antarctic snow accumulation mapped using polarization of 4 3 cm wavelength microwave emission different parts of antarctica receive different amounts of snowfall each year in this paper we map the variations of the mean annual snow accumulation across the ice sheet we also quantify the uncertainty in our estimates more objectively than has been possible for earlier maps the new map is produced using observations from satellites and ground based measurements after a logarithmic transformation these are combined using the geostatistical method of continuous part universal kriging to give an estimate of the snow accumulation within each cell of a rectangular grid covering antarctica we also derive spatial averages over the major drainage systems of the ice sheet along with their confidence intervals we obtain a value of 143 4 kg m 2 a 1 for the average rate of snow accumulation upon the grounded ice sheet of antarctica

surface and bed topography of trapridge glacier yukon territory canada digital elevation models and derived hydraulic geometry measurements of ice thickness and surface elevation are prerequisite to many glaci ological investigations a variety of techniques has been develo ped for inter pret ation of these data including means of constructing regularly gridded digital eleva tion models dem s for use in numcrical studies here we present a simple yet stati sti cally sound method for processing ice pe netr ating radar data and descr ibe a tech nique for interpol ating these data onto a regular grid dems generatcd fort rapridge glacier yukon territory canada are used to derive geometric quantities lhal give pre liminary insights into the underlying basin scale hydrol ogical syste m this simple geo metric analysis suggests that at low water press ures a dendrilic drainage netw ork exists that evolves into a uniaxial morphology as water pressure approaches notation these pre dictions are compared to hydraulic connection probabilities based on bore hole drilling

flow dynamics of the rutford ice stream ice drainage basin west antarctica from radar stratigraphy rutford ice stream west antarctica drains a catchment of 45 000 km 2 into the ronne ice shelf through a 26 km wide 2 4 km deep subglacial trough adjacent to the ellsworth mountains forty two per cent of its catchment boundary is common with pine island glacier where rapid change to ice dynamics is currently underway these changes may eventually affect adjacent catchments such as rutford radar sounding data were acquired over the rutford ice drainage basin that show the internal structure in particular distinctive reflector groups were identified that mark the boundaries between four different flow elements the flow margin reflector groups include curvilinear events that cross cut isochrones and are therefore likely to be post depositional these reflections may arise from crystal orientation fabrics generated by localized strain in a flow margin one of the sectors of the ice drainage basin supplies the largest share 38 of the ice volume flux through the main trunk of rutford ice stream this sector may be preferentially affected by continuing surface lowering in the pine island glacier catchment

late surge glacial conditions on bakaninbreen svalbard and implications for surge termination 1 bakaninbreen is a polythermal glacier in southern spitsbergen svalbard that last surged between 1985 and 1995 seismic reflection data were acquired during early quiescence in spring 1998 just upstream of the surge front the results were combined with complementary ground penetrating radar data to investigate the glacial structure and basal conditions we find no difference between the ice thickness values determined from the seismic and radar methods suggesting that any layer of basal ice cannot be greater than 5 m thick interpretation of the amplitude of the seismic reflections indicates the presence of permafrost close to the glacier base a thin layer of thawed deforming sediment separates the glacier from this underlying permafrost in an area just upstream of the surge front the permafrost becomes discontinuous and may even be absent the ice being underlain by 10 15 m of thawed sediments overlying deeper bedrock high pressure water is believed to have been required to maintain the propagation of the surge and this area of thawed sediment is interpreted as a route for that water to escape from the basal system when the surge front passed over this thawed bed the escaping water reduced the pressure in the subglacial hydraulic system initiating the termination of the surge surge termination was therefore primarily controlled by the presurge permafrost distribution beneath the glacier rather than any feature of the surge itself this termination mechanism is probably limited to surges in polythermal glaciers but the techniques used may have wider glaciological applications

