J oumal oJ Glaciology, r·ol. 42, S o. 142, 1996
Late Pleistocene interactions of East and West Antarctic ice-flow regim.es: evidence from. the McMurdo Ice Shelf
THO}'IAS B . KELLOGG, TERRY H UG HES AND D .\VJD!\ E. KELLOGG Depa rtmen t oJ Geo logical Sciences alld Institute for QJlatemm) Studies, UI/ iversilj' oJ ,\Jail/ e, Orono , "faine 04469. [j.S. A.
ABSTRACT. \Ve prese nt new interpreta ti ons of d eglacia tion in M cMurdo Sound and the wes tern R oss Sea, with o bservati onall y based reconstructi ons of interacti ons between Eas t a nd \Ves t Antarcti c ice a t the las t glacial maximum (LG YI ), 16 000, 12 000, 8000 a nd 4000 BP. At the LG M , East Anta rctic ice fr om Muloek Glacier spli t; one bra nch turned wes tward south of R oss Tsland b ut the other bra nch rounded R oss Island before fl owing south"'est in to lVf cMurdo Sound. This fl ow regime, constrained b y a n ice sa ddle north of R n. s Isla nd, is consisten t wi th the reconstruc ti on of Stuiyer a nd others (198I a ) . After the LG lVI. , grounding-line retreat was m ost ra pid in areas \~ ' i th greates t wa ter d epth, es pecially a long th e Vic toria Land coast. By 12 000 BP , the ice-flow regime in :'.1cMurdo Sound c ha nged to through-flowing l\1ulock G lacier ice, with lesse r contributions from K oettlitz, Blue a nd F crra r Glaciers, because the formcr ice saddle north of R oss Isla nd was repl aced by a d om e. The modern fl ow regime was esta blished ",4000 BP. Ice deri ved from hi gh elevation s on th e Pola r Pla teau but now stra nded on the M Cl\1urdo Ice Shelf, a nd th e pa ttern of the Transanta rc ti c Mountains erra ti cs support our reconstruction s of Muloc k Glacier ice rounding Minna Bluff but with a ll ire from S kelton Glacier a bl a ting so uth of the bluff. They a rc inconsistent with Drewry's (1979) LGl\1 reconstruc ti on th a t in cludes Skelton Glacier ice in the l\IcMurdo Sound through-flow. Drewry's (1979) n1.od el cl osely a pproxima tes our results for 12 000-4000 BP. Ice-sh eet m odeling hold s p romise for de te rm ining whether d eglacia ti on proceeded by grounding-line retreat of a n ice sheet tha t was la rgely stagna nt, because it ne\'er approach ed equilibrium fl owline profiles a fter the Ross I ce Shelf grounded , or of a dyna mic ice sheet with fl owline profil es kept low by active ice streams that extended northwa rd from prese nt-day outlet glaciers a ft e r the R oss Ice Shelf grounded .
INTRODUCTION glacia l geologic observa ti ons and th e o bserved presen t day ice d ynamics of the M c:'1urdo I ce Shelf (MIS), a One key objecti\'e of the \\' es t An ta rcti c ice sheet (\V A I S) part of the R oss Ice S helf. The reconstructi ons aid in initia ti\'e is documenta tion of eusta ti c sea-level c h a nge elucida ting modern glaciologica l processes operating on res ulting from the possible disintegra tion of the \Ves t this ice shelf and suppo rt sugges ti ons by K ellogg a nd An ta reti c ice sheet (Bindsc hadler, 199 1), This effort oth ers ( 1990) tha t som e existing J\IIS features a re requires detailed knowledge of ice-sheet history in \Vest remna nts from a fo rmer ice-flow regime, MIS d a ta Anta rcti ca, including the history of grounding-line a nd permit eva lu a ti on of two different published reconstruc calving-margin retreat to the positi ons now occupied by ti ons o f the fl ow r egim e during the LGM, a nd these features a nd a n acc urate d yna mic ove rvi ew of the develo pment of four new reconstructions for the R oss \1\1 es t An ta rcti c ice sheet, i ncl ud i ng prese n t a nd former Sea embayment during the deglacial tra nsition fr om the precipita ti on sources, fl ow regimes a nd cha nging inte ract grounded la te Wi sco nsin R oss Sea ice sh eet to the modern ions wi th ice derived from Eas t Anta rcti ca, The d evelop R oss I ce Shelf, all of wh ic h include ice d erived from both m ent of relia ble predicti\'e mod els for future ice-sheet Eas t Anta rcti ca and \Vest Antarcti ca, retreat depends on th ese data, Yet, so far most \ VAT S W est Antarcti ca is a key a rea for studying glacia l studies ha\'e concentrated either on modern ice d yn a mics history a nd dynamics, b ecause th e world's largest ex ta nt in \Ves t Anta rctica or on elucid a ting former ice m axima, ma rine-based ice sheet is located there. Of particul a r This paper presents a series of prelimina ry o b serv importa nce are the Dry V a ll eys of southern Victori a a ti ona ll y based reconstructi ons of interacti ons b e tween La nd , situa ted between the seasona ll y open waters of the the Eas t and W est Anta rcti c ice sheets during a nd since R oss Sea a nd MeMurdo Sound on the east and the E ast the last glacial m aximum (LGM) . Thesc (\\'0 ice sh eets Anta rc tic ice shee t to the wes t. These ice-free valleys a re a re se pa rated by a dividing wall (the Tra nsan ta rc tic shi eld ed from direct E ast A nta rctic ice-sh eet influence b y M o untain s) a nd interact today prima rily where thro ugh th e Tra nsantarctic l\1 0 untains, It can be a rgued th a t a fl owing outlet glaciers from Eas t Anta rctica impinge on third m aj or factor, in addition to Eas t a nd \Vest Anta rcti c the R oss Ice Shelf. Our reconstructi ons are based on ice flu c tua tions, op e ra tes in this a rea: local glaciers
Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 486 h-ellogg alld others: Late Pleistocene illteractions of East alld Il 'est Allta rctic ice-jloU' regimes
res pond to the proximity of a n open-wate r moisture so urce in the R oss Sea . This influen ce is actu a ll y controlled by \Ves t Antarc ti c ice ex tent, being insignif icant during glacial maxima a nd reaching its g rea tes t im pon a nce during interglacia ls wh en shelf- a nd sea-i ce limits are least ex tensive. The a\'ail a bility of a local moisture source is importa nt fo r this pa per prima ril y with respect to flu c tua ti ons of K oettlitz and Skelto n Glaciers. A detailed la te Qua terna r y pa leoclima ti c record for th e Dry \' alleys region (D enLo n a nd oth ers, 19 71 , 1989; ~ . R OSS SEA Srui ver a nd o thers, 198 1a ) sho\\'s tha t the d omina nt ~ "fi". Nove Ohief GI ~!. Boy
features were peri odic ad va nces of th e \\' est An ta rctic ice : 1" ",' DrYCJalsk i Ice Tonli\lJt shee t, which thickened a nd g ro unded in th e R oss Sea and Ma .... SOn GI. Cope ~ Franklin I. 0: Hiekey \lc~furd o Sound, pushing lobes of grounded ice in to the ee(Jufort I. D ry \ ' a lleys a nd leaving a record of ice-dammed lakes, Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 487 Journal oJ Glaeiology Mc M urdo Sound z ROSS SCA ;:~ ..,,,,, '" '"''' ~ . ~ ROSS r. ICE 5H£l.F ",, ISLAND RIF T Whi te SC ALLOP Isla nd HilL Blo Ck Is lan d \ \ M I DiscO\I ery 5 0 5 10 15km b8~~d3===~S,8~l t==~I==~1 Fig . 2. NIcMurdo i ee Shelf ( Jl lIS) area, showing locations mentioned in text and inJormalnamesJor study areas ( Black Island debris bands (BiD B ), "Swirls", central area , etc.). •v ote that because the j\.1 IS is so (omple,\, only major debris bands and features are shown. Base map used here is modified f rom Stuiver and others (1981a) , is based on U.S. Geological Survey tOjJograjJhic majJs, aerial pho tographs and material from other sources. Very little ice is advected tod ay into th e western MIS a nd \Vhite Islands. This " norm al Oow model" permits fr om th e R oss I ce Shelf (Swithinbank, 1970; Bentley and postulation of a fl ow regim e entirely different from tha t o thers, 1979) or from Koe lllitz G lacier (Gow and Epstein , discussed abo\'e, with different locati o ns for debris a nd 1972). Hence, the mass balance of this area is domina ted fos il o rigin , and hence can haw a significant bearing on by basal freezing a nd surface a bla ti on, th e la tter caused interpretati ons of present and former ice Oowlines . primaril y by adia ba ti ca ll y warmed kata ba ti c winds K ellogg and o thers (1990 ) recognized two distinctly Oowin g down o n to th e MIS fr om Minna Bluff and different types of d ebris bands on the MIS. The first M ount Discovery (Stuiver a nd oth ers, 1981 a ). I ce gro u p , disc ussed a bove, is charac teri zed by thin (usua ll y velocity measurements in the western r..ns arc less th an < 10 cm thick) debris overl ying cl ean shelf ice, in which 5 m year 1 towards the north be tween Mount Discovery ma rine shells yield 14C ages ranging up to 7700 BP. I ce and Bl ack Isla nd and north of the strait between White underlying debris in this yo ung gro up of debris ba nds 18 a nd Black Isla nds (Swithinbank, 1970). Higher velocities usuall y has 8 0 val ues ranging from -5.0 to + 5.0%0, of 18- 22 m year 1 directed wes t-northwes t to northwest indicating a marine o ri gin. T he presumed northwa rd were