past ice sheet flow east of svalbard inferred from streamlined subglacial landforms the pattern of late weichselian ca 20 ka ice flow in the northern barents sea is not well known due mainly to a lack of marine data east of svalbard several years with little summer sea ice have allowed acquisition of swath bathymetric imagery of well preserved subglacial landforms characterizing late weichselian ice flow directions over 150 000 km2 of the northwestern barents sea we show that a major ice dome was located on easternmost spitsbergen or southern hinlopen strait at least 500 km west of its previously inferred position in the northern barents sea this dome controlled the regional flow pattern ice flowed eastward around kong karls land into franz victoria trough and north through hinlopen strait an ice dome west of kong karls land is required to explain the observed ice flow pattern but does not preclude an additional ice dome to the southeast discrepancies with earlier ice sheet reconstructions reflect the lack of previous seafloor observations with evidence limited mainly to past ice loading and postglacial rebound the new pattern of ice flow directions shows predominantly eastward rather than northward flow with franz victoria trough a major drainage pathway with a full glacial balance flux of 40 km3 yr 1

assemblages of submarine landforms produced by tidewater glaciers in svalbard 1 high resolution swath bathymetry from the marine margins of several svalbard tidewater glaciers shows an assemblage of submarine landforms that is probably linked to glacier surging these landforms are essentially unmodified since their initial deposition over the past hundred years or so because they have not been subjected to subaerial erosion or periglacial activity swath images comprise an assemblage of superimposed landforms allowing reconstruction of relative age of deposition 1 large transverse ridges interpreted as recessional moraines overridden by a subsequent ice advance 2 a series of curvilinear streamlined bedforms orientated parallel to former ice flow interpreted as lineations formed subglacially during rapid advance 3 large terminal ridges marking the farthest extent of ice at the last advance with flow lobes immediately beyond interpreted as submarine debris flows 4 a series of interconnected rhombohedral ridges interpreted as a product of soft sediment squeezing into crevasses formed at the glacier bed probably formed during immediate post surge stagnation and 5 a series of fairly evenly spaced small transverse ridges interpreted as push moraines produced annually at tidewater glacier termini during retreat a simple descriptive landsystem model for tidewater glaciers of probable surge type is derived from these observations we also show that megascale glacial lineations can form not only beneath large ice streams but are also produced beneath surging tidewater glaciers lying on deforming sedimentary beds

size and shape characteristics of drumlins derived from a large sample and associated scaling laws abstract ice sheets flowing across a sedimentary bed usually produce a landscape of blister like landforms streamlined in the direction of the ice flow and with each bump of the order of 102 to 103 m in length and 101 m in relief such landforms known as drumlins have mystified investigators for over a hundred years a satisfactory explanation for their formation and thus an appreciation of their glaciological significance has remained elusive a recent advance has been in numerical modelling of the land forming process in anticipation of future modelling endeavours this paper is motivated by the requirement for robust data on drumlin size and shape for model testing from a systematic programme of drumlin mapping from digital elevation models and satellite images of britain and ireland we used a geographic information system to compile a range of statistics on length l width w and elongation ratio e where e l w for a large sample mean l is found to be 629 m n 58 983 mean w is 209 m and mean e is 2 9 n 37 043 most drumlins are between 250 and 1000 metres in length between 120 and 300 metres in width and between 1 7 and 4 1 times as long as they are wide analysis of such data and plots of drumlin width against length reveals some new insights all frequency distributions are unimodal from which we infer that the geomorphological label of drumlin is fair in that this is a true single population of landforms rather than an amalgam of different landform types drumlin size shows a clear minimum bound of around 100 m horizontal maybe drumlins are generated at many scales and this is the minimum or this value may be an indication of the fundamental scale of bump generation proto drumlins prior to them growing and elongating a relationship between drumlin width and length is found with r2 0 48 and that is approximately w 7 l 1 2 when measured in metres a surprising and sharply defined line bounds the data cloud plotted in e w l space and records a scale dependent maximum elongation limit approximated by emax l1 3 when l measured in metres for a given length for some reason as yet unknown drumlins do not exceed the elongation ratio defined by this scaling law we also report and compare our statistics to an amalgamated sample 25 907 drumlins of measures derived from around 50 published investigations any theory must be able to explain the drumlin statistics and fundamental scaling properties reported herein and they thus provide powerful tests for drumlin modelling

