E: Ma rc us.ha wa uta s.e d u.a u Co p yrig ht: The Anta rc tic Clima te & Ec o syste ms Co o p e ra tive Re se a rc h Ce ntre This wo rk is c o p yrig ht. It ma y b e re p ro d uc e d in who le o r in p a rt fo r stud y o r tra ining p urp o se s sub je c t to the inc lusio n o f a n a c kno wle d g e me nt o f the so urc e, b ut no t fo r c o mme rc ia l sa le o r use. Re p ro d uc tio n fo r p urp o se s o the r tha n tho se liste d a b o ve re q uire s the writte n p e rmissio n o f the Anta rc tic Clima te & Ec o syste ms Co o p e ra tive Re se a rc h Ce ntre. Re que sts a nd e nquirie s c onc e rning re produc tion rig hts should be a ddre sse d to: The Ma na g e r Co mmunic a tio ns Anta rc tic Clima te & Ec o syste ms Co o p e ra tive Re se a rc h Ce ntre Priva te Ba g 80 Ho b a rt Ta sma nia 7001 Te l: Fa x: Ema il: me d a c e c rc.o rg.a u c e c rc.o rg.a u Cove r ima g e : Ic e sta tio ns se t up fro m RV Auro ra Austra lis d uring the se c o nd Se a Ic e Physic s & Ec o syste ms e Xp e rime nt (SIPEX 2), Ea st Anta rc tic a, sp ring, Pho to b y Ja n L. Lie se r The ACE CRC is a uniq ue c o lla b o ra tio n b e twe e n c o re p a rtne rs the Austra lia n Anta rc tic Divisio n, CSIRO, the Unive rsity o f Ta sma nia, the Austra lia n G o ve rnme nt s De p a rtme nt o f Ind ustry, the Alfre d We g e ne r Institute fo r Po la r a nd Ma rine Re se a rc h (G e rma ny), a nd the Na tio na l Institute o f Wa te r a nd Atmo sp he ric Re se a rc h Ltd (Ne w Ze a la nd ) a nd a c o nso rtium o f sup p o rting p a rtne rs. It is fund e d b y the Austra lia n G o ve rnme nt s Co o p e ra tive Re se a rc h Ce ntre s Pro g ra m. Printed on forestry stewardship certiied paper ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

3 POSITION ANALYSIS: Anta rc tic Se a Ic e a nd Clima te Cha ng e 2014 Contributing Authors Ja n L Lie se r* 1, Ro b e rt A Ma sso m 1,2, Ale xa nd e r D Fra se r 1, Ma rc us G Ha wa rd 1,3, Pe tra He il 1,2, De lp hine La nnuze l 1,3, Kla us M Me ine rs 1,2, Je ssic a Me lb o urne -Tho ma s 1,2, A J (To ny) Pre ss 1, G uy D Willia ms 1 Afiliations 1 Anta rc tic Clima te & Ec o syste ms Co o p e ra tive Re se a rc h Ce ntre, Unive rsity o f Ta sma nia, Priva te Ba g 80, Ho b a rt, 7001, Austra lia. 2 Austra lia n Anta rc tic Divisio n, Cha nne l Hig hwa y, King sto n, Ta sma nia 7050, Austra lia. 3 Institute fo r Ma rine a nd Anta rc tic Stud ie s, Unive rsity o f Ta sma nia, Priva te Ba g 129, Ho b a rt, Ta sma nia, 7001, Austra lia. * c o o rd ina ting a utho r: Ja n.lie se r@ a c e c rc.o rg.a u This position a na lysis a ims to: 1. Info rm Austra lia n g o ve rnme nts a nd the c o mmunity a b o ut o ur c urre nt sta te o f kno wle d g e a b o ut Anta rc tic se a ic e ; 2. Outline how sea ice inluences, and responds to, global climate variability a nd c ha ng e ; a nd 3. Id e ntify issue s fo r c o nsid e ra tio n in p o lic y d e ve lo p me nt. Cita tion: Lie se r JL, Ma sso m RA, Fra se r AD, Ha wa rd MG, He il P, La nnuze l D, Me ine rs KM, Me lb o urne -Tho ma s J, Pre ss AJ & Willia ms G D (2013), Po sitio n a na lysis: Anta rc tic se a ic e a nd c lima te c ha ng e 2014, Anta rc tic Clima te & Ec o syste ms Co o p e ra tive Re se a rc h Ce ntre, Ho b a rt, Ta sma nia, Austra lia 3

4 G LOSSARY OF TERMS AND ACRONYMS USED AADC Austra lia n Anta rc tic Da ta Ce ntre ; Adve c tion Predominantly horizontal movement of a mass of luid; Albe do The ratio of the relected solar radiation to the incident solar radiation, usually referring e ithe r to the e ntire sp e c trum (b ro a d b a nd a lb e d o ) o r just to the visib le p a rt o f the sp e c trum; Altime try - Me a sure me nt o f a ltitud e using re mo te se nsing te c hniq ue, fo r e xa mp le a ra d a r o r la se r instrume nt; Anta rc tic Bottom Wa te r - Cold dense water that is formed near the Antarctic coast, lows down the c o ntine nta l slo p e to the a b yssa l p la ins a nd d rive s g lo b a l o c e a n c urre nts; Anta rc tic Dive rg e nc e - Atmospheric/oceanic boundary between the eastward-lowing Antarctic Circumpolar Current and the westward-lowing Antarctic Coastal Current; Are a l e xte nt The size o f the a re a c o ve re d ( g se a ic e e xte nt); ASAR Ad va nc e d Synthe tic Ap e rture Ra d a r, a n instrume nt o n b o a rd the Euro p e a n ENVISAT sa te llite ; ATS Anta rc tic Tre a ty Syste m; AUV Auto no mo us Und e rwa te r Ve hic le, a n ind e p e nd e nt ro b o t use d fo r ma rine re se a rc h; AWI Alfre d We g e ne r Institute, He lmho ltz Ce ntre fo r Po la r a nd Ma rine Re se a rc h, G e rma ny; CCAMLR Co mmissio n fo r the Co nse rva tio n o f Anta rc tic Ma rine Living Re so urc e s, p a rt o f the Anta rc tic Tre a ty Syste m; Conve c tion Heat transfer by mass motion of a luid; Couple d c lima te mode l Nume ric a l mo d e ls o f c o mp o ne nts o f the c lima te syste m c o up le d to g e the r; CPOM, UCL Ce ntre fo r Po la r Ob se rva tio n a nd Mo d e lling a t Unive rsity Co lle g e Lo nd o n, Unite d King d o m; CRYOS, EPFL La b o ra to ry o f Cryo sp he ric Sc ie nc e s a t Éc o le Po lythe c hniq ue Fé d é ra le d e La usa nne, Switze rla nd ; CSIRO - Commonwealth Scientiic and Industrial Research Organisation, Australia; De nse She lf Wa te r Dense water mass formed on the continental shelf from signiicant brinere je c tio n d uring e nha nc e d se a ic e fo rma tio n, suc h a s in g p o lynya s; Dime thylsulfoniopropiona te (DMSP) - Me ta b o lite fo und in ma rine p hyto p la nkto n, se a we e d s, a nd so me sp e c ie s o f a q ua tic va sc ula r p la nts; Ekma n tra nsport - Wind -d rive n tra nsp o rt o f surfa c e se a wa te r, to the le ft o f the wind d ire c tio n in the So uthe rn He misp he re ; El- Niño/ Southe rn Osc illa tion (ENSO) A c yc le o f c o he re nt a nd so me time s ve ry stro ng ye a r- to -ye a r va ria tio ns in se a -surfa c e te mp e ra ture s, c o nve c tive ra infa ll, surfa c e a ir p re ssure a nd atmospheric circulation that occur across the equatorial Paciic Ocean (source: NOAA); Fa st ic e Se a ic e tha t ha s b e c o me "fa ste ne d " to the sho re o r b e twe e n g ro und e d ic e b e rg s; Fe e dba c k When a process triggers a change that in return inluences the initial one; Firn - G ra nula r, p a rtia lly c o nso lid a te d sno w tha t ha s c o mme nc e d the tra nsitio n to ic e ; Fre e boa rd A me a sure o f he ig ht o f a n ic e (o r sno w) surfa c e a b o ve a re fe re nc e le ve l, typ ic a lly the se a le ve l; Hydrosta tic e quilibrium A luid is in hydrostatic equilibrium (or balance) when it is at rest, which me a ns tha t e xte rna l fo rc e s suc h a s g ra vity a nd p re ssure a re b a la nc e d ; Ic e dra ft - Me a sure me nt o f the se a ic e thic kne ss b e lo w the wa te rline ; Ic e ra fting Ho rizo nta l p re ssure p ro c e ss whe re b y o ne p ie c e o f se a ic e o ve rrid e s a no the r; Ic e ridg ing Sea ice loes collide and pile up along a line, causing a steep-sloped ridge to rise up a b o ve the a d ja c e nt stre tc he s o f le ve l ic e, to g e the r with a muc h la rg e r ke e l b e lo w se a le ve l; Ic e she lf - A thick and extensive body of glacial ice attached to a coast and loating on the sea, ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

5 that gains mass by low from the grounded continental ice sheet and by local snowfall; Inte r- a nnua l - Time sc a le o f mo re tha n o ne ye a r b ut usua lly le ss tha n 10 ye a rs; Inte r- se a sona l Time sc a le b e twe e n se a so ns; IPCC AR5 Inte rg o ve rnme nta l Pa ne l o n Clima te Cha ng e Fifth Asse ssme nt Re p o rt; LiDAR - Lig ht De te c tio n And Ra ng ing, o ne o f the te c hniq ue s a p p lie d fo r ra ng e me a sure me nts in a ltime try; Me ridiona l e xc ha ng e No rth-so uth e xc ha ng e (a lo ng a me rid ia n); Me ridiona l ove rturning c irc ula tion G lo b a l o c e a n c irc ula tio n d rive n b y te mp e ra ture a nd sa linity g ra d ie nts (a lso re fe rre d to a s g the rmo ha line c irc ula tio n), whic h tra nsp o rts lo w-d e nsity wa te rs to hig he r-la titud e s in the up p e r la ye r a nd re turns hig h-d e nsity wa te rs e q ua to rwa rd a t d e p th. Mixe d la ye r Wind -mixe d a nd b rine -fo rc e d c o nve c tio n la ye r b e twe e n the o c e a n surfa c e a nd a d e p th usua lly ra ng ing b e twe e n 25 a nd 200 me tre s d e p e nd ing o n the se a so n; NASA Na tio na l Ae ro na utic s a nd Sp a c e Ad ministra tio n, Unite d Sta te s; NOAA - Na tio na l Oc e a nic a nd Atmo sp he ric Ad ministra tio n, Unite d Sta te s; Pa c k ic e Any a re a o f se a ic e tha t is no t la nd fa st; Phe nolog y - Timing o f se a so na l b io lo g ic a l e ve nts; Polynya - An a no ma lo us re g io n o f o p e n wa te r o r lo w ic e c o nc e ntra tio n within the se a ic e zo ne. Po lynya s a ro und the Anta rc tic c o a st a re ma inta ine d whe re wind o r o c e a n c urre nts mo ve ic e a wa y a nd a re re g io ns o f e nha nc e d ic e p ro d uc tio n; Oc e a n forc ing Physic a l c o nstra ints e xe rte d b y the o c e a n o n the a tmo sp he re o r se a ic e ; Oute r pa c k No rthe rn p a rt o f the se a ic e zo ne a ro und Anta rc tic a, c o nne c ts to the ma rg ina l ic e zo ne in the no rth a nd the inne r p a c k (c lo se r to the c o a st) in the so uth; ROV Re mo te ly Ope ra te d Ve hic le, a d e p e nd e nt ro b o t o p e ra te d thro ug h a te the r; Se a ic e c onc e ntra tion - Pro p o rtio n o f the o c e a n surfa c e a re a a c tua lly c o ve re d b y se a ic e in a given unit area, such as a satellite pixel. For example, 90% ice concentration signiies that 90% of the g ive n a re a is c o ve re d with se a ic e, with the re ma ining 10% b e ing o p e n wa te r; Se a ic e e xte nt - Area of the ocean covered by sea ice within the bounds of a speciied minimum thre sho ld ic e c o nc e ntra tio n (typ ic a lly ta ke n to b e 15%) in a ny g ive n se c to r; Se a WiFS - Sea-viewing Wide Field-of-view Sensor, the only scientiic instrument on GeoEye's Orb Vie w-2 (a lso kno wn a s Se a Sta r) sa te llite ; Snow ic e Ic e la ye r a t the inte rfa c e b e twe e n se a ic e a nd the sno w o n to p fo rme d fro m sno w a nd e ntra ine d se a wa te r; SIPEX 2 The se c o nd Se a Ic e Physic s a nd Ec o syste m e Xp e rime nt, a n inte rna tio na l multidisciplinary research voyage, into the Antarctic sea ice zone in 2012 (the irst SIPEX was in 2007); Southe rn Annula r Mode (SAM) - Pa tte rn o f c lima te va ria b ility b e twe e n 40 º S a nd 65 º S; Synthe tic Ape rture Ra da r (SAR) - A form of radar whose deining characteristic is its use of relative mo tio n, b e twe e n a n a nte nna a nd its ta rg e t re g io n, to p ro vid e d istinc tive lo ng -te rm c o he re ntsignal variations, which are exploited to obtain iner spatial resolution than is possible with c o nve ntio na l b e a m-sc a nning me a ns (so urc e : Wikip e d ia ); The rmoha line c irc ula tion g me rid io na l o ve rturning c irc ula tio n; TLS - Te rre stria l La se r Sc a nne r; WHOI Wo o d s Ho le Oc e a no g ra p hic Institute, MA, Unite d Sta te s. 5

