marine geophysical evidence for former expansion and flow of the greenland ice sheet across the...

JOURNAL OF QUATERNARY SCIENCE (2009) 24(3) 279–293Copyright � 2008 John Wiley & Sons, Ltd.Published online 23 October 2008 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/jqs.1231
Marine geophysical evidence for formerexpansion and flow of the Greenland Ice Sheetacross the north-east Greenland continental shelfJEFFREY EVANS,1* COLM O COFAIGH,2 JULIAN A. DOWDESWELL3 and PETER WADHAMS41 Department of Geography, University of Loughborough, Loughborough, UK2 Department of Geography, Durham University, Durham, UK3 Scott Polar Research Institute, University of Cambridge, Cambridge, UK4 Sea Ice Group, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, UK

Evans, J., O Cofaigh, C., Dowdeswell, J. A. and Wadhams, P. 2009. Marine geophysical evidence for former expansion and flow of the Greenland Ice Sheet across thenorth-east Greenland continental shelf. J. Quaternary Sci., Vol. 24 pp. 279–293. ISSN 0267-8179.

Received 26 February 2008; Revised 11 July 2008; Accepted 17 July 2008

ABSTRACT: High-resolution swath bathymetry and TOPAS sub-bottom profiler acoustic data fromthe inner and middle continental shelf of north-east Greenland record the presence of streamlinedmega-scale glacial lineations and other subglacial landforms that are formed in the surface of acontinuous soft sediment layer. The best-developed lineations are found in Westwind Trough, abathymetric trough connecting Nioghalvfjerdsfjorden Gletscher and Zachariae Isstrøm to the con-tinental shelf edge. The geomorphological and stratigraphical data indicate that the Greenland IceSheet covered the inner-middle shelf in north-east Greenland during the most recent ice advance of the
Late Weichselian glaciation. Earlier sedimentological and chronological studies indicated that the lastmajor delivery of glacigenic sediment to the shelf and Fram Strait was prior to the Holocene duringMarine Isotope Stage 2, supporting our assertion that the subglacial landforms and ice sheet expansionin north-east Greenland occurred during the Late Weichselian. Glacimarine sediment gravity flowdeposits found on the north-east Greenland continental slope imply that the ice sheet extendedbeyond the middle continental shelf, and supplied subglacial sediment direct to the shelf edge withsubsequent remobilisation downslope. These marine geophysical data indicate that the flow of theLate Weichselian Greenland Ice Sheet through Westwind Trough was in the form of a fast-flowingpalaeo-ice stream, and that it provides the first direct geomorphological evidence for the formerpresence of ice streams on the Greenland continental shelf. The presence of streamlined subglaciallyderived landforms and till layers on the shallow AWI Bank and Northwind Shoal indicates that icesheet flow was not only channelled through the cross-shelf bathymetric troughs but also occurredacross the shallow intra-trough regions of north-east Greenland. Collectively these data record for thefirst time that ice streams were an important glacio-dynamic feature that drained interior basins of theLate Weichselian Greenland Ice Sheet across the adjacent continental margin, and that the ice sheetwas far more extensive in north-east Greenland during the Last Glacial Maximum than the previousterrestrial–glacial reconstructions showed. Copyright # 2008 John Wiley & Sons, Ltd.
KEYWORDS: Greenland Ice Sheet; Late Weichselian; subglacial bedforms; LGM ice sheet configuration; palaeo-ice stream.

Introduction

Fast-flowing outlet glaciers draining the Greenland Ice Sheetsouth of 708 N are at present undergoing rapid melting andthinning in response to increased surface temperatures, whichcould lead to partial or total collapse of the ice sheet,contributing to a rise in sea level of up to 7 m (Oppenheimer,1998; Rignot et al., 2001; Rignot and Kanagaratnam, 2006). In

* Correspondence to: J. Evans, Department of Geography, University of Lough-borough, Loughborough LE11 3TU, UK.E-mail: [email protected]

north-east Greenland today, over 300 000 km2 or 20% of theice sheet are drained from interior drainage basins to the coastby the fast-flowing glaciers of Storstrømmen, L. Bistrup Brae,Zachariae Isstrøm, Nioghalvfjerdsfjorden and Hagen BraeGletschers (e.g. Reeh et al., 1994; Rignot et al., 1997; Thomsenet al., 1997; Mayer et al., 2000; Rignot and Kanagaratnam,2006). Evidence shows that glaciers in this region are alsoexperiencing environmental change to a certain extent, whereZachariae Isstrøm and Nioghalvfjerdsbrae have undergonevertical thinning and subsequent retreat over recent years(Rignot et al., 2001). Reconstructing the former history of thenorth-eastern margin of the Greenland Ice Sheet during the lastglacial cycle provides important constraints on how this area of

280 JOURNAL OF QUATERNARY SCIENCE

the ice sheet will behave in response to present-day, and anyfuture, environmental change.

Outlet glaciers in north-east Greenland discharge about25 km3 a�1 of ice into the Greenland Sea through basalmelting and iceberg production (Rignot and Kanagaratnam,2006). However, the past behaviour and flow dynamics ofthe north-eastern part of the Greenland Ice Sheet during thelate Quaternary remain little known compared with the icemargins around the remainder of the Norwegian–GreenlandSea (e.g. Funder et al., 1998; Landvik et al., 1998; Mangerudet al., 1998). This is largely because of the inaccessibility ofthe area as ship access is often limited by shorefast ice and seaice transported in the East Greenland Current. The north-eastern sector of the ice sheet has often been regarded asrelatively stable, based mainly on terrestrial geologicalobservations (Hjort, 1981, 1997; Funder, 1989), undergoingonly quite minor fluctuations between the last full-glacial andthe present interglacial periods (Hjort, 1981, 1997; Funder,1989; Funder and Hansen, 1996; Funder et al., 1998). In awider context, the accurate reconstruction of the wholeGreenland Ice Sheet during the late Quaternary is necessaryin order to constrain and improve models of ice sheet volumechange during the last full-glacial with implications for globaleustatic sea-level rise during deglaciation (Letreguilly et al.,1991a,b; Funder et al., 1998; Clark and Mix, 2002;Huybrechts, 2002).

In this paper, we present and interpret marine geophysicalrecords from the continental shelf of north-east Greenland andadjacent continental slope and deep sea of the Fram Strait andGreenland Sea (Fig. 1). First, we describe and interpret thegeomorphology of submarine glacial landforms and sediments,and the shallow acoustic stratigraphy of the continental shelfand slope. We then discuss the implications of this geomor-phology and acoustic stratigraphy for the former dynamics andextent of the Greenland Ice Sheet along its north-eastern marginduring the Late Weichselian glaciation.

Background and study area

Physiography, glaciology and bathymetry

The study area is located on the north-east Greenlandcontinental margin and adjacent western and central regionof the Fram Strait and north-west Greenland Sea between 768 Nand 81.58 N (Fig. 1(a)). The north-east Greenland continentalshelf and slope is an important region for sea ice formation, andbottom water formed here is an important driver of globalocean circulation (Wadhams, 1981). In addition, the con-tinental margin is influenced by the cold (�18C), southward-flowing East Greenland Current (Hopkins, 1991).

The north-east Greenland coast is dissected by a number offjords or inlets from Dove Bugt in the south to Heckla Sund/Dijmphna Sund and Ingolf Fjord in the north (Fig. 1(a)). TheGreenland Ice Sheet is drained via several fast-flowing outletglaciers to the north-east Greenland fjords; Zachariae Isstrømdrains into Jøkelbugten, Nioghalvfjerdsbrae into Nioghalvf-jerdsfjorden and Storstrømmen and L. Bistrup Bræ into DoveBugt. These glaciers drain about 320 000 km2 or 21% of theGreenland Ice Sheet to the north-east Greenland margin withglacier velocities between 1100–1300 m a�1 for ZachariaeIsstrøm and Nioghalvfjerdsbrae; L. Bistrup Bræ and Storstrøm-men are slow moving at present, since they are surge-typeglaciers in a quiescent phase (Reeh et al., 1994; Rignot et al.,1997, 2001; Rignot and Kanagaratnam, 2006). Zachariae

Copyright � 2008 John Wiley & Sons, Ltd.

Isstrøm and Nioghalvfjerdsbrae retreated between 1992 and1999 in response to vertical thinning, which has been estimatedat 1.7 m a�1 for Nioghalvfjerdsbrae (Rignot et al., 2001).

The IBCAO Arctic bathymetry database (Jakobsson et al.,2000) shows that the 400 km wide (at its maximum) north-eastGreenland continental shelf comprises prominent shallowbanks intersected by deeper cross-shelf bathymetric troughs(Fig. 1(b) and (c)). Belgica Bank, Northwind Shoal, AWI Bankand Ob Bank form the most prominent shallow shelf regionsbetween 788 N and 818 N, with other deeper banks furtheroffshore (Fig. 1(b) and (c)). Westwind Trough to the westand north, and Norske Trough to the west and south, formmajor bathymetric features that dissect the shelf banks, andconnect the coastal fjords to the continental shelf edge(Fig. 1(b) and (c)). In addition, small-scale troughs originateon, and dissect, the shallow banks, and extend to theouter shelf (Fig. 1(b) and (c)). A broad outward bulging ofbathymetric contours at the continental shelf edge and on theadjacent continental slope down to �3000 m occurs in frontof these cross-shelf troughs between �768 N and 818 N, withabyssal regions of the Fram Strait and Greenland Sea below3000 m further offshore.

