stratigraphic and sedimentological evidence for late wisconsinan sub glacial outburst floods to laurentian fan abstract sub glacial meltwater produces a distinctive stratigraphic and sedimentological response on the continental margin seismo stratigraphy of laurentian channel reveals thick till deposits at its seaward end that pass laterally into stratified sediment in deeper basins that may record periods of water build up beneath the ice two scales of meltwater discharge are recognised large scale that caused catastrophic erosion and transported large volumes of coarse sediment to the abyssal plain and smaller scale yielding principally muddy sediment sub glacial outburst floods from the laurentian channel ice stream delivered distinctive red sediment derived from permian carboniferous strata of the gulf of st lawrence directly to laurentian fan between ca 17 and 14 14 c ka separate from north atlantic heinrich events on levees of laurentian fan three major pulses of meltwater plume muds are separated by intervals dominated by hemipelagic sediments these meltwater intervals are recognised distally as periods of plume sedimentation on the scotian slope and ice rafting of hematite stained quartz to the north atlantic ocean in channels of laurentian fan at least one major sediment transport event is recognised that eroded the upper slope and the major fan valleys depositing a bed of gravel at least 3 m thick in the characteristically wide fan valleys and thick sand on the sohm abyssal plain the same event was probably responsible for giant flute like scours the age of the gravel bed is directly constrained only by the presence of local overlying holocene sediment much of the surface of the gravel bed was re worked by the 1929 grand banks turbidity current an erosional event on the upper slope likely correlative with the flood generated gravel bed has been dated at 16 5 14 c ka such large scale erosional flood events can be recognised back through several glacial cycles and have played an important role in the architectural evolution of laurentian fan

late wisconsinan stratigraphy and chronology of southern st george s bay newfoundland a re appraisal reply brookes identifies two points of difference in his discussion of our re appraisal of the late wisconsinan stratigraphy and chronology of southern st george s bay newfoundland i the applicability of our sedimentological model and ii the relation of sediments to late glacial sea level the latter point is the subject of a manuscript submitted for review to this journal incorporating 91 radiocarbon dates from onshore and offshore marine records 19 of which are reported for the first time we therefore restrict our rebuttal to what we believe are the critical disagreements in field observations and interpretations that underpin the two points of difference and invite readers to visit the contentious coastal sections to compare published accounts access to these sites is described in several field guides to southern st george s bay liverman and batterson 1995 liverman et al 2001 in our paper we explicitly state that for 80 of the 39 km long coastal exposure our non ridge sections p 866 our observations broadly confirm earlier interpretations by brookes 1969 1974 1977 and macclintock and twenhofel 1940 with the one important exception that we found no evidence for glacial readvance following initial deglaciation and marine submergence of the present coastline in almost 100 logged sections through non ridge exposures we did not encounter an upper till or ice contact gravels robinsons head drift indicative of a glacial readvance instead we described laterally continuous moderately to well sorted planar bedded and trough cross bedded fine gravel capping sections which we interpreted as glaciofluvial outwash p 859 figs 4 5 c consequently our deglacial depositional model for a large part of the coast of southern st george s bay is neither compatible with nor applicable to published sedimentary sequences in the remaining 20 of coastal exposure our ridge sections p 866 our mapping revealed complex sedimentary sequences of interbedded diamicton gravel and mud above

lift off moraines markers of last ice flow directions on the scotian shelf lift off moraines are acoustically incoherent subparallel ridges observed on sidescan sonograms and high resolution reflection seismic profiles on the southeastern continental margin of canada they are up to 3 m high 20 80 m wide and are commonly overlain by stratified proglacial sediments although little is known about them detailed study of high resolution seismic profiles from the emerald basin and the lahave basin on the scotian shelf show that their height width ratio varies with the sounder seabed separation suggesting that the ridges may be narrower than they appear their morphology is similar to degeer moraines or cross valley moraines which form perpendicular to ice flow direction as their orientations can be estimated at the intersection of seismic lines they can be used to estimate ice flow directions since proglacial sediments are draped directly over top of them they are assumed to record the direction of last ice flow this directional data suggests that ice retreated not only

latest pleistocene ice rafting events on the scotian margin eastern canada and their relationship to heinrich events piston cores from the continental margin off nova scotia show up to four discrete intervals of brick red sandy mud which are up to 20 cm thick the ages of these intervals are bracketed by several radiocarbon dates and three fall in the range 12 5 14 1 ka radiocarbon years with 0 4 kyr reservoir correction the youngest dates from 10 4 ka placing it within the younger dryas the distribution of the beds and their petrographic character indicate a source in the gulf of saint lawrence the grain size of these beds suggests that they comprise a coarse component transported by ice rafting that diminishes distally and a fine component that represents suspension fallout from a surface plume and resulting nepheloid layers graded brick red beds in some cores were probably redeposited from turbidity currents the lowermost bed on the laurentian fan and east scotian rise is immediately overlain by a carbonate rich interval that can be identified all around the margin of the grand banks this interval is correlated with detrital carbonate bed dc 1 in the labrador sea and heinrich event h1 in the north atlantic the sequential occurrence of the two beds suggests that they may be a response to the same trigger probably sea level rise but that the gulf of saint lawrence source was more easily destabilized

the quaternary geology of the labrador shelf the regional distribution of glacial and postglacial sediments on the labrador shelf was mapped by medium and high resolution seismics and shows a succession of tills that extend to the continental shelf edge at approximately 600 m the uppermost of these tills is less laterally extensive and does not occur on the labrador shelf bank tops in water depths less than 160 m we infer that the last glacial episode was less extensive than the preceding ones glaciomarine stratified silts and postglacial muds are found overlying the upper till in the deep basins that separate the banks the upper till glaciomarine silts and postglacial muds are interpreted to constitute one complete deglacial cycle radiocarbon age determination suggests this deglacial sequence began at approximately 20 000 years bp on the northernmost labrador shelf and hudson strait seismic evidence indicates a late glacial readvance locally deposited a till that overlies the glaciomarine sediments associated with the last glacial advance

quaternary sedimentary processes and budgets in orphan basin southwestern labrador sea abstract the continental slope in orphan basin northeast of newfoundland is underlain by several seaward thinning debris flow wedges alternating with acoustically stratified regionally extensive mainly hemipelagic sediments 18o stratigraphy and volcanic ash layers in a 11 67 m core indicate that the uppermost debris flow wedge formed during the last of several sea level lowstands in isotopic stages 2 4 similarly seismic reflection correlation of dated levels at dsdp site 111 with the orphan basin succession suggests that two deeper debris flow wedges were deposited during oxygen isotopic stages 6 and 8 the oldest of the debris flow deposits in at least three of the wedges formed well into the corresponding glacial cycle after ice sheets had reached the edge of the continental shelf slower deposition by hemipelagic processes and ice rafting formed the acoustically stratified units including heinrich layers the youngest three debris flow wedges each have volumes of 1300 1650 km3 approximately two thirds of this material is attributed to glacial erosion of mesozoic and tertiary strata beneath the northeast newfoundland shelf the remainder is believed to have been derived by glacial erosion of older bedrock that now forms the island of newfoundland the observed sediment volumes and the inferred basal and upper ages of the debris flow wedges imply an average glacial denudation rate of about 0 13 mm yr for this older bedrock and an average of about 60 m of glacial bedrock erosion since oxygen isotope stage 22 this denudation rate is similar to estimates from the barents sea region off norway