6 EXEC UTIVE SUMMARY The a nnua l e xp a nsio n a nd c o ntra c tio n o f se a ic e in the Anta rc tic re p re se nts o ne o f the b ig g e st na tura l c ha ng e s o n Ea rth. At its ma ximum a nnua l e xte nt in Se p te mb e r/ Oc to b e r se a ic e c o ve r e xte nd s a b o ut 19 millio n sq ua re kilo me tre s o f the o c e a n a ro und Anta rc tic a o ne a nd ha lf time s the size o f the c o ntine nt itse lf. In the summe r se a ic e shrinks to a ro und 3 millio n sq ua re kilo me tre s. Anta rc tic se a ic e p la ys a ma jo r ro le in the g lo b a l c lima te syste m a nd in the e c o lo g y o f the So uthe rn Oc e a n. The se a ic e re g io n is the so urc e o f Anta rc tic Bo tto m Wa te r, a ma jo r driver of global ocean overturning circulation. Sea ice is important in relecting solar e ne rg y b a c k into sp a c e. It is a ha b ita t a nd a so urc e o f p rima ry p ro d uc tio n fo r So uthe rn Oc e a n e c o syste ms. Se a ic e c o ve r in the Anta rc tic is c ha ng ing. In the we st Anta rc tic Pe ninsula re g io n, se a ic e e xte nt ha s d ra ma tic a lly re d uc e d, a nd the le ng th o f the se a ic e se a so n ha s a lso sho rte ne d. In the Ro ss Se a re g io n o f the Anta rc tic, ho we ve r, the ma ximum a nnua l e xte nt o f se a ic e c o ve r ha s inc re a se d a nd its se a so n e xte nd e d. Ove ra ll, the ma ximum a nnua l e xte nt o f Anta rc tic se a ic e ha s inc re a se d b y a ro und 1.5% p e r d e c a d e sinc e 1979 (o r b y a ro und 285,000 sq ua re kilo me tre s). This c o mp a re s to a lo ss o f 1.8 millio n sq ua re kilo me tre s o f se a ic e ma ximum a nnua l e xte nt in the Arc tic. One imp o rta nt a sp e c t o f Anta rc tic se a ic e tha t we kno w ve ry little a b o ut is c ha ng e to its vo lume. While sa te llite s c a n me a sure the a e ria l e xte nt o f se a ic e, re lia b le me tho d s to re mo te ly me a sure se a -ic e thic kne ss a re o nly just e me rg ing. In c o ntra st, d a ta fro m sub ma rine s in the Arc tic ha ve a llo we d d e ta ile d mo nito ring o f re g io na l c ha ng e s to Arc tic se a -ic e thic kne ss o ve r a numb e r o f d e c a d e s. Wha t is ha p p e ning in the p hysic a l, c he mic a l a nd b io lo g ic a l syste ms b e ne a th Anta rc tic se a ic e is p o o rly und e rsto o d. Be c a use o f the c ritic a l ro le o f se a ic e, it is vita l tha t we d e ve lo p a b e tte r und e rsta nd ing o f the future tre nd s in se a ic e e xte nt a nd vo lume, a nd c o nse q ue nc e s fo r Anta rc tic a nd So uthe rn o c e a n e c o syste ms. Austra lia is we ll p la c e d to ta ke a le a d ro le in the se stud ie s - e sp e c ia lly in the Ea st Anta rc tic. Austra lia ha s a ma ture Anta rc tic re se a rc h p ro g ra m tha t ha s d e mo nstra te d tha t it c a n collaborate with other nations, and across scientiic disciplines, to do the complex sc ie nc e tha t is re q uire d to und e rsta nd the se imp o rta nt issue s. Ha ving the lo g istic a nd infra struc ture c a p a b ilitie s will b e vita l to e nsuring tha t this imp o rta nt re g io n o f the p la ne t is und e rsto o d. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

7 WHAT IS SEA IC E Se a ic e is fro ze n se a wa te r tha t fo rms whe n the surfa c e o f the o c e a n c o o ls to the p o int o f fre e zing (a t a p p ro xima te ly -1.8 C ). Eve ry winte r, e xte nsive fre e zing o f the So uthe rn O c e a n fo rms a va st se a ic e c o ve r tha t surro und s the Anta rc tic c o ntine nt - to d ra stic a lly mo d ify the p ro p e rtie s o f the o c e a n surfa c e a nd the inte ra c tio n b e twe e n two ke y e le me nts o f the g lo b a l c lima te syste m, na me ly the o c e a n a nd a tmo sp he re. As its d e nsity is le ss tha n tha t of seawater, sea ice loats on the ocean surface, where it forms a heterogeneous matrix c o nsisting ma inly o f ic e a nd sma ll p o c ke ts (c e lls) o f b rine [ Pe tric h a nd Eic ke n, 2010], a nd its characteristics are modiied by physical, chemical and biological processes. Bouvet I (NOR) Prince Edward Is (ZAF) South Sandwich Is (GBR)/ Islas Sandwich del Sur (ARG) South Georgia (GBR)/ Islas Georgias del Sur (ARG) S O U T H E R N Crozet Is (FRA) O C Anta rctic Cir cle HA AKO South Orkney Is Falkland Is (GBR)/ Islas Malvinas (ARG) Is AN! SE E A A N DRONNING MAUD LAND South Shetland Ushuaia Punta Arenas! N V II TA R Alex and e CT WEDDELL SEA IC Be PE rk NIN ne SU ri LA ri Kerguelen Is (FRA) ENDERBY LAND Heard I (AUS) COATS LAND ON TS ER OB D C.R LAN MA RONNE ICE SHELF BELLINGSHAUSEN SEA DA VIS Peter I Øy SE A Max im um ex AMUN DSEN MARIE BYRD LAND Min tent o SEA WILKES f Se iimu ROSS ICE SHELF ROSS SEA T 20 H 1 E AN R N T AR CT IC DUMONT D'URVILLE SEA ) Scott I IE GEORGE V LAND ge ÉL ge 0) U a v e ra AD ar e e ra O RE (3 0y v ear a ce R TE (30 y S of S e ai OR IA VICT D LAN xt me e a Ic LAND en t Balleny Is N E A O C TR EATY BO UNDA R Y (6 0 S) Macquarie I (AUS) Polar Stereographic Projection, True scale at 71 S Campbell I (NZ) Auckland Is (NZ) Hobart! Fig ure 1. Ma ximum a nd minimum e xte nt o f Anta rc tic se a ic e (30-ye a r a ve ra g e fo r ). 7

8 Are a l e xte nt a nd se a sona lity At its ma ximum a nnua l e xte nt in Se p te mb e r/ Oc to b e r a nd a s d e p ic te d in Fig ure 1, this se a ic e c o ve r e xte nd s o ve r a n e xtra o rd ina ry ~19 millio n sq ua re kilo me tre s o f the So uthe rn Oc e a n [Cavalie ri and Parkinso n, 2008; Co miso, 2010]; b y c o mp a riso n, the a re a o f the Anta rc tic c o ntine nt is ~14 millio n sq ua re kilo me tre s, while tha t o f Austra lia is ~7.7 millio n sq ua re kilo me tre s. During summe r, this a re a l e xte nt shrinks to ~3 millio n sq ua re kilo me tre s (in Fe b rua ry). As d e sc rib e d b e lo w, this se a so na l e xp a nsio n a nd c o ntra c tio n is o f imme nse climatic, biological and biogeochemical importance, and it follows that any signiicant c ha ng e s in se a ic e a re a l e xte nt a nd se a so na lity (a nd o the r c ha ra c te ristic s) ha ve wid e - ranging and indeed global ramiications. Whereas areal extent is a measure of the area o f the o c e a n surfa c e c o ve re d b y se a ic e a t a ny g ive n time, se a so na lity c o lle c tive ly d e sc rib e s the timing s o f a nnua l se a ic e a d va nc e a nd re tre a t a nd the re sulta nt d ura tio n o f se a ic e c o ve ra g e fo r a p a rtic ula r lo c a tio n. The wid th o f the se a ic e zo ne a t ma ximum e xte nt va rie s sub sta ntia lly a ro und the c o ntine nt fro m up to ~2200 km in the We d d e ll Se a se c to r (whe re it o c c up ie s a d e e p p o le wa rd e mb a yme nt) to o nly a fe w hund re d kilo me tre s in so me p la c e s, no ta b ly b e twe e n 120 E a nd 135 E. In this re g io n, the c o a st e xte nd s furthe r no rth tha n in o the r re g io ns (with the e xc e p tio n o f the ro ug hly no rth-so uth tre nd ing Anta rc tic Pe ninsula ). How doe s se a ic e form? The irst stage in sea ice development is the formation of individual crystals comprising ine spicules or platelets known as frazil ic e. With furthe r fre e zing, fra zil c rysta ls c o a g ula te into a so up y la ye r o n the o c e a n surfa c e kno wn a s g re ase ic e. Sub se q ue nt d e ve lo p me nt d e p e nd s o n whe the r c a lm o r sto rmy c o nd itio ns p re va il. Und e r c a lm c o nd itio ns, fra zil and grease ice tend to consolidate into thin lexible sheets called nilas, whic h thic ke n o ve r time. Und e r sto rmie r c o nd itio ns, a wid e sp re a d p ro c e ss o f se a ic e d e ve lo p me nt a ro und Anta rc tic a is the panc ake c yc le. By this process and under the inluence of wind and wave action, frazil crystals coagulate to form small pancakes or small loes with up turne d e d g e s - o n the o c e a n surfa c e (a loe is deined as a contiguous piece of ice o n the wa te r surfa c e ). The se p a nc a ke s sub se q ue ntly b o nd to g e the r a nd ra ft (o ve r-rid e by colliding with each other), to eventually form larger loes or a consolidated ice cover. Ic e g ro wth a lso o c c urs o n the und e rsid e o f e xisting se a ic e a s he a t is c o nd uc te d up wa rd s fro m the ic e -o c e a n inte rfa c e a nd thro ug h the ic e, tha t is b y the rmo dynamic g ro wth. This typ e o f ic e is c a lle d c o ng e la tio n o r c o lumna r ic e. In g e ne ra l, the a c c umula tio n o f sno w o n se a ic e o ld e r tha n a fe w d a ys p la ys a ke y ro le in d e te rmining the p ro p e rtie s a nd d e ve lo p me nt o f the und e rlying ic e, d ue to its stro ng insula ting c ha ra c te ristic s a nd hig h a lb e d o [Sturm and Masso m, 2010]. This in turn modiies the o ve ra ll c lima tic, b io lo g ic a l a nd b io g e o c he mic a l func tio n o f the ic e. Importantly, snow also makes a signiicant contribution to Antarctic sea ice formation via the fo rma tio n o f sno w ic e [Maksym and Markus, 2008]. This wid e sp re a d p he no me no n largely occurs when the weight of the snow is suficient to depress the ice surface below sea level. The resultant inlux of seawater saturates the lower snow layer, which may ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

9 UNDERSTANDING HO W SEA IC E THIC KNESS IS MEASURED The se a surfa c e is ind ic a te d b y the thic k b la c k line a s a re fe re nc e surface. Sea ice (grey) loats at the surface of the ocean with a sno w c o ve r o n to p (white ). Bla c k a rro ws sho w the ic e thic kne ss, b lue a rro ws sno w thic kne ss; the c o mb ina tio n o f b o th is re fe rre d to a s to ta l thic kne ss. The ic e fre e b o a rd is ind ic a te d b y the re d line a nd typ ic a lly sits a b o ve the se a surfa c e (a t the inte rfa c e between the sea ice and the snow), but with suficient snow load c a n b e sup p re sse d b e lo w the se a surfa c e, whic h the n le a d s to sno w ic e fo rma tio n (lig ht g re y). The sum o f sno w thic kne ss a nd ic e fre e b o a rd is c a lle d to ta l fre e b o a rd. Ic e d ra ft is me a sure d b e lo w the surfa c e (g re e n a rro ws). Diffe re nt re mo te se nsing te c hniq ue s can see different surfaces. LiDAR relects from the snow surface (o r ic e surfa c e in c a se o f no sno w c o ve r) a nd the re fo re g ive s a n e stima te o f sno w fre e b o a rd. The RADAR p e ne tra te s the sno w c o ve r a nd g ive s a n e stima te o f sno w thic kne ss. Ele c tro ma g ne tic Ind uc tio n (EMI) syste ms g ive a n e stima te o f to ta l thic kne ss in c o mb ina tio n with LiDAR. Sp a c e -b o rne re mo te se nsing te c hniq ue s (LiDAR o r RADAR) p ro vid e me a sure me nts o f ic e o r sno w fre e b o a rd, fro m whic h ic e thic kne ss c a n b e c o mp ute d if ic e, sno w a nd wa te r d e nsity a nd sno w thic kne ss a re kno wn. 9

10 sub se q ue ntly fre e ze to fo rm a typ e o f sa lty a nd g ra nula r se a ic e tha t a c c re te s to the surfa c e o f the e xisting ic e [Je ffrie s e t al., 2001]. How old is the se a ic e? In c o ntra st to the c o ntine nta l ic e ma ss c o ve ring Anta rc tic a, whic h ha s b uilt up o ve r hund re d s o f tho usa nd s o f ye a rs o f a c c umula te d sno wfa ll, mo st o f the se a ic e a ro und Anta rc tic a is se a so na l a nd the re fo re le ss tha n o ne ye a r o ld - so -c a lle d irst-year ice. This typ e o f ic e ha s a thic kne ss ra ng e o f m (typ ic a lly), a ltho ug h g re a te r thic kne sse s c a n o c c ur b y ic e d e fo rma tio n. Pe re nnia l se a ic e (ic e tha t survive s o ne o r mo re summe r me lt se a so ns) is g e ne ra lly thic ke r b ut is largely conined to the Weddell, Amundsen and eastern Ross seas (Figure 1). These are not o nly so me o f the so uthe rnmo st re g io ns a ro und the c o ntine nt, b ut the y a re a lso a re a s whe re ic e is pushe d b y winds a nd o c e a n c urre nts to wa rd the c o a st [Co miso and Nishio, 2008]. Ic e motion a nd de forma tion Ra the r tha n fo rming a sta tic, unb ro ke n ve ne e r o n the o c e a n surfa c e, mo st o f the se a ic e around Antarctica comprises a highly-mobile aggregation of loes that constantly move with the wind a nd c urre nts. This is te rme d pac k ic e. Due to the hig hly-d yna mic re sp o nse o f the p a c k ic e zo ne to the p a ssa g e o f sto rms, its c ha ra c te ristic s a lso c ha ng e c o nsta ntly. Ne w areas of open water between loes (termed le ads) fre e ze ra p id ly und e r winte r c o nd itio ns to fo rm a re a s o f ne w ic e, whe re a s e xisting ic e thic ke ns no t o nly the rmo d yna mic a lly (via he a t lo ss to the a tmo sp he re ) b ut a lso dynamic ally as loes are pushed together and d e fo rm und e r c o nve rg e nt c o nd itio ns. Mo re o ve r, the c ha ra c te ristic s o f the o ute r p a rt o f the p a c k, c a lle d the marg inal ic e zo ne, a re stro ng ly a ffe c te d b y o c e a n wa ve s tha t no t only generate new pancake ice formation but also break up existing loes. Ac ro ss the g re a te r Anta rc tic pa c k, se a ic e g ro wth b y the rmo dyna mic pro c e sse s a lo ne is se lf-limiting a s the ic e thic ke ns to insula te the o c e a n surfa c e fro m the c o ld a tmo sphe re. Ic e mo tio n a nd de fo rma tio n the n pla y a do mina nt ro le in thic ke ning the ic e b e yo nd ~0.5 m - ic e se ld o m a tta ins a thic kne ss o f > m b e fo re b e ing ra fte d o r p ile d into p re ssure rid g e s b y the a c tio n o f wind, wa ve s, o c e a n c urre nts a nd tid e s [Alliso n e t al., 1993; Wo rb y e t al., 1998]. Suc h is the p o we r o f the se me c ha nic a l d e fo rma tio n p ro c e sse s tha t p re ssure rid g e s can be up to ten or more metres thick in regions of irst-year ice [Masso m e t al., 2006; Williams e t al., 2013]. On ho rizo nta l sc a le s o f te ns o f me tre s to te ns o f kilo me tre s, the ne t re sult o f this c o mp le x inte rp la y o f the rmo d yna mic (fre e ze / me lt) a nd d yna mic (d e fo rma tio n) p ro c e sse s is a c o mp lic a te d mixture o f d iffe re nt typ e s, a g e s a nd thic kne sse s o f ic e. On the b ro a d e r sc a le o f hund re d s o f kilo me tre s, ho we ve r, re g io ns o r zo ne s with simila r c ha ra c te ristic s b e c o me a p p a re nt [Masso m e t al., 1999; Masso m and Stamme rjo hn, 2010]. Se a ic e mo tio n is a lso a ke y fa c to r in tra nsp o rting se a ic e (a nd its sno w c o ve r) fro m o ne re g io n to a no the r, tha t is fro m a n a re a o f fo rma tio n to a n a re a o f me lt, to a ffe c t the fre shwa te r b ud g e t o f the hig h-la titud e So uthe rn Oc e a n. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

