the antarctic ice sheet during the last glacial maximum and its subsequent retreat history

Quaternary Science Reviews 21 (2002) 49–70

The Antarctic Ice Sheet during the Last Glacial Maximum and itssubsequent retreat history: a review

John B. Anderson*, Stephanie S. Shipp, Ashley L. Lowe, Julia Smith Wellner,Amanda B. Mosola

Department of Earth Science, Rice University, 6100 Main Street, Houston, TX 77251, USA

Received 7 March 2001; accepted 2 August 2001

Abstract

An emerging body of evidence from studies of the last glacial/interglacial cycle suggests that the East and West Antarctic icesheets have not advanced and retreated in concert. The West Antarctic ice sheet advanced to the outer shelf in most regions during

the Last Glacial Maximum (LGM). The retreat from the shelf commenced shortly after the LGM and continued into the lateHolocene. The West Antarctic Ice Sheet in Ross and Amundsen seas slid across a deforming bed, at least during the final phases ofextended glaciation. This implies that at this time the ice sheet had a low profile. Differences in the number and locations of

grounding-zone wedges and smaller grounding zone features from trough to trough imply that individual West Antarctic Ice Sheetice streams retreated episodically.Details concerning the expansion, retreat, and behavior of the East Antarctic Ice Sheet (EAIS) are more sparse. The picture

emerging is that the EAIS did not expand to the continental shelf edge during the LGM; rather, it achieved a maximum extent of amid-shelf position in some locations, while in other areas the ice terminus was situated near its present location. The timing of retreatalong sectors within the EAIS appears diachronous, and in places occurred prior to the LGM. The Antarctic Peninsula shelfcontained considerably more ice during the LGM than previously proposed.

The results presented in this paper support more recent published ice-sheet models that call for greater contributions of melting icefrom West Antarctica, including the Antarctic Peninsula, to the post-glacial rise in sea level.r 2001 Elsevier Science Ltd. All rightsreserved.

1. Introduction

Configuration of the Antarctic Ice Sheet during theLast Glacial Maximum (LGM), which in this paper isdefined as Marine Oxygen Isotope Stage 2, and itscontribution to the post LGM sea-level rise have beenmodeled by several investigators, with widely varyingresults (Fig. 1).Stuiver et al. (1981; CLIMAP reconstruction) devel-

oped a LGM ice-sheet reconstruction that places the icesheet at the continental shelf edge around Antarctica.Denton et al. (1991) revised the model to show littleinterior surface elevation change during the LGM, butconsiderable thickening of peripheral ice (Fig. 1). Huy-brechts (1990) constructed a three-dimensional, thermo-mechanical ice-sheet model with a glacial maximum

configuration smaller than that of Denton et al. (1991)and a sea-level contribution of only 12m (Fig. 1).Glacio-hydro-isostatic models, including the ICE-3Gmodel of Tushingham and Peltier (1991), ICE-4G modelof Peltier (1994), and the ANT3 and ANT4 models ofNakada and Lambeck (1988) are based on CLIMAPreconstructions, which assume a steady-state ice sheet atthe LGM (Fig. 1). These models call for approximately20–30m of sea-level contribution from Antarctica. Theprinciple difference between the models is where iceoccurs on the continent (Fig. 1). The results from recentmodels (ANT5 and ANT6) by Nakada et al. (2000) differfrom previous models in that more ice exists over theWeddell Sea and the Antarctic Peninsula region (Fig. 1).Testing the LGM models requires information about

the elevation and extent of the ice sheet, and the timingof advance and retreat. Elevation information is derivedfrom land-based studies of glacial features at elevationsabove the present ice-sheet surface and indirectly fromraised beaches. Ice-sheet profiles are constructed from

*Corresponding author. Tel.: +1-713-348-4884; fax: +1-713-348-

5214.

E-mail address: [email protected] (J.B. Anderson).

0277-3791/02/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved.

PII: S 0 2 7 7 - 3 7 9 1 ( 0 1 ) 0 0 0 8 3 - X

Fig. 1. Results of different ice sheet reconstruction models. ANT 3=Nakada and Lambeck (1988); D91=Denton et al. (1991); ICE-

3G=Tushingham and Peltier (1991); HB=Huybrechts (1990); ANT 5 and ANT 6=Nakada et al. (2000); int=contour interval; ESL=eustatic

sea level.

J.B. Anderson et al. / Quaternary Science Reviews 21 (2002) 49–7050

these combined data. The maximum extent of the icesheet is recorded by glacial unconformities, geomorphicfeatures, and sedimentary deposits on the continentalshelf. Establishing the timing of ice-sheet advance andretreat is the most difficult challenge and, as a result, thisremains one of the largest uncertainties.The results from land-based studies have been

summarized by Colhoun, 1991, Denton et al. (1991),Bentley and Anderson (1998), Ingolfsson et al. (1998),Miura et al. (1998), Anderson (1999) and Bentley (1999).This paper focuses on marine-geological evidence forextent of the ice sheet during the LGM and on thetiming of ice-sheet retreat from the shelf. The discussionconcentrates on the three components of the Antarcticcryosphere, the West Antarctic Ice Sheet (WAIS), theEast Antarctic Ice Sheet (EAIS), and the smaller glacial

systems of the Antarctic Peninsula region (Fig. 2). Abrief review of the criteria used to map the extent of theice sheet on the shelf is provided first.

1.1. Problems with radiocarbon dating

Uncertainties in radiocarbon ages, particularly withrespect to the carbon reservoir effect, pose a problemwith studies of this type (e.g., Andrews et al., 1999).Because of 14C recycling, the biggest source of error iswith total organic carbon dates. This is complicated bythe fact that the type of glacial-marine sediment fromwhich total organic carbon dates are obtained isdiatomaceous mud and ooze. These materials revealthe onset of open marine conditions, not retreat of thegrounding line. The best glacial-marine sediments for

Fig. 2. Drainage map for the Antarctic Ice Sheet showing areas where marine-geological surveys aimed at reconstructing the LGM configuration of

the ice sheet have been conducted. The different sectors of the continental shelf where detailed marine-geological investigations have been conducted

are labeled as follows. NWWS=northwestern Weddell Sea; BS=Bransfield Strait; AP=Antarctic Peninsula; MB=Marguerite Bay; EB=Eltanin

Bay; PIB=Pine Island Bay; BC=Bakutis Coast; WG=Wrigley Gulf; SB=Sulzberger Bay; WRS=Western Ross Sea; CRS=Central Ross Sea;

ERS=Eastern Ross Sea; NVL=Northern Victoria Land; WLC=Wilkes Land Coast; PC=Pennell Coast; BC=Budd Coast; WI=Windmill

Islands; PB=Petersen Bank; VB=Vincennes Bay; VH=Vestfold Hills; PB=Prydz Bay; MRL=Mac Robertson Land; LHB=Lutzow Holm Bay;

EWS=eastern Weddell Sea; and SWS=southwestern Weddell Sea.

J.B. Anderson et al. / Quaternary Science Reviews 21 (2002) 49–70 51

dating ice sheet retreat from the shelf are those that aredeposited near the grounding line, and these deposits arenotoriously lacking in calcareous material. Such datesare harder to obtain, but they are worth the effort. Thereis general agreement that the correction factor used forcalcareous marine fossils is between 1300 and 1400 yr(Gordon and Harkness, 1992; Berkman and Forman,1996).We have used a reservoir correction of 1300 yr for our

dates, as suggested in Berkman and Forman (1996); inTable 1 we also present uncorrected dates. Datespreviously published by our research group are alsocorrected with a 1300 correction factor. Hall and Denton(2000) compared dates from algae and co-precipitatedcalcium carbonate from lake sediments in the DryValleys and found that the dates were in agreement. Weuse their study as an indicator that our algal andcarbonate dates should be comparable. The same 1300 yrcorrection (Berkman and Forman, 1996) was applied tothe three dates we obtained on algal samples.With regard to the published literature, we present

radiocarbon dates as they were corrected for reservoireffects in the original source. If no correction was madein the original source, we report only the uncorrecteddate. Each date used in the text appears with a note onthe correction used. We also reference dates obtained bysurface exposure dating methods. We present these datesas they were presented by the original authors.The maximum age that can be determined using AMS

radiocarbon methods is about 46,000–50,000 yr BP(Linick et al., 1986) (http://www.physics.arizona.edu/ams/index.html). None of the dates we present exceed40,000 yr and we have not excluded any samples forwhich radiocarbon dates were obtained. Additionally,for each of the dates older than 30,000 14C yr at leasttwo dates from the same unit were obtained.

2. Criteria for mapping the LGM configuration of the ice

sheet

The first seismic profiles from the continental shelfshowed widespread unconformities in the youngerstratigraphic section that were interpreted as glacialunconformities (Houtz and Meijer, 1970; Hayes andDavey, 1975). Mapping of these unconformities revealeda landward slope and relief that mimics the presenttrough and bank topography of the shelf (e.g., Alonsoet al., 1992). The youngest unconformity occurs at ornear the sea floor and typically amalgamates with olderunconformities in a landward direction. Exposed bed-rock often occurs on the inner shelf.Conspicuous evidence for ice sheet advance onto the

Antarctic continental shelf is the occurrence of glacialtroughs offshore of major drainage outlets. Thesetroughs typically have u-shaped cross-sectional profiles

where they dissect sedimentary strata and morev-shaped profiles where they occur on crystallinebasement. The troughs slope toward the continentand typically extend to the outer continental shelf(Anderson, 1999).Piston cores sampled deposits above the youngest

glacial unconformity in a number of localities aroundthe continent. A range of techniques have been used toanalyze these deposits, often resulting in differentcriteria for distinguishing till from glacial-marine sedi-ment. In some cases, the absence of sorting (diamicton)alone has been the basis for inferring a subglacial origin.However, a diamicton is not always a till, and differenttill types (e.g., lodgment versus deformation) havedifferent properties. If the proper criteria are used, it ispossible to distinguish subglacial from glacial-marinedeposits, and reasonably detailed interpretations can bemade about the glacial-marine setting (see Anderson,1999 for review).Multibeam swath bathymetry and deep-tow side-scan

sonar records provide compelling evidence for ice-sheetgrounding. These surveys record geomorphic featuressuch as grooves, roches moutonn!ees, drumlins, flutes,mega-scale glacial lineations, deep iceberg furrows,meltwater channels and tunnel valleys (Anderson,1999; O’Brien et al., 1999; Shipp et al., 1999; Canalset al., 2000; Anderson and Shipp, 2001). The mostspectacular features occur within glacial troughs andinclude mega-scale glacial lineations that extend vir-tually across the entire shelf in some areas, such as inRoss Sea (Shipp et al., 1999) and on the AntarcticPeninsula shelf (Canals et al., 2000). Lineations indicatethat ice streams occupied troughs and that these icestreams flowed for many tens of kilometers over adeforming bed (Shipp et al., 1999; Wellner et al., inpress). The presence of a deforming bed suggests a lowice-sheet profile, at least during the final phase of thegrounding event.Swath bathymetry and side-scan sonar profiles

also record a variety of geomorphic features formedby the retreating ice margin, including grounding-zone wedges, morainal ridges, and corrugationmoraines (Anderson, 1999; O’Brien et al., 1999; Shippet al., 1999). These features provide an importantcontext for interpreting sedimentary facies and radio-carbon ages.

3. LGM reconstruction and retreat history

3.1. West Antarctic Ice Sheet

The WAIS is considered more unstable than the EAIS(Hughes, 1973). It is a marine ice sheet, grounded wellbelow sea level and characterized by rapid flow anddischarge relative to the EAIS. Most of this discharge


occurs through ice streams that reach flow velocities ofhundreds of meters per year (Fig. 2). Marine-geologicalresearch conducted in recent years has focused on the

principle drainage outlets of the WAIS (Shipp et al.,1999; Anderson and Shipp, 2001; Wellner et al., inpress).

Table 1

Sample information for radiocarbon analyses from the Pennell Coast, Pine Island Bay, and the Getz Ice Shelf region

Core number Depth (cm) Lab number Material dated Uncorrected

Age (yr BP)

Error (7yr) Corrected datea Environment of

deposition

Pennell coast

DF80-153-1 8 AA35934 Foraminifera 2220 70 920 Open-marine

121 AA35935 Foraminifera 4850 50 3550 Open-marine

DF80-158-1 180 AA31727 Bryozoan 8835 60 7535 Open-marine

NBP9801-17 96-99 AA35936 Bryozoan 8940 65 7640 Open-marine

200-204 AA35939 Algae 8200 90 6900 Open-marine

(above contact with till)

218 AA31713 Foraminifera 38,420 980 37,120 Till




NBP9801-19 14 AA31717 Shell 9500 65 8200 Open-marine

90 AA31718 Bryozoan 13,260 80 11,960 Open-marine




NBP9801-22 470 AA35940 Algae 7080 55 5780 Open-marine

629 AA35941 Algae 9260 70 7960 Open-marine

NBP9801-26 20 AA31721 Foraminifera 3895 50 2595 Open-marine

55 AA31722 Shell 6425 55 5125 Open-marine

67 AA31723 Foraminifera 10,265 70 8965 Open-marine



139 AA31726 Foraminifera 15,645 95 14,345 Open-marine

Pine Island Bay

NBP9902-37 28 AA38695 Foraminifera 3040 66 1740 Glacial-marine

70 AA38696 Foraminifera 7430 160 6130 Glacial-marine

192 AA38697 Foraminifera 5119 81 3819 Glacial-marine

NBP9902-39 14 AA38699 Foraminifera 15,800 3900 14,500 Glacial-marine

NBP9902-41 213 AA38701 Foraminifera 10,150 370 8850 Glacial-marine

NBP9902-49 25 AA38702 Foraminifera 2270 800 970 Meltwater deposit

Getz Ice shelf

NBP9902-22(t)b 46 AA40392 Shell 13,576 74 12,276 Open-marine

NBP9902-23 2 AA10390 Shell 12,804 82 11,504 Open-marine


(t) 23 AA40267 Bryozoan 13,873 86 12,573 Open-marine

(t) 36 AA40268 Bryozoan 13,514 85 12,214 Open-marine

(above contact

with glacial-marine)

NBP9902-26 4 AA40391 Foraminifera 7949 51 6679 Open-marine

(debris flow)

19 AA40393 Bryozoan 1848 40 548 Open-marine

(debris flow)

36 AA40389 Shell 11,817 69 10,517 Open-marine

58 AA40266 Shell 14,194 82 12,894 Open-marine

a1300 years has been subtracted from raw dates. See text for discussion.b (t) indicates trigger core.


3.1.1. Eastern and central Ross SeaThe central and eastern sectors of Ross Sea pre-

dominantly draw ice from the WAIS. In contrast,western Ross Sea is nourished by ice from EastAntarctica. This difference in source results in importantcontrasts in extent of ice during the LGM, and timing ofretreat (Anderson, 1999; Shipp et al., 1999).High-resolution seismic profiles from across the Ross

Sea continental shelf record a number of unconformitiesin the younger stratigraphic section (e.g., Hayes andDavey, 1975; Alonso et al., 1992). The most recentunconformity formed during the LGM (Shipp et al.,1999). The deposits above the LGM unconformity havebeen sampled by piston and gravity cores and analyzedfor a variety of sedimentary properties (Anderson et al.,1980, 1984; Licht et al., 1996, 1999; Domack et al.,1999a; Fig. 3a). The stratigraphy includes diatomaceousglacial-marine sediment over transitional (grounding-zone proximal) glacial-marine sediment over till. Twotypes of till are recognized, stiff lodgment till, and soft,water-saturated deformation till (Domack et al., 1999a;Shipp et al., 1999). Swath bathymetry and side-scansonar records from Ross Sea record ice-contact featuressuch as grounding-zone wedges and mega-scale glaciallineations, and provide indisputable evidence that the icesheet grounded on the continental shelf (Shipp et al.,1999). These data, coupled with results from petro-graphic analyses of the till, were used to reconstructRoss Sea paleodrainage (Anderson et al., 1984, 1992;Jahns, 1994; Shipp et al., 1999; Fig. 3b).In the eastern Ross Sea, two troughs drained the

interior of west Antarctica. Mega-scale glacial lineationsextend across the shelf to the continental shelf edge(Fig. 4), and wedges occur at the shelf break above theyoungest unconformity. Till was sampled in cores alongthe length of the troughs. The combined sedimentolo-gical and geophysical data from the eastern Ross Seasupport a maximum grounding line at the shelf breakbut more age control is needed (Fig. 3). The WAIS alsois believed to have grounded to the shelf break in centralRoss Sea, with small, ice-free shelf-edge regions (Shippet al., 1999).A large hiatus in radiocarbon ages between 19,500

14C yrBP (bulk-organic carbon date corrected by sur-face age of 3200 yr) and 26,500 14C yrBP (corrected withsurface age of 3500 yr) on the central Ross Sea shelf isbelieved to mark the time when the ice sheet grounded(Domack et al., 1999a). Licht (1999) stated thatgrounded ice was present on the outer shelf afterapproximately 13,770 14C yrBP (carbonate date cor-rected for reservoir effects by 1200 yr).Conway et al. (1999) suggest that the grounding line

retreated across Ross Sea like a swinging gate, hinged onthe eastern side of the sea. However, there are fewradiocarbon ages from the central and eastern Ross Seato test this model, and geomorphic features on the shelf

suggest a more complex retreat history. Specifically,differences in the number and spacing of grounding-zone wedges within each of the major troughs in centraland eastern Ross Sea indicate that different ice streamsbehaved independently during their retreat from theshelf (Fig. 3b).

3.1.2. Amundsen SeaMountain ranges in Marie Byrd Land were overrun

by thick ice during the LGM, and recessional morainedeposits have been dated to determine the thinninghistory of the WAIS in this region. Surface exposureages from a lateral moraine band on Mount Waescheindicate that the ice sheet was approximately 45mthicker than present as recently as 10,000 yr ago (Ackertet al., 1999). Deglaciation was still in progress atB3500 yr BP and outlet glaciers were B400m abovetheir present levels (Stone et al., 2000).The major drainage outlets of Marie Byrd Land flow

into the Amundsen Sea (Fig. 2). Without exception,large glacial troughs occur on the continental shelfoffshore of these outlets and provide the first line ofevidence that ice sheets advanced across the shelf(Anderson and Shipp, 2001; Fig. 5). Landward portionsof troughs contain exposed, striated bedrock withsubglacial meltwater channels in water depths of over1000m (Wellner et al., in press). Drumlins occur at thetransition between exposed bedrock, and an offlappingwedge of sedimentary strata covers the outer shelf(Fig. 6). Seaward of the drumlins, mega-scale glaciallineations extend for many tens of kilometers across thetrough axes. These combined features indicate that theice sheet was firmly coupled to the sea floor on the innershelf and on banks and that ice streams, sliding across amobile bed, occupied the troughs (Wellner et al., inpress).The exact location of the Amundsen Sea grounding

line during the LGM remains uncertain, but subglacialgeomorphic features indicate the ice sheet advanced atleast to the mid-shelf (Fig. 5). Iceberg furrows cross-cutthe shallower, outer shelf and perhaps obliterate oldersubglacial features. There is no conclusive evidence forthe presence of till on the outer shelf; Kellogg andKellogg (1987) suggested that diamicton sampled inouter shelf cores of Pine Island Bay was till but thecriteria for this determination is unclear. Hiemstra(2001) attributes micro-scale features identified indiamictons from the outer shelf of Pine Island Bay tosubglacial deformation. However, other deformingmechanisms, such as iceberg plowing, can not be ruledout completely. Near-sea-floor unconformities withinthe troughs extend across the outer shelf to the shelfbreak. The unconformities have not been dated, buttheir proximity to the sea floor suggests grounded icereached the outer shelf in recent times. Gullies have beenmapped at the shelf break. These are thought to form by


