PALAEO -ICE STREAM S IN TH E
NO RTH -EASTERN LAURENTID E ICE SH EET
H e rnán D e Ange l is
D octoral dis s e rtation 2007
D e partm e nt of Ph ys ical Ge ograph y and Quate rnary Ge ology Stock h olm Unive rs ity
ISSN: 1653-7211
ISBN: 9 78-9 1-7155-509 -0
Article II © Inte rnational Glaciological Socie ty 2005 Article III © Els e vie r Publis h ing Co. 2007
Layout: H e rnán D e Ange lis (e xce pt article s II and III)
Cove r ph oto: Palae o-ice s tre am be d in s outh -e as te rn Victoria Is land, Arctic Canada.
Vie w tow ards north -e as t (Ph oto: H e rnán D e Ange lis , July 2005).
Printe d in Sw e de n by PrintCe nte r US-AB
Palae o-ice s tre am s in th e north -e as te rn Laure ntide Ice Sh e e t
Th is th e s is pre s e nts a palae oglaciological s tudy aim e d to de te rm ine th e location, ge om e try and te m poral e volution of palae o-ice s tre am s of th e north -e as te rnm os t Laure ntide Ice Sh e e t. Th e w ork w as accom plis h e d th rough th e ge om orph ological inte rpre tation of s ate llite im age ry ove r 3.19 x 106 k m2 of th e Canadian Arctic, us ing a glaciological inve rs ion s ch e m e . Ice s tre am s w e re active in th is re gion during m os t of th e tim e be tw e e n th e Las t Glacial Maxim um and th e las t de glaciation.
A w e b of ice s tre am s and inte r-ice s tre am are as e xis te d. Th re e m ajor ice s tre am ne tw ork s are ide ntifie d: th e M'Clintock Ch anne l, Gulf of Booth ia – Lancas te r Sound and H uds on Strait. Th e M'Clintock Ch anne l be ars th e m os t com ple x landform re cord, com pris ing th re e ge ne rations of palae o-ice s tre am s . Th e ir location w as w e ak ly controlle d by th e s ubglacial topograph y and th e ir ge om e try w as de te rm ine d by froze n-be d portions of th e ice s h e e t, th us providing e vide nce for pure ice s tre am s in th e Laure ntide Ice Sh e e t. In contras t, th e m ore pronounce d re lie f of th e Gulf of Booth ia – Lancas te r Sound corridor s upporte d topograph ically controlle d ice s tre am s . Th e landform re cord on e m e rge d land along H uds on Strait is ins ufficie nt to s upport th e e xis te nce of ice s tre am s . It is th e re fore propos e d th at ice s tre am s w e re cons traine d w ith in th e de e p parts of th e s trait w h ile flank e d by cold-bas e d zone s on th e m argins . Sm all trans ie nt ice s tre am s on Baffin and Prince of W ale s is lands draine d local re m nant ice caps during th e collaps e of th e ice s h e e t.
Analys is of th e controls on th e location and flow of palae o-ice s tre am s s ugge s ts th at th e inte raction be tw e e n th e s ubglacial topograph y and th e rm al s tate of th e s ubs trate plays a m ore fundam e ntal role th an th e ge ology. It is conclude d th at th e be h aviour of ice s tre am s cannot be e xplaine d in te rm s of e nvironm e ntal controls alone , but th e com ple x dynam ics of ice s tre am s h e ar m argins and ons e t zone s m us t be cons ide re d.
K e yw ords : ice s h e e t, ice s tre am , palae o-ice s h e e t, palae o-ice s tre am , glaciology, palae oglaciology, Laure ntide Ice Sh e e t.
ABSTRACT
D octoral dis s e rtation 2007
D e partm e nt of Ph ys ical Ge ograph y and Quate rnary Ge ology Stock h olm Unive rs ity
Th is th e s is cons is ts of a s um m ary and five article s :
Article I
D e Ange lis , H . In pre s s . Glacial landform s of th e e as t-ce ntral Canadian Arctic. Journal of Maps . Acce pte d for publication in Journal of Maps .
Article II
D e Ange lis , H . and J. Kle m an. 2005. Palae o-ice s tre am s in th e north e rn Ke e w atin s e ctor of th e Laure ntide Ice Sh e e t. Annals of Glaciology 42, 135-144.
Re printe d w ith pe rm is s ion from th e Inte rnational Glaciological Socie ty.
Article III
D e Ange lis , H . and J. Kle m an. 2007. Palae o-ice s tre am s in th e Foxe -Baffin s e ctor of th e Laure ntide Ice Sh e e t. Quate rnary Scie nce Re vie w s 26 (9 -10), 1313-1331.
Re printe d w ith pe rm is s ion from th e Els e vie r Publis h ing Co..
Article IV
D e Ange lis , H . and J. Kle m an. Palae o-ice s tre am e volution in th e north -e as te rn Laure ntide Ice Sh e e t.
Manus cript.
Article V
D e Ange lis , H . and J. Kle m an. In pre s s . Palae o-ice s tre am ons e ts : e xam ple s from th e north - e as te rn Laure ntide Ice Sh e e t.
Acce pte d for publication in Earth Surface Landform s and Proce s s e s .
All pape rs are auth ore d by m e and Joh an Kle m an e xce pt th e firs t, in w h ich I am th e only auth or. In all pape rs , I did th e m apping, im age proce s s ing, databas e m anage m e nt, figure draw ing and m os t of th e w riting. In pape rs II to V, Prof. Joh an Kle m an contribute d w ith m any ide as and s om e w riting. H e als o s tarte d th is proje ct and provide d m os t of th e ne ce s s ary funding. Along th e te xt, th e s e article s are re fe rre d to by th e ir Rom an num e ral.