11 As suc h, ic e d rift is o ne o f the mo st imp o rta nt fe a ture s o f the Anta rc tic se a ic e zo ne. As d isc usse d la te r, the re a re ind ic a tio ns tha t re g io na l p a tte rns o f ic e d rift a re c ha ng ing a ro und Anta rc tic a [Ho lland and Kwo k, 2012], with ma jo r imp lic a tio ns fo r ic e c o nc e ntra tio n, e xte nt, thic kne ss, a g e a nd se a so na lity. Se a ic e c o nc e ntratio n is deined a s the p e rc e nta g e c o ve ra g e o f se a ic e (ve rsus o p e n o c e a n) within a g ive n o c e a n a re a. Fig ure 2. Me a n se a ic e mo tio n in the So uthe rn Oc e a n a ve ra g e d o ve r a 10-ye a r pe rio d ( ), with ic e drift spe e ds indic a te d b y le ng ths o f ve c to rs a nd the b a c kg ro und c o lo urs. This la rg e -sc a le ma p o f ic e mo tio n wa s de rive d fro m a na lysis o f sa te llite da ta. Fro m Kimura [2004]. 11

12 0 E 10 E 20 E 30 E 40 E 50 E 60 E 70 E 80 E 65 S 70 S 65 S 70 S So uthern Ocean 100% Fa st ice c overage, % Antarctica 90 E 1 00 E 1 10 E 1 20 E 1 30 E 1 40 E 1 50 E 1 60 E 1 70 E As a b a c kg ro und a g a inst whic h to d isc uss re c e nt ic e mo tio n c ha ng e (in Se c tio n 4), Fig ure 2 sho ws me a n Anta rc tic se a ic e mo tio n o ve r a 10-ye a r p e rio d (d e rive d fro m sa te llite d a ta ). Be ing a lo ng -te rm a ve ra g e, the se ic e -d rift p a tte rns strongly relect climatological wind a nd o c e a n surfa c e c urre nt p a tte rns. Outsta nd ing fe a ture s a re the c irc ump o la r b a nd o f me a n e a stwa rd ic e mo tio n c e ntre d o n ~60 S in the Atla ntic se c to r a nd ~65 S in the Paciic sector, and a narrow westward-lowing coastal c urre nt tha t is p re d o mina ntly in the Atla ntic a nd Ind ia n se c to rs. The se two re g ime s, na me ly the Antarc tic Circ umpo lar Curre nt to the no rth a nd Antarc tic Co astal Curre nt to the so uth, a re se p a ra te d a lo ng the Antarc tic Dive rg e nc e [He il and Alliso n, 1999], b ut a re c o nne c te d in c e rta in re g io ns b y no rthwa rd retrolections, for example along 85 E [Rinto ul e t al., 2008]. Othe r ke y fe a ture s a re ma jo r g yre syste ms in the We d d e ll a nd Ro ss se a s a nd the Pryd z Ba y re g io n o f Ea st Anta rc tic a. Fig ure 3. A p ro je c tio n o f the Ea st Anta rc tic c o a st, sho wing the me a n p e rc e nta g e o f time (p e r ye a r) with fa st ic e c o ve ra g e fro m 2000 to 2008 (d e rive d fro m sa te llite data). A igure of 100% indicates fast ice tha t p e rsists thro ug ho ut e a c h ye a r (tha t is multi-ye a r fa st ic e, whic h c a n a tta in c o nsid e ra b le thic kne ss). Fro m Frase r e t al. [2012]. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

13 Fa st ic e No t a ll se a ic e is c o nsta ntly mo ving in re spo nse to wind s a nd c urre nts. A re la tive ly na rro w (up to ~200 km wid e ) b ut g e ne ra lly c o nso lid a te d b a nd o f sta tio na ry o r la nd fa st se a ic e (fa st ic e ) o c c urs a ro und the c o a sta l ma rg ins o f the c o ntine nt (Fig ure 3), whe re it is he ld in pla c e b y c o a sta l pro mo nto rie s, e mb a yme nts a nd / o r g ro und e d ic e b e rg s [Gile s e t al., 2008]. Fa st ic e c a n fo rm a nd b re a k o ut a nnua lly [He il, 2006; Frase r e t al., 2012], o r c a n a tta in g re a t a g e s a nd thic kne sse s in re g io ns whe re the ic e is mo re tig htly lo c ke d to the c o a sta l ma rg ins [Masso m e t al., 2010]. THE ROLE OF ANTARCTIC SEA ICE IN THE CLIMATE SYSTEM Why is se a ic e importa nt? Anta rc tic se a ic e fo rms a re la tive ly thin b ut se a so na lly-e xte nsive a nd hig hly-d yna mic c o ve r o n the surfa c e o f the hig h-la titud e So uthe rn Oc e a n tha t is intima te ly tie d to p a tte rns o f a tmo sp he ric a nd o c e a nic te mp e ra ture a nd c irc ula tio n. As a re sult, it is o ne o f the mo st se nsitive ind ic a to rs o f c lima te c ha ng e a nd va ria b ility o n Ea rth. Cruc ia lly, the ic e c o ve r is no t o nly a ffe c te d b y a c ha ng ing a nd va ria b le e nviro nme nt, it a lso p la ys a n a c tive tho ug h p o o rly-und e rsto o d ro le in mo d ula ting suc h c ha ng e a nd va ria b ility via its inluence on the ocean and atmosphere. Thus the sea ice, ocean and atmosphere fo rm a c o mp le x inte ra c tive syste m. On sho rte r time sc a le s, it is intima te ly tie d to the we a the r, a nd re sp o nd s ra p id ly to c ha ng e s in wind d ire c tio n a nd stre ng th a sso c ia te d with the p a ssa g e o f syno p tic syste ms. In this wa y, the ic e e d g e lo c a tio n c a n va ry b y te ns o f kilo me tre s fro m o ne d a y to the ne xt. The climatic signiicance of Antarctic sea ice lies in the major modifying effect it has o n a tmo sp he re -o c e a n inte ra c tio n p ro c e sse s a nd the surfa c e ra d ia tio n b ud g e t, with the a nnua l c yc le o f a re a l e xp a nsio n a nd c o ntra c tio n c o nstituting o ne o f the la rg e st se a so na l g e o p hysic a l c ha ng e s o n the surfa c e o f the p la ne t. Prima rily, the ic e a c ts a s a n insula ting b la nke t b e twe e n the c o ld a tmo sp he re a nd re la tive ly wa rm o c e a n, a nd a s a p hysic a l b a rrie r to the e xc ha ng e o f mo isture, g a se s a nd mo me ntum b e twe e n the two. Be ing white, sea ice also relects substantially more sunlight back into space than does open o c e a n, whic h is d a rk a nd the re fo re a b so rb s mo re sunlig ht a nd he a ts up. This hig h a lb e d o (relectivity) characteristic of sea ice is important for climate feedback and ampliication p ro c e sse s [Pe ro vic h e t al., 2008]. These effects are strongly modiied by the presence of sub sta ntia l a c c umula tio ns o f sno w o n the surfa c e o f Anta rc tic se a ic e, g ive n the e ve n greater insulating and relective properties of the snow [Sturm and Masso m, 2010]. In g e ne ra l, the d e g re e to whic h se a ic e a ffe c ts o c e a n-a tmo sp he re inte ra c tio ns d e p e nd s o n the ic e e xte nt, its c o nc e ntra tio n a nd its thic kne ss d istrib utio n. Antarctic sea ice also plays a key role in ocean water mass modiication and formation. As it fo rms a nd g ro ws, the ic e e xp e ls sa lt into the und e rlying o c e a n a s b rine, to inc re a se the sa linity a nd d e nsity o f the wa te r c o lumn [To g g we ile r and Samue ls, 1995]. Co nve rse ly a nd in sp ring, se a ic e me lt re le a se s fre she r wa te r, to fo rm a sta b le lo w-sa linity o c e a n surfa c e la ye r. 13

14 WHAT HAS THE MERTZ GLACIER CALVING SHOWN US? Se a ic e pro duc tio n in c o a sta l po lynya s, whic h is c ritic a l to the fo rma tio n o f Anta rc tic Bo tto m Wa te r (AABW), ha s de c line d signiicantly off George V Land in East Antarctica since the calving of the Me rtz Gla c ie r To ng ue in Fe b rua ry Fro m Tamura e t a l. [2012]. Sc ie ntists fro m the ACE CRC use d sa te llite d a ta to d e te c t re g io ns of thin ice and attribute the associated heat lux to estimate se a ic e p ro d uc tio n (c o lo ur sha d e d a b o ve in me tre s p e r ye a r). A 14 20% d e c re a se (re la tive to the me a n fro m ) wa s d e te c te d in se a ic e p ro d uc tio n o ff G e o rg e V La nd in the two winte rs a fte r the g la c ie r to ng ue s c a lving a nd the a sso c ia te d re - alignment of vast iceberg B9B [Tamura et al., 2012]. These indings sug g e st tha t 50% o f this d e c re a se in se a ic e p ro d uc tio n c a n b e a ttrib ute d to the c ha ng e s in the ic e sc a p e p o st-c a lving (thic k re d line ) imp a c ting the d istrib utio n a nd stre ng th o f p o lynya a c tivity. The Me rtz G la c ie r Po lynya is imp o rta nt to g lo b a l c lima te a s a site of signiicant AABW formation [Rinto ul, 1998]. Ano the r ACE CRC stud y, b y Shadwic k e t al. [2013], ha s hig hlig hte d stro ng links b e twe e n this a b rup t na tura l e ve nt a nd b io lo g ic a l productivity and carbon drawdown in the region. Speciically, b re a ko ut a nd me lt o f thic k multi-ye a r fa st ic e re le a se d b y the mo ve me nt o f ic e b e rg B9B a nd the Me rtz G la c ie r To ng ue le d to signiicant input of meltwater into the ocean surface layers. This like ly e nha nc e d the a va ila b ility o f lig ht a nd iro n, sup p o rting a d ia to m b lo o m tha t d o ub le d c a rb o n up ta ke re la tive to p re - c a lving c o nd itio ns. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

15 Pa rtic ula rly hig h ra te s o f o c e a n-a tmo sp he re he a t lo ss a nd re sulta nt ic e fo rma tio n a nd b rine re je c tio n o c c ur in re c urre nt a nd p e rsiste nt a re a s o f o p e n wa te r a nd thin ic e a t c e rta in lo c a tio ns a ro und the Anta rc tic c o a st kno wn a s po lynyas. Within the se re g io ns, se a ic e is swe p t a wa y b y stro ng wind s a nd c urre nts a s q uic kly a s it fo rms. In this wa y, p o lynya s a c t a s ic e fa c to rie s fo r the wid e r se a -ic e zo ne. This e nha nc e d se a -ic e fo rma tio n a nd c o rre sp o nd ing sa lt re je c tio n fo rms c o ld, sa line De nse She lf Wate r tha t in discrete locations can be transported northward across the shelf break, with suficient d e nsity to mix d o wn the c o ntine nta l slo p e a nd p ro d uc e Antarc tic Bo tto m Wate r (AABW). This AABW in turn p la ys a ke y ro le in d riving g lo b a l o c e a n the rmo ha line c irc ula tio n. As suc h, Anta rc tic c o a sta l p o lynya s in the so uthe rn We d d e ll a nd Ro ss se a s a nd a d ja c e nt to the Mertz Glacier tongue and Cape Darnley in East Antarctica are of global signiicance in spite of being relatively small (10s to 100s of kilometres across). In this way, the inluence o f se a ic e re a c he s the o c e a n a b yss a s we ll a s the tro p ic s [Rinto ul e t al., 2001]. Mo re o ve r, High-Salinity Shelf Water a sso c ia te d with se a ic e fo rma tio n c o ntro ls c irc ula tio n a nd me lt p ro c e sse s und e r ic e she lve s [Galton-Fenzi et al., 2012]. It fo llo ws tha t a ny la sting c ha ng e to p o lynya syste ms c o uld ha ve fa r-re a c hing c lima tic c o nse q ue nc e s. Altho ug h fa st ic e c o mp rise s a re la tive ly sma ll fra c tio n o f o ve ra ll se a ic e a re a it va rie s se a so na lly b e twe e n 5% (in winte r) a nd 35% (in summe r) fo r Ea st Anta rc tic a (Fig ure 3) [Frase r e t al., 2012] - it is imp o rta nt fo r a numb e r o f ke y re a so ns. Fo r o ne thing, it to o is a se nsitive ind ic a to r o f c lima te c ha ng e a nd va ria b ility a ro und the Anta rc tic c o a sta l ma rg ins [Murphy e t al., 1995; He il, 2006]. It c a n a lso a tta in a c o nsid e ra b le thic kne ss, o f >5 m in p la c e s [Masso m e t al., 2010], and thus represents a signiicant freshwater store. Mo re o ve r, fa st ic e p la ys a n ind ire c t ro le in g lo b a l the rmo ha line o c e a n c irc ula tio n b y fo rming a ma jo r c o mp o ne nt in c o a sta l p o lynya syste ms [Tamura e t al. 2012], a nd it ma y in certain regions around the Antarctic coast act to mechanically stabilise loating glacier to ng ue s a nd ic e she lve s [Masso m e t al., 2010]. La st b ut no t le a st, its p re se nc e c a n b o th imp e d e a nd fa c ilita te lo g istic a l a c c e ss to Anta rc tic b a se s. In a d d itio n to its imp o rta nt p hysic a l ro le, se a ic e d o mina te s the p hysic a l a nd c he mic a l se a so na l d yna mic s o f the hig h-la titud e So uthe rn Oc e a n a nd p la ys a c ruc ia l ro le in ma rine e c o syste ms [Sme tac e k and Nic o l, 2005; Tho mas and Die c kmann, 2010]. Aro und the c o a st, fa st ic e fo rms a c ruc ia l b re e d ing p la tfo rm fo r Emp e ro r p e ng uins (Apte no dyte s fo rste ri) a nd We d d e ll se a ls (Le pto nyc ho te s we dde lli) [Ko o yman and Burns, 1999], a nd its b re a kup a nd the re sulta nt re le a se o f nutrie nts a nd fre shwa te r into the wa te r c o lumn ha s b e e n a sso c ia te d with a lg a l b lo o ms [Shadwic k e t al., 2013]. Importa nt c ha ng e s In the p a st fe w ye a rs, a n inc re a sing numb e r o f he a d line s ha ve re p o rte d d ra ma tic c ha ng e s o c c urring in the hig h la titud e s (b o th no rth a nd so uth) - with Arc tic summe rtime (minimum a nnua l) se a ic e e xte nt re a c hing a re c o rd minimum in 2012 sinc e sa te llite re c o rd s b e g a n in 1979 [Simmo nds and Rude va, 2012] a nd ic e she lve s d isinte g ra ting a lo ng the Anta rc tic Pe ninsula [Co o k and Vaug han, 2010]. This ind ic a te s tha t c lima te c ha ng e is o c c urring a lre a d y, a nd in a wa y tha t wa s no t fo re se e n o nly a fe w ye a rs a g o. 15