recorded near th e calving margin between R oss pa ttern of modern ice move ment has been discussed Island and th e Dry Vall eys (Swithinbank , 1970). M ost a bove. ice movemen t north of Bl ack Isla nd is towards the north The second type of debris band is located prima rily or northwest, pa rallel to debris ba nds, es pecially a lo ng the a lo ng the east coast of Brown Peninsula in th e "Swirls" striking debris band ex tending ",30 km from Black Island area (Fig. 2). Debris thickn ess here appears to exceed to the calving m a rgin (Bl ack Isla nd debris ba nds: BIDB), 10 cm but its full ex tent has not bee n determined, because Ix'cause of th e progression of 14C ages mentioned a bove it is ice-cemented below 5- IO cm. A significant part of the (K ell ogg and others, 1990). H owever, an anon ymous boulders here have lithologies indicating transport fr om reviewer suggested that now migh t have been p erpend th e Transantarctic M ountains. Some of the bands cross icul ar to debris bands, in whi ch case debris comprising th e tide crack along the r..n s grounding line and extend the BIDB might have origina ted a long th e coasts of Bl ack on to the nanks of Brown Peninsula and even cross the Downloaded488 from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. Ke/logg and others: Late Pleistocelle illteraetiolls oJ East alld I Vest Antarctic ice-J7ow regim es 165" Mc M urdo Sound 15 • GOW 4 ..$ • GO W ~ ~ 50 · ~ . 30 '"'--'~ --.....:\, · 50 . 100 71:1"15 / ./ ./ ') ,.,0 ./ --- MI Discovery ./ ,/-00 / / ., ~ / . 'l;0° 5 0 5 10 15\", 88~~d~~s~, :~,,===t' ==~1 '" Fig . 3. M c.l/urdo Ice Shelf thicklless alld iCC-J701l' data ({if/er k eLLogg alld otliers . /990, jig. 17) . Solid dots alld arrows are thickness ( ill Ill ) alld 1'e loci~l' ( 1Il)'ear I) measurements (Su'ithillballk, 1970 ) . res/J('cti ve f)' : solid squares are drillhole :, ( Gow and i:..psteill, 1972) , napt 15 I7Z ice depth near the easternmost Dail!!..)' Islallds which was e.\ tra/Jolated b), Zotikol' alld Cow ( 1967); solid tria llgles are thickllesses rounded to the II earest 5111 from seismic SOlllldillgS ( Cook, 1963) ; 35 III dejlt li is from a drill/zole th rough the ice shelf ( Paige, /968) . Dashed cOllt oll r lilies 1I0rth oJ M il1lla Bh!!] are ice thickllesses ( U.S. Geological Survey, 1972) . D ashed lilies labeled "A" . . , B" alld "C' are from Switliillbank ( 1970 ). " A " marks the boundm] betweell rough ice with melt streams and considerable rehif (ill the It'est) alld mllch slllo otlier bare ice . .. B" appro \ ill1ates the surface equilibriulII line and is extell ded ill to the .I1inl1a B luJf area based Oil our observations . See Swithillbank ( 1970 ) Jor significance oJ " (;'·. Additional thickness and ve loci~v da ta Jar the eastem /Ja rt oJ th e .\IIS (a(ClIllllllation area ) ha ve bee1l given ~) ' .lfcCrae (1984) . Ice-J rolltal /Jo sitioll in /947 is /JrObab£y incorrect as e.\p/ained b), Kellogg and others (1990) . D ashed lili es 011 Brow lI Peninsula, A101lllt DiscovelY alld Black Island are maximum extent oJ Ross Sea Drift ( Stuil'e r alld others . 198 Ia) . BrOlI'll Peninsul a saddle (Stuive r and others, 198 Ia). remnants from the grounded la te Wisconsin R oss Sea Some shell d a tes fl'om the no rthern part of the " Swirls" ice shee t. Gl acia l fl ow was apparently direc ted from east and adjacent ba nds and pa tches th at are tho ug ht to ha\'e to wes t across southern M el\1urdo So und, with a n bee n former pa rts of the "Swirls" area yield I ~e ages a bla ting ma rg in pushing in to the mouths of the Dry 18 > 20 000 BP. Some ice sa m pies fr om this a rea yield 5 0 V all eys to the wes t (Fig. 4). The distribution of la te va lu es ra ng ing from - 25 .35 to - 48 .96%0, suggesting th e Wisconsin-aged R oss Sea drift on Black [sia nd a nd Brown prese nce of pa tches of glacial ice th at form ed a t elevations P eninsula suggests th a t hi gh peaks protruded thro ug h the above 3000 m ( ~[ o r ga n , 1982) and was a d vected to ice shee t as nuna ta ks (Stuive r a nd o thers, 198 1a ); Black so u thern l\lcl\ [u rdo Sound. The "cen tra l" a rea, loca ted a nd White Isla nds, and Brown Peninsul a, proba bl y between Brown Peninsula a nd Bl ack Isla nd, where thick sen 'ed as effec ti ve ba rri ers, reta rding fl ow ra tes . D ebris debris is a lso present, may also represe nt reli ct debris entrained in the grounded ice pro ba bl y accumula ted on 1H bands. The spa rse 14 e and 5 O data avail a b le fr om th is the surface in the M cMurdo So und abla tion a rea, area are not consistent with remnant ice but additional producing so me o f the debris ha nds now preserved in fi eld work is required to test this hypoth esis. the " Swirls", because th e prevailing surface-abla ti on 1R Sedimenrologic, lie a nd 5 O data d escribed abm'e, regime here (Stuiver and others, 198 1a) res ulted in combined with the observed pattern of d ebris bands, upward-direetedice fl O\dines . This co ncludes o ur suggest th a t th e " Swirls" a rea includes d eform ed summary of previous work on the M IS (K ell ogg a nd Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 489 J ournal cif GlaciologJl , 16""° ...... 1680 '" \ •• 0 •••• ' '0 Beaufort Istand .0 ••••••• •• _0. ~~~~--~-:~--~--~~--~.. ~.. ~...~ .. ~ .. ~... -.-t--~~~~... --~ ' ...... '·0 ..... '- • ...... ' .... ". ' . ' ...... '" ...... -J....-""";'--:--"':;;'-700 ~ c_~-r--;---';~-i-; aoc< ~'n;--';"--i-' soo ...... ' ••••• 0 ° '. ' . ' . .... : .M, Lilt.r ..'" ~2S 0: ...,. iJ'" .,o ,....J o 0: ....r :' lilt Morn inv. o ~k .. "0 :. L'... -:- ___:--....,...... ' [ ...... f .. , :::': f...... ,'..... ' .. "" ''I ...... ' '. :":.::" ..: : ...... :.:: .::...... :: ...... -:...... ,'...... ' ...... ' ... " .' ...... ,/' / / FijI, . 4. Surface cOllloll rs (solid lin es : elevaliolls in m a.s.!.) al7 dflowlines (do lled) cif Ih e la le II 'is(ol7sill Ross Sea ice sheel ill M cM urdo Sound (aJler Stlliver and olhers, 1981a, jig. 7-16) . others, 1990). had receded to the vicinity of Brown P eninsul a saddle b y \lV e turn now to a disc ussion of possibl e ramificati ons 77 50 BP" of MIS a nd o ther geologic d a ta for recognizing \Ves t Calving-margin recession may be tracked using le,c A nta rcti c ice retreat. Grounded ice cO\'ered m ost of the da ted ra ised beach es, w hi ch require seasonal open wa ter R oss Sea con tinen tal shelf during the la te \ \'isconsin to fo rm. Stui\"e r a nd others (19B l a ) d a ted numerous m aximum, as disc ussed later in this paper (Fig. 7). raised beaches along the R oss Sea coast a nd om ying D eglacia ti on to the present configuration , wi th th e isla nds, a nd concluded tha t th e calving m argin extended noating R oss Ice Shelf co\'ering the so uthern h a lf of the from ?v1 a rble Point to a position no rth of Beaufort a nd R oss Sea, prob a bly invoh 'ed g lacia l thinning a nd Fra nklin Islands sho rtly before 5650 14C BP a nd ha d ungrounding. 'Ve should be a ble to recogni ze two events retreated to a positio n from Cape Bernacchi to n ear a t a ny pa rti cula r locati on north of the presen t ice-shelf M o un t Bird on R oss Isla nd shortly a fter 5650 I-I C BP. The front: the times when (I) th e grounding lin e a nd (2) th e first observa tions of the MIS during Scott's 19 10- 13 calving ice-shelf m a rgin retreated past th e locati on. In exp ed i ti on showed the w es tern pa rt of the calving m a rgin principle, 14C d a ting of basal p ostglac ial sedimen ts in ex te nding from Cape C hocolate to near th e present R oss Sea cores should provide a deta il ed pic ture of termin us of th e Black I sla nd debris ba nd; the ea tern p a rt grounding-line recession. This h as not proyed possible was much like today. C a lving-ma rgin re treat since 1910- with conve ntional 14C dating because R oss Sea sediments 13 h as occurred prima rily in this wes te rn section. have a low organic carbon content and calcareous shell s During th e period from th e LGM to about 77 50 BP, a re ra re, a nd few AI\IS d a tes have been o bta ined. thinning proba bl y continued to con centra te eng lacia l H owe\"e r, I 'C d a tes from the MIS also provide limits on debris a t th e surface in southern Nl cl\lurdo Sound . In the timing of g rounding-line recession. All these d a tes a re addition, as th e ice wasted, exposing m ore and more of either > 20 000 BP or < 77 50 BP. If th e abse nce o f d a tes Black a nd White Isla nds and Brown Peninsul a, the ice between these ages represe nts the time wh en grounded ice now pa ttern cha nged . The form er east-to-wes t pa ttern fill ed so uthern M cMurdo Sound, the yo unger popula ti on was pro ba bl y replaced by nearl y stagn a n t condi tion s or of d ates records events foll owing thinning, grounding-line sluggish