Palae o-ice s tre am s in th e north -e as te rn Laure ntide Ice Sh e e t
“ ... th e unive rs e w e s e e is a ce as e le s s cre ation, e volution, and de s truction of form s and th e purpos e of s cie nce is to fore s e e th is
ch ange of form and, if pos s ible , e xplain it.”
Re né Th om (19 23 - 2002), Fre nch m ath e m atician and ph ilos oph e r.
INTRO D UCTIO N
Ice s h e e ts are e s s e ntial com pone nts of th e clim ate s ys te m be caus e of th e ir m ark e d influe nce upon th e e ne rgy balance and th e oce anic and atm os ph e ric circulations (O e rle m ans and van de r Ve e n, 19 84).
Th is re le vance als o e m e rge s from th e analys is of proxy re cords th at s h ow s ubs tantial diffe re nce s be tw e e n clim ate s be fore and afte r th e appe arance of large ice s h e e ts in th e e arly O ligoce ne , approxim ate ly 34 m illion ye ars ago (Z ach os and oth e rs , 2001). Com pre h e ns ive k now le dge about th e dynam ics , inte rnal organization, s tability and e volution of m ode rn and ancie nt ice s h e e ts is th e re fore crucial for unde rs tanding th e caus e s and e valuating th e cons e q ue nce s of clim ate and e nvironm e ntal ch ange s (Alle y and oth e rs , 2005;
Bam be r and oth e rs , 2007). Large ice s h e e ts m ay de ve lop com ple x inte rnal arch ite cture s , fe aturing s e ve ral dynam ic and m orph ological s ubs ys te m s , i.e . ice dom e s , ice s tre am s , outle t glacie rs and ice s h e lve s (Kotlyak ov and Sm olyarova, 19 9 0; H ugh e s , 19 9 8). Am ong th e s e , ice s tre am s are arguably th e m os t com ple x and intriguing (Be ntle y, 19 87; Alle y and oth e rs , 2004). Th e s e fe ature s w e re firs t re porte d from Gre e nland (Rink , 1877) and late r from th e Antarctic, w h e re ice s tre am s w e re de fine d as part of an ice s h e e t w h e re ice flow s fas te r and not ne ce s s arily in th e s am e dire ction as th e s urrounding ice (Sw ith inbank , 19 54). In addition, during re ce nt de cade s ce rtain landform as s e m blage s h ave be e n convincingly as s ociate d to ancie nt s tre am ing flow , i.e . palae o-ice s tre am s (Stok e s and Clark , 2001).
Th is h as re s ulte d in th e w ide s pre ad ide ntification of palae o-ice s tre am s in th e form e r be ds of th e Antarctic (Canals and oth e rs , 2000; O 'Cofaigh and oth e rs , 2002; Mos ola and Ande rs on, 2006), Laure ntide (D yk e and Morris , 19 88; H odgs on, 19 9 4;
Clark and Stok e s , 2001; Jans s on and oth e rs , 2003;
Stok e s and Clark , 2003a; W ins borrow and oth e rs , 2004), Cordille ran (Kovane n and Slaym ak e r, 2004), Fe nnos candian (Punk ari, 19 80; Kle m an and oth e rs , 19 9 7; O tte s e n and oth e rs , 2005), Bare nts Se a (Andre as s e n and oth e rs , 2004), Patagonian (Be nn and Clappe rton, 2000; Glas s e r and Jans s on, 2003;
H ubbard and oth e rs , 2005) and Britis h -Iris h (Jans s on and Glas s e r, 2005; Robe rts and oth e rs , 2007) palae o-ice s h e e ts . Th e s e s tudie s s h ow e d th e broad s tructural and dynam ical s im ilarity be tw e e n m ode rn and ancie nt ice s h e e ts and provide us e ful m e ans for illum inating our unde rs tanding of ice s h e e ts . Th is is be caus e th e form e r be ds of palae o-ice s tre am s are now acce s s ible , m ak ing it pos s ible to m ap th e ge om e try and te m poral e volution of th e ir ne tw ork s w ith full re cognition of th e topograph ical, ge ological and ge om orph ological conte xts . In th is w ay, palae oglaciological re s e arch ope ns ne w , com ple m e ntary w ays for th e as s e s s m e nt of h ypoth e s e s on ice s tre am flow , s ubglacial ph ys ics and landform ge ne ration. More ove r, re s e arch on palae o-ice s tre am s provide s uniq ue ins igh ts into pas t s tate s of ice s tre am s ys te m s th at re m ain pre s e ntly unobs e rve d. Th e re fore , by e xte nding th e pre s e nt range of obs e rvations into th e pas t it be com e s a valuable tool for th e unde rs tanding of th e dynam ics of ice s h e e ts .
Mode rn Antarctic ice s tre am s are re m ark able fe ature s th at, w h ile draining a s ubs tantial portion of th e Antarctic Ice Sh e e t, dis play notorious s patio-
te m poral variability and s e lf-organization in com ple x large -s cale ne tw ork s (Bam be r and oth e rs , 2000;
Rém y and oth e rs , 2001; Conw ay and oth e rs , 2002;
Jough in and oth e rs , 2002; H ulbe and Fah ne s tock , 2004; Sie ge rt and oth e rs 2004a). In addition, th e ir m ode of flow is uniq ue be caus e h igh s urface ve locitie s are attaine d at low driving s tre s s e s (up to 800 m yr-1 at ~ 10 k Pa), in s h arp contras t w ith th e s low ly flow ing ne igh bouring ice (0-25 m yr-1 at ~ 100 k Pa) (Jough in and oth e rs , 2002). Glaciological re s e arch h as s h ow n th at th is dynam ical s ituation s te m s from particular bas al conditions , nam e ly e fficie nt s liding and pe rvas ive de form ation of s ubglacial s e dim e nts , w h ich h igh ligh ts th e re le vance of th e topograph y, h ydraulics , ge ology and th e rm al s tate of th e s ubs trate (Kam b, 2001;
Bougam ont and oth e rs , 2003; Ch ris toffe rs e n and Tulaczyk , 2003; Alle y and oth e rs , 2004). In ge ne ral, fas t ice flow w ith in ice s h e e ts occurs along a w ide range of topograph ical s e ttings , from w e ll de fine d trough s in th e be d, i.e . topograph ical ice -s tre am s , to are as lack ing notice able topograph ical controls , i.e . pure ice s tre am s (Truffe r and Ech e lm e ye r, 2003).