16 In re sp o nse to a wa rming c lima te, a nnua l me a n Anta rc tic se a ic e e xte nt a nd vo lume is fo re c a st to re d uc e b y 24% a nd 34%, re sp e c tive ly, b y 2100 [Arze l e t al., 2006], with the mo st p ro no unc e d re d uc tio n b e ing a t the e nd o f summe r. This c o uld ha ve fa r-re a c hing e ffe c ts o n g lo b a l c lima te a nd ma rine e c o syste ms. It wo uld a lso a llo w g re a te r a c c e ss to Anta rc tic wa te rs fo r b o th c o mme rc ia l a nd re se a rc h ve sse ls. RECENT CHANG ES IN ANTARCTIC SEA ICE Se a ic e e xte nt: Anta rc tic ve rsus Arc tic Sinc e 1979, whe n re lia b le se a ic e d a ta b e c a me a va ila b le fro m sa te llite se nso rs, the two p o la r re g io ns ha ve e xp e rie nc e d ma rke d ly d iffe re nt tre nd s in the o ve ra ll (c irc ump o la r) e xte nt o f se a ic e c o ve ra g e. In the Arc tic, the e xtra o rd ina ry d e c line in a nnua l se a ic e e xte nt - of % per decade (95% conidence level) for the period [IPCC, 2013] - is o ne o f the mo st d ra ma tic a nd c o nsp ic uo us e xa mp le s o f c lima te c ha ng e a nywhe re o n Ea rth [Pe ro vic h, 2011]. The ra te o f se a ic e lo ss in the Arc tic, whic h is p a rtic ula rly stro ng in summe r, is e ve n mo re ra p id tha n tha t p re d ic te d b y mo d e ls [Stro e ve e t al., 2007], a nd ha s initia te d stro ng c lima te fe e d b a c ks tha t ha ve e nha nc e d the wa rming in the re g io n [Sc re e n and Simmo nds, 2010]. By c o ntra st a nd a s de pic te d in Fig ure 4a, a nnua l se a ic e e xte nt a ro und Anta rc tic a ha s shown a small increasing trend of % per decade (around 95% conidence level) fo r 1979 to 2012 [IPCC, 2013]. The c a use o f the c o ntra sting re sp o nse s o f the two p o la r se a -ic e c o ve rs is sub je c t to live ly d e b a te, b ut is tho ug ht to re la te to d iffe re nc e s in the ir g e o g ra p hic a l se tting s, re sp e c tive se a ic e g ro wth a nd d e c a y p ro c e sse s, la rg e -sc a le c lima te inte ra c tio ns, a nd ic e -o c e a n inte ra c tio ns a nd fe e d b a c ks [Turne r and Ove rland, 2009; Maksym e t al, 2012]. The slig ht e xp a nsio n o b se rve d in o ve ra ll Anta rc tic se a -ic e a re a l e xte nt in fa c t ma sks d ra ma tic re g io na lly-c o ntra sting c ha ng e s tha t ha ve o c c urre d in b o th the e xte nt a nd se a so na lity o f se a ic e c o ve ra g e [Co miso e t al., 2011; Stamme rjo hn e t al., 2012]. Fo r ic e e xte nt, the se re g io na l d iffe re nc e s in tre nd s a re sho wn in Fig ure 4. Mo st no ta b ly, se a ic e e xte nt ha s inc re a se d in the Ro ss Se a se c to r b y 5.0 ±0.6% p e r d e c a d e (fo r the p e rio d ), while ma jo r lo ss ha s o c c urre d in the Be lling sha use n/ Amund se n se a s se c to r (a t a ra te o f -7.1% ±0.9% p e r d e c a d e ). By c o mp a riso n, tre nd s in the re ma ining Anta rc tic se c to rs a re simila r to the o ve ra ll c irc ump o la r tre nd. As suc h, the o b se rve d tre nd to wa rd s inc re a se d Anta rc tic se a ic e e xte nt o ve ra ll is in fa c t the sum o f simila r tre nd s in Ea st Anta rc tic a a nd muc h la rg e r a nd o p p o sing tre nd s in We st Anta rc tic a. A numb e r o f hyp o the se s ha ve b e e n p ro p o se d ; a ll sug g e st tha t the re sp o nse o f Anta rc tic se a ic e to c lima te c ha ng e (a nd va ria b ility) is fa r fro m simp le. A re c e nt sa te llite -b a se d stud y, fo r e xa mp le, sug g e sts tha t wind -d rive n c ha ng e s in se a ic e a d ve c tio n a re a d o mina nt d rive r o f tre nd s a ro und muc h o f We st Anta rc tic a, whe re a s wind -d rive n the rmo d yna mic c ha ng e s d o mina te e lse whe re [Ho lland and Kwo k, 2012]. Othe r stud ie s ha ve p ro p o se d tha t c ha ng e s in a tmo sp he ric te mp e ra ture a nd wind stre ss [fo r e xa mp le Liu e t al., 2004; Turne r e t al., 2009; Le fe b vre and Go o sse, 2008] to g e the r with ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

17 Fig ure 4. Tre nds in mo nthly ic e e xte nt, de rive d fro m sa te llite da ta a nd e xpre sse d a s a no ma lie s a g a inst the lo ng -te rm me a n ( ), in the (a ) e ntire So uthe rn Oc e a n, (b ) We dde ll Se a, (c ) India n Oc e a n, (d) Western Paciic Ocean, (e) Ross Sea, and (f) Bellingshausen/Amundsen seas. From Co miso e t al., Lo c a tio ns a re ma rke d o n Fig ure 1. 17

18 c ha ng e s in p re c ip ita tio n [Liu and Curry, 2010], o c e a n te mp e ra ture [Jac o b s and Co miso, 1997; Me re dith and King, 2005], a nd a tmo sp he re a nd / o r o c e a n fe e d b a c ks [Zhang, 2007; Stamme rjo hn e t al., 2012] a re re sp o nsib le. The re ma y a lso b e a n imp o rta nt link to the ic e she e t. Bintanja e t al. [2013] p ro p o se tha t e nha nc e d inp ut o f me ltwa te r fro m b a sa l me lting o f Anta rc tic ic e she lve s (Pritc hard e t al. [2012]) into the up p e r o c e a n le a d s to the fo rma tio n o f a re la tive ly c o o l a nd fre sh surfa c e la ye r tha t shie ld s the surfa c e o c e a n fro m the wa rme r d e e p e r wa te rs. The se surfa c e la ye rs c a n the n fre e ze mo re e a sily, whic h c o uld e xp la in why o b se rve d o ve ra ll Anta rc tic se a -ic e e xte nt tre nd s p e a k in a utumn a nd e a rly winte r. Und e rp inning the c ha ng e s a nd re g io na l c o ntra sts o utline d a b o ve a re la rg e -sc a le p a tte rns o f a tmo sp he ric fo rc ing a sso c ia te d with the So uthe rn Annula r Mo d e (SAM) a nd to El Niño -So uthe rn Osc illa tio n (ENSO)-re la te d te le c o nne c tio ns a c ro ss the so uthe rn Paciic Ocean [for example Re nwic k, 2002; Yuan and Li, 2008; Stamme rjo hn e t al., 2008; Turne r e t al., 2009; Pe zza e t al., 2012]. Cruc ia lly, the d o mina nt c irc ump o la r we ste rly wind b e lt o ve r the So uthe rn Oc e a n ha s stre ng the ne d b y 15-20% a nd ha s mig ra te d p o le wa rd s b y 1-2 o f la titud e sinc e the la te 1970s [Ko rho ne n e t al., 2010; Turne r and Marshall, 2011]. This c ha ng e ha s b e e n linke d to a c ha ng e in the a tmo sp he ric p re ssure g ra d ie nt in the So uthe rn He misp he re : p re ssure ha s inc re a se d a t mid -la titud e s b ut d e c re a se d a ro und the Anta rc tic c o a st [Tho mpso n e t al., 2011]. The SAM, whic h is a me a sure o f this g ra d ie nt a nd is the d o mina nt mo d e o f va ria b ility in a tmo sp he ric c irc ula tio n a t hig h so uthe rn la titud e s [Simmo nds, 2003], ha s c ha ng e d to a mo re p o sitive p ha se in the a ustra l summe r a nd a utumn o ve r the p a st ha lf c e ntury. This c ha ng e ha s b e e n linke d to o zo ne d e p le tio n [Gille tt e t al., 2009; Tho mpso n e t al., 2011] a nd inc re a se d g re e nho use g a s c o nc e ntra tio ns in the a tmo sp he re [Marshall e t al., 2004]. It ha s b e e n no te d e lse whe re tha t c ha ng e a nd va ria b ility in ke y la rg e -sc a le c lima te mo d e s suc h SAM a nd ENSO c o uld a lso a rise thro ug h na tura l va ria b ility [Ho lland and Kwo k, 2012]. A ke y fa c to r a ffe c ting the d ra ma tic c ha ng e s in se a ic e e xte nt in the We st Anta rc tic se c to r ha s b e e n the d e e p e ning o f the Amund se n Se a Lo w (ASL), whic h is a re c urre nt low atmospheric pressure anomaly in the South Paciic, due to the increased intensity of westerly winds and the geographical coniguration of the Antarctic continent [Turne r e t al., 2013a ]. Re sulta nt stro ng e r a nd / o r mo re p e rsiste nt so uthe rly (c o ld e r) wind s a lo ng the western lank of the ASL have generated more extensive sea ice in the Ross Sea, while no rthe rly (wa rme r) wind s in the Be lling sha use n Se a ha ve le d to le ss e xte nsive ic e the re. Pro xy info rma tio n o n histo ric a l se a ic e e xte nt whic h c a n b e o b ta ine d fro m ic e c o re s fro m the Anta rc tic Ic e She e t [Curran e t al., 2003] a nd so urc e s suc h a s wha ling d a ta [de la Mare 1997, 2008] a re c ruc ia l in te rms o f e xte nd ing the sa te llite d a ta re c o rd b a c k in time (b e fo re the 1970s) - to p la c e re c e nt c ha ng e / va ria b ility into lo ng e r-te rm c o nte xt. Fo r e xa mp le, ic e c o re d a ta fro m the Anta rc tic Pe ninsula sug g e st tha t se a ic e d e c line in the Be lling sha use n Se a sinc e 1979 is p a rt o f a tre nd tha t ha s p e rsiste d sinc e the e a rly 1900s d ue to a p ro g re ssive d e e p e ning o f the Amund se n Se a Lo w [Ab ram e t al., 2010]. Se a ic e se a sona lity In a d d itio n to se a ic e e xte nt, c ha ng e s in se a -ic e se a so na lity a re c ruc ia lly imp o rta nt fo r a ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

19 numb e r o f re a so ns [Masso m and Stamme rjo hn, 2010; Maksym e t al., 2012]. Ic e -fre e summe r d ura tio n c o ntro ls so la r he a ting a nd wind -mixing o f the up p e r o c e a n [Montes-Hugo et al., 2009; Pe ro vic h e t al., 2008], thus a ffe c ting se a -surfa c e te mp e ra ture s [Me re dith and King, 2005] a nd o c e a n up we lling [Martinso n, 2012]. Mo re o ve r, the life c yc le s o f hig h-la titud e marine organisms (from micro-organisms to whales) are speciically adapted to sea ice a nd its se a so na l rhythms [Tho mas and Die c kmann, 2010], a nd se rio us c o nse q ue nc e s c a n a rise whe n the se rhythms c ha ng e (se e Se c tio n 4). Bellingshausen Sea Western Ross Sea Figure 5. Tre nds in the le ng th o f the Anta rc tic se a ic e -c o ve re d se a so n (ic e dura tio n) fo r the pe rio d 1979/ / 11. The se a re de rive d fro m da ily sa te llite ic e e xte nt re c o rds (1979-pre se nt), whic h ha ve b e e n use d to de te rmine, fo r e a c h se a ic e ye a r (Fe b rua ry to Fe b rua ry) a nd e a c h sa te llite pixe l lo c a tio n, the da y se a ic e a dva nc e d to tha t lo c a tio n a nd the da y it re tre a te d fro m tha t lo c a tio n. Me tho ds a re de sc rib e d in Stamme rjo hn e t al. [2008], a fte r Parkinso n [2002]. The b la c k line s de no te the me a n minimum a nd ma ximum ic e e xte nts fo r the sa me time pe rio d. Fro m Maksym e t al. [2012]. Stro ng ly c o ntra sting re g io na l c ha ng e s ha ve a lso o c c urre d in timing s o f a nnua l se a -ic e a d va nc e a nd re tre a t a nd re sulta nt se a ic e d ura tio n a ro und Anta rc tic a (Fig ure 5). In c o ntra st to the Arc tic, whe re mo st re g io ns sho w tre nd s to wa rd s sho rte r se a ic e d ura tio n, p a tte rns o f re g io na l-sc a le c ha ng e in Anta rc tic se a ic e se a so na lity a re a c c e ntua te d b y two re g io ns in p a rtic ula r [Simpkins e t al., 2013; Stamme rjo hn e t al., 2012]. The se a re the Anta rc tic Pe ninsula -Be lling sha use n Se a (AP-BS) a nd We ste rn Ro ss Se a (WRS) re g io ns. Of ma jo r c o nc e rn fro m b o th a p hysic a l a nd b io lo g ic a l p e rsp e c tive is a sub sta ntia l sho rte ning o f the se a ic e se a so n (le ng the ning o f the o p e n wa te r se a so n) in the AP-BS re g io n o f 3.3 mo nths o ve r the p e rio d 1979/ 80 to 2010/ 11. This e xtra o rd ina ry c ha ng e re sults fro m la te r a d va nc e (b y ~2 mo nths) a nd e a rlie r re tre a t (b y ~1.3 mo nths). In fa c t, the ra te o f inc re a se in ic e -fre e c o nd itio ns in the Be lling sha use n Se a re g io n (o f 3.1 ±1.0 d a ys p e r ye a r a s d e p ic te d in Fig ure 5) is e ve n g re a te r tha n tha t whic h is o c c urring in re g io ns o f g re a te st ic e lo ss in the Arc tic [Stamme rjo hn e t al., 2012]. 19