northward m ovement (on the order of a few m recession a nd the incursion of m a rine waters ben eath the year I) betwee n the isla nds and Bro wn Peninsul a, a nd MIS. The old er popula ti on provides minimum d a tes for existing debris ba nds were proba bly d eform ed or bent preglacial m a rine conditions. Thus, th e grounding line into the shapes tha t give th e " Swirls" a rea its na m e. Downloaded49 from0 https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. A-e/Logg alld others: Late Pleistocene illteractiollJ cif East and r rest Alltarctic ice-flow regimes K ellogg and others (1990) pos tula ted th at while m ost of the remainder of the :'IIS becam e progressively a fl oat, the " Swirls" rem a ined grounded , because it res ted on a wide sha ll ow shelf east o[ Brown Pen insul a a nd that ungroundi ng here is a \'ery recent event. GLACIOLOGICAL RECONSTRUCTIONS I ce ele\'a ti ons a nd fl owlines fo r our glacio logical reconstructions a re based on da ta for the area between 150v E and 1800 a nd from 70° to 83°S (Fig. 1), that is, the Tra nsa ntarcti c ?o. Iountains from northern Vi ctori a La nd south to nea r Nimrod Glacier and adjacent areas o f Eas t a nd \ Ves t Antarctica. We reconstructed ice Oowlines a nd ice elevations in this sec tor to conform with these fi eJd d a ta, not with a theoreti call y based computer ice-sheet m odel. Fi gure 5 shows the bed rock topograph y fo r the mod ern ice sheet (Drewry, 1983) that co nstrains o ur reconstructi ons. The modern ice-sheet profil e (Fig. 6) and the LGi\I reconstruction (Fi g. 7) represent two cnd members in o ur series of reconstructi ons. They a re constra ined b y obse n 'ati onal d a ta a nd/or' a weaJth of glacial geologic Fig. 6. P resen t- d(~J' ice elevalions (ruter D rew l), . 1983) coll toured at 500, 1000 and at 1007ll intm'als above 2000 Ill . Flozl'lines indicated ~J' dashed lilies. " D" = ice dome; "S" = ice saddle. StiNled /Jallem illdicates bedrock elaations abal'e 1000 Ill . . \ ate the /JI'omillent dome west cif 1I0rthem ["ictaria Land . .1 smaller dOllle ( T (o'lor D ome IIOt labeled) is situated wesl oJ Jl cJ / Zlrdo SOl/lid. Flow jrom T{~) ' lor Dome is down Skeftoll Glacier but termillates soulh of Al iI/I/ O Bluff Flowjroll7 ,Ill/lock Glacier roul/ds ,lfin/la BIl!!/ lI.'ith 1I10st ice /)(Issillg east cif R oss iJla ll d. informa ti on co ll ec ted a lo ng th e Vi cto ri a Land coast a nd 0 11 o m ying islands (e.g . D enton and o thers, 1971 , 1989; Stui\'C r a nd oth ers, 198 1a, b; Kell ogg a nd oth ers, 1990; Ba ro n i a nd Orom belli, 199 1, 1994; D oc ha t, 1994) including ages and eln 'a ti ons of R oss Seil drift a nd raised beaches, and loea ti ons of ken yi te en"a ti es . These data help to co nstrain L G I\ I ice eleva ti o ns along th e coast oC V iClo ri a Land and in so me cases suggest form er fl ow direc ti ons. More geologic da ta from the R oss Sea would be hig hl y des irabl e to refin e oLlr \\'ork but are currently unaya ila bl e. Our reconstructi ons for 16000, 12000, 8000 and 4000 BP (Figs 9- 12) a re less ri goro us. They re presen t seq uen tia l modilica ti o ns of the LG 1\1 reco nstructio n Fig . 5. ,llodem sllbglacial 10jJogra/J/O' (aJter Drew1)', constrain ed by the limited a\'a il abl e g lacia l geologic d a ta . 1983), con toured at 50011/ illtervals . PreseJIt sea level is shown b), a heav)' solid lille where 1101 covered ~) ' the ice Modern ice-flow regi:rne sheel, alld elsewhere by a hem,)' dashed lill e. Solid jJ allem indirates elevalio ns above 1000 m; stiN led /Ja llern One o bj ective of our wo rk is to dc-ve lo p a model o[ th e indica tes de/Jtlis grea ter thall 1000 /1l. . \ 'ote tlia t Ihese dyna mics of th e m o d ern ;\IlS ice-fl ow regim e. Of great dejJ ths are resl ricted to all tIel-glacier troughs ?I OW pa rtic ula r importa nce is ice advec ted into th e I\ IIS oall/lied b)' l3.-Jlrd, lU lllock, David all d Renllick Glaciers. area, because ice deri\'ed from precipita ti on outsid e the Present northern margin cif the Ross l ee shelf is indica ted immed ia te area may be ex pec ted to display differe nt b)' a lighl dashed line . sta ble-isotope compositio ns and ca rry exo ti c erra tic Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 49 1 JOllmal of Glaciology disc harge is m ore or less directly into th e sea, a nd the ice is re moved as fl oa ting icebergs. However, south of R oss Island, th e Eas t Antarcti c di sc harge feeds the fl oating Ross I ce Shelf where it is supplemen ted by local precipitati on. These two so urces of ice are ba la nced by bottom melting a nd calving from the ice-shelf fro nt, at least in historic time. An exception is th e wes tern part of the NIIS w h ere a pec uli a r combina ti o n of b asal adfreezing, surface ablation and cah-ing-margi n retreat h ave been observed as di sc ussed a bove. Fl owlines shown for the Ross I ce Shelf are co nsistent with obse rved now di recti ons (Sw ithinbank , 1970, p erso nal communication; D .S. Geological Survey, 1972 ). Possible contributions of ice advected to M cMurdo Sound can be r elated to different poss ible precipita tion sources and or ice-eleva ti on flu ctuati ons: (I ) K oettlitz Glacier, representing local precipitation in southern Victori a Land , (2) Skelton Glacier, represe nting mos tly local precipitation and precipita ti on further west on the fl an k of the E ast Antarctic ice sheet, and (3) Mulock Glacier, representing a nearly pure hi gh- elevation Eas t Antarcti c precipita ti on so urce. W e combine m od el res ults with 8180 ana lyses of MIS ice, I"C dates on MIS shells a nd :\lIS boulder-provenance d a ta to evalu a te the ways in whi ch this ice-supply pattern changed in the past, during (Fig. 7) a nd since the LGM (Figs 9- 12). This a na lysis helps to d eta il th e deglacial transi ti on from the Fig. 7. L GM ice-sheet reconstntctioll contoured at 100 m grounded R oss Sea ice sheet to sh elf ice and may p ermit a intervals (solid lines). "GL" = grounding line; other closer correl atio n of late Qua ternary Dry V a ll eys and symbols and patterns as in Figure 6. Note the similarily of R oss Sea sedimen t record s. ice elevations west of the T ransantarctic Mountains to 'vVe mad e som e prelimina r y meas urem ents and modem con ditions . Major differences are in West calculati ons fo r the modern Skelto n and Mulock Glaciers Antarctica where a low-j)rofile ice sheet occupied tlte d rainage basins a nd th e Ross I ce Shelf adjacent to th e entire R oss Sea. The /Jrominent saddle north cif R oss island MIS to sUpplelTlen t the glaciologic model res ults in the permitted southward ice flow into J,1cMurdo Sound, p reparation of o ur LGM reconstructi on. Using D rewry's consistent with the Stuiver and others (1981 a) reconstruc (1983) surface-elevati on data, we plotted surface fl owlines tion . Flowfrom Taylor Dome (west of McMurdo Sound) to determi ne the Mulock Glacier catchment a rea. This was down Skelton Glacier but terminated south of J,1inna catchment was subdivided in to 1550 km wide sectors, for BlujJ. Flow ji-om Mulock Glacier rounded Nfinna Bluff each of whi ch w e measured area. The tota l catchment and Ross Island before flowing soulh into McNl urdo area is ",95 000 km2 We were una bl e to do a similar Sound. a nalys is for Skelton Glacier, because the drainage area is so small on Drewry's (1983 ) m a p a nd so cluttered with Transantarcti c M ountain s topog raphy and flig ht lines debris. MIS features which are not accounted for by th e tha t we could not di scern surface-e1e\'a tion contours. mod ern fl ow regim e can be ass umed to be reli ct, H ence, we es timated a total catchment area for Skelton 18 2 especia lly if the 8 0 of ice in these a reas has the Glacier of ~ I 0 000 km , a value that we beli eve over signature of ice formed by precipitation at high elevati ons es timates the true a rea. Using surface mass-ba lan ce data on the E as t Antarcti c ice sh eet (e.g. the " Swirls" and (Giovin etto a nd others, 1989, fi g. 2), we assigned mass possibly the central area). Knowledge of the m od ern now balance ra tes (kg m 2 year I) to each sector to calculate regime permits us to test a nd evalua te conflicting net accumula ti o n. T he tota l calculated fo r Mulock hypotheses a bout grounded ice ex tent in the R oss Sea Glacier is ~8.5 x 108 k gyear~ 1 a nd th at for Skelton 8 during the last glacial maximum (e.g. Drewry, 1979; Glacier is ~ 1. 5 x 10 kg year I . The to tal Ou x through Stuiver a nd others, 198 Ia ). the Transantarctic Mountains w as calcula ted for each M odern ice eleva ti ons (Drewry, 1983) w ere used to g lacier using a d ensity of 0.9 M g m 3 T otal fluxes are construct ice now lin es for the East An tarctic ice sheet ~9 . 