bedform topography and basal conditions beneath a fast flowing west antarctic ice stream a grid of seismic reflection lines has been used to image basal topography and infer basal conditions and flow processes beneath similar to 140 km 2 of rutford ice stream west antarctica the subglacial topography in this region consists of two troughs flanking a central high and the bed is composed of water saturated sediments the two troughs are filled with deforming sediment whereas the bed in the central region appears to undergo a transition from largely deforming conditions upstream to basal sliding downstream the deforming bed is very flat along flow but undulates across flow sliding areas show rougher bed topography cross stream bed topography is characterised by streamlined mounds of deforming sediment aligned in the ice flow direction these bedforms occur superimposed on the bed in regions of both basal sliding and sediment deformation in places they form finger like mounds of material which extend into the sliding region further downstream mean bedform height is 22 m mean width is 267 m and many of them extend for at least 1 2 km along flow we interpret most of these bedforms as drumlins and one as a mega scale glacial lineation the juxtaposition of different basal conditions is consistent with models proposed from terrestrial studies in which the glacier bed is a mosaic of stable and deforming bed areas variable both spatially and temporally any theory of subglacial sediment rheology must also be able to account for our conclusion that at any given time pervasive deformation extends at least a few metres into the bed and can persist over a considerable area many km 2 bedform geometry and basal conditions concur with interpretations of former ice streams with evidence for increasing elongation ratio with distance downstream however those studies also identified bedrock cropping out at the ice bed interface for which there is no evidence on rutford ice stream c 2008 elsevier ltd all rights reserved

variations in basal conditions on rutford ice stream west antarctica seismic reflection data from two lines on rutford ice stream are presented and are compared with data already published from a third line on the ice stream the amplitude and phase of the reflections have been used to investigate the properties of the sub ice material multiple reflections on long record length data allowed calibration of the reflection coefficient at the ice bed interface and determination of the acoustic impedance of the bed material the characteristics of the bed material vary both along and across the ice stream the average acoustic impedance of the bed material across the glacier at the upstream line is 3 88 x 106 kg m 2s 1 this decreases to 3 19 x 106kg m 2s 1 52 km further downstream these values are within the range which is typical of soft sediments using acoustic impedance as an indicator of subglacial porosity some areas of the ice stream bed are interpreted as dilatant water saturated sediments undergoing pervasive deformation in other areas the bed is not deforming and basal sliding may be a more important process the proportion of the ice stream width over which bed deformation occurs increases downstream

positive mass balance of the ross ice streams west antarctica we have used ice flow velocity measurements from synthetic aperture radar to reassess the mass balance of the ross ice streams west antarctica we find strong evidence for ice sheet growth 26 8 gigatons per year in contrast to earlier estimates indicating a mass deficit 20 9 gigatons per year average thickening is equal to 25 of the accumulation rate with most of this growth occurring on ice stream c whillans ice stream which was thought to have a significantly negative mass balance is close to balance reflecting its continuing slowdown the overall positive mass balance may signal an end to the holocene retreat of these ice streams

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century

theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products publisher elsevier articletitle theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products journaltitle earth science reviews articlelink http dx doi org 10 1016 j earscirev 2016 01 010 content type article copyright copyright 2016 elsevier b v all rights reserved

geometry bed topography and drainage system structure of the haut glacier d arolla switzerland as part of an integrated study of the hydrology meltwater quality and dynamics of the haut glacier d arolla switzerland the glacier s drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier this structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by a the subglacial hydraulic potential surface and b the subglacial bedrock surface these reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio echo sounding techniques the two reconstructions simulate the drainage system structures expected for a closed channels in which water is pressurized by the overlying ice and b gravity driven open channel flow the closed channel model provides the best fit to the observed structure even though theoretical calculations suggest that under summer discharge conditions open channel flow may be widespread beneath the glacier possible reasons for this apparent discrepancy are discussed

geophysical constraints on the dynamics and retreat of the barents sea ice sheet as a paleobenchmark for models of marine ice sheet deglaciation our understanding of processes relating to the retreat of marine based ice sheets such as the west antarctic ice sheet and tidewater terminating glaciers in greenland today is still limited in particular the role of ice stream instabilities and oceanographic dynamics in driving their collapse are poorly constrained beyond observational timescales over numerous glaciations during the quaternary a marine based ice sheet has waxed and waned over the barents sea continental shelf characterized by a number of ice streams that extended to the shelf edge and subsequently collapsed during periods of climate and ocean warming increasing availability of offshore and onshore geophysical data over the last decade has significantly enhanced our knowledge of the pattern and timing of retreat of this barents sea ice sheet bsis particularly so from its late weichselian maximum extent we present a review of existing geophysical constraints that detail the dynamic evolution of the bsis through the last glacial cycle providing numerical modelers and geophysical workers with a benchmark data set with which to tune ice sheet reconstructions and explore ice sheet sensitivities and drivers of dynamic behavior although constraining data are generally spatially sporadic across the barents and kara seas behaviors such as ice sheet thinning major ice divide migration asynchronous and rapid flow switching and ice stream collapses are all evident further investigation into the drivers and mechanisms of such dynamics within this unique paleo analogue is seen as a key priority for advancing our understanding of marine based ice sheet deglaciations both in the deep past and in the short term future