20 In stark contrast, the annual sea ice season in the WRS region has signiicantly lengthened, b y ~2.6 mo nths o ve r the p e rio d 1979/ 80 to 2010/ 11. He re, e a rlie r se a ic e a d va nc e (b y ~1.4 mo nths) is fo llo we d b y a la te r re tre a t (b y ~1.2 mo nths). By c o mp a riso n, a nd a s sho wn in Fig ure 6, p a tte rns o f c ha ng e in the re la tive ly na rro w Ea st Anta rc tic se a -ic e zo ne a re fa r mo re c o mp le x, c o mp rising mixe d sig na ls o n re g io na l to lo c a l sc a le s [Masso m e t al., 2013]. Ind e e d, p o c ke ts o f stro ng ly p o sitive a nd ne g a tive tre nd s in ic e se a so n d ura tio n (o f ±2-3 d a ys p e r ye a r) o c c ur in ne a r juxta p o sitio n in c e rta in re g io ns, fo r e xa mp le Pryd z Ba y. A ne g a tive tre nd in se a ic e d ura tio n (o f -1 to -3 d a ys p e r a nnum) o c c urs in fa irly iso la te d p o c ke ts in the o ute r se a ic e zo ne a t ~60 S to 62 S a nd ~95 E to 110 E, a nd in va rio us ne a r-c o a sta l a re a s, inc lud ing a n a re a o f p a rtic ula rly stro ng a nd p e rsiste nt c ha ng e ne a r Da vis Sta tio n a nd b e twe e n the Ame ry a nd We st Ic e She lve s. The se a re a s a re la rg e ly a sso c ia te d with c o a sta l p o lynya s tha t a re re g io na llyimp o rta nt a s site s o f e nha nc e d se a ic e p ro d uc tio n/ me lt. 54 Longitude, o E Trend in Duration, 1979/ /10 58 Latitude, o S Mawson Syowa Shorter -3 Davis -2 Casey DD MGT Longer Days per year Cape Adare Fig ure 6. Ma p o f tre nds in se a ic e se a so n dura tio n a c ro ss Ea st Anta rc tic a, fo r the pe rio d 1979/ / 10. Co nto urs de no te sta tistic a l signiicance at the 95% level. DD is Dumo nt d Urville a nd MGT Me rtz Gla c ie r To ng ue. Fro m Masso m e t al. [2013]. While the inte rp la y b e twe e n la rg e -sc a le a tmo sp he ric p a tte rns (like SAM a nd ENSO) to some extent explains sea ice variability in the South Paciic sector of the Southern Ocean, it d o e s no t e xp la in re g io na l c ha ng e s o b se rve d e lse whe re a ro und Anta rc tic a. Mo re o ve r, it fa ils to a c c o unt fo r the p o te ntia lly imp o rta nt ro le o f o c e a n fo rc ing a nd fe e d b a c ks. The o b se rve d ma g nitud e a nd timing o f se a so na l/ re g io na l se a ic e c ha ng e s in fa c t p o int to invo lve me nt o f stro ng p o sitive fe e d b a c ks. Fo r e xa mp le, a stro ng re la tio nship b e twe e n sp ring se a ic e re tre a t a nd sub se q ue nt a utumn a d va nc e o b se rve d in the AP-BS (a nd WRS) re g io ns is c o nsiste nt with a n e a rlie r (la te r) sp ring re tre a t le a d ing to inc re a se d (d e c re a se d ) so la r he a ting o f the up p e r o c e a n, whic h the n re sults in a la te r (e a rlie r) se a ic e a d va nc e in the fo llo wing a utumn [Stamme rjo hn e t al., 2012]. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

21 Se a ic e thic kne ss a nd volume In the Arc tic, a c o mb ina tio n o f sub ma rine so na r a nd e xte nsive sa te llite a ltime te r d a ta ha s re ve a le d a sub sta ntia l thinning o f the ic e c o ve r the re tha t is c o nsiste nt with the lo ss o f p e re nnia l ic e fro m the Arc tic Ba sin [Ro thro c k e t al., 2008; Kwo k and Ro thro c k, 2009]. Ho we ve r, no suc h d a ta a re a va ila b le fo r the Anta rc tic se a ic e zo ne, whe re o ur c urre nt kno wle d g e o f se a -ic e thic kne ss is limite d to c o mp ila tio ns o f va rio us in-situ a nd re mo te se nsing o b se rva tio ns [fo r e xa mp le Wo rb y e t al., 2008] tha t a re c ha ra c te rise d b y la rg e sp a tio -te mp o ra l g a p s a nd ma y b e b ia se d to wa rd s thinne r ic e [Maksym e t al., 2012], a nd ic e c ha rt a nd sa te llite a ltime te r d a ta tha t a re limite d to c e rta in se c to rs o r sho rt time p e rio d s [fo r e xa mp le Zwally e t al., 2008; De Lib e rty e t al., 2011; Yi e t al., 2011; Kurtz and Markus, 2012]. As suc h, imp o rta nt la rg e -sc a le c ha ng e s in Anta rc tic se a -ic e thic kne ss a nd vo lume ma y b e g o ing unno tic e d. Sa te llite re mo te se nsing, using la se r a nd ra d a r a ltime te rs suc h a s tho se o nb o a rd ICESa t a nd Cryo Sa t 2 to a c c ura te ly me a sure surfa c e e le va tio n re la tive to se a le ve l [Yi e t al., 2011; Laxo n e t al., 2013], c le a rly re p re se nts the o nly p ra c tic a l me a ns o f b rid g ing this c ritic a l g a p [Fig ure 7]. Unfo rtuna te ly, ho we ve r, the re a re c o nsid e ra b le c ha lle ng e s to d e riving a c c ura te a nd re lia b le se a -ic e thic kne ss e stima te s fro m the se d a ta in the Anta rc tic c o mp a re d to the Arc tic. The se c ha lle ng e s a re a sse sse d la te r in this d o c ume nt. Figure 7. Estima te s (unc a lib ra te d) o f Anta rc tic se a ic e fre e b o a rd (surfa c e he ig ht a b o ve se a le ve l) a t the e nd o f winte r in Oc to b e r 2011, de rive d fro m Cryo Sa t 2 ra da r a ltime te r da ta. Co nve rting sa te llite fre e b o a rd me a sure me nts to ic e thic kne sse s re ma ins a pre ssing c ha lle ng e, re q uiring a c c ura te inde pe nde nt info rma tio n o n sno w thic kne ss a nd vo lume a nd ic e de nsity [Zwally e t al., 2008]. Da ta suc h a s the se o nly re c e ntly b e c a me a va ila b le a nd pre se nt a n e xc iting ne w de ve lo pme nt in sa te llite re mo te se nsing, pro viding the third dime nsio n o f se a ic e e stima te s. Fig ure c o urte sy Ra c he l Tilling, Ka tha rine Gile s, Andy Rido ut (a ll CPOM, UCL) a nd Na tha n Kurtz (NASA). 21

22 AN INTEGRATED AIRBORNE IMAGING SYSTEM: BRIDGING THE GAP BETWEEN HIGHLY DETAILED IN- SITU OBSERVATIONS AND LARGE SCALE SATELLITE REMOTE SENSING. The Austra lia n Anta rc tic p ro g ra m d e p lo ys a n a irb o rne multise nso r p la tfo rm to d e te rmine a ra ng e o f se a ic e p hysic a l p a ra me te rs. The instrume nte d he lic o p te r sho wn c a rrie s a d o wnwa rd -lo o king sc a nning LiDAR a nd the rma l infra re d te mp e ra ture se nso r (p yro me te r) und e r the c o wling in the fro nt, a nd a d o wnwa rd lo o king hig h-re so lutio n, me d ium fo rma t d ig ita l camera in the camera bucket below the loor of the helicopter. The LiDAR p ro vid e s info rma tio n o n c o mb ine d se a ic e a nd sno w c o ve r surfa c e e le va tio n (fro m whic h se a ic e thic kne ss c a n b e c o mp ute d ); the p yro me te r me a sure s the te mp e ra ture o f the surfa c e ; a nd the c a me ra re c o rd s a re a l c o ve ra g e o f se a ic e a nd ro ug hne ss c ha ra c te ristic s. A sno w thic kne ss ra d a r is a c ruc ia l fourth scientiic payload and is being developed. This will enable mo re p re c ise e stima te s o f the sno w c o ve r thic kne ss o n se a ic e, whic h is o ne o f the imp o rta nt va ria b le s whe n c o mp uting se a ic e thic kne ss fro m surfa c e e le va tio n d a ta. All o f the se instrume nts a re b e ing use d to c a lib ra te a nd va lid a te sa te llite re mo te se nsing d a ta, fo r e xa mple fro m Cryo Sa t-2 (c a rrying a ra d a r a ltime te r), o r the rma l infra re d d a ta fro m po la r- o rb iting sa te llite s. Suc h a irb o rne c a pa b ility is ke y to linking in-situ o b se rva tio ns ma d e o n a ve ry sma ll lo c a l sc a le (100s o f me tre s) with sa te llite d a ta o n muc h la rg e r (re g io na l to he misphe ric ) sc a le s. to impro ving g e o physic a l pro d uc ts d e rive d fro m the la tte r. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

23 While sa te llite s ho ld the ke y to the la rg e -sc a le mo nito ring o f se a ic e thic kne ss, in-situ mo nito ring p ro g ra mme s re ma in c ruc ia lly imp o rta nt in the fa st-ic e zo ne, whe re the ic e thic kne ss is intima te ly a sso c ia te d with a tmo sp he ric a nd o c e a nic c irc ula tio n a nd te mp e ra ture. Und e r the a usp ic e s o f the inte rna tio na lly c o o rd ina te d Anta rc tic Fa st- Ic e Ne two rk (AFIN) [He il e t al., 2011a ], susta ine d me a sure me nts o f fa st-ic e thic kne ss, fre e b o a rd a nd sno w thic kne ss a re c o nd uc te d a t six lo c a tio ns o ff the Anta rc tic c o a st. Me a sure me nts a re ta ke n a b o ut o nc e a we e k. Se ve ra l AFIN lo c a tio ns ind ic a te inc re a se d inte ra nnua l va ria b ility in a nnua l ma ximum ic e thic kne ss o ve r the la st 15 ye a rs, a c c o mp a nie d b y mo re fa st-ic e b re a ko ut e ve nts thro ug ho ut a ye a r whic h re d uc e the inte g ra te d fa st-ic e vo lume. Ic e dyna mic s In-situ o b se rva tio ns o f Ea st Anta rc tic se a -ic e d rift ha ve sho wn tha t a tmo sp he ric fo rc ing is the ma in d rive r o f ic e mo tio n [He il e t al., 2009, 2011b], with recent intensiication of sto rm a c tivity in c e rta in re g io ns o f Ea st Anta rc tic a le a d ing to inc re a se d d e fo rma tio n a nd rid g ing (a nd the re fo re thic ke ning ) o f the ic e c o ve r [He il e t al., 2011b ]. On the b ro a d e r c irc um-anta rc tic sc a le, sa te llite -d e rive d ic e mo tio n a na lysis [Ho lland and Kwo k, 2012] ha s re ve a le d re g io na l inc re a se s in a utumn-winte r se a ic e sp e e d o f up to 30% fro m 1992 to 2009 mo st no ta b ly in the se c to rs 20 W-20 E a nd 90 W-140 E, with d e c re a se s o f simila r ma g nitud e in the we ste rn-c e ntra l p a rt o f the We d d e ll G yre, the Be lling sha use n Se a a nd o ff muc h o f Ea st Anta rc tic a (Fig ure 8). The se la rg e a nd statistically-signiicant changes are linked to observed changes in surface wind speed a nd d ire c tio n a sso c ia te d with c ha ng e in la rg e -sc a le mo d e s o f c lima te va ria b ility, suc h a s SAM a nd ENSO [Ho lland and Kwo k, 2012]. Othe r wo rk c a rrie d o ut within the ACE CRC (He il e t al., in p ro g re ss) ha s re ve a le d hig h inte ra nnua l va ria b ility in ic e mo tio n. a m s m s 1 yr 1 b Fig ure 8. Anta rc tic a utumn-winte r (Ap ril- Oc to b e r) se a ic e mo tio n tre nd ve c to rs fo r the pe rio d , de rive d fro m sa te llite da ta a nd o ve rla in o n c o lo ur c o de d 19-ye a r c ha ng e in me ridio na l ic e spe e d. Fig ure a da pte d fro m Ho lland and Kwo k [2012]. 23

24 SIPEX 2: A MILESTONE IN UNDERSTANDING ANTARCTIC SEA ICE The Se a Ic e Physic s & Ec o syste ms e Xp e rime nt 2 (SIPEX 2) wa s jo intly c o o rd ina te d b y the ACE CRC a nd the Austra lia n Anta rc tic Division. This multi-disciplinary study was speciically designed to a d d re ss ma jo r kno wle d g e g a p s in Anta rc tic se a ic e zo ne processes as identiied by national and international end-users. It wa s c o nd uc te d using RSV Auro ra Australis in the re g io n o f 100 E to 120 E o ff Ea st Anta rc tic a fro m Se p te mb e r to No ve mb e r 2012, a nd b ro ug ht to g e the r o ve r 50 sc ie ntists fro m nine na tio ns. The inte rna tio na l te a m me a sure d the p hysic a l, b io lo g ic a l a nd b io g e o c he mic a l p ro p e rtie s o f se a ic e o n sma ll-to -re g io na l sc a le s using c la ssic a l me tho d s a nd sta te -o f-the -a rt te c hno lo g y, inc lud ing ic e c o ring surve ys, re mo te ly-o p e ra te d a nd a uto no mo us und e rwa te r ve hic le s, d rifting b uo ys a nd instrume nte d he lic o p te rs. Da ta fro m the vo ya g e b e ing p ro c e sse d b y ACE CRC a nd inte rna tio na l re se a rc he rs will e nha nc e o ur und e rsta nd ing o f the ro le o f se a ic e in Anta rc tic c lima te a nd e c o syste m p ro c e sse s. The se d a ta will a lso b e utilise d in the va lid a tio n o f sa te llite -d e rive d se a ic e thic kne ss p ro d uc ts a nd the p a ra me te risa tio n o f se a ic e p ro c e sse s in c lima te a nd e c o syste m mo d e ls. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

25 An e xa mp le o f the c o lla b o ra tive a nd inte g ra tive d a ta c o lle c te d d uring SIPEX 2 is sho wn in the g ra p hic b e lo w. At the lo c a l sc a le (o ve r a 100 m 100 m g rid ), c o inc id e nt me a sure me nt o f the ic e d ra ft, fre e b o a rd a nd sno w lo a d ing c a n p ro vid e c ruc ia l three-dimensional information at sub-loe scale. This is now possible through the new methodologies for in-situ ieldwork using a uto no mo us und e rwa te r ve hic le s (AUV) a nd la se r a nd G PS te c hno lo g ie s [Williams e t al., 2013]. An AUV fro m the Wo o d s Ho le Oc e a no g ra p hic Institutio n (WHOI), e q uip p e d with a swa th multi-b e a m so na r, o b ta ine d hig h-re so lutio n g e o lo c a te d 3-D ma p s o f Anta rc tic se a ic e d ra ft. Co inc id e nt, hig h-re so lutio n 3-D me a sure me nts o f sno w a nd ic e surfa c e mo rp ho lo g y we re o b ta ine d using te rre stria l la se r sc a nne rs (TLS) a nd a n a uto ma te d sno w p ro b e. The ne xt ste p s in this a p p ro a c h a re to e xte nd the methodology beyond sub-loe scale - to provide regional sa mp ling using, fo r e xa mp le, p o we rful a uto no mo us und e rwa te r and airborne instrument packages. The success of these loe-scale missions could pave the way for a new era of ield experiments c a p a b le o f e xp lo ring o c e a n a nd se a ic e p ro c e sse s o n sc a le s up to kilo me tre s. This inc re a se in sc a le is imp o rta nt fo r the g o a l o f d ire c tly linking in-situ d a ta with sa te llite se nso r fo o tp rints a nd c o up le d c lima te mo d e l g rid c e lls a nd e c o syste m stud ie s. Se a ic e surfa c e e le va tio n a nd d ra ft a nd sno w surfa c e e le va tio n d a ta a s c o lle c te d a t a typic a l se a ic e sta tio n d uring SIPEX 2 (units in me tre s). TLS a nd sno w pro b e d a ta c o urte sy Te d Ma ksym (WHOI) a nd Erne sto Trujillo (CRYOS, EPFL). Fro m Williams e t al.,