Topograph ical ice s tre am s form as ice conve rge s into s ubglacial valle ys be caus e m as s continuity re q uire s ice ve locity to incre as e , le ading to e nh ance d bas al m e lting and s liding, w h ich furth e r e nh ance s ve locity. Th is pos itive fe e dback m ay be lim ite d e ith e r by incre as e d late ral s h e ar or by de ple tion of th e ice s ource , both le ading to th e oppos ite fe e dback , i.e . de cre as e d ice flux le ading to de cre as e d bas al m e lt and s liding (van de r Ve e n, 19 9 9 ; Pate rs on, 2001). O n th e oth e r h and, pure ice s tre am s are m ore com ple x s ince th e s e occur in are as w ith out obvious topograph ical controls and in th e s e cas e s oth e r factors be com e re le vant, s uch as th e ge ology, h ydraulics and th e rm al s tate of th e be d. Ge ology is im portant be caus e th e pre s e nce of ce rtain lith ologie s , lik e clay-rich s e dim e ntary rock s , contribute s to th e build-up of h igh s ubglacial h ydraulic pre s s ure , e nh ancing bas al s liding and de form ation of th e s ubglacial s e dim e nts (Be ll and oth e rs , 19 9 8; Anandak ris h nan and oth e rs , 19 9 8;
Bam be r and oth e rs , 2006; Pe te rs and oth e rs , 2006).
In th is re gard, th e occurre nce of be drock th at is dom inantly com pos e d of th is type of rock s is us ually re fe rre d to as “rh e ologically s oft be drock ”, w h e re as a be drock dom inantly com pos e d by crys talline rock s , i.e . granite s and m e tam orph ite s , is us ually re fe rre d to as “rh e ologically h ard be drock ”.
Alth ough th is broad clas s ification is loos e and arguably inade q uate , it is us e d in th is w ork due to its ge ne rally unde rs tood m e aning and to be cons is te nt w ith curre nt glaciological re s e arch . Th e th e rm al s tate of th e be d is critical be caus e a m e lting be d allow s bas al s liding, w h e re as a froze n be d pre ve nts it. A m e lte d be d als o favours th e initiation of a w ide range of h ydraulic proce s s e s in th e s ubs trate , w h ich m ay h ave a s trong influe nce on ice s tre am be h aviour. Inde e d, a grow ing body of w ork on s ubglacial s e dim e nts indicate s th at com ple x proce s s e s occur w ith in a w ate r s aturate d s ubglacial s e dim e nt laye r unde r ch anging th e rm al conditions (Kam b, 2001; Tulaczyk and oth e rs , 2000a; Ch ris toffe rs e n and Tulaczyk , 2003). For ins tance , ice s tre am s tagnation m igh t occur as s ubglacial s e dim e nts unde rgo progre s s ive fre e zing, w h e re as progre s s ive m e lting unde r a s tagnate d ice s tre am m igh t le ad to its re activation (Bougam ont and oth e rs , 2003; Voge l and oth e rs , 2005).
Palae o-ice s tre am s in th e north -e as te rn Laure ntide Ice Sh e e t
D e s pite th e s e advance s in unde rs tanding ice s tre am s , pre s e nt glaciological k now le dge is s till ins ufficie nt to e xplain th e ir obs e rve d be h aviour at th e ice s h e e t s cale . Th is conce rns particularly th e occurre nce and e volution of ice s tre am ne tw ork s (Bam be r and oth e rs , 2000; Rém y and oth e rs , 2001;
Article II; Kle m an and Glas s e r, 2007) and th e ir role in th e long-te rm s tability of ice s h e e ts .
Re garding th e de ve lopm e nt of ice s tre am ne tw ork s , unde rs tanding th e controls involve d in th e location and longe vity of s h e ar m argins and ons e t zone s be com e s re le vant be caus e th e s e are th e dis continuitie s be tw e e n s h e e t and s tre am flow type s (Binds ch adle r and oth e rs , 2001; Raym ond and oth e rs , 2001). In th e cas e of s h e ar m argins , it h as be e n s ugge s te d th at th e actual e xis te nce of ice s tre am s m igh t de pe nd on th e de licate th e rm o- m e ch anical balance at th e m argins , w h e re a critical com pe tition is e s tablis h e d be tw e e n m e lting outw ard (w ide ning) and fre e zing inw ard (narrow ing) (Jacobs on and Raym ond, 19 9 8; Raym ond, 2000).