seismic evidence for a water filled canal in deforming till beneath rutford ice stream west antarctica 1 seismic data from rutford ice stream west antarctica show high amplitude reversed polarity reflections from parts of the bed only interfaces between ice and water or between water and sediment have the acoustic properties to produce such strong reflections ice sediment interfaces produce much weaker echoes the evidence suggests that an area of the ice stream measuring at least 1 km by 0 2 km is underlain by water with a depth of less than 1 m the data are consistent with the presence of a sub ice drainage system comprising shallow canals cut into the sedimentary substrate as predicted by theory

rapid erosion drumlin formation and changing hydrology beneath an antarctic ice stream what happens beneath a glacier affects the way it flows and the landforms left behind when it retreats direct observations from beneath glaciers are however rare and the subglacial environment remains poorly understood we present new repeat observations from west antarctica that show active processes beneath a modern glacier which can normally only be postulated from the geological record we interpret erosion at a rate of 1 m a 1 beneath a fast flowing ice stream followed by cessation of erosion and the formation of a drumlin from mobilized sediment we also interpret both mobilization and increased compaction of basal sediment with associated hydrological changes within the glacier bed all these changes occurred on time scales of a few years or less this variability suggests that an ice stream can reorganize its bed rapidly and that present models of ice dynamics may not simulate all the relevant subglacial processes

a study of the low frequency inertio gravity waves observed during the pyrenees experiment the purpose of this paper is to analyze and interpret the onset of some well characterized transient inertio gravity waves observed during the pyrex pyrenees experiment campaign the data used are the high resolution soundings launched every 6 hours on both sides of the ridge in agreement with other observations made during the field campaign certain among those soundings often show steady mountain waves it appears that those waves are often transients and are followed by well characterized inertio gravity waves propagating upward and downward from the level where the initial mountain waves are large to interpret those observations it is suggested that the observed inertio gravity waves result from the geostrophic adjustment of the large scale flow that follows the transit and eventually the breaking of the main mountain wave this hypothesis is supported by an analytical calculation of inertio gravity waves emission from a momentum deposit that lasts a finite time the spatial extent of this forcing are also finite and its maximum amplitude is a fraction of the measured mountain drag

flow switching and water piracy between rutford ice stream and carlson inlet west antarctica rutford ice stream and carlson inlet are neighbouring glaciers in west antarctica rutford ice stream flows at speeds greater than 350m a 1 whereas carlson inlet which has some similar dimensions and supports a similar driving stress flows 10 50 times slower we discuss a range of observations concerning carlson inlet and conclude that there is good indirect evidence that it is a relict ice stream which ceased streaming more than 240 years bp but sufficiently recently that its surface morphology basal water content and basal morphology still retain characteristics produced by streaming an analysis of expected subglacial drainage pathways indicates that carlson inlet is not streaming because it is currently starved of subglacial water which is currently directed beneath rutford ice stream this current state of water piracy by rutford ice stream is however sensitive to minor thickness changes on the ice streams a similar to 120 m 4 thickening of rutford ice stream would divert almost all the subglacial water in the system towards carlson inlet and could reactivate its flow the result highlights the importance of subglacial drainage in controlling ice stream evolution and the requirement for ice sheet models to couple ice flow with subglacial drainage

subglacial water drainage storage and piracy beneath the greenland ice sheet meltwater drainage across the surface of the greenland ice sheet gris is well constrained by measurements and modeling yet despite its critical role knowledge of its transit through the subglac

