geothermal control on flow patterns in the last glacial maximum ice sheet of iceland because it is located both on the mid atlantic ridge and on a mantle plume iceland is a region of intense tectonics and volcanism during the last glaciation the island was covered by an ice sheet approximately 1000 m thick a reconstruction of the ice flow lines based on glacial directional features shows that the ice sheet was partly drained through fast flowing streams fast flow of the ice streams has been recorded in megascale lineations and flutes visible on the currently deglaciated bedrock and is confirmed by simple mass balance considerations locations of the major drainage routes correlate with locations of geothermal anomalies suggesting that ice stream activity was favoured by lubrication of the bed by meltwater produced in regions of high geothermal heat flux similar control of ice flow by geothermal activity is expected in ice sheets currently covering tectonically and volcanically active area such as the west antarctic ice sheet copyright 2000 john wiley sons ltd

the stratigraphic and sedimentological significance of late devensian ice sheet surging in holderness yorkshire u k amino acid analyses of marine mollusc valves show that the basement till of holderness yorkshire is of late devensian age ca 20 000 bp and not pre ipswichian 125 000 bp as is traditionally supposed together with the overlying skipsea and withernsea tills the basement till is argued to be a deformation till resulting from the repeated onshore surging of late devensian ice over a muddy sea floor and the subglacial transport attenuation and mixing of marine sediment silts on the surface of the basement till yielding 14c dates of 18 500 and 18 240 bp have been regarded as minimum ages for late devensian glaciation in eastern england e g the dimlington stadial of rose 1985 1989 the amino acid data presented here indicates that the maximum of the late devensian glaciation in eastern england occurred earlier sedimentological interpretation of the late devensian tills of holderness as glacially reworked marine sediments supports previous glaciological models of the british ice sheet involving surging of ice lobes along the coast of eastern england the basement skipsea and withernsea tills are separated by shallow marine sediments and may be representative of deformable bed till facies deposited below pleistocene ice sheets moving over soft fine grained sediments

impact of bedrock surface topography on spatial distribution of quaternary sediments and on the flow pattern of late weichselian glaciers on the east european craton russian plain this paper presents the first high quality maps of the bedrock surface topography and the quaternary sediment distribution for the late weichselian glaciation area on the east european craton eec and the reasoning behind the estimated sediment distribution geographic information system gis based three dimensional model of the bedrock surface topography the current digital terrain model dtm and the ice flow pattern of the last glaciation provided the main source data for the analyses and interpretations in the current continental area of the western eec which was covered by the last scandinavian ice sheet sis the bedrock lies overwhelmingly 85 above the contemporary sea level with an average altitude of 54 m above sea level the topography of the bedrock surface is very well reflected in the current topography and an 80 m difference in the ice bed surface altitudes results in the topographic focusing of the ice flow and thus all late weichselian ice streams were accommodated to the depressions in the subglacial surface such depressions are characterised by a thin 10 m layer of sediment with one till bed just 50 m upslope from the bottom of the depressions the thickness of the sediment increases two to threefold and comprises five or more till layers indicating relief enhancement through subsequent glaciations the average calculated thickness of the quaternary deposits in the study area was 49 m and the total volume of sediments was 20 280 km3

drumlins carved by deforming till streams below the laurentide ice sheet the peterborough drumlin field 5000 km 2 is the largest in central canada and was formed during readvance of the laurentide ice sheet shortly after 13 000 b p morphometric analysis of 998 drumlins combined with study of 6921 borehole logs and downhole geophysical data has established the distribution of drumlin types and their stratigraphy along a 70 km flow line through the drumlin field in the north drumlins are spindle shaped composed of till resting directly on bedrock and were formed by deformation of till into low pressure zones in the lee of bedrock scarps eskers record subglacial drainage by channeled meltwaters flowing on bedrock to the south drift thickness increases and eskers are absent drumlins are larger and more ovoid and are composed of overridden proglacial and glaciolacustrine sediments overlain erosively by deformation till till is thin over drumlin crests and thick in interdrumlin swales and records subglacial cannibalization and mixing of overridden sediments the drumlin form is the product of erosion by streams of deforming till flowing in swales separating cores composed of older sediments systematic down field changes in drumlin shape and size can be related to decreased duration of subglacial deformation toward the limit of the readvance and increased thickness of preexisting sediments available for dissection by subglacial till streams absence of eskers in the central and southern parts of the drumlin field suggests that the ice base was drained by mass flow of the deforming substrate the substantial subsurface data available from the peterborough area indicate that drumlins are predominantly erosional in origin and are the geomorphological expression of a deforming subglacial bed below the margin of the laurentide ice sheet

southern laurentide ice lobes were created by ice streams des moines lobe in minnesota usa abstract regional mapping in southern minnesota has illuminated a suite of landforms developed by the des moines lobe that delimit the position of the lobe at its maximum and at lesser readvances the ice lobe repeatedly advanced discharged its subglacial water and subsequently stagnated recent glaciological research on antarctic ice streams has led some glacial geologists to postulate that ice streams drained parts of the marine based areas of the laurentide ice sheet i postulate that such ice streams may develop in land based areas of an ice sheet as well and that the des moines lobe 200 km wide and 900 km long was an outlet glacier of an ice stream it appears to have been able to advance beyond the laurentide ice sheet as long as adequate water pressure was maintained however the outer part of the lobe stagnated because subglacial water that facilitated the flow was able to drain away through tunnel valleys stagnation of the lobe is not equivalent to stoppage of the ice stream because ice repeatedly advanced into and onto the stagnant margins stacking ice and debris similar landforms are also seen in other lobes of the upper midwestern united states

lobal interactions rheologic superposition and implications for a pleistocene ice stream on the continental shelf of british columbia abstract data on structures stone striae clast pavements fabrics morphology provenance and matrix grain size of four pre late wisconsinan diamictons are presented from the lower accessible part of an 855 m long sea cliff at cape ball east coast of graham island queen charlotte archipelago british columbia the data indicate that an ice stream crossed the continental shelf from the british columbian mainland to the queen charlotte islands local queen charlotte piedmont ice coalesced with the western edge of the cordilleran ice sheet resulting in northward flow deflection along the east coast of graham island generally consistent structural and stone data indicate that diamictons were deposited as primary subglacial tills and that subglacial dynamics and rheologic conditions were complex two of the tills can be traced continuously over the cape ball section which provides a north south transect oblique to ice flow each of the two tills reveals five major changes in rheology and genesis ranging from a strong lodgement component to dominantly deformation mainly by subglacial squeeze flow true end member tills are rare and in almost all places the tills are hybrids that formed within a continuum of till forming processes commonly involving stone rotation and superposition of structures and rheologic states this could have occurred mainly in response to fluctuating till pore water content along the transect two dimensional stretches of contrasting till types probably represent a three dimensional patchwork of contrasting till rheologies and pore waters if patches of ductily deforming till were common and or widespread they could have accounted for much of the movement of cordilleran ice over glaciomarine mud on the continental shelf when sea level was much lower than present deforming probably saturated muddy till reconstituted glaciomarine would have possessed negligible shear strength resulting in a thin rapidly moving glacier most likely an ice stream that reached cape ball but failed to remove the record of previous glacial events the ice stream probably issued out of the mainland s skeena valley which is aligned with cape ball and is approximately the size of valleys in antarctica that today conduct small outlet glaciers and ice streams evidence for this and other ice streams on the northwestern continental shelf of north america imply that destabilization and rapid decay of the western edge of the cordilleran ice sheet may have been accomplished by a combination of ice streams sea level rise and extensive calving

a continuum mixture model of ice stream thermomechanics in the laurentide ice sheet 1 theory we employ a continuum mixture framework to incorporate ice streams in a three dimensional thermomechanical model of the laurentide ice sheet the ice mass is composed of a binary mixture of sheet ice which deforms by viscous creep and stream ice which flows by sliding and or sediment deformation at the bed dynamic and thermal evolutions are solved for each component in the mixture with coupling rules to govern transfer between flow regimes we describe two different transfer mechanisms 1 creep exchange the nourishment of ice streams by viscous creep inflow from the surrounding ice sheet and 2 bed exchange the activation growth and deactivation of ice streams perpetrated by transfers of bed area between flow constituents this paper develops the underlying mixture theory we express the governing equations for mass momentum and energy balance in a form suitable for direct incorporation in existing numerical models of ice thermomechanics a companion paper in this issue explores mixture and ice stream behavior in applications with the laurentide ice sheet

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 1 geophysical results in the 1994 1995 and 1998 austral field seasons geophysical research efforts in the ross sea focused on acquiring a high resolution database designed to permit 1 reconstruction of the maximum extent and configuration of the ice sheet during the last glacial maximum i e oxygen isotope stage 2 2 reconstruction of conditions at the base of the ice sheet and 3 assessment of the relative retreat history of the ice sheet following the last glacial maximum five seismic facies are distinguished on the basis of external geometry relationships among features bounding surface amplitude intensity of internal acoustic signature and geometry of internal reflectors seismic facies 1 is a transparent draping unit correlated to diatomaceous mud interpreted as being deposited under open marine conditions seismic facies 2 and 3 are comprised of units displaying subdued massive internal signatures with smooth lower bounding surfaces and hummocky upper surfaces characterized by glacial lineations these units are interpreted to be grounding zone proximal deposits overridden by the expanded ice sheet seismic facies 2 may be a deforming till unit seismic facies 4a is characterized by an internally massive to chaotic signature an erosional often flat lower surface and a hummocky upper surface displaying glacial lineations this unit is interpreted to be till and is divided into deposits associated with the most recent glacial expansion 4a and with an earlier pre last glacial maximum expansion 4b seismic facies 5 is an acoustically laminated ponded and draping deposit interpreted to contain proglacial and sub ice shelf materials deposited continuously since the last interglacial period the associations of these units provide context for the interpretation of the ice edge maximum position conditions at the base of the ice sheet and the relative retreat history of the region there is compelling evidence for a much expanded ice sheet in the ross sea during the last glacial maximum in the western ross sea the maximum grounding position is marked by an isolated grounding zone wedge and placed in the vicinity of coulman island approximately 150 km from the continental shelf edge in the central ross sea the maximum grounding position is close to the continental shelf break based primarily on the presence of an extensive 60 m thick sheet like deposit with a fluted upper surface streaming ice may have occupied bathymetric lows on the continental shelf as suggested by 1 the configuration of bathymetry 2 the presence of glacially eroded troughs 3 the concentration of sediment interpreted to be deforming till within the middle to outer shelf reaches of the troughs and 4 the fluted nature of the upper surface absolute rates of streaming ice flow relative to inter ice stream areas are not implied the western ross sea continental shelf deposits record the retreat history of ice derived predominantly from the east antarctic ice sheet and glaciers of the transantarctic mountains ice flow on the continental shelf is interpreted to have remained fixed in position restricted by the walls of the troughs on the inner shelf of the western ross sea the ice flowed over and eroded lithified sedimentary strata slower moving ice occupied flat topped banks a single grounding zone wedge occurs on the western ross sea central shelf no substantial deposits are observed on the inner continental shelf this lack of grounding zone features reflects a restricted sediment supply and a relatively steady rapid retreat of the ice sheet during retreat ice flow acted independently in each major trough and on the bank tops ice retreated from victoria land basin drygalski trough before it retreated from joides basin ice remained on the bank tops shedding material into the abandoned troughs grounded ice in the central ross sea was derived predominantly from an expanded west antarctic ice sheet the ice sheet remained grounded on the continental shelf edge after retreat of ice from the western ross sea expanded ice eroded the inner shelf and deposited sheets of till on the central and outer shelf ice stream drainage shifted laterally as recorded by rounded laterally accreting ridges that separate bathymetric troughs the central ross sea is the repository for larger volumes of sediment derived from ice flow across basins of relatively thick unlithified sedimentary deposits two till sheets mark grounding zone positions in the central ross sea reflecting the higher sediment supply and a stepped deglaciation ice remained grounded on the pennell bank to the west a series of moraines marks the retreat of ice across the bank mega scale glacial lineations and other streamlined subglacial geomorphic features occur across the continental shelf primarily within the troughs the lineations substantiate the maximum reconstruction and support the interpretation of a deforming substrate beneath the outer reaches of the expanded ice sheet this deforming substrate may have contributed to the onset of deglaciation features associated with meltwater are rare or absent suggesting that basal meltwater played a minor role in retreat of the ice sheet

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

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

the norwegian greenland sea continental margins morphology and late quaternary sedimentary processes and environment the continental margins surrounding the norwegian greenland sea are to a large degree shaped by processes during the late quaternary the paper gives an overview of the morphology and the processes responsible for the formation of three main groups of morphological features slides trough mouth fans and channels several large late quaternary slides have been identified on the eastern norwegian greenland sea continental margin the origin of the slides may be due to high sedimentation rates leading to a build up of excess pore water pressure perhaps with additional pressure caused by gas bubbles triggering might have been prompted by earthquakes or by decomposition of gas hydrates trough mouth fans tmf are fans at the mouths of transverse troughs on presently or formerly glaciated continental shelves in the norwegian greenland sea seven tmfs have been identified varying in area from 2700 km2 to 215 000 km2 the trough mouth fans are depocentres of sediments which have accumulated in front of ice streams draining the large northwest european ice sheets the sediments deposited at the shelf break upper slope by the ice stream were remobilized and transported downslope mostly as debris flows the trough mouth fans hold the potential for giving information about the various ice streams feeding them with regard to velocity and ice discharge two large deep sea channel systems have been observed along the norwegian continental margin the lofoten basin channel and the inbis channel along the east greenland margin several channel systems have been identified the deep sea channels may have been formed by dense water originating from cooling sea ice formation and brine rejection close to the glacier margin or they may originate from small slides on the upper slope transforming into debris flows and turbidity currents

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

geologic and topographic controls on fast flow in the laurentide and cordilleran ice sheets ice streams are fast flowing arteries which play a vital role in the dynamics and mass balance of present day ice sheets although not fully understood fast flow dynamics are intimately coupled with geologic topographic thermal and hydrologic conditions of the underlying bed these are difficult observables beneath contemporary ice sheets hindering elucidation of the processes which govern ice streaxn behavior for past ice sheets the problem is antithetic geologic evidence of former ice streams exists but spatim and temporal histories are uncertain however detailed knowledge of bed geology and topography is available in many places we take advantage of this information to compile terrain characteristics relevant to fast flow dynamics in the laurentide and cordilleran ice sheets using seed points where fast flowing wisconsinan ice has been geologically inferred discriminant analysis of a suite of north american geologic and topographic properties yields a concise measure of ice bed coupling strength our analysis suggests that the interior plains and continental shelf regions of north america have low basal coupling relative to areas of variable relief or exposed bedrock in the cordillera and on the canadian shield we conclude that the interior plains and continental shelves are both topographically and geologically predisposed to large scale basal flows i e ice streaxns or surge lobes this result holds independent of whether the mechanism of fast flow is sediment deformation or decoupled sliding over the bed

origin of glacial ridges ois 6 in the kaskaskia sublobe southwestern illinois usa abstract the origin of illinois episode ois 6 glacial ridges formerly ridged drift in the kaskaskia basin of southwestern illinois is controversial despite a century of research two studied ridges containing mostly fluvial sand osl ages 150 19 ka with associated debris flows and high angle reverse faults are interpreted as ice walled channels a third studied ridge containing mostly fine grained till is arcuate and morainal the spatial arrangement of various ridge types can be explained by a glacial sublobe in the kaskaskia basin with mainly fine grained ridges along the sublobe margins and coarse grained glaciofluvial ridges in a paleodrainage network within the sublobe interior illinois episode till fabric and striation data demonstrate southwesterly ice flow that may diverge near the sublobe terminus the sublobe likely formed as glacial ice thinned and receded from its maximum extent the kaskaskia basin contains some of the best preserved illinois episode constructional glacial landforms in the north american midcontinent such distinctive features probably result from ice flow and sedimentation into this former lowland in addition to minimal postglacial erosion other similar ois 6 glacial landforms may exist in association with previously unrecognized sublobes in the midcontinent where paleo lowlands might also have focused glacial sedimentation

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

sedimentation beneath ice shelves the view from ice stream b abstract ice shelf development is favored by rapid flow of cold ice from outlet glaciers or ice streams into protected embayments with localized high spots basal melting of ice shelves is rapid near the ice front and may occur near the grounding line ice from outlet glaciers may contain significant englacial debris that is deposited as a dropstone diamicton in regions of basal melting englacial debris is sparse or absent in ice streams evidence from ice stream b draining into the ross ice shelf of west antarctica suggests that the rapid ice velocity arises from deformation of a several meter thick water saturated basal till layer that is eroding an unconformity on sediments beneath and that has deposited a till delta tens of meters thick and tens of kilometers long at the grounding line sea level fall would cause conveyor belt recycling of this till delta and grounding line advance across the ross sea to the edge of the continental shelf forming an ice sheet with a low ice stream profile resting on a several meter thick deforming till layer eroding an unconformity the modern ross sea is characterized by a regional unconformity overlain by a diamicton of probable latest pliocene pleistocene age measuring several meters to tens of meters thick we hypothesize that this diamicton is a deformed glacial till and that the ross sea sediments record one or more expansions of the till lubricated west antarctic ice sheet to the edge of the continental shelf

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

alkenones and coccoliths in ice rafted debris during the last glacial maximum in the north atlantic implications for the use of uk37 as a sea surface temperature proxy the uk37 index has proven to be a robust proxy to estimate past sea surface temperatures ssts over a range of time scales but like any other proxy it has uncertainties for instance in reconstructions of the last glacial maximum lgm in the northern north atlantic uk37 indicates higher temperatures than those derived from foraminiferal proxies here we evaluate whether such warm glacial estimates are caused by the advection of reworked alkenones in ice rafted debris ird to deep sea sediments we have quantified both coccolith assemblages and alkenones in sediments from glaciogenic debris flows in the continental margins of the northern north atlantic and from a deep sea core from the reykjanes ridge certain debris flow deposits in the north atlantic were generated by the presence of massive ice sheets in the past and their associated ice streams such deposits are composed of the same materials that were present in the ird at the time they were generated we conclude that ice rafting from some locations was a transport pathway to the deep sea floor of reworked alkenones and pre quaternary coccolith species during glacial stages but that not all of the ird contained alkenones even when reworked coccoliths were present we speculate that the ratio of reworked coccoliths to alkenone concentration might be useful to infer whether significant reworked alkenone inputs from ird did occur at a particular site in the glacial north atlantic we also observe that alkenones in some of the debris flows contain a colder signal than estimated for lgm sediments in the northern north atlantic this is also clear in the deep sea core studied where the warmest intervals do not correspond to the intervals with large inputs of reworked coccoliths or ird we conclude that any possible bias to uk37 estimates associated with reworked alkenones is not necessarily towards higher values and that the high sst anomalies for the lgm are unlikely to be the result of a bias caused by ird inputs

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

laurentide glacial landscapes the role of ice streams glacial landforms of the north american prairie can be divided into two suites that result from different styles of ice flow 1 a lowland suite of level to streamlined till consistent with formation beneath ice streams and 2 an upland and lobe margin suite of thick hummocky till and glacial thrust blocks consistent with formation at ice stream and ice lobe margins southern laurentide ice lobes hypothetically functioned as outlets of ice streams broad branching lowlands bounded by escarpments mark the stable positions of the ice streams that fed the lobes if the lobes and ice streams were similar to modern ice streams their fast flow was facilitated by high subglacial water pressure favorable geology and topography in the midcontinent encouraged nonuniform ice flow and controlled the location of ice streams and outlet lobes

ice sheet erosion and the stripping of tertiary regolith from baffin island eastern canadian arctic abstract the erosion of glaciated regions and concomitant changes in ice sheet dynamics through the pleistocene are poorly documented the baffin island landscape which has been shaped by the foxe sector of the laurentide ice sheet lis contains a variety of glacial and proximal glaciomarine sedimentary archives spanning the pleistocene we examine these records to better understand when tertiary regolith was stripped from beneath the foxe sector of the lis till on the interior plateaux of the island in areas with scoured bedrock have low chemical index of alteration cia values low meteoric 10 be 10 be met concentrations and clay mineralogy consistent with erosion from an unweathered bedrock source however in some areas in between fiord onset zones more weathered till is present containing considerably higher cia values high 10 be met concentrations and secondary clay mineral weathering products implying that the till has persisted on the landscape and weathered during successive glaciations using these weathering signatures we analyze the coastal glaciogenic deposits of the clyde foreland formation cff at two sites for evidence of tertiary regolith removal from the interior of baffin island by lis erosion provenance indicators within the cff demonstrate that pleistocene lis ice flow lines across baffin island have remained generally constant the oldest cff glaciogenic unit likely representing one of the first if not the first lis advances across baffin island had high 10 be met concentrations at the time of deposition consistent with extensive regolith erosion evidence of notably weathered sediment is absent in all younger units suggesting that tertiary regolith was likely largely stripped from the interior of the island by 1 6 0 2 ma

large scale sedimentation on the glacier influenced polar north atlantic margins long range side scan sonar evidence long range side scan sonar gloria imagery of over 600 000 km of the polar north atlantic provides a large scale view of sedimentation patterns on this glacier influenced continental margin high latitude margins are influenced strongly by glacial history and ice dynamics and linked to this the rate of sediment supply extensive glacial fans up to 350 000 km were built up from stacked series of large debris flows transferring sediment down the continental slope the fans were linked with high debris inputs from quaternary glaciers at the mouths of cross shelf troughs and deep fjords where ice was slower moving but still extended to the shelf break large scale slide deposits are observed where ice failed to cross the continental shelf during full glacials the continental slope was sediment starved and submarine channels and smaller slides developed a simple model for large scale sedimentation on the glaciated continental margins of the polar north atlantic is presented

stress induced spatiotemporal variations in anisotropic structures beneath hakone volcano japan detected by s wave splitting a tool for volcanic activity monitoring hakone volcano located at the northern tip of the izu mariana volcanic arc japan has a large caldera structure containing numerous volcanic hot springs earthquake swarms have occurred repeatedly within the caldera the largest seismic swarm since the commencement of modern seismic observations in 1968 occurred in 2001 we investigated the anisotropic structure of hakone volcano based on s wave splitting analysis and found spatiotemporal changes in the splitting parameters accompanying the seismic swarm activity depth dependent anisotropic structures are clearly observed a highly anisotropic layer with a thickness of 1 5 km is located beneath the koziri kzr and kozukayama kzy stations the anisotropic intensity in the region reaches a maximum of 6 7 at a depth of 1 km and decreases markedly to less than 1 at a depth of 2 km the anisotropic intensity beneath komagatake station kom decreases gradually from a maximum of 6 at the surface to 0 at a depth of 5 km but is still greater than 2 5 at a depth of 3 km at kzy the anisotropic intensity along a travel path of which the back azimuth was the south decreased noticeably after the 2001 seismic swarm activity during the swarm activity tilt meters and gps recorded the crustal deformation the observed decrease in anisotropic intensity is presumed to be caused by the closing of microcracks by stress changes accompanying crustal deformation near the travel path

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

quaternary glaciations in southern fennoscandia evidence from southwestern norway and the northern north sea region abstract based on records from the northern north sea and southern norway quaternary fennoscandian glaciations are described and discussed maximum glaciation defined as the presence of shelf edge glaciation an ice stream flowing out of the norwegian channel and most likely an ice divide over the central part of fennoscandia sweden gulf of bothnia occurred for the first time in the late cenozoic at ca 1 1 myr the fedje glaciation this glaciation was followed by a ca 600 kyr period with at least two glaciations with ice extension somewhat larger than the younger dryas event in the region the first maximum glaciation of the bruhnes chron was during isotope stage 12 and was followed by repeated maximum glaciations within each of the light isotopic stages until stage 2 during the weichselian the southwestern part of the fennoscandian ice sheet reached maximum position three times sometime between 22 and 28 37 and 50 and 60 and 80 ka limited glaciations probably occurred during stadials between the early and middle weichselian interstadials between 500 ka and 1 1 myr and most likely also prior to 1 1 myr deep norwegian sea ice rafted detritus ird records reflecting contributions from several different ice sheets fennoscandian barents sea iceland and greenland each with large variations in history of ice extent to their respective margins yet to some degree they reflect the glaciation of the northern north sea region with an increasing ird input around 1 1 myr and a relatively low input of north sea components during some cycles around the b m boundary maximum glaciations occurred during insolation minima in the earlier part of the middle pleistocene however not all such minima are reflected by maximum glaciation in southern parts of fennoscandia the relatively poor chronological control and non continuous character of the data on weichselian interstadials stadials precludes a clear relationship to atmospheric changes recorded in greenland ice cores as well as to precession and or obliquity cycles in insolation

geomorphology and sedimentology of surging glaciers a land systems approach the identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice sheet dynamics and for reconstructing ice sheets and climate no single landform or diagnostic criterion has yet been found with which to identify surging glaciers a surging glacier land system model is constructed using observations and measurements from contemporary surging glacier snouts in iceland svalbard u s a and canada for differentiating ancient surging margins from other non surging palaeoglaciers this integrates the suite of landforms sediments and stratigraphy produced at surging glacier margins landforms produced during surging include thrust moraines concertina eskers and subglacial crevasse squeeze ridges sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds which display severe glaciotectonic contortion and faulting hummocky moraine comprising interbedded stratified sediments and mass flow diamictons has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ an example of the application of the land system model is presented for east central alberta canada a surging palaeo ice stream is identified within this part of the southwestern laurentide ice sheet where thrust block moraines crevasse squeeze ridges flutings hummocky moraine and glaciotectonized sediments are juxtaposed

a continuum mixture model of ice stream thermomechanics in the laurentide ice sheet 2 application to the hudson strait ice stream episodic exportations of ice rafted debris to the north atlantic in the late pleistocene suggest quasiperiodic ice streaming or surging activity on the northeastern margin of the laurentide ice sheet much of this efflux of ice may originate from an ice stream issuing from hudson strait and tapping into core regions of the laurentide in hudson bay labrador and the foxe basin applying the continuum mixture theory outlined by marshall and clarke this issue we model the thermomechanical evolution of the hudson strait ice stream in a three dimensional finite difference model of the laurentide ice sheet our simulations focus on internal dynamics of the ice stream under thermal regulation of basal flow we find surge cycles of stream activity interspersed with quiescent periods where the ice stream is frozen to the bed modeled surge durations vary from 105 to 3260 years while surge periodicities range from 585 to 22 410 years with pervasively warm or cold internal temperature distributions in the ice ice streams can also establish modes of permanent activity or inactivity under thermal regulation our most vigorous ice streams produce peak values of approximately 0 03 sv of freshwater flux to the north atlantic from basal meltwater and iceberg production associated ice stream velocities in this maximum case approach 6700 m yr 1 the total ice volume mobilized in a single surge event is equivalent to a global sea level rise of 0 04m in the most tranquil surge and almost 0 6m in the most extreme case these velocities and sea level impacts are an order of magnitude less than those predicted by macayeal 1993a b and only our most exuberant streams approach the iceberg flux estimates of dowdeswell et al 1995 we propose that the sediment load of icebergs emanating from hudson strait in a surge event may exceed expectations from contemporary icebergs

landform modification by palaeo ice streams in east central ireland in eastern ireland subglacial bedforms including drumlins and rogen moraines were modified by headward erosion along two ice streams which had over lapping flow tracks the ice streams which hadtidewater termini are dated by geochrono metric and morphostratigraphic methods to 5 15 0 14 ckyr bp castleblaney ice stream and 13 8 14 ckyr bp armagh ice stream bedforms along ice stream tracks show a morphological continuum which reflects a down ice increase in the degree of modification by ice stream activity i e resulting in unmodified remoulded overprinted cross cut streamlined bedforms the down ice changes inbedform types are inferred to relate to changes in subglacial drainage and sediment transport mechanisms bedform and sedi mentary evidence suggest that discrete subglacial meltwater channels which developed up ice changed in a down ice direction to unchannelized flows which deepened towards the ice margin meltwater release from subglacial cavities and produced by strain heating at sheared ice stream margins probably helped support ice stream flow which ended as the volume of subglacial meltwater discharge decreased dated millennial scale cycles of ice activity may be related to instability at tidewater margins followed by complex thermal and hydraulic responses within the ice mass

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

changes in the west antarctic ice sheet since 1963 from declassified satellite photography comparison of declassified satellite photography taken in 1963 with more recent satellite imagery reveals that large changes have occurred in the region where an active ice stream enters the ross ice shelf ice stream b has widened by 4 kilometers at a rate much faster than suggested by models and has decreased in speed by 50 percent the ice ridge between ice streams b and c has eroded 14 kilometers these changes along with changes in the crevassing around crary ice rise imply that this region s velocity field shifted during this century

flow dynamics and till genesis associated with a marine based antarctic palaeo ice stream geophysical and geological data indicate that during the last glacial cycle a palaeo ice stream drained the antarctic peninsula ice sheet apis through marguerite bay to the edge of the continental shelf via a bathymetric trough marguerite trough mega scale glacial lineations msgl in outer marguerite trough are formed in an acoustically transparent sediment unit consisting of a soft deformation till the association of msgl with deformation till indicates that bed deformation occurred beneath the ice stream and the thickness of the subglacial deforming layer was on the order of several metres msgl within outer marguerite trough are related to a pre existing thick sequence of soft sediments on the outer shelf and are inferred to have formed by a combination of subglacial sediment deformation by attenuation from a point source and groove ploughing morphologically the msgl differ in several respects from those documented elsewhere and this variation suggests a polygenetic origin for this subglacial landform an initial advance of the apis across the marguerite bay continental shelf at the lgm deposited a stiff subglacial till following this advance the ice margin within marguerite trough retreated 70 100 km before stabilising and depositing a grounding zone wedge an ice stream then developed in the trough and extended to the shelf edge forming a soft deformation till development of the ice stream may have been a glacio dynamic response to regional deglaciation subsequent retreat of the marguerite trough ice stream was underway by 13 490 uncorrected 14c years before present based on the geophysical and core data ice stream retreat appears to have been rapid and it contrasts with reconstructions of palaeo ice streams from other locations in antarctica this implies marked regional variations in antarctic ice stream dynamics during late quaternary deglaciation

glacial landsystems of the southwest laurentide ice sheet modern icelandic analogues landform assemblages and associated stratigraphy sedimentology and structure are used in the reconstruction of palaeo ice sheet dynamics in alberta western canada interpretations are based upon the modern analogues from four outlet glaciers at the margins of vatnajokull and myrdalsjokull iceland in the area between lloydminster and lac la biche central alberta an extensive landform assemblage of megaflutings crevasse squeeze ridges and thrust block moraine arcs document the former surging of part of the margin of the laurentide ice sheet during later stages of recession this landform assemblage including numerous exposures of glacitectonised bedrock and quaternary sediments is comparable to the landsystem of the surging glaciers eyjabakkajokull and bruarjokull in iceland near high river southern alberta the former existence of an ice lobe characterised by active recession is recorded by closely spaced low amplitude recessional push moraines that drape tunnel valleys these are comparable in form and pattern to annual push moraines and fluted till surfaces produced by breidamerkurjokull and sandfellsjokull iceland and also include rimmed depressions produced by the escape of artesian water during ice marginal pushing this study provides interpretations of the regional glacial geomorphology of alberta based upon comparisons of form and stratigraphy with modern glacial analogues and provides an alternative to recent models which invoke large floods of subglacial meltwater to explain many of these same features implications for ice dynamics and regional till stratigraphies are discussed copyright 1999 john wiley sons ltd

climate sensitivity to continental ice sheet size and configuration abstract a version of the ncar community climate model ccm has been used to carry out a study of climate sensitivity to the size and distribution of continental ice sheets by comparing two perpetual season fixed sea surface temperature sst winter simulations of the climate at a glacial maximum the two simulations differ only in the size and configuration of the continental ice sheet boundary conditions these conditions represent minimum and maximum ice sheet extent for a glacial maximum as presently constrained by the geologic evidence all other boundary conditions are as specified by climap 1981 for winter surface conditions during the last glacial maximum lgm the ice sheets specified by climap 1981 used by many previous researchers to simulate ice age climate conditions are intermediate in size between the minimum and maximum ice sheets used for the simulations described here the maximum case simulation resulted in unexpected positive temperature anomalies over the northern hemisphere

spatial complexity of ice flow across the antarctic ice sheet ice streams control the discharge of ice from the interior of the antarctic ice sheet to the coast a map of flow convergence suggests that ice stream flow is subject to a mechanical regulation that limits flow orthonormal strain rates

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

development of the topography controlled upper odra ice lobe scandinavian ice sheet in the fore mountain area of southern poland during the saalian glaciation abstract during the saalian drenthe glaciation the upper odra ice lobe constituted the most southern part of the scandinavian ice sheet in central europe the lobe was situated in an area with varied topography in the foreland of a mountain range the ice lobe had a complex form because it was subdivided into several smaller sublobes the primary factors that controlled the lobe were investigated it was found that the ice lobe development depended largely on the topography but the lithology of the ice sheet substratum was also highly important the topography controlled the main movement direction of the ice and caused a concentration of the ice flow in the axial part of the silesian lowland between subglacial morphological barriers which thereby formed a corridor of relatively fast flowing ice which was probably streaming and which supplied the lobe the topography also determined the ice flow within the lobe which strongly matched the valley system the presence of sediments with relatively low permeability at the base of the lobe the quaternary deposits are underlain by neogene clays caused high pore water pressure in the subglacial zone and triggered the basal movement of the ice sheet which promoted a rapid flow of the ice and favoured the development of the lobe the basal tills deposited from the active and passive ice and extant till patches without a fluvioglacial cover atop some parts of the studied area indicate spatially varying ice flow dynamics especially in the later stage of glaciation certain parts of the lobe underwent stagnation while in other parts the ice was probably still active the varied behaviour of the ice within the lobe was determined primarily by the topography and lithology of the substratum which produced spatially varied marginal compression and basal friction a model of the development of the lobe is proposed

the jaeren area a border zone of the norwegian channel ice stream abstract the coastal lowlands of jaeren southwestern norway have an extensive cover of quaternary sediments lithological biostratigraphical and geochronological investigations of a series of boreholes across jaeren have allowed us to combine earlier and new information on these deposits into a temporal model of quaternary sedimentation the cores show evidence of at least four ice free episodes with marine deposition during mainly arctic conditions the oldest of these is considered to be ca 200 ka old and the youngest one is the sandnes interstadial which is 14 c ams dated to 32 ka bp interbedded between these units are 10 40 m thick units of till with components of marine material these findings together with a re evaluation of distinct morphological features on jaeren as well as earlier provenance studies strongly suggest that jaeren has been a boundary zone between an ice stream following the norwegian channel draining a substantial part of the southern region of the fennoscandian ice sheet and local ice from south western norway through multiple periods of glaciation starting ca 1 1 myr million years ago the norwegian channel ice stream has been the main conduit of erosion products from southern scandinavia to the deep norwegian sea comparison with ice stream profiles from antarctica suggests that the deposition of relatively young marine sediments as high as ca 200 m a s l on jaeren is a result of glacial isostasy rather than regional tectonic movements

extent and basal characteristics of the m clintock channel ice stream abstract the m clintock channel palaeo ice stream drained the northwestern margin victoria island arctic canada of the laurentide ice sheet functioning for 200 years prior to 10 ka bp from its bed imprint it is reconstructed as 720 140 km with a cross sectional area of 100 km2 comparable in size to the hudson strait ice stream it drained an estimated 80 000 km3 of ice enough to significantly affect the shrinking ice sheet and drive the keewatin ice divide south eastwards such discharges likely produced heinrich events and influenced the temperature and salinity of the western arctic ocean ice stream location was controlled by a topographic trough but glaciological regulation rather than properties of the bed controlled margin locations and hence ice stream width the ice stream eroded into pre existing unconsolidated sediments and left a pattern of subglacially produced landforms recording a snapshot view of the bed prior to shutdown frictional shutdown occurred once downcutting through sediments reached bedrock in places high sediment availability appears critical for ice stream functioning with a drift thickness of 50 m required to sustain its 200 year lifespan debris discharge was exceptionally high 73 000 m3 a 1 m 1 this ice stream demonstrates non steady response of ice sheets to climate change and their large impact on mass balance and stability of ice sheets

ice sheet numerical modeling and marine geophysical measurements of glacier derived sedimentation on the eurasian arctic continental margins long range side scan sonar images of the barents sea continental margin have been analyzed in conjunction with results from previous geophysical investigations to determine a qualitative model for sedimentation over the bear island and storfjorden trough mouth fans these data indicate that gravity driven debris flows are major processes in the downslope transport of glacial material delivered to the shelf break when ice sheets advanced across the continental shelf during late weichselian time 4000 km 3 of sediments were deposited over the bear island fan 280 000 km 2 while 700 km 3 of sediments were deposited over the storfjorden fan 40 000 km 2 a numerical ice sheet model including sediment deformation and transport beneath ice streams reconstructs the glacial conditions required to transport large volumes of sediment to the late weichselian eurasian continental margin model results indicate that glaciation of the eurasian high arctic occurred after 28 ka and that ice streams within bathymetric troughs were active by ca 25 ka the maximum ice sheet thickness over the barents sea was about 1400 m there was a secondary dome 1 0 13 cm yr 1 averaged over the fan the rate was 6 cm yr 1 equivalent to 0 6 cm yr 1 over the fan over the storfjorden trough mouth the modeled sediment volume at the continental margin of the bear island and storfjorden troughs agrees well with the volumes of late weichselian sediment inferred from seismic records from these large prograding submarine fans sensitivity experiments show that adjustments to model environmental inputs do not significantly affect the results

abrupt early holocene 9 9 9 6 ka ice stream advance at the mouth of hudson strait arctic canada radiocarbon dated glacial geologic evidence documents an abrupt advance of the northern margin of the labrador sector of the laurentide ice sheet during the last deglaciation ice flow directional indicators together with ice marginal features found onshore and offshore delimit an ice stream that advanced north northeast 300 km crossed the mouth of hudson strait and outer frobisher bay and overran summits 400 m above sea level on outer hall peninsula southeast baffin island fifty eight 14 c ages including 27 accelerator mass spectrometry ages on single shells indicate that the advance was extremely rapid the entire advance retreat cycle took place in an 300 yr 14 c interval 9 9 9 6 ka at its maximum extent the ice stream supported a calving margin 200 km long terminating in open water 500 m deep implying a massive iceberg release marine evidence for the outflow is preserved along the labrador sea shelf as thick carbonate rich glacial marine drift but has not been recognized farther east in the north atlantic either the discharge of icebergs was insufficient to produce a trans north atlantic carbonate rich heinrich layer or the icebergs tracked southward where they encountered warming sea surface temperatures although the advance seems to have been coincident with a brief interval of minor regional cooling it failed to trigger a significant climate perturbation suggesting that the ocean atmosphere system had attained its stable interglacial condition by that time

ice proximal glaciomarine sedimentation and sea level change in the inverness area scotland a review of the deglaciation of a major ice stream of the british late devensian ice sheet abstract evidence of both rising and falling relative sea levels and glacitectonic movements is preserved in two formations of raised glaciomarine deposits that were laid down in front of an oscillating grounded tidewater glacier in the inverness firth these changes occurred during the latter stages of the disintegration of the moray firth ice stream one of the major ice streams that drained the british main late devensian ice sheet most of the glaciomarine deposits antedate a sequence of glacio isostatically tilted late devensian marine shorelines and associated littoral and estuarine deposits the shorelines began forming at about 13 000 bp and record a progressive fall in relative sea level a new model for the deglaciation of the moray firth region is proposed after a critical appraisal of published accounts of both onshore and offshore quaternary sequences the disintegration of the moray firth ice stream involved several rapid phases of retreat to pinning points caused by iceberg calving and triggered by rising global sea level each retreat was followed by minor readvances or stillstands possibly caused by short lived accelerated periods of glacio isostatic rebound and concomitant temporary falls in relative sea level two such events occurred in the inverness firth the ardersier oscillation and the alturlie stillstand substantial differences lower relative sea levels later deglaciation are apparent between the pattern of ice retreat in the moray firth region and published accounts of the deglaciation of the irish sea basin these differences require a reassessment of some current hypotheses concerning the disintegration of major ice streams associated with high relative sea levels furthermore geological and geomorphological evidence suggesting both rising and falling sea levels in the inverness area prior to ca 13 500 bp is not fully compatible with recently published computer simulations of the dissolution of the british main late devensian ice sheet

zooming in on frozen bed patches scale dependent controls on fennoscandian ice sheet basal thermal zonation in this paper we explore geomorphological evidence allowing a first order reconstruction of the extent and pattern of frozen bed conditions under the last fennoscandian ice sheet we mapped relict landscapes i e glacial landforms and subaerially developed ground surfaces predating the last ice sheet and marking sustained frozen bed conditions at four different spatial scales at the ice sheet scale relict landscapes are most abundant between the last glacial maximum ice divide and the elevation axis of the scandinavian mountain range the location of frozen bed zones was mainly a function of dispersal centre location low surface temperatures and small strain heating and small ice thickness over the eastern flank of the mountain range at the mesoscale 260 360 km map area the pattern of relict surfaces is governed by inward cutting ice stream erosion topographical control was weak but relation to flow pattern was strong with the major frozen bed zone located where ice flow was strongly divergent at the regional scale 40 65 km map area in hilly terrain topographical control was strong with relict surfaces only appearing above a plane dipping in the up ice direction at the local scale 12 14 km map area control by topography was likewise strong but the detailed boundary pattern was irregular with specific landforms occurring both up and down ice of frozen patches

basal hydraulic system of a west antarctic ice stream constraints from borehole observations pressure and tracer measurements in boreholes drilled to the bottom of ice stream b west antarctica are used to obtain information about the basal water conduit system in which high water pressures are developed these high pressures presumably make possible the rapid movement of the ice stream pressure in the system is indicated by the borehole water level once connection to the conduit system is made on initial connection here also called breakthrough to the basal water system the water level drops in a few minutes to an initial depth in the range 96 117 m below the surface these water levels are near but mostly somewhat deeper than the flotation level of about 100m depth water level at which basal water pressure and ice overburden pressure are equal which is calculated from depth density profiles and is measured in one borehole the conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed the thickness of the gap has to be about 2 mm to account for the water level drop on breakthrough and about 4 mm to fit the results of a salt tracer experiment indicating downstream transport at a speed of 7 5 mm s 1 the above gap conduit model is however ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole and also by the large hole to hole variation in measured basal pressure which if present in a gap conduit system with 2 or 4 mm would result in unacceptably large local water fluxes an alternative model that avoids the e objections called the gap opening model involves opening a gap as injection proceeds starting with a thin film the injection of water under pressure lifts the ice mass a round the borehole creating a gap 3 or 4 mm wide at the ice bed interface evaluated quantitatively the gap opening model accounts for the volume of water that the basal watery system accepts on breakthrough which obviates the gap conduit model in order to transport basal meltwater from upstream it is then necessary for the complete hydraulic model to contain also a network of relatively large conduits of which the most promising type is the canal conduit proposed theoretically by walder and fowler 1994 flat low conduits incised into the till 0 1 m deep and perhaps 1 m wide with a flat ice roof the basal water pressure data suggest that the canals are spaced 50 300 m apart much closer than r tunnel would be the deepest observed water level 117 m i the most likely to reflect the actual water pressure in the canals corresponding to a basal effective pressure of 1 6 bar in this interpretation the shallower water levels are affected by loss of hydraulic head in the narrow passageway s that connect along the bed from borehole to canal s once a borehole has frozen up and any passageways connecting with canals have become closed a pressure sensor in contact with the unfrozen till that underlies the ice will measure the pore pressure in the till given enough time for pressure equilibration this pressure varies considerably with time over the equivalent water level range from 100 to 113 m basal pressure sensors 500 m apart report uncorrelated variations whereas sensors in boreholes 25 m apart report mostly but not entirely well correlated variations of unknown origin in part of the record remarkable anticorrelated variations are interspersed with positively correlated one and there are rare abrupt excursions to extreme water levels as deep as 125m and as shallow as 74 m a diurnal pressure fluctuation intermittently observed may possibly be caused by the ocean tide in the ross sea the lack of any observed variation in ice stream motion when large percentagewise variations in basal effective pressure were occurring according to our data suggests that the observed pressure variations are sufficiently local and so randomly variable from place to place that they are averaged out in the process by which the basal motion of the ice stream is determined by an integration over a large area of the bed

ice sheet dynamics and ice streaming along the coastal parts of northern norway abstract in this paper regional and high resolution bathymetric data are used to reconstruct the pattern and dynamics of ice sheet flow in the fjord and shelf areas of northern norway interpretation of the morphology of the sea floor reveals a series of glacigenic features which are mainly related to the most recent glaciation of the area the shelf area of troms county comprises four cross shelf troughs with intermediate shallow banks glacial features within the cross shelf troughs mega scale glacial lineations msgl lateral shear margin moraines grounding zone wedges are interpreted to have been formed under fast flowing ice streams on the shallow bank areas there are far fewer ice flow indicators and here relatively passive ice acted as interstream ridges outside the finnmark coast to the north and east a coast parallel depression djuprenna deflected rapidly flowing ice from the fjords in a generally east to west direction and then farther out through ingoydjupet and into the bear island trough the fjords guided most of the ice flow and functioned as tributaries to the major ice streams on the shelf including the vast bear island trough ice stream at the last glacial maximum the landform distribution and their cross cutting relationships indicate that major switches in ice stream flow direction took place during deglaciation additionally grounding zone wedges are found within the cross shelf troughs and these reveal temporal variability in ice stream dynamics in different troughs during deglaciation the distribution of glacigenic features on the ice stream beds also reveals a downstream evolution that has been reported by other workers whereby small bedrock features progressively merge into more elongate forms and msgl this downstream evolution in subglacial geology subglacial bedforms implies that the force balance e g basal shear stress of the ice streams also evolves in the downstream direction and more crucially that the flow mechanism of the ice stream is spatially variable along its length

glacial flow systems in the zone of confluence between the scandinavian and novaja zemlya ice sheets abstract the glacial geomorphology of the eastern kola peninsula northwestern russian plain pechora lowland northern ural mountains and southern novaya zemlya 1 000 000 km 2 was mapped using landsat satellite imagery glacial flow parallel lineations and marginal and interlobate features were identified the directions of glacial flow and the patterns of deglaciation were reconstructed the scandinavian ice sheet expanded northeastwards into the southern barents sea while the novaya zemlya ice sheet spread southwestwards into the same area the two coalesced in the kanin region and subsequently flowed from the barents sea towards the land during the deglaciation of the scandinavian ice sheet flow was initially oriented from the white sea region towards the barents sea subsequently several ice streams controlled by the regional topography were formed the growth of the novaya zemlya ice sheet occurred east of the islands whereas during the decay there was more ice on the western side a compilation of dated sequences up to 300 km inland from the coast indicate a late weichselian age of deglaciation separation of the two ice sheets occurred along the saddle between the kanin and kola peninsulas at about 13 000 bp 15 500 cal years bp which became the locus for discharge of the proglacial dvina pechora lake into the sea beyond the presumed late weichselian limits older flow patterns are recognised these patterns along with dispersal of erratics suggest that the growth of a more extensive glaciation started in the novaya zemlya region later the scandinavian ice sheet occupied areas previously covered by the novaya zemlya ice sheet

the last glacial maximum of svalbard and the barents sea area ice sheet extent and configuration abstract the timing extent and configuration of the late weichselian barents ice sheet has been debated for several decades this debate has arisen largely because of the limited or conflicting field evidence on which most models have been based in particular reconstruction of the marine parts of the former barents ice sheet has been controversial this paper aims to review the geological observations and interpretations regarding the size and timing of the late weichselian ice sheet combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour sub glacial till with overlying glacimarine deposits dated to the late weichselian is found over most of the barents sea floor and the continental shelf west of svalbard glacially induced debris flow deposits on the large bjonoya and isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation isobase maps show a centre of post glacial uplift in the north central barents sea and glaciological and isostatic modelling suggest that the ice sheet was 2000 3000 m thick in this area the ice sheet was confluent with ice over the kara sea but the interaction between the barents and kara ice sheets is not yet fully understood the deglaciation of the barents ice sheet started ca 15 ka probably by calving within the deeper troughs by 12 ka most of the central barents sea was ice free and ice remained over the svalbard franz josef land and novaja zemlya archipelagos and adjacent shallow shelf areas the coasts and fjords of these islands were ice free by 10 ka

glacial and glaciofluvial deposits in the interlobate areas of the scandinavian ice sheet abstract rapid flow within ice streams took place in a broad marginal zone of the scandinavian ice sheet during deglaciation ice streams and interlobate zones have been characterised by analysis of glacial flow patterns and examination of sedimentary features of interlobate glacial and glaciofluvial deposits reconstructed glaciodynamic systems are compared with ice streams of modem ice sheets wide interstream areas of inactive ice were left between some adjacent ice streams where they separated during the retreat of the margin these areas are characterised by morainic hummocks composed of both till and glaciofluvial sediment and sections show indications of subglacial deformation observations from fennoscandia suggest that these interstream areas were sites of net accumulation of glacial and glaciofluvial sediment during deglaciation glaciofluvial sediment was deposited in subglacial tunnels or cavities simultaneously with till deformation and deposition resulting from subglacial melting substantial glaciofluvial complexes were formed in narrow interlobate joints where adjacent ice lobes coalesced a case study made in southern finland shows converging flow patterns of two ice lobes and intervening glaciofluvial deposits concentration of meltwater in interlobate zones was a consequence of ice sheet configuration thinner ice in interlobate zones caused convergence of supraglacial and subglacial drainage the crevassed and strain softened ice may also have allowed surface meltwater to penetrate down to the ice bed interface close to the ice margin steep ice velocity gradients in interlobate zones would have increased subglacial melting rates and this environment was favourable for establishment of a subglacial drainage network and deposition of glaciofluvial sediment

landform and sediment imprints of fast glacier flow in the southwest laurentide ice sheet evidence for former fast glacier flow ice streaming in the southwest laurentide ice sheet is identified on the basis of regional glacial geomorphology and sedimentology highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream preliminary mapping from a digital elevation model of alberta identifies corridors of smoothed topography and corridor parallel streamlined landforms megaflutes to mega lineations that display high levels of spatial coherency ridges that lie transverse to the dominant streamlining patterns are interpreted as a series of minor recessional push moraines b thrust block moraines or composite ridges hill hole pairs constructed during readvances surges and c overridden moraines cupola hills apparently of thrust origin together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms localised cross cutting and or misalignment of flow sets indicates temporal separation and the overprinting of ice streams lobes the fast flow tracks are separated by areas of interlobate or inter stream terrain in which moraines have been constructed at the margins of neighbouring competing ice streams outlet glaciers this inter stream terrain was covered by more sluggish non streaming ice during full glacial conditions thin tills at the centres of the fast flow corridors in many places unconformably overlying stratified sediments suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams outlet glaciers is consistent with subglacial deformation theory in this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory sometimes with fast flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally the occurrence of minor push moraines and flutings and associated landforms because of their similarity to modern active temperate glacial landsystems are interpreted as indicative of ice lobe marginal oscillations possibly in response to seasonal climatic forcing in locations where meltwater was more effectively drained from the glacier bed further north the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice bed decoupling and drawdown initiated by the development of ice dammed lakes copyright 2008 john wiley sons ltd

glacimarine sedimentary processes and facies on the polar north atlantic margins abstract major contrasts in the glaciological oceanic and atmospheric parameters affecting the polar north atlantic both over space between its eastern and western margins and through time from full glacial to interglacial conditions have lead to the deposition of a wide variety of sedimentary facies in these ice influenced seas the dynamics of the glaciers and ice sheets on the hinterlands surrounding the polar north atlantic have exterted a major influence on the processes rates and patterns of sedimentation on the continental margins of the norwegian and greenland seas over the late cenozoic the western margin is influenced by the cold east greenland current and the svalbard margin by the northernmost extent of the warm north atlantic drift and the passage of relatively warm cyclonic air masses in the fjords of spitsbergen and the northwestern barents sea glacial meltwater is dominant in delivering sediments in the fjords of east greenland the large numbers of icebergs produced from fast flowing outlets of the greenland ice sheet play a more significant role in sedimentation during full glacials sediments are delivered to the shelf break from fast flowing ice streams which drain huge basins within the parent ice sheet large prograding fans located on the continental slope offshore of these ice streams are made up of stacked debris flows large scale mass failures turbidity currents and gas escape structures also rework debris in continental slope and shelf settings even during interglacials both the margins and the deep ocean basins beyond them retain a glacimarine overprint derived from debris in far travelled icebergs and sea ice under full glacial conditions the glacier influence is correspondingly stronger and this is reflected in the glacial and glacimarine facies deposited at these times

glacial geology of western hudson strait canada with reference to laurentide ice sheet dynamics hudson strait is a large marine trough that connected the marine based interior of the laurentide ice sheet with the ocean field investigations of the glacial geology of western hudson strait have helped to define the role of the strait in laurentide ice sheet dynamics in general ice converged on western hudson strait from the north west and south upon reaching the strait ice flowing from foxe and ungava peninsulas turned eastward within less than 10 km of the coast to parallel eastwardly flowing ice in the strait glacial erosion of western hudson strait is identified as slight the texture carbonate content ph and the presence of several types of erratics distinguish till on nottingham salisbury and mill islands in western hudson strait from till on southern foxe peninsula and northern ungava peninsula till on the islands is characterized by higher ph and higher proportions of silt clay and carbonate than till on either adjacent peninsula in addition the presence of red sandstones porphyritic intrusives stromatolites omarolluks and iron formation are restricted to the islands with few exceptions that can be explained by ice rafting carbonate is present in the pebble and boulder fractions of till on foxe peninsula and in all fractions of till on the islands but is absent from till on ungava peninsula these data suggest that ice from distant and widely distributed source regions affected western hudson strait and along with evidence for a rapid change in ice flow direction along the margins of hudson strait suggest that the strait was occupied by a relatively fast moving ice stream that had a substantial impact on the interior of the ice sheet through downdraw

lower palaeozoic unconformities in an intracratonic platform setting glacial erosion versus tectonics in the eastern murzuq basin southern libya the stratigraphic record of the eastern murzuq basin has been importantly influenced by deformation resulting in angular and or deeply erosional unconformities though the overall context is intracratonic major transgressive events and the ordovician glaciation are nevertheless documented allowing the delineation of tectonic eustasy or climate driven unconformities lower palaeozoic key events and related unconformities that characterize the north gondwana platform have therefore a signature in the eastern murzuq basin the basement cover unconformity also known as the infra tassilian surface truncates all the deformed and metamorphosed lower cambrian and older rocks above is a middle cambrian to lower ordovician megasequence murizidie and hasawnah fms which is in turn truncated by an intra ordovician angular unconformity this megasequence is unconformably overlain by a middle ordovician hawaz fm to silurian tanzzuft and akakus fms megasequence which includes the upper ordovician glaciogenic unit mamuniyat fm bounded at the base by a polygenic glacial erosion surface showing corrugated glacial lineations tillites and glaciotectonic structures the middle ordovician to silurian megasequence is finally truncated by a base devonian angular unconformity overlain by fluvial sandstones regarding the possibility that those fluvial deposits may be as younger as late devonian in the eastern murzuq basin based on palaeoflora the so called caledonian unconformity might be here a much younger mid eifelian surface and the occurrence of the lower devonian tadrart fm is questioned the upper ordovician glacial erosion surface which is sometimes referred to as the taconic unconformity usually truncates middle ordovician strata in the murzuq basin but reaches significantly deeper stratigraphic levels in places that have been previously involved in the intra ordovician deformation event in the murizidie southeastern murzuq basin the infra tassilian surface the intra ordovician unconformity and the upper ordovician glacial erosion surface amalgamate together here an estimate of the glacial erosion depth cannot be derived from the stratigraphic hiatus beneath the glacial incision the main part of which relate to the intra ordovician tectonic event the upper ordovician climate related glacial erosion surface is not a valid unconformity for a sequence hierarchy framework of the lower palaeozoic although it presents most of the physical attributes of tectonic driven unconformities

reconstruction of palaeo ice sheets the use of geomorphological data the article discusses the nature of the glacial inversion problem which is defined as the extraction of time slice ice sheet flow patterns from the patchy and partly overprinted landform record present in former ice sheet areas a coherent inversion model for derivation of flow patterns and interior ice sheet configuration from geomorphological data is presented glacial landscapes are classified according to the three criteria of internal age gradients presence or absence of meltwater traces aligned to flow traces and basal condition frozen bed thawed bed inferred from morphology the inversion model uses landscapes classified accordingly spatially delineated into fans as input data relative chronologies at fan intersections are used to sort fans in a relative age stack that can be linked to stratigraphic dating information

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

iceberg production debris rafting and the extent and thickness of heinrich layers h 1 h 2 in north atlantic sediments the pattern of heinrich layer distribution for the last two events h 1 14 5 and h 2 21 1 ka mapped from magnetic susceptibility analysis of more than 50 north atlantic ocean cores provides the most detailed information to date on their extent and thickness an integrated spatial average thickness for the layers is 10 15 cm and there is a strong distance decay eastward the pattern of deposition over the north atlantic is similar for events h 1 and h 2 indicating that icebergs followed similar drift tracks rates of iceberg production and sediment flux from the hudson strait drainage basin of the north american laurentide ice sheet the major iceberg source for the events were calculated by using a mass balance approach this provides an envelope of sedimentation rates and the prediction that it would take between 50 and 1250 yr of iceberg sediment delivery to accumulate a heinrich layer averaging 10 cm thick over the north atlantic depending on the model assumptions used the most likely duration of heinrich events is 250 1250 yr

fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model the evolution of ice sheet configuration and flow pattern in fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model i e a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets the model uses mapped flow traces and deglacial melt water landforms as well as relative chronologies derived from cross cutting striae and till lineations as input data flow trace systems were classified into four types i time transgressive wet bed deglacial fans ii time transgressive frozen bed deglacial fans iii surge fans and iv synchronous non deglacial event fans using relative chronologies and aggregation of fans into glaciologically plausible patterns a series of ice sheet configurations at different time slices was erected a chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume geological evidence exists for several discrete ice sheet configurations centred over the scandinavian mountain range during the early weichselian the build up of the main weichselian fennoscandian ice sheet started at approximately 70 ka and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern norway this configuration had a flow pattern which is poorly reproduced by current numerical models of the fennoscandian ice sheet at the last glacial maximum the main ice divide was located overthe gulf of bothnia a major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the scandinavian mountain chain widespread areas of preserved pre late weichselian landscapes indicate that the ice sheet had a frozen bed core area which was only partly diminished in size by inward transgressive wet bed zones during the decay phase

identification and significance of ice flow transverse subglacial ridges rogen moraines in northern central ireland in the omagh basin north central ireland subglacial diamict ridges lie transverse to southwestward late devensian ca 23 13 ka ice flow these ridges 0 5 2 5 km long 100 450 m wide 15 35 m high are similar morphologically to rogen moraines which have not been described previously from the british isles the crests of some transverse ridges are streamlined cross cut or overprinted by drumlins whereas other ridges are unmodified and were not affected by later drumlinisation at kilskeery west east trending eskers overlying unmodified transverse ridges post date drumlinisation 17 14 14c ka esker formation shows that the subglacial thermal regime changed from cold based favouring bedform preservation to warm based with meltwater flowing through enclosed subglacial channels patterns of flow transverse ridges and spatial variations in the degree of bedform modification record dynamic changes in regional subglacial environments during the last deglacial cycle this ice mass variability cannot be reconciled with current irish glacial models which are based on immobile ice centres and ordered stages of ice retreat in a wider context these changes in bedform patterns and basal ice regimes have a similar signature to millennial scale ice mass oscillations recorded by dated proxy evidence elsewhere in the amphi north atlantic 1997 john wiley sons ltd

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

linking benthic community structure to terrestrial runoff and upwelling in the coral reefs of northeastern hainan island abstract near shore coral reefs in northeastern hainan island are close to river mouths and aquaculture ponds and also located at the center of the qiongdong upwelling qdu however it is still unclear how terrestrial runoff and upwelling influence the community composition and spatial distribution of the benthos during three cruises in 2010 and 2011 in wenchang northeastern hainan island we determined a subset of environmental parameters in seawater e g temperature salinity do dissolved inorganic nutrient din turbidity and transparency and macroalgal 15 n and investigated the benthic communities e g live coral cover coral species richness juvenile coral density macroalgal cover and coverage of calcified algae by video transect and visual census techniques at 10 stations i e 1s 6d the results showed that the qdu has influenced the reef waters in wenchang in 2011 the upwelling started in early may peaked in july and disappeared in september and most upwelling events lasted for 1 2 weeks between may and july the results also demonstrated that the reef water was nutrient enriched stations close to the river mouth and aquaculture ponds had higher levels of din and a higher percentage of ammonia in din and there was consistently lower live coral cover juvenile coral density and higher macroalgal cover at some stations in this study live coral cover was negatively correlated with macroalgal cover i e 2s 6d live coral cover species richness and juvenile coral density all increased with the distance away from the river outlet and decreased with the rise of din these results suggest that terrestrial runoff and upwelling stimulate nutrient enrichment and that overgrowing macroalgae has an important influence on the coral communities in northeastern hainan island

influence of subglacial geology on the position of a west antarctic ice stream from seismic observations ice streams drain much of the interior west antarctic ice sheet and buffer the main ice reservoir from oceanic influences1 2 the slow flowing interior feeds the floating ross ice shelf with ice via fast flowing ice streams3 that are believed to modulate sea level change through their control of inland ice storage understanding ice stream behaviour and predicting the response to climate change4 requires a better knowledge of the subglacial geology5 6 it is known that a thawed ice bed and high pressure basal water are necessary but not sufficient conditions to cause ice streaming7 8 moreover it has been hypothesized that a soft sedimentary bed is also required because of its intrinsic low frictional resistance to flow9 and owing to its high erodibility so as to generate till that can deform and lubricate ice motion10 11 or to bury rough features and smooth the bed for sliding here we use seismic observations to provide evidence that one margin of the upglacier part of an ice stream is directly above the boundary of a basin with such sedimentary fill the ice stream is within the basin and the ice outside the basin is slow flowing the basin fill presents an order of magnitude lower frictional resistance to ice flow than the subglacial material outside the basin we conclude that the ice stream position is dependent on subglacial geology

stagnation of ice stream c west antarctica by water piracy the dynamic behavior of the west antarctic ice sheet is of interest because of the possibility that it may change and cause rapid sea level rise attention is focused on the fast moving and rapidly responding ice streams that drain the ice sheet one of these ice stream c largely stopped about a century ago and some models for this shutdown postulate negative feedbacks that would tend to stabilize the ice sheet here new data are presented indicating that the slowdown of the ice stream is restricted to its lower part and occurred because of loss of lubrication on localized sticky spots at the bed of the ice stream the increased friction probably arises from a topographic accident of the glacier bed that has directed lubricating water to the neighboring ice stream b together with slow drawdown of the ice sheet rather than from any general stabilizing feedbacks

record of the vistula ice lobe advances in the late weichselian glacial sequence in north central poland during the last glacial maximum lgm the vistula ice lobe was one of the key morphological elements at the southern margin of the scandinavian ice sheet in north central poland the area of the vistula ice lobe experienced two ice sheet advances of varied extent the older one is correlated with the leszno brandenburg phase and the younger one is correlated with the poznan frankfurt phase sedimentological research and luminescence dating of the late weichselian glacial sequence in the vistula ice lobe area was conducted a new scenario of the late weichselian ice events in the area is presented the limit of the leszno phase within the vistula ice lobe was much smaller than had been accepted previously and its age is estimated to be about 20 300 bp significant ice sheet retreat was

abraded rock landforms whalebacks developed under ice streams in mountain areas like many mountain ranges the coast mountains of british columbia canada have undergone both local and ice sheet glaciation effects of ice sheets are concentrated along major valleys and on adjacent spurs and passes which carried strong flows of diffluent ice the major valleys are broad glacial troughs with frequent rock basins their slopes are broken into rounded steep sided bosses whalebacks abraded on all sides they are of the order of 100 m to 1 km long and 10 m high in the southern coast mountains the distribution of these whalebacks is consistent with a proposed pattern of former ice streams 1 0 2 1 km thick within the cordilleran ice sheet they are best developed where geological structures parallel the valley and thus the former ice flow direction but they are found on a range of lithologies and some are transverse to structure the whalebacks provide an impression of glacial streamlining and occasionally grade into rock drumlins roches moutonnees are rare in the major troughs it is hypothesised that these whalebacks and rock drumlins develop under ice streams of greenland or east antarctic type sliding rapidly over bedrock and exploiting rock weaknesses to produce streamlined features lee slopes are abraded when thick ice suppresses bed separation even with rapid flow basal ice of low viscosity would aid this suppression water pressures under the ice streams may have remained high so that lee side plucking was rare such plucking is most likely where pressure fluctuates dramatically and especially when lee cavities under active ice reach atmospheric pressure

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of 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 the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

an inter ice stream glaciated margin submarine landforms and a geomorphic model based on marine geophysical data from svalbard well preserved submarine landforms from the continental shelf and fjords of northwest ernmost svalbard provide an example of ice sheet deposition in an inter ice stream setting em1002 swath bathymetric imagery covering 1280 km 2 was examined at the shelf edge a distinctive and continuous belt of hum mocky topography represents the grounding zone of a slow moving late weichselian ice sheet active ice on the outer shelf is inferred from subtle lineations orientated parallel to fl ow low amplitude transverse moraines crosscut the lineations suggesting ice retreat across the outer shelf with brief stillstands on the middle and inner shelf large moraine ridges indicate multiple stillstands during de glaciation there are arcuate moraine ridges at fjord mouths streamlined crag and tail landforms are preserved from when ac tive full glacial ice fl owed out of the fjords clusters of smaller transverse ridges indi cate slow retreat of grounded ice through the fjords holocene sedimentation is by rainout from sediment rich meltwater producing smooth basin fi ll small slides from the fjord walls are common little ice age glacier readvance produced another set of terminal moraines and smaller retreat moraines in the innermost fjords a schematic model of this inter ice stream glacial landform assem blage summarizes the geomorphic record it is compared with a model derived from sev eral svalbard cross shelf troughs occupied by fast fl owing late weichselian ice streams in general the seafl oor morphology of continen tal margins affected by ice streams is domi nated by streamlined subglacially produced landforms oriented in the former ice fl ow direction interrupted by major grounding zone wedges formed during temporary halts in ice retreat by contrast between ice streams shelf and fjord morphology records submarine landforms of various dimensions oriented mainly transverse to ice fl ow pro duced at slowly retreating grounded ice sheet margins there is little evidence for channeled subglacial water fl ow in the form of eskers and ice contact fans on the sval bard margin implying that basal water is drained or advected mainly within soft sub glacial sediments

trough mouth fans palaeoclimate and ice sheet monitors abstract trough mouth fans are fans at the mouth of transverse troughs channels on glaciated continental shelves on the northwest european glaciated continental margin eight trough mouth fans varying in size between 2700 and 215 000 km 2 have been identified the trough mouth fans are depocentres dominated by debris flows accumulated in front of ice streams draining the former large northwest european ice sheets the debris flow units are separated by hemmipelagic interglacial interstadial sediments it is inferred that the number of debris flow units record the number of shelfbreak positions of the ice sheet margins the number found varies between three in the south and eight in the north typical trough mouth fans and related debris flow units seem to have been formed later than the early mid pleistocene thus the north european ice sheets did not form ice streams extending to the shelfbreak in any appreciable length before the mid pleistocene besides being loci for sediment deposition the trough mouth fans were also the main sites of fresh water supply to the ocean in the form of icebergs during the mid late pleistocene ice ages

antarctic ice streams a review an ice stream is a part of an inland ice sheet that flows rapidly through the surrounding ice the distinction between an ice sheet and an outlet glacier is clear in principle but muddy in practice many antarctic glaciers are intermediate in character the ross ice streams which flow through the west antarctic inland ice into the ross ice shelf are distinct in character differing even from other ice streams in the marine ice sheet of west antarctica their surface elevation profiles are low their bed slopes are low and smooth and their driving stresses diminish monotonically downglacier in transverse profile they are broader in relation to ice thickness and exhibit shallower subglacial troughs than other ice streams many models for the fast sliding of glaciers have been applied to the ross ice streams most have included in some form a reduction in basal drag resulting from a lesser effective than glaciostatic pressure at the bed most models are only semi physical at best so need to be tuned by fitting to assumed parameters at some place or places in the real ice sheet the recent discovery of a very small effective pressure beneath one ice stream consequently has led to some gross errors in the velocities predicted by the models the difficulty may be resolved if it is true as recent experiments suggest that ice stream b and by extrapolation other ross ice streams as well slide on a deforming bed that absorbs most or all of the differential motion between the ice and the bedrock