Fig. 3. (a) Ross Sea region data set used for our LGM reconstruction. Troughs are shown in gray. (b) Locations of geomorphic features and

paleodrainage map for Ross Sea.


expulsion of debris-laden meltwater expelled at the baseof an ice sheet grounded at the shelf break (Anderson,1999). Their presence is further evidence that ice reachedthe shelf break in the past. A virtual absence of morainalridges and wedges in the troughs on the inner shelfimplies rapid retreat of the ice sheet during the finalstages of deglaciation. This is supported by theoccurrence of iceberg furrows in water depths too deep(up to 760m) to have been cut by icebergs calving froman ice shelf. These may have formed during breakup ofthe ice sheet, as masses of large icebergs moved togetherseaward.Radiocarbon dates obtained from marine sediments

offshore of the Getz Ice Shelf have a maximum age of12,894 14C yr BP (corrected; Table 1). Two other coressampled the transition from glacial to marine conditionsand provided dates of 11,504 and 12,214 14C yr BP(corrected dates; Table 1). These dates indicate retreat of

the ice sheet from the shelf by about 12,900 14C yr BP. InPine Island Bay, glacial-marine sediment overlyingsubglacial features and till has a maximum age of14,500 14C yrBP (corrected; Table 1). Prior to this time,ice had begun to retreat from at least the middle portionof the Amundsen Sea shelf. A pause in retreat is markedby a grounding-zone wedge on the middle shelf of PineIsland Bay. On the inner shelf, only thin deposits ofglacial-marine sediment drape the underlying bedrock.The oldest date from this sediment is 8850 14C yr BP(corrected; Table 1), and was obtained from a corecollected near the present-day front of Pine IslandGlacier. It suggests the bay was ice-free by at least 885014C yr BP

3.1.3. Weddell SeaBentley and Anderson (1998) summarized evidence

for a higher-than-present WAIS elevation in the

Fig. 4. Multibeam image from the eastern Ross Sea showing mega-scale glacial lineations that extend to the shelf break and gullies on the upper

slope. Scale is appropriate to the center of the figure. Location of image shown in Fig. 3a.


southern Weddell Sea region during the LGM. Theextent of the WAIS on the continental shelf is poorlyconstrained. The largest geomorphic feature on the shelfis Crary Trough on the southeastern shelf (Fig. 7).Piston cores from Crary Trough sampled till, indicatingthat the ice sheet grounded to depths of just over 1000m(Anderson et al., 1980; Fig. 7). The till compositionindicates a West Antarctic origin (Anderson et al.,1991a). Cores acquired from the western front of theRonne Ice Shelf penetrated ‘‘stiff’’ diamicton, inter-preted as till (F .utterer and Melles, 1990). However, nodetailed sedimentological information has been pub-lished on these cores. The glacial reconstruction forsouthern Weddell Sea, where the WAIS could havegrounded on the shelf, is constrained only by resultsfrom Crary Trough (Fig. 7).

Attempts to radiocarbon date glacial-marine sedimenton the southern Weddell Sea shelf have been hamperedby a paucity of sediment cores and a general absence ofcarbonate material in these cores (Bentley and Ander-son, 1998). Glacial-marine sediment in a core from theouter shelf yielded uncorrected radiocarbon ages thatextend back to approximately 12,700 14C yrBP (cor-rected with a reservoir effect of 1300 yr for this paper),but inverted radiocarbon stratigraphy prevents preciseage dating of sediments on this portion of the shelf. Allthat can be said with confidence is that the ice sheetretreated from the outer shelf by this time.Anderson and Andrews (1999) attempted to date the

LGM in western Weddell Sea by searching for ice-rafteddebris (IRD) events in sediment cores from thecontinental slope and rise. The youngest IRD event in

Fig. 5. (a) Data from Amundsen Sea region used to map the LGM ice sheet configuration. Troughs are shown in gray. (b) LGM reconstruction and

paleodrainage map for the Amundsen Sea showing major geomorphic features.


Fig. 6. (a) Bathymetry of Wrigley Gulf region. (b) Multibeam image from the Wrigley Gulf showing grooves on basement rock of the inner shelf and

mega-scale glacial lineations on sedimentary strata of the outer shelf. (c) Blow-up of multibeam data showing grooves and drumlins on the inner

shelf. (d) A seismic profile across the Wrigley Gulf showing crystalline bedrock extending offshore into sedimentary strata.


these cores was older than 24,700 14C yrBP (correctedwith a reservoir effect of 1300 yr for this paper), which ismore consistent with retreat of the EAIS from theeastern Weddell Sea shelf.

3.2. East Antarctic Ice Sheet

Although geological investigations around East Ant-arctica remain sparse, the available data suggest that theice sheet was less extensive along most of its margin atthe LGM than originally proposed. Stuiver et al. (1981)

modeled the ice-sheet edge at the continental shelfbreak; Colhoun, 1991 reviewed evidence for thinner iceand less extensive LGM expansion. Data also suggestthat the EAIS did not expand and contract in concertalong its margin (Berkman et al., 1998; Anderson, 1999).Much of the evidence for reconstruction is derived fromglaciological and terrestrial data including ice core data,raised marine deposits, drift deposits, glacial erratics,and striated bedrock surfaces, which have been incor-porated into glaciological models (e.g., Goodwin, 1993;Goodwin and Zweck, 2000). More recently, marine-geological and -geophysical surveys provide controls onthe EAIS maximum reconstruction and retreat history.