Glacial history of north-east Greenland

Terrestrial glacial–geological reconstructions, based on marinelimits and ice marginal deposits, indicate that outlet glaciers ofthe Greenland Ice Sheet advanced only a short distance fromtheir present-day limits and filled the fjords of north-eastGreenland (north of 758 N), with their margins on the innermostcontinental shelf, during the Late Weichselian glaciation (Funderand Hansen, 1996; Hjort, 1997; Bennike and Weidick, 2001).Piedmont glaciers drained coastal mountains and covered mostof the forelands between the fjords. However, a limited icemargin in north-east Greenland has subsequently been ques-tioned, where circumstantial evidence in the form of radio-carbon ages showing late deglaciation of the outer fjords priorto 9 14C ka BP, coupled to the broad, shallow shelf bathymetry,have been used to hypothesise that an ice sheet may haveexpanded across much of the shelf during the last glaciation(Bennike and Bjorck, 2002). The rationale behind this suggestionwas that if the shallow shelf was glaciated then ice recession tothe outer coast could have taken a relatively long time,explaining the late deglaciation of the outer fjords. An ice shelfis thought to have filled Dove Bugt/Jøkelbugten region of north-east Greenland with the outer margin pinned on inner shelfislands at this time (Hjort and Bjorck, 1984; Landvik, 1994).

Similarly, traditional ice sheet reconstructions from furthersouth along the central East Greenland seaboard to as far southas Scoresby Sund showing only a limited advance of glacier iceas far as the innermost shelf during the Late Weichselianglaciation have also been questioned (Funder and Hjort, 1973;Hjort, 1979, 1981; Funder, 1989; Marienfeld, 1992; Dowdes-well et al., 1994; Funder et al., 1994, 1998; Funder andHansen, 1996). More recent evidence in the form of glacier-fedsubmarine channels on the continental slope, 10Be ages fromerratic boulders and a terminal moraine (coupled to potentialtill layers) on the outer continental shelf indicates that theGreenland Ice Sheet is likely to have extended much the wayacross the central East Greenland continental margin between708 and 738 N (Evans et al., 2002; O Cofaigh et al., 2004;Hakansson et al., 2007).

A prominent light-spike within stable oxygen isotope recordsdocuments a large influx of meltwater to the eastern seaboard ofGreenland and Fram Strait associated with the onset of the last

J. Quaternary Sci., Vol. 24(3) 279–293 (2009)DOI: 10.1002/jqs

Figure 1 (a) Location map of the north-east Greenland continental margin. Locations of Figure 1(b) and (c) and swath imagery records of Figure 4(a)and (b) are shown as boxes. Dashed lines represent the cruise tracks of JR106 to north-east Greenland. (b, c) Composite bathymetric map showing theswath bathymetry acquired from the north-east Greenland continental shelf during JR106, and the published IBCAO bathymetry dataset of the north-east Greenland continental margin (Jakobsson et al., 2000). Swath imagery in Figs. 2–4, and TOPAS sub-bottom acoustic profiles in Figs. 6 and 7, arelocated by the labelled boxes in both (a) and (b). This figure is available in colour online at www.interscience.wiley.com/journal/jqs

LATE WEICHSELIAN ICE SHEET FLOW, NE GREENLAND CONTINENTAL SHELF 281

deglaciation before 15.3 14C ka BP (e.g. Jones and Keigwin,1988; Nam et al., 1995; Stein et al., 1996; Funder et al., 1998;Hebbeln et al., 1998; Evans et al., 2002). The outer fjords andcoast in north-east Greenland were ice free shortly before 914C ka BP (or 9.7 cal. ka BP; corresponding to the onset of thehypsithermal period), and the inner fjords were deglaciated


prior to 7 14C ka BP, suggesting a recessional rate of 30–40 m a�1 (Hjort, 1997; Bennike and Bjorck, 2002). Glaciersmay have withdrawn behind their present-day positions at thehypsithermal, but appear to have undergone limited readvancein association with climate deterioration after about 5 14C ka BP(Funder, 1989; Hjort, 1997).



Data acquisition and methods

Geophysical and bathymetric data were acquired from thecontinental shelf and slope of north-east Greenland andadjacent Fram Strait and north-west Greenland Sea duringcruise JR106 of the RRS James Clark Ross in 2004 (Fig. 1).Adverse sea ice conditions on the inner shelf preventedgeophysical data from being acquired from along the coast, andin the fjords of north-east Greenland. Two hull-mountedsystems were used to acquire geophysical data: a Kongsberg-Simrad EM120 multi-beam swath-bathymetry system andTopographic Parametric Sonar (TOPAS) sub-bottom profiler.

The EM120 swath bathymetric system emits 191 beams, eachwith a frequency of 12 kHz and a maximum port- andstarboard-side angle of 758. This gives, for example, a totalswath width of about 3–4 km in a water depth of 500 m. Swathdata were processed through the removal of anomalous pingsand gridded at a range of cell sizes from 15 to 50 m using theKongsberg-Simrad NEPTUNE software. The TOPAS systemuses parametric interference between two primary waves ofhigh frequency to produce a secondary acoustic beam ofnarrow width (for greater resolution and reduced side-lobeinterference) and low-frequency range of 0.5–5 kHz. Verticalresolution is better than 1 m. Navigation data were acquiredusing differential GPS.

Submarine landforms and morphology

North-east Greenland continental shelf:westwind trough

Sea floor swath bathymetry from Westwind Trough records thewidespread presence of well-developed, highly attenuated

Figure 2 (a, b) EM120 shaded swath imagery from Westwind Trough show


lineations (Fig. 2(a) and (b)). Lineations range from >2500 to�10 000 m in length and from 200 to 340 m in width, and haveelongation (length to width) ratios of >12:1 to �33:1.Orientation of lineations is parallel to the axis of WestwindTrough, ranging from WSW–ENE in more inshore regions(Fig. 2(a)) to NW–SE further offshore across the shelf (Fig. 2(b)).

North-east Greenland continental shelf:northwind shoal, AWI bank and outer shelf

Sea floor morphology across Northwind Shoal and AWI Bank isvariable (Fig. 3) and comprises characteristics or features thatare divided into four main groups. (1) The first comprises linear,curvilinear or irregularly shaped grooves that are orientatedmainly N–S and NW–SE (Fig. 3(a)–(d)). They appear to be thedominant morphological feature across the shallower shelfoutside Westwind Trough, in small-scale troughs or depres-sions incising Northwind Shoal and AWI Bank, and acrossthe outer shelf (up to the shelf edge). The grooves occur eitheras isolated individuals or are clustered into groups with,locally, evidence of overprinting and cross-cutting relation-ships. (2) The second group comprises subtle, highly elongateand attenuated lineations that are up to several kilometres inlength, and tens to hundreds of metres in width (elongation ratioof >10:1). They are orientated SW–NE but become W–E furtheroffshore, and are sparsely distributed across the western side ofNorthwind Shoal (Fig. 3(a)). (3) The third group comprisessmooth, rugged (irregular) or smooth-hummocky sea floor areas(Fig. 3a). (4) The fourth, and final, group comprises small-scaleridges that are metres to tens of metres in height, tens tohundreds of metres in width and extend for up to severalhundred metres (Fig. 3(e)). Ridges are sinuous or linear inshape, and form a cluster of continuous or semi-continuousfeatures that are orientated approximately SW–NE. The

ing well-developed lineations and mega-scale glacial lineations


Figure 3 EM120 shaded swath imagery from the north-east Greenland continental shelf (located in Figure 1(b)) showing: (a) main sea floorcharacteristics comprising grooves (or scours), subtle elongate bedforms, and irregular or hummocky sea floor across Northwind Shoal. Bedforms areorientated SW–NE; (b–d) iceberg scouring with a strong N–S to NE–SW orientation across Northwind Shoal, AWI Bank and the mid–outer continentalshelf; and (e) small-scale ridges that are several tens of metres in height, trend NE–SW and comprise acoustically transparent sediment (indicated by thewhite arrowheads)

Copyright � 2008 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 24(3) 279–293 (2009)DOI: 10.1002/jqs



orientation of the ridges deviates sharply from the SW–NE andW–E orientated lineations of group 2 across Northwind Shoal.Locally, ridges are replaced by a morphology that closelyresembles bathymetric scarps, and these features retainorientations, dimensions and distributions that are similar tothe ridges.

North-east Greenland continental slope andabyssal plain

A series of connecting concave-shaped bathymetric escarp-ments (producing a sinuous morphology) that are perpendicu-lar to the shelf edge and cut back into the continental slope arelocated on the upper–mid continental slope of the north-westBoreas Basin (Fig. 4(a)). Water depths on the lower, southernside of the escarpment are �40–180 m below those of thehigher, northern side of the escarpment, with the consistentlyhighest depth difference along its central and lowermostpart (100–180 m). The abrupt escarpment wall is verysteep, with slope gradients that range between �98 and�258, with the consistently steepest gradients (18–258) on themiddle–lower part of the bathymetric escarpment. An undulat-ing or hummocky sea floor characterises the downslope orsouthern side of the scarp. More subtle bathymetric escarp-ments are also located to the south of the prominentnortherly escarpment described above, where gradientsare <158 and the height differences between the higherand lower sides is <50 m (Fig. 4). It is uncertain whetherthe more southerly subtle bathymetric escarpments formdiscrete or interconnecting local morphological features, orconnect with the northern escarpment to form a large-scaleescarpment system that extends �60 km in width acrossthe upper–middle region of the north-east Greenland con-tinental slope (Fig. 4(b)).

Figure 4 (a, b) EM120 shaded swath imagery from the north-east Greenlandconsistent with a slide scar produced during the process of sediment failure


Regional acoustic stratigraphy

North-east Greenland continental shelf:westwind trough

TOPAS sub-bottom profiler records show the presence of a seafloor/near-sea floor unit of mainly acoustically transparentsediment (locally there is some acoustic stratification present)in Westwind Trough (Fig. 5). The unit is up to 30–40 m inthickness and is semi-continuous laterally, although itsapparent absence in some locations may relate to its thicknessbeing below the vertical resolution of the TOPAS system(<1 m). The unit thins towards the SE to <10 m thick (Fig. 5).Linear landforms imaged in swath bathymetric records areformed in the surface or throughout this acoustic unit (Fig. 5).The unit has a prominent, distinct and flat basal reflector that iscontinuous across the trough. There is a general lack of acousticstructure within sediments beneath the basal reflector, althoughlocally there are some semi-continuous reflectors.

North-east Greenland continental shelf:northwind shoal, AWI bank and outer shelf

The sea floor reflector across Northwind Shoal and AWI Bank(70–120 m of water), and across the outermost shelf to depths of370 m, is highly irregular. Individually, the sea floor irregula-rities comprise well-defined troughs or grooves accompaniedin many places by two adjacent peaks, and the intensity ofirregularity can vary from sparse to intense. Sub-sea floorsediment architecture is preserved where irregularity is leastdeveloped (mostly over Northwind Shoal and AWI Bank).

continental slope showing a prominent and sinuous bathymetric scarpand sliding. The images are located in Figure 1(b)


Figure 5 (a–c) TOPAS sub-bottom profiler records from Westwind Trough showing distinct ridges representing lineations formed in the surface of anacoustically transparent sediment layer with a flat to irregular and distinct basal reflector marked by black arrows (located in Figure 1(c))


The unit of acoustically transparent sediment imaged onTOPAS records from Westwind Trough is also present acrossthe shallow banks/shoals, and within the small-scale, deepertroughs of Northwind Shoal and AWI Bank (most common onthe western region of Northwind Shoal and AWI Bank) (Fig. 6).Subtle streamlined bedforms (small-scale to very broad) areformed in the surface of this sediment unit, and locally formdistinct, asymmetric-shaped sediment accumulations. Internalstratification is present occasionally. The basal reflector of thisacoustically transparent sediment unit varies from planar tohummocky in nature. Underlying this acoustic facies on thewesternmost side of Northwind Shoal are numerous buried,acoustically transparent sediment mounds (dome shaped with aflat to slightly hummocky base) or continuous layers (possiblythe sediment mounds are cross-sections of these layers)providing a stacked sedimentary architecture (Fig. 6(a) and(b)). The top-surface reflector is hummocky and corresponds tothe basal reflector of the sea floor/near-sea floor unit ofacoustically transparent sediment. The basal reflector of thelower unit/sediment bodies is similarly distinct but varies fromhummocky to flat and is not always imaged.

A further acoustic facies found on the western–central area ofNorthwind Shoal, and across AWI Bank, comprises a series ofparallel steeply dipping, sub-sea floor reflectors (Fig. 7(a) and

Figure 6 (a, b) TOPAS sub-bottom profiler records from Northwind Shoal shoacoustically transparent sediment mounds or layer interpreted as subglacacoustically transparent sediment layer corresponding to the top surface of theFigure 1(c)


(b)). Generally, these reflectors dip towards the outer shelf, butlocally reflectors are folded into broad synform and antiformstructures (Fig. 7(a) and (b)). The top of the reflectors areterminated, or truncated, by an irregular sea floor reflector orthe hummocky to flat basal reflector of an overlyingacoustically transparent sediment layer in which the linearlandforms are formed.

North-east Greenland continental slope (FramStrait and Greenland Sea)

There are three distinct acoustic zones on the continental slopeand in the abyssal depths of the Boreas Basin in the GreenlandSea and western Fram Strait (Fig. 8(a)–(g)).

Acoustic zone 1

The uppermost continental slope, from the shelf edge at 400 mdown to water depths of �1200–1800 m, comprises anacoustically prolonged and hummocky sea floor reflector with

wing a surface acoustically transparent sediment layer overlying buriedial bedforms. The hummocky, distinct basal reflector of the surfaceburied sediment mounds is marked by black arrows. Profiles located in


Figure 7 TOPAS sub-bottom profiler records from Northwind Shoal showing: (a–c) Acoustically stratified sediment comprising gently dippingreflectors that are overlain or truncated by an irregular sea floor reflector or distinct basal reflector of a surface acoustically transparent sediment layer.Reflectors dip towards the outer shelf, and in some places they are folded into synform and antiform structures; and (d) small-scale acousticallytransparent sediment ridges or mounds located immediately above the end tips of some of these dipping reflectors. Profiles located in Figure 1(c)


small-scale ’V’-shaped incisions in its surface (Fig. 8(b) and (c)).There is a lack of acoustic penetration below the sea floorreflector although, locally, a sub-sea floor acoustic reflector issometimes present. The water depth at which Acoustic facies 1transforms to Acoustic 2 varies across the upper continentalslope.

Acoustic zone 2

In water depths below �1200–1800 m, TOPAS sub-bottomprofiles record the presence of individual or stacked, well-developed acoustically transparent sediment lobes (up to�20 m thick) that are orientated, and pinch out, in a downslopedirection (Fig. 8(d)), and are lens shaped in cross-section(Fig. 8(e)). The basal reflector of each acoustic sediment lobe isdistinct and ranges from hummocky to flat. Acousticallytransparent sediment lobes are also commonly interbeddedwith acoustically stratified sediments in this zone.

Acoustic zone 3

The deepest part of the continental slope and abyssal depths ofthe Fram Strait (water depths below 2500 m) are characterisedby well-developed acoustically stratified sediments that TOPASpenetrates to over 40–80 m (Fig. 8(f)). The parallel reflectors areorganised into large- to small-amplitude waves, or are flat innature over several kilometres in length (Fig. 8(f)). Acoustic sub-


bottom profiler records show the presence of a number ofsubmarine channels cut into acoustically stratified sediment (upto tens of metres thick) on the north-east Greenland continentalslope and abyssal plain of the north-west Greenland Basinfurther south at �75–768 N (i.e. offshore of Hochstetter andStore Storebælt cross-shelf troughs in the Hochstetter Bugtenand Store Koldewey region of north-east Greenland) (Fig. 8(g)).Channels are up to �50–70 m in depth and tens to hundreds ofmetres wide, and are floored by a prolonged sea floorreflector overlying a thin stratified layer (Fig. 8(g)). Acousticallystratified sediments lateral to these channels are organised intosediment waves with well-developed, steeply inclined linearsynsedimentary faults that dislocate stratification (Fig. 8(g)).Lenses of acoustically transparent sediment identical to those inAcoustic Zone 2 (see above) are present further up thecontinental slope.

Interpretation

Glacial landforms and sediments on the north-east Greenland continental shelf

The well-developed streamlined linear landforms in WestwindTrough, together with the more subtle forms across parts ofNorthwind Shoal (Figs. 2 and 3(a)), are identical bothmorphologically and, in dimensions, to subglacial landforms,comprising lineations and mega-scale glacial lineations


Figure 8 (a) Bathymetry of the north-east Greenland continental margin and Fram Strait derived from the IBCAO bathymetrical dataset (Jakobssonet al., 2000) with the locations of TOPAS sub-bottom acoustic profiles shown by solid lines. The traditional LGM ice sheet limit reconstructed fromexisting published terrestrial glacial evidence, and minimum and maximum ice limits based on the shelf and slope record from this study are illustrated.(b–g) TOPAS sub-bottom profiler records from the north-east Greenland continental slope and abyssal depths of western Fram Strait and GreenlandBasin showing: (b) acoustically structureless sediment and a prolonged and hummocky sea floor reflector on the upper slope; (c) downslope profilefrom the middle to lower slope showing stacked acoustically transparent sediment lobes; (d) alongslope profile from the upper-middle slope showingacoustically transparent sediment lenses; (e) thick sequences of acoustically stratified sediment with continuous parallel sea floor and sub-sea floorreflectors organised into distinct sediment waves of varying amplitudes in the Fram Strait; and (f, g) submarine channels and associated acousticallystratified sediment organised into sediment waves from the abyssal depths of the Greenland Basin at �75–768 N. Acoustically transparent sedimentlenses represent deposits associated with downslope debris flows derived from the eastern Greenland continental shelf

Copyright � 2008 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 24(3) 279–293 (2009)DOI: 10.1002/jqs



(MSGL), described in other formerly glaciated regions (Clark,1993; Stokes and Clark, 1999, 2001, 2002). The term ’mega-scale glacial lineations’ is applied to landforms >6 km in lengthwith elongation ratios >10:1, and lineations for linear land-forms < 6 km in length, and both are recognised on the north-east Greenland shelf. Lineations and MSGL have been reportedfrom a number of formerly ice-filled cross-shelf bathymetrictroughs on, for example, the continental margins of Antarctica,Svalbard and Norway (e.g. Canals et al., 2000; Anderson et al.,2002; O Cofaigh et al., 2002, 2005a,b; Evans et al., 2004, 2005,2006; Ottesen et al., 2005). These bedforms are interpreted tohave formed subglacially by grounded glacier ice that flowedthrough Westwind Trough and across Northwind Shoal duringa former glaciation (Figs. 2 and 3(a)).

Glacial lineations and MSGL on the north-east Greenlandshelf are formed in the surface of an acoustically transparentsediment unit with a distinct basal reflector (Figs. 5–7). Theacoustic properties and the close association of the acousticallytransparent unit with subglacial lineations and MSGL suggestthat it comprises soft, porous sediment (and likely to comprisetill) with a relatively high water content. This interpretation issupported by examples from bathymetric troughs in Antarctica,where sediment cores recovered from acoustically transparentsediment layers and associated MSGL identical to thosedocumented in this study demonstrate the presence of weak,dilatant till (soft and porous, massive diamicton) (Wellner et al.,2001; Dowdeswell et al., 2004; Evans et al., 2005; O Cofaighet al., 2005a). The general absence of any internal stratificationwithin the acoustically transparent sedimentary unit in north-east Greenland suggests that, at a macro-scale, the sediment (ortill) layer has a massive structure (Figs. 5–7). However, theminor stratification that is present shows that macro-scalelayering of the sediment (till) within the subglacial bed canoccur locally. The underlying dome-shaped mounds ofacoustically transparent sediment represent cross-sections ofburied subglacial bedforms (Fig. 6(a)). Sediment mounds andthe associated lowermost acoustically transparent sedimentlayer, interpreted as till, represent an earlier glacier flow phasethan that which produced the uppermost acoustically trans-parent till layer.

The acoustic facies of dipping reflectors on Northwind Shoaland AWI Bank (Fig. 7) could be the product of two possibleprocesses. First, the dipping reflectors could represent foresetbeds of Gilbert-type deltas similar to those found in glacialgrounding-zone wedges (GZW) or till deltas. Such features area product of subaqueous sediment gravity flows derived fromthe remobilisation of till advected beneath, and released at thegrounded margin of a retreating, advancing or readvancing icesheet (cf. Alley et al., 1989; Larter and Vanneste, 1995;Anderson, 1997; Bart and Anderson, 1997; O Cofaigh et al.,2005b). In this interpretation the acoustically transparent layerof till overlying the dipping foreset beds in some areas ofNorthwind Shoal and AWI Bank could represent topset bedscorresponding to the till layer advected beneath the ice sheetand released at the margin (Fig. 7(a) and (b)). The antiform andsynform structures within the acoustic facies would resultfrom glaciotectonic deformation of the foreset beds withinthe grounding zone wedge during advance or oscillations ofthe ice margin (Fig. 7(a)–(c)). An alternative interpretation of thedipping, synform and antiform reflectors is that, rather thanbeing the product of primary deposition as a GZW, they recorddeformation and glaciotectonism of pre-existing Quaternary orolder unconsolidated sediments as ice advanced over North-wind Shoal and AWI Bank (cf. Aber et al., 1989).

The small-scale ridges across Northwind Shoal (Fig. 3(e)) areinterpreted as transverse ridges or moraines produced along theretreating tidewater margins of the Greenland Ice Sheet. This is


supported by three lines of evidence: (1) the SW–NE orientationof the ridges is almost perpendicular to SW–NE to W–Eorientated subglacial lineations produced by ice flow in anortheasterly to easterly direction (Fig. 3(e)); 2) the transverseridges or moraines are well preserved and distributed close to orat the sea floor (and not buried), indicating they were morelikely to have been produced during ice retreat, as ice terminuslandforms would be smudged or destroyed by ice sheetadvance; and (3) the ridges are morphologically identical totransverse ridges produced along retreating tidewater glaciertermini on the Svalbard continental margin (Ottesen andDowdeswell, 2006). Therefore, this evidence indicates that theridges are moraines produced by ice sheet retreat acrossNorthwind Shoal.

Patterns and processes of sedimentation on thecontinental slope

TOPAS sub-bottom profiler records reveal three distinctacoustic zones on the continental slope and in the deeperwestern Fram Strait (Fig. 8). The acoustically prolonged seafloor reflector of Acoustic Zone 1, where there is little or nopenetration (Fig. 8(b)), is interpreted to reflect coarse-grainedsediments derived from the shelf edge by undifferentiated,proximal subaqueous mass flows typical of the continentalslopes of East Greenland further to the south, and of Antarctica(Kuhn and Weber, 1993; Dowdeswell et al., 1997; Evans et al.,2002).

The downslope and alongslope morphology and form of thestacked acoustically transparent sediment lobes in AcousticZone 2 (Fig. 8(b)–(e)) indicate that these sediments are theproduct of episodic subaqueous debris flows associated withdownslope transport of glacigenic sediment from the uppercontinental slope (cf. Kuhn and Weber, 1993; Niessen andWhittington, 1997; Evans et al., 2002; Wilken and Mienert,2006). Such processes and sediments are important buildingblocks of the sedimentary record of trough mouth fans (TMF)and some non-TMF areas on the ice-influenced continentalslopes of the polar North Atlantic Ocean and Antarctica (e.g.Anderson et al., 1979, 1986; Kuvaas and Kristoffersen, 1991;Laberg and Vorren, 1995; De Batist et al., 1997; Dowdeswellet al., 1997, 2006; King et al., 1998; Evans et al., 2002; OCofaigh et al., 2003; Wilken and Mienert, 2006). The closeassociation of large-scale debris flow lobes with acousticallystratified sediments indicates that sedimentation by hemipela-gic rainout, small-scale debris flows and other forms ofsediment gravity flow occurs between the large-scale debrisflow events on some areas of the slope.

Acoustic Zone 3 on the lower continental slope and in theabyssal depths of the Boreas Basin, below 2500 m (Fig. 8(f) and(g)) is dominated by acoustically stratified sediments andsediment waves. This is interpreted as being a product of low-energy hemipelagic rainout punctuated by turbidity current andiceberg rafting activity, with an additional contouritic com-ponent. Hemipelagic sedimentation and downslope turbiditycurrents associated with sediment gravity flows further up thenorth-east Greenland slope are likely to have supplied a majorcomponent of these sediments with subsequent modificationand sedimentation by bottom currents to form sediment waves.Contourite or bottom currents associated with the ReturnAtlantic Current submerged beneath the polar East GreenlandCurrent flow southward through the western Fram Strait, andalong the north-east/East Greenland continental margin(Gascard et al., 1988). Both currents are compressed in thisregion of north-east Greenland to form the strong East



Greenland Frontal Jet (Swift and Aagaard, 1981; Aagaard et al.,1985).

The submarine channels recorded on swath bathymetry fromthe north-east Greenland continental slope and abyssal plain ofthe north-west Greenland Basin at �75–768 N (Fig. 8(g)) are thesame as some of those recorded in the GLORIA sidescan sonarimages of Mienert et al. (1993, 1995). These channels areinterpreted to have formed by sediment gravity flows derivedfrom glacigenic sediment fed directly to the continental slopeby expansion of the Greenland Ice Sheet across the shelf duringglacial periods (O Cofaigh et al., 2004). Thick sequences ofacoustically stratified sediment associated with the channelsrepresent deposits from overbank sediment gravity flows.

Discussion

Ice sheet configuration and flow on the north-east Greenland continental margin

The streamlined glacial landforms and sediments observed onswath bathymetric and TOPAS sub-bottom acoustic profilerrecords are interpreted to have formed beneath a grounded icesheet (Figs. 2–7). The subglacial lineations and MSGL andassociated glacigenic sediments in Westwind Trough andacross Northwind Shoal and AWI Bank demonstrate that themost recent advance of the Greenland Ice Sheet across thenorth-eastern margin of Greenland extended to at least aminimum position on the middle–outer continental shelf (as farwest as 118 W; �80 km from the shelf edge; Fig. 8(a)). While asignificant volume of ice is likely to have been channelisedthrough the cross-shelf bathymetric troughs such as WestwindTrough, linear submarine landforms can also be seen across theshallow intra-trough regions of Northwind Shoal and AWI Bank(Fig. 3(a)). This suggests that ice flow was active even acrossrelatively shallow banks and was not confined only to thetroughs themselves.

Ice flow through Westwind Trough associated with this lastadvance of the Greenland Ice Sheet is likely to have been in theform of a fast-flowing ice stream based on several geomor-phological, geological and geophysical lines of evidence. Thebest-defined and most elongate (elongation ratios >10:1)glacial lineations and mega-scale glacial lineations are locatedin Westwind Trough (Fig. 2). Such bedforms are a key criterionfor identifying the former presence of Quaternary palaeo-icestreams in both offshore and onland settings (Stokes and Clark,1999, 2001, 2002; Wellner et al., 2001; O Cofaigh et al., 2002).Bedforms with elongation ratios >10:1 (such as MSGL) arecommonly produced along the fastest flowing sections ofpalaeo-ice streams (i.e. the main trunk of a palaeo-ice stream)(Wellner et al., 2001; Stokes and Clark, 2001, 2002). Cross-shelf troughs act as conduits for fast-flowing ice drainingmodern and Quaternary ice sheets, as they facilitate greaterstrain heating that enhances basal lubrication and initiates fastice flow (Vaughan et al., 2003; Bennett, 2003; Ottesen et al.,2005). The glacial lineations and MSGL are also formed in anacoustically transparent sediment layer that is interpreted assoft, dilatant till (Figs. 5–7). Similar acoustic facies associatedwith lineations and MSGL have been imaged in cross-shelfbathymetric troughs around Antarctica, and sediment coresshow that these subglacial bedforms and soft till layer are theproduct of subglacial deformation associated with fast icestream flow through the troughs (O Cofaigh et al., 2002, 2005;Dowdeswell et al., 2004; Evans et al., 2005). The closesimilarity to examples from Antarctica suggests that the


elongate subglacial bedforms and associated soft sedimentlayer in Westwind Trough, north-east Greenland, are also theproduct, at least in part, of subglacial deformation associatedwith fast ice flow. The highly elongate MSGL in WestwindTrough record the fastest ice flow along the palaeo-ice streamtrack (cf. Wellner et al., 2001) and they correspond with thepresence of the soft sediment layer interpreted as the subglacialbed. The location of modern and Quaternary ice streams iscontrolled in part by subglacial geology where areas ofstreaming flow occur over a soft substrate that facilitates fast iceflow through subglacial deformation (Anandakrishnan et al.,1998; Studinger et al., 2001; O Cofaigh et al., 2002, 2005b;Dowdeswell et al., 2004; Evans et al., 2005). Therefore, the softsedimentary substrate probably acted to both lubricate andfacilitate fast ice-stream flow in Westwind Trough when theGreenland Ice Sheet last extended across the north-eastGreenland continental shelf.

On the basis of the evidence for the existence of a former fast-flowing ice sheet outlet draining through Westwind Trough, it isalso envisaged that, regionally, fast ice flow is likely to haveoccurred in other cross-shelf bathymetric troughs on the north-east Greenland continental margin during the last advance ofGreenland Ice Sheet. Even though acoustically transparentsediment layers of soft till are also found across the shallowintra-trough region of Northwind Shoal and AWI Bank,consistent with ice sheet flow, only very subtle elongatebedforms are observed (Figs. 3(a) and 6). Therefore, it is unclearwhether the fast ice flow that occurred in Westwind Trough alsoinfluenced the intra-trough regions on the north-east Greenlandcontinental margin. Subglacial bedforms buried beneath theuppermost, surface glacial landforms and till layer acrossNorthwind Shoal, representative of the last advance of the icesheet across the shelf, were formed during a different ice flowphase either during the same glacial advance or a separate iceadvance associated with an earlier glaciation.

Sedimentation processes on the north-eastGreenland continental slope

Sub-bottom profiler records (TOPAS) show that the surveyedregions of the north-east Greenland slope are characterised bysediments derived mainly from subaqueous sediment gravityflows (Acoustic Zones 1–3) (Fig. 8(a)–(f)). The upper slope(<1000–1800 m water depth) comprises undifferentiated massflow deposits (Zone 1) that transform on the middle slope(1000–2500 m) into stacked sediment lobes derived from debrisflows (Zone 2). Finally, Zone 2 debris flow deposits evolve tostratified sediments deposited by hemipelagic rainout andepisodic turbidity current activity, with subsequent modifi-cation into sediment waves by contourite bottom currents onthe lower slope and abyssal depths of the Boreas Basin in theGreenland Sea and western Fram Strait (>2500 m) (Zone 3). It ispossible that the downslope transition in sediment architecturerecords a process continuum where upper slope mass flows andmid-slope debris flows are related to, and trigger, lower slopeturbidity currents during episodic downslope mass-wastingevents (cf. Hampton, 1972; Dowdeswell et al., 1997).

The pattern and processes of sedimentation on the north-eastGreenland continental slope adjacent to the cross-shelf troughand intra-trough regions is consistent with that found on otherArctic and Antarctic continental slopes (Kuhn and Weber,1993; Dowdeswell et al., 1997; Evans et al., 2002; O Cofaighet al., 2004). Widespread episodic submarine sediment gravityflow activity, mainly in the form of glacigenic debris flows infront of cross-shelf bathymetric troughs, has been observed



from many formerly glacially influenced continental slopes inAntarctica and the Arctic (Kuvaas and Kristoffersen, 1991;Laberg and Vorren, 1995; Dowdeswell et al., 1996, 1997; DeBatist et al., 1997; King et al., 1998; Vorren et al., 1998; Evanset al., 2002; Wilken and Mienert, 2006). This style ofsedimentation typically occurs under full-glacial conditionswhen fast-flowing ice streams draining the major ice sheetsreached the continental shelf edge, and delivered largevolumes of glacigenic sediment directly to the uppermostcontinental slope with subsequent downslope remobilisationby sediment gravity flows (Laberg and Vorren, 1995;Dowdeswell et al., 1996, 1997; O Cofaigh et al., 2003).Considering these examples, the widespread debris flowdeposits on the north-east Greenland continental slope weredeveloped during a former glacial period when the GreenlandIce Sheet extended across much of the continental shelf, andfed glacigenic sediment directly to the continental slope. Wesuggest, therefore, that the last advance of the GreenlandIce Sheet across the northeastern seaboard is likely to haveextended beyond a minimum position on the middle–outercontinental shelf and reached the shelf edge where it suppliedthe glacigenic sediment that is remobilised by sediment gravityflows down the north-east Greenland slope.

Wider implications

The submarine glacial landforms and sediments on the north-east Greenland shelf are well preserved and, stratigraphically,represent the uppermost and most recent glacial deposits. Asurface drape of glacimarine or hemipelagic sediment is eithervery thin or absent. On this basis, the landforms represent themost recent advance of the Greenland Ice Sheet acrossthe north-eastern continental shelf. Cores recovered from themiddle–outer continental shelf within the area of ourgeophysical data coverage (�808 N, 148 W and 808 N 68 W)contain sea floor and near sea floor sediments of Holocene age(Notholt, 1998). Therefore, it is reasonable to assert that the thinsurface sediment drape overlying the glacigenic landforms andsediments in this study are similarly Holocene in age. It thenfollows that the subglacial landforms were produced immedi-ately prior to the Holocene, presumably during the LateWeichselian glaciation. Marine Isotope Stage (MIS) 2 (LateWechselian glaciation) is identified in a number of sedimentcores from the north-east Greenland continental shelf breakand slope beginning before 23 700 14C a BP and terminatingafter 16 570 14C a BP (onset of the Last Glacial Maximum (LGM)�21 500 14C a BP), and is marked by an increase in ice-rafteddebris and lithogenic carbonate delivered to the slopeassociated with glacial activity on the shelf (Notholt, 1998).A significant increase in ice-rafted debris and bulk accumu-lation rates are also dated in sediment cores from central andeastern Fram Strait at �19 500–14 500 cal. a ago (LGM), and iscorrelated to the major glaciations on Svalbard and Fennos-candia (Hebbeln et al., 1994; Hebbeln and Wefer, 1997). Thesimplest and most likely explanation is that the last ice advanceand associated glacial landforms and sediments occurredduring the Late Weichselian glaciation, and that the GreenlandIce Sheet and associated fast-ice-flowing outlets extended to atleast a minimum position on the middle–outer shelf during thistime.

An increase in the rate of ice-rafted debris and sedimentdelivered to the continental slope and Fram Strait occurredduring the Late Weichselian glaciation (MIS 2) in responseto the advance of ice sheets across the neighbouringcontinental margins of Greenland and Svalbard (Hebbeln


et al., 1994; Hebbeln and Wefer, 1997; Notholt, 1998).Subaqueous sediment gravity flows are significant processes onice-sheet-influenced continental slopes associated with ahigher rate of sediment delivery by ice sheets terminating at,or close to the shelf edge during full glacial conditions (e.g.Laberg and Vorren, 1995; King et al., 1998). Therefore, thesubaqueous sediment–gravity flow activity recorded on thenorth-east Greenland continental slope resulted from anincrease in glacigenic sediment delivered to the outercontinental margin by a Late Weichselian Greenland Ice Sheetthat is likely to have extended beyond its minimum mid-shelfposition, and reached the outer shelf/shelf edge (Fig. 8(a)).

Glacigenic sediments in the form of foreset and topset bedsare present across the shallow Northwind Shoal and AWI Bank,and represent a Late Weichselian grounding zone wedge(s).Therefore, Northwind Shoal and AWI Bank are likely to haveformed, at least in part, from subglacial, ice-proximal andglacimarine sedimentation and glaciotectonism. Two possibi-lities exist for the timing and significance of the deposition ofthe subglacial and ice-marginal sediment. First, the ice-marginal sediments could represent progradational sequencesdeposited during advance of the ice sheet across the continentalshelf prior to the LGM, which was dated to begin at �21 500 a14C BP for the north-east Greenland margin (Notholt, 1998).Secondly, they were produced along a stabilised ice marginduring deglaciation (i.e. stillstands during punctuated ice sheetretreat) of the shelf some time between 16 570 and 9500 a14C BP (deglaciation of coastal lands dated to have occurred by9500 a 14C BP) (Hjort, 1997; Notholt, 1998; Bennike andBjorck, 2002), with possible minor readvances during regionaldeglaciation. A number of small-scale transverse ridges ormoraines are also present in the same area of Northwind Shoalas the grounding zone wedge(s), and these record punctuatedice sheet retreat separated by periods of stillstand. The well-preserved nature of the moraines and their distribution at orclose to the sea floor indicate that they record the most recentglacial event and punctuated retreat of the Greenland Ice Sheetacross the north-east Greenland shelf during the LateWeichselian deglaciation. The proximity of the groundingzone wedge(s) to the small-scale moraines suggests that theywere also produced during the Late Weichselian deglaciationassociated with ice sheet retreat. However, the exact timing ofthe formation of the grounding zone wedge(s) cannot bedetermined due to the paucity of TOPAS sub-bottom profilerdata showing the stratigraphical relationship between thesmall-scale moraines and the topset and foreset beds of thegrounding-zone wedge(s).

The data presented in this paper provide significantinformation about the Greenland Ice Sheet during the LateWeichselian glaciation, and challenge previous reconstruc-tions for the northeastern margin. The traditional reconstructionof the extent of glaciation in north-east Greenland during theLate Weichselian (based on direct glacial–terrestrial evidence)is that it only advanced to the outer coast (Funder, 1989;Houmark-Nielsen et al., 1994; Funder et al., 1994; Funder andHansen, 1996; Hjort, 1979, 1981, 1997; Funder et al., 1998),although the possible extension of the ice sheet across much ofthe shelf has been suggested on the basis of circumstantialevidence (Bennike and Bjorck, 2002). Our marine geophysicaldata provide direct geomorphological and geological evidenceindicating that the Greenland Ice Sheet was far more extensiveduring the Late Weichselian glaciation in north-east Greenlandthan was previously reconstructed from terrestrial glacialgeological records. The Greenland Ice Sheet advanced to aminimum position on the middle shelf at least, and probablythe outer shelf/shelf edge, on the basis of the presence ofmass-wasting deposits across the continental slope thought to



be Late Weichselian in age (Fig. 8(a)). The presence of a fast-flowing palaeo-ice stream in Westwind Trough indicates a verydynamic ice sheet that would have been fed by the interiorbasin that presently drains a significant part of the modern-dayGreenland Ice Sheet to the north-east Greenland margin viaNioghalvfjerdsfjorden Gletscher, Zachariae Isstrøm and otherglaciers. Fast-flowing palaeo-ice streams similar to that inWestwind Trough are more than likely to have also drainedthrough other north-east Greenland coastal fjords and cross-shelf bathymetric troughs such as the Norske Trough.

In the wider context, our data provide the first geomorpho-logical evidence from the Greenland continental shelf record-ing that fast-flowing ice streams were an important andsignificant glacio-dynamic feature draining interior basins ofthe Late Weichselian Greenland Ice Sheet across thecontinental margin. In conjunction with investigations in EastGreenland as far south as Scoresby Sund (708 N), these recordsshow that an extensive and glacio-dynamic ice sheetconfiguration occurred along the northeastern and easternGreenland margin during the Late Weichselian (Evans et al.,2002; O Cofaigh et al., 2004; Wilken and Mienert, 2006;Hakansson et al., 2007). A more extensive and dynamic LateWeichselian Greenland Ice Sheet would make a highercontribution to postglacial global eustatic sea level rise thanthe present calculation of up to 3 m, which was based onprevious ice sheet reconstructions (Letreguilly et al., 1991a,b;Huybrechts, 2002; Clark and Mix, 2002). Reconstructions suchas ours, in combination with ice core and glacial geologicalrecords, will help to constrain and improve models ofGreenland Ice Sheet volume change during the last glacial–interglacial cycle and its influence on global eustatic sea levelrise during deglaciation (e.g. Letreguilly et al., 1991a,b; Funderet al., 1998).

Conclusions

1. Marine geophysical records reveal the presence of sub-marine streamlined glacial landforms and sediments on thenorth-east Greenland continental shelf. The landforms wereproduced subglacially in association with the last advanceof the Greenland Ice Sheet to at least the middle–outercontinental shelf.

2. The former presence of a fast-flowing ice stream drainingthrough Westwind Trough is recorded by highly elongatelineations and MSGL formed in a layer of soft till (Figs. 3and 5). Active ice was also present across the shallow, intra-trough regions of Northwind Shoal and AWI Bank as twodistinct flow phases either during the same glacial cycle orsuccessive glaciations, although this ice is unlikely to havebeen streaming (Fig. 3(a)).

3. Swath bathymetric records show the presence of bathy-metric escarpments on the upper–middle continental slopeof north-east Greenland that are consistent with headwallsof slope areas that underwent mass wasting. Acoustic sub-bottom profiles indicate that the upper slope comprisesmainly acoustically structureless sediment deposited byundifferentiated sediment gravity flows, and that the mid-slope contains stacked acoustically transparent sedimentlobes resulting from subaqueous debris flows, and possiblyturbidity currents. Acoustically stratified sediment organisedinto sediment waves on the lower slope is derived fromglacially influenced hemipelagic sedimentation and turbid-ity currents, with subsequent modification into sedimentwaves by contouritic bottom currents.


4. During the Late Weichselian glaciation, the Greenland IceSheet extended across the northeastern seaboard to at leastthe middle–outer shelf, and probably to the shelf edge. Icesheet flow through Westwind Trough, and probably othercross-shelf bathymetric troughs, was in the form of a fast-flowing palaeo-ice stream. Large quantities of glacigenicsediment were delivered to the outer continental marginwith subsequent downslope remobilisation of this materialby subaqueous sediment gravity flows and formation ofprominent bathymetric escarpments representing the head-walls of slide or slump systems.

5. The advance of the Greenland Ice Sheet to the middle–outercontinental shelf along its northeastern margin during theLate Weichselian was far more extensive than previousterrestrial glacial geological reconstructions showed.Furthermore, fast-flowing ice streams were an importantglacio-dynamic feature that drained interior basins of theGreenland Ice Sheet to the outer continental margin. A moreextensive and dynamic Greenland Ice Sheet along itseastern and northeastern margin has implications for itscontribution to postglacial global eustatic sea level rise.Earlier calculations of the contribution that Greenland hadon postglacial eustatic sea level rise of up to 3 m, based onprevious ice sheet reconstructions, is likely to be anunderestimation.

Acknowledgements This project was undertaken as part of the UKNERC Autosub under the Ice Thematic Programme. We thank thecaptain, officers and crew of the RRS James Clark Ross for theirassistance in the difficult ice conditions encountered on Cruise JR-106a.

References

Aagaard K, Swift JH, Carmack EC. 1985. Thermoline circulation in theArctic Mediterranean Seas. Journal of Geophysical Research 90:4833–4846.

Aber JS, Croot DG, Fenton MM. 1989. Glaciotectonic Landforms andStructures. Kluwer Academic: Dordrecht.

Alley RB, Blankenship DD, Rooney ST, Bentley CR. 1989. Sedimen-tation beneath ice shelves: the view from Ice Stream B. MarineGeology 85: 101–120.

Anandakrishnan S, Blankenship DD, Alley RB, Stoffa PL. 1998. Influ-ence of subglacial geology on the position of a West Antarctic icestream from seismic observations. Nature 394: 62–65.

Anderson JB. 1997. Grounding zone wedges on the Antarctic con-tinental shelf, Weddell Sea. In Glaciated Continental Margins: AnAtlas of Acoustic Images, Davies TA, Bell T, Cooper AK, JosenhansH, Polyak L, Solheim A, Stoker MS, Stravers JA (eds). Chapman &Hall: London; 98–99.

Anderson JB, Kurtz DD, Weaver FM. 1979. Sedimentation on theAntarctic Continental Slope. In The Geology of Continental Slopes,Pilkey O, Doyle L (eds). Special Publication Society of EconomicPalaeontology and Mineralogy No. 27. Tulsa; 265–283.

Anderson JB, Wright R, Andrews B. 1986. Weddell fan and associatedabyssal plain, Antarctica: morphology, sediment processes, andfactors influencing sediment supply. Geo-Marine Letters 6: 121–129.

Anderson JB, Shipp SS, Lowe AL, Wellner JS, Mosola AB. 2002. TheAntarctic ice sheet during the last glacial maximum and its sub-sequent retreat history: a review. Quaternary Science Reviews 21:49–70.

Bart PJ, Anderson JB. 1997. Grounding zone wedges on the Antarcticcontinental shelf, Antarctic Peninsula. In Glaciated ContinentalMargins: An Atlas of Acoustic Images, Davies TA, Bell T, CooperAK, Josenhans H, Polyak L, Solheim A, Stoker MS, Stravers JA (eds).Chapman & Hall: London; 96–97.



Bennett MR. 2003. Ice streams as the arteries of an ice sheet: theirmechanics, stability and significance. Earth Science Reviews 61:309–339.

Bennike O, Bjorck S. 2002. Chronology of the last recession of theGreenland Ice Sheet. Journal of Quaternary Science 17: 211–219.

Bennike O, Weidick A. 2001. Late Quaternary history around Nio-ghalvfjerdsfjorden, North-East Greenland. Boreas 30: 205–227.

Canals M, Urgeles R, Calafat AM. 2000. Deep sea-floor evidence of pastice streams off the Antarctic Peninsula. Geology 28: 31–34.

Clark CD. 1993. Mega-scale glacial lineations and cross-cutting ice-flow landforms. Earth Surface Processes and Landforms 18: 1–29.

Clark PU, Mix AC. 2002. Ice Sheets and sea level of the Last GlacialMaximum. Quaternary Science Reviews 21: 1–7.

De Batist M, Bart P, Miller H. 1997. Trough-mouth fans: Crary Fan,Eastern Weddell Sea, Antarctica. In Glaciated Continental Margins:An Atlas of Acoustic Images, Davies TA, Bell T, Cooper AK,Josenhans H, Polyak L, Solheim A, Stoker MS, Stravers JA (eds).Chapman & Hall: London; 276–279.

Dowdeswell JA, Uenzelmann-Neben G, Whittington RJ, Marienfeld P.1994. The Late Quaternary sedimentary record in Scoresby Sund,East Greenland. Boreas 23: 294–310.

Dowdeswell JA, Kenyon NH, Elverhøi A, Laberg JS, Hollender F-J,Mienert J, Siegert MJ. 1996. Large-scale sedimentation on the glacier-influenced Polar North Atlantic margins: long-range side-scan sonarevidence. Geophysical Research Letters 23: 3535–3538.

Dowdeswell JA, Kenyon NH, Laberg JS. 1997. The glacier-influencedScoresby Sund Fan, East Greenland continental margin: evidencefrom GLORIA and 3.5 kHz records. Marine Geology 143: 207–221.

Dowdeswell JA, Cofaigh C, O Pudsey CJ. 2004. Thickness and extent ofthe subglacial till layer beneath an Antarctic palaeo-ice stream.Geology 32: 13–16.

Dowdeswell JA, Evans J, O Cofaigh C, Anderson JB. 2006. Morphologyand processes on the continental slope off Pine Island Bay, Amund-sen Sea, West Antarctica. Bulletin of the Geological Society ofAmerica 118: 606–619.

Evans J, Dowdeswell JA, Grobe H, Niessen F, Stein R, Hubberten HW,Whittington RJ. 2002. Late Quaternary sedimentation in Kejser FranzJoseph Fjord and the continental margin of East Greenland. InGlacier-Influenced Sedimentation on High-Latitude ContinentalMargins, Dowdeswell JA, O Cofaigh C (eds). Special PublicationNo. 203. Geological Society: London; 149–179.

Evans J, Dowdeswell JA, O Cofaigh C. 2004. Late Quaternary sub-marine bedforms and ice-sheet flow in Gerlache Strait and on theadjacent continental shelf, Antarctic Peninsula. Journal of Quatern-ary Science 19: 397–407.

Evans J, Pudsey CJ, O Cofaigh C, Morris PW, Domack EW. 2005. LateQuaternary glacial history, dynamics and sedimentation of the east-ern margin of the Antarctic Peninsula Ice Sheet. Quaternary ScienceReviews 24: 741–774.

Evans J, Dowdeswell JA, O Cofaigh C, Benham TJ, Anderson JB. 2006.Extent and dynamics of the West Antarctic Ice Sheet on the outercontinental shelf of Pine Island Bay, Amundsen Sea, during the lastglaciation. Marine Geology 230: 53–72.

Funder S. 1989. Quaternary geology of the shelves adjacent to Green-land. In Quaternary Geology of Canada and Greenland, Fulton RJ(ed.) Geological Survey of Canada: Ottawa; 769–772.

Funder S, Hansen L. 1996. The Greenland Ice Sheet: a model for itsculmination and decay during and after the last glacial maximum.Bulletin of the Geological Society of Denmark 42: 137–152.

Funder S, Hjort C. 1973. Aspects of the Weichselian chronology incentral East Greenland. Boreas 2: 69–84.

Funder S, Hjort C, Landvik JY. 1994. The last glacial cycles in EastGreenland, an overview. Boreas 23: 283–293.

Funder S, Hjort C, Landvik JY, Nam S-I, Reeh N, Stein R. 1998. Historyof a stable ice margin: East Greenland during the middle and upperPleistocene. Quaternary Science Reviews 17: 77–123.

Gascard JC, Kergomard PF, Jeannin PF, Fily M. 1988. Diagnostic studyof the Fram Strait marginal ice zone during summer. Journal ofGeophysical Research 93: 3613–3641.

Hakansson L, Briner J, Alexanderson H, Aldahan A, Possnert G. 2007.10Be ages from central east Greenland constrain the extent of theGreenland ice sheet during the Last Glacial Maximum. QuaternaryScience Reviews 26: 2316–2321.


Hampton MA. 1972. The role of subaqueous debris flow in generatingturbidity currents. Journal of Sedimentary Petrology 42: 775–793.

Hebbeln D, Wefer G. 1997. Late Quaternary paleoceanography in theFram Strait. Paleoceanography 12: 65–78.

Hebbeln D, Dokken T, Andersen ES, Hald M, Elverhøi A. 1994.Moisture supply to northern ice-sheet growth during the Last GlacialMaximum. Nature 370: 357–360.

Hebbeln D, Henrich R, Baumann K-H. 1998. Paleoceanography of thelast interglacial/glacial cycle in the Polar North Atlantic. QuaternaryScience Reviews 17: 125–153.

Hjort C. 1979. Glaciation in northern East Greenland during the LateWeichselian and Early Flanderian. Boreas 8: 281–296.

Hjort C. 1981. A glacial chronology for northern East Greenland.Boreas 10: 259–274.

Hjort C. 1997. Glaciation, climate history, changing marine levels andthe evolution of the north-east water polynya. Journal of MarineSystems 10: 23–33.

Hjort C, Bjorck S. 1984. A re-evaluated glacial chronology for northernEast Greenland. Geologiska Foreningens i Stockholm Forhandlingar105: 235–242.

Hopkins TS. 1991. The GIN Sea: a synthesis of its physical oceanographyand literature reviews 1972–1985. Earth Science Reviews 30: 175–318.

Houmark-Nielsen M, Hansen L, Jørgensen ME, Kronborg C. 1994.Stratigraphy of a Late Pleistocene ice-cored moraine at KapHerschell, north-east Greenland. Boreas 23: 505–513.

Huybrechts P. 2002. Sea-level changes at the LGM from ice-dynamicreconstructions of the Greenland and Antarctic ice sheets during theglacial cycles. Quaternary Science Reviews 21: 203–231.

Jakobsson M, Cherkis N, Woodward J, Coakley B, MacNab R. 2000.A new grid of Arctic bathymetry: a significant resource for scientistsand mapmakers. EOS Transactions, American Geophysical Union81: 89, 93, 96.

Jones GA, Keigwin LD. 1988. Evidence from Fram Strait (78-N) for earlydeglaciation. Nature 336: 56–59.

King EL, Haflidason H, Sejrup HP, Løvlie R. 1998. Glacigenic debrisflows on the North Sea Trough Mouth Fan during ice-stream maxima.Marine Geology 152: 217–246.

Kuhn G, Weber ME. 1993. Acoustic characterization of sediments byParasound and 3.5 kHz systems: related sedimentary processes onthe southeastern Weddell Sea continental slope, Antarctica. MarineGeology 113: 201–217.

Kuvaas B, Kristoffersen Y. 1991. The Crary Fan: a trough-mouth fan onthe Weddell Sea continental margin, Antarctica. Marine Geology 97:345–362.

Laberg JS, Vorren TO. 1995. Late Weichselian submarine debris flowdeposits on the Bear Island Trough Mouth Fan. Marine Geology 127:45–72.

Landvik JY. 1994. The last glaciation of Germania Land andadjacent areas, north-east Greenland. Journal of Quaternary Science9: 81–92.

Landvik JY, Bondevik S, Elverhøi A, Fjeldskaar W, Mangerud J, Sal-vigsen O, Siegert MJ, Svendsen JI, Vorren TO. 1998. The last glacialmaximum of the Barents Sea and Svalbard area: ice sheet extent andconfiguration. Quaternary Science Reviews 17: 43–75.

Larter RD, Vanneste LE. 1995. Relict subglacial deltas on the AntarcticPeninsula outer shelf. Geology 23: 33–36.

Letreguilly A, Reeh N, Huybrechts P. 1991a. The Greenland ice sheetthrough the last glacial-interglacial cycle. Palaeogeography, Paleo-climatology, Palaeoecology 90: 385–394.

Letreguilly A, Huybrechts P, Reeh N. 1991b. Steady-state character-istics of the Greenland ice sheet under different climates. Journal ofGlaciology 37: 149–157.

Mangerud J, Dokken TM, Hebbeln D, Heggen B, Ingolfsson O, LandvikJY, Mejdahl V, Svendsen JI, Vorren TO. 1998. Fluctuations of theSvalbard-Barents Sea Ice Sheet the last 150,000 years. QuaternaryScience Reviews 17: 11–42.

Marienfeld P. 1992. Postglacial sedimentary history of Scoresby Sund,East Greenland. Polarforschung 60: 181–195.

Mayer C, Reeh N, Jung-Rothenhausler F, Huybrechts P, Oerter H. 2000.The subglacial cavity and implied dynamics under Nioghalvfjerdsf-jorden Glacier, NE Greenland. Geophysical Research Letters 27:2289–2292.



Mienert J, Kenyon NH, Thiede J, Hollender FJ. 1993. Polar continentalmargins: studies off East Greenland. EOS 74: 225, 234, 236.

Mienert J, Hollender FJ, Kenyon NH. 1995. GLORIA survey of the EastGreenland margin: 70- N to 80- N. In Seafloor Atlas of the NorthernNorwegian-Greenland Sea, Crane K, Solheim A (eds). NorskPolarinstitutt: Oslo; 150–151.

Nam S-I, Stein R, Grobe H, Hubberten H-W. 1995. Late Quaternaryglacial/interglacial changes in sediment composition at the EastGreenland continental margin and their palaeoceanographicimplications. Marine Geology 122: 243–262.

Niessen F, Whittington RJ. 1997. Typical sections along a transect of afjord in East Greenland. InGlaciatedContinentalMargins: An Atlas ofAcoustic Images, Davies TA, Bell T, Cooper AK, Josenhans H,Polyak L, Solheim A, Stoker MS, Stravers JA (eds). Chapman & Hall:London; 182–186.

Notholt H. 1998. Die Auswirkungen der ’North-eastWater’-Polynya aufdie Sedimentation vor NO Gronland und Untersuchungen zur Palao-Ozeanographie seit dem Mittelweichsel. Berichte zur PolarforschungNo. 275.

Oppenheimer M. 1998. Global warming and the stability of the WestAntarctic Ice Sheet. Nature 393: 325–332.

O Cofaigh C, Pudsey CJ, Dowdeswell JA, Morris P. 2002. Evolution ofsubglacial bedforms along a paleo-ice stream, Antarctic Peninsulacontinental shelf. Geophysical Research Letters 29: 1199.

O Cofaigh C, Taylor J, Dowdeswell JA, Pudsey CJ. 2003. Palaeo-icestreams, trough-mouth fans and high-latitude continental slope sedi-mentation. Boreas 32: 37–3755.

O Cofaigh C, Dowdeswell JA, Evans J, Kenyon NH, Taylor J, Mienert J,Wilken M. 2004. Timing and significance of glacially-influencedmass-flow activity in the submarine channels of the Greenland Basin.Marine Geology 207: 39–54.

O Cofaigh C, Dowdeswell JA, Allen CS, Hiemstra JF, Pudsey CJ, Evans J,Evans DJA. 2005a. Flow dynamics and till genesis associated with amarine-based Antarctic palaeo-ice stream. Quaternary ScienceReviews 24: 709–740.

O Cofaigh C, Larter RD, Dowdeswell JA, Hillenbrand C-D, Pudsey CJ,Evans J, Morris P. 2005b. Flow of the West Antarctic Ice Sheet on thecontinental margin of the Bellingshausen Sea at the Last GlacialMaximum. Journal of Geophysical Research 110: B11103.

Ottesen D, Dowdeswell JA, Rise L. 2005. Submarine landforms and thereconstruction of fast-flowing ice streams within a large Quaternaryice sheet: the 2500 km-long Norwegian–Svalbard margin (578-808N). Bulletin of the Geological Society of America 117: 1033–1050.

Ottesen D, Dowdeswell JA. 2006. Assemblages of submarine landformsproduced by tidewater glaciers in Svalbard. Journal of GeophysicalResearch 111: F01016.

Reeh N, Bøggild CE, Oerter H. 1994. Surge of Storstrømmen, a largeoutlet glacier from the inland ice of North-East Greenland. RapportGrønlands Geologiske Undersøgelse 162: 201–209.


Rignot E, Kanagaratnam P. 2006. Changes in the velocity structure ofthe Greenland Ice Sheet. Science 17: 986–990.

Rignot E, Gogineni SP, Krabill WB, Ekholm S. 1997. North and north-east Greenland ice discharge from satellite radar interferometry.Science 276: 934–937.

Rignot E, Gogineni S, Joughin I, Krabill W. 2001. Contribution to theglaciology of northern Greenland from satellite radar interferometry.Journal of Geophysical Research 106: 34 007–34 020.

Stein R, Nam S-I, Grobe H, Hubberten H-W. 1996. Late Quaternaryglacial history and short term ice rafted debris fluctuations along theEast Greenland continental margin. In Late Quaternary Palaeocea-nography of the North Atlantic Margins, Andrews JT, Austin WEN,Bergsten H, Jennings AE (eds). Special Publication 111. GeologicalSociety: London; 135–151.

Stokes CR, Clark CD. 1999. Geomorphological criteria for identifyingPleistocene ice streams. Annals of Glaciology 28: 67–74.

Stokes CR, Clark CD. 2001. Palaeo-ice streams. Quaternary ScienceReviews 20: 1437–1457.

Stokes CR, Clark CD. 2002. Are long subglacial bedforms indicative offast ice flow? Boreas 31: 239–249.

Studinger M, Bell RE, Blankenship DD, Finn CA, Arko RA, Morse DL,Joughin I. 2001. Subglacial sediments: a regional geological templatefor ice flow in West Antarctica. Geophysical Research Letters 28:3493–3496.

Swift JH, Aagaard K. 1981. Seasonal transitions and water mass for-mation in Iceland and Greenland Seas. Deep-Sea Research 28:1107–1129.

Thomsen HH, Reeh N, Olesen OB, Bøggild CE, Starzer W, Weidick A,Higgins AK. 1997. The Nioghalvfjerdsfjorden glacier project, North-East Greenland: a study of ice sheet response to climatic change.Geology of Greenland Survey Bulletin 176: 95–103.

Vaughan DG, Smith AM, Nath PC, Le Meur E. 2003. Acoustic impe-dance and basal shear stress beneath four Antarctic ice streams.Annals of Glaciology 36: 225–232.

Vorren TO, Laberg JS, Blaume F, Dowdeswell JA, Kenyon NH, MienertJ, Rumohr J, Werner F. 1998. The Norwegian–Greenland Sea con-tinental margins: morphology and Late Quaternary sedimentaryprocesses and environment. Quaternary Science Reviews 17: 273–302.

Wadhams P. 1981. The ice cover in the Greenland and NorwegianSeas. Reviews of Geophysics and Space Physics 19: 345–393.

Wellner JS, Lowe AL, Shipp SS, Anderson JB. 2001. Distribution ofglacial geomorphic features on the Antarctic continental shelf andcorrelation with substrate: implications for ice behaviour. Journal ofGlaciology 47: 397–411.

Wilken M, Mienert J. 2006. Submarine glacigenic debris flows deep-sea channels and past ice-stream behaviour of the EastGreenland continental margin. Quaternary Science Reviews 25:784–810.


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