26 Fa st ic e Recent work conducted at the ACE CRC produced the irst high-resolution time series o f fa st ic e ma p s fo r the Ea st Anta rc tic c o a st (c o ve ring the Ind ia n Oc e a n a nd We ste rn Paciic Ocean sectors) [Frase r e t al., 2012]. This stud y sho ws tha t fa st-ic e c o ve ra g e displays large inter-annual variability, but no statistically-signiicant trend, in the Western Paciic Ocean sector. In contrast, the Indian Ocean sector showed relatively smaller variability, but a statistically-signiicant positive trend in fast ice extent of 4.1 ±0.4% per ye a r. Ho we ve r, the se c a lc ula tio ns a re b a se d o n a sho rt p e rio d o nly (~9 ye a rs, ), a nd a lo ng e r time se rie s is re q uire d to c o nc lusive ly id e ntify lo ng -te rm tre nd s. Exte nd ing the fa st ic e re c o rd b o th te mp o ra lly a nd to c irc um-anta rc tic is a n o ng o ing fo c us o f wo rk a t the ACE CRC. SEA ICE IN SOUTHERN OCEAN BIOGEOCHEMICAL CYCLES AND ECOSYSTEMS Se a ic e is a ke y d rive r o f So uthe rn Oc e a n b io g e o c he mic a l c yc le s a nd p la ys a n imp o rta nt ro le in struc turing Anta rc tic ma rine e c o syste ms [Tho mas and Die c kmann, 2010]. Anta rc tic se a ic e c o ve r a ffe c ts the So uthe rn Oc e a n c he mic a l a nd b io lo g ic a l p ro c e sse s in va ria b le a nd c o mp le x wa ys [Masso m and Stamme rjo hn, 2010; Vanc o ppe no lle e t al., 2013]. Cha ng e s in se a ic e will the re fo re ha ve multip le imp a c ts o n the So uthe rn Oc e a n b y a ffe c ting its e le me nta l c yc ling, p ro d uc tivity a nd fo o d we b struc ture s. While ma ny coupled sea ice physical-chemical-biological processes have been identiied, they are not generally well understood or quantiied at large scales. The potential future impacts o f c ha ng ing se a ic e o n So uthe rn Oc e a n b io g e o c he mistry a nd e c o syste m struc ture a nd func tio n a re the re fo re hig hly unc e rta in. Se a ic e biog e oc he mistry Re c e nt o b se rva tio ns sho w tha t iro n a c c umula te s in se a ic e d uring a utumn a nd winte r a nd is re le a se d b a c k into the o c e a n in sp ring [Lannuze l e t al., 2007; van de r Me rwe e t al., 2011]. Iro n is a n e sse ntia l nutrie nt fo r a lg a l g ro wth. The So uthe rn Oc e a n is a hig h-nutrie ntlo w-c hlo ro p hyll a re a, whic h is c ha ra c te rise d b y hig h c o nc e ntra tio ns o f ma c ro nutrie nts (fo r e xa mp le nitra te a nd p ho sp ha te ) b ut lo w c o nc e ntra tio ns o f iro n. The re fo re iro n a va ila b ility is a ke y fa c to r c o ntro lling a lg a l g ro wth in the So uthe rn Oc e a n a nd se a ic e c a n a c t a s a ma jo r iro n sto re [Lannuze l e t al., 2007]. Re le a se o f iro n d uring ic e me lt c o ntrib ute s to the d e ve lo p me nt o f ic e -e d g e b lo o ms whic h se rve a s e c o lo g ic a l ho tsp o ts p ro vid ing fo o d fo r Anta rc tic krill (Euphausia supe rb a ). The krill a re in turn e xp lo ite d b y ma ny hig he r p re d a to rs inc lud ing se a ls, se a b ird s a nd wha le s, whic h o fte n c o ng re g a te a t re tre a ting ic e e d g e s (fo r e xa mp le Nic o l e t al. [2008]). Pre vio usly, se a ic e wa s b e lie ve d to b e imp e rme a b le to g a se s. La rg e -sc a le o c e a n- a tmo sp he re c a rb o n d io xid e (CO 2 ) e xc ha ng e wa s tho ug ht to o c c ur o nly d uring the o p e n water season. However, recent studies point towards signiicant CO 2 luxes through sea ic e, mo d ula te d b y a p e rme a b le se a ic e c o ve r a nd d yna mic b io lo g ic a l a nd c he mic a l p ro c e sse s within the se a ic e [De lille e t al., 2007; No mura e t al., 2010; Rysg aard e t al., 2007]. Current knowledge suggests that sea ice is permeable to gas luxes and can act a s b o th a so urc e o f CO 2 in winte r a nd a sink in summe r a nd a utumn, a nd thus a ffe c ts the ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

27 o c e a nic up ta ke o f this imp o rta nt g re e nho use g a s in c o mp le x wa ys. On-g o ing re se a rc h is a ime d a t d e te rmining the p ro c e sse s re sp o nsib le fo r the re le a se a nd up ta ke o f va rio us c lima te re le va nt g a se s fro m ic e -c o ve re d o c e a ns [Vanc o ppe no lle e t al., 2013]. Sea ice processes are also considered to make a signiicant contribution to the sulphur c yc le thro ug h the hig h p ro d uc tio n o f d ime thylsulfo nio p ro p io na te (DMSP) b y ic e a lg a e. DMSP se rve s a s a p re c urso r o f sulp ha te a e ro so ls, whic h a re c lo ud c o nd e nsa tio n nuc le i a nd ha ve a p o te ntia l c o o ling e ffe c t o n the p la ne t b y inc re a sing c lo ud a lb e d o [Malin and Kirst, 1997; Ste fe ls e t al., 2007; Tre ve na and Jo ne s, 2006]. Se a ic e a lg a e a nd phytopla nkton Se a ic e fo rma tio n sta rts in a utumn whe n the re a re sub sta ntia l c o nc e ntra tio ns o f mic ro - o rg a nisms in Anta rc tic surfa c e wa te rs. The se o rg a nisms a re inc o rp o ra te d into the ne wly fo rming se a ic e b y p hysic a l p ro c e sse s a nd c re a te d ive rse, ic e -a sso c ia te d mic ro b ia l c o mmunitie s (Tho mas and Die c kmann, 2010 a nd re fe re nc e s the re in). In te rms o f b io ma ss, the se c o mmunitie s a re g e ne ra lly d o mina te d b y mic ro a lg a e. In fa c t, the a lg a e c a n g ro w to suc h hig h b io ma sse s tha t the y d isc o lo ur the se a ic e (Fig ure 9). Figure 9. An overturned irst-year sea ice loe showing the high concentration of algae growing on the unde rside. Pho to b y Ja n L. Lie se r (No ve mb e r 2009, Ea st Anta rc tic a ). 27

28 Ob se rva tio ns a nd mo d e l re sults ind ic a te tha t 10-20% o f the to ta l a nnua l p rima ry p ro d uc tio n in the ic e -c o ve re d p a rts o f the So uthe rn Oc e a n is d e rive d fro m a lg a e whic h live within, o r a re a tta c he d to, the b o tto m o f the se a ic e [Arrig o and Tho mas, 2004; Le g e ndre e t al., 1992]. Ho we ve r, the se e stima te s a re sub je c t to c o nsid e ra b le unc e rta inty as ield observations, which are necessary to validate newly emerging models, remain sp a rse a nd a re c o stly to o b ta in (se e Fig ure 10) [Me ine rs e t al., 2012]. Fig ure 10. Co lo ur c o d e d d o ts sho wing the lo c a tio n o f ic e c o re s a nd the a sso c ia te d ic e -a lg a l p ig me nt (ic e -a lg a l p ig me nt is me a sure d a s millig ra ms o f c hlo ro p hyll-a p e r me tre sq ua re d ). The sp a tia l c o ve ra g e a c ro ss six se c to rs a ro und Anta rc tic a is q uite he te ro g e ne o us, d e mo nstra ting the ne e d fo r mo re c o mp re he nsive d a ta c o lle c tio n. Fro m Me ine rs e t al. [2012]. While the c o ntrib utio n o f se a ic e a lg a e to o ve ra ll p rima ry p ro d uc tivity in the So uthe rn Oc e a n is c o nsid e re d to b e re la tive ly lo w, the se a lg a e p ro vid e a c ritic a l fo o d so urc e fo r ma rine he rb ivo re s suc h a s Anta rc tic krill, e sp e c ia lly d uring winte r a nd e a rly sp ring whe n fo o d in the wa te r c o lumn is sc a rc e [Flo re s e t al., 2012]. A krill fe e d ing a t the und e rsid e o f an ice loe is shown in Figure 11. Whe n se a ic e me lts d uring sp ring a nd summe r, lo w-sa linity a nd le ss-d e nse wa te r is a d d e d to the ocean surface, which creates stratiied conditions that are favourable to algal g ro wth. The me lting ic e re le a se s nutrie nts, inc lud ing iro n a s we ll a s ic e a lg a e, into the sta b le surfa c e la ye r o f the o c e a n whe re the mic ro a lg a e c a n c o ntinue to g ro w. In c o mb ina tio n, the se p ro c e sse s c o ntrib ute to the fo rma tio n o f ma jo r sp ring -time p hyto p la nkto n b lo o ms in the vic inity o f re tre a ting se a ic e e d g e s. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

29 Figure 11. Krill unde r se a ic e. Pho to c o urte sy Ha uke Flo re s (AWI). Fig ure 12. Sa te llite d a ta c o mp o site fro m Ja nua ry 2009 sho wing surfa c e o c e a n c o lo ur ind ic a tive o f a lg a l p ig me nt c o nc e ntra tio n, whic h is me a sure d in millig ra ms o f c hlo ro p hyll-a p e r c ub ic me tre. Da ta a re ta ke n fro m the Se a WiFs sa te llite p ro je c t, ind ic a ting p a tc hine ss in the ic e -e d g e b lo o m a ro und Anta rc tic a. The se a ic e is sho wn in d a rk g re y. Unfo rtuna te ly, sa te llite s c a nno t me a sure a lg a l b io ma ss in the se a ic e zo ne. Fig ure c o urte sy Be n Ra ymo nd (AAD). 29

30 Ic e -e d g e b lo o ms c a n p ro vid e, a t time s a nd in d istinc t re g io ns, a hig hly p ro d uc tive e nviro nme nt sup p o rting hig he r tro p hic le ve ls a nd b io g e o c he mic a l c yc ling [Arrig o e t al., 1998; Smith and Ne lso n, 1985]. Fig ure 12 sho ws the p a tc hine ss o f c hlo ro p hyll-a in a c o mp o site o f sa te llite o c e a n c o lo ur d a ta fo r Ja nua ry 2009, with so me ho t sp o ts o f hig h p ro d uc tivity fo r e xa mp le in the Amund se n Se a, e a ste rn Ro ss Se a a nd e a ste rn Da vis Se a. Cha ng e s in se a ic e e xte nt, thic kne ss a nd / o r d ura tio n a ffe c t b o th the timing a nd ma g nitud e o f se a ic e a lg a l p ro d uc tio n a nd p hyto p la nkto n p ro d uc tio n in the So uthe rn Oc e a n [Smith and Co miso, 2008; Montes-Hugo et al., 2009]. Mo d e ls ind ic a te tha t a d e c re a se in se a ic e e xte nt ma y re sult in a n inc re a se in o ve ra ll ma rine p rima ry p ro d uc tio n d ue to hig he r lig ht a va ila b ility in the ic e -fre e a re a s [Arrig o and Tho mas, 2004; Arrig o e t al., 2008]. Ho we ve r, o the r re se a rc h ind ic a te s tha t a d e c re a se in se a ic e ma y re d uc e So uthe rn Oc e a n iro n sup p ly a nd ma y re d uc e o ve ra ll p ro d uc tio n [Lanc e lo t e t al., 2009; Lannuze l e t al., 2010]. Imp o rta ntly, a d e c re a se in se a ic e e xte nt will re sult in a re d uc tio n in the sp ring time ic e - e d g e a lg a l b lo o ms. While re se a rc h in the we st Anta rc tic Pe ninsula re g io n ha s sho wn a g e ne ra l d e c re a se in p hyto p la nkto n p ro d uc tio n in re la tio n to d e c re a sing se a ic e e xte nt and duration, this response varies signiicantly along a north-south gradient [Montes- Hug o e t al., 2009]. Wildlife and isheries Se a ic e is a ke y ha b ita t fo r Anta rc tic ma rine e c o syste ms, no t just in winte r b ut thro ug ho ut the ye a r [Tho mas and Die c kmann, 2010]. So me sp e c ie s suc h a s Cra b e a te r se a ls (Lo b o do n c arc ino phag us) b re e d o n the mo b ile p a c k ic e while o the rs, suc h a s the We d d e ll se a ls (Le pto nyc ho te s we dde llii) a nd Emp e ro r p e ng uins (Apte no dyte s fo rste ri) (Fig ure 13) re ly o n sta b le la nd fa st ic e a s a b re e d ing p la tfo rm [Ko o yman and Burns, 1999]. Se a ic e c a n a c t a s a b a rrie r se p a ra ting a nima ls fro m the ir fo o d so urc e, a nd c a n a lso a ffe c t the fo o d so urc e itse lf. Ad é lie p e ng uins (Pyg o sc e lis ade liae ) a nd Emp e ro r p e ng uins must c ro ss ma ny te ns o f kilo me tre s o f c o a sta l la nd fa st ic e fro m the ir c o lo nie s o n the Anta rc tic c o ntine nt to re a c h fo o d sup p lie s fo r the mse lve s a nd the ir ne wly ha tc he d o ffsp ring [Emme rso n and So uthwe ll, 2008; Masso m e t al., 2009]. In fa c t, a c lo se re la tio nship ha s b e e n sho wn to e xist b e twe e n a nnua l fa st ic e e xte nt/ tre kking d ista nc e a nd Emp e ro r p e ng uin b re e d ing suc c e ss a t Dumo nt d Urville Sta tio n [Masso m e t al., 2009]. Figure 13. Empe ro r Pe ng uin (Apte no dyte s fo rste ri) ma ting pa ir with ne wly ha tc he d c hic k. Pho to b y Ja n L. Lie se r. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

31 A c lo se re la tio nship b e twe e n winte r se a ic e e xte nt a nd the b io ma ss, c o nd itio n a nd re p ro d uc tive suc c e ss o f krill ha s b e e n d e mo nstra te d in the Anta rc tic Pe ninsula re g io n a nd o ff Ea st Anta rc tic a [Atkinso n e t al., 2004; Nic o l e t al., 2000]. Se a ic e p ro vid e s ic e a lg a e a s a fo o d so urc e fo r krill a nd a lso se rve s a s a re fug e fro m p re d a tio n fo r a ir-b re a thing vertebrates, which have dificulty accessing the population during the winter [Flo re s e t al., 2012; Nic o l, 2006]. Ba le e n wha le s mig ra ting so uth fro m the ir tro p ic a l winte ring g ro und s a g g re g a te a lo ng the e d g e o f the p a c k ic e a s it re tre a ts in sp ring, to fe e d o n krill tha t ha ve sp e nt the ir winte r und e r the fro ze n se a [Nic o l e t al., 2008]. Cha ng e s in se a ic e e xte nt a re the re fo re like ly to a ffe c t ic e -a sso c ia te d b a le e n wha le sp e c ie s suc h a s Minke wha le s (Balae no pte ra b o nae re nsis) a nd Blue wha le s (Balae no pte ra musc ulus), a s we ll a s Orc a wha le s (Orc inus o rc a ). Cha ng e s in se a ic e e xte nt in the we st Anta rc tic Pe ninsula re g io n ha ve a lso ha d consequences for the Antarctic krill ishery. In particular, reduced ice cover has allowed increased access to ishing grounds during winter [Kawag uc hi e t al., 2009; Nic o l e t al., 2012]. The ecosystem consequences of changes in ishing activity combined with c ha ng e s in se a ic e ha b ita ts a re so me wha t unc le a r, ho we ve r [Melbourne-Thomas et al., 2013; Trive lpie c e e t al., 2011]. So uthe rn Oc e a n fo o d we b s a nd the life c yc le s o f ma ny Anta rc tic ma rine a nima ls a re c lo se ly a ttune d to the se a so na l rhythms o f the ir p hysic a l e nviro nme nt, in p a rtic ula r the a nnua l a d va nc e a nd re tre a t o f se a ic e. The se nsitivity o f Anta rc tic e c o syste ms to c ha ng ing se a ic e c o nd itio ns ha s b e c o me inc re a sing ly a p p a re nt in re c e nt ye a rs. Fo r e xa mp le, in the we st Anta rc tic Pe ninsula re g io n, the tre nd to wa rd s re d uc e d se a ic e ha s re sulte d in population changes for ice-dependent Adélie penguins. Speciically, there is some e vid e nc e tha t p o p ula tio ns o f the se p e ng uins ha ve mo ve d so uthwa rd s to b e re p la c e d b y G e nto o p e ng uins (Pyg o sc e lis papua ) a nd Chinstra p p e ng uins (Pyg o sc e lis antarc tic a ) tha t p re vio usly b re d p re d o mina ntly o n no rthe rly sub -Anta rc tic isla nd s [Mc Clinto c k e t al., 2008]. Ho we ve r, the e c o syste m c o nse q ue nc e s o f c ha ng e s in se a ic e ha b ita ts o n the we st Anta rc tic Pe ninsula re g io n a re c o mp lic a te d [Melbourne-Thomas et al., 2013; Montes- Hug o e t al., 2009; Trive lpie c e e t al., 2011], a nd it is unlike ly tha t o b se rva tio ns ma d e in this region can be extrapolated to other regions of the Southern Ocean. Regionally-speciic p ro c e ss a nd mo d e lling stud ie s, a nd imp o rta ntly lo ng -te rm a nd c o o rd ina te d o b se rva tio ns, a re ne e d e d to und e rsta nd a nd p re d ic t the imp a c ts o f c ha ng ing se a ic e o n Anta rc tic e c o syste m struc ture a nd func tio n. FUTURE IMPACTS OF CLIMATE CHANG E ON ANTARCTIC SEA ICE Mode l issue s a nd pre dic tions Ac c ura te ly p re d ic ting the future sta te a nd d istrib utio n o f Anta rc tic se a ic e re p re se nts a c o nsid e ra b le c ha lle ng e fo r c lima te mo d e lle rs. Altho ug h so p histic a te d, the c urre nt g e ne ra tio n o f c o up le d c lima te mo d e ls e xhib it a wid e ra ng e o f Anta rc tic se a ic e c lima to lo g ie s, with fe w re p ro d uc ing the inc re a se in o ve ra ll se a ic e e xte nt o b se rve d sinc e the la te 1970s [Eise nman e t al., 2011; Maksym e t al., 2012; Turne r e t al., 2013b ]. Mo st c lima te mo d e ls fa il to a c c ura te ly simula te me a n ic e e xte nt, p a rtic ula rly in summe r, a nd 31

32 o ve re stima te its ye a r-to -ye a r va ria b ility [Maksym e t al., 2012]. The se fa c to rs, whic h sug g e st tha t ke y p ro c e sse s a re b e ing simula te d inc o rre c tly a nd / o r ne g le c te d, unfo rtuna te ly undermine the degree of conidence that can be placed in predictions of likely sea-ice c o nd itio ns o ve r the c o ming d e c a d e s [Turne r e t al., 2013a ]. The y a lso und e rline a c ritic a l ne e d to c a rry o ut c o o rd ina te d in-situ me a sure me nt p ro g ra ms to b e tte r und e rsta nd se a ic e -a tmo sp he re -o c e a n p ro c e sse s a t p la y. Figure 14. Pre dic te d c ha ng e s in Anta rc tic se a ic e e xte nt a nd c o nc e ntra tio n fro m the Austra lia n Co mmunity Clima te a nd Ea rth Syste m Simula to r. Fig ure c o urte sy Sio b ha n O Fa rre ll (CSIRO). ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

33 Ne ve rthe le ss, c lima te mo d e ls g e ne ra lly p re d ic t a n o ve ra ll re d uc tio n in Anta rc tic se a ic e b y the e nd o f this c e ntury, a s the e ffe c ts o f g re e nho use g a s inc re a se s b e c o me mo re signiicant and seasonal inluences of stratospheric ozone loss decline (due to recovery o f the Anta rc tic Ozo ne Ho le ). Simula tio ns a nd p ro je c tio ns fro m o ne mo d e l, the Austra lia n Co mmunity Clima te a nd Ea rth-syste m Simula to r o r ACCESS mo d e l (Bi e t al., 2013), a re sho wn in Fig ure 14. An e nse mb le me a n o f the IPCC AR4 mo d e ls sug g e st tha t the a nnua l a ve ra g e to ta l se a ic e a re a will d e c line b y a third b y 2100 [Brac e g irdle e t al., 2008]. This re tre a t is p re d ic te d to b e g re a te st in sp ring a nd winte r whe n a nnua l ic e e xte nt is la rg e st, whic h wo uld d e c re a se the a mp litud e o f the se a so na l c yc le o f se a ic e a re a l e xte nt. Ho we ve r, c urre nt c lima te mo d e ls a re una b le to p ro vid e a p re c ise re g io na l (a nd se a so na l) a sse ssme nt o f e xp e c te d c ha ng e s [Le fe b vre and Go o sse, 2008; Turne r e t al., 2013a ]. In te rms o f se a so na lity, Stamme rjo hn e t al. [2012] sp e c ula te tha t c urre nt tre nd s to wa rd s la te r a utumn a d va nc e a nd e a rlie r sp ring re tre a t ma y we ll c o ntinue. Future c o ve ra g e o f fa st ic e is unkno wn, a s it is no t inc lud e d in g lo b a l c lima te mo d e ls. Mo d e l re sults sug g e st tha t ic e thic kne ss ma y b e e ve n mo re se nsitive to c lima te c ha ng e tha n ic e e xte nt [Arze l e t al., 2006]. In the ir stud y o f e nse mb le o utp ut fro m IPCC AR4 c o up le d c lima te mo d e ls, Sen-Gupta et al. [2009] sho we d a ro b ust d e c re a se in a ve ra g e ic e thic kne ss a nd vo lume a c ro ss the mo d e ls fo r b o th summe r a nd winte r. The multi-mo d e l me a n furthe r ind ic a te s tha t fo r the winte r se a so n, sub sta ntia l se a ic e lo ss will o c c ur a t a ll lo ng itud e s, with the g re a te st lo ss o c c urring in the we ste rn Anta rc tic - p a rtic ula rly fro m the o ute r e d g e o f the We d d e ll re g io n (0 W to 30 W) a nd b e twe e n 90 W a nd 150 W. In summe r, the g re a te st ic e lo ss is p re d ic te d to b e to the e a st o f the Anta rc tic Pe ninsula. As hig hlig hte d e a rlie r, a c c ura te a sse ssme nts o f c ha ng e in Anta rc tic se a ic e thic kne ss a nd vo lume a re se ve re ly ha mp e re d b y the la c k o f b a se line info rma tio n [Maksym e t al., 2012]. Othe r like ly impa c ts Pre d ic te d inc re a se s in wind stre ng th/ sto rmine ss in summe r a nd a utumn in p a rtic ula r [Brac e g irdle e t al., 2008; Turne r e t al., 2013a ], wa vine ss a nd sno wfa ll [Brac e g irdle e t al., 2008; Emo ri and Bro wn, 2005; Me e hl e t al., 2006] a re like ly to ha ve a ma jo r e ffe c t o n the future Anta rc tic se a ic e e nviro nme nt, a nd in a c o mp le x fa shio n [Masso m and Stamme rjo hn, 2010]. Stro ng e r wind s a nd / o r g re a te r p re va le nc e o f e xtre me wind e ve nts wo uld le a d to mo re ic e ra fting a nd rid g ing a nd inc re a se d ic e thic kne ss in so me a re a s (fo r e xa mp le Masso m e t al. [2006]), while greatly affecting the loe size distribution of the sea ic e c o ve r. G re a te r wa ve e ne rg y g e ne ra te d b y a n inc re a se in sto rmine ss wo uld a ffe c t the wid th a nd c ha ra c te ristic s o f the ma rg ina l ic e zo ne a nd e ve n the c ha ra c te ristic s o f the inne r p a c k (fo r e xa mp le Masso m e t al., 1999), a s we ll a s the b re a kup o f fa st ic e (p a rtic ula rly whe n the la tte r is unp ro te c te d b y a n e xte nsive p a c k ic e c o ve r, se a so na lly o r o the rwise ). Fa st-ic e fo rma tio n a nd se a so na lity a re a lso hig hly se nsitive to wind sp e e d a nd d ire c tio n [He il, 2006; Masso m e t al., 2010]. Ic e c o nd itio ns, e sp e c ia lly in b a ys, will b e sub sta ntia lly d iffe re nt in a c lima te with d iffe re nt wind p a tte rns tha n a t p re se nt. The b re a k- up o r e nha nc e d me lt o f fa st ic e c o uld, ho we ve r, b e c o unte rb a la nc e d b y the inc re a se d d isc ha rg e o f ic e b e rg s sinc e g ro und e d ic e b e rg s a c t a s ke y a nc ho r p o ints fo r fa st ic e fo rma tio n in ma ny lo c a tio ns [Gile s e t al., 2008]. Inc re a se d she e t d isc ha rg e (p o te ntia l ic e b e rg p ro d uc tio n) is p re d ic te d to o c c ur und e r wa rming c o nd itio ns [Be ntle y e t al., 2007]. 33

34 Impa c t of inc re a se d snow Inc re a se d sno w a c c umula tio n o n se a ic e c o uld p o te ntia lly le a d to a n inc re a se in surfa c e looding by depressing the ice surface below sea level and warming the ice (a warmer ic e c o ve r is mo re p e rme a b le to the p a ssa g e o f se a wa te r thro ug h it [Go lde n e t al., 1998]). In this wa y, inc re a se d sno wfa ll c o uld le a d to e nha nc e d fo rma tio n o f sno w ic e [Fic he fe t and Mo rale s Maq ue da, 1999]. This can be a more eficient means of ice thickening, g ive n tha t fre e zing o c c urs o n the ic e surfa c e ra the r tha n the b a se [Lytle and Ac kle y, 2001]. In o the r wo rd s, e nha nc e d sno w ic e fo rma tio n c o uld ma inta in se a ic e thic kne ss to so me (unkno wn) e xte nt b y c o unte rb a la nc ing a ny inc re a se in ic e b a sa l me lting und e r o c e a n wa rming c o nd itio ns [Maksym and Markus, 2008; Wu e t al., 1999]. At the sa me time, the p re se nc e o f a thic ke r sno w c o ve r c o uld d e la y the summe r ic e me lt d ue to its hig h a lb e d o to p o te ntia lly le ng the n the se a ic e se a so n in c e rta in re g io ns [Eic ke n e t al., 1995; Le dle y, 1991]. Ano the r p o te ntia l imp a c t o f g re a te r sno w a c c umula tio n is a n increase in freshwater lux into the ocean when the ice melts, leading to increased ocean surface stratiication. This could in turn lead to reductions in the upward lux of ocean heat fo r b a sa l se a ic e me lt, imp lying tha t se a ic e d ura tio n a nd e xte nt ma y a c tua lly inc re a se und e r wa rming c o nd itio ns (fo r e xa mp le Zhang [2007]). The se p o te ntia l sc e na rio s o nc e a g a in und e rline the c o mp le xity o f the se a ic e -o c e a n-a tmo sp he re inte ra c tio n syste m. FUTURE CHALLENG ES Improving the pe rforma nc e of mode ls In sp ite o f ma jo r a d va nc e s in o ur und e rsta nd ing o f Anta rc tic se a ic e o ve r the p a st thre e d e c a d e s, the re is still muc h to b e le a rne d a b o ut its c ha ra c te ristic s; its inte ra c tio ns a nd c o nne c tio ns with the a tmo sp he re, o c e a n a nd e c o syste m; a nd its c o mp le x re sp o nse to, a nd ro le in, p re se nt a nd future c lima te c ha ng e [Maksym e t al., 2012]. A ke y c ha lle ng e is to imp ro ve the p e rfo rma nc e o f nume ric a l mo d e ls in simula ting re c e nt, a nd p re d ic ting future, Anta rc tic se a ic e d istrib utio n a nd sta te, a nd to inc lud e se a so na l a nd re g io na l se nsitivitie s in the mo d e ls [Maksym e t al., 2012; Turne r e t al., 2013a ]. Imp ro ve d p a ra me te risa tio n a nd und e rsta nd ing o f c ha ng e a nd va ria b ility no t o nly re q uire s mo re and improved observations. It also necessitates identiication and better understanding o f p ro c e sse s a nd me c ha nisms invo lve d. The se inc lud e o c e a n fo rc ing a nd fe e d b a c ks [Russe ll e t al., 2006], a s we ll a s the ro le tha t se a ic e itse lf ma y p la y in mo d ula ting the re sp o nse to e xte rna l (a tmo sp he ric a nd o c e a nic ) fo rc ing [Raphae l e t al., 2011; Maksym e t al., 2012]. Estima ting se a ic e thic kne ss A ma jo r stumb ling b lo c k a t p re se nt is o ur la c k o f kno wle d g e o f the c urre nt d istrib utio n o f the thic kne ss o f Anta rc tic se a ic e a nd its sno w c o ve r, a nd o f ho w the se a re c ha ng ing a nd wha t p ro c e sse s a re invo lve d ; tha t is, the re la tive c o ntrib utio ns o f d yna mic a nd the rmo d yna mic p ro c e sse s (inc lud ing sno w-ic e fo rma tio n). The ic e thic kne ss d istrib utio n p ro vid e s a n inte g ra te d me a sure o f to ta l se a ic e p ro d uc tio n a nd, thus, to ta l o c e a n- atmosphere heat loss, the surface salinity lux in winter and freshwater input into the ocean ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

35 SEALS, POLYNYAS AND A 30- YEAR- OLD MYSTERY OF THE DEEP Sc ie ntists b e lie ve d tha t the c o ld, d e nse b o tto m wa te rs o f the g lo b a l o c e a n o rig ina te d a t thre e d iffe re nt lo c a tio ns in Anta rc tic a - the We d d e ll Se a, the Ro ss Se a a nd the Ad é lie Co a st o f Ea st Anta rc tic a. Thirty ye a rs a g o, a fo urth so urc e wa s sp e c ula te d to e xist somewhere in the Prydz Bay region, but until now scientists have been unable to conirm if, whe re a nd ho w it is b e ing fo rme d. No w, thro ug h so p histic a te d sa te llite d a ta, o c e a no g ra p hic mo o ring s a nd ta g g e d se a ls, a te a m invo lving ACE CRC re se a rc he rs ha s d isc o ve re d tha t a fo urth stre a m o f Anta rc tic Bo tto m Wa te r (AABW) is b e ing p ro d uc e d fro m inte nse se a ic e fo rma tio n in the Ca p e Da rnle y Po lynya (65 E 69 E, 67.5 S), no rth-we st o f the Ame ry Ic e She lf. Oshima e t a l. [2013] e stima te tha t this so urc e o f AABW re p re se nts b e twe e n 6% a nd 13% o f the circumpolar total. Its signiicance is underlined by the fact that AABW is a key driver of the g lo b a l o c e a n c irc ula tio n a nd the re fo re o f the Ea rth s c lima te. Da ta c o lle c te d b y instrume nte d So uthe rn e le p ha nt se a ls a llo we d sc ie ntists to p inp o int the p a th o f the d e nse sa lty wa te r a nd the re fo re id e ntify the a re a fro m whic h it o rig ina te s. This o c e a no g ra p hic d a ta c o lle c te d b y the se a ls is p a rt o f a la rg e r e c o lo g ic a l p ro je c t a t Institute fo r Ma rine a nd Anta rc tic Stud ie s (IMAS) to stud y the ir b e ha vio ur. Whe n the se a ls surfa c e, the ir instrume nt ta g s re la y info rma tio n (via sa te llite ) b a c k to la nd, whe re it is collected by the Integrated Marine Observing System (IMOS). The newly identiied so urc e o f AABW is d iffe re nt fro m the o the r thre e so urc e s. Its e xiste nc e d e mo nstra te s tha t polynyas are capable of forming suficiently dense Shelf Water over a narrow section of c o ntine nta l she lf witho ut the tra d itio na l a ssista nc e o f a la rg e ic e she lf o r c o a sta l sto ra g e vo lume. This o p e ns the p o ssib ility fo r furthe r d isc o ve rie s o f AABW p ro d uc tio n fro m the o the r p o lynya re g io ns a ro und the Anta rc tic c o a stline.!"#$%&"'()$*% Sa linitie s a t b o tto m-o f-dive fo r a ll a va ila b le o c e a n te mpe ra ture and salinity proiles measured b y instrume nte d se a ls o ve r the c o ntine nta l she lf o ff Cape Da rnle y a nd in Prydz Ba y whe re the b o tto m de pth wa s >250m a nd po te ntia l temperature <1.7 C. All other d ive lo c a tio ns a re ind ic a te d b y sma ll g re y p o ints. Fro m Ohshima e t al. [2013]. 35

36 in summe r. Curre nt la rg e o b se rva tio na l unc e rta intie s in the se q ua ntitie s (o f 50%-100%) se ve re ly c o mp ro mise the a b ility to e ffe c tive ly e va lua te mo d e ls - a nd thus und e rmine o ur conidence in the accuracy of future predictions [Maksym e t al., 2012]. G ive n the se fa c to rs, it is c ritic a l to d e rive mo re a c c ura te b a se line info rma tio n o n the thic kne ss a nd vo lume o f se a ic e o n re g io na l to c irc ump o la r sc a le s b y sa te llite re mo te se nsing. This c a n o nly b e a c hie ve d thro ug h e ffe c tive c a lib ra tio n a nd va lid a tio n p ro g ra ms invo lving c a re ful c o o rd ina tio n o f in-situ o b se rva tio ns with c o inc id e nt sa te llite, a irb o rne a nd und e r-ic e re mo te se nsing (fo r e xa mp le Lie se r e t al. [2011, 2013], Williams e t al. [2013]). This in itse lf re p re se nts a c o nsid e ra b le c ha lle ng e, g ive n the ra ng e o f sc a le s invo lve d. Othe r ke y c ha lle ng e s to the d e riva tio n o f se a ic e thic kne ss info rma tio n fro m sa te llite a ltime try (b o th la se r a nd ra d a r) a re the re la tive ly sma ll fre e b o a rd o f Anta rc tic (c o mp a re d to Arc tic ) se a ice, the widespread (though as yet unquantiied) occurrence of surface looding, and the ne e d fo r a c c ura te ind e p e nd e nt info rma tio n o n sno w thic kne ss a nd d e nsity a nd ic e d e nsity [Gile s e t al., 2008a ; Maksym and Markus, 2008]. Othe r c ha lle ng e s Cle a rly, imp ro ve d kno wle d g e o f the p re c ise me c ha nisms invo lving, a nd fe e d b a c ks between, snowfall, ice growth and melt, and upper-ocean stability (stratiication) and ve rtic a l he a t tra nsp o rt is c ritic a l fo r und e rsta nd ing the c urre nt b e ha vio ur a nd c ha ra c te ristic s o f Anta rc tic se a ic e a nd its future tra je c to ry [Maksym e t al., 2012]. This a g a in re p re se nts a c o nsid e ra b le c ha lle ng e, g ive n the c o mp le xitie s a nd re g io na l a nd se a so na l se nsitivitie s invo lve d. Fo rtuna te ly, we a re o n the c usp o f a n e xc iting ne w e ra in o b se rva tio na l c a p a b ility fo r mo nito ring the Anta rc tic se a ic e e nviro nme nt, using a uto no mo us d rifting a nd ic e -te the re d p la tfo rms [Maksym e t al., 2012]. The se c a n p ro vid e c o ntinuo us, se a so n- lo ng o b se rva tio ns o f a tmo sp he re -ic e -o c e a n inte ra c tio ns a nd the e vo lutio n o f the se a ic e a nd its sno w c o ve r tha t ha ve b e e n la rg e ly la c king to d a te. While suc h p la tfo rms ha ve the p o te ntia l to re vo lutio nise o ur und e rsta nd ing o f the se ve re ly und e r-sa mp le d Anta rc tic se a ic e zo ne, re la tive ly fe w ha ve b e e n d e p lo ye d to d a te. The c ha lle ng e is a g a in to ste p up d e p lo yme nt, b ut in a c o o rd ina te d fa shio n a ro und Anta rc tic a (inc lud ing o n fa st ic e a nd in the ma rg ina l ic e zo ne ). G ive n the ra p id d e c line in Arc tic se a ic e a nd o ur unc e rta in kno wle d g e o f Anta rc tic se a ic e, the re is stro ng imp e tus fo r p ro c e ss stud ie s a nd mo re susta ine d inte g ra te d o b se rva tio ns that span disciplines and a range of space and time scales. The continuation of ieldb a se d o b se rva tio ns using ic e b re a ke rs is c ruc ia l in this re sp e c t [Maksym e t al., 2012]. STRATEG IC FOCUS The Inte rg o ve rnme nta l Pa ne l o n Clima te Cha ng e c o nc lud e d in its Fifth Asse ssme nt Re p o rt [IPCC, 2013] tha t the o b se rve d wa rming o f the Ea rth is stro ng e st in the p o la r re g io ns. Surfa c e te mp e ra ture s o ve r la rg e a re a s o f the Anta rc tic Pe ninsula ha ve rise n c o nsid e ra b ly fa ste r tha n the g lo b a l a ve ra g e. The So uthe rn Oc e a n is a lso wa rming mo re ra p id ly tha n the g lo b a l o c e a n a ve ra g e. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

37 Antarctic and Southern Ocean processes inluence weather and climate on both re g io na l a nd g lo b a l sc a le s, a nd imp a c t the wid e r e nviro nme nt a nd e c o syste ms. The Anta rc tic se a -ic e zo ne is a ma jo r c o mp o ne nt o f the Ea rth s c lima te syste m, a nd we kno w tha t it is c ha ng ing. As this Po sitio n Ana lysis sho ws, the re a re ke y c o mp o ne nts o f Anta rc tic se a ic e tha t we kno w little a b o ut. Filling this la c k o f kno wle d g e o f suc h a vita l re g io n o f the g lo b e is a n imp o rta nt re se a rc h ta sk fo r the c o ming d e c a d e. In re c e nt ye a rs, the te c hno lo g y ne e d e d to o b se rve the o c e a n ha s d e ve lo p e d ra p id ly. The use o f this ne w te c hno lo g y ha s the p o te ntia l to re d uc e the c o st o f re se a rc h in the re g io n. Pla tfo rms ra ng ing fro m d rifting b uo ys, to a uto no mo us und e rwa te r ro b o ts a nd re mo te ly-o p e ra te d a irc ra ft c a n b e use d to c o mp le me nt tra d itio na l (a nd e sse ntia l) icebreaker research platforms and aircraft. These on-site ieldwork measurements can b e ma tc he d with sa te llite te c hno lo g ie s to o b se rve the se a -ic e zo ne o n the he misp he ric a nd g lo b a l sc a le. It will b e e sse ntia l to inc lud e ma ny d iffe re nt d isc ip line s in this e ffo rt, a s fe e d b a c ks a c ro ss va rio us re g io na l sc a le s will link into the d iffe re nt sp he re s o f the g lo b a l syste m. This re se a rc h must b e inte g ra te d with na tio na l a nd inte rna tio na l e ffo rts in the re g io n. While sa te llite s c a n me a sure se a -ic e e xte nt, it will b e imp o rta nt to g e t a me a sure o f a nd d e ve lo p me tho d s fo r p re d ic ting se a ic e thic kne ss in the e ntire se a -ic e zo ne o f the Anta rc tic. This ne w kno wle d g e will sup p o rt imp ro ve me nts to nume ric a l mo d e ls o f the c o up le d a tmo sp he re -o c e a n-c ryo sp he re syste m, a nd thro ug h this, the p re d ic ta b ility o f the c lima te syste m a nd, a s a n e xte nsio n, a lso tha t o f e c o syste m mo d e ls. Austra lia n re se a rc h is imp o rta nt in und e rsta nd ing imp a c ts a rising fro m c ha ng e s in Anta rc tic se a ic e, b ut Austra lia a lso ha s a ke y ro le in e nsuring tha t suc h re se a rc h is a va ila b le in re le va nt fo rums o f the Anta rc tic Tre a ty Syste m (ATS), mo st no ta b ly the Anta rc tic Tre a ty Co nsulta tive Me e ting a nd the Co mmissio n fo r the Co nse rva tio n o f Anta rc tic Ma rine Living Re so urc e s (CCAMLR). Ea rlie r wo rk b y the ACE CRC no te d tha t c ha ng e s in se a ic e a re like ly to imp a c t o n a numb e r o f a c tivitie s within the Anta rc tic Tre a ty a re a. Re d uc tio ns in se a ic e will re d uc e natural barriers to shipping access in high latitudes and open up otherwise dificult a re a s fo r ma rine re so urc e s ha rve sting. While the se a c tivitie s a re ma na g e d und e r the ATS, Austra lia ha s a n inte re st in e nsuring tha t the se d e c isio ns ta ke a c c o unt o f c urre nt sc ie nc e. Austra lia s c o mmitme nt to inte g ra te d re se a rc h, fo r e xa mp le the two SIPEX vo ya g e s (in 2007 a nd 2012), p ro vid e s c ruc ia lly imp o rta nt c o ntrib utio ns to inte rna tio na l e ffo rts to und e rsta nd o b se rve d a nd p o te ntia l c ha ng e s to se a ic e. This re se a rc h a nd its o utc o me s a re d ire c tly linke d to Austra lia n inte re sts a nd g o ve rnme nt g o a ls fo r the Austra lia n Anta rc tic Pro g ra m. Austra lia s wo rk o n se a ic e b uild s o n a le ng thy c o mmitme nt to ma rine sc ie nc e a nd Anta rc tic infra struc ture. While suc h c o mmitme nts a re c ha lle ng ing, Austra lia will b e we ll served by maintaining capacity and assets in high-latitude marine science with suficient 37

38 capacity to undertake winter sea ice expeditions. This means maintaining suficient ic e b re a king c a p a c ity in its o ng o ing Anta rc tic lo g istic s a nd infra struc ture p la nning, a nd e mb ra c ing the use o f ne w te c hno lo g ie s tha t g re a tly a id me a sure me nt a nd mo nito ring of the dificult sea-ice environment. Suc h inve stme nts p ro vid e o p p o rtunitie s to wo rk with inte rna tio na l p a rtne rs in c ha lle ng ing environments and to continue a century of scientiic endeavour that addresses critical q ue stio ns a nd sup p o rts ma na g e me nt o f a re g io n tha t is o f d ire c t inte re st to Austra lia. CONCLUSION Anta rc tic se a ic e is re g a rd e d a s a se nsitive ind ic a to r o f c lima te c ha ng e. Its p re se nc e a t the inte rfa c e b e twe e n the a tmo sp he re a nd the o c e a n in p o la r la titud e s ma ke s it hig hly susc e p tib le to d yna mic a nd the rmo d yna mic c ha ng e s a nd va ria tio ns fro m a b o ve a nd b e lo w. It re sp o nd s to c ha ng e s in the e nviro nme nta l c o nd itio ns in a c o mp le x wa y. Fo r e xa mp le, while a wa rming a tmo sp he re a nd inc re a se d he a t c o nte nt in the o c e a n will ha ve a thinning e ffe c t o n the se a ic e, g re a te r wind a nd wa ve e ne rg y c a n b re a k up se a ic e to p o te ntia lly inc re a se the ic e thic kne ss b y ra fting a nd rid g ing. An inc re a se in sno w c o ve r o n to p o f the se a ic e will he lp to the rma lly insula te the o c e a n fro m the a tmo sp he re a nd the re fo re re d uc e fre e zing ra te s o f se a ic e, b ut a t the sa me time c a n sup p re ss a thinne r ic e c o ve r b e lo w the wa te r line a nd fa c ilita te inc re a se in ic e thic kne ss b y sno w-ic e fo rma tio n. The o b se rve d p a tte rns o f c ha ng e in Anta rc tic se a ic e a re ma nifo ld a nd no t unifo rm a c ro ss the re g io n. While the o ve ra ll e xte nt o f se a ic e, fo r e xa mp le, sho ws a slig ht inc re a sing tre nd (p a ne l a. in Fig ure 4), the re a re sta rkly c o ntra sting tre nd s o n o c e a nic b a sin sc a le s (Ro ss Se a ve rsus Be lling sha use n/ Amund se n se a s). Simila r he te ro g e ne o us p a tte rns c a n b e fo und in ma p s o f tre nd s in se a ic e d ura tio n/ se a so na lity (Fig ure s 5 a nd 6). Se a ic e pla ys a c ritic a l ro le in b io g e o c he mic a l c yc le s a nd the ma rine e c o syste m in the hig h-la titud e So uthe rn Oc e a n. The life c yc le s o f ma ny ma rine a nima ls a re c lo se ly linke d to the se a so na l rhythm o f the physic a l e nviro nme nt, a nd c ha ng ing se a ic e c o nd itio ns mig ht have beneicial effects for some species, but can be potentially devastating for others. Recent advances in space-borne remote sensing enable a irst assessment of largesc a le se a ic e thic kne ss (a nd sub se q ue ntly se a ic e vo lume ) b a se d o n surfa c e e le va tio n (fre e b o a rd ) me a sure me nts. Suc h me a sure me nts will e na b le a re lia b le e stima te o f se a ic e vo lume o ve r time if c a rrie d o ut in the sa me a re a re p e a te d ly with c o nsta nt p re c isio n. In order to better understand the inluence of a changing environment on the geophysical properties of sea ice and low-on effects on the ice-associated ecosystem, as well as to c a lib ra te a nd va lid a te e sta b lishe d a nd e me rg ing re mo te -se nsing p ro d uc ts, a c o ntinue d inte rna tio na lly c o lla b o ra tive a nd inte r-d isc ip lina ry in-situ mo nito ring a nd re se a rc h e ffo rt is c ruc ia l. ACE CRC ANTARCTIC SEA ICE AND CLIMATE CHANG E POSITION ANALYSIS

39 Sc ie ntists a nd suppo rt sta ff a t wo rk o n Ea st Anta rc tic se a ic e during the se c o nd Se a Ic e Physic s & Ec o syste ms e Xpe rime nt (SIPEX 2) in Pho to b y Bria n Wa lpo le 39

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