low gradient outlet glaciers ice streams drained the laurentide ice sheet observations of geomorphic features dated with cosmogenic nuclides are used to determine the configuration of glaciation in cumberland sound baffin island during the last glacial maximum cumberland sound which was a major drainage of the laurentide ice sheet at its northeastern arctic canada margin contained low gradient ice with a surface slope of 0 038 and a driving stress between 2 and 7 kpa these values are similar to those observed for the ice streams that dominate the dynamics of the west antarctic ice sheet today the presence of low gradient ice in cumberland sound and other major outlets may similarly have influenced laurentide ice sheet behavior and would account for the iceberg discharge episodes that produced the heinrich event debris layers observed in north atlantic ocean sediments

late quaternary stratigraphy of laurentian fan a record of events off the eastern canadian continental margin during the last deglacial period abstract examination and correlation of 10 piston cores from laurentian fan off the eastern canadian continental margin revealed a high resolution stratigraphic record of events since the last glacial maximum lgm the five lithofacies identified in the cores are 1 bioturbated olive grey silty mud with varying amounts of biogenic carbonate 2 olive grey and reddish brown silt laminated mud with rare fine to very fine sand beds 3 poorly sorted light grey and brick red gravelly sandy mud 4 colour banded silty mud with colours alternating at a centimetre scale between olive grey and reddish brown and 5 brown silty mud commonly massive but occasionally silt laminated the dominant depositional processes include hemipelagic sedimentation turbidity currents and ice rafting in these sediments colour is diagnostic of the sediment source area with reddish sediment being delivered to the fan from the gulf of st lawrence and laurentian channel whereas greenish sediment arrives on the fan from st pierre bank through grand banks valley turbidites are the most volumetrically significant facies conversely ice rafted beds are volumetrically minor but they are the most chronostratigraphically significant facies and include heinrich layers h0 h1 and h2 the chronological control provided by radiocarbon dating and stable oxygen isotopes suggests that sedimentation rates for the reddish brown turbidites deposited between the lgm and 14 ka exceeded 10 m kyr 1 mapping of the units together with a simple sediment deposition model suggest that these beds resulted from deposition by turbidity currents over 1 km thick that lasted on the order of weeks less information can be ascertained from the olive grey turbidites that interbed with h2 and directly overlie h1 because of a lack of sampling except that they had a lower sedimentation rate and include sediment derived from newfoundland and the grand banks comparison of the stratigraphy on laurentian fan with that of other deep water areas further north southwest grand banks margin flemish pass and the labrador sea shows striking similarities over the late quaternary with the deglacial period characterized by rapid sediment accumulation however only on laurentian fan does sediment gravity flow deposition occur during the lgm reddish brown turbidites deposited on laurentian fan during the deglacial period have no equivalent facies further north these unique features suggest important glaciological differences between the ice stream occupying laurentian channel and ice streams farther north the onset of widespread hemipelagic deposition occurred after ca 12 ka on laurentian fan and in flemish pass but not until ca 8 2 ka in the labrador sea consistent with the earlier retreat of glacial ice out of laurentian channel as compared to hudson strait

catastrophic ice shelf breakup as the source of heinrich event icebergs 1 heinrich layers of the glacial north atlantic record abrupt widespread iceberg rafting of detrital carbonate and other lithic material at the extreme cold culminations of bond climate cycles both internal glaciologic and external climate forcings have been proposed here we suggest an explanation for the iceberg release that encompasses external climate forcing on the basis of a new glaciological process recently witnessed along the antarctic peninsula rapid disintegrations of fringing ice shelves induced by climate controlled meltwater infilling of surface crevasses we postulate that peripheral ice shelves formed along the eastern canadian seaboard during extreme cold conditions would be vulnerable to sudden climate driven disintegration during any climate amelioration ice shelf disintegration then would be the source of heinrich event icebergs

palaeogeography of atlantic canada 13 0 kyr abstract we combine isobase maps with a digital terrain model of atlantic canada to map coastlines from 13 14c kyr bp to the present at 13 14c kyr bp there are ridges of high relative sea level rsl values over newfoundland and the maritime provinces and a re entrant of low values in the gulf of st lawrence this pattern persists well into the holocene and reflects crustal response to the slow wasting of ice caps that persisted in newfoundland and the maritime provinces for up to five millennia after the removal of ice from the gulf of st lawrence by a migrating calving embayment the palaeogeographic reconstructions reveal an archipelago on the outer shelf from grand bank to the continent that persisted from 13 14c kyr bp until ca 8 14c kyr bp much of the magdalen shelf was exposed but the magdalen islands were never connected to the mainland prince edward island was initially separated from the mainland became connected after 11 14c kyr bp and was separated again just before 6 14c kyr bp when northumberland strait formed the reconstructions are highly sensitive to relatively small changes in isobase values especially on the shallow banks on the continental shelf

the deglaciation of atlantic canada as reconstructed from the postglacial relative sea level record the post wisconsinan relative sea level record from atlantic canada is used to reconstruct the morphology of late wisconsinan age ice cover during its retreat from the atlantic region the proposed reconstruction has little or no grounded ice in the southern gulf of st lawrence an ice dome over the north shore of the st lawrence and thin ice often less than 1 km thick over much of the rest of the area a sensitivity analysis shows that the proposed reconstruction is not unique in its ability to account for the relative sea level record but that the thickness of ice in any individual area of the reconstruction is unlikely to be in error by more than a factor of two the exact position of the ice margin in some areas is not well constrained by the model an example is in southeastern newfoundland the numerical model used to relate ice morphology to postglacial relative sea level assumes that the ice sheets are isostatically equilibrated at the glacial maximum and therefore that load changes associat

numerical modelling of the laurentide ice sheet in the baffin island region the role of a cumberland sound ice stream a numerical model reconstruction was made of the northeastern laurentide ice sheet in the baffin island foxe basin region using geophysical terrestrial and marine geologic evidence for initial