quantifying subglacial bed roughness in antarctica implications for ice sheet dynamics and history abstract glaciated landscapes consist of complex assemblages of landforms resulting from ice flow dynamic regimes and ice sheet history superimposed over and in turn modifying preglacial topography lithology and geological structure insights into the formation of glaciated landscapes can in principle be obtained by analysing modern ice sheet beds but terrain analyses beneath modern ice sheets are restricted by the inaccessibility of the bed it is however possible to quantify roughness the vertical variation of the subglacial interface with horizontal distance along two dimensional images of the bed obtained from radio echo sounding res here we collate several case studies from antarctica where roughness calculations have been used as a glaciological tool to infer basal processes and ice sheet history over large 500 km 2 areas we present two examples from west antarctica which demonstrate the utility of bed roughness in determining the presence and extent of subglacial sediments glacial dynamics and former ice sheet size we also present two examples from east antarctica which illustrate how roughness provides knowledge of ice sheet dynamics in the interior and pre quaternary ice sheet histories in modern ice sheet settings characterising bed roughness along res tracks has the twin advantages of being relatively simple to calculate while producing informative subsurface data and is especially powerful at furthering understanding when coupled with knowledge of ice flow from field satellite and modelling investigations the technique also offers significant potential for the comparison of modern and former ice sheet terrains contributing to an improved understanding of the formation and evolution of glaciated landscapes

a mesoscale gravity wave event observed during ccope iii wave environment and probable source mechanisms abstract synoptic and special mesoscale observations taken during the cooperative convective precipitation experiment ccope are used to describe the multiscale environment of a gravity wave event understand the wave environment interactions that led to the development of severe thunderstorms and asses possible wave generation mechanisms the storms formed sequentially as a packet of gravity waves propagated across a stationary thunderstorm outflow boundary convection developed most rapidly in that part of the mesonetwork in which existed the combination of relatively high parcel buoyant energy weak restraining inversion strong storm downdraft potential and substantial vertical wind shear associated with a mesoscale jet streak synoptic scale analysis reveals that the waves were excited north of a stationary front and within the right exit region of the jet streak as it approached a stationary ridge in the 300 mb height field strong indications of unbalanced flow were diagnosed within the gravit

drainage networks lakes and water fluxes beneath the antarctic ice sheet antarctica bedmap2 datasets are used to calculate subglacial hydraulic potential and the area depth and volume of hydraulic potential sinks there are over 32 000 contiguous sinks which can be thought of as predicted lakes patterns of subglacial melt are modelled with a balanced ice flux flow model and water fluxes are cumulated along predicted flow pathways to quantify steady state fluxes from the main basin outlets and from known subglacial lakes the total flux from the continent is 21 km3 a 1 byrd glacier has the greatest basin flux of 2 7 km3 a 1 fluxes from subglacial lakes range from 1 10 4 to 1 5 km3 a 1 lake turnover times are calculated from their volumes and fluxes and have median values of 100 a for known active lakes and 500 a for other lakes recurrence intervals of a 0 25 km3 flood range from 2 months to 2000 a median 130 a for known active lakes and from 2 to 2400 a median 360 a for other lakes thus several lakes that have recently been observed to fill and drain may not do so again for many centuries and several lakes that have not so far been observed to fill and drain have the potential to do so even at annual to decadal timescales

evidence for subglacial water transport in the west antarctic ice sheet through three dimensional satellite radar interferometry 1 radarsat data from the 1997 antarctic mapping mission are used interferometrically to solve for the 3 dimensional surface ice motion in the interior of the west antarctic ice sheet wais an area of 125 km2 in a tributary of the kamb ice stream slumped vertically downwards by up to 50 cm between september 26 and october 18 1997 areas in the bindschadler ice stream also exhibited comparable upward and downward surface displacements as the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well we suggest transient movement of pockets of subglacial water as the most likely cause for the vertical surface displacements these results and related lidar observations imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult to observe subglacial environment and its important influence on ice dynamics