5 x 10 5 m 3 year~1 for Mulock Glacier and ~ 1. 6 x 105 (Fig. 6). Three prominen t d o m es are loca ted in the study m 3 year-I for Skelton Glacier. In both cases, this volume area: T alos D ome in northern Victori a Land, D ome Circe of ice passes through a narrow channel ap proximately west of northern Victori a L a nd and T aylor D om e wes t of 10 km wid e on to the Ross Ice S helf. Grounding-line ice the Dry V a ll eys area. East Antarcti c ice is discharged thickn esses ar e a pproximately 1000 and 850 m , respec through the Transantarctic M ountains at a number of tively (Fig. 5). locati ons (nota bly Byrd , Mulock and David Glaciers), all l ee disch a rged from Skelton a nd Mulock Glaciers of which coincid e with d eep bedrock troughs (Fig. 5). tod ay becom es a fl oat as it p asses through the Trans North of NlcMurdo So und and R oss I sla nd, this a ntarcti c M ounta ins. Thickness d a ta for the Ross Ice Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 492 h'eLLogg alld others: Late Pleislocene interac/iolls oJ Eas/ alld West AIl/arc /ie ice-jlow regimes Shelf (U .S. Geological Survey, 1972) sh ow a complicated Glacier ice a pparently ei ther melts off the base of the Ross pa ttern rela ted to the numerous ice streams. like Skelton, [ce Shelf o r Oows east of Minna Bluff a nd R oss Island to ~IlIl oc k and Byrd Glaciers, blltthere is a general thinning calve into the R oss Sea. This analysis d em o nstrates th a t fr om \'alues close to 500 m wh ere ice streams enter the ice the :'IIS ice samples w ith hi gh negati\'e 8180 \'alu es shelf to less th an 300 m near the cah 'ing margin. This ca nno t be related to the mod ern fl o\\' regime. pa ttern is complicated by surface accumulati on a nd by K oettli tz Glacier tod ay contributes ice o nly to th e area basal melting, whi ch is apparently very im portant within wes t of Brown Peninsul a, a nd even here, ice formed by ~2 00 km of the calving margin (except beneath the precipi ta ti o n in th e local catchment a rea of so uthern western :'fIS) a nd which ca uses much of the n o ted Vi ctoria L a nd mos tl y mcl ts ofI' th e base of the glacier soon thinning. after it becomes aOoat, so that th e lower reaches are Tracing individ ua l ice-stream com ponents to the ice formed fro m frozen sea v\' a ter (Gow and Epstein , 1972). shelf margin is no t trivial because of th ese complex Stui ver a nd others ( 198 Ia ) sugges ted tha t K oettlitz interactions. Wha t is cl ear fr om the U .S. Geological Glacier is probabl y near its maximum extent today, and Survey (1972 ) thi ckness data is tha t ice rounding Minna was even less advanced du ring the LG1\1 . H O\l'e\'er, Bl u ff a nd OO\l'ing west between :'Iinna Bl uff and \\'hite Koettlilz G lacier may ha \'e contributed more ice to the Isla nd today is not d erived from Skelton G lacier but from ?\II S during the Holocen e (Fig. 8b), es pecia ll y if th e R oss Mulock Glacier a nd from local precipita ti on off Minna Sea th en was more open a nd hence a mo re important Bluff. Swithinba nk (1970, person a l communicatio n ) precipi ta ti on so urce th a n tod ay (e.g. K e ll ogg a nd others, believed tha t thi s Oow is negligible tod ay, with m ost 1979). R oss Ice Shelf ice passing eas t of \-\'hite Island and R oss I sla nd. Our a na lys is supports this \·iew (Fig. 8a ). Last glacial m.axim.urn (LGM) Ass uming th a t the Skelton Gl acier ice-II ow ba nd is 20 km wide, its area is approx im a tely one-third tha t of The LGM reconstruction is presented in Fig ure 7. Wes t of the catchment a r ea. ~1 0 d es t basal melting rates, on the th e T ransantarcti c ~I o unt a in s in Eas t Anta rctica, ice order of 10 cm year I , should rem O\'e a ll th e glacial ice shee t e1e \'ati ons we re little d ifferent fr om those of today befo re it rounds ~Iinn a Bluff. In a ny case, Skelton Glacier (cf. Figs 6 a nd 7). The m ajor differences were in Wes t ice could not ex pl a in th e sca llered la rge negati ve 15 18 0 Anta rc ti ca wh ere the R oss Ice Shelf g rounded a nd values from th e ~HS , because the catchment area for this ex panded to fill mos t of the R oss Sea embaymenl. The glacier is belo\\' 2500 m . In contrast, the t\Iuloc k Glacier pos itio n of the grounded margin o n the R oss Sea catchment area ex tends \I'e ll up on to the East Anta rcti c co n tinenta l shelf is problematic. We show grounded ice sheet (EAI S) to ele\'ati ons O\'e r 3000 m. ~r os t t\fulock L G ~I ice ex tending to the shelf break in contras t to recent interpretations b y Denton a nd o thers (1989 ), Anderso n a nd oth ers ( 1992) and Shipp a nd Anderso n (1994) . A nderson and others (1992 ) suggested tha t th e grounding lin e in the \\" es ternmos t troug h in the north wes tern R oss Sea could be es ta blished by the presence of basal tills in sediment cores. Such tills were not found in co res coll ec ted fr om just no rth of Coulma n I sla nd to th e shelf break bu t were wides pread over th e rem a inder of the continenta l shelf. Radiocarbon dates from a core at the shel f break north of Coulma n Isla nd yielded ages of > 35 5 10 BP a nd about 17390 BP (reported as correc ted by - 1200 year). We note tha t th e trough ex tending so uth wa rd from this loca ti on a nd past th e east side of Coulma n Island has a sha ll ow sill a t its outer (northern) end and a second sill occurs off Coulman Isla nd. This trough is simila r to ma ny other cO lllinental shelf troughs in hi gh latitude regions, di spl aying foredeepening which is oft en a ttri bu tecl to modifica ti o n by grou nded ice. For th is reason, we beli eve the LG M grounding li ne a t "-'22 000 Bl' was proba bl y located a t the shelf break. This maximum pos ition proba bl y was no t maintain ed for long, because sea b 'el rose by 10- 20m b y 17000BP (F a irba nks, 1989; B1 anchon a nd Shaw, 1995), a ll ow ing for grounding-line retreat to the position just north of Coulma n Island. An alterna ti\'e ex pl ana ti on is tha t th e LGt\l grounding lin e was located just north of Coulman [sland, sli ghtly beyond th e pos i ti o n we show in o u I' 16 000 BP reconstructi on, and Fig. 8. Ca r/oolls iLLlI stra /ing differen / iee-jlow jJaltems ill th e fored cepcncd ou ter pa rt of this tro ug h d a tes from 111c,llll rdo SOllnd: a. /\lodem ice-jlow regime; b. M id so me earlier glacia ti on, In either case, grounded ice in the f! %ane (4000- 8000 BP ). c. LG NI modified from Ross Sea sector probabl y h ad a low surface profil e, rising Drewl), (1979), d. LGM modified from S/lIivel" and to eleva ti o ns near 1000 m o nl y close to the prese nt coast others ( 198 Ia) . and well south of Minna Bluff. A prominent saddle is Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 493 Journal oJ Glaciology shown north of R oss I sla nd at the LGl\I (and a t catchmet1l ar ea today is a bo u t 150 kg m 2 year I but 16 000 BP) to di vert ice fi ow so uthward in to I\Id.lurd o woul d have been e\'en less durin g the last glac ial Sound , consisten t with glacial geologic evidence, espec maximum, w hen the nearest precipita ti on source was iall y the d istri bution of ken), ite errati cs in the Dry Vall eys located north of the co ntinental shelf break. V cry modes t (Stuiver a nd others, 198 Ia ). sublimati on r a tes co uld easily ha\'e balanced the f10 11' Fig ure 8c and d shows two confli cting LGi\[ recon fr om Skelton Glacier, as they d o today . The case for structi ons for the 1\1cl\1urdo Sound area, one based on Muloc k Glacier ice is simila r. The area o[ M cMurdo 2 2 Drewry (1979; Fig. 8c) and one based on S LUi ve r a nd Sound is onl y a bout 5500 km , compared with 95 000 km oth ers, (198 Ia; Fig. 8d ). Drewry sugges ted tha t grounded [or the i\fulock Glacier catchmen t area . H ence, Mulock ice did not cover much of the R oss Sea continenta l shel f Glacier ice could ha\'e fill ed this a rea easil y a nd perhaps but tha t th e R oss Ice Shelf grounding line and calving m ost of th e region north to D a vid Glac ier, and still have marg in ad vanced north ward a nd local ground ing maintain ed a bl a ti on ra tes suffi cient to bala nce th e occurred on topogra phic highs. One of these highs was average accumulati on ra te of ,,-,500 kg m~ 2 year I ill th e occupied by th e " Byrd- I\Iulock- Skelton" (B:'1S) fl ow modern catchment area. band. H e showed a branch of this fi ow ba nd, consisting o f ice fr om Skelton and :Nlulock Glaciers, turning wes twa rd 16 000 BP between vVhite and R oss Isla nds (bu t not between Minna Bluff a nd White and Bl ack Isla nds) a nd northward into Our reconstructi on for 16 000 BP (Fi g. 9) is based on the :'1cl\1urdo Sound. D re\Vr)' sta ted th a t ice in M ci\Iurdo LGI\1 reconstructi on (Fig. 7) m odified by gro unding-line Sound was grounded a nd th a t it merged wi th ice from retrea t to the vicinity of Coulma n Island (Fig. 8), which Koettlitz, Ferrar a nd Blue Glaciers. Pres umably, no occurred by a bout 17000 BP (Anderso n and others, 1992). abl a ti on occurred a long the BylS fl ow ba nd befor e the Grounding-line recession occurred mos t rapidly in dee p lobe bra nched off into l'vlclVlurdo Sound but, ra ther, troughs on lhe continenta l shelf (Fig. 5) so th at the precipita ti on on this grounded ice proba bly caused the grounding line took on a wayy character, reta ining a northward dec reasing surface slope to be less th a n if more northerl y position on inter\"e ning to pogra phic abla ti on had occ urred. Drewry was no t spec ifi c on this point but pres umably M cMurdo Sound was an abl a ti on zone (Stuiver and others, 198 1a ). Because th e grounded ice here was th ro ugh-fl owing rath er tha n te rmina ting as in the S tuive r and others' (198 Ia) reconstruction (Fig. 8d ) a nd because Drewry was not specifi c on the so urce of this ice ((i'om Skel ton a nd Muloc k G laciers, or rrom Skelton , Muloc k and Byrd G laciers? ), we can onl y guess at a bl a ti on rates . Only one of our th ree l\tH S ice sa mples with hig h negative 8 18 0 \'alu es (north of Brown Peninsula ) can be expla ined by the Drewry (1979) mod el. T he two other samples occur ofI' the north shore of Minna Bluff and in the strait between \,Vhite and Bl ack Islands. Thus, our existing stable-isotope data appear to be inconsistct1l with Drewry's (1979 ) reconstructi on, as do o ur numerous d a ta on boulders d eri ved from the Transanta rcti c M ountains tha t occ ur on MIS debris bands north of Minna Bluff a nd east of Brown Peninsul a saddle. Our preferred interpreta ti on for ice fl ow during the LGM (Fig. 8d ) is based on Stuiver a nd oth ers (198 I a ) (see also Figure 7). According to this mod el, Koettlitz Glacier wi thd rew behind its prese n t Ii mi t, grounded Skelton G lacier ice a bl a ted south of Minna Bluff a nd Mulock G lacier ice formed two grounded lobes: one turning westward south of R oss Island and the other passing east or R oss Isla nd to turn back toward the wes t and so uthwes t, filling M cMurdo So und . Stuive r a nd others (198 Ia) suggested tha t the a rea wes t of White Isla nd was probabl y a surface-abl a ti on zo ne, ice loss Fig. 9. 16000 BP ice-shee t recollstruction . Symbols, bein g caused largely by ublimati on ra ther th an mel ting. /)(lttems and colllours as in Figure 7. The grounding line Surface a bl a ti on probably also domina ted the m ass has retreated Jrom the continental shelf break, with deep balance of the area so uth of Minna Bluff, as it d oes emba)lments il1 troughs 011 the Ross Sea continental shelf, today. Ice at th e LGM did not overtop I\Iinna Bluff especially north oJ COlllma ll Island. An ice shelf still co vers (Stui\'er a nd oth ers, 198 1a ). This a rea, fed by Skel ton much of lhe norlhem jJart oJ the contillental shelf As 2 Glacier, has a n area of a bout 3000 km , approxim ately discllssed in tlu text . this reconstructioll might represent the one-third of th e p resent Skelton Glacier accumula tion LGM , if the true LGM grounding line was just north oJ area. The accumula ti on ra te in the Skelton Glacier Coulman Island. Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 494 A-e/fogg alld olhers: Lale Pleislocelle ill leracliolls of Easl alld r I'esl il l/ larclie ice-j1ow regimes hi ghs. The saddle north of R oss lsla nd a t the LG:'I m ajor change in ice DO\\· in :-Iddurdo Sound a nd north probably existed until aft er 16 000 BP. to near :-Iawso n Glacier. Instead of so uthward Dow (of Muloc k Gl acier ice) into :-lcl\Iurdo Sound, th e a rea was 12 000 BP occupied by northwa rd throug h-D ow of ;\lulock Glacier ice with contributions from K oettlitz, Blu e a nd Ferrar By 12000 BP, th e grounding line had retreated from the Glaciers. This pattern bea rs a striking simila rity to outer R oss Sea continental sh elf to a pos itio n near Cape Drewry's LG M reconstructi on (c f. Fi g. 10 wi th Fig. 8b Hickey (Fig. 10 ). R adiocarbon-dated peng uin remains a nd c). from Ca pe Hickey (near :'Ia\\·so n Glacier) shO\\· the prese nce o f open wa ter b y 10824 BP (Ba roni a nd 8000 BP Orombelli , 1994). Grounded ice on to pogra phic hi ghs in th e R oss Sea, such as l\la wson Bank, became th e loci The 8000 BP reconstructi on (Fi g. I I ) traces th e ground lor sma ll ice domes, one of which ex tended north\\'ard ing-line recession eyen further south in to th e R oss Sea. from R oss Isl a nd, replacing the LG:-l saddle that had The old est reported pos tglacia l m a rine fossil s a t C ape Bird are sli ghtly old er than 8000 BP (Speir and Cowling, 1984; Hein e and Speir, 1989; D ocha t, 1994) and 7750131' a t l\IoUI1t Discovery (Kell ogg a nd others, 1990). H ence, m a rine wa ters penetrated to these locati ons by a bout 8000 BP as the g rounding line retreated. We show the g rounding line e:-;tending from l\IOUlll Discoyery- Black Isla nd- \\'hite Isla nd- Rass Isla nd a nd continuing to the east in about the same positio n as lhe modern calving ma rgin . The ice-shelf front also pro ba bl y receded but was located \\'e ll north of Cape Bird, because th e old es t raised beaches th ere a rc d ated at 4885 BP (Doc hat, 1994 ). The ice-front positi on ShO\\'ll is poorl y constrain ed . \Ve show two small ice rises in th e \'icinity o f Beaufort and Fra nklin Fig. 10. 12 000 BP ice-Jil eel recomlruclio ll. ,S)mbols. /Ja/le rn s and COli /aliI'S as ill Figure 7. The groundillg line adjacen l 10 1I 0rlhem Vicloria Lalld has relrealed 10 Ihe 1Iicill ii)1 qf Cape l-Iickf)' alld a small ice .l helj o((upies Ih is emb(l)lmm/ norlh /0 Drygalski Ice TOIl/;lIe . ,'Vole Ihal l/ze LG.I] saddle Ilorlh of Ross islalld has beell re/)Iaced ~J ' a dome , hence ice }lOll' Ihrollgh ,\IcJ/llrdo Sou nd ( mos/[J' ji'01ll ,l/ulock and A-oelllil;:. Glacier.l) is IIOW norlhward. bee n loca ted here. The g ro unding line a ppa rentl y intersec ted the coast so mewha t so uth of Cape Hickey (Krisse k, 1988; Reid , 1989; Baroni and Orombelli , 199 1). An ice shelf is shown occ upying part of the area from Fig. /1. 8000 BP ice-sheel reco llslrllclio ll . ,S)/IIbols, pal/ems Cape' H ickey to Drygalski I ce T ongue. This ice shell was all d con/ali I's as ill Fig ll re 7. ,. R" = ice rises , where shelj probabl y no t \'ery extensive, because an acti\'e penguin ice gro ullds 011 shallows. The gro lllldi llg line has reIr ailed rookery ex isted at Cape Hic key by 10824 BP, suggesting 10 a /)osilio ll ill soulhem M c,\JlIrdo SOll ll d and all shelf ice nearby open water. ill Ihe sound is oj local origin or ji-om A'oflllil::. an d Fen ar The cha nge from a saddle north of Ross Isla nd at th e Glaciers. Posilion qf Ihe ice-shelj margill lI orlh of Franklill LGl\1 and 16000 BP to a do m e a t 12 000 BP necessita ted a all d Be([lUorl Islands is ap/)ro \ imale. Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 495 Journal oJ Glaciology Islands where the ice shelf may have grounded. Ice flow DISCUSSION in McMurdo Sound continued to be northward through flow, as at 12000 BP, with the same sources as at that time. The observation-based reconstructions at the LGM in Figure 7 and during deglaciation in Figures 9-12 have 4000 BP very low ice-sheet flow line profiles that are as low as or lower than any found in West Antarctica today. This can The grounding line retreated to an unknown position be explained in two ways. First, when sea level lowered south of Minna Bluff by 4000BP (Fig. 12 ), because 120 m or more during the last glaciation and caused the numerous younger radiocarbon-dated macrofossils have Ross Ice Shel[ to become grounded in the Ross Sea been recovered from the IvIIS in so uthern McMurdo embayment, the ice surface would have been ,·irtually Sound (K ellogg and others, 1990) . The calving margin horizontal and many millennia would be required at was so u th of Cape Bird, where the oldest 14C dated raised present-day rates of accumulation to produce flowline beaches occur at 4885BP (Dochat, 1994). On the Victoria profiles [or nearly steady-state ice-sheet flow that are Land coast, the calving margin was probably at Marble observed today [or the East Antarctic ice shee t, especially Point or even further south, consistent with a penguin if the bed became frozen upon grounding and remained guano date of 3905 BP (Baroni and Orombelli, 1994) . The frozen. In this case, the low flowline profiles existed ice-flow pattern in McMurdo Sound was much like that because grounding was so late in the glaciation cycle that of today, although ice from Koettlitz, Blue and Ferrar time was merely insufficient to produce the steeper Glaciers probably occupied some of the westernmost part steady-state flowline profiles typical of East Antarctica of the so und. The ice-shelf frontal position shown east of today. However, if the bed was thawed and remained Ross Island is unconstrained. Grounding-line retreat thawed when the Ross Ice Shelf grounded, then East continued after 4000 BP to the modern position but when Antarctic outlet glaciers through the Transantarctic this position was attained is unknown. Also unknown is Mountains (specifically Byrd, Mullock and David Glac whether the grounding line con tinues to retreat, if it has iers in our study) may have continued as ice streams attained a temporary stable position, or if it is now occupying the linear troughs that extend seaward across advancing. the continental shelf from these outlet glaciers. In this case, the low flowline profiles existed because water saturated sediments in the troughs provided low traction that allowed the low flowline profiles typical of West Antarctic ice streams today. As in West Antarctica, these sediments must be either very thick or continuously resupplied in order to prevent fast ice-stream now from becOlTling slow ice-sheet flow as glacial erosion trans ported the sediments seaward, thereby exposing high traction bedrock in the troughs. A fi eld test 0(" the two hypotheses would involve finding thick sediment wedges on the continental slope beyond the Ross Sea embayment. If none exist, ice-shelf grounding late in the glaciation cycle may not have allowed suffi cient time for ice streams to deposit their wedges before rising sea level forced grounding lines to retreat into the Ross Sea embayment. Field studies would then not provide a definitive test of the competi ng hypotheses. Glaciological theory can provide a test of each hypothesis by using ice-sheet modeling to reconstruct flow line profiles that match th e profiles in Figures 7 and 9-12 for the deglacia tion hemi-cycle. Following Hughes ( 1992), the surface profile along a flowline can be calculated by co mbining the force-balance and mass balance equations. A simultaneous solution of these two equations results in the following expression for the surface slope: 2 6.h = (1 -~) (PW) Fig. 12. 4000 BP ice-sheet reconstruction. Symbols, jJatterns 6.x pw Pr and contours as in Figure 7. The grounding Line has retreated to a jJositioll south of Minna Bhiff and the Ross Ice She?! margin is apjJrOaching its present fJosi/ion . Shelf ice in Mc/vlurdo Sound is from Koettlitz Glacier and local precipitation, and some i\!lulock Glacier ice. Ice-shelf marginal position in i\!IcM urdo Sound is jJooriy constrained but south oJ Cape Bird. where 6.h IS th e change o[ ice heigh t h 111 horizon tal Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 496 KeLlogg and others: Late Pleistocene interactio ns oJ East and J I 'est Antarctic ice-J7ow regimes length inc rem ent 6. x a lo ng leng th :1' of a fl owline, with o\'er bed rock bumps of critical heig ht 1\ and spacing 1\' x = 0 a t the grounding line a nd x = L a t the ice divide, a nd m = (n + 1) 12 in th e \\' certma n ( 1957 ) theor y of ice hI is ice thic kness along the fl owline, w is width of the fl ow sliding o\'C r wet bedroc k, Pw / PI = 0 when n o wet ba nd th a t e ncloses th e fl owline, a is a\'e rage accumula ti on sediments cover bedrock, Pw l PI = 1 wh en wet sedimcnts ra te a long the fl ow ba nd, a nd ho a nd Uo a re the res pec tive bury bcdroc k bumps and 0 < P"" I PI < 1 when so mc grounding-line ice thickness a nd \'elocity a t x = 0, ~, is bumps arc no t buried, ~ o t e th a t To ---* 0 as Pw I Pr ---* 1, so sid e shear stress alongside the fl ow ba nd, To is basal shear Us is indeterminate in Equa ti on (5) whcn ice-stream fl ow stress beneath the fl ow ba nd, 9z is gravity accelera ti on, PI becomes ice-shelf fl ow beyond the g rounding lin e, is ice density, pw is \\'ater d ensity, f2J = Pl 9z h] is basal ice For ice-sheet fl O\v O\'er bed rock, To = (To)c fo r creep press ure, p\\, = PW9zh\\, is basal water pressure equiv over a frozen bed according to Equa ti on (4 ), a nd a lent to th a t benea th a water column of heig ht h \\' and To = (To), fo r sliding 0 \ 'Cr a thawed bed according to P\\' I PI = p\\, h\\' l plhl is a b asal buoyancy fac tor such tha t Eq ua ti on (5), 'where (To)(' > (To) " because a fr ozen bed Pwl H = 0 fo r ice-sh eet Oo w over a fr ozen b ed , prO\'ides more tracti on to resist sliding, When a a nd ware p\r! PI = 1 fo r ice-shelf Oo w o\'er sea water, a nd constant a nd p\\, I Pr -+ 0 a long a [l o wline, Hughes ( 198 1) o < Pw I PI < 1 for ice-stream fl ow over wet sedimen ts, showcd tha t (To )" and (To), a re: A and give the res pective ha rdness a nd viscoplasti c n 1 properti es o f ice, th e effect of longitudina l d evia tor stress (n + 2)Pr9zaAn(L - X) (1I +1)/n1 /( /I +l) (J~", is conta ined in th e first term, the efrect of longitudinal (6) [ 4 [L (Il +l)/n _ (L _ x)(n+l )/ n] de\'ia tor stress gradient 6(J'l'1,/ 6.x is conta ined in the second term, the efrect of tra nsverse shear stress (JJ'Y is 1 2B2m(L ) (2",+ I)/m / (2111 + 1) contained in th e third term, the efrec t o f vertical shear (m + 1) PI9za - x 1 ( ) stress (J ,.. is conta ined in the fourth te rm, and , • 2 2 R [ (2m + 1) [vm-1 )/m _ (L _ x)(m+l )/m] 7 = [1+ ((J,ry lcl,.,,.) + ( (J ' l' z /~ , .1 ' ) 1 \\'hen tra ns\'erse dev- iator stress clyy is ignored, Equa ti o n ( I ) ca n be used to reconstruc t surface-ice If f is the th awed fracti on of the bed , c/Js a nd c/J" a re fac tors pro Gl es a lo n g th e entire len gth of a fl owline, including ice th a t a ll ow fo r va ria ble acc umula ti o n rates a nd fl o w-band sheet fl ow , ice-stream flow and ice-shelf fl ow , merely by vvid ths a long the f1 0wline a nd Pw I Pr vari es a long the fl ow a ll owing P"v I PI to vary a lo ng th e fl owline , For example, ba nd, because we t sediments cover pa rt or all of bed rock, consid er the two ex trem es o f ice-shee t fl ow over a frozen th en (To) , in Equa ti on (7) is multipli ed by (1- p \\' / Pr) 417l / (217l+1) bed a nd ice-shelf fl ow O\'er sea water in a fl ow band of a nd To fo r both ice-shee t fl ow a nd ice-stream fl ow is gi\'en consta nt w idth, Equa ti on ( I) gi\'es fl owline slopes [or by: lin ear ice-sheet fl o\\' o\'er a frozen bed , for \\' hi ch To = N s(To)s(l - p\\/ Pr )4 m/ (2111 + t) + (1- f) c/JC (TO) " , (8) P,r!PI = -r:, = 0: 6.17, (2) 6.x Hughes ( 198 1) included glacio-isosta ti c depressio n of bedrock bcneath ice-shee t f1 0wlines by introducing the Equa ti o n ( I ) a lso gi\'es fl o wline slopes fo r linear ice-shelf ratio 1" of low e red bed elcvati o n to lowcred surface fl ow, for w hi ch To = 0 a nd Pw I H = 1: e levati on due to isosta ti c deprcssio n , For a bed lo wering be neath thicke ning ice: 6h ( pr) {hja 17,[ 2 R"- l 6 x = 1 - p\\' ax + hono - ax + ho1£o 1" = 1"0 ( 1 - exp ( - tl to)) (9) I hl [ P 9Z (1 - ~) ]" } + ( ~ ) , (3) where To ~ 1f o r isosta tic equilibrium, t is time since th e 4A P\\' PI9zW ice load was a pplied a nd to is the relaxati on time, Fo r a hed rebounding beneath thinning ice: Equa ti o n (2) can be integra ted to gi\'e the pa raboli c fl owline pro fil e for ice-sheet [l ow when To is constant and 1" = Ta exp ( - tlto) (10) th e bed is ho ri zo nta l. Equation (3) gives the ice-thickn ess gradi ent 6h / 6. x = (6.hI 6 x)/(1 - PII pw) for fl oating l w herc ice began to thin at t = 0 a nd 1'a is gi\'e n a t time tin ice th a t O e rl emans a nd V a n d e l' \fee n ( 1984) deri ved for Equati on (9) when thickening ended a nd thinning began, R = 1 a nd -r:, = 0, Equa ti o ns (6)- ( 10) can b e in corpora ted into a The [l o w law of ice can be in tegra ted to gi\'e the num e ri ca l so luti o n of Equ a ti o n ( I ) b y se tti ng ,we rage creep \'eloc ity a t position x a long the fl owline: 6h = h ;+ 1 - hi a nd 17,1 = 17, - h R, where i is the number of 6 x step from the grounding line to distance x a lo ng th e 1£ = ~(To ) ll : (4) c n+ 2 A ' [l owlin e a nd hR is bedroc k heig ht a bo\'C (pos iti ve hR ) or d epth below (negative hR ) present-day sea le\'el. If h* is the the sliding law of ice for ice-sheet fl ow can be modiG ed to isosta ti ca ll y lowered surface, hRi s the isos ta ti ca ll y lowerccl include ice-stream fl ow by including Pw I H , The sliding bed a nd h ~ 1 is hn at th e LGM icc m a rgin where isos ta ti c ve loc i t y is then (H ughes, 1992): adjustments a re sma ll enough to ig no re (Hughes, 1981 ): 111 (Tol B ) I US = 2111 (5) h = h ~ 1 (1 T)'(h* - h ~ t ) (11) (1 - p\\) PI ) + + I h ~ = h* - (1 + T)( h* - h ~t) + (1 + r-)'( hR - h ~ l ) , (12) where B ineludes bed-ro ug hness factor 1\11\' for ice sliding Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 49 7 J Ollm aL Qf