Th is s ubtle e q uilibrium appe ars to be furth e r com plicate d by th e inte rplay of additional non-line ar proce s s e s lik e ice fabric de ve lopm e nt due to e xtre m e s h e ar, fracture , fracture -induce d ch ange s in th e ice te m pe rature fie lds , s ubglacial h ydraulic proce s s e s and cold-ice adve ction from up-ice and ne igh bouring zone s (Raym ond and oth e rs , 2001;
Sch oof, 2004). In th e cas e of ons e t zone s , th e ore tical s tudie s bas e d on analogie s be tw e e n ice s tre am s and s urging glacie rs indicate d th at th e ons e t zone s of ice s tre am s m igh t be s ubje ct to up- ice m igration (Binds ch adle r, 19 9 7). Th is h ypoth e s is h as be e n q ue s tione d by s tudie s s h ow ing th at m igration of th e ons e t w ould be lim ite d by th e e xte nt of s ubglacial bas ins providing s oft s ubs trate (Pe te rs and oth e rs , 2006) or by incre as e d be d rough ne s s in re gions locate d up-ice of ice s tre am s (Sie ge rt and oth e rs , 2004b). Ne ve rth e le s s , palae oglaciological inte rpre tation of ons e t zone s of palae o-ice s tre am s indicate s th at m igration m igh t h ave occurre d in s om e cas e s during pe riods of rapid ice s h e e t re tre at (Article V). Th e re ce nt dis cove ry of s ubglacial lak e s at th e h e ad of s om e Eas t Antarctic ice s tre am s (Be ll and oth e rs , 2007) and th e ore tical de ve lopm e nts on th e h ydraulics of ons e t zone s (Binds ch adle r and Ch oi, 2007) indicate th at ons e t zone s m igh t be affe cte d by pre vious ly unfore s e e n com ple xitie s , s uch as fe e dback s be tw e e n w ate r s torage , bas al and s urface topograph y and ice ve locity.
Re garding th e role of ice s tre am s in th e s tability of ice s h e e ts , one of th e m os t ch alle nging proble m s is th e nature of th e trans itional flow re gim e involve d in th e m as s trans fe r be tw e e n ice dom e s and ice s h e lve s , w h ich bas ically conce rns th e couple d dynam ics of ice s tre am s and grounding line s (Vie li and Payne , 2005; W ilch ins k y, 2007). Th e s e is s ue s aris e from difficultie s in tre atm e nt and form alization of th e m e ch anical trans ition be tw e e n s h e e t-type flow , w h e re ice de form ation large ly occurs due to ve rtical s h e ar, and s h e lf-type flow , w h e re ice de form ation is dom inantly due to h orizontal s h e ar (H ugh e s , 2003). Th e m atte r is re le vant for th e as s e s s m e nt of th e s tability of m arine ice s h e e ts (H ollin, 19 62; Me rce r, 19 68; H ugh e s , 19 73), w h ich h as be e n q ue s tione d due to th e inh e re nt com ple xitie s of th e ice s tre am – ice s h e lf coupling
(W e e rtm an, 19 74; Th om as , 19 79 ; H ugh e s , 19 81).
Th is h ypoth e s is e m ph as ize s th e role of ice s h e lve s in th e s tability of th e grounde d ice and im plie s th at th e dis appe arance of ice s h e lve s m igh t trigge r th e pour of vas t am ounts of ice into th e oce ans , le ading to a s ubs tantial incre as e in s e a le ve l. Alth ough th is h ypoth e s is h as be e n dis re garde d by late r th e ore tical w ork (H e rte rich , 19 87; H indm ars h and Le Me ur, 2001), th e re ce nt s urge s of form e r tributarie s to th e Lars e n Ice Sh e lf, Antarctic Pe nins ula, follow ing its collaps e call to a re cons ide ration of th e m e ch anical as s um ptions be h ind th e s e m ode ls (D e Ange lis and Sk varca, 2003; Rignot and oth e rs , 2004). In th is particular conte xt, th e dynam ics of ice s tre am s is im portant be caus e obs e rvations in m ode rn ice s h e e ts s h ow th at it is large ly along th e ir track s th at th e above de s cribe d m e ch anical trans ition is m ate rialize d (H ugh e s , 2003). Furth e rm ore , th e re is s trong th e ore tical s upport for th e ide a th at m e ch anical pe rturbations at th e grounding line can be rapidly propagate d to th e ice s h e e t inte riors via ice s tre am s (Rém y and Le grés y, 2004; H indm ars h , 2006). H e re it is w orth to note th at, alth ough th e s e ide as m igh t indicate a clos e as s ociation be tw e e n ice s tre am s and ice s h e e t ins tability, a note of caution s h ould be adde d be caus e , as s pe culate d by H indm ars h (19 9 3;
19 9 6), th e occurre nce and e volution of ice s tre am s m igh t tak e place w ith in a m ore ge ne ral m anifold of ice s h e e t e q uilibria. In fact, re ce nt s tudie s com bining obs e rvations on m ode rn and ancie nt ice s h e e ts h ave s ugge s te d th at ice s tre am s are one as pe ct of th e m ore e xte ns ive and ge ne ric s ubglacial th e rm al organization of ice s h e e ts , w h ich m igh t re organize and adapt, for e xam ple , in re s pons e to clim ate ch ange s (Kle m an and Glas s e r, 2007).
Furth e rm ore , s ubs tantial e vide nce s h ow s th at s e dim e nt de pos ition tak e s place at th e grounding line s of ice s tre am s (O 'Cofaigh and oth e rs , 2003;
Alle y and oth e rs , 2007; Anandak ris h nan and oth e rs , 2007), a proce s s th at m igh t play a s tabilizing role and pos s ibly re tard th e dynam ic e ffe cts of rais ing s e a le ve ls (Sch oof, 2007).
MO TIVATIO NAND O BJECTIVESO FTH EPRESENTSTUD Y Th e pre s e nt s tudy w as m otivate d by th e ne e d of a de taile d account of th e ch aracte ris tics and e volution of palae o-ice s tre am s in th e north -e as te rn Laure ntide Ice Sh e e t, a re gion th at be ars one of th e m os t com ple te re cords of palae o-ice s tre am s in a form e rly glaciate d re gion. Th e aim w as to de ciph e r th e location, e xte nt, ge om e try, and re lative te m poral e volution of palae o-ice s tre am s and to analys e th e ir dynam ics and influe nce in th e functioning and m ode of de cay of th e ice s h e e t.