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

distortion of isochronous layers in ice revealed by ground penetrating radar in addition to measuring ice sheet thickness ground penetrating radar can be used to delineate reflections in ice sheets1 2 3 these reflections are generally accepted to result from layers of isochronous deposition of snow and can reveal much about the dynamics of the ice flow here we present ground penetrating radar data from fletcher promontory antarctica which show arches and troughs in isochronous ice layers to a depth of 100 m we demonstrate that the origin of these features can be determined by their growth with depth and many features result from local anomalies in accumulation rate which can be correlated with the ice surface slope one arch appears to be the result of a local anomaly in vertical strain rate its proximity to the ice divide width and growth with depth indicate that this arch is one of a class of features postulated by raymond4 but not previously shown to exist in the field such a feature is an indication of the nonlinear rheology of ice and requires that palaeoclimate records from ice cores extracted from the vicinity of ice divides underlain by similar features should be specifically corrected for such effects on ice flow

fortnightly variations in the flow velocity of rutford ice stream west antarctica ice sheets like that of antarctica lose much of their ice via fast flowing ice streams hilmar gudmundsson has monitored the flow in one such stream the rutford ice stream in west antarctica over a period of two months the findings are a surprise surface flow velocities here fluctuate by as much as 20 over a period of two weeks perhaps under the influence of the spring neap fortnightly tidal cycle although the mechanism that couples these tides to ice flow has yet to be elucidated these observations caution against the use of velocity measurements over limited periods to infer long term changes in flow rate monitoring of the flow of an ice sheet in antarctica finds that the surface velocity oscillates by as much as 20 per cent every two weeks the spring to neap tidal cycle seems to be the cause although the mechanism through which these tides couple to ice flow has yet to be elucidated these observations caution against the use of velocity measurements over limited periods to infer long term changes in flow rate most of the ice lost from the antarctic ice sheet passes through a few fast flowing and highly dynamic ice streams1 quantifying temporal variations in flow in these ice streams and understanding their causes is a prerequisite for estimating the potential contribution of the antarctic ice sheet to global sea level change2 3 here i show that surface velocities on a major west antarctic ice stream rutford ice stream vary periodically by about 20 per cent every two weeks as a result of tidal forcing tidally induced motion on ice streams has previously been thought to be limited to diurnal or even shorter term variations4 5 6 7 8 9 the existence of strong fortnightly variations in flow demonstrates the potential pitfalls of using repeated velocity measurements over intervals of days to infer long term change

a shaking table model test on a rock slope anchored with adaptive anchor cables abstract to determine the load transfer mechanism and dynamic response characteristics of an adaptive anchor cable aac equipped with a mechanical energy dissipation device a shaking table model test was conducted on rock slope test models anchored with a system consisting of several aacs that were fabricated based on a landslide mass in xiangjiapo during the test the strain of the aac structure and the dynamic response of the slope model were monitored to determine the anchoring mechanism of the aac system and the dynamic characteristics of the aac system anchored slope model the sliding sleeve energy dissipation device of the aac automatically adjusted its tension or deformation to allow its deformation to be consistent with that of the rock and earth mass thereby buffering the impact at the instant of the start of seismic loading the constant sliding resistance of the aac determined its working conditions under a certain seismic loading condition when the constant sliding resistance was set excessively high the energy dissipation device was ineffective under the seismic loading when the constant sliding resistance was set too small the aac slid at the instant of the start of seismic loading however when the constant sliding resistance and the sliding distance were set to proper values the aac slid gradually in a stepwise motion and its peak strain was significantly lower the test results can be used as a reference for designing cut slopes in regions of high seismicity and in selecting anti seismic engineering measures for these slopes

geomorphic signature of antarctic submarine gullies implications for continental slope processes five quantitatively distinct gully types are identified on the antarctic continental margin from swath bathymetric data of over 1100 individual features the gullies differ in terms of length width depth width depth ratio cross sectional shape branching order sinuosity and spatial density quantitative analysis suggests that antarctic gully morphology varies with local slope character i e slope geometry gradient regional factors i e location of cross shelf troughs trough mouth fans subglacial meltwater production rates drainage basin size sediment yield and ice sheet history in keeping with interpretations of previous researchers most gullies are probably formed by hyperpycnal flows of sediment laden subglacial meltwater released from beneath ice sheets grounded at the continental shelf edge during glacial maxima the limited down slope extent of gullies on the western antarctic peninsula is explained by the steep gradient and slope geometry at the mouth of marguerite trough which cause flows to accelerate and entrain seawater more quickly resulting in a reduction of the negative buoyancy effect of the sediment load due to pressure gradients at the ice sheet bed caused by variations in ice thickness inside and outside palaeo ice stream troughs subglacial meltwater flow was generally focussed towards trough margins this has resulted in gullies with larger cross sectional areas and higher sinuosities at the trough margins a unique style of gullying is observed off one part of the western antarctic peninsula corresponding to an area in which the ice sheet grounding line is not thought to have reached the shelf edge during the last glacial maximum we interpret the features in this area as the cumulative result of slope processes that operated over a long period of time in the absence of hyperpycnal meltwater flows

