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Late Pleistocene Interactions of East and West Antarctic Ice-Flow Regimes: Evidence from the Mcmurdo Ice Shelf Thomas B

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Late Pleistocene Interactions of East and West Antarctic Ice-Flow Regimes: Evidence from the Mcmurdo Ice Shelf Thomas B The University of Maine DigitalCommons@UMaine Earth Science Faculty Scholarship Earth Sciences 1996 Late Pleistocene Interactions of East and West Antarctic Ice-Flow Regimes: Evidence from the McMurdo Ice Shelf Thomas B. Kellogg Terence J. Hughes University of Maine - Main, [email protected] Davida E. Kellogg Follow this and additional works at: https://digitalcommons.library.umaine.edu/ers_facpub Part of the Earth Sciences Commons Repository Citation Kellogg, Thomas B.; Hughes, Terence J.; and Kellogg, Davida E., "Late Pleistocene Interactions of East and West Antarctic Ice-Flow Regimes: Evidence from the McMurdo Ice Shelf" (1996). Earth Science Faculty Scholarship. 56. https://digitalcommons.library.umaine.edu/ers_facpub/56 This Article is brought to you for free and open access by DigitalCommons@UMaine. It has been accepted for inclusion in Earth Science Faculty Scholarship by an authorized administrator of DigitalCommons@UMaine. For more information, please contact [email protected]. Journal oJ Glaciology, Vol. 42, No. 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 HUGHES DAVTDA KELLOGG AND E. Department of Geological Sciel1ces and Institute Jo r Qjwlem(l}) Studies, University oJ Maine, Orono, Maine 04469, U.S.A. ABSTRACT. We present new interpretations of deglaciation in McMurdo Sound and the western Ross Sea, with observationally based reconstructions of interactions between East and West Antarctic ice at the last glacial maximum (LGM), 16000, 12000, 8000 and 4000 BP. At the LGM, East Antarctic ice fr om Mulock Glacier spli t; one branch turned westward south of Ross Island but the other branch rounded Ross Island before flowing southwest into McMurdo Sound. This flow regime, constrained by an ice saddl e north of Ross Island, is consistent wi th the reconstruction of StuiYer and others (198Ia). After the LGl\1, grounding-line retreat was most rapid in areas with greatest water depth, especially along the Victoria Land coast. By 12000 BP, the ice-flow regime in r..,1cMurdo Sound changed to through-flowing tv1ulock Glacier ice, with lesser contributions from Koettlitz, Blue and Ferrar Glaciers, because the former ice saddle north of Ross Island was replaced by a dome. The modern flow regime was established ",4000BP. Ice derived from high elevations on the Polar Plateau but now stranded on the l\IIclV[urdo lee Shelf, and the patternof the Transantarctic Mountains erratics support our reconstructions of Mulock Glacier ice rounding Minna Bluff but with all ice from Skelton Glacier ablating south of the bluff. They are inconsistent with Drewry's (1979) LGM reconstruction that includes Skelton Glacier ice in the McMurdo Sound through-flow. Drewry's (1979) model closely approximates our results fo r 12000-4000 BP. Ice-sheet modeling holds promise fo r determ ining whether deglaciation proceeded by grounding-line retreat of an ice sheet that was largely stagnanr, because it ne\'er approached equilibrium flowline profiles after the Ross Ice Shelf grounded, or of a dynamic ice sheet wi th flowline profiles kept low by active ice streams that extended northward from present-day outlet glaciers after the Ross Ice Shelf grounded. INTRODUCTION glacial geologic observations and the observed presen t­ day ice dynamics of the McMurdo Ice Shelf (MIS), a One key objective of the West An tarctic ice sheet (VV AI S) part of the Ross Ice Shelf. The reconstructions aid in initiati\'e is documentation of eustatic sea-level change elucidating modern glaciological processes operating on resulting fr om the possible disintegration of the \Vest this ice shelf and support suggestions by Kellogg and An tarctic ice sheet (Bindschad ler, 1991). This effort others (1990) that some existing MIS fea tu res arc requires detailed knowledge of ice-sheet history in \Vest remnants fr om a fo rmer ice-flow regime. MIS data Antarctica, including the history of grounding-line and permit evaluation of two differenr published reconstruc­ calving-margin retreat to the positions now occupied by tions of the flow rcgime du ring the LGM, and these features and an accurate dynamic overview of the development of fo ur new reconstructions fo r the Ross 'vVes t Antarctic ice sheet, i ncludi ng presen t and former Sea embayment during the deglacial transition fr om thc precipitation sources, flow regimes and changing interact­ grounded late Wisconsin Ross Sea ice sheet to the modern ions wi th ice derived from East An tarctica. The develop­ Ross Ice Shelf, all of which include ice derived fr om both ment of reliable predictive models for fu ture ice-sheet East Antarctica and \Vest Antarctica. retreat depends on these da ta. Yet, so fa r most VVAIS West Antarctica is a key area for studying glacial studies have concentrated either on modern ice dynamics history and dynamics, because the world's largest extant in \Vest Antarctica or on elucidating fo rmer ice maxima. marine-based ice sheet is located there. Of particular This paper presents a series of preliminary observ­ importance are the Dry Valleys of southern Victoria ationally based reconstructions of interactions between Land, situated between the seasonally open waters of the the East and West Antarctic ice sheets during and since Ross Sea and McMurdo Sound on the east and the East the last glacial maximum (LGM). These two ice sheets Antarctic ice sheet to the west. These ice-free valleys are are separated by a dividing wall (the Transan tarctic shielded from direct East Antarctic ice-sheet influence by Mountains) and interact today primarily where through­ the Transantarctic Mountains. It can be argued that a flowing outlet glaciers from East Antarctica impinge on third major factor, in addition to East and \'VestAn tarctic the Ross Ice Shelf. Our reconstructions are based on ice fluctu ations, operates in this area: local glaciers 486 Kellogg and others: Late Pleistocene illteractiolls oJ Eas! alld 11 'est Antarctic ice-j1ow regimes respond to the proximity of an open-water moisture source in the Ross Sea, This influence is actually controlled by \Vest Antarctic ice extent, being insignif­ icant during glacial maxima and reaching its greatest importance during interglacials when shelf- and sea-ice limits are least extensive, The availability of a local moisture source is important for this paper primarily with respect to fluctuations of Koettlitz and Skelton Glaciers. <J Coulmon I. A detailed late Qu aternary paleoclimatic record for the :, Dry Valleys region (Denton and others, 1971, 1989; t ROSS SEA � ",finD Nova Stuiver and others, 1981a) shows that the dominant \.. OOl/id J jJL . Boy features were periodic advances of the 'Vest An tarctic ice : G sheet, which thickened and grounded in the Ross Sea and _ Mowson GI. Cope Franklin I. Hiekey McMurdo Sound, pushing lobes of grounded ice into the a: 1" eeQu'ort I. Dry Valleys and leaving a record of ice-dammed lakes, <f c • '" marginal and recessional moraines and raised beaches. " \ : DrYc;lolski Ice Tongue Numerous conven tional 14e dates on mari ne shells and I-- terrestrial fresh-water algae suggest a late Quaternary age ;" of ",1 8-20 BP for the most recent adl'ance of West Antarctic ice (Ross Sea ice sheet). Drewry (1979) suggested that grounded ice extent was considerably less extensive than portrayed by Stuiver and others (198Ia) and hence that their ice-flow trajectories were unlikely. In particular, Drewry (1979) called for northward flo\l· of grounded ice past Ross Island in Mc:'lurdo Sound, with no westward flow into the Dry Valleys. The mechanism and history of deglaciation following Fig. i. index //Zap showing locations mentiolled 1I1 text. See the late VVisconsin ice maximum in West Antarctica is a Figure 2 Jor details oJ the M/S. S)lmbols: B = Blue significant glacial geologic problem, i,wolving ice thin­ Glacier; CB = Cape Bird: eR = Cape Ro)'ds; F = Fenar ning and grounding-line retreat of the Ross Sea ice sheet Glacier: A" = A"oel/lit::. Glacier: MP = J\Jarb/e Point. in the central and outer Ross Sra, and flotation to form the Ross Ice Shelf in the central and southern Ross Sea. MclVr urdo Sound is of particular importance for under­ standing this transition, because apparent remnants of iment and biota were incorporated into the l\US by basal former grounded ice are presen·ed as part of the ;'lIS adfreezing, to ('merge el·entually on the ;'US surface (Kellogg and others, 1990). because of net annual surface ablation. Subsequent workers, who have reported biotic remains on the MJS, include: Debenham, 1949, 1961; Swithinbank and others, GLACIAL GEOLOGY OF THE McMURDO ICE SHELF 1961; Speden, 1962; Gow and others, 1965; Kellogg and others, 1977; Brady, 1978; Hayward and Taylor, 1984; The \IIS is an extension of the Ross Ice Shelf that Kellogg, 1987; Howard-\\'illiams and others, 1989, 1990; occupies southern McMurdo Sound (Stuart and Bull, Hart, 1990; Suren, 1990. GOvlI and Epstein (1972), 1963). It is bounded on the south by Minna Bluff, on the Stuiver and others ( 1981 b) and Kellogg and others north by Ross Island and the seasonally open waters of (1990) used oxygen-isotopic analyscs of l\I!S ice to show Mc;'Iurdo Sound, on the west by !\fount Discol'ery and that lowermost Koettlitz Glacier and most ice in thl' the Dry Valleys of southern Victoria Land, and on the surface-ablation zone formed from frozen sea water, east by the Ross Ice Shelf and White Island (Figs I and supporting Debenham's hypothesis. 2). Koettlitz Glacier flows into the MIS west of Brown Ice-thickness data obtained by radio echo-sounding Peninsula. The eastern part of the �IIS is dominated by (Swithinbank, 1970) and drilling (Gow and Epstein, net annual surface accumulation, like the remainder of 1972) are shown in Figure 3.
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