ice flow patterns and glacial transport in the eastern hudson bay region implications for the late quaternary dynamics of the laurentide ice sheet recent field surveys in the eastern hudson bay region have led to the discovery of regional ice flow sequences that require a significant reassessment of the late quaternary dynamics of the laurentide ice sheet two regional ice flow phases can be recognized from till compositional data and from crosscutting relationships observed on striated bedrock surfaces the oldest is directed toward the northwest and north northwest while the youngest is directed toward the west and includes a late glacial deflection toward the southwest the wide regional distribution of striae formed during the early northwestward glacial movement together with the recognition of palimpsest glacial dispersal trains associated with this phase suggest that it was a long lived time transgressive regional event the ensuing glacial movement is a regionally dominant westward ice flow phase during which several large glacial dispersal trains were formed downglacier from distinctive bedrock sources the largest of these trains extends

seismic measurements reveal a saturated porous layer beneath an active antarctic ice stream seismic reflection studies recently conducted on ice stream b part of the marine ice sheet of west antarctica show a metres thick layer immediately beneath the ice in which both compressional p and shear s wave speeds are very low these low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure from this and from arguments presented in an accompanying paper1 to the effect that the layer would be too weak to support the shear stress exerted by the overlying ice we conclude that the layer is deforming and that the ice stream probably moves principally by such deformation

final stages in the collapse of the laurentide ice sheet hudson strait canada nwt 14c ams dates seismics stratigraphy and magnetic susceptibility logs hudson strait is a key element in the history of ice sheet ocean interactions during the deglaciation of the laurentide ice sheet data from over 30 giant piston cores supplemented by ca 40 14c ams dates on foraminifers and shells from sites within and adjacent to hudson strait are used to describe the timing and sediment processes associated with the final complex phases of deglaciation in hudson strait each core is placed in a regional seismic architectural context through examination of deep tow huntec profiles most cores sample a thin postglacial unit and extend several meters into glacial marine sediment mainly silty clays 14c dates on cores from the adjacent shelf indicate that deglaciation occurred by 13 ka we have not been unable to confirm that hudson strait was ice free by 11 12 ka although this is a probable scenario whole core magnetic susceptibility wcms data are used as the primary signature of changes in the style of sedimentation and provenance and to correlate between cores wcms indicates that there is a regional differentiation in the ms signal associated with bedrock provenance changes in contribution of detrital carbonate and style of sedimentation one low wcms event is present in cores from both the western and eastern basins it dates from 8 0 ka and provides an important regional stratigraphic marker probably associated with the final deglaciation of hudson bay and hudson strait sediment from a southerly source ungava bay continued to be contributed into the 900 m deep eastern basin of hudson strait 8 and 7 ka and thick postglacial sequences were piled within ungava bay between 6 and 7 ka

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

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

seabed geomorphic features in a glaciated shelf of the baltic sea abstract due to a continuous increase in human activities occurring throughout marine and coastal areas worldwide e g marine traffic and construction the lack of in depth information on vast marine areas is problematic however the spatial informatics field has enabled the development of new applications based on pre existing spatial data this paper discusses the physical structure and complexity of the continental shelf seafloor using geospatial modelling and gis analysis to gain insight into the physical environment of the baltic sea seafloor as a basis for ecosystem management we demonstrate the mapping of coherent features over a broad region and identify geomorphic features of the seabed by analysing and modelling bathymetric seabed substrate and photic depth datasets the analysis was performed at the kilometre scale using a grid size of 200 m in total 18 unique seabed geomorphic features were identified from the entire baltic sea including the skagerrak the features are similar to geomorphic seafloor structures typically occurring on glaciated continental shelves the baltic sea is primarily characterized by various plains and basins and on average one third of the seafloor can be regarded as a sediment accumulation area other seabed geomorphic features are mainly present in certain local sub regions the archipelagos as well as the coastal areas of southern sweden and the bothnian bay have a heterogeneous seafloor environment these areas are characterized by sea valleys and holes sea troughs and bedrock elevations partly due to a crystalline basement and glacial erosion in addition the shallow coastal areas suffer from intense wave exposure and have erosional features that differ from those in open sea areas effective transnational marine spatial planning requires extensive knowledge of the environmental characteristics of the region in question background data for marine spatial planning can be obtained through an analysis of seabed geomorphic features which provides consistent information on the physical marine environment over a broad area

geodynamic mechanism and classification of basins in the earth system abstract the sedimentary basin is a basic geological unit in the earth system its formation and evolution are controlled mainly by plate tectonics and geodynamics which have produced a variety of basin types the development and evolution of various basins depend not only on the tectonic effect of lithospheric plate but also on sublithospheric and earth surface actions basin classification schemes based on the theories of platform geosyncline or plate tectonics could neither include all basin types nor reflect the complex processes of basin formation and evolution from the viewpoint of earth system we proposed a new basin classification scheme based on geodynamic mechanism that is lithospheric plate sublithospheric and earth surface actions in our geodynamic classification we employed a series of geodynamic settings of basin formation and evolution including the lithospheric plate sublithospheric and earth surface environments the dynamic regimes of basin formation and evolution such as tectonic setting extension compression and shearing the thermal processes and gravity effects the various natures of basin basement and crustal types continental oceanic or transitional crust and the history of basin sedimentary filling and tectonic paleogeography successively as the controlling factors for basin classification this new geodynamic classification scheme highlights both the role of the lithosphere and the effects of the sublithospheric and the earth surface actions on controlling the basin formation and evolution the basic dynamic types of basin classification include the prototype basin forming under a single tectonic thermal or gravity regime and the superimposed basin as well as residual basin forming under multistage thermal and or tectonic regimes thus this classification scheme could provide an evolving understanding of lithosphere crust mantle interaction and geodynamic processes as well as of hydrocarbon accumulation and metallogenic mechanisms in sedimentary basins and would help in the synthetic exploration of various resources

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

stratigraphy paleoecology and glacial history of the gillam area manitoba sections along the nelson river in northern manitoba outcropping upstream and downstream from limestone dam record a long succession of late quaternary events the oldest sediment exposed consists of sandy nonfossiliferous sundance till of northwestern provenance and related to a kansan or illinoian glaciation the paleosol developed in the sundance till is assigned to the yarmouthian or sangamon interglacial on its stratigraphic position and depth of weathering fossiliferous clayey amery till of eastern provenance overlies the sundance till and underlies the nonglacial nelson river sediments aspartic acid d l ratios of wood fragments from the nelson river sediments correlate with an aspartic acid d l ratio of similar wood from the missinaibi formation in ontario beetle analysis indicates the nelson river sediments were deposited north of the tree line under conditions more severe than those found in the area today the deposits are believed to be of latest sangamon or possibly mid wisconsinan age

peatland succession and long term apparent carbon accumulation in central and northern ontario canada despite their importance as globally significant carbon c stores basic knowledge of post glacial peatland history and c accumulation are lacking for the canadian boreal shield and james bay lowland jbl of central and northern ontario canada radiocarbon dates plant macrofossil analysis and soil c estimates from an eight core transect of the jbl and surrounding regions are used to reconstruct the timings and patterns of fen to bog transitions and the ranges and patterns of long term apparent rate of c accumulation larca peatland initiation lagged the retreat of the laurentide ice sheet the drainage of glacial lakes and isostatic uplift by 810 6050 years transition from carex dominated fen to sphagnum dominated bog had a median timing of 3500 years following peatland establishment and ranged from 640 to 6970 years larca was variable geographically and over time with median values ranging from 13 4 to 31 6 g c m2 yr larca anomalies were generally high 6 1 kyr kyr 1000 calibrated years be

lake agassiz outburst age and routing by labrador current and the 8 2 cal ka cold event abstract catastrophic drainage of glacial lake agassiz impounded by the laurentide ice sheet lis into hudson bay and strait is widely thought to have caused the 8 2 cal ka cold event though the path of its drainage in the north atlantic is poorly known analysis and compilation of 10 sediment cores from 8 sites distributed on the eastern canadian continental shelf and upper slope south of hudson strait revealed distinct beds with elevated detrital carbonate dc concentrations known by their distinct composition to originate from erosion of carbonate bedrock and carbonate rich glacial sediments in the hudson bay hudson strait region at all but one site radiocarbon ages bracketing and within the thickest and most widespread of these beds are coeval with the age constraints for the agassiz floods in hudson strait and southeastern hudson bay the dc distribution and concentration of this bed are consistent with southward transport in the labrador current transfer function analysis of dinoflagellate assemblage data from cores on the central labrador shelf in hudson bay and on the northeast newfoundland shelf reveal that early holocene seasonal ice cover was 5 6 months longer than at present requiring the application of a 200 year reduction to the radiocarbon age constraints on the lake agassiz outburst floods the age of the floods is reduced to about 8 33 cal ka 7 5 14 c ka from the previous determination of 8 47 cal ka 7 7 14 c ka with a similar reduction in their error ranges to 8 04 8 49 cal ka from 8 16 8 74 cal ka based on present current routing the agassiz floodwaters and icebergs are inferred to have travelled south in the labrador current and to have possibly become incorporated into the north atlantic current and transported to the nordic seas there the freshwater additions would have lessened deepwater production with a concomitant reduction in northward heat transport in the upper limb of the atlantic meridional overturning circulation thereby contributing to the 8 2 cal ka cold event variation in the calcite and dolomite content of the agassiz dc bed two salinity reductions during agassiz bed deposition and low level shorelines of lakes agassiz and ojibway suggest that more than one outburst was delivered during the final agassiz drainage the 8 2 cal ka cold event registered in greenland was coeval with a second or later flood which possibly accompanied the final collapse of the lis in hudson bay

high resolution seismic stratigraphy of late quaternary deposits in manitounouk sound northern quebec effects of rapid postglacial emergence manitounouk sound contains a succession of postglacial deposits consisting of three acoustic units separated by disconformities from base to top these are 1 a stratified draped unit interpreted as of glaciolacustrine and glaciomarine origin 2 an onlapping basin fill unit of thick transparent beds interpreted as gravity flow deposits and 3 a divergent fill unit of stratified and transparent modern marine deposits the gravity flow deposits of unit 2 pass laterally into slide scars that truncate unit 1 pollen and dinoflagellate analysis of cores correlated with the acoustic sections indicate that unit 1 is of early holocene age and confirms a glaciomarine environment unit 3 contains modern assemblages of pollen and dinoflagellates the slide scar and gravity flow deposits of unit 2 correspond to the period of transition from glaciomarine to modern conditions and are interpreted to result from a period of relatively intense earthquake activity due to stress release along faults during or shortly

the subglacial origin of the lake agassiz ojibway final outburst flood arc shaped scours sandwaves and channels on the hudson bay seafloor suggest that the catastrophic drainage of lake agassiz ojibway occurred as a subglacial flood beneath the laurentide ice sheet which covered northern north america

dynamics of the laurentide ice sheet in hudson bay canada abstract interpretation of sidescan sonar and high resolution sub bottom seismic data from hudson bay has led to the development of a model for final disintegration of the laurentide ice sheet the well preserved geomorphic features observed from the bay floor are similar to subaerially exposed glaciogenic features observed around the perimeter of hudson bay and can be related to the following three paleoenvironments subglacial erosion deposition ice margin deposition and reworking and post glacial reworking and burial subglacial features observed include fluted terrains with superimposed rogen moraines relief attributed to ice surging eskers subglacial channels and dead ice topography de geer moraines and recessional moraine complexes indicate the mechanism and orientation of ice breakup retreat the orientations of these features are locally consistent with regional trends indicating the overall direction of ice sheet flow and retreat during the last phase of the laurentide ice sheet subglacial channel complexes incised into the till and bedrock and high energy bedforms deposited on the till surface occur in present day water depths down to 160 m due to isostatic depression these could have been as much as 315 m deeper at the time of formation they indicate a wet based glacier with high energy subglacial drainage during the late phases of ice retreat the sidescan sonar data also reveal numerous zones of distinctive morphology attributed to ice breakup and post glacial processes cross cutting relationships allow the determination of the relative ages of these zones from oldest to youngest these zones are interpreted to represent scouring of the bedrock and overburden by the remnants of the ice sheet seafloor scouring by tabular icebergs which moved in a tidally induced arcuate pattern or under the influence of massive glacial lake outflows development of dead ice topography under residual ice masses and random iceberg scouring by smaller icebergs restricted to present day water depths of less than 180 m recently published reconstructions of the collapse of the laurentide ice sheet based on dated quaternary sections on land suggest that the bay was rapidly deglaciated in approximately 400 years the well preserved and distinctive glaciogenic and stratigraphic indicators observed from the bay floor suggest that they were formed by a succession of mechanisms which were too short lived to obliterate the underlying evidence of deglaciation this supports the interpretation of extremely rapid deglaciation of hudson bay and points out that subsequent marine processes have not been sufficient to obliterate the glacial features

hudson bay river sediments and regional glaciation i iron and carbonate dispersal trains southwest of hudson and james bays sands deposited from rivers draining the southwesterly trending watershed of the cape henrietta maria area are enriched in calcite and are characterized by higher calcite dolomite ratios than the sands from rivers north and south of the cape this pattern suggests that a train of drift with distinctive carbonate composition extends southwest of cape henrietta maria indicating a dominant pattern of southwesterly ice flow in this region iron contents are highest for sands from rivers on cape henrietta maria suggesting iron enrichment in the sand fraction of tills in the cape area and the existence of a broad dispersal train extending southwest of the cape the dispersal train inferred from the calcite dolomite ratios overprints part but not all of the dispersal train inferred from the iron content

early holocene deglaciation of northern hudson bay and foxe channel constrained by new radiocarbon ages and marine reservoir correction abstract radiocarbon ages from southampton island canada provide new chronological control on the deglaciation of foxe channel and northern hudson bay a strategic area for understanding the demise of a marine based portion of the laurentide ice sheet a regional marine reservoir age of 630 45 yr and a reservoir offset r of 263 48 yr were calculated from two early to mid holocene terrestrial marine radiocarbon age pairs these values are consistent with corrections based on early 20th century mollusks suggesting that following deglaciation the oceanic conditions controlling the regional reservoir effect rapidly became similar to those of modern times however our r value is 352 52 yr less than another correction from eastern foxe basin which may be affected by 14 c dilution from carbonate rocks our r value is used to calibrate new marine radiocarbon ages which help further develop the deglaciation history of southampton island especially along the north coast where deglaciation of foxe channel appears to have been completed by 8100 7800 cal yr bp 2 this provides key chronological constraints on the development of a long marine ice margin in southern foxe basin prior to the final breakup of the foxe ice dome

explained and unexplained spatial and temporal variability in rates of marine sediment accumulation along the northeast margin of the laurentide ice sheet 14 ka abstract changes in sediment accumulation rate sar cm ky for fifteen ams 14c dated late quaternary sites from along the ne margin of canada between 66 and 54 n are examined these 15 cores cover the last deglacial cycle of sediment input from the decaying laurentide ice sheet and subsequent postglacial marine sedimentation on these arctic and subarctic shelves and basins it is shown that the spatial and temporal variability of the 15 sar time series do not simply parallel the known glacial chronology deglaciation of the shelves initially occurred after heinrich event 1 h 1 14 5 ka all dates are in 14c yr subsequently there were major ice advances during the younger dryas yd h 0 10 11 ka and the noble inlet glacial events 8 6 ka with final collapse of the ice sheet ca 8 0 ka a total of 73 radiocarbon dates were used which led to 58 sar estimates the median sar is 69 cm ky however the distribution is strongly positively skewed because of short lived intervals of very high sar 5000 cm ky ca 5000 kg m 2 ky 1 on the labrador shelf high sar are associated with ice retreat from the noble inlet maximum 8 6 ka whereas on the se baffin shelf there is little response in the sediment system to this event conversely during the younger dryas heinrich 0 yd h 0 event high sars occur on the se baffin shelf but along the labrador shelf the interval 10 11 ka is marked by modest sars both the 11 10 and 8 6 8 ka rapid sediment accumulation events are marked by considerable increases in the detrital carbonate content hence bear similarities to the major heinrich events in the nw labrador sea these unexpected spatial and temporal differences in sediment deposition probably reflect changes in sediment transport trajectories associated with differences in ice glacial or sea ice extent and atmospheric oceanic circulations

superlakes megafloods and abrupt climate change about 8200 years ago the climate of much of the northern hemisphere cooled abruptly for a period of about 200 years in their perspective clarke et al examine the most likely culprit for this cooling an outburst of fresh water from a vast ice dammed glacial lake in north america the superlake had formed when the kilometers thick ice sheet covering much of north america disintegrated when the ice dam became unstable fresh water flooded from the lake into the north atlantic it remains unclear how this fresh water affected ocean circulation or whether the outburst occurred in more than one stage but the timing points strongly to the outburst flood as the trigger of the 8200 year climate event

insights on the events surrounding the final drainage of lake ojibway based on james bay stratigraphic sequences abstract deglaciation of the james bay region was highly dynamic with the occurrence of ice cochrane readvances into glacial lake ojibway around final deglaciation time which culminated with the drainage of ojibway waters into hudson bay and subsequent incursion of the tyrrell sea at 8 ka renewed interest on these events comes from the possible link between the drainage of the ice dammed lake agassiz ojibway and a major climate deterioration known as the 8 2 ka cooling event recent glaciological modeling suggests that this drainage may have occurred subglacially a mechanism that can accommodate more than one lake discharge as suggested by marine records the exact number and timing of drainage events as well as location of the lake discharge pathway s remain however largely unconstrained here we focus on the events that led to the drainage of lake ojibway by documenting late glacial sedimentary sequences located east of james bay our investigations indicate that the deglacial sequence consists of a readvance till extensive ojibway rhythmites and thick marine sediments the glaciolacustrine and marine units are separated by a 60 cm thick horizon composed of laminated silt beds containing rounded clay balls and disseminated clasts resulting from the abrupt drainage of the lake radiocarbon dating of marine fossils lying above the drainage horizon indicates that the glaciolacustrine episode ended around 8128 8282 cal yr bp micropaleontological analyses reveal that freshwater ostracods candona sp and marine microfossils foraminifers dinocysts occur together in the upper part of the ojibway sediments analysis of oxygen isotopes 18 o of ostracods and foraminifers originating from the same stratigraphic position show highly contrasting values that suggest possible subglacial exchanges between lake ojibway and tyrrell sea waters prior to the final drainage event the complexity of the deglacial events is further indicated by radiocarbon dating of marine shells retrieved from a cochrane till that suggests that the last ice readvance occurred almost simultaneously with the final lake discharge these results bring additional constraints on the drainage mechanism of the coalesced lake agassiz ojibway and indicate that the james bay region formed an important drainage pathway for meltwaters at the end of the last deglaciation

glacial geomorphology of the central arctic ocean the chukchi borderland and the lomonosov ridge the last decade of geophysical seafloor mapping in the arctic ocean from nuclear submarines and icebreakers reveals a wide variety of glaciogenic geomorphic features at water depths reaching 1000 in these findings provide new and intriguing insights into the quaternary glacial history of the northern hemisphere here we integrate multi and single beam bathymetric data chirp sonar profiles and sidescan images from the chukchi borderland and lomonosov ridge to perform a comparative morphological seafloor study this investigation aims to elucidate the nature and provenance of ice masses that impacted the arctic ocean sea floor during the quaternary mapped glaciogenic bedforms include iceberg keel scours most abundant at water depths shallower than similar to 350 400 m flutes and megascale glacial lineations extending as deep as similar to 1000 m below the present sea level small drumlin like features and morainic ridges and grounding zone wedges the combination of these features indicates that very large glacial ice masses extended into the central arctic ocean from surrounding north american and eurasian ice sheets several times during the quaternary ice shelves occupied large parts of the arctic ocean during glacial maxima and ice rises were formed over the chukchi borderland and portions of the lomonosov ridge more geophysical and sediment core data combined with modeling experiments are needed to reconstruct the timing and patterns of these events

early holocene deglaciation of the eastern coast of hudson bay abstract the final stage of deglaciation of hudson bay was a major holocene catastrophic event marked by the drainage of lake agassiz ojibway at 8 47 ka cal bp and the rapid collapse of the laurentide ice sheet previous work undertaken in the nastapoka river area eastern hudson bay demonstrated that during the relative sea level highstand that shortly followed the drainage of the lake the western margin of the quebec labrador ice sector rapidly retreated eastward to reach a stillstand position in a coastal hill range in this study an analysis of landsat 7tm images has allowed a mapping of large scale glacial landforms outwash deposits eskers flutings and de geer and rogen moraines between kuujjuaraapik se hudson bay and puvirnituq ne hudson bay the key results from this mapping are i ice contact outwash deposits mapped along the entire arc shaped coastline of the eastern hudson bay outline a major ice stillstand phase in the coastal hills that extended at least from kuujjuaraapik to inukjuak the presence of these hills allowed a stabilisation of the ice margin that led to the accumulation of thick and extensive ice contact submarine fans ii the position of these deposits on the down ice side west of large sets of flutings indicates an important phase of sediment delivery by a rapid ice flow phase toward a marine based ice margin iii a second system of outwash deposits observed farther inland indicates a subsequent phase of stabilisation of the ice margin during its retreat toward central quebec labrador

theoretical framework and diagnostic criteria for the identification of palaeo subglacial lakes abstract the antarctic ice sheet is underlain by numerous subglacial lakes which comprise a significant and active component of its hydrological network these lakes are widespread and occur at a range of scales under a variety of conditions at present much glaciological research is concerned with the role of modern subglacial lake systems in antarctica another approach to the exploration of subglacial lakes involves identification of the geological record of subglacial lakes that once existed beneath former ice sheets this is challenging both conceptually in identifying whether and where subglacial lakes may have formed and also distinguishing the signature of former subglacial lakes in the geological record in this work we provide a synthesis of subglacial lake types that have been identified or may theoretically exist beneath contemporary or palaeo ice sheets this includes a discussion of the formative mechanisms that could trigger onset of or drain subglacial lakes these concepts provide a framework for discussing the probability that subglacial lakes exist ed beneath other palaeo ice sheets indeed we conclude that the former mid latitude ice sheets are likely to have hosted subglacial lakes although the spatial distribution frequency and type of lakes may have differed from today s ice sheets and between palaeo ice sheets given this possibility we propose diagnostic criteria for identifying palaeo subglacial lakes in the geological record these criteria are derived from contemporary observations hydrological theory and process analogues and provide an observational template for detailed field investigations

late glacial stratigraphy and history of the gulf of st lawrence reply the three dimensional configuration of the quaternary sediments in the gulf of st lawrence is described based on analysis of 8000 km of high resolution seismic reflection data complemented by anal

drumlin formation related to inverted melt water erosional marks drumlin forms are described from maps and air photographs of a part of the athabasca plains northern saskatchewan three major forms spindle parabolic and transverse asymmetrical are recognized these forms which may show superimposed minor elements depart from classical descriptions of drumlins but are similar to moulds of erosional marks created by separated fluid flows assemblages of drumlins also show characteristics similar to those of erosional marks the form analogy between drumlins and moulds of erosional marks is carried to a conclusion that drumlins may be formed by the infilling of erosional marks created on the under side of glaciers by separated subglacial melt water flows estimates of specific discharge are obtained by means of an expected range of reynolds number geomorphological evidence is given for large scale erosion by subglacial melt water a discussion of the sedimentology stratigraphy and deformational structure of the interiors of drumlins shows that they may be explained by the erosional mark hypothesis this paper emphasizes the importance of melt water as a geomorphic agent and may have broad implications for ice sheet dynamics and profiles rates of deglaciation and the occurrence of bedrock thrusting by ice

seafloor evidence for ice shelf flow across the alaska beaufort margin of the arctic ocean new imagery of 14 100 km2 of seafloor along a 640 km stretch of the alaska and beaufort margins abm in water depths from 250 to 2800 m depicts a repetitive association of glaciogenic bedforms lineations and iceberg scours broad erosional bathymetric features and adjacent downslope turbidite gullies these bedforms have styles depths and orientations similar to features discovered earlier on the chukchi borderland up to 800 km northwest of the abm lineations occur across the surface of a flattened bathymetric bench interpreted to have formed by an ice shelf sliding along the continental slope and scraping the seafloor at temporary grounding locations the glacial geology of surrounding areas suggests that an ice shelf probably flowed from the mouths of overdeepened glacial troughs in the canadian arctic archipelago westward along the abm and across the chukchi borderland this curved pathway indicates an obstruction to ice flow in the central canada basin possibly caused by either a basin wide ice shelf or by a pile up of mega bergs originating from the eurasian side of the arctic ocean the ice shelf that affected the abm may have formed between oxygen isotopic stage 4 to 5b possibly correlating to an inferred intra stage 5 widespread beringian glaciation evidence for glaciogenic features on the abm corroborates suggestions that large ice volumes and extents existed in the arctic during pleistocene glacial periods these findings have far reaching implications for arctic climate studies ocean circulation sediment stratigraphy and the stability of circum arctic continental ice masses copyright 2007 john wiley sons ltd

high resolution seismo stratigraphy and sedimentological properties of late and postglacial sediments in lac guillaume delisle estuary and nastapoka sound eastern hudson bay lac guillaume delisle estuary and nastapoka sound are two sedimentary basins that recorded the late quaternary deglaciation on the eastern coast of hudson bay acoustic profiles reveal an average sediments thickness of 15 m in the estuary and 6 m in the sound these sediments reach 70 m thick in deep glacial troughs within the studied basins four seismo stratigraphic units overlying the acoustic basement were recognized unit 1 subaqueous ice contact and draped glaciomarine deposits associated with the quebec labrador ice sector qlis of the laurentide ice sheet lis and the tyrrell sea records the presence of a short ice marginal stillstand during glacial retreat unit 2 paraglacial and postglacial fluvial deltaic deposits and unit 3 postglacial silty deposits result from erosion of emerged sediments and redeposition in response to changes in relative sea level rsl finally unit 4 is composed of deformed deposits associated with a mass wasting event the stratigraphic sequence and the spatia

hudson bay river sediments and regional glaciation iii implications of mineralogical studies for wisconsinan and earlier ice flow patterns mineralogical studies of river sediments from the hudson bay and james bay lowlands suggest that the glacial erosion of pre devonian paleozoic carbonate rocks played an important role in the production of calcite enriched debris in the cape henrietta maria watershed ice flowing southwesterly across devonian basins in western hudson bay and the james bay lowlands would largely bypass the intervening cape area enrichment of iron in river sands of the cape watershed is attributed to proterozoic ferruginous sources now largely submerged under the waters of eastern hudson bay distributional patterns of carbonates and iron indicate that the dominant flow of ice from eastern hudson bay was southwesterly toward cape henrietta maria without major flow from the area of proterozoic bedrock into the nelson river watershed in the cape area iron enrichment due to proterozoic sources significantly overshadows possible contributions from siderite bearing devonian bedrock the fluvial sediment data are consistent with

a detailed lake level reconstruction shows evidence for two abrupt lake drawdowns in the late stage history of the eastern lake agassiz ojibway basin abstract glacial lake ojibway occupied large areas in northeastern ontario and northwestern quebec during the last deglaciation paleogeographic reconstructions depict lake ojibway and lake agassiz sharing a common water plane shortly before the final drainage of this lake 8200 years ago however the pre drainage surface elevation and extent of this large coalesced lake is based on scattered raised shorelines in the ojibway basin and poorly constrained geomorphological considerations which convey large uncertainties in lake level reconstructions and the attendant meltwater volume estimates used to assess the impact of this freshwater discharge here we address this issue by using 3098 elevation measurements of shorelines mapped on a lidar digital terrain model covering a key area in the ojibway basin our reconstruction is based on a gis model integrating the paleotopography which reinforces correlation of shorelines and the identification of lake levels the spatial distribution of shoreline elevation data points shows well defined clusters of shorelines aligned on distinct elevation ranges that delineate three widespread lake levels which are separated by two intervals with atypically low number of shorelines reflecting abrupt lake drawdowns this reconstruction considerably refines the sequence in the eastern ojibway basin and shows evidence for a two step drainage of lake agassiz ojibway the results provide constraints on the magnitude of the lake level drops and indicate that the pre drainage surface elevation of lake agassiz ojibway of earlier reconstructions was likely overestimated accordingly the configuration and structure of this lake stage should be re evaluated to that effect the new shoreline record provides an important framework for assessing late stage changes in lake levels across the agassiz ojibway basin which is a critical step towards the production of realistic models depicting the drainage of this large lake

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

sea floor morphology outside a grounded surging glacier brasvellbreen svalbard abstract acoustical profiling and bottom photography reveal several different sea floor morphological features adjacent to the grounded brasvellbreen glacier on svalbard northwestern barents sea some of the features and their distribution may be closely related to a major glacial surge in 1936 1938 and as such are valuable in identifying former surges in other locations a continuous wide ridge with a characteristic asymmetrical cross section running subparallel to the glacier is the end moraine defining the maximum extent of the surge a large part of the material forming this ridge is most likely rapidly deposited from meltwater during the surge a rhombohedral pattern of smaller mounds inside the ridge is probably an expression of relief in the glacier sole during the surge discontinuous arcuate ridges define local minor oscillations during retreat of the ice at a later stage iceberg plough marks are most frequent seaward of the end moraine their orientation is controlled by the combination of a coastal current offshore katabatic winds and topography superimposed on plough marks are secondary features such as a washboard pattern and striae most likely caused by push up of overconsolidated material during gouging and multi keel icebergs respectively bottom sediments observed in photographs and cores are loose pebbly muds with high variability in clast content resting on overconsolidated material probably basal till mud deposition presently prevails close to the glacier

late weichselian deglacial history of the svyataya saint anna trough northern kara sea arctic russia abstract marine sediment core and seismic records from the svyataya saint anna trough provide new insight into the distribution of late weichselian glacial coverage ice retreat pattern and post glacial environments in the northern barents and kara seas these records indicate that the saint anna trough was filled with grounded glacier ice which likely reached the shelf edge during the late weichselian maximum several radiocarbon dates suggest early deglaciation of the deep axial part of the trough prior to 13 3 ka two sandy beds in the deglacial section of the cores imply distinct pulses of iceberg calving and or melting which were probably associated with stepwise retreat of the ice margin morainic ridges and glacial sole markings in the western part of the saint anna trough indicate that the northern central barents sea was a site of a large ice mass during deglaciation a smaller ice cap is inferred for the northern kara plateau at later stages ice retreat on the western flank of the trough was directed towards franz josef land and was presumably facilitated by a separation of the barents sea and novaya zemlya ice domes deglaciation of the saint anna trough was completed by ca 10 ka high post glacial sediment fluxes between 10 and 8 ka were probably related to sea floor coastal erosion and or siberian river discharge during the rising sea level

vegetation and climate of auckland new zealand since ca 32 000 cal yr ago support for an extended lgm auckland occupies a climatically sensitive position close to a major biogeographic boundary in the southern mid latitudes a new pollen record from kohuora maar crater auckland displays vegetation and climatic changes for the past ca 32 000 years of particular interest are the inferred climatic patterns for the first part of the interval encompassing the last glacial maximum lgm the kohuora record corresponds closely with pollen records from other auckland sites indicating that the patterns observed are at least regional in extent it is also broadly consistent with a variety of palaeoenvironmental evidence from across new zealand including the glacial record from westland other palynological records from north island other palaeoecological records from the south island and aeolian quartz sequences from western north island these records show that glacial conditions prevailed across most if not all of new zealand during the interval ca 29 19 k cal yr bp longer and earlier than the lgm sensu stricto we suggest that the term extended lgm elgm may be more appropriate for the new zealand region within this predominantly cold interval the auckland pollen records indicate a climatic amelioration for the interval ca 26 24 k cal yr bp also consistent with other palaeocological data from canterbury that fall within a period of climate amelioration recognised between the first two elgm glacial advances in westland we refer to this warming interval as the elgm interstadial the ca 27 k cal yr bp kawakawa oruanui tephra is instrumental in most of these inter site comparisons and occurs after the first peak of elgm cooling in a short lived comparatively mild phase a subsequent return to apparently colder climate in the auckland records may indicate a volcanic cooling effect or more likely widespread landscape disturbance following this major eruption event strong correspondence between biotic responses glacial fluctuations and aeolian quartz deposition linked to major shifts in strength and latitudinal extent of the southern westerlies suggest that both the elgm and elgm interstadial may be more widely registered at least across the southern ocean support for this assertion comes from parallel investigations in western and southernmost south america and isotopic and palaeoecological records from southern ocean marine cores recent reconstructions of the globally averaged ice equivalent sea level history are in line with this evidence from the southern hemisphere suggesting that the elgm may have a global registration in light of these observations we suggest a re examination of the defined timing of the lgm along with renewed effort to establish climatic patterns during this period and understand their causes copyright 2007 john wiley sons ltd

lakes of the huron basin their record of runoff from the laurentide ice sheet the 189 000 km2 hur n basin is central in the catchment area f the present q s r lanrentian great lakes that now drain via the st lawrence river to the north atlantic ocean during deglaciation from 21 7 5 ka bp and owing to the interactions of ice margin positions crustal rebound and regional topography this basin was much more widely connected hydrologi cally draining by various routes to the gulf of mexico and atlantic ocean and receiving over flows from lakes impounded north and west of the great lakes hudson bay drainage divide early ice marginal lakes formed by impoundment between the laurentide ice sheet and the southern margin of the basin during recessions to interstadial positions at 15 5 and 13 2 ka be in i each of these recessions lake drainage was initially southward to the mississippi river and gulf of mexico in the first recession drainage subsequently switched eastward along the ice margin to the north atlantic ocean in the second recession drainage continued southward through the michigan basin and later eastward via the ontario basin and mohawk river valley to the north atlantic ocean during the final retreat of ice in the huron basin from 13 to 10 ka be proglacial lake drainage switched twice from the michigan basin and the mississippi river system to the i north atlantic via the ontario basin and mohawk river valley finally diverting to the champlain sea in the st lawrence river valley at about 11 6 ka be new seismo and litbo stratigraphic information with ostracode data from the offshore lacustrine sediments were integrated with the traditional data of shorelines uplift histories of outlets and radio carbon dated shallow water evidence of transgressions and regressions to reconstruct the water level history and paleolimnological record for the northern huron basin for the 11 7 ka bp period negative excursions in the 8 80 isotopic composition of ostracodes and bivalves in southern lake michigan southwestern lake huron and eastern lake erie indicate an influx of water from ice marginal lake agassiz in central north america about 11 ka be a major decline in water levels of the huron basin after 10 5 ka bp followed the high level main lake algonquin phase as ice receded and drainage was established through the north bay area to ottawa river valley during the subsequent mattawa stanley phase the lake level history was dominated by fluctuations of tens of meters highstands of the earliest oscillations whose origin is not clear might be related to some of the well known post algonquin shorelines after 9 6 ka be it is suggested that large inflows from lake agassiz and hydraulic damming in downstream outlets were the likely cause of the lake mattawa highstands a lowstand at 9 3 9 1 ka bp occurred when these inflows were diverted or impeded by an ice advance in the nipigon basin area while undiluted meltwater continued to enter the huron basin assemblages and isotopic composition of the ostracode fauna indicate very dilute meltwater during the lowstands as late as 7 5 ka be and precipitation runoff with comparatively higher dissolved solids dur ing the highstands we speculate that the water composition of the lake mattawa highstands was dom inated by the agassiz inflows by that time much of lake agassiz was remote from ice marginal envi ronments and the inflows were drawn from surface water of the southern sector of the lake which was largely supplied by runoff and dissolved solids from the exposed land area of western canada major inflows apparently ended about 8 ka be but northern proglacial lakes apparently continued as melt water persisted in the huron basin until about 7 5 ka bp the cessation of major inflows initiated the final lowstand in the huron basin and the present hydrological regime of local runoff

hudson bay river sediments and regional glaciation ii comparison of carbonate mineralogy of size fractions for ice movement inference comparison of the carbonate mineralogy of sand coarse silt fine silt and coarse clay fractions of river sediments from the hudson bay region demonstrates that dolomite is more abundant than calcite in the coarse silts but is less abundant than calcite in other size fractions in coarse silts dolomite commonly occurs as single crystals in the shape of well defined rhombs whereas calcite is present as equant to subequant grains few rhomb shaped crystals dolomite grains appear to have greater resistance to abrasion than calcite grains after particles have been reduced to sizes lying in the coarse silt range although differing physical properties may play a role it appears likely that the primary control on the particle size distributions of the carbonate minerals is their original crystal size in the source bedrock the calcite dolomite ratio for dolomite enriched coarse silt parallels the regional distribution observed for sand fine silt and coarse clay with highest values occurring in the cape

genesis of de geer moraines in finland abstract the proposed model of the genesis of de geer moraines in finland is based mainly on the distribution of the moraine areas in relation to the palaeohydrological environment and on the composition and two and three dimensional fabrics of the material in order to shed some light on the geochronological problem involved the distances between successive ridges in a number of de geer moraine series are also compared with clay varve data on deglaciation rates in finland granulometrically petrographically and morphometrically de geer moraine till does not differ significantly from tills of surrounding areas two dimensional fabrics stress orientations at right angles to the ridge crest and three dimensional analyses reveal the slope conformable character of pebble inclinations generally spacings of the de geer moraine ridges do not confirm annual deglaciation rates as conveyed by clay varve data it is suggested the moraines were formed in basal crevasses of the ice following active flow phases of a local surging nature during the quiescent phase of the surge cycle the ice subsided into a water soaked till mattress filling up basal cavities from the proximal or the distal side finnish de geer moraines are thus neither annual nor end moraines they are subglacial bedforms with no geochronological meaning except that they formed during one single surge cycle as the marginal zone of the ice sheet calved and thinned it was lifted by proglacial water and the whole group of moraines became free of ice almost simultaneously

abrupt deglaciation events and holocene palaeoceanography from high resolution cores cartwright saddle labrador shelf canada the uppermost quaternary sediments in cartwright saddle labrador shelf are acoustically laminated with reflectors that can be traced over long distances two piston cores from the saddle record changes in sediment and meltwater delivery from the northeast margin of the laurentide ice sheet lis during deglaciation variations in sediment properties indicate a similar history of sediment accumulation over the last 12 kyr the temporal sampling interval reaches decadal resolution in the last deglacial period 7 9 ka analyses of total carbonate content sediment magnetic variables foraminiferal species and stable isotope measurements on planktic foraminifers show that abrupt changes occurred ca 10 9 9 2 8 8 7 9 and 7 ka with 450 yr correction there was no distinct change in sediment character during much of the younger dryas chronozone in the 18o record the 8 8 ka event is a dramatic 1 shift toward lower values which we associate with the noble inlet glacial event within hudson strait we do not see the pronounced low 18o event at 7 1 ka reported off nova scotia but surprisingly neither the nova scotia records nor other records in the labrador sea capture the impressive 8 8 ka change serious consideration must be given to the final collapse of the lis as the cause of the 8 2 cal ka cold event recorded in greenland and northwest europe copyright 1999 john wiley sons ltd

icebergs rework shelf sediments to 500 m off antarctica icebergs and sea ice rework the sediments of high latitude shelves producing modern diamicts ice keel turbates unrelated to glacial proximity off antarctica sidescan sonar data indicate the presence of ice gouge features formed by the physical interaction between ice keels and the sea bed these are recognized as incisions a few metres deep and tens of metres wide in water depths up to 500 m on the submarine bank tops and slopes off wilkes land and in the weddell sea subcircular depressions 30 to 150 m in diameter a washboard pattern and hummocky bed features also represent iceberg resting sites the freshness of sea bed morphology nearby holocene sediment ponding and active hydraulic sedimentary processes indicate that the sea floor is being reworked by iceberg keels tabular iceberg drafts in excess of 330 m have been measured and modeling studies suggest that nontabular iceberg drafts of 500 m are possible we conclude that a modern ice keel turbate deposit in the form of a poorly stratified diamicton is probably widespread on that part 54 of the antarctic shelf less than 500 m deep

retreat signature of a polar ice stream sub glacial geomorphic features and sediments from the ross sea antarctica abstract three research expeditions to the ross sea antarctica resulted in collection of a dataset of more than 270 km of side scan and chirp sonar data more than 330 km of swath bathymetry and 3 5 khz data and 24 cores within a glacially carved trough the former ice stream flow path is divided into six zones covering a distance of approximately 370 km distinguished by unique stratigraphic signatures and geomorphic features an erosional surface with thin patchy lodgement till characterizes zone 1 this region is interpreted as having experienced relatively high basal shear stress conditions zones 2 3 and 4 are characterized by an erosional surface and thin time transgressive subglacial and grounding line proximal deposits that include back stepping moraines flutes transverse moraines and corrugation moraines these zones represent the transition between erosional and depositional regimes under the expanded lgm ice sheet material eroded from the inner shelf was transported toward the outer shelf possibly as a thin deforming till layer the two outer zones are depositional and include maximum grounding line zone 5 and pro glacial deposits that were overridden subsequently by the ice sheet zone 6 surface features include mega scale glacial lineations corrugation moraines and iceberg furrows ice in these zones is interpreted as having experienced relatively lower basal shear stress an extensional regime and faster flow this advance may have destabilized the ice sheet initiating local draw down and production of icebergs that furrowed the sea floor corrugation moraines are thought to represent annual retreat moraines constraining the retreat rate of the ice sheet across the continental shelf to a consistent 40 to 100 m a 1

water sheet outburst floods from the laurentide ice sheet field evidence and a theoretical model support the concept that during wisconsinan glaciation subglacial water sheet outburst floods issued from a large subglacial lake located in the hudson bay ba

on the formation of large subglacial lakes the role of subglacial water storage beneath continental ice sheets is investigated primarily for a deformable bed subglacial ponding is shown to occur under most regions of warm based ice sheets and large subglacial lakes can become established for example in the hudson bay basin the formation of large lakes depends upon the fact that the ice surface gradient is reduced once subglacial ponding occurs and upon the feedback between the reduced ice surface gradient and increased subglacial ponding subglacial ponding likely played a large role in determining the ice sheet topography during late deglaciation and in speeding up the deglaciation process

dynamics of the north american ice sheet complex during its inception and build up to the last glacial maximum the north american ice sheet complex played a major role in global sea level fluctuations during the late quaternary but our knowledge of its dynamics is based mostly on its demise from the last glacial maximum lgm a period characterised by non linear behaviour in the form of punctuated ice margin recession episodic ice streaming and major shifts in the location of ice divides in comparison knowledge of the pre lgm ice complex is poorly constrained largely because of the fragmentary nature of the evidence relating to ice sheet build up in this paper we explore the inception and growth of ice 120 20 ka using a glacial systems model which has been calibrated against a large and diverse set of data relating to the deglacial interval we make use of calibration data prior to the lgm but its scarcity introduces greater uncertainty which is partly alleviated by our large ensemble analysis results suggest that following the last interglaciation oxygen isotope stage ois 5e the ice complex initiated over the north eastern canadian arctic and in the cordillera within a few thousand years it then underwent rapid growth to an ois 5 maximum at 110 ka 5d and covered 70 of the area occupied by the lgm ice cover although only 30 by volume an ois 5 minimum is modelled at 80 ka 5a before a second phase of rapid growth at the start of ois 4 which culminated in a large ice complex at 65 ka almost as large as at the lgm subsequent deglaciation was rapid maximum modelled sea level contribution of 16 cm per century and resulted in an ois 3 minimum between ca 55 60 ka thereafter the ice complex grew towards its lgm configuration interrupted by several phases of successively less significant mass loss our results support and extend previous inferences based on geological evidence and reinforce the notion of a highly dynamic pre lgm ice complex e g with episodes of 10 s m of eustatic sea level equivalent in 50 but even the thin ois 5 ice sheets exhibit fast flow features several 1000 m a 1 in major topographic troughs notwithstanding the severe limitations imposed by the use of the shallow ice approximation we note that most fast flow features generated prior to the lgm correspond to the location of known ice streams during deglaciation i e in major topographic troughs and over soft sediments at the southern and western margins moreover the modelled flux of these ice streams sensu lato appears to be non linearly scaled to ice sheet volume i e there is no evidence that decay phases were associated with significantly increased ice stream activity this hypothesis requires testing using a model with higher order physics and future modelling would also benefit from additional pre lgm constraints e g dated ice free margin positions to help reduce and quantify uncertainties

holocene deltaic sedimentation along an emerging coast nastapoka river delta eastern hudson bay quebec eastern hudson bay is characterized by falling relative sea level as a result of post glacial isostatic rebound which makes the region a natural laboratory for rapid forced regression where the evolution of deltaic systems and offshore sedimentation patterns can be studied a multidisciplinary approach involving airphoto analysis offshore geophysical surveys sediment coring and facies and diatom analyses was used in this study of the nastapoka river delta the delta has formed as a result of the fluvial erosion of emerged quaternary sediments but is mainly subaqueous offshore in the prodelta zone the oldest deposits are glaciomarine laid down when the ice front of the receding laurentide ice sheet stood on the nastapoka hills some 7700 6800 years bp lateral equivalents of this glaciomarine unit are presently exposed on land the shallow water platform of the delta shows a thin surficial unit of wave worked sand that overlies fine grained deeper water deposits derived from erosion of clay soils

bedforms of the canadian eastern seaboard a comparison with global occurrences this paper presents a compilation of sedimentary bedforms identified from acoustic and seismic records collected over the southeastern canadian continental shelf in order to make the compilation it was found necessary to firstly review and synthesise the various terminologies used to describe the bedforms found and thereafter to relate the subsequent terminology to any diagnostic generic characteristic identifiable from the records sand waves are considered to be those forms that are composite in nature and are generated solely by the action of superimposed megaripples these latter features are identifiable adopting the classification of dalrymple et al 1978 which proves adequate for the acoustic differentiation of 2 d and 3 d types though we observed a greater coherence in bedform spacing of the 2 d types than reported hitherto sand ridges were adequately defined and recognised using the description of swift et al 1978 with respect to storm generated ridges and that of off 1963 and others with respect to tidal current ridges such ridges appear not to be uniquely described by ratios of their metrics the bedforms on the southeastern canadian continental shelf are abundant and wide spread virtually all types of bedforms recognisable on the u s shelf are present to the north the majority of these bedforms appear to be storm generated and are considered intermittently active many of the sand waves s s have no measureable relief though retaining their distinctive spatial geometry both active and moribund sand ridges were found of these ridges both tidal and storm generated types were identified the storm generated ridges were further broken down into shoreface connected ridges and offshore ridges a metrical analysis of the various bedforms show that a differentiation into stable bed phases can be made using height length ratios provided the bedforms are active and fully developed there is some overlap between megaripples and small sand waves and indeed between 2 d and 3 d megaripples yet the distinction is good between sand waves and sand ridges even moribund types sand ribbons in general can be confused with moribund sand waves and megaripples a detailed morphological examination is required to distinguish each feature data from sand ridges of the eastern canadian shelf combined with data from similar features found globally shows that ridge heights tend to cluster into three distinctive modes these modes are at heights of 7 13 and 27 m the first mode is correlated with storm generated ridges the second with tidal current ridges and the third possibly with submerged barrier islands

aquisgrani terrae motus factus est part 2 evidence for medieval earthquake damage in the aachen cathedral germany abstract during archaeological and geotechnical investigations the carolingian part of the aachen cathedral germany was excavated the aachen cathedral was the first building in germany to join the unesco world heritage list in the rock walls of the fundament and medieval floors open cracks were found subsidence of the mortar floor of about 50 cm with lateral dragging which was reconstructed during the construction of the cathedral can be observed the main building is founded on devonian limestones and shales pleistocene loess and roman urban debris the loess and loamy sediments show angular cracks and fragments which are not related to permafrost features but are interpreted as shear and extensional fractures some of the cracks are filled with black clay from below as they open downwards these structures are interpreted as injection features caused by thixotropy of clays open cracks lateral spread and injections structures occur usually during earthquakes with a magnitude higher than 5 5 the historical german earthquake catalogues provide three important passages for historical earthquakes in the region of aachen both fall into a relatively short time interval one occurred in winter 803 ad another one in 823 ad and the last one in 829 ad between ash wednesday and easter both notes tell of earthquake shaking and significant structural damage and fatalities this and the constructional history allowed dating of the event favouring the 803 ad event as the causative damaging earthquake observed in the aachen cathedral

towards a sediment and organic carbon budget for hudson bay abstract a preliminary sediment and organic carbon budget is constructed for the hudson bay marine system based on published literature and new data collected from nine rivers and 13 sediment boxcores the budget considers the main inputs of terrestrial and marine components of sediment and organic carbon and the main sinks sediment burial and losses oxidation export to hudson strait sedimentation rates 0 032 0 23 g cm 2 yr 1 were estimated from 210 pb profiles and a sediment advection diffusion model in our cores and in two cores collected previously by lockhart et al lockhart w l et al 1998 fluxes of mercury to lake sediments in central and northern canada inferred from dated sediment cores biogeochemistry 40 163 173 sedimentation rates implied by the 210 pb profiles were verified against profiles of 137 cs and for some of the cores contaminant pb the sediment sink in hudson bay was estimated at 138 64 10 6 t a 1 by applying the average sedimentation rate to the area of active sedimentation in the bay 15 of the seafloor calculated according to a regional sedimentation map developed from seismic data josenhans h w et al 1988 preliminary seismostratigraphic and geomorphic interpretations of the quaternary sediments of hudson bay natural resources canada the known sediment sources to hudson bay include river input 11 6 6 10 6 t a 1 subaerial coastal erosion 8 4 10 6 t a 1 marine primary production 24 2 17 10 6 t a 1 and atmospheric deposition 0 5 10 6 t a 1 based on the available data the modern sediment input 44 3 18 10 6 t a 1 represents only about one third of the apparent sediment sink in hudson bay resuspension and lateral transport of shallow water deposits primarily glacigenic and winnowing from topographic highs likely consequences of the exceptional continuous relative sea level rsl fall in hudson bay provides a plausible source for the 116 10 6 t a 1 imbalance using organic carbon and 13 c values in the cores we estimate the burial of particulate organic carbon poc in sediments at 1 3 0 6 10 6 t c a 1 of which 80 is marine the importance of reworked glaciomarine carbon to the burial flux is difficult to estimate because modern autochthonous primary production provides a large source of poc to the system 16 1 7 10 6 t c a 1 and its degradation is not well constrained the 0 58 10 6 t c a 1 terrestrial carbon estimated to be transported as part of the redistributed sediment load accounts for almost one half the total terrigenous poc inputs to the bay if sediment and oc supply and burial in the hudson bay system are presently responding to the history of isostatic rebound as proposed here the task of predicting and measuring the additional consequences of river diversions and climate change e g sea ice permafrost runoff is rendered considerably more difficult

the nastapoka drift belt eastern hudson bay implications of a stillstand of the quebec labrador ice margin in the tyrrell sea at 8 ka bp during deglaciation of eastern hudson bay the western margin of the quebec labrador sector of the laurentide ice sheet came to a stillstand about 8 14c ka bp along the nastapoka hills a series of topographic highs along the bay these hills are the northward continuation of the eastern hudson bay cuesta system it left a drift belt consisting of ice contact submarine fans along the western slopes of the hills small frontal moraines on hilltops and grounding line deposits on sills between the hills geomorphological sedimentary and radiometric evidence suggest that the stillstand responsible for deposition of the nastapoka drift belt was either entirely or partly synchronous with the deposition of the sakami moraine farther south there was a period when these two morainic systems marked a continuous ice margin these stillstands occurred due to reduction of ablation at the ice margin in the nastapoka hills ablation slowed down when the ice margin was anchored on higher relief and stood at a region

subglacial imprints associated with the isolation and decay of an ice mass in the lower lough erne basin co fermanagh nw ireland high resolution chirp sub bottom profiler and side scan sonar data record the final phases of ice margin activity in the lower lough erne basin at the end of the last cycle of quaternary glaciations in ireland relative to the terrestrial glacial landforms the features in the lough are smaller in scale and are considered to represent local ice mass dynamics that followed regional scale events four phases are identified 1 after the last ice sheet wide readvance associated with the killard point stadial between 15 0 and 14 1 14 c ka bp stagnation zone retreat resulted in isolation of a residual ice block in the lower lough erne basin 2 proglacial waters developed coeval with retreat of the western margin of the ice block drawdown induced localized surging and the generation of push features and lineations 3 squeeze up features reflecting a heavily crevassed ice margin mark the quiescent phase of the local surge cycle 4 iceberg grounding pits and keel marks record calving and rapid disintegration of the lough erne ice margin the well preserved glacigenic features observed in the lake basin suggest formation by a succession of mechanisms that were too short lived to obliterate the underlying evidence of ice margin dynamics

seabed geodiversity in a glaciated shelf area the baltic sea abstract geodiversity describes the heterogeneity of the physical terrain we have performed basin wide geodiversity analysis on a glaciated epicontinental seabed to assess geodiversity measures and patterns locate areas with high geodiversity and draw conclusions on contributing processes geodiversity quantification is a rather new topic and is mainly practiced in land areas we applied geodiversity methods developed for terrestrial studies to a seabed environment three geodiversity parameters including the richness patchiness and geodiversity index of the baltic sea were assessed in a gis environment based on broad scale datasets on seabed substrates structures and bedrock a set of environmental and geological variables which were considered to reflect geological processes under seabed conditions were compared with the geodiversity to identify some of its drivers we observed differences in the geodiversity levels of the baltic subbasins which are mainly due to basement type bedrock roughness shore density and glacier derived processes the geodiversity of the baltic sea generally increases from south to north and from open sea to high shore density areas archipelagos crystalline bedrock areas provide more diverse seabed environments than sedimentary rock areas the analysis helps to inform scientists marine spatial planners and managers about abiotic conservation values the dynamics of the seabed environment and potential areas with elevated biodiversity

lake agassiz drainage bracketed holocene hudson bay ice saddle collapse abstract the duration and intensity of the early holocene freshening events has been explained by subglacial outburst s from lake agassiz the collapse of a laurentide ice sheet saddle overlying hudson bay and or a combination of the two events our field evidence provides new radiocarbon ages and geomorphologic observations to assess the deglacial history of this important region allowing for revision of the sequence of events we show that the collapse of the hudson bay ice saddle in southwestern hudson bay occurred between 8 57 0 28 ka bp and 8 11 0 19 ka bp this event was preceded by at least one subglacial drainage event through numerous newly mapped subglacial channels onshore of southwestern hudson bay lake agassiz may have experienced multiple subglacial drainage events prior to the final hbis collapse accounting for the timing discrepancies in freshwater cooling observed in the north atlantic importantly this new work links the chronology of events on the southwest land based side of the hbis to the northeast marine based side of the ice sheet additionally this work provides a potential analog for the behaviour of other ice sheets whose beds lie well below sea level such as the west antarctic ice sheet during periods of warming climate

postglacial emergence of ungava peninsula and its relationship to glacial history a series of 178 radiocarbon dates of late glacial and postglacial age from raised marine terraces on the hudson strait hudson bay and ungava bay coasts permit a new synthesis of deglaciation h

late glacial and post glacial deposition in a large low relief epicontinental basin the northern baltic sea this paper presents a model of late glacial and post glacial deposition for the late neogene sedimentary succession of the archipelago sea in the northern baltic sea four genetically related facies associations are described i an ice proximal acoustically stratified draped unit of glaciolacustrine rhythmites ii an onlapping basin fill unit of rotated rhythmite clasts in an acoustically transparent to chaotic matrix interpreted as debris flow deposits iii an ice distal acoustically stratified to transparent draped unit of post glacial lacustrine weakly laminated to homogeneous deposits and iv an acoustically stratified to transparent unit of brackish water organic rich sediment drifts the debris flow deposits of the unit 2 pass laterally into slide scars that truncate the unit 1 they are interpreted to result from a time interval of intense seismic activity due to bedrock stress release shortly after deglaciation of the area ice berg scouring and gravitational failure of oversteepened depositional slopes may also have contributed to the debris flow deposition comparisons to other late neogene glaciated basins such as the hudson bay or glacial lakes formed along the laurentide ice sheet suggest that the archipelago sea succession may record development typical for the deglaciation phase of large low relief epicontinental basins the carboniferous permian glacigenic dwyka formation in south africa may provide an ancient analogue for the studied succession chronological control for the studied sediments is provided by the independent palaeomagnetic and ams 14c dating methods in order to facilitate dating of the organic poor early post glacial deposits of the northern baltic sea the 10 000 year long lake nautajarvi palaeomagnetic reference chronology ojala saarinen 2002 is extended by 1200 years

postglacial paleoceanography of hudson bay stratigraphic microfaunal and palynological evidence cores containing representative sequences of postglacial sediments in northern and southern hudson bay were analyzed for their microfaunal foraminifers and ostracods and palynological dinocysts

the 8200 year b p event in the slope water system western subpolar north atlantic 1 stable isotope trace metal alkenone paleothermometry and radiocarbon methods have been applied to sediment cores in the western subpolar north atlantic between hudson strait and cape hatteras to reveal the history of climate in that region over the past 11 kyr we focus on cores from the laurentian fan which is known to have rapid and continuous accumulation of hemipelagic sediment although results among our various proxy data are not always in agreement the weight of the evidence alkenone sea surface temperature sst 18o and abundance of globigerinoides ruber indicates a continual cooling of surface waters over laurentian fan from about 18 c in the early holocene to about 8 c today alternatively mg ca data on planktonic foraminifera indicate no systematic change in holocene sst the inferred long term decrease in sst was probably driven by decreasing seasonality of northern hemisphere insolation two series of proxy data show the gradual cooling was interrupted by a two step cold pulse that began 8500 years ago and lasted about 700 years although this event is associated with the final deglaciation of hudson bay there is no 18o minimum anywhere in the labrador sea yet there is some evidence for it as far south as cape hatteras finally although the 8200 year b p event has been implicated in decreasing north atlantic ventilation and hence widespread temperature depression on land and at sea we find inconsistent evidence for a change at that time in deep ocean nutrient content at 4 km water depth