3.2.1. Eastern Weddell SeaSedimentologic work by Anderson et al. (1980, 1991a)

led to the identification of till on the eastern Weddell Seashelf, offshore of Queen Maud Land. High-resolutionseismic profiles collected by Elverh�i and Maisey (1983)record a mid-shelf grounding-zone wedge resting abovea glacial unconformity that extends to the outer shelf. Atill provenance study by Anderson et al. (1991a)demonstrated that the till on the shelf was derived fromEast Antarctica.Age control on the glacial deposits of the Weddell Sea

is limited. Elverh�i (1981) obtained radiocarbon datesranging from 37,830 to 21,240 14C yrBP (uncorrected;the author did not provide corrected dates), on shellhash beds that overlie till and glacial-marine sedimenton the outer shelf and upper slope. Bentley andAnderson (1999) obtained additional radiocarbon agesfrom glacial-marine sediment samples in cores from theouter shelf. Glacial-marine sediment resting on till in acore from the northeastern shelf off Princess MarthaCoast yielded ages in the range of 14,940 (205 cm coredepth) and 22,570 14C yrBP (400 cm core depth)(corrected with a reservoir effect of 1300 yr for thispaper). Radiocarbon ages from glacial-marine sedimentin another core from the southeastern shelf, range backto 25,360 14C yrBP (corrected with a reservoir effect of1300 yr for this paper). These combined data indicatethat the EAIS advanced across the continental shelf andretreated from the shelf by about 25,000 14C yrBP.

3.2.2. Lutzow-Holm BayEvidence for LGM reconstructions in the Queen

Maud Land region are derived from inland geomorphicstudies and from coastal data. Hirakawa and Moriwaki(1990) present evidence that the EAIS was at least 400mhigher, possibly during the LGM, than at present in thecentral S�r Rondane Mountains. Considerable work hasfocused on raised beaches along the margins of Lutzow-Holm Bay, and from these data the timing and extent ofthe LGM ice sheet have been reconstructed (e.g., Miuraet al., 1998). While offshore troughs are identified andinterpreted to reflect erosion by expanded glacial

Fig. 7. (a) Data from the Weddell Sea region used for LGM

reconstruction. Troughs are shown in gray. (b) LGM reconstruction

and paleodrainage map for the Weddell Sea. Scale is appropriate to the

center of the figure.


systems, no offshore geophysical or geological studieshave been undertaken.The emerged beaches and marine sediment of the

Prince Olav and Soya coasts yield two groups of dates(Omoto, 1977, 1983; Yoshida, 1983, 1989). One group isof approximately Holocene age (B3000 to B800014C yrBP uncorrected AMS dates on marine fossils;the authors do not provide corrected dates) and asecond group provides dates older than 30,000 14C yr BP(B33,000 toB42,000 14C yrBP uncorrected AMS dateson marine fossils; Yoshida, 1983, Miura et al., 1998).There is little distinction in the elevations of the twogroups, so it is possible that the older dates indicate ice-free conditions, and the marine materials were incorpo-rated into the deposits of the LGM (Colhoun, 1991;Denton et al., 1991). Alternatively, Yoshida (1983) andMiura et al. (1998) interpret the dates to indicate ice-freeconditions since approximately 30,000 14C yrBP (un-corrected dates), and support their conclusions with theobservation that shell material older than LGM in thevicinity of East Ongul Island and northern Langhivde isneither reworked nor broken. In summary, during theLGM, the EAIS is interpreted to have either notadvanced, or to have advanced little from its presentposition along the eastern Queen Maud Land Margin.

3.2.3. Mac Robertson LandHarris and O’Brien (1996) characterized the geomor-

phology of the Mac Robertson shelf and related itserosional nature to subglacial incision and erosionduring ice-sheet advance. They also noted severalpossible morainal features related to retreating glaciers.Later work by these authors (Harris and O’Brien, 1998)placed the grounding line on the outer shelf, landwardof the shelf break, based on the presence of a groundingline moraine. They did not sample the subglacialdeposits, and thus cannot absolutely reconstruct aLGM grounded ice sheet. However, cores into glacial-marine deposits provide radiocarbon control on glacialretreat events. A mid-outer shelf sample of glacial-marine mud yielded a bulk-organic age of 17,15014C yrBP (uncorrected; the authors did not providecorrected dates). Based on the poorly sorted nature ofthe deposits, Harris and O’Brien (1998) interpreted themud unit to have been deposited under a floating iceshelf, close to the grounding line (marked by thegrounding line moraine). Overlying, better sorteddeposits may reflect the initial phases of retreat fromthe outer continental shelf. Open marine conditions areinterpreted by Harris and O’Brien (1998) to haveoccurred on the outer shelf approximately 10,00014C yrBP (uncorrected), based on radiocarbon datesfrom the base of a siliceous mud and ooze unit. Harriset al. (1996) place fully open marine conditions withinthe inner shelf basins prior to 5498 (uncorrected bulk-organic carbon; the authors do not provided corrected

dates), possibly as early as 7000 and open mid-shelfbanks at least by 8030 14C yrBP (uncorrected).

3.2.4. Prydz BayAdamson and Pickard (1983) proposed greater EAIS

thickness in the Vestfold Hills region during the LGMbased on high-elevation drift, trimlines, perched glacialerratics and striated bedrock. Mabin (1992) suggestedthat moraines, at elevations approximately 100m abovepresent levels, mark ice surface elevations during theLGM in the Lambert Glacier area. Farther to the east,dates from elevated marine deposits of the Vestfold Hillsyield 14C ages of 8620 (age corrected for reservoir effectby 1300 yr; Colhoun et al., 1992), interpreted to be thelatest possible age of deglaciation. Colhoun (1991),reviewing the ice elevation data from moraines andother terrestrial sources, suggested that the low LGMsurface levels of the Lambert Glacier and its tributariessupport a thickening of no more than 200m abovepresent level, and that the related ice volume wasinsufficient to reach the shelf edge.Prydz Bay is the site of the most extensive marine-

geological and -geophysical surveys along the EastAntarctic margin. O’Brien (1994) and O’Brien andHarris (1996) used bottom profiler records to character-ize the bottom morphology of Prydz Bay. Their map ofthe seafloor shows troughs, and bottom profiler recordsshow features interpreted as megaflutes. These com-bined data were used to infer that the ice sheet groundedto the shelf edge during the late Pleistocene.Based on gravity cores, and high-resolution seismic

and sides-can sonar data, Domack et al. (1999b)correlated sedimentologic facies with grounding zonefeatures in Prydz Bay and concluded that the LGM wasnot a shelf-wide event. Grounding line moraines occuralong the periphery of Prydz Channel, marking themaximum ice position. Structureless to massive diamic-ton occurs landward of the moraines and correlates withgrounding-zone proximal and sub-ice shelf facies withinthe channel. A unit interpreted to be an iceberg-rafteddiamicton marks the retreat of the calving line. Datesconstrain deposition of this unit to have occurred after20,770 and 20,230 14C yrBP (uncorrected foraminiferadates; the authors did not provide corrected dates) andbefore the transition to open-marine environments at12,680 14C yrBP (uncorrected bulk-organic carbon date)(Domack et al., 1999b).