deglaciation of a marine based ice sheet late weichselian palaeo ice dynamics and retreat in the southern barents sea reconstructed from onshore and offshore glacial geomorphology abstract marine and terrestrial datasets swath bathymetry 2d and 3d seismic and remote sensing data are used to map the megascale glacial geomorphology of the southern barents sea seafloor northern fennoscandia and the kola peninsula giving new insights into the dynamics and behaviour of the barents sea ice sheet during retreat the glacial geomorphology indicates clear spatial and temporal variations in ice dynamics with evidence for both active ice streaming and frozen bed conditions at the maximum and during deglaciation a five stage reconstruction of the late weichselian deglaciation is proposed at the late weichselian maximum ice covered the whole of the barents sea shelf and the configuration and dynamics of the ice sheet were controlled by the bjornoyrenna bear island trough ice stream this was fed by source areas in the central and north eastern barents sea and in the fennoscandian mainland deglaciation was initiated along the western continental margin available dating results show that this occurred after 19 cal ka bp the bjornoyrenna ice stream retreated rapidly ice margin retreat rates of 275 m a 1 but was periodically grounded as evidenced by a well developed series of grounding zone wedges this was followed by an advance of two short lived ice streams from the eastern sector of the ice sheet into the south western barents sea these ice streams advanced and retreated very rapidly with no evidence for ice margin standstills correlation to dated cores suggests an age of around 16 000 cal ka bp for this readvance the period of operation of these two ice streams was coincident with maximum ice extent along the eastern margin in russia the western barents sea ice margin then retreated onshore with deglaciation continuing at a reduced rate the initiation of deglaciation coincided with rising global eustatic sea level acceleration of calving due to grounding line floatation rapidly opened up a major calving bay in bjornoyrenna encouraging rapid loss of the marine based ice the retreat rate stabilised only once the ice sheet retreated onshore and calving ceased we note that the observed pattern of rapid retreat with high variability in ice streaming for the marine based barents sea ice sheet is similar to that of the marine based sectors of the late weichselian british laurentide and west antarctic ice sheets

second order segmentation the relationship between volcanism and tectonism at the mar 38 n 35 40 n deep tow sidescan sonar data acquired along 240 km of the mid atlantic ridge mar between 35 40 n and 38 n have been combined with new bathymetric compilations and used to establish the recent tectonic and volcanic history of six second order segments and their bounding non transform offsets ntos the segments show a range of volcanic and tectonic types but in general the northernmost segments i e those with greater influence from the azorean hotspot are shallower and more volcanically robust than those to the south with hydrothermal activity in segment centres for example menez gwen and lucky strike nonetheless this generalisation requires some modification due to temporal variations in the balance between magmatic supply and tectonic dismemberment the ntos are broad right stepping discontinuities locally up to 25 km wide and accommodate offsets between 10 and 50 km the discontinuities are mostly sediment floored and link the spreading segment tips with a range of structures these include locally dense arrays of en echelon extensional normal faults short lengths of linear strike slip fault strands occasionally cutting basement blocks apparently stranded within the offsets basement blocks within the offsets are cross cut by complexes of intersecting faults suggesting that deformation is distributed across the zone the pervasive faulting taking place at the ntos favours fluid circulation and associated hydrothermal activity as at the rainbow site at 36 17 n