W ork w as accom plis h e d th rough th e ge om orph ological inte rpre tation of s ate llite im age s and s ubs e q ue nt proce s s ing of th e re s ulting m ap us ing a glaciological inve rs ion s ch e m e . Cons ide rations about th e s e palae o-ice s tre am s and th e ir im plications for th e Laure ntide Ice Sh e e t w e re pe rform e d in th e ligh t of conte m porary th e orie s and h ypoth e s e s on th e be h aviour of ice s tre am s and ice s h e e ts .
REGIO N O F INTEREST
TO PO GRAPH Y, GEO LO GYAND GEO MO RPH O LO GY
Th is w ork de als w ith th e portion of th e Canadian Arctic form e rly cove re d by th e north -e as te rnm os t Laure ntide Ice Sh e e t, e m bracing an are a of 3.19 x 106 k m2 (Fig. 1). Th is re gion e ncom pas s e s m ajor topograph ical fe ature s of palae oglaciological s ignificance lik e th e s h allow (~ 25 m de e p) Foxe Bas in, th e axe s of Booth ia Pe nins ula and Baffin Is land, th e s ubm arine trough s of M'Clintock Ch anne l, Gulf of Booth ia and H uds on Strait and th e plains of north e rn Ke e w atin (Fig. 2). Be drock is ge ne rally com pos e d of Pre cam brian crys talline rock s of th e Ch urch ill Province and e arly Palae ozoic carbonate s and s e dim e ntite s of th e Arctic Platform and H uds on Bay Low land province s (W h e e le r and oth e rs , 19 9 6). Re gional ge om orph ology is dom inate d by th e im print of th e re ce nt glacial pas t (Fig. 3). Lands cape s of are al s cour are w ide s pre ad, occurring m os t notably on north e rn Ke e w atin, s outh e rn Booth ia Pe nins ula, ce ntral Baffin Is land, Me lville Pe nins ula and is lands at th e h e ad of th e H uds on Strait (Sugde n, 19 78; Andre w s , 19 89 ).
Clas s ical e xam ple s of s e le ctive line ar e ros ion occur along th e fjords of e as te rn Baffin Is land. Lands cape s of little or no glacial e ros ion are pre s e nt on Booth ia, Me lville and Brode ur pe nins ulas and Som e rs e t, South am pton and Baffin is lands . In s om e of th e s e are as w e ll de ve lope d pre -Quate rnary fluvial lands cape s h ave be e n pre s e rve d unde r dom inantly
cold-bas e d portions of th e ice s h e e t (D yk e , 19 9 3;
Kle m an and H ätte s trand, 19 9 9 ; Fig. 4). A w ide varie ty of glacial landform s is obs e rve d. W e ll pre s e rve d dire ctional landform s lik e drum lins , flutings and m e ga-s cale glacial line ations (Clark , 19 9 3) are found on north e rn Ke e w atin (Fig. 3a), north -ce ntral Baffin Is land, w e s te rn South am pton Is land, ce ntral Booth ia Pe nins ula (Fig. 5), and unde r th e s ubm arine are as of M'Clintock Ch anne l and Pe e l and Lancas te r s ounds . Prom ine nt e s k e rs form th e w e ll de fine d de glacial landform s ys te m in north e rn Ke e w atin (Fig. 3b). Ribbe d m oraine s are w ide s pre ad and e xte ns ive , particularly in north e rn Ke e w atin.
D e Ge e r m oraine s are m ore re s tricte d, but cove r e xte ns ive are as at fe w locations lik e Québe c- Labrador and Prince of W ale s and South am pton is lands . Th e till cove r is th in and dis continuous and th e de gre e of pre s e rvation of th e landform s is h e te roge ne ous . Pre s e nt glaciation occurs along th e e as te rn part of Baffin Is land. Ve ge tation is low , s pars e and in s om e are as e ntire ly lack ing.
Pos tglacial m odification by coas tal and pe rm afros t proce s s e s is locally s e ve re , be ing in ce rtain cas e s an obs tacle for th e inte rpre tation of landform s .
GENERALPALAEO GLACIO LO GICALSETTINGAT LAST
GLACIAL MAXIMUM
According to s e ve ral re cons tructions (e .g. D yk e and Pre s t, 19 87; H ugh e s , 19 9 8) at Las t Glacial Maxim um th e re gion w as cove re d by th e north e rn Ke e w atin, Foxe /Baffin and Québe c/Labrador s e ctors of th e Figure 1. Map of north e rn North Am e rica s h ow ing th e location of th e s tudy re gion (das h e d fram e ), th e outline of th e Laure ntide Ice Sh e e t at 21.4 k a BP (afte r D yk e and oth e rs , 2003) and th e location and nam e of its s e ctors and ne igh bouring ice s h e e ts . Th e arrow s and s h ade d are a de pict ge ne ralize d ice e xport route s and th e approxim ate location of th e Ke e w atin Ice D ivide (afte r Ayls w orth and Sh ilts , 19 89 ), re s pe ctive ly.
Palae o-ice s tre am s in th e north -e as te rn Laure ntide Ice Sh e e t
Figure 2. Com bine d topograph y and bath ym e try of th e re gion w ith nam e s of m ajor ph ys iograph ic fe ature s .