3.2.5. Vincennes BayEarly ice-sheet reconstructions for the Vincennes Bay

area placed ice at the continental shelf edge, andproposed a thickness of >1000m over the coast line(Denton et al., 1991). The ice-sheet reconstruction in theBudd Coast region relies heavily on land-based ob-servations and glaciological modeling. Erratics, stria-tions, and u-shaped valleys are interpreted to indicate an


increased EAIS thickness (Goodwin, 1993). Thesefeatures are assumed to be related to the LGM, butlittle exists in the way of direct dates. In addition, raisedHolocene shorelines provide constraints for ice thicknessand retreat ages. Beaches and penguin rookeries alongthe coast of the Windmill Islands (as well as otherlocations) are elevated approximately 30m. The oldestraised deposits in the region constrain deglaciation to bebefore 7460–7710 14C yr BP (corrected with a reservoirbetween 450 and 700 yr; Goodwin, 1993) (Colhoun et al.,1992, Goodwin, 1993; Goodwin and Zweck, 2000).Colhoun et al. (1992) proposed a less extensive expan-sion, and therefore a thinner ice sheet (>400–500m),based on re-interpretation of the terrestrial geologicevidence.Region-specific ice-sheet reconstructions suggest that

the ice associated with the EAIS Law Dome covered theWindmill Islands and Petersen Bank during Stage 2. Theice was up to 500m thick and necessarily advanced theextent of glaciers by 20–25 km seaward of their presentpositions (Goodwin, 1993).Recent marine-geophysical surveys reveal that the

inner shelf of Vincennes Bay is deeply eroded, reflectingglacial scour (Harris et al., 1997). The middle to outershelf is comprised of a seaward-thickening sedimentaryprism that is cut by u-shaped valleys tied to present on-shore glacial systems. Harris et al. (1997) suggest thatthe eroded inner shelf and distribution of geomorphicfeatures support Goodwin’s (1993) expansion of EAISice associated with Law Dome onto the middlecontinental shelf during the LGM.More recently, Goodwin and Zweck (2000) incorpo-

rated new ice thickness data from ice-bubble gas-volumemeasurements, continuous q18O profiles and marinedata into an LMG model of Law Dome. The modelshows the EAIS thickened around its margin andextended onto the continental shelf approximately40 km. Goodwin and Zweck (2000) contend that lossof 770–1000m of ice thickness around the margin ofLaw Dome and adjacent EAIS would create the relativesea-level change history observed in the raised marinedeposits. Retreat in the model, constrained by the oldestage of the raised deposits, occurs between 13,000 and8000 14C yr BP (model based on corrected dates using a1300 yr reservoir correction). More work is required inthe marine realm to map geomorphic features anddetermine the age of events; this information will helpconstrain the model.

3.2.6. Wilkes LandGoodwin and Zweck (2000) suggest that a thickness

of 1000m of ice occurred during the LGM along theEAIS margin between Wilkes Land and Oates Land.Based on more limited coastal emergence betweenQueen Maud Land and Queen Mary Land (less thanhalf the emergence observed along Wilkes Land), they

suggest that ice thickness would have been reduced andthe ice would have extended only to the inner or middleshelf in these areas.One of the earliest detailed marine-geological studies

undertaken to reconstruct the EAIS during the LGMfocused on the Wilkes Land margin (Anderson et al.,1979). The identification of till on the shelf led to theinterpretation that the ice sheet grounded on the outershelf during the LGM (Anderson et al., 1980). Aprovenance study of the till by Domack (1982) resultedin a paleodrainage map that showed two major outletsflowing through Mertz and Ninnis troughs (Domacket al., 1991). Later work by Eittreim et al. (1995)extended this paleodrainage map to the west.Domack et al. (1989, 1991) proposed that the

transition from subglacial to glacial-marine sedimenta-tion occurred prior to B9000 14C yrBP (corrected dateusing a reservoir of 5500 yr), based on extrapolationfrom radiocarbon ages from diatomaceous sedimentthat overlies diamicton. They suggest that the retreat ofthe grounding line to its present coastal position wascomplete by B3000 14C yrBP (corrected with reservoirvalues between 1700 and 5500 depending on the core) inthe Mertz and Ninnis region of Wilkes Land.

3.2.7. Pennell shelfThe Pennell Coast area of North Victoria Land

receives drainage from the Transantarctic Mountains(TAM) (Fig. 2). Currently, only small valley glaciersdrain into the region. Because the Ross Sea LGMgrounding line has an embayment on the western side(Shipp et al., 1999), it is not possible that grounded icecame from the Ross Sea during the LGM. Therefore, forice to ground on the continental shelf offshore ofPennell, a significantly larger volume of ice must havebeen draining into the area from the TAM. Thus,evidence for grounded ice in the Pennell region isevidence for a much expanded EAIS during the LGM.The continental shelf offshore the Pennell Coast was

surveyed in 1980 (Brake and Anderson, 1983) and againin 1998 when multibeam, seismic, and core data werecollected (Fig. 3). The Pennell shelf has prominentglacial troughs extending across the shelf. Erosionalgrooves occur throughout the area of crystalline bed-rock. Cores from the region sampled diamicton overlainby a lift-off facies. This relationship, along withmicropaleontological and magnetic data, indicates thatthe diamicton is till. These features indicate that ice wasgrounded on the continental shelf in the region.Twenty-one new radiocarbon dates have been ob-

tained from this region (Table 1, Fig. 8). These datesindicate that ice that was grounded at least to the middleshelf during the LGM pulled back sometime prior to11,960 14C yrBP (corrected) and probably by 14,34514C yrBP (corrected).


3.2.8. Western Ross SeaThe expanded ice sheet in western Ross Sea was

nourished by ice from East Antarctica. Perched erraticson Beaufort and Franklin islands in southwestern RossSea occur at elevations up to 320m above sea level(Stuiver et al., 1981). Moraines of the Ross Sea Drift,350m above sea level, occur in the TAM and indicatethat the ice sheet extended across the shelf during theLGM. These are only two examples of onshore data thatindicate higher-than-present ice-sheet elevation in theRoss Sea region during the recent past. Denton et al.(1991) and Hall and Denton (1999) provide thoroughreviews of the onshore record of ice-sheet configuration.Ice in western Ross Sea extended to approximately

100 km inland of the shelf break near Coulman Island(Shipp et al., 1999). The embayment in the groundingline in the western Ross Sea is consistent with results ofKellogg et al. (1996) and Licht et al. (1999), although thelatter authors place the grounding line approximately75 km south of where Shipp et al. (1999) place it.Studies of late Quaternary deposits exposed along the

seaward side of the TAM, and in the western Ross Sea,have yielded the most detailed chronostratigraphicrecord of WAIS grounding and retreat in Antarctica(Stuiver et al., 1981; Baroni and Orombelli, 1991;Denton et al., 1991; Conway et al., 1999). Theembayment in the grounding line in northwestern RossSea is supported by radiocarbon dates on calcareous

fossils from the Terra Nova drift in northern VictoriaLand, which yield ages 25,300 14C yr BP (uncorrecteddate; the authors do not provide corrected dates) andolder (Orombelli et al., 1990). The embayment also isindicated by glacial-marine sediment and bioclasticcarbonate on the outer shelf that have yielded radio-carbon ages greater than 28,000 yr BP (Taviani et al.,1993; Licht et al., 1996). Conway et al. (1999) concludethat the Ross Sea ice sheet grounded on the outer shelffrom at least 27,820–12,880 calendar yr BP. (Marinematerials were corrected by 1300 yr reservoir effect andno correction was applied to algal dates. Dates werethen converted to calendar years.) This is consistent withthe occurrence of glacio-volcanic deposits at B350mabove the present ice surface at Mount Takahe that haveyielded 40Ar/39Ar ages of 29,000–12,000 yr BP andrecord the maximum glaciation in this region (Wilch,1997). Cores collected south of the grounding-zonewedge in the western Ross Sea yielded ages that rangefrom B18,000 to B11,000 14C yrBP (Anderson et al.,1992, 1200 yr correction; Licht et al., 1996, 1200 yrcorrection factor; Domack et al., 1999a, variablecorrection factor). ByB7000 yr BP it reached a positionnear Ross Island (Conway et al., 1999). The completionof the Holocene grounding-line recession, between RossIsland and present grounded position, occurred betweenB7000 yr BP and the present in the western Ross Searegion (Conway et al., 1999).

3.3. Antarctic Peninsula

The recent ice-sheet reconstruction of Nakada et al.(2000) includes two models (ANT 5 and ANT 6) thatshow much larger ice masses in the Antarctic Peninsulathan exist today (Fig. 1). These models are consistentwith the geological data from the region (Bentley andAnderson, 1999). Additional data have been acquiredsince the Bentley and Anderson (1999) reconstructionwas published.

3.3.1. Marguerite BayA study by Kennedy and Anderson (1989) revealed a

prominent glacial erosion surface extending acrossMarguerite Bay. Later seismic studies showed that thisunconformity extends to the shelf break (Bart andAnderson, 1996). The largest glacial trough in the regionis Marguerite Trough, which extends to the outer shelf(Fig. 9). Swath bathymetry records, acquired during arecent survey of the area, showed drumlins, flutes andstriations in the landward portions of the trough andmega-scale glacial lineations in the seaward portions ofthe trough. The lineations extend seaward into aprominent grounding-zone wedge on the mid-shelf(Fig. 9). To date, no swath bathymetry data werecollected seaward of this wedge.

Fig. 8. Sedimentological logs for sediment cores NBP9801-PC17 and

NBP9801-PC19 from the continental shelf offshore of the Pennell

Coast showing radiocarbon ages.


Detailed sedimentological and petrographic analysesof piston cores showed that till occurs within MargueriteTrough and on the inner shelf (Kennedy and Anderson,1989; Pope and Anderson, 1992). Till was not sampledon the outer shelf.Radiocarbon dates from glacial-marine sediment

above the grounding-zone proximal facies in four coresfrom Marguerite Trough on the shelf yielded ages of12,190–11,125 14C yrBP (corrected for this paper with acorrection factor of 1300 yr; Pope and Anderson, 1992).Thus, the ice sheet is interpreted to have retreated fromthe shelf prior to B12,000 yr ago. Clapperton andSugden (1982) suggested that George VI Sound was ice-free by B6500 14C yrBP (corrected by 750 yr) based onpelecypod shells of that age in a moraine on AlexanderIsland. Radiocarbon dates from diatomaceous glacial-marine sediment in Marguerite Bay extend back toB6000 to B6700 14C yrBP (uncorrected dates; theauthors do not report corrected dates) (Harden et al.,1992). These dates record the time when open-marineconditions were established, not the retreat of the icesheet. Radiocarbon dates from Lallemand Fjord,located just north of Marguerite Bay, indicate that iceretreated form the fjord by 8000 14C yrBP (correctedwith a reservoir equal to 1300 yr) (Shevenell et al.,1996).

3.3.2. Northern Antarctic Peninsula regionHigh-resolution seismic records from the Gerlache

Strait and Inland Passage show large areas where thesediment cover has been eroded, and swath bathymetryrecords show glacial groves and striations. Seismicrecords from the continental shelf imaged a glacialunconformity that extends to the shelf break (Bart andAnderson, 1996). Pudsey et al. (1994) acquired side-scansonar records offshore of Anvers Island that showglacial flutes on the inner shelf. Larter and Vanneste(1995) identified a possible grounding-zone wedge onthe outer shelf in this region (Fig. 9).Domack et al. (2001b) obtained an extensive radio-

carbon stratigraphy for diatomaceous glacial-marinesediment that overlies diamicton in Palmer Deep, on theinner shelf near Anvers Island. Their results provideconstraints on the retreat of the ice sheet and indicatethat it retreated from the area around 13,000 yr BP(corrected with a reservoir effect equal to 1230 yr andthen corrected to calendar years). This is consistent withearlier work by Pudsey et al. (1994) who acquired agedates younger than 11,000 14C yrBP (corrected using acarbon reservoir equal to 1500 yr) on glacial-marinesediment from the continental shelf offshore of AnversIsland, seaward of Palmer Deep. Radiocarbon agesfrom a core collected in the central part of the GerlacheStrait indicate that glacial-marine sedimentation begansometime after 8000 14C yr BP (uncorrected date; Hard-en et al., 1992).

Fig. 9. (a) Data from the Antarctic Peninsula region used for LGM

reconstruction. Troughs are shown in gray. (b) LGM reconstruction

and paleodrainage map for the Antarctic Peninsula region showing

major geomorphic features. Scale is appropriate to the center of the

figure.


Fig. 10. (a) Data from the Bransfield Strait region used for LGM reconstruction. (b) LGM reconstruction and paleodrainage map for the Bransfield

Strait region. Scale is appropriate to the center of the figure.