new boundary conditions for the west antarctic ice sheet subglacial topography beneath pine island glacier 1 predictions about future changes in the amundsen sea sector of the west antarctic ice sheet wais have been hampered by poorly known subglacial topography extensive airborne survey has allowed us to derive improved subglacial topography for the pine island glacier basin the trunk of this glacier lies in a narrow 250 km long 500 m deep sub glacial trough suggesting a long lived and constrained ice stream two tributaries lie in similar troughs others lie in less defined shallower troughs the lower basin of the glacier is surrounded by bedrock which after deglaciation and isostatic rebound could rise above sea level this feature would impede ice sheet collapse initiated near the grounding line of this glacier and prevent its progress into the deepest portions of wais the inland slope of the bed beneath the trunk of the glacier however confirms potential instability of the lower basin containing sufficient ice to raise global sea by 24 cm

structure morphology and water flux of a subglacial drainage system midtdalsbreen norway digital elevation models of the surface and bed of midtdalsbreen norway are used to calculate subglacial hydraulic potential and infer drainage system structure for a series of subglacial water pressure assumptions ranging from atmospheric to ice overburden a distributed degree day model is used to calculate the spatial distribution of melt on the glacier surface throughout a typical summer which is accumulated along the various drainage system structures to calculate water fluxes beneath the glacier and exiting the portals for the different water pressure assumptions in addition 78 dye tracing tests were performed from 33 injection sites and numerous measurements of water discharge were made on the main proglacial streams over several summer melt seasons comparison of the calculated drainage system structures and water fluxes with dye tracing results and measured proglacial stream discharges suggests that the temporally and spatially averaged steady state water pressures beneath the glacier are 70 of ice overburden analysis of the dye return curves together with the calculated subglacial water fluxes shows that the main drainage network on the eastern half of the glacier consists of a hydraulically efficient system of broad low channels average width height ratio 75 the smaller drainage network on the west consists of a hydraulically inefficient distributed system dominated by channels that are exceptionally broad and very low average width height ratio 350 the even smaller central drainage network also consists of a hydraulically inefficient distributed system dominated by channels that are very broad and exceptionally low average width height ratio 450 the channels beneath the western and central glacier must be so broad and low that they can essentially be thought of as a linked cavity system

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

thermodynamics of basal freeze on predicting basal and subglacial signatures of stopped ice streams and interstream ridges we have constructed a numerical model that simulates the response of subglacial sediments to basal freeze on the model is set up to emulate the basal zone of drilling sites in the ross sea sector of thewest antarctic ice sheet we treatbasal freeze on atanice sedimentinterfaceasathermodynamicprocessthatcouplestheflowofwater heat and solutes inunfrozensubglacial sedimentsunderlyinga freezingicebase thecouplingof these flows occurs through the clapeyron equation which specifies the dependence of the basal freezing melting temperature on ice pressure water pressure solute concentration and surface tension effects thermally driven water flow is induced when an ice base becomes supercooled below the pressure melting point because ice water surface tension inhibits ice growth in small pore spaces of fine grained subglacial sediments our model results show that basal freeze on is capable of inducing considerable changes in the basal zone of both ice streams and interstream ridges these changes are associated with specific signatures that compare with borehole observations and geophysical surveys water pres sure levels are reduced and thick layers of debris laden basal ice develop these basal ice layers andunderlying sedimentscontain a distinct isotopic signal the predicted stable iso tope ratios reflect rayleigh type isotopic fractionation whose significance increases with increasing freezing rates supercooling of the ice base induces also measurable changes in the ice temperature profile of the glacier till porosity represents another quantity whose evolution is influenced strongly by basal freeze on in particular measurements of vertical porositydistributionbeneathstoppedicestreamscouldbeusedtoback calculatethetiming of the onsetof basal freezing our modelresults show thatthebasal zoneof ice streams and interstream ridges responds sensitively to changes inbasal melting freezing rates this sen sitivity may allow reconstruction of past conditions beneath ice streams and interstream ridges from measurements made on basal ice samples and subglacial sediment samples our model resultsalso indicate thatmeltwater from fast flowing ice streams may be driven towardsthe freezing icebase of interstream ridges