Glacio logy Since I' ya ri es much more slo\\'ly than 6h O\'er dista nce obta ined fr om geophysical profi ling but even this is 6 x, Equa ti on ( I ) can be written as the following initial lacking along the entire lengths of fl owlines in Figure 7 \'alue fini te -difference rec ursi\ "C formula for the glacio a nd Fig ures 9- 12, isos ta ti cally lo\\'ered ice surface a lo ng a fl owline: Can matching observati on-based low llowline profil es 2 in Fig ure 7 and Fig ures 9- 12 to theoretical profiles using * _ , *+ (l - pr!p\y ) (PW ) Eq ua tion (13 ) decide between th e two possibilities tha t h,+1 - ' i I (1+r-)2 Pr i we have pos tulated? The low profil es all ow either ice tha t thickens slowl y, because it is in nearl y stagnant ice-sheet a[ h ~ 1 + (1 + r )1( h* - h ~ l ) - hRL fl ow oyer a froze n bed , or ice tha t canno t thicken at all , { ax + houo because it is in ra pid ice-stream fl ow O\'e r water-soaked 2 sediments, Low fl owline profil es for nearly stagnant ice [ h ~ 1 + (1 + r)~( h * - h,,, ) - hRJ7+ sheet fl ow O\'e r a frozen bed are obtained from Equa ti on ax + hou() ( 13) when p\\-jPr'= 0 , f = 0 and (To)c is small. Equa ti on (6) gives (To)c and a in Equa ti on (6) is an effec ti ve ice [p~~z (1 - :~,) (~;) ~ T l }~ .x accumula tion rate given by th e actua l. ice-accumula ti on rate ci minus th e ice-thickening ra te h I. I ce is stagna nt + { (1+ r)l [h" + (1+;)l (h" - h,,) - he L wh en the two rates a re equal, so tha t a = it - liJ = O. Therefore, the more stagnant th e ice, the lower (To)c becom es in Equati ons (6) and (13). Low fl owline profil es w for fast ice-stream fl ow o\" er wa ter-soaked sediments a re 1 - -pr) --6(P ) 2 } 6 x + { - 2( -T5) ( p\y 6 x PI i PIgZ W i obta ined from Equa ti on (13) wh en p\\" / H ---> 1, j = 1, T s is sm a ll a nd W is large. A fas t wid e ice stream will ha\'e a i } [N sh)s(l - ~y1ll / (2 111+l ) + (1 - f) Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 498 ]" ellogg and others: La/e Ple is/ocelle ill terac/iolls oJ East alld " 'es / .-IIl/a rc/ic icejloU' regll17ej more sea-Door ba th ymetric data in 1\l c ~lurd o Sound and ACKNOWLEDGEMENTS beneath the MTS and Ross I ce Shelf are need ed before a deglacia ti on model can be pro perl y co nstra ined, Also, \Ve tha nk C. Swithinbank, R . Acken , C . Lepage a nd the more \'eloci ty measurem en ts a re needed on the ;.. rrs, helicopter pilots a nd cre\\'men of Anta rcti c De\'elopmel1l These da ta could bt" obtained from Landsa t images or Squadron VXE-6 for th eir fi eld support. Disc uss ions with aeri al photogra phs, using the m ethod of Lucchitta and C . Swithinba nk, A. Gow a nd C. Bentley helped us oth ers (1989) a nd :-IacDona ld a nd others ( 1989), The d evelop ollr unde rsta nding of ice ci yna mi cs of the MIS. ,,'AIS initia tive should be expa nded to include these so n s Su pport for our 19 75-8 1 fi eld work on th e l\IIS was of studies, if we a re to e\"C r reali ze the ,,'AIS goals of full y pro\'ided by U .S. K a ti onal Scie nce Founda ti on g ra ms understa nding th t" R oss Sea d eglacia ti on hi story , OPP75 -1 5524, DPP-77 -2 1083, DPP79-20 11 2 a nd DPP- Our ana lys is shows th a t glacia l erra ti cs deri\'ed !I'om th e 8020000 to TB.K. a nd D.E.K. T. Hughes ac kn owledges Tra nsantarcti c M ountains a nd d eposited on th e i\IIS. and support from Ba ttell e, Pac ifi c N orthwes t La bora tories, ror ice with hi gh nega ti ve 5 18 0 va lu es imbedded in the ~llS , the LGl\I glaciological reconstruc tion. cann ot be explained by the mod ern ice-OO\\· regime. They a lm os t certainly reco rd a form er ice-O O\\' r e~ im e when ice derived from l\[uloc k Glacier was adl'ec ted into southern REFERENCES M cMurdo Sound. The loca tions whcre th ese samples were found, combined with our reconstructi ons, suggest th at .\ nderson. J. B.. S. S. S hipp. L. R. Banck a nd D . E. Rcid. 1992. E\'idcncc emplacement occurred during the LGl\f or perha ps during 10 1' a g-rou ndcd icc shcct on thc Ross Sea cOlltinClllal , helf d uring- the deglacia ti on but prior to a bout 4000 BP, by \\'hi ch time the La te Plcisto('cl1e a nd preli mina ry palco clra in age reconstruc ti o n. III Elli ot. D.I-1.. cd. COII/ribu/ioIlJ /0 . III/ardi,- re.learch 111. \\'ashington , DC, modern ice-fl ow regim e \\'as es ta blished . .\l1lerica n Geoph\'sical Uniun. 39 62. (Anta rct ic Resea rch Snies Our da ta a ll ow us to eva lu a te two competing models 57.) for ice Oow and ex tent during the LGi\l. The Drewr\, Baroni. C. a nd G. O rol1lbell i. 199 1. Holoccn e ra ised beaches a t T erra ( 1979) model fa ils to explain the boulder prove na nce and :"I o\'a Bay. \ 'icLO ri a L a nd .. \l1larnica. QJla/. Res .. 36 2, 157-177. Baroni , C. and G. O ro l1lbcl li. 199L .\ba ndo ned penguin rookerie, as sta ble-iso to pe d a ta, because ice fr om Skelto n Gl acier. H olocenc pa /eocii l1lat ic ind ica tors in .\ nlarctica. Ge%l{)'. 22. 23 26. ra ther than l\Iulock Glacier, would ha\'e domina ted in Be ntlc·). C. R ., J \\'. C loug-h. K . C. J ezek a nd S. Shabtaie. 1979. Icc· so uthern Mc l\Iurdo Sound. \\'e prefer th e Stuiver and thickn ess pall erns and the cly namics o /" the R o", Ice Sh (' lf ~ Anta rc ti ca. oth ers' (198Ia) model, because it is easil y expla ined by J- (;I{/(/o/,. 24190 1. '287 294. Bi nc\schacller. R .. \ ., I'd. 1991. lI"eJ/ .III/arc/ic' Ice Sheet IlIi/ia/ive. r'olulI/(' I. our glaciologie reconstructi o n, a nd a reasona bl e bala nce S,-iellcf alld illl/J/ellll'll/a/ioll /llall. \\'ashi ngLO n . DC . .'\"tion"1 .\ eron a u tic, between preliminary a bl a ti o n a nd prec ipita ti on d a ta for and Space .\ dllli nistra tion. C P·31 15. 1 th e Skelton and 1\1 1I1 0ck Glaciers catchment a reas. Oow Bl a nchon. P. and .1 . S haw. 1995. R ee/" drowning during th e last ba nds a nd lo hes a nd , because the Oow pa ttern a ppea rs d c-g lac iati on: l" 'jcknc(" for catast rophi c sca-Ic"c l ri se and icC' -sheet collapse. (;C'o/".~J ' . 23 I ,. '1- 8, compa tible \\·i th sta bl e-i soto pe a nd boulder-prO\'e nancc Brad), l-I.T. 197B. Gcolog-ica l , tu d ies in sou thern \ 'inori a L a nd. on da ta rrom the \IlS. Additiona l supporting e\·idence is Black Isla nd. a nd on the r-fr~l u rdo fe e S hel f. .III/ard. J- C .S.. 13 + . pro\'id ed by a recent stud y of glacial a nd H olocene 13 1+. sediments a nd la nd forms a t Cape Bird. Docha t (1994) Cbrk, .1 .. \ . and C. S. Lingle. 1979. Prcdicted rciatiH' sea·le\'C1 ch a nge, I IB.OOO )ear, 13 .1'. to p n''''nt l ca used b ) la te-glacia l rc trea t of til e concluded tha t ice Oo\\'ed wes t a nd so uth a round Cape "ntarcti c ice shecL Qjla/, RC'J .. 1l (3 ), 279 298, Bird into M cl\[urdo Sound during th e LG\f because no Cook. J c:. 1953. Scsimic rcconnaissa nCl' on a n ice·co\Trcd All tarctic kenyite erra ti cs \\"Cre found a t Cape Bird. The onl y known sea. J- G/ati,,/,. 4 35 . 559 568. Anta rcti c source for kenyite is a t Ca pe R oyds on the wes t Dc bc nham, F. 19 19 .. \ 11('\\ l1lode of tra nspo rtation b) ice. Q, J- Ceo/. SUL l,olltlcJl!. 75 '2 , 5 I 76. coast of R oss Isla nd . On th e m a inla nd. kenyite was not /)c bc nhalll, F, 19+9. The problem or the g rea t Ross Ba rrier. ( ;eogr. J-. depos ited north of M a rble Point, so Oow into l\Icl\Iurdo 112,+-6 1. 19·1·8, 196 2 18. Sound from a saddle on the ice di\·id e north of Ross J) c bc nham. F. 196 1. " li sh , ton ' li'o m the ,\nlarc ti ... (;eogr .. llag .. 34 (6). Isla nd a nd Oow a rollnd R oss Isla nd met at \Jarble Point. 360 368. DClIIo n, G. H .. R. L .. \rmstrong and ~1. S tui\'cr, 1971. The La tc H LG:'I ice Oow foll owed the Drewry model, kem'it e Ccnozoic glacia l hisLOr) of .\ Illarct ica. 111 Turek ian, K . K ., I'd. The should be present in R oss Sea Drift a t Cape Bird a nd no I ,a/e C:el/o~oi( g/acial age\. :"JC\\ Ha\"(' n. CT . a nd London. Yale kenyite sho uld exi st so uth of :\Ia rble Point. L ni \'ersit\ Pn·ss. 267 306. Del1lo n. G. H .. G. Bockhcill1. S, C. \\'ilson a nd r-1. Stui\'C r, 1989. La te While we rej ect th e DrewI')' model [or the LG~I , our J \\'isconsin a nd Ea rl y Holnee nl' glacia l history. in nn Ross em!,ay, d a ta sho\\' tha t th e northwa rd through-O ow of ice mem .. \Il Larnica. QJla/. Rn .. 31 '2. 15 1 182. predi cted by his model did pre\'ail in \Ici\Iurdo Sound Dochat, T. ~1. 199 1. S urfieia l slratigraph) a nd gcol1lo rphology o f Cape during dcglacia ti on, from a bo ut 12 000 to 8000 BP. In Bird. Ro", Isla nd . Amarnica: impli cati ons for Latc \\'isconsill glacia tion in til l' R oss Sea emila)nWn L ('\LSc. til esis. L'llin'rsit ) or fact, our glacia l reconstructi on for 12000 BP fo r th e a rea .