3.3.3. Bransfield StraitBanfield and Anderson (1995) examined High-resolu-

tion seismic reflection profiles and piston cores acquiredfrom the eastern (Trinity Peninsula) side of BransfieldStrait (Fig. 10). They recognized a prominent glacialunconformity that extends to the shelf break and a set ofmorainal ridges within troughs that record the retreat ofthe ice cap from the shelf (Fig. 11). The most compellingevidence that the ice cap advanced across the shelfcomes from swath bathymetry records that show mega-scale glacial lineations that extend to the shelf break justwest of the South Sandwich Islands (Canals et al., 2000;Fig. 10b).Dates obtained from ice-proximal glacial-marine

deposits in a piston core from the Trinity Peninsulashelf are 19,055 14C yrBP (bulk-organic carbon, cor-rected with a reservoir effect of 1300 yr for this paper)and 14,365 14C yrBP (carbonate material, corrected witha reservoir effect of 1300 yr for this paper). These datesindicate that the ice sheet retreated from the outercontinental shelf at least prior to 14,365 14C yr BP(Banfield and Anderson, 1995).

3.3.4. Weddell SeaHigh-resolution seismic records and sediment

cores collected within Prince Gustav Channel and fjordsalong the channel show that these areas virtually

have been scraped clean of sediment (Anderson et al.,1992), with the exception of sediment drifts near themouths of the channel and fjords (Domack et al.,2001a). Multibeam records from the inner shelf showflutes and other lineations (Domack et al., 2001a).Seismic records from the continental shelf offshore ofJames Ross and Seymour islands in northwesternWeddell Sea show a widespread glacial unconformitythat extends to the shelf break (Anderson et al., 1992;Sloan et al., 1995; Fig. 12). A prominent grounding-zonewedge rests above this unconformity on the mid-shelf(Fig. 12).Detailed analyses of piston cores from the shelf,

including petrographic analyses, showed strong provin-ciality of transitional glacial-marine deposits (Andersonet al., 1991a). This was taken as evidence for depositionbeneath a fringing ice shelf that extended to the shelfedge (Anderson et al., 1991b), but the diamicton waslater interpreted as possible deformation till (Anderson,1999).Only a few radiocarbon ages have been acquired from

glacial-marine deposits from the northwestern Weddellsea continental shelf (B. Sloan, pers. comm.). Two of thecores analyzed by Sloan yielded inverted ages andanother core from the middle shelf yielded ages forglacial-marine sediment ranging from 4620 to 719014C yrBP (uncorrected dates). However, these samples

Fig. 12. Seismic profile PD 91–22 showing glacial unconformity and grounding-zone wedge on the northwestern Weddell Sea continental shelf

(modified from Anderson, 1999). See Fig. 7a for profile location.

Fig. 11. Seismic profile PD 91–20 showing morainal ridge in the Bransfield Strait (modified from Anderson, 1999). See Fig. 8a for profile location.


do not record initial retreat of the ice sheet from theshelf. Onshore studies in the area indicate thatdeglaciation occurred prior to 7400 14C yrBP (correctedusing a 1200 yr reservoir) (Hjort et al., 1992; Hjort et al.,1997).

4. Results

Our LGM reconstruction is shown in Fig. 13. Thegrounding line location shown is a minimum groundingline that is based on the presence of subglacialgeomorphic features and/or till. A maximum groundingline at the shelf margin is inferred from a glacialunconformity that extends to the shelf break in manyareas. However, the age of this unconformity isuncertain.

The marine data place constraints on the expansion(and therefore coastal thickness) of the ice sheet duringthe LGM. Our LGM reconstruction best matches theextent of ice portrayed in geophysical models thatpropose a moderately expanded ice sheet (e.g., ICE-3G),but the specifics for each region require attention. Giventhat the probable contribution of the Antarctic Ice Sheetto sea-level change appears to be less than the earliestmodels contend, the ice must either be placed inlocations other than Antarctica, or the record of sea-level change must be re-evaluated. In addition, thetiming of advance and retreat of the WAIS and EAISprobably were not in phase; the greatest uncertainty is inthe timing of EAIS advance and retreat.Fig. 13 also shows the approximate times when the ice

sheet retreated from the shelf, based on radiocarbonages of glacial-marine sediment resting above till. Not

Fig. 13. Sketch of LGM ice sheet reconstruction from this study. Also shown are the oldest radiocarbon ages from glacial-marine deposits. See text

for discussion of dates. They are the approximate age of initial ice sheet retreat from the shelf. Map of bed topography from Lythe et al. (2000).

Deeper gray shades indicate the continental slope and abyssal plain.


all are corrected ages and the glacial-marine depositsthat were dated are not always the oldest glacial-marinedeposits in an area. Still, two important trends emerge.One is that retreat of the EAIS appears to have beendiachronous around the continent and, in some areas,retreat occurred prior to the LGM. Second, retreat fromthe West Antarctic shelf appears to have occurred atabout the same time all around West Antarctica,between 15,000 and 12,000 yr ago. In Ross Sea and theAntarctic Peninsula regions, retreat continued well intothe Holocene. Clearly, more and better radiocarbondates are needed, especially around East Antarctica,before more precise retreat histories can be established.

5. Conclusions

1. During the LGM, the WAIS advanced across thecontinental shelf, and reached the shelf margin in thecentral and eastern Ross Sea. Ice advanced at least tothe middle continental shelf along the rest of theWAIS margin.

2. Initial retreat of the WAIS appears to have occurredbetween 15,000 and 12,000 yr and continues into theHolocene. There was significant retreat of the icesheet in the Ross Sea, and possibly Weddell Sea, after7000 yr BP.

3. During at least the final stages of the glacialmaximum, the expanded WAIS was flowing acrossan extensive deforming bed. This implies gentleprofiles, high rates of flow and discharge, andpossibly rapid retreat. Thus, the LGM configurationmay have changed during the LGM.

4. Advance and retreat of the EAIS did not occureverywhere around the continent at the same timeand to the same extent. During the LGM, the EAISice sheet advanced only to the middle or mid-outercontinental shelf, with the exception of the easternQueen Maud Land/Lutzow Holm Bay region, whereit is possible that there was no advance. In somelocations, the maximum extent was achieved prior tothe LGM. Retreat from the mid-shelf LGM positionwas diachronous around the continent and occurredbetween approximately 25,000 and 9000 yr BP, andpossibly as early as 30,000 yr BP in Lutzow-HolmBay.

5. The Antarctic Peninsula housed much greater vo-lumes of ice during the LGM than was previouslythought, and therefore made a greater contribution tothe post-glacial sea-level rise.

Acknowledgements

This research was funded by the National ScienceFoundation, Office of Polar Programs grant number

OPP-9527876. Radiocarbon dating was performed atthe University of Arizona AMS laboratory. Weappreciate the input from two anonymous reviews andeditor Peter Clark.

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