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

flow and retreat of the late quaternary pine island thwaites palaeo ice stream west antarctica multibeam swath bathymetry and sub bottom profiler data are used to establish constraints on the flow and retreat history of a major palaeo ice stream that carried the combined discharge from the parts of the west antarctic ice sheet now occupied by the pine island and thwaites glacier basins sets of highly elongated bedforms show that at the last glacial maximum the route of the pine island thwaites palaeo ice stream arced north northeast following a prominent cross shelf trough in this area the grounding line advanced to within similar to 68 km of and probably reached the shelf edge minimum ice thickness is estimated at 715 m on the outer shelf and we estimate a minimum ice discharge of similar to 108 km 3 yr 1 assuming velocities similar to today s pine island glacier similar to 2 5 km yr 1 additional bed forms observed in a trough northwest of pine island bay likely formed via diachronous ice flows across the outer shelf and demonstrate switching ice stream behavior the style of ice retreat is also evident in five grounding zone wedges which suggest episodic deglaciation characterized by halts in grounding line migration up trough stillstands occurred in association with changes in ice bed gradient and phases of inferred rapid retreat correlate to higher bed slopes supporting theoretical studies that show bed geometry as a control on ice margin recession however estimates that individual wedges could have formed within several centuries still imply a relatively rapid overall retreat our findings show that the ice stream channeled a substantial fraction of west antarctica s discharge in the past just as the pine island and thwaites glaciers do today

antarctic peninsula ice sheet evolution during the cenozoic era the antarctic peninsula region is currently undergoing rapid environmental change resulting in the thinning acceleration and recession of glaciers and the sequential collapse of ice shelves it is important to view these changes in the context of long term palaeoenvironmental complexity and to understand the key processes controlling ice sheet growth and recession in addition numerical ice sheet models require detailed geological data for tuning and testing therefore this paper systematically and holistically reviews published geological evidence for antarctic peninsula ice sheet variability for each key locality throughout the cenozoic and brings together the prevailing consensus of the extent character and behaviour of the glaciations of the antarctic peninsula region major contributions include a downloadable database of 186 terrestrial and marine calibrated dates an original reconstruction of the lgm ice sheet and a new series of isochrones detailing ice sheet retreat following the lgm glaciation of antarctica was initiated around the eocene oligocene transition in east antarctica palaeogene records of antarctic peninsula glaciation are primarily restricted to king george island where glacigenic sediments provide a record of early east antarctic glaciations but with modification of far travelled erratics by local south shetland island ice caps evidence for neogene glaciation is derived primarily from king george island and james ross island where glaciovolcanic strata indicate that ice thicknesses reached 500 850 m during glacials this suggests that the antarctic peninsula ice sheet draped rather than drowned the topography marine geophysical investigations indicate multiple ice sheet advances during this time seismic profiling of continental shelf slope deposits indicates up to ten large advances of the antarctic peninsula ice sheet during the early pleistocene when the ice sheet was dominated by 40 kyr cycles glacials became more pronounced reaching the continental shelf edge and of longer duration during the middle pleistocene during the late pleistocene repeated glacials reached the shelf edge but ice shelves inhibited iceberg rafting the last glacial maximum lgm occurred at 18 ka bp after which transitional glaciomarine sediments on the continental shelf indicate ice sheet retreat the continental shelf contains large bathymetric troughs which were repeatedly occupied by large ice streams during pleistocene glaciations retreat after the lgm was episodic in the weddell sea with multiple readvances and changes in ice flow direction but rapid in the bellingshausen sea the late holocene epoch was characterised by repeated fluctuations in palaeoenvironmental conditions with associated glacial readvances however this has been subsumed by rapid warming and ice shelf collapse during the twentieth century

timing of recent accelerations of pine island glacier antarctica 1 we have used interferometric synthetic aperture radar insar data and sequential landsat imagery to identