a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

morphological evidence for marine ice stream shutdown central barents sea abstract marine based ice streams are responsible for a significant proportion of the ice mass loss from the present day greenland ice sheet east antarctic ice sheet eais and west antarctic ice sheet wais but the processes controlling their initiation evolution and shutdown remain elusive hindering our understanding of how existing ice masses will respond to predicted future warming the exposed beds of palaeo ice streams offer a unique opportunity to study subglacial processes which are largely inaccessible in contemporary settings we use high resolution multibeam swath bathymetry data from the barents sea to map the geomorphology of a palaeo ice stream bed located in olgastretet olga trough approximately 75 km southeast of kong karls land and 200 km east of central svalbard this reveals evidence for shut down of a marine based ice stream followed by a phase of passive retreat or lift off of the ice stream facilitating preservation of crevasse squeeze ridges csrs subsequently active retreat of the ice margin was re established and is marked by recessional moraine ridges located upstream of the csrs previously csrs have been mainly associated with surging land terminating ice margins however our work adds to recent observations of csrs on the beds of marine based ice streams implying that they may be more common than previously thought it also indicates that marine based ice streams may switch on and off in a surge like manner which has important implications for our understanding of ice stream life cycles and the modelling of ice sheets

overdeepened quaternary valleys in the eastern danish north sea morphology and origin abstract a system of 100 350 m deep overdeepened and buried valleys has been mapped in the eastern danish north sea individual valleys can be traced for several tens of kilometres and valleys generally begin and terminate abruptly a correlation to buried valleys onshore southwest denmark is possible the valleys post date glaciotectonic structures and are interpreted to be elsterian and possibly saalian in age the origin of valleys in the eastern danish north sea is explained by repeated cycles of sub glacial down cutting of meltwater channels and channel closure due to ice creep eventually producing deeply incised valleys glacial erosion may have been significant in cases where valleys are broad and shallow the origin of overdeepened quaternary valleys in general can be attributed to a combination of three end member processes i steady state drainage of meltwater ii catastrophic outbursts of meltwater and iii glacial erosion the main requirement for sub glacial valley formation is the presence of a melting ice sheet overlying a poorly consolidated substrate permeability variations of the substrate may produce subregional variations in the pattern of valley incision while pre glacial rivers faults or salt structures are of local importance only

the origin of deep buried channels of elsterian age in northwest germany buried channels cut to a depth of over 100m into the underlying substratum of north germany are almost exclusively of elsterian age evaluation of geophysical well logs in the hamburg area for the first time allows the construction of detailed longitudinal and transverse profiles it can be shown that an apparently chaotic infill known from borehole records in some cases is actually a regular sedimentary sequence fining from proximal to distal channel formation seems to have been the result of catastrophic meltwater release in the marginal parts of the ice sheet the channel infill reflects these episodic outbursts of meltwater during deglaciation the channel remnants became infilled with fine sediments the channels ceased to exist as morphologically detectable forms at the end of the holsteinian stage

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

a comparison of information value and logistic regression models in landslide susceptibility mapping by using gis this study investigates the application of information value inv and logistic regression lr models for producing landslide susceptibility maps lsms of the zigui badong area near the three gorges reservoir in china this area is subject to anthropogenic influences because the reservoir s water level cyclically fluctuates between 145 and 175 m in addition the area suffers from extreme rainfall events due to the local climate and has experienced significant and widespread landslide events in recent years in this study a landslide inventory map was initially constructed using field surveys aerial photographs and a literature search of historical landslide records eight causative factors including lithology bedding structure slope aspect elevation profile curvature plane curvature and fractional vegetation cover were then considered in the generation of lsms by using the inv and lr models finally the prediction performances of these maps were assessed through receiver operating characteristics roc that utilized both success rate and prediction rate curves the validation results showed that the area under the roc curve for the inv model was 0 859 for the success rate curve and 0 865 for prediction rate curve these results indicate the inv model surpassed the lr model 0 742 for success rate curve and 0 740 for prediction rate curve overall the two models provided nearly similar results the results of this study show that landslide susceptibility mapping in the zigui badong area is viable with both approaches

deglaciation of the central barents sea abstract the marine based barents sea ice sheet covered the polar continental shelf north of norway and western russia during the last glacial maximum initial ice sheet retreat along the western margin is well established while the retreat pattern in the interior parts of the ice sheet remains poorly known here we present new geological data from the central barents sea the results are based on analysis of several marine geophysical datasets including geomorphological mapping of multibeam swath bathymetry data and analysis of seismic and acoustic stratigraphy the new results provide insights into the configuration and dynamics of the ice sheet during its retreat across the central barents sea in particular they show clear changes in the location of the main ice divides and domes with ice flow becoming gradually more topographically controlled as deglaciation progressed major troughs were characterised by episodic retreat and reoccurring cycles of fast and slow ice flow sometimes leading to stagnation and ice shelf formation meanwhile adjacent bank areas were covered by comparatively slowly retreating ice although evidence of streaming ice is also seen locally

seafloor geomorphology of the sw barents sea and its glaci dynamic implications abstract three dimensional 3d reflection seismic imaging techniques provide a unique means of identifying large scale submarine geomorphic features produced by former ice sheets we have used such techniques to image the geomorphology of the sw barents sea but using a dense grid of 2d seismic covering a 240 000 2 km large study area supplemented with 3d seismic from selected areas the study area is located at the convergence of ice flow from the former fennoscandian barents sea and svalbard ice sheets the morphology of the major cross shelf troughs is characterized by elongated ridge groove features interpreted to be glacial bedforms produced by fast flowing grounded glaciers mega scale glacial lineations have been grouped into distinct flow sets related to three specific ice flow events these events document the last glacial maximum lgm and two readvances during deglaciation of specific interest is a detailed and well preserved set of seafloor imprints in the bjornoyrenna trough which acted as the main pathway for ice streams draining the surrounding ice sheets the geomorphic features indicate that bjornoyrenna hosted six separate ice stream lobes that diverged fan like at their margins but were not all active simultaneously an end moraine zone 68 km wide up to 85 m high and 300 km long filled the whole width of this major glacial trough as a result of high sediment flux within sub ice stream deformable beds the imprint of this ice stream system can be followed on our seabed images for 500 km however detailed geomorphologic elements demonstrate that these imprints reflect time transgressive behaviour and do not indicate the length or width of single ice streams the seismic derived seafloor geomorphology demonstrates that the barents sea ice behaved in a much more dynamic way during the last glaciation than previously assumed with major shifts between ice originating from the fennoscandian spitsbergen and barents sea ice sheets

retreat patterns and dynamics of the sentralbankrenna glacial system central barents sea accepted manuscript version published version available at https doi org 10 1016 j quascirev 2017 06 004 accepted manuscript version licensed cc by nc nd 4 0

two step deglaciation of the southeastern barents sea marine geologic evidence from the western barents sea shelf leaves little doubt that theareawascoveredbygroundediceduringthelastglaciation butthepatternandtiming of the subsequent deglaciation were not well determined here we reconstruct the timing and mechanism of ice sheet retreat as constrained by seismic stratigraphy and lithostratigraphy and accelerator mass spectrometer 14 c dating of foraminifera and mollusc shellsinsedimentboringsfromthesoutheasternbarentssea 1000kmfromthewestern shelf edge and former ice sheet margin the deposition of ice proximal glaciomarine sediments upon till began at or shortly before 12 7 ka indicating that the ice sheet retreat whichmostlikelycommencedalongthewesternmarginofthebarentsseashelfat15 14 5 ka reached the southeastern part of the shelf in 2 ka the subsequent accumulation of glaciomarinesedimentstookplaceintwodistinctpulses 12 7 12 1kaand 10 5 9 4ka separatedbyanintervalofnondepositionlasting 1 5ka thetwopulsesofsedimentation were coeval with periods of increasing surface water and air temperatures in the northern atlanticregionandacceleratedeustaticsea levelrise suggestingthattheremainingretreat of the barents shelf ice sheet was paced by these factors

large subglacial meltwater features in the central barents sea during the last glacial period large parts of the arctic including the barents sea north of norway and russia were covered by ice sheets despite several studies indicating that melting occurred beneath much of the barents sea ice sheet very few meltwater related landforms have been identified we document 200 seafloor valleys in the central barents sea and interpret them to be tunnel valleys formed by meltwater erosion beneath an ice sheet this is the first account of widespread networks of tunnel valleys in the barents sea and confirms previous predictions that large parts of the ice sheet were warm based the tunnel valleys are interpreted to be formed through a combination of steady state drainage and outburst floods close to the ice margin as a result of increased melting within a period of rapid climate warming during late deglaciation this is the first study documenting widespread tunnel valley formation at the northern reaches of a northern hemisphere paleo ice sheet during advanced deglaciation and beneath a much reduced ice sheet this indicates that suitable conditions for tunnel valley formation may have occurred more widely than previously reported and emphasizes the need to properly incorporate hydrological processes in current efforts to model ice sheet response to climate warming this study provides valuable empirical data to which modeling results can be compared

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

morphometry of bedrock meltwater channels on antarctic inner continental shelves implications for channel development and subglacial hydrology abstract expanding multibeam bathymetric data coverage over the last two decades has revealed extensive networks of submarine channels incised into bedrock on the antarctic inner continental shelf the large dimensions and prevalence of the channels implies the presence of an active subglacial hydrological system beneath the past antarctic ice sheet which we can use to learn more about inaccessible subglacial processes here we map and analyse over 2700 bedrock channels situated across 100 000 km2 of continental shelf in the western antarctic peninsula and amundsen sea to produce the first inventory of submarine channels on the antarctic inner continental shelf morphometric analysis reveals highly similar distributions of channel widths depths cross sectional areas and geometric properties with subtle differences between channels in the western antarctic peninsula compared to those in the amundsen sea at 75 3400 m wide 3 280 m deep 160 290 000 m2 in cross sectional area and typically 8 times as wide as they are deep the channels have similar morphologies to tunnel valleys and meltwater channel systems observed from other formerly glaciated landscapes despite differences in substrate geology and glaciological regime we propose that the antarctic bedrock channels formed over multiple glacial cycles through the episodic drainage of at least 59 former subglacial lakes identified on the inner continental shelf

formational history of the wicklow trough a marine transgressed tunnel valley revealing ice flow velocity and retreat rates for the largest ice stream draining the late devensian british irish ice sheet

tunnel valley formation in northwest germany geology mechanisms of formation and subglacial bed conditions for the bornhoved tunnel valley the bornhoved tunnel valley consists of a relatively broad elongated depression filled primarily with tills and a narrow channel in the axial part filled with outwash glaciolacustrine sediments and tills the tunnel valley is at least 13 km long 222 m deep bottom at 191 m b s l and extends parallel to the axis of a peripheral sink between two permian salt diapirs in the substratum it is suggested that the initiation of the tunnel valley was controlled by a differential response of the bed materials to ice overriding on top of and between the salt structures the bornhoved tunnel valley is a polygenetic feature that resulted from different erosional processes throughout all three main glaciations in northern germany during the elsterian glaciation glaciotectonic squeezing occurred to be later replaced by subglacial meltwater erosion during the ice retreat and the holsteinian interglacial the valley was filled with fine grained glaciolacustrine and marine sediments which were subsequently removed and redeposited further down ice as a 200 m thick glaciotectonic melange by the first saalian advance the second saalian advance caused only minor changes and the tunnel valley was reactivated as a subglacial channel during the weichselian glaciation it is suggested that at the time of the first weichselian ice advance a large subglacial water reservoir developed in the area of the baltic sea basin and caused a rapid surge like ice movement as the ice sheet advanced out of the baltic sea basin drainage of the water reservoir was prevented by the ice toe overriding the permafrost on the saalian highlands during the ice retreat frozen ground was left beyond the ice margin and subglacial meltwater catastrophically drained through the tunnel valley with a discharge roughly estimated at about 3 75 103 m3 s it seems possible that drainage of the subglacial water collector through the bornhoved tunnel valley and other similar channels south of the baltic sea led to increased ice sheet basal friction and was one reason for successively smaller extents of the subsequent weichselian advances evidence against pervasively deforming bed materials in the vicinity of the bornhoved tunnel valley in the weichselian glaciation indicates that the valley served as an efficient drainage path for porewater from the subglacial sediments

on the formation of the tunnel valleys of the southern laurentide ice sheet abstract catastrophic releases of meltwater produced by basal melting and stored for decades in subglacial reservoirs at high pressure may have been responsible for eroding the broad deep tunnel valleys that are common along the margins of some lobes of the southern laurentide ice sheet we surmise that these releases began when the high water pressure was transmitted to the margin through the substrate the water pressure in the substrate at the margin would then have been significantly above the overburden pressure leading to sapping failure headward erosion of a conduit in the substrate piping could then tap the stored water resulting in the outburst in some situations development of a siphon may have lowered the reservoir below its overflow level thus tapping additional water following the flood the seal could have reformed and the reservoir refilled setting up conditions for another outburst order of magnitude calculations suggest that once emptied a subglacial reservoir could refill in a matter of decades the amount of water released during several outbursts appears to be sufficient to erode a tunnel valley we think that tunnel valleys are most likely to have formed in this way where and when the glacier margin was frozen to the bed and permafrost extended from the glacier forefield several kilometers back under the glacier as reservoirs would then have been larger and more common and the seal more robust and more likely to reform after an outburst

ice stream retreat dynamics inferred from an assemblage of landforms in the northern barents sea abstract palaeo records of rapid ice stream retreat are important as they can be used to identify the processes involved and inform investigations of present day ice masses here we document a previously unknown retreat stage in northernmost bjornoyrenna bear island trough in the northern barents sea representing the youngest stage in a stepwise retreat of the bjornoyrenna ice stream we present a descriptive landsystem model for retreat of a marine based ice stream which provides new insights into the glacial dynamics of the episodic retreat stages this model captures the landforms produced during a cycle of 1 fast ice stream flow 2 intense calving of large icebergs locked in a dense matrix of smaller icebergs probably from a collapsed ice shelf 3 ice stream stagnation 4 ice stream floating off forming an ice shelf as the grounding line retreats and eventually 5 ice shelf disintegration we hypothesize that the presented ice stream retreat model reflects glacial surging the formation of corrugated furrows in the study area is consistent with interpretation of similar features in pine island bay west antarctica which are interpreted to have been formed during a massive ice shelf break up and associated grounding line retreat two directions of past ice flow are indicated from streamlined glacial landforms in the study area ice flow from north north east is indicated for the last glacial maximum and an early phase of deglaciation whereas a shift to flow from north north west from an ice dome located over hinlopenstretet svalbard is indicated for the latest deglaciation phases of the bjornoyrenna ice stream

3d seismic analysis of buried tunnel valleys in the central north sea morphology cross cutting generations and glacial history abstract this work presents the results of morpho stratigraphic analyses carried out on more than 180 buried tunnel valleys imaged in the central north sea using 3d seismic data at a variety of resolutions the buried tunnel valleys form complex networks of multiple cross cutting generations in the northern part of the study area cross cutting relationships within higher resolution 3d seismic data are used to extrapolate seven generations of tunnel valleys over an area of 14 400 km 2 three generations of cross cutting tunnel valleys are also observed within higher resolution 3d seismic data in the southern part of the study area detailed morphological measurements of individual tunnel valleys reveal average widths between 300 m and 3000 m lengths in the region of tens of kilometres and relatively straight and simple planform geometries the majority of the tunnel valleys display undulating basal profiles which provide evidence for the uphill movement of water over distances greater than 10 km and indicate formation by meltwater under pressure tunnel valley geometries vary between generations and defy a simple link between formation process and end form detailed orientation measurements for the tunnel valley generations reveal an overall ne sw trend in the northern part of the study area and a nw se directionality in the south when considered in light of palaeoglaciological models for the british and scandinavian ice sheets during the pleistocene tunnel valley orientation and distribution are consistent with the majority of tunnel valley generations forming perpendicular to a retreating british ice sheet changes in orientations between generations in both northern and southern study areas provide evidence for changes in the dynamics of the british and scandinavian ice sheets between subsequent glaciations of the central north sea

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

seismic architecture and sedimentology of a major grounding zone system deposited by the bjornoyrenna ice stream during late weichselian deglaciation abstract a 280 km wide sediment wedge in outer bjornoyrenna bear island trough south western barents sea has been investigated using 2d and 3d seismic data sediment gravity cores as well as regional swath and large scale bathymetry data the bathymetry data indicate a division into an up to 35 m high frontal wedge with large depressions and an upstream part characterized by mega scale glacial lineations msgl from seismic sections increasing erosion is demonstrated for the upstream part coinciding with the location of msgl whether the latter are depositional features postdating an extensive erosional event or formed by erosion remains inconclusive based on the distinct morphology and internal structures we infer that the system was deposited during a rapid readvance whereby the ice front pushed and bulldozed predominantly soft diluted proglacial sediments analyses in the eastern part of the sediment system reveal the existence of imbricated thrust sheets in the frontal part of the wedge this is suggested to imply upstream erosion of sedimentary rock and incorporation of thrusted blocks into the moraine forming a composite ridge locally we argue that observed large scale depressions are dead ice features in the marine environment it is envisioned that intense englacial thrusting may have developed into a decollement as the cold glacier snout got overrun by ice masses from the interior thereby enabling the inclusion of slabs of ice in the push moraine mass radiocarbon dates indicate that the sediment wedge was deposited around 17 090 cal yrs bp 14 530 14 c yrs bp and that the ice front probably remained stable until 16 580 cal yrs bp 13 835 14 c yrs bp

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

subglacial water storage and drainage beneath the fennoscandian and barents sea ice sheets abstract subglacial hydrology modulates how ice sheets flow respond to climate and deliver meltwater sediment and nutrients to proglacial and marine environments here we investigate the development of subglacial lakes and drainage networks beneath the fennoscandian and barents sea ice sheets over the late weichselian utilizing an established coupled climate ice flow model we calculate high resolution spatio temporal changes in subglacial hydraulic potential from ice sheet build up 37 ka bp to complete deglaciation 10 ka bp our analysis predicts up to 3500 potential subglacial lakes the largest of which was 658 km2 and over 70 of which had surface areas

buried and open tunnel valleys in denmark erosion beneath multiple ice sheets abstract tunnel valleys are large elongate and irregular depressions cut beneath the margin of former ice sheets they are generally believed to play a substantial role for the entire hydraulic system beneath ice sheets and thus also for ice sheet behaviour their origin however remains poorly understood examination of newly collected danish hydrogeophysical and lithological data has revealed numerous systems of buried valleys 50 350 m deep and 0 5 4 km wide these valleys are similar to the open tunnel valleys found in the present day landscape infills comprise a variety of sediments often with subglacial clay till and meltwater deposits the incised substratum consists of limestone heavy paleogene clay sand and silt the tunnel valleys have preferred orientations and can be divided into several generations each ascribed individual ice advances or ice sheets occurring during multiple glaciations the processes forming the valleys appear to prefer pre existing open and buried valleys for the renewed erosion thus old subglacial erosion pathways have been re used several times and some of the present tunnel valleys may have been established in the middle or early quaternary or even earlier this valley re use effect causes apparently anastomosed valley systems to emerge in the data images the valleys were mainly eroded by meltwater supposed to have drained from subglacially stored reservoirs probably behind a frozen margin the water was most likely released in repeated jokulhlaups and flowed in relatively small channels on the floors of the tunnel valleys which gradually became ice filled with the lowering of the bed selective linear glacial erosion is also believed to have contributed to the erosion this however was most pronounced for the widest valleys and is supposed to have played a secondary role

deglaciation of the eurasian ice sheet complex the eurasian ice sheet complex eisc was the third largest ice mass during the last glacial maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea level lowering whilst recent terrestrial and marine empirical insights have improved understanding of the chronology pattern and rates of retreat of this vast ice sheet a concerted attempt to model the deglaciation of the eisc honouring these new constraints is conspicuously lacking here we apply a first order thermomechanical ice sheet model validated against a diverse suite of empirical data to investigate the retreat of the eisc after 23 ka bp directly extending the work of patton et al 2016 who modelled the build up to its maximum extent retreat of the ice sheet complex was highly asynchronous reflecting contrasting regional sensitivities to climate forcing oceanic influence and internal dynamics most rapid retreat was experienced across the barents sea sector after 17 8 ka bp when this marine based ice sheet disintegrated at a rate of 670 gigatonnes per year gt a 1 through enhanced calving and interior dynamic thinning driven by oceanic atmospheric warming and exacerbated by eustatic sea level rise from 14 9 to 12 9 ka bp the eisc lost on average 750 gt a 1 peaking at rates 3000 gt a 1 roughly equally partitioned between surface melt and dynamic losses and potentially contributing up to 2 5 m to global sea level rise during meltwater pulse 1a independent glacio isostatic modelling constrained by an extensive inventory of relative sea level change corroborates our ice sheet loading history of the barents sea sector subglacial conditions were predominately temperate during deglaciation with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network moreover the maximum eisc and its isostatic footprint had a profound impact on the proglacial hydrological network forming the fleuve manche mega catchment which had an area of 2 5 106 km2 and drained the present day vistula elbe rhine and thames rivers through the seine estuary during the bolling allerod oscillation after c 14 6 ka bp two major proglacial lakes formed in the baltic and white seas buffering meltwater pulses from eastern fennoscandia through to the younger dryas when these massive proglacial freshwater lakes flooded into the north atlantic ocean deglaciation temporarily abated during the younger dryas stadial at 12 9 ka bp when remnant ice across svalbard franz josef land novaya zemlya fennoscandia and scotland experienced a short lived but dynamic re advance the final stage of deglaciation converged on present day ice cover around the scandes mountains and the barents sea by 8 7 ka bp although the phase lagged isostatic recovery still continues today

cross equatorial geostrophic adjustment abstract a geostrophic adjustment model is used to find out how water can cross the equator and how far it can reach while conserving its potential vorticity in the context of geostrophic adjustment a series of problems is considered all but the last permit variation north south only the first problem discusses the equatorial version of the classic midlatitude adjustment problem of a one layer reduced gravity fluid in the southern hemisphere which is suddenly permitted to slump away from its initially uniform height distribution fluid which crosses the equator reaches farther northward than it began south of the equator the configuration in which fluid reaches the farthest north requires fluid starting as far south as is possible subject to water actually crossing the equator particles move north a distance of at most 2 32 deformation radii this problem is then extended in turn to a one layer fluid occupying all space whose depth changes abruptly from one value to another and to the linearize

tunnel channels and associated landforms south central ontario their implications for ice sheet hydrology the peterborough trenton drumlin field and associated meltwater erosion marks s forms were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet the algonquin event recent theoretical modelling of ice sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet inductive testing of this hypothesis using observations in south central ontario forms the crux of this paper a geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns such a rough interactive geometry is suggested as the bed is drumlinized and flows responsible for drumlins may be expected to have eroded similar forms into the ice base three landforms in south central ontario namely tunnel channels megachannels and late stage sheet flow scours are described and interpreted as evidence of progressive channelization and flow diversion processes governed by the geometri

initiation and long term instability of the east antarctic ice sheet antarctica s continental scale ice sheets have evolved over the past 50 million years however the dearth of ice proximal geological records limits our understanding of past east antarctic ice sheet eais behaviour and thus our ability to evaluate its response to ongoing environmental change the eais is marine terminating and grounded below sea level within the aurora subglacial basin indicating that this catchment which drains ice to the sabrina coast may be sensitive to climate perturbations here we show using marine geological and geophysical data from the continental shelf seaward of the aurora subglacial basin that marine terminating glaciers existed at the sabrina coast by the early to middle eocene epoch this finding implies the existence of substantial ice volume in the aurora subglacial basin before continental scale ice sheets were established about 34 million years ago subsequently ice advanced across and retreated from the sabrina coast continental shelf at least 11 times during the oligocene and miocene epochs tunnel valleys associated with half of these glaciations indicate that a surface meltwater rich sub polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming cooling since the late miocene resulted in an expanded polar eais and a limited glacial response to pliocene warmth in the aurora subglacial basin catchment geological records from the sabrina coast shelf indicate that in addition to ocean temperature atmospheric temperature and surface derived meltwater influenced east antarctic ice mass balance under warmer than present climate conditions our results imply a dynamic eais response with continued anthropogenic warming and suggest that the eais contribution to future global sea level projections may be under estimated