a comparison of models of glacial sedimentation along the eastern canadian margin abstract the distribution and thickness of glacial and postglacial sediments of the eastern gulf of maine scotian shelf grand banks of newfoundland labrador shelf and hudson strait have been mapped using seismic reflection systems and lithological chronological and biostratigraphic data from cores and seabed samples deposits of till represented by incoherent seismic reflections commonly occur as sheets but also as linear ridges lenses and tongues discontinuous multiple till sequences whose thicknesses range from 1 300 m occur across the shelves and pinch out in water depths of 500 700 m till thickness and distribution is in part controlled by erodability and geomorphology of the underlying substrate glaciomarine sediments up to 300 m thick represented by medium to high intensity parallel continuous coherent seismic reflections occur as conformable to slightly ponded deposits glaciomarine sediments can interfinger conformably overlie or abruptly terminate against the till surfaces on the southern shelves from the gulf of maine to northeast newfoundland shelf and also in eastern hudson strait the glaciomarine sediments are typically interbedded with the tills at former ice sheet buoyancy zones where much of the material has been derived from subglacial meltout on the labrador shelf subglacial meltout did not occur as the till and glaciomarine sediments are of different lithology and do not interfinger from the gulf of maine to the grand banks of newfoundland acoustically weakly stratified ponded postglacial muds were eroded from the shallow bank surfaces by a marine transgression and deposited in the basins of the shelf on the labrador shelf iceberg scouring has reworked the entire bank top surface into an ice keel turbate up to 10 m thick and released the fines which now occupy the basins the thick mid late wisconsinan multiple till sections and associated glaciomarine sediments in the basins of the southern shelves suggest the presence of an ice shelf for 20 000 years beneath which large volumes of sediment were deposited in contrast the relatively thin mid late wisconsinan glacial sequence of the labrador shelf and the lack of subglacial deposits within the glaciomarine sequence may indicate either a rapid ice sheet retreat for that area or an ice shelf largely devoid of englacial debris

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

late pleistocene holocene paleoceanographic changes on the eastern canadian margin stable isotopic evidence abstract earlier studies of this area show profound holocene pleistocene paleoceanographic changes along the eastern continental margin of canada based on benthic foraminiferal assemblages here we demonstrate that stable isotopic measurements from benthonic foraminifera substantiate and place numerical limits on physical parameters from some of the glacial postglacial environments in holocene intervals where modern analogues of present day benthonic foraminiferal faunas can be used to delimit the physical environment the isotopic results closely parallel the faunal results in the glacial marine intervals where we have no modern analogues the isotopic results provide us with the first independent evidence that the salinities were not lower than 30 in the bottom waters along this former ice margin at the time of peak glaciation salinities may actually have been above normal we see no indication of a large meltwater event in the 10 11 k y b p time period that has been suggested to occur with the younger dryas events these results demonstrate that stable isotopes can be useful outside the context of relatively stable deep sea environments

mid cretaceous alluvial plain incision related to eustasy southeastern colorado plateau eustatic effects on the deposition of ancient coastal and marine rocks are well known but eustasy also can affect depositional patterns and processes well inland from the sea and play an important role in the development of nonmarine unconformities in the southeastern part of the colorado plateau fluvial rocks of the lowermost cenomanian lowermost upper cretaceous encinal canyon member at the base of the dakota sandstone fill paleovalleys incised into underlying formations in most of region the encinal canyon disconformably overlies fluvial rocks of the aptian to middle albian upper lower cretaceous burro canyon formation along the southern margin of the plateau the encinal canyon overlies progressively older mesozoic and paleozoic formations toward the south in the latter part of the early cretaceous an epicontinental sea lay about 240 km east of the southeastern colorado plateau and was base level for streams in the plateau region near the end of the early cretaceous sea level fell base level was lowered and streams incised valleys into alluvial deposits of the burro canyon formation and into older formations the resulting incised paleodrainage surface was preserved as the sub dakota unconformity when the succeeding sea level rise in earliest late cretaceous time caused dakota streams to aggrade and backfill the paleovalleys with alluvial sediments of the encinal canyon member unconformities in continental rocks have rarely been attributed to sea level changes the example of sub dakota unconformity however suggests that eustatic lowering of sea level can result in erosion far inland from the sea and play an important role in the formation of unconformities in continental strata

evidence for wisconsinan glaciations in the verrill canyon area scotian slope a composite thickness of about 25 m of sediment has been cored from the verrill canyon on the scotian slope it is interpreted that the majority of this sequence was deposited in a glaciomarine environment during oxygen isotopic stage 2 and the top of stage 3 these sediments as seen in high resolution seismic reflection profiles are well stratified become thicker upslope are laterally variable in thickness and pass upslope into possible outer shelf tills three wedge shaped units of incoherent reflections interfinger with the parallel reflections and terminate in water depths greater than 700 m these wedge shaped units are interpreted as slumped diamict and outwash deposits the age of the uppermost wedge shaped unit is 26 000 21 000 yr based on extrapolation of radiocarbon dates this unit documents a late wisconsinan glacier readvance on the outer scotian shelf the underlying wedge shaped unit estimated to be 70 000 yrs old extends further west along the continental slope and may represent a more extensive early wisconsinan ice advance a third wedge shaped unit inferred to have formed during isotopic stage 6 is possibly a remnant of the first glaciation in the study area

a groove ploughing theory for the production of mega scale glacial lineations and implications for ice stream mechanics mega scale glacial lineations msgls are longitudinally aligned corrugations ridge groove structures 6 100 km long in sediment produced subglacially they are indicators of fast flow and a common signature of ice stream beds we develop a qualitative theory that accounts for their formation and use numerical modelling and observations of ice stream beds to provide supporting evidence ice in contact with a rough scale of 10 10 3 m bedrock surface will mimic the form of the bed because of flow acceleration and convergence in ice stream onset zones the ice base roughness elements experience transverse strain transforming them from irregular bumps into longitudinally aligned keels of ice protruding downwards where such keels slide across a soft sedimentary bed they plough through the sediments carving elongate grooves and deforming material up into intervening ridges this explains msgls and has important implications for ice stream mechanics groove ploughing provides the means to acquire new lubricating sediment and to transport large volumes of it downstream keels may provide basal drag in the force budget of ice streams thereby playing a role in flow regulation and stability we speculate that groove ploughing permits significant ice stream widening thus facilitating high magnitude ice discharge

palaeo ice streams abstract the location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability in order to reconstruct former ice sheets we need to know ice stream location and timing once identified the beds of palaeo ice streams provide an unprecedented opportunity to glean information about their basal environment something that remains very difficult under contemporary ice streams this paper represents the first synthesis and discussion of palaeo ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind the ambiguous use of the term ice stream is addressed and four possible configurations for ice streams are presented diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a rubber stamped or smudged bedform imprint resulting from isochronous or time transgressive landform generation in particular we focus on the configuration of terrestrially terminating ice streams for which there are no modern analogues technological advances in marine geophysics are helping to generate a convergence of interest between antarctic glaciology and palaeo glaciology it is suggested that investigations around the fringes of contemporary ice sheets i e west antarctica can provide evidence that directly links the geomorphological record of palaeo ice streams with their contemporary counterparts in addition computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models we argue that data from palaeo ice stream beds are invaluable to ice sheet stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets

submarine moraines in newfoundland coastal waters implications for the deglaciation of newfoundland and adjacent areas abstract submarine moraines near modern coasts of newfoundland show regional variations in architecture off the west coast arcuate moraines in shallow water were altered to varying degrees by postglacial sea level lowering off the southwest coast arcuate moraines on deep fiord mouth sills interdigitate with glaciomarine deposits whose maximum age is 14 17 ka bp off the northeast coast submarine moraines are absent at the mouths of the deep fiords morainal ridges outside the fiords are coast parallel it is proposed that the moraines formed during deglaciation of the region the late wisconsinan ice sheet extended to the edge of the continental shelf and was divided into catchments with fast flow concentrated in deep channels ice calved back along channels isolating the newfoundland ice cap and ice caps on the offshore banks ca 14 ka drawdown from the interior was localized in fiords and ice margins stabilized just offshore forming the submarine moraines described here off the southwest coasts the ice margin was maintained for up to 1 5 ka at fiord mouths off the northeast coast many of the deep wide fiords are without sills and retreat was nearly continual until the margin stabilized at fiord heads just before 13 ka

till tongue stratigraphy seismostratigraphic studies on the scotian and mid norwegian continental shelves have led to the development of a conceptual model for glacial deposition and erosion by ice sheets in a marine environment till tongue model some of the terminal deposits of the marine ending glaciers are composed in part of acoustically incoherent wedge shaped bodies the wedges are thought to be part of a grounding line system associated with a floating terminus according to the model the sedimentary wedges are formed through the accumulation of glacial debris by subglacial processes proximal to the grounding line together with a penecontemporaneous proglacial contribution from sediment gravity flows sedimentation rates appear to be highest near and proximal to the grounding line that is within a grounding line zone ice proximal stratified glaciomarine sediment accumulates from plumes within the water column and rain out of ice rafted debris the glaciomarine sediment interfingers with the till tongues resulting from oscillations of the grounding line till tongues represent discrete stratigraphic units formed in both vertical and lateral successions marginal to massive till deposits major till tongues can be correlated regionally for hundreds of kilometers and thus can provide a basis for stratigraphic correlation on the mid norwegian shelf lateral and vertical successions of till tongues delineate several large scale till units which represent major advances and retreats of the ice that probably were of both stadial and glacial rank we refer to this type of succession as a till tongue stratigraphy it appears that till tongue formation is limited to intermediate water depths which range from 75 to 1 000 m present water depth but those formed in water depths 600 700 in may not be strictly subglacial in origin we speculate that processes leading to the development of till tongues possibly give rise to the formation of subglacial undermelt till together with thin flow tills near the grounding line it is also possible that another type of subglacial till embracing concepts inherent in the expression deforming basal tills as described by alley and others 1989 may contribute to the formation of till tongues boundaries between the major till units of the mid norwegian shelf are mainly depositional in the zone of maximum glaciation near the shelf edge and upper slope proximal to this zone of major deposition intraformational erosional processes dominate and give rise to smooth widespread time transgressive erosional surfaces erosion progressively increases in a proximal direction beveling the earlier glacial deposits and ultimately reaches and modifies the bedrock surface these regional surfaces are analogous to the ross sea unconformity which was also formed by glacial erosion morainic deposits within a till tongue stratigraphy are termed grounding zone moraines and are subdivided into advance and retreat varieties with linear tabular and hummocky attributes fields of small morainic ridges lift off moraines form in basinal areas during recession

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

a new late glacial sea level record for st george s bay newfoundland a new relative sea level curve is presented for st george s bay southwest newfoundland based on i a revised stratigraphic framework and depositional model for glacial and marine deposits exposed in coastal sections and ii 19 new radiocarbon dates on shells from emerged and submerged marine deposits including fossiliferous diamictons the data produce a type b sea level curve falling steeply from an extrapolated marine limit of 105 m above sea level at 14 0 14 c ka bp passing below modern sea level at 10 6 14 c ka bp to a lowstand of 25 m at 9 4 14 ck a bp and rising again close to modern sea level by 5 0 14 c ka bp marine limits in the northern part of the bay have lower elevations 27 65 m due to delayed ice retreat of up to 1 2 ka between 12 8 and at least 12 3 14 c ka bp glaciofluvial outwash graded to falling sea levels between 27 and 17 m above present throughout the bay whereas lowstand deltas were constructed in sheltered locations at the outlets of major river systems when sea level was 25 m below present establishment of the sea level lowstand at 9 4 14 c ka bp is supported by new seismic data and radiocarbon dates from st george s bay and also from white bear bay on the south coast of newfoundland short term fluctuations in emergence rates of 1 2 m century between 12 5 and 9 5 14 c ka bp are attributed to variable eustatic sea level rise superimposed on a declining local glacio isostatic adjustment

late quaternary glacial and sedimentary history of bonavista bay northeast newfoundland high resolution seismic profiles and core data from bonavista bay northeast newfoundland show that the sedimentary package above acoustic basement was deposited during the deglaciation of the late wisconsinan ice sheet during the late wisconsinan maximum 20 000 bp bonavista bay was occupied by a grounded ice sheet that extended farther offshore deglaciation of the bay was rapid and occurred prior to 13 500 bp during a time of rising sea level a basal till was deposited beneath the grounded ice and after lift off an ice shelf developed over the outer basins where diamicton was deposited the inner bay gradually deglaciated as the ice margin retreated to the present day shoreline by 13 000 bp and fine grained outwash sediments transported by interflows were rapidly deposited the inner bay remained under the influence of one or more remnant ice centres until 10 000 bp with ice positioned on the bonavista and gander peninsulas normal marine conditions were established in the outer bay by

wisconsinan glacial and sea level history of maritime canada and the adjacent continental shelf a correlation of land and sea events the wisconsinan glacial history of maritime canada records the interaction of land based glaciers with the sea which dissects the region along the deep embayments of the bay of fundy and the laurentian channel ice centers collectively termed the appalachian ice complex shifted in a clockwise manner across the varied bedrock terranes of the region producing cross striated bedrock outcrops and compositionally distinct till sheets on land offshore glacial sediments can be correlated to their terrestrial counterparts on the basis of provenance thus establishing crucial land sea links in the glacial record five glacier flow events have been recognized during the caledonia phase in early to middle wisconsinan time ice from eastern appalachian upland sources crossed nova scotia and extended to the continental shelf edge where a calving margin was established slumping at this margin produced proximal wedge shaped bodies of diamicton that interfinger with glaciomarine sediments the caledonia phase glacier retreated during middle wisconsinan time to the inner scotian shelf during the escuminac phase in late wisconsinan time 22 19 ka an ice center formed over the magdalen shelf escuminac ice center and transported large quantities of local red bed material southward to the outer shelf slope margin this glacier retreated about 18 ka to a tidewater margin at sable island bank and banquereau sea level during this time was falling as a result of isostatic recovery from earlier escuminac phase maximum ice loads just after 18 ka ice wasted back across the midshelf basins to the tidewater margin of the scotian shelf end moraine complex and was stabilized by falling sea levels escuminac ice was reorganized into the scotian ice divide scotian phase over mainland nova scotia and the continental shelf south of cape breton island between 15 and 13 ka another period of glacier retreat ensued and the margin settled close to the present day land areas between 13 and 12 5 ka an ice margin was established from local terrestrial ice centers in northern nova scotia chignecto phase into the bay of fundy and just beyond the present day atlantic coast responding to increasing climatic warming these smaller glaciers dissipated and their margins retreated landward a sea level lowstand of 65 m on the inner shelf occurred ca 11 7 ka isolated terrestrial remnants of chignecto phase glaciers were reactivated as a result of cooling during the collins pond phase younger dryas ca 10 8 ka enhanced ice rafting evident in the north atlantic deep oceanic record appears to correlate with periods of glacier retreat in the appalachian ice complex during melting and sea level rise both the quantity and thickness of icebergs increased due to grounding line retreat within the magdalen shelf thereby increasing the net flux of hematite stained quartz to the north atlantic

late wisconsinan ice retreat from the scotian shelf the late middle to late wisconsinan laurentide ice sheet terminated at the edge of the scotian shelf ca 21 ka in close temporal agreement with the h 2 heinrich event of the north atlantic stratigraphy the ice began its recession along the western edge of the shelf prior to 20 ka by 15 ka the ice front had retreated in a northeastward direction exposing much of the western half of the shelf although ice appears to have remained on the inner shelf north of a morainal system for another 2 k y the retreat was probably controlled by an ice divide along the axis of the mainland until after 16 ka at which time an ice flow pattern began to emanate from local remnant ice centers on the mainland late wisconsinan ice seems to have remained on much of the eastern portion of the shelf as late as 12 14 5 ka and probably deposited several outer bank moraines younger dryas ice probably was present at isolated land and coastal areas for a short period ca 10 5 ka but its offshore influence appears to have been restricted to floating ice and storm related events

late quaternary paleoceanography of deep and intermediate water masses off gaspe peninsula gulf of st lawrence foraminiferal evidence radiocarbon dated benthonic foraminiferal zones in three cores provide new information on the evolution of the deep and intermediate water masses off gaspe peninsula the deglacial phase in the deep laurentian channel began before 14 000 bp and was characterized by low salinity 20 or alternating low salinity and saline 35 water this was followed by a cold saline phase which ended ca 13 500 bp and a salinity minimum 30 33 5 which began ca 12 100 bp between 8700 and 7900 bp the temperature and salinity of the deep water mass increased resulting in the modern deep water mass temperature 4 6 c salinity 34 5 34 9 at the end of the goldthwait sea episode the salinity of the deep water was apparently controlled by the meltwater flux from the ice front during the deglacial phase after the deglacial phase the characteristics of the deep water mass were determined by the composition of offshore water entering the laurentian channel runoff from the lake agassiz great lakes system does n

glacial debris flow deposits on the baffin island shelf seismic facies architecture of till tongue like deposits abstract 3 d seismic facies modeling of late foxe wisconsin glacial deposits in the savage basin provides important new data concerning the morphology and origin of acoustically unstratified seismic units on high latitude continental shelves savage basin contains a thick sequence up to 110 m of morainal bank deposits unit ii similar to till tongue root deposits described from the scotian and norwegian shelves in 2 d longitudinal cross section unit ii thins and differentiates northward into two acoustically unstratified wedges or till tongue like deposits units iiaw and iibw which are observed to interbed with stratified glacimarine sediments unit i sediment transport was northeastward away from a late glacial ice margin in outer frobisher bay both unstratified wedges are lobate in plan view with the thickest portion 5 m to 50 m lying along the lobe axis upper surface contours are convex to the north and concentric to the lobate margin southward at the transition to the morainal bank the contours become concave to the north this morphology is consistent with that of lobate debris flow deposits with the concave contours defining a zone of sediment failure the data indicate sediment failure within morainal bank deposits which accumulated near the terminus of a temperate tide water ice sheet truncations of unit i reflectors against the lower surface of the debris flows indicate that the flows were deposited episodically and that they remobilized or eroded some of the unit i sediments this unconformable relationship gives the same stratigraphic sequence that king et al 1991 proposed to explain till tongue formation from subglacial meltout beneath buoyant glacier ice in contact with the seabed coalescing debris flow lobes are observed along the entire distal slope of the morainal bank these give the appearance of a continuous till tongue wedge in seismic cross sections taken parallel and distal to the paleoice margin without 3 d geometry reconstructed at contour intervals 10 m the complex lobate morphology could not be resolved

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

till in the marine environment till is of common occurrence in the marine environment and can be both subglacial and proglacial in origin former glacial margins are often represented by till tongues that are interbedded with stratified glaciomarine sediment and the relationship is readily mappable using seismic reflection techniques it is inferred that within individual till tongues sediment gravity flow deposits form transitional contacts with till of subglacial origin but these contacts cannot be distinguished on seismic profiles these unstratified gravity induced deposits formed in close proximity to the glacial source at the grounding line are considered to be secondary tills flow till complex in terms of the inqua classification of tills till tongue successions and till deltas are large ice marginal depocentres associated with floating front ice margins and appear to be closely related in origin tabular and hummocky moraines of the mid norwegian shelf also are considered to be products of floating front margins and represent a large proportion of the retreat tills formed during ice recession seismostratigraphic evidence for channelisation in ice marginal deposits appears to provide a means of distinguishing between former tidewater and floating front margins

proposed younger dryas glaciation of the eastern scotian shelf a refined synthesis of the stratigraphy of the scotian shelf is presented based on recently published borehole and seismic reflection data and detailed correlation along high resolution seismic profiles between the outer banks and the central basins one of the new stratigraphic units of the outer bank region is of glacigenic origin and represents the last glacial event near the margin of the shelf these deposits appear to be part of a morainal bank complex formed at a tidewater front a younger dryas age is proposed for the glacial deposits and the ice may have been widely distributed across the eastern scotian shelf evidence for the late glaciation is expressed in the central shelf area by an unconformity which on the bank areas is associated with subglacial meltwater channels 14c dates for the basin sediments of this region provide the most reliable chronology for the shelf stratigraphy the origin of sable island is closely related to the depositional history of the moraine and its surface has be

in situ geotechnical characterization of sediments on the nova scotian slope eastern canadian continental margin abstract a seabed 2 m long cone penetrometer and coring system geotechnical module has been used at 17 stations in four transects on the scotian slope to characterise in situ shear strength and induced pore pressure on several different types of late pleistocene and early holocene failure study sites were selected using the sar high resolution deep towed acoustic system equipped with a digital 160 190 khz sidescan sonar and a 3 5 khz subbottom profiler several distinctive types of geotechnical signature were recognised from plots of cone resistance and induced pore pressure with depth in the sediment normally consolidated sediments show a progressive increase in cone resistance with depth to about 75 kpa at 2 m subbottom holocene surficial muds show spectacular apparent overconsolidation reaching a peak of 250 kpa at about 50 cm subbottom and then decreasing down to 1 5 m this overconsolidation is associated with zoophycos burrows late pleistocene sediments exhumed by bedding plane slides show strong true overconsolidation consistent with the original depth of burial inferred from high resolution seismic stratigraphy debris flows show only a slight shear stress gradient with depth 40 45 kpa over 0 5 1 m subbottom with under consolidation due to remoulding of sediment

quaternary geology and surficial sediment processes browns bank scotian shelf based on multibeam bathymetry abstract browns bank is located on the glaciated continental shelf off southern nova scotia geological mapping of browns bank is based on interpretation of multibeam bathymetric and backscatter data in conjunction with 220 line km of seismic reflection profiles and sidescan sonograms sea floor sediment samples and bottom photographs the fundian moraine part of the previously identified end moraine system on the continental shelf off nova scotia is a prominent west east flat topped multi lobate ridge identifiable in the multibeam bathymetric data and in geophysical records the fundian moraine was subjected to erosion in the surf zone during sea level rise in depths less than 100 m a series of north south roughly parallel till ridges continuous in the subsurface with the fundian moraine is interpreted as interlobate moraines suggesting formation by a tidewater glacier the browns bank moraine connected to the fundian moraine is evidence of a newly identified grounded ice position farther seaward than the latter bedforms including obstacle marks comet marks sand waves and megaripples are evidence of a vigorous anticyclonic current pattern on browns bank the combination of multibeam bathymetric imagery with high resolution geoscientific information represents a powerful technique for sea floor geological investigations

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

erosion velocity of large grains subjected to a high uniform flow velocity abstractthere is limited knowledge on the erosion rates of large grains the available erosion models of granular material at large flow velocities are only validated up to a median particle diamet

a new high resolution digital elevation model of greenland fully validated with airborne laser altimeter data a new digital elevation model of the greenland ice sheet and surrounding rock outcrops has been produced at 1 km postings from a comprehensive suite of satellite remote sensing and cartographic data sets height data over the ice sheet were mainly from ers 1 and geosat radar altimetry these data were corrected for a slope dependent bias that had been identified in a previous study the radar altimetry was supplemented with stereophotogrammetric data sets synthetic aperture radar interferometry and digitized cartographic maps over regions of bare rock and where gaps in the satellite altimeter coverage existed the data were interpolated onto a regular grid with a spacing of 1 km the accuracy of the resultant digital elevation model over the ice sheet was assessed using independent and spatially extensive measurements from an airborne laser altimeter that had an accuracy of between 10 and 12 cm in a comparison with the laser altimetry the digital elevation model was found to have a slope dependent accuracy ranging from 1 04 1 98 m to 0 06 14 33 m over the ice sheet for a slope range of 0 0 1 0 the mean accuracy over the whole ice sheet was 0 33 6 97 m over the bare rock areas the accuracy ranged from 20 to 200 m dependent on the data source available the new digital elevation model was used as an input data set for a positive degree day model of ablation the new elevation model was found to reduce ablation by only 2 compared with using an older 2 5 km resolution model which suggests that resolution induced errors in estimating ablation are no longer important

late wisconsinan deglaciation of emerald basin scotian shelf emerald basin is a glacially overdeepened basin located on the central scotian shelf where quaternary sediments form a thin veneer over tertiary bedrock nineteen piston cores and 1200 line km of seismic data were obtained from the basin from which seven acoustic facies were recognized i cambro ordivician metasediments ii tertiary sediments iii scotian shelf drift till iv acoustically stratified emerald silt v acoustically unstratified emerald silt vi lahave clay vii diffused gas six depositional sequences were recognized in the emerald silt and lahave clay facics and were correlated with sediments recovered in piston cores depositional sequence 0 is a strongly stratified package which drapes over the scotian shelf drift it is correlated with stiff unbioturbated slightly gravelly sandy muds with no in situ molluscs and is characterised by an ice marginal foraminiferal assemblage depositional sequence 1 drapes over depositional sequence 0 and shows onlap on topographical highs it is correlated with slightly gravelly muds which are characterised by alternating bioturbated and unbioturbated hands and monospecific molluscan and foraminiferal assemblages depositional sequence 2 asymmetrically drapes over and onlaps onto depositional sequence 1 and is correlated with bioturbated slighty gravelly muds with monospecific molluscan and foraminiferal assemblages depositional sequence 3 infills the basin deeps erosionally truncating reflections of depositional sequence 2 it is correlated with bioturbated muds which are characterised by a monospecific foraminiferal assemblage and a slightly diverse molluscan assemblage depositional sequence 4 drapes over the erosional upper surface of depositional sequence 3 and is correlated with bioturbated muds which are characterised by a diverse molluscan assemblage depositional sequence 5 onlaps onto depositional sequence 4 infilling the basin deeps and is correlated with soft bioturbated sandy silts which are characterised by diverse molluscan and foraminiferal assemblages the present day seafloor in emerald basin is marked by small gas escape structures intepreted as pockmarks buried pockmards are observed in depositional sequences 4 and 5 buried iceberg scours are observed on the upper surface of depositional sequence 0 and within depositional sequences 1 and 2 small ridges interpreted as lift off moraines are formed on the upper surface of the scotian shelf drift and are oriented transverse to ice flow directions during glacial retreat wedge shaped acoustically unstratified features interpeted as till tongues are rooted in moraines on the basin flanks and were deposited simultaneously with depositional sequences 0 1 and 2 detailed interpretation of the seismic and core data suggest that glacial ice advanced across emerald basin reaching the shelf edge at approximately 24 ka melting of the ice sheet resulted in deglaciation of emerald basin at 17 5 ka by lift off of the grounded ice sheet to form a floating ice shelf of 10 100 yr duration sediment beneath the ice shelf was primarily supplied by subglacial meltwater streams prior to lift off till was squeezed into basal crevasses in the ice to form features known as lift off moraines the ice shelf calved at approximately 17 4 ka causing intense scouring of the seafloor by in situ icebergs and isolating ice rises on the banks surrounding emerald basin these ice rises disintegrated rapidly except for the rise on emerald bank which contributed sediment to emerald basin until 12 ka sediment was primarily supplied by subglacial meltwater and deposited out of suspension except near the ice margin where ice rafting and gravity flow mechanisms were important iceberg scouring occurred until about 14 ka the main ice margin remained on the northern flank of the basin until 15 4 ka at which time it retreated landward a widespread erosive event caused by storm driven currents occurred at 13 ka rain out from suspended sediment plumes was the dominant depositional mechanism until 12 ka lahave clay is primarily derived from inner shelf sediments reworked by rising sea level storm generated currents have created an erosional surface at the present day seafloor around the flanks of the basin

a comparison of observed and theoretical postglacial relative sea level in atlantic canada two extreme models of late wisconsinan ice cover in atlantic canada and the northeastern u s a are shown to produce postglacial relative sea level curves that bracket existing field observations at six sites throughout the region this suggests that the true late wisconsinan ice distribution is probably intermediate to the two contrasting reconstructions proposed both ice models predict the existence of four relative sea level zones an innermost zone closest to the centre of glaciation in which relative sea level falls continuously throughout postglacial time an outermost zone in which it rises continuously and two transitional zones in which it first falls and then rises in varying proportions according to the distance from the ice margin the distinctive forms of the relative sea level curves are probably representative of each of the zones and are unlikely to be significantly perturbed even by large local ice readvances they therefore establish patterns with which future field data are expected to conform the form that the geological record of relative sea level change is likely to take within each zone is discussed and promising settings for the collection of new data are proposed the common practice of separating relative sea level into an isostatic and a eustatic component is analysed and shown to be incorrect as usually applied the practice is also shown to be unnecessary because the models discussed in this paper predict changes in relative sea level that can be compared directly with the observations

the goldilocks dilemma big ice little ice or just right ice in the eastern canadian arctic our conceptions of the ne sector of the laurentide ice sheet lis at the last glacial maximum lgm have evolved through three major paradigms over the past 50 years until the late 1960s the conventional view was that the eastern canadian arctic preserved only a simple deglacial sequence from a lis margin everywhere at the continental shelf edge flint paradigm glacial geologic field studies began in earnest in this region in the early 1960s and within the first decade field evidence documenting undisturbed deposits predating the lgm led a pendulum swing to a consensus view that large coastal stretches of the eastern canadian arctic remained free of actively eroding glacial ice at the lgm and that the most extensive ice margins occurred early in the last glacial cycle this minimalist paradigm dominated until the late1980s when an expanded data set from shallow marine studies indicated lgm ice at least locally reached the continental shelf within the past decade the marine data coupled with new evidence from lake sediments and cosmogenic exposure dates on moraines and glaciated terrain in the eastern canadian arctic has led to a new paradigm that better reconciles the terrestrial and marine evidence collectively these lines of evidence indicate that all of southern baffin island was glaciated at the lgm but that some coastal uplands north of cumberland sound remained above the limit of actively eroding glacial ice even though outlet glaciers reached the continental shelf in front of most fiords and sounds the most plausible explanation for the observed glacial limits is that low gradient relatively fast moving outlet glaciers sliding on deformable sediments occupied marine embayments and fiords contrasting with slower moving ice frozen to its bed on the intervening crystalline terrain slow moving ice frozen to its bed would have had steeper surface gradients hence would have terminated inland from the coast this scenario is consistent with observations indicating high elevation coastal terrain remained unglaciated even though outlet glaciers reached the continental shelf lgm summer temperatures were apparently much lower than present as lakes in the ice free regions were permanently frozen

continental slope sedimentation adjacent to an ice margin iii the upper labrador slope abstract the upper labrador slope is the key area for sediment transfer from the northeastern margin of the pleistocene laurentide ice sheets lis to the deep basin it is subdivided from north to south into 8 sectors based on relief differences and echo character on 750 line km of continuous sleeve gun and 3 5 khz seismic profiles high to moderate relief sectors 2 and 4 and in part 6 and 8 are seismically transparent and well stratified with continuous individual high amplitude reflections and deep penetration low relief sectors 1 3 5 and 7 show strong bottom reflections and with the exception of sector 1 low seismic penetration poor stratification and low amplitude if any subbottom reflections the lateral distribution of these alternating high to moderate and low relief sectors reflects fundamental differences in the sediment transfer mechanisms through outlets from the lis onto the slope low relief slope sectors represent debrite and turbidite slopes and are located in front of ice outlets on the slope and adjacent regions to the north they originate from mass wasting on the upper slope of glacial detritus with a significant coarse component originally delivered as englacial or subglacial material and deposited in end moraines or as bedload by subglacial or supraglacial rivers high to moderate relief sectors originate from fall out of suspended sediment from turbid surface plumes tsp and preferentially occur off the southern half of outlets and south of major outlets as exemplified by sector 2 south of the hudson strait outlet this asymmetry is caused by the south flowing labrador current which entrains the buoyantly rising turbid meltwater plumes at the glacier front the present high relief topography which shows a dendritic pattern of upslope canyon branching is the result of retrograde headward canyon erosion by mass wasting processes of an originally much smoother mud blanket surface the sediment is remobilized by slumping and entrained in debris flows and turbidity currents the occurrence of tsp deposits on the high to moderate relief upper slope sectors requires a summer sea surface not frozen over during major parts of the pleistocene including glacial maxima tps deposition on the upper slope ice rafting and a plethora of ice margin depositional phenomena many of which give rise to mass wasting and mass flow phenomena are the main features that make high latitude continental slopes adjacent to continental ice sheets different from their lower latitude counterparts

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

deep sea floor evidence of past ice streams off the antarctic peninsula the past existence of a giant ice stream off the northern end of the antarctic peninsula is suggested by a convex upward elongated sediment body now at a mean water depth of 1000 m because of its morphological characteristics i e a set of parallel to subparallel ridges and grooves to 100 km long with an overall width of 25 km we call this depositional body a bundle structure we hypothesize that bundle structures form by accumulation of basal deformation till under their parent ice streams from its location size and overall characteristics the bundle structure described here constitutes the best preserved largest deepest and relatively low latitude evidence of giant ice streams that flowed offshore antarctica during glacial maxima bundle structures reveal the very dynamic behavior of ice caps in the northern antarctic peninsula during the last glacial maximum with catchment areas draining rapidly under marine based critical subglacial conditions bundle structures represent a new megascale streamlined glacial landform

north american ice sheet reconstructions at the last glacial maximum abstract the areal extent of the last glacial maximum lgm ice sheets is well known in north america but there is no direct geological proxy for ice sheet thickness or volume uncertainties associated with glaciological and geophysical reconstructions give widely varying estimates of north american ice sheet nais volume at lgm in an effort to quantify the uncertainty associated with glaciological reconstructions we conducted a suite of 190 numerical simulations of the last glacial cycle in north america prescribing different climatic mass balance glaciologic and isostatic treatments for the least constrained model variables lgm ice sheet reconstructions were evaluated using the well established geologic record of ice sheet area and southern extent at lgm dyke and prest 1987 these constraints give a subset of 33 simulations that produce reasonable lgm ice cover in north america ice sheet dispositions and the associated parameter settings in this subset of tests provide insight into the plausible range of nais thickness form and mass balance regime at lgm ice volume in this subset of tests spans a range of 28 5 38 9 10 15 m 3 at lgm with a predominant cluster at 32 36 10 15 m 3 taking floating ice and displaced continental water into account this corresponds to 69 94 m eustatic sea level msl more than 75 of the accepted tests fall in the range 78 88 msl we argue that this is a plausible estimate of the volume of water locked up in the nais at lgm

chronology of late wisconsinan glaciation emerald basin scotian shelf eight new accelerator mass spectrometry ams radiocarbon dates from proglacial sediments in emerald basin indicate that the previously proposed chronology based on dates of total organic matter is much too old the new chronology indicates that grounded ice occupied emerald basin in the late wisconsinan

widespread complex flow in the interior of the antarctic ice sheet it has been suggested that as much as 90 of the discharge from the antarctic ice sheet is drained through a small number of fast moving ice streams and outlet glaciers fed by relatively stable and inactive catchment areas here evidence obtained from balance velocity estimates suggests that each major drainage basin is fed by complex systems of tributaries that penetrate up to 1000 kilometers from the grounding line into the interior of the ice sheet this finding has important consequences for the modeled or estimated dynamic response time of past and present ice sheets to climate forcing

petrographic evidence from the eastern canadian margin of shelf crossing glaciations abstract it is difficult to evaluate when and where glaciers extended across the outer continental shelf off eastern canada the outer shelf and upper slope are commonly hard bottomed or have a great thickness of post glacial sediment in either case making direct sampling and dating of ice margin sediment impossible the timing and extent of glacier ice is important for understanding continental slope sedimentation and ice sheet dynamics we have therefore determined the lithologic components of the 1 4 mm granule fraction of over 100 well dated samples from 40 cores from the more distal parts of the deep water margin off nova scotia and newfoundland this fraction is demonstrably ice rafted in these cores and geographic variation in component results from input of icebergs at different calving margins the samples show that heinrich layers have a distinctive granule fraction that shows some areal variation as a result of dilution by sources other than hudson strait heinrich event 2 ca 21 ka is widespread as far southwest as the west scotian slope but by the last glacial maximum lgm numerous discrete sources of ice rafted granules are recognised implying that calving ice margins were present in several places off newfoundland and nova scotia including off banquereau a distinctive purplish lgm gravelly mud is recognised on the eastern newfoundland margin derived from a calving margin on the ne newfoundland shelf at the time of heinrich event 1 ca 14 ka there was a calving ice outlet somewhere on the grand banks and another in halibut channel retreat of ice from the gulf of st lawrence can be tracked by changing granule petrology from the lgm to 13 ka these data suggest that final ice retreat from many parts of the outer shelf was later than is shown in many recent ice margin reconstructions

a conceptual model of the deglaciation of atlantic canada abstract we present a conceptual model for the deglaciation of atlantic canada in which a role is played by ice streams the ice margin lay close to the edge of the continental shelf at the last glacial maximum ice streams occupying shelf troughs comprised 1 a major ice stream in the laurentian channel 2 secondary streams in the bay of fundy gulf of maine trinity trough and notre dame channel and 3 lesser ice streams elsewhere early retreat in the northeast notre dame bay and in the southwest bay of fundy gulf of maine was mainly by calving along embayments by 18 ka radiocarbon years a calving embayment had opened on emerald basin scotian shelf retreat along channels marooned ice on intervening banks a major calving episode beginning just before 14 ka removed ice from the gulf of st lawrence triggering re advances down secondary troughs isolation of a newfoundland ice cap produced radial drainage via fiords and more extensive flow into the st george s bay lowlands on the west coast by 13 ka most ice was on land and was ablating by melting rather than calving shelf ice caps persisted until 11 ka

balance velocities of the greenland ice sheet we present a map of balance velocities for the greenland ice sheet the resolution of the underlying dem which was derived primarily from radar altimetery data yields far greater detail than earlier balance velocity estimates for greenland the velocity contours reveal in striking detail the location of an ice stream in northeastern greenland which was only recently discovered using satellite imagery enhanced flow associated with all of the major outlets is clearly visible although small errors in the source data result in less accurate estimates of the absolute flow speeds nevertheless the balance map is useful for ice sheet modelling mass balance studies and field planning

probable late wisconsinan ice margin on the upper continental slope off st pierre bank eastern canada seismic reflection profiles from the continental slope off st pierre bank show a distinctive acoustic facies characterized by incoherent reflections unit e overlain by 5 20 m of stratified sediments units d a cores from unit e include poorly sorted silty diamict locally overconsolidated and including in places some foraminifera stratified sediments also occur in places in this facies the overlying sediments of units d a except for the topmost metre of unit a have a foraminiferal fauna dominated by elphidium excavatum forma clavata and cassidulina reniforme which has been interpreted elsewhere as indicating ice margin sedimentation the sediments contain turbidites and rare ice rafted detritus and are bioturbated accelerometer mass spectrometer radiocarbon dating of shells from the stratified sediments yielded dates between 3 3 and 11 8 ka facies e the top of which has an extrapolated age of 11 5 12 0 ka is interpreted as slumped morainal diamict and proglacial sediment resulting from a lat

evidence of late glacial permafrost in newfoundland abstract structures interpreted as ice wedge pseudomorphs are developed in postglacial sediments at several locations in coastal areas of western central and eastern newfoundland the ice wedge casts indicate that permafrost was prevalent in exposed coastal locations following late wisconsinan deglaciation and marine regression due to isostatic uplift formation of the ice wedge casts indicates that the mean annual temperatures were colder than at present along the newfoundland coast and that snow pack depths were less and snow cover less persistent the environment following marine regression was marked by cold windswept conditions which permitted the development of permafrost in the coastal regions much of the interior of newfoundland remained covered by glacial ice and consequently did not support subaerial permafrost direct numerical dating of the ice wedge casts is not possible at present however the geomorphic settings and stratigraphic positions of the features indicate that they developed subsequent to latest wisconsinan glacial retreat and followed regression from the postglacial marine limit permafrost formation preceded climatic warming and establishment of arboreal vegetation in the early holocene the time of formation of the ice wedges therefore is constrained between the initiation of postglacial marine regression ca 12 300 11 000 bp uncal and the initiation of climate amelioration ca 10 400 bp uncal this chronological range corresponds to the combined duration of the initial postglacial cooling episode and the subsequent younger dryas cold climate event documented in palaeoenvironmental records from newfoundland as lasting from shortly before ca 11 200 to ca 10 400 bp