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, <t c • ma rgina l a nd recessiona l m o ra in es and ra ised beaches . '" f-- \ Numero us con\'entiona l l ie d a tes on ma rine shell s and terres tria l fresh-wa ter algae suggest a la te Qua terna ry age of ", 18-20BP for the m ost recent ad\'ance of Wes t Anta rctic ice (R oss Sea ice shee t). Drewry ( 1979 ) suggested tha t g rounded ice ex tent was considera bl y less ex tensive tha n portrayed by Srui\'er a nd o thers (198I a) a nd hence tha t their ice-flow traj ec tori es were unlikely. In pa rticula r, D re\\'ry (1979) call ed for northward fl o\\' of grounded ice past R oss Isla nd in :'Ic\Iurdo Sound, with no wes twa rd fl ow into the Dry Vall eys. The m echa nism a nd histo ry of deglacia ti o n following Fig. 1. I/ldex IIIG/) showing locations mentioned ill text .