Laure ntide Ice Sh e e t (Fig. 1). Palae o-ice flow from th e Ke e w atin Ice D ivide proce e de d rough ly north w ards and w e s tw ards th rough th e Que e n Maud Gulf, north -w e s tw ards th rough th e M'Clintock Ch anne l and e as tw ards tow ards H uds on Bay. Palae o- ice flow from th e Foxe /Baffin s e ctor proce e de d radially out of a dis pe rs al ce ntre rough ly locate d ove r Foxe Bas in, flow ing e as tw ards acros s th e m ountain range of Baffin Is land, w e s tw ards ove r Me lville Pe nins ula and s outh -e as tw ards tow ards th e H uds on Strait. Flow from Québe c/Labrador into th e re gion proce e de d north w ards tow ards th e H uds on Strait (Clark and oth e rs , 2000; Jans s on and oth e rs , 2003).
PREVIO USRESEARCH O NPALAEO-ICESTREAMS
Palae o-ice s tre am re s e arch in th e re gion h as particularly focus e d on th e H uds on Strait (Laym on, 19 9 2; Manle y, 19 9 6; H ugh e s , 19 9 8; Gray, 2001;
Andre w s and MacLe an, 2003; H ulbe and oth e rs , 2004). Re curre nt s tre am ing flow e ve nts along th e H uds on Strait h ave be e n invok e d to e xplain th e e xis te nce of ubiq uitous laye rs of coars e -graine d lith ic fragm e nts , partly de rive d from th e H uds on Strait, in m arine s e dim e nts of th e North Atlantic (H e inrich , 19 88; H e m m ing, 2004). Th e ide a is robus tly s upporte d by th e ability of num e rical m ode ls to re produce s tre am ing flow in th is location (MacAye al, 19 9 3; Mars h all and Clark e , 19 9 7), th e pronounce d topograph ical profile of th e s trait, and its floor com pos e d by rh e ologically “s oft” be drock (Andre w s and MacLe an, 2003). H ow e ve r, th e ge om orph ological e vide nce for s tre am ing flow on e m e rge d land is s carce and it h as th e re fore be e n propos e d th at H uds on Strait palae o-ice s tre am s m us t h ave flow e d w ith in th e de e pe r parts of th e ch anne l, w h ich are pre s e ntly unde r w ate r, w h ile
flank e d by atte ndant froze n-be d are as locate d ove r pre s e ntly e m e rge d land (Article III). Fragm e nts of palae o-ice s tre am s h ave oth e rw is e be e n pos itive ly ide ntifie d in s e ve ral locations . D yk e (19 84) de s cribe d e longate d and w e ll de fine d line ations in paralle l arrange m e nts acros s Booth ia Pe nins ula (Fig.
5) and re cognize d th e m as e vide nce for fas t palae o- ice flow . D yk e and Morris (19 88) notice d conve rge nt patte rns of glacial line ations and carbonate dis pe rs al trains in Prince of W ale s Is land and inte rpre te d th e m as a s ignature of a palae o-ice s tre am , i.e . th e Trans ition Bay Ice Stre am (Fig. 6;
W ins borrow and oth e rs , 2005). Clark and Stok e s (2001) s um m arize d ge om orph ological e vide nce for fas t palae o-ice flow along th e M'Clintock Ch anne l and, partially bas e d on e vide nce provide d by H ogds on (19 9 4), pos tulate d th e e xis te nce of an ice s tre am during de glacial tim e s . Late r re s e arch by D e Ange lis and Kle m an (Article II) and Stok e s and oth e rs (2005) h as s h ow n th at th e ge om orph ological e vide nce s h ow s s e ve ral dis cre te e ve nts and th at th e M'Clintock Ch anne l Ice Stre am w as a m ultige ne rational fe ature (Fig. 6). O n e as te rn Victoria Is land, and in place s s upe rim pos e d w ith th e re cord of M'Clintock Ch anne l ice s tre am s , a com ple x re cord of m inor palae o-ice s tre am s h as be e n re ve ale d by Stok e s and oth e rs (2005) and D e Ange lis and Kle m an (Article II). In north -w e s te rn Ke e w atin, ne ar D ubaw nt Lak e , Kle m an and Borgs tröm (19 9 6) notice d a w e ll de fine d patte rn of line ations on th e Glacial Map of Canada (Pre s t and oth e rs , 19 68) and inte rpre te d it as th e cons e q ue nce of a m e ga-s urge of th e las t portion of th e Ke e w atin s e ctor during de glacial tim e s . Late r analys e s by Stok e s and Clark (2003a) pos tulate d th at th is s urge took place in th e form of s tre am ing flow and de nom inate d it th e D ubaw nt Lak e Ice Stre am . In
north -ce ntral Ke e w atin, McMartin and H e nde rs on (2004) and D e Ange lis and Kle m an (Article II) inde pe nde ntly ide ntifie d a cle ar patte rn of fas t palae o-ice flow from th e form e r Ke e w atin Ice D ivide (Ayls w orth and Sh ilts , 19 89 ). Th is patte rn s h ow s th e occurre nce of palae o-ice s tre am flow clos e to th e core of th e ice s h e e t and h as be e n inte rpre te d as a form e r tributary to palae o-ice s tre am s along th e M'Clintock Ch anne l (Article II). D re dge (19 9 5) re cognize d w ide s pre ad carbonate dis pe rs al trains in north e rn Me lville Pe nins ula, inte rpre ting th e m as e vide nce for palae o-ice s tre am s of th e Foxe /Baffin s e ctor (D re dge , 2001). D e Ange lis and Kle m an (Article II) de s cribe d a m as s ive conve rge nt patte rn at Rae Is th m us , inte rpre ting it as th e s ignature of ice flow at th e h e ad of ice s tre am s and ice s h e lve s along th e Gulf of Booth ia and Lancas te r Sound. O n e as te rn Baffin Is land, Mille r and oth e rs (2002) and Brine r and oth e rs (2003) found e vide nce for fas t palae o-ice flow along th e fjords in th e form of low gradie nt outle t glacie rs , particularly along Cum be rland Sound (Kaplan and oth e rs , 2001). O n north e rn Baffin Is land, D e Ange lis and Kle m an (Article s II and III) notice d patte rns of fas t palae o-ice flow at th e e dge s of Brode ur and Borde n Pe nins ulas , w h ich w e re inte rpre te d as topograph ically controlle d outle t glacie rs and ice s tre am s draining local ice caps . Baffin Is land als o be ars re m ark able landform as s e m blage s around Erich s e n and Am adjuak lak e s , w h ich w e re inte rpre te d as th e re cord of trans ie nt s ucce s s ions of s m all de glacial ice s tre am s (Article III).
M ATERIALS AND M ETH O D S TH E GLACIO LO GICALINVERSIO NSCH EME
Th is w ork re lie s on th e us e of a glaciological inve rs ion s ch e m e for th e inte rpre tation of landform as s e m blage s m appe d from s ate llite im age ry. Th is conce ptual m ode l is conce ive d as an obje ctive fram e w ork to form alize th e data re duction ne ce s s ary for us e of th e landform re cord to re cons truct ice s h e e t configurations . Th e s ch e m e w as originally pre s e nte d in Kle m an and Borgs tröm (19 9 6), furth e r de ve lope d in Kle m an and oth e rs (19 9 7) and fully e xplaine d in its re vis e d form in Figure 3. O bliq ue ae rial picture s of are as in north -w e s te rn
Ke e w atin, s h ow ing typical lands cape s of th e re gion: a.
cros s -cutting re lations h ips be tw e e n glacial line ations of diffe re nt age . b. de glacial e s k e r. Note th e low and s pars e ve ge tation cove r. Both picture s are tak e n during a re connais s ance fligh t conducte d on 29 July 2005 at an altitude of about 1200 m above th e ground (Ph otos : H e rnán D e Ange lis ).
Table 1. Crite ria for th e re cognition of palae o-ice s tre am s . Afte r Stok e s and Clark (19 9 9 ).
Palae o-ice s tre am s in th e north -e as te rn Laure ntide Ice Sh e e t
Kle m an and oth e rs (2006). A s im ilar approach h as als o be e n de ve lope d and applie d by Boulton and Clark (19 9 0) and Clark (19 9 7). Bas ically, th e s ch e m e m ak e s us e of th e dis tribution of glacial ge om orph ological data, i.e . s triae , line ations , e s k e rs and m oraine s , in orde r to re cons truct th e ge om e try and e volution of ice s h e e ts . Th e m ain ide a be h ind th e s ch e m e is to clas s ify th e landform s according to form ative conditions , particularly cons ide ring th at
landform cre ation, de s truction and pre s e rvation are controlle d by th e th e rm al s tate of th e be d. Th is m e ans th at w e t- (or m e lte d-, or w arm -) bas e d conditions prom ote re s h aping of th e lands cape w h e re as dry- (or froze n-, or cold-) bas e d conditions trans late into lands cape pre s e rvation (Lage rbäck , 19 88b; Kle m an, 19 9 4). Accordingly, th e s ch e m e tak e s into cons ide ration th at olde r landform s ys te m s m igh t h ave s urvive d due to pre s e rvation Figure 4. Se ction of Lands at 7 ETM+ im age (path /row 035/009 , 29 July 2001) panch rom atic band s h ow ing th e ch aracte ris tic lands cape s at th e ons e t of an ice s tre am on Brode ur Pe nins ula. An olde r fluvial lands cape w ith prom ine nt incis e d fluvial ch anne ls lie s ne xt to a w e ll de ve lope d, m ore re ce nt glacial lands cape . Note th e lak e rim at th e ne at contact be tw e e n th e tw o lands cape s , i.e . th e ons e t zone of th e palae o-ice s tre am , and th e s ource are as of carbonate plum e s .
Figure 5. Se ction of Lands at 7 ETM+ im age (path /row 036/012, 3 Se pte m be r 2000) panch rom atic band s h ow ing w e ll de ve lope d e xam ple s of m e ga-s cale glacial line ations in ce ntral Booth ia Pe nins ula.
unde r cold-bas e d ice and th e re fore portions of th e be d m ay s h ow anom alous or contras ting flow patte rns . In practice th e s ch e m e is applie d by re cognizing landform as s e m blage s form ing coh e re nt patte rns and s ubs e q ue ntly inte grating th e m into landform s w arm s . Th e s e s w arm s are de fine d on th e bas is of s patial continuity and re s e m blance to a glaciologically plaus ible patte rn, follow ing th e le as t com ple x pos s ible s olution. O nce ide ntifie d, s w arm s are draw n us ing line s th at are paralle l to th e vis ually coh e re nt landform patte rn, w ith trans ve rs e up and dow ns tre am lim its (Fig. 7). Landform s w arm s re pre s e nt th e firs t le ve l of abs traction in th e re gional inte rpre tation s ch e m e and s e rve to re duce th e cartograph ic inform ation into a m anage able num be r of e ntitie s (Kle m an and oth e rs , 19 9 7).