the death mask of the antarctic ice sheet comparison of glacial geomorphic features across the continental shelf abstract multibeam swath bathymetry data seismic lines and shallow cores were collected seaward of all of the major drainage outlets of the antarctic ice sheet from the pennell coast of north victoria land to the northwestern weddell sea the results show that during the last glacial maximum the ice sheet extended onto the outer shelf in all areas to the shelf break in many swath bathymetry and deep tow sidescan sonar data from the continental shelf also record the geomorphology left by the retreating ice sheet glacial troughs occur offshore of all major glacial outlets in each drainage area except for parts of the ross sea the inner shelf is characterized by acoustic basement interpreted as crystalline substrate the geomorphology of these inner shelf areas consists of erosional features such as grooves that show that ice flow tended to follow the structural grain of the bedrock outer shelf areas are floored by sedimentary substrate where the direction of ice flow was more directly offshore and depositional features characterize the seafloor in these areas the signature of the grounded ice consists of till deposits and large scale geomorphic features mega scale glacial lineations drumlins occur within the region of contact between crystalline and sedimentary substrates meltwater channels also have been imaged in both inner and outer shelf settings while the presence of meltwater across the shelf has long been suspected we present here the first multibeam image of a meltwater channel on the outer continental shelf of antarctica at the shelf break gullies are in all areas where we know ice reached the shelf break we note the remarkable similarity in form of mega scale glacial lineations observed on the outer shelf over sedimentary substrate across all areas surveyed typically measuring 200 600 m crest to crest this suggests that the shape of these landforms is governed by the same process in each drainage area and that process was occurring under a large area of the ice sheet the erosional and transitional features show much variability in form and distribution

prediction of iceberg trajectories for the north atlantic and arctic oceans icebergs are a well known hazard for shipping their study also provides information about diverse geophysical processes as varied as ocean circulation air sea fluxes calving rates of glaciers or the mass balance of ice sheets as a first step to obtaining this information from iceberg data we have developed a model of iceberg drift driven by ocean and atmospheric forcing derived from general circulation models we have applied the drift model to a distribution of typical icebergs released from the main tidewater glaciers of the north atlantic and arctic oceans we demonstrate that the main driving force of iceberg motion is rooted in the unsteady component of oceanic advection from simulated trajectories we are able to reproduce the observed southwards limit of iceberg penetration and demonstrate sometimes surprising geographical links between iceberg origin and ultimate melting zones

sonography of a glaciated continental shelf sonographs of the inner continental shelf off halifax nova scotia show a large part of the inner shelf area consisting of exposed bedrock in which the inferred sequence of structural events is clearer than the record on land ribbed moraines overlie eroded drumlins and provide new information on the deglaciation history morphologic features allow a precise definition of the maximum postglacial lowstand of sealevel at 65 to 70 m a 1000 km 2 area in eastern canada was surveyed with a multibeam sounder em100 manufactured by simrad of norway a 100 coverage of the sea floor was achieved with 50 to 100 m track spacing and position control was achieved using the differential global positioning system dgps with an accuracy of 1 2 m data were corrected for ship motion gridded at a 10 m spacing and displayed as obliquely illuminated relief image the sonograph revealed characteristics of the sea bed in detail for the interpretation of bedrock and surficial structures and processes the bathymetric images may be more useful for geologic mapping than air photographs and satellite images on nearby land where vegetation commonly obscures the geologic features

stabilization of glaciers terminating in closed water bodies evidence and broader implications 1 the behavior of glaciers terminating in deep water is determined by the interaction of buoyancy iceberg production and the sensitivity of ice flow to subtle changes in resistance at the glacier bed modeling efforts assume rapid evacuation of icebergs but some glaciers terminate in closed basins where icebergs may accumulate multibeam bathymetric survey of a glacial lake in iceland that received outlet glaciers during the little ice age document near parallel flow of narrow ice fingers that extended up to 1 km beyond the grounding line these previously unseen features apparently occurred when iceberg production exceeded iceberg melt resulting in iceberg buttressing of the ice margin similar stabilization of ice flow may resolve long standing debates about past continental ice sheet behavior including the rapid readvance of the laurentide ice sheet into lake superior ca 11 ka and the genesis of glacial flutes observed in the central arctic ocean basin

comparison of trends of iceberg scour marks with iceberg trajectories and evidence of paleocurrent trends on saglek bank northern labrador shelf high resolution seismic and sidescan sonar surveys on saglek bank indicate extensive areas of iceberg scoured sea bottom and provide data for an analysis of 6075 iceberg scour marks in 537 samples each of 0 25 km by 2 0 km area the general trends of iceberg scours measured on sidescan sonographs are comparable to iceberg trajectories which are mostly controlled by currents on saglek bank iceberg scour and iceberg drift directions are generally northwest southeast straight scours predominate on the shelf edge reflecting the influence of unidirectional oceanic labrador currents bank top scours are commonly curved reflecting the influence of slower moving water more subject to the effects of rotary tidal currents and storms this difference in dispersion of scour trends between the bank top and shelf edge is due to the relative strengths of variable tidal and storm driven currents and unidirectional oceanic currents pack ice forces may also influence iceberg movement modern icebergs scour the she

large scale ice moulding a discussion of genesis and glaciological significance abstract landsat images reveal a previously unsuspected large scale pattern of streamlining within drift which comprises a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain consideration of the genesis and glaciological significance of such landforms leads to a number of conclusions it is suggested that mega scale glacial lineations were formed under conditions of fast ice flow and their presence may thus record former locations of ice streams or surge events many lineations of varying scales display a pattern that reveals that they were not formed in sub marginal positions extensive sets of lineations must have been formed approximately synchronously thus indicating that lineation generation occurs over a wide range of glaciodynamic conditions from sub marginal positions to interior portions of ice sheets subglacial deformation of tills has been widely invoked to account for rapid glacier motion criteria for identifying such tills are restricted to structures viewed in cross section and it is thus hard to assess how widespread the processes of deformation may have been lineations provide a surface marker of structure that records subsequent deformation from other ice flow events it is argued that the palaeo flow record including cross cutting patterns provides the surface or plan expression of subglacial deformation the degree of modification to pre existing lineations should permit the identification of zones favoured by deformation and thus assist in an assessment of how pervasive deforming bed processes were in influencing ice sheet dynamics

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

submarine glacial landforms and rates of ice stream collapse the rate of deglacial ice sheet retreat across polar continental shelves and possible ice stream collapse and sea level rise has been much debated high resolution imagery of seafloor morphology is available for many polar shelves and fjords the rapidity of ice retreat is inferred from diagnostic assemblages of submarine landforms produced at ice stream sedimentary beds these landforms exposed by ice retreat across high latitude shelves demonstrate that deglaciation occurs in three main ways rapidly by flotation and breakup episodically by still stands and or grounding events punctuating rapid retreat or by slower retreat of grounded ice submarine landform assemblages imply through the presence of grounding zone wedges overprinting mega scale glacial lineations on many polar shelves that ice stream retreat is more often episodic than catastrophic these observations provide a robust test of the ability of numerical models to predict the varied response of ice sheet basins to environmental changes

marginal formation of de geer moraines and their implications to the dynamics of grounding line recession de geer moraine ridges occur in abundance in the coastal zone of northern sweden preferentially in areas with proglacial water depths in excess of 150 m at deglaciation from detailed sedimentological and structural investigations in machine dug trenches across de geer ridges it is concluded that the moraines formed due to subglacial sediment advection to the ice margin during temporary halts in grounding line retreat forming gradually thickening sediment wedges the proximal part of the moraines were built up in submarginal position as stacked sequences of deforming bed diamictons intercalated with glaciofluvial canal infill sediments whereas the distal parts were built up from the grounding line by prograding sediment gravity flow deposits distally interfingering with glaciolacustrine sediments the rapid grounding line retreat ca 400 m yr 1 was driven by rapid calving in turn enhanced by fast iceflow and marginal thinning of ice due to deforming bed conditions the spatial distribution of the moraine ridges indicates stepwise retreat of the grounding line it is suggested that this is due to slab and flake calving of the ice cliff above the waterline forming a gradually widening subaqueous ice ledge which eventually breaks off to a new grounding line followed by regained sediment delivery and ridge build up less

bottom currents interpreted from iceberg ploughmarks revealed by multibeam data at tromsoflaket barents sea abstract multibeam data have been acquired on eastern tromsoflaket a bank in the southwestern barents sea comprising a plateau detailed examination of the multibeam backscatter data however reveals a high variability of sediments especially in and around iceberg ploughmarks we observe coarser sediments on the levees either side of the ploughmarks than inside the furrows moreover we frequently note asymmetries in the distribution of fine sediments across these ploughmark features drawing inspiration from previous studies of bottom currents which use the distribution of sediments across bedforms e g sand waves we have interpreted the direction of bottom currents on tromsoflaket by examining the local distribution of fine sediments across iceberg ploughmarks which are the most prominent bedform in this area further integration of our results with existing grain size current speed models have allowed estimates of the bottom current speeds to be obtained such interpretations are particularly valuable in this area where availability of bottom current measurements sparse our approach makes valuable and novel use of multibeam data and results show good agreement with the limited set of available current data and models we can identify near bottom pathways for the norwegian atlantic current and norwegian coastal current the two major current systems in this region and the patterns of circulation help to explain the sedimentation regime and identify recent erosion and deposition areas

subglacial bedforms an introduction abstract this introduction provides of a brief review of a set of papers based on a special symposium held at the xii inqua congress ottawa 1987 attention is also drawn to the major concepts and controversies behind the formation of subglacial bedforms and to major issues for future research

late quaternary sedimentation on the southwestern scotian slope eastern canada relationship to glaciationgeological survey of canada contribution 20070176 the sedimentary record on continental slopes has the potential to preserve a record of glacial retreat on the adjacent continental shelf the glacial history of the southwestern part of the scotian shelf is poorly known air gun and high resolution sparker profiles and numerous sediment cores up to 10 m long have been used to determine the character of sedimentation on the southwestern scotian slope since the last glacial maximum lgm seismic reflection profiles show that glacial till was deposited at shallow depths on the upper continental slope and correlation to dated piston cores farther downslope show that this till dates from the lgm slope sedimentation at this time was dominated by local ice and deposited as plume fallout and turbidites progressively increasing importance of red brown sediment derived from glacial supply to laurentian channel indicates retreat of ice from the shelf edge and diminishing supply of proglacial sediment from the calving embayment in the mid scotian shelf with the

identification and preservation of landforms diagnostic of past ice sheet activity on continental shelves from three dimensional seismic evidence ice ages have occurred a number of times in earth9s history and are important in understanding changes in long term climate however it is difficult to demonstrate the presence of ice sheets in the ancient record because their sedimentary products can resemble those from nonglacial processes e g debris flows diagnostic large scale glacial landforms produced beneath ice sheets and preserved on continental shelves after deglaciation can establish a glacial origin three dimensional seismic evidence from the 2 7 ma naust formation norwegian margin illustrates several glacial landforms that are also commonly occurring features on modern high latitude shelves 1 streamlined mega scale lineations produced by fast flowing ice streams 2 ploughmarks formed by iceberg keels and 3 regularly spaced transverse ridges or push moraines formed during ice retreat we have found for example buried ice keel ploughmarks on a paleoshelf dating to ca 2 ma norwegian margin seismic stratigraphy data show that ice advanced and retreated many times and some paleoshelf surfaces were preserved such paleosurfaces must survive ocean basin destruction for glacial landforms to be useful in identification of ancient depositional environments

distribution of glacial geomorphic features on the antarctic continental shelf and correlation with substrate implications for ice behavior surveys were conducted seaward of all the major drainage outlets of the antarctic ice sheet from the pennell coast north victoria land to marguerite bay antarctic peninsula the results show that the ice sheet extended onto the outer shelf glacial troughs occur offshore of all major glacial outlets where the substrate is crystalline bedrock ice flow tended to follow the structural grain of the bedrock deposited little sediment and eroded the underlying bedrock where ice flowed over relatively soft more easily eroded sedimentary strata the direction of ice flow was more directly offshore and depositional features characterize the sea floor in these areas the signature of the grounded ice consists of till deposits and large scale geomorphic features drumlins occur within the region of contact between crystalline and sedimentary substrates the different geological substrates are interpreted to have exerted a fundamental control on the behavior of past ice sheets the troughs in the areas of bedrock composed of sedimentary substrate are interpreted to have been occupied by relatively fast flowing ice ice streams and the troughs in the areas of crystalline substrate are interpreted to have been occupied by slower moving ice the area between these two zones was characterized by ice acceleration and is marked by drumlins

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

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

selective heat producing element enrichment in a crustal segment of the mid european variscan chain abstract heat production has been calculated from u th and k content measurements on selected rock from the armorican massif western france geographical geochemical and age criteria have been introduced during the selection in order to obtain a representative sampling of the outcropping formations this procedure allows the delineation of a high heat production zone with values nearly twice the average upper crustal heat production ones the high heat production zone laterally ends through a high gradient belt indicating an upper crustal origin this zone cross cuts the geological structures and encompasses various granitoid plutons of different geochemical typologies and ages however among the granites belonging to the same geochemical type only those plutons located in this zone are enriched in radioelements those located outside with the exception of a few massifs present normal radiogenic element concentrations the enrichment affects all intruded granitoids or orthogneisses irrespective of their age when geographical features are restored prior to the late carboniferous shear deformation then the high heat production zone no longer appears as fortuitous it shapes a region intruded by numerous granitoids and structured during the early proterozoic we therefore propose that the high heat production zone reflects a previous selective enrichment of this crustal segment related to the late cambrian plutons

megagrooves and streamlined bedrock in nw scotland the role of ice streams in landscape evolution abstract new multibeam bathymetry data onshore high resolution elevation data nextmap and fieldwork in the ullapool area of nw scotland reveal large scale megagrooves and streamlined bedrock forms in a well defined 20 km wide zone the landsystem is typical of a coherent flow corridor within a grounded ice sheet on bedrock dominated terrain we describe the morphology of the large scale features discuss their likely formation and consider the wider implications for ice sheet dynamics based on the strongly convergent bedform distribution the presence of megagrooves and highly elongate bedrock forms we interpret the erosional landscape to be the signature of a fast flowing tributary that once fed the the minch palaeo ice stream a major artery of the last british irish ice sheet the exact genesis of bedrock megagrooves remains uncertain although focused subglacial abrasion is likely to have carved most of the shallow strongly parallel features whilst glacial meltwater may have carved or modified others bedform morphometry is used to discriminate zones reflecting the degree of glacial streamlining elongation ratios 5 1 we interpret these zones to represent the transition from potentially cold based slow ice sheet flow to warm based fast flow based on these results and the presence of ribbed moraines we suggest a bedform continuum model for onset zones of palaeo ice streams on rigid beds rapid spatial bedform evolution is suggested to reflect an increase in subglacial erosive power that may be diagnostic of palaeo ice sheet thermal boundaries i e from cold to warm based and is also consistent with the expected downstream increase in ice velocity within an ice stream onset zone finally this study speculates on the role played by basal meltwater in ice stream initiation and the role of ice streams and their tributaries in landscape evolution

laurentide ice sheet dynamics in the bay of fundy canada revealed through multibeam sonar mapping of glacial landsystems abstract recent multibeam sonar data collected in the bay of fundy canada interpreted in conjunction with geophysical profiling and sediment sampling reveal in unprecedented detail a suite of glacial landforms associated with the southwest margin of the laurentide ice sheet these landforms constitute four glacial landsystems 1 subglacial landsystem i in southwestern bay of fundy the elongated grand manan basin contains ice contact sediments of possible mid wisconsinan age overlain by late wisconsinan ice contact sediments strongly imprinted by iceberg furrows and pits in places possible mid wisconsinan glaciomarine sediments have been eroded by late wisconsinan ice creating streamlined landforms eroded bedrock and megafluted ice contact sediment on the flanks of grand manan basin indicate the southwest direction of topographically steered ice 2 subglacial landsystem ii along the southern margin of the bay of fundy an array of drumlins with superimposed esker complexes was formed by glacial ice that emanated northwest from the interior of nova scotia and was deflected to the southwest by the ice flowing out of the bay of fundy to the gulf of maine the esker complexes formed later when the nova scotia ice sheet stagnated and meltwater escaped northwest via topographic gaps 3 ice marginal landsystem i in northern bay of fundy both small de geer moraines and larger basin bounding moraines were created when retreating late wisconsinan ice became grounded in relatively shallow water new radiocarbon ages show that the owen basin moraine in this landsystem was abandoned prior to c 14 600 14 c yr bp cal bp 17 015 17 270 0 7 17 286 17 405 0 3 4 ice marginal landsystem ii this distinctive landsystem consists of numerous arcuate moraines commonly superimposed on one another this landsystem was formed by thin 170 m lightly grounded ice that retreated northeast into the bay of fundy the splayed pattern of the ice margin was a response to a large accommodation space and velocity variations within the ice the isle haute moraine is a large lobate moraine its age is poorly constrained by shells from glaciomarine sediments 13 750 60 14 c yr bp cal bp 15 970 15 996 0 03 16 047 16 665 0 97 but the moraine may be coeval with the onset of a terrestrial ice margin established at the head of the bay of fundy by c 14 300 14 c yr bp cal bp 16 824 17 013