\la in t' . O rono, ) north a nd cast of R oss Isla nd resem bl es Drewr)"s (1979) I)l'c\\'I'\'. D.J. 1979. La tc \\'iscunsin reconstruc ti on fll r the R oss Sc" reconstructi o n. H ence, \\'e suggest th a t hi s model is I'cg-ion .. \ ntarnica. ]. Ctafill/.. 24 90 ,23 1 2+1. excellent for the middle stages of deglacia ti o n. if the Dre\\TY· D.J. fd. 1983 . .- III/arclim: g/aciologictll alld .~"o/II!J ' Ji[({/ Jotio. con tribu ti on of ice from Skelton Glacier to the a rea north Cambridge. Scott Po lar Resea rch Inst illltc. Fairbanb. R. G. 1989. A 17,000· \ear g lacio -c ustatic sea Ic\'C1 record: ~Iinn a or BlufT is omitted. The low Oowlin e profil es in in n ucllce o f' glac ial l11 d ti ng ratl'S on th e Younger Dryas (T('nt and Figure 7 a nd Fig ures 9 12 can be ex pl ain ed as res ulting (leep·occan circul a ti on . . \ (I/IUC. 342(6250),637 642. fr om ice th a t was eith er la rgel y stagna nt or became hi ghl y G i",·inctto. ~I. B. . c:. R . Bendc) a nd C. 13 . 13 . Bull. 1989. Choming d yna mi c aft e r grounding, d epending on whethe r the bed b ct\\('cll "iOI11(' inco 'TIpa tible n.'~i()na l surfacc-mas"J -ba lanct da ta se ts in .\ nLarnica . . I/I/arr/. J- C .S .. 24 I . 7 13. became fr ozen or remained tha wed . Dec iding betwee n Go\\' .. \ . .1- 1967 .. \ Illarctic glaciologica l swcJics . . III/arr/.]. C.S . . 2 4. these two p ossibilities is a difTi c ult but not imposs ibl e 12 1 In problem in ice-shee t modeling. Go\\', A.J a nd S. EpslC' in . 1972. O lllhc use o Csta blc iso topes to trace the Downloaded from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use. 499 Journal 0/ Glaci%gy origins of ice in a floating ice tongue. J. Geoph)'S. Res., 77(33), 6552- sediment: theory and application to Ice Stream B. Antarctica. ]. 6557. Geo/)/~)'s . Res .. 94 B4 ), 407 1-4087. "nw, A.J .. \\'. F. \\'eeks. G. Hend ri ekson and R. Ro\\"land. 1965. :"le\\" i\[cCrae, I. R. 1984. A SIIlWnal] oJ glaciologiml lIIeasurements made betwefll li ght on the mode of lIplili of the fi sh and fossiliferolls moraines of the 1.960 alld 198~ Oil tlu' JIJdiurdo Ice Sltelf. Alltarctiw. Auckland, Ne\\' .\le\IlIrdo lee Shelf: :\nrarcLica. J. Glaciol .. Y 42 1. 813-828. Zealand, L:ni\'ersi t), of Auckland. Sc hool of' Engineering. D epart H a n , C. P. 1990. H oloeene megafauna in .\l c.\IlIrdo Ice Shelf ment of Theoretical and Applied i\!cehanics. (Repon 360. sediments fossil iza ti oll and implications for glacial processes. ~IacDonald, T. R. , .1 . G. Ferrigno, R. S. \\'ilii ams, Jr and B. K. Antarct. J. C.S .. 25(2) . 11 - 14. Lucchitta. 1989. \ 'elocities of Antarctic outlet glac iers determined Hayward. P.J. and P. D. Taylor. I 98.J.. Fossil and recent Clwilostomata li'om sequential Landsat images . . llItarct. J. C.S .. 24 (5). 105- 106. (Bryozoa l from the Ross Sea. Antarctica.]' .rat. Hist., 18 .7 1 94. .\lorgan, \'. l. 1982. Antarctic ice sheet surface oxygen isotope \·a lues. J. H eine, J. C. and T. \ \'. Speir. 1989. Ornithogenic so ils of the Cape Bi rd Glaciol., 28(99), 315 323. Adi:lie penguin rookeries, Antarctica. Po!ar Bio! .. 10 (2), 89 99. Oerlcmans, J. and C. J. van der \ 'een, eds. 1984. Ice JiICets alld climate. H oward-\\'illiams. C., R. Pridmore . .\1. T. Downcs and W. F. \ ' in ccn t. D ordrecht, etc .. D. R eidel Publishing Co. 1989. i\licrobial biomass. photosynthesis and chlorophyli a related Paige. R. 1\. 1968 . .IJa/) '!J. lIcMardo SOl/lid, .. lntarctica . Port Hueneme, CA. pigments in the ponds of the i\lci\Iurdo Ice Shelf. Antarctica. illltarct. Na"al Ci\'i l Engineering Laboratory. (Drawing 68 -1 7-1 F. ) Sci .. 1(2), 125 131. Reid , D . E. 1989. Quaternary marine geology of the northwestern R oss H oward-Willi ams. C ., R. D. Pridmorc, P. A. Broady and W . F. \ ' in cen t. Sea. Alltarct. J. U.S .. 24 (5), 12 8 130. 1990. Envi ronnwntal and biological variabilit y in the i\Ici\furdo Ice Shipp, S. S. and j. B. Anderson. 1994. High-resolution seism ic sun'ey of Shrlf ecosys tem. i ll Kcrry, K. R. and G. Hcmpel. eds. Antarctic the Ross Sea continental shelf: implications fo r ice-sheet retreat a0J)'jtellls. Berlin, Springn-\ 'erlag, 23 31. beha\·ior. Alltant. J. l/ .S .. 29 (5), 137- 138. Hughcs, T. 1977. Wcst Alltarctic ice streams. RCI'. Geo/)I,)'s. S/)ac(' PIl)'s .. Speden, I. G. 1962. Fossiliferous Quaternary marine deposits in the 15( 1 . I 46. M c\furdo Sou nd region. Antarctica . . Y.Z. J. Geol. Geo/)I!),s .. 5(5), Hughcs, T.j. 1981. Numerical reconstruction of paleo-ice sheets. In 746 777. Denton. G. H. and 1'.J. Hughes. eds . The last grrat ice ,heels. ~e\\ ' York. Speir. 1'. \\'. and j. C. Cowling. 1984. Ornithogenic soils of the Cape etc., J ohn \\'il cy and Sons, 22 1-26 1. Bird Ad['lie penguin rookeries, Antarctic3. I. Chemical properties. H lIghcs, 1'. 1992. On the pulling power of ice st reams. J. G!aciol .. Polar Bioi., 214), 199- 205. 38( 128 , 125- 151. SlUart. A. \\'. alld C. Bull. 1963. Glaciological observations on the R oss K eli ogg, D. E. and T. B. Kell ogg. 1987. Di atoms of the \Ic\lurdo lee Ice Shelf near Scot! B3se. Antarctica. J. Glaciol., 4 (341,399-4 14. Shelf, Antarctica: implications for sedimcnt and biotic reworking. Stuivcr, \1.. C.I-I. Denton, T ..J. Hughes a nd J. L. Fastook. 1981 a. Pala eogeogr., Palaeociill/atol., Palaeoecol .. 60( 1- 2),77 96. Historv of'the mari ne ice shee t in \ \'est Antarctica during the last K eli ogg. T. B., i\1. SlUi\'er. D. E. Kcliogg and G. H. D enton. 1977. glaciati on: a working hypothesis. i n D enton, G.H. and T.J . .\ larine microfossils on the \lc\[urdo Ice Shelf. Alltarc/. J. C.S .. Hughes, eds. The la.lt great ice sheets. \fcw York, etc .. J ohn \\'ilc\, and Sons, 12(4), 82 83. 3 19-436. K eliogg, T. B.. R. S. Truesda le and L. E. Osterman. 1979. Late Stuivcr. ~f. , I.C. Yang, G.H. Denton and TB. Kcll ogg. 1981b. Quaternary extent of the \\'est Antarctic ice sheet: ne\\' e\·iden('e O xygen isotope ratios of Antarctic permafi'ost and glacier ice. III from Ross Sea cores. Geolog)' , 7, 249 253. .\lcGinnis, L. D. , ed. DI)' I'alley Drilling Project. \\'ashington, D C, K el logg. 1'. B., D. E. K ell ogg and M. Stui\·er. 1990. Late Quaternary American Geophysica l Union, 131 139. (Antarctic Research Series 33. \ history of' the southwestern Ross Sea: e\'idence from debris bands on Surcn, A. 1990 . .\Iicrofauna associated with a lgal mats in melt ponds of the ~I (' '\lurd o Ice Shel f', .\ntarctica. i l/ Bentley. C. R .. ed. COlltributiollS the Ross Icc Shelf. Polar Bioi .. 10(5), 329 335. to illllarc/ic reJearril l. \\'ashington, D C, American Geophysical Union, S\\ ithinbank, C. \\' . .\f. 1970. lee mO\'Cment in the i\1c:--rurd o Sound 25 56. (AntarCtic R esea rch Series 50.) area of Antarctica. IlItenwtiona! Associatioll DJ Srielltific II}'drolog), Krisse k, L. A. 1988. Sedimentation hi story of' the Terra NO\'a Ba y Pu bliratioll 86 (Symposium at Hano\'C r 1968 Antarctic Glariological region, Ross Sea, Antarctica. Antant. J. C.S .. 23(5). 104-105. EljJloratioll ( ISAGE)), 472-487. Ling le. C.S. and T.J. Bro\\'n. 1987. A subglacial aq uifer bed model S\\'i thinbank, C. \\'. !\l., D . G. Darb), and D. E. \\'ohlsc hl ag. 1961. a nd water press ure dependent basal sliding relationship for a Faunal remains on an Antarctic ice shelf. Science, 133(3455), 764-766. \ Vest Antarctic ice stream. 111 Van del' \'ecn. C.J. and J. U nited States Geological Survey. 1972. Ross i ee Shelf, Antarctica. ReslOn. Oerlemans, ed.l . D,]llIamirs of the II 'est Alltarctic ice slt eet . D ordrecht. VA, United States Gcological SlIl'\'ey. (Antarctica ske tch map, polar etc., D. R cidc1 Publishing Co., 249-285. IGlaciolog\' and stereographie projecti on. scalc I : 1.000,000.) Quaternary Geology .J.. \ \'certman,]. 1957. On the sliding of'glaciers. J. Glaciol .. 3 21),33 38. Linglr, C. S. and J. A. Clark. 1985. A numerical model of interactions Whillans, 1. i\1. and C . .1 . \'an der \ 'een. 1993. Ke\\' and impro\'ed between a marine ice sheet and the solid Earth: application to a \\'es t de terminations ofvciocity of lee Streams Band C. \\'es t Antarctica. Antarctic ice stream.]. Gea/)h),s. Res., 90(CI ), 1100 1114. J. Glaciol .. 39( 133 ), 4·83-490. Lucchitta. B. K., H . \1. ferguson. F.J. Schafcr, J. G. Ferrigno and R. S. 7:otikO\', I.A. and A.J. Gow. 1967. The thermal and eo mpositional \\,iliiams. Jr. 1989. ,\ntarc ti c glacier \'clocities from Landsat images. structure of the Koettlitz ice tongue, ~lci\ f urdo Sound. !\ntarctica . . Jlltarct. ]. C.S .. 24(5). 106- 107. In Oura, H. , ed. Physics oJ SIlOU' alld ice. r'o/' 1. Part I. Sapporo, ~I acA\'eal. D. R . 1989. Large-scale ice now Q\'CI' a \'iscous basa l H okkaido L:ni\·ersity. Institute of'Lo\\' Temperature Science, 469-478. MS received 31 July 1995 al7d accepted in revised/orm 4 February 1996 Downloaded500 from https://www.cambridge.org/core. 25 Sep 2021 at 18:27:55, subject to the Cambridge Core terms of use.