PALAEO-ICESTREAMS INTH ELAND FO RM RECO RD
Palae o-ice s tre am s h ave be e n long s us pe cte d and propos e d, alth ough th e ir s ys te m atic re cognition in form e r ice s h e e t be ds re q uire d th e ade q uate tools to be de ve lope d (Clark and Stok e s , 2003). Th e s e tools com pris e : 1. s ate llite im age ry, 2. advance d im aging s onar s ys te m s and 3. crite ria to ide ntify th e ge om orph ological s ignature of s tre am ing flow in th e palae o-re cord. Sate llite im age ry is im portant be caus e th e e xte ns ive are a cove re d by s ingle s ce ne s (e .g. 180 x 180 k m in a Lands at im age ) s h ow s s ignificant portions of ice s tre am path s in a s ingle vie w , w h ile at th e s am e tim e re ve aling th e large landform s as s ociate d w ith palae o-ice s tre am flow (Clark , 19 9 7; Stok e s , 2002). Th e introduction of advance d im aging s onar s ys te m s allow e d th e w ide s pre ad ide ntification of s ubm e rge d palae o-ice Figure 6. Se ction of Lands at 7 ETM+ im age (path /row 043/009 , 3 Augus t 2000) panch rom atic band s h ow ing th e s outh - ce ntral portion of Prince of W ale s Is land. Note th e w e ll de fine d palae o-ice s tre am path s of th e tw o ge ne rations of M'Clintock Ch anne l ice s tre am s and th e Trans ition Bay Ice Stre am . Th e ins e t s h ow s an e xam ple of cros s -cutting re lations h ip at th e ons e t zone of th e Trans ition Bay Ice Stre am , s h ow ing th at it is younge r th an M'Clintock Ch anne l ice s tre am track ove r w h ich it is s upe rim pos e d.
Figure 7. Practical s te ps of th e glaciological inve rs ion s ch e m e , from a glacial-ge om orph ological m ap to th e palae oglaciological re cons truction.
Palae o-ice s tre am s in th e north -e as te rn Laure ntide Ice Sh e e t
flow patte rns , e xte nding th e re ach of palae oglaciological re s e arch into contine ntal platform s (O 'Cofaigh and oth e rs , 2005; O tte s e n and oth e rs , 2005). Finally, a m ajor advance m e nt in th e s ys te m atic re cognition of palae o-ice s tre am s w as th e introduction of coh e re nt crite ria for th e ir ide ntification in th e landform re cord (Stok e s and Clark , 19 9 9 ; Table 1). Th e s e crite ria involve th e ide ntification of landform patte rns of ch aracte ris tic s h ape and dim e ns ion, conve rge nt h e ads (Figs . 4 and 6), abrupt late ral m argins (Figs . 6 and 8), late ral s h e ar m oraine s (Figs . 6 and 8), e longate d and s ubdue d landform s (Figs . 4 and 9 ) and Booth ia-type dis pe rs al trains (D yk e and Morris , 19 88). Us e of th e s e crite ria provide s unam biguous rule s th at cons ide rably re duce th e s ubje ctivity in th e ide ntification of palae o-ice s tre am s , in particular w h e n th e y are us e d w ith in th e com pre h e ns ive fram e w ork of th e glaciological inve rs ion s ch e m e . IMPLEMENTATIO NO FTH EMETH O D O LO GY
All inform ation involve d in m apping and inte rpre tation w as h andle d w ith in a ge ograph ic inform ation s ys te m (GIS). In orde r to k e e p
ge om e trical uniform ity w ith Canadian cartograph y, our GIS databas e is bas e d on a Lam be rt Conform al Conical proje ction re fe rre d to th e North Am e rican D atum 19 83 (NAD 83). Standard paralle ls are locate d at 49 °N and 77°N and th e ce ntre of proje ction is at 83°W , 68°N. D ata is organize d in four le ve ls : s ource , m apping, re fe re nce and inte rpre tation. Th e conte nt, s tructure , as s um ptions and m e th odological de tails of th e s e le ve ls are e xplaine d be low and s um m arize d in Table 2.
D igitizing w as accom plis h e d firs t on ESRI ArcGIS©
s oftw are and late r on O pe nEV (h ttp://ope ne v.s ource forge .ne t/). Ve ctor laye rs w e re originally s tore d as ESRI Sh ape file s and w e re afte rw ards im porte d into a Pos tGIS (h ttp://w w w .pos tgis .org/) databas e for proce s s ing and analys is . Th is w as pe rform e d us ing Pos tGIS SQL com m ands via cus tom Pe rl (h ttp://w w w .pe rl.org/) program s and Ge ograph ic Re s ource s Analys is Support Sys te m (GRASS, h ttp://gras s .itc.it/). Map production w as accom plis h e d w ith Ge ne ric Mapping Tools (GMT) s oftw are (W e s s e l and Sm ith , 19 9 8) and cos m e tic de tails finis h e d w ith Ink s cape (h ttp://w w w .ink s cape .org/).
Figure 8. Se ction of Lands at 7 ETM+ im age (path /row 036/012, 3 Se pte m be r 2000) panch rom atic band s h ow ing th e s outh -w e s te rn m argin of King W illiam Is land. Th e w h ite das h e d line de picts th e inte rpre te d pos ition of a palae o-ice s tre am m argin. Note th e m orph ological diffe re nce and th e ne at contact be tw e e n th e are as w ith in th e ice s tre am and non-s tre am ing ice . Tw o s ligh tly diffe re nt palae o-ice flow dire ctions are re cognize d.
Figure 9 . Exam ple s of till line ations of diffe re nt proportions . Le ngth /w idth ratios large r th an 10:1 are cons ide re d to be th e re s ult of fas t glacie r flow (Stok e s and Clark , 2002). Th e s e large s t form s are us ually de nom inate d m e ga s cale glacial line ations (MSGL, Clark , 19 9 3).
Figure 10. Cove rage by s ate llite im age s (s q uare s ) of th e re gion of inte re s t and track s of th e s onar s urve ys : North w e s t Pas s age Trans it (das h and dot) and H uds on Bay Trans it & Nas tapok a Is lands (full), both pe rform e d by th e O ce an Mapping Group, Unive rs ity of Ne w Bruns w ick , Canada (h ttp://w w w .om g.unb.ca/). Num be rs ce ntre d in th e Lands at s ce ne s indicate path /row pairs .
Table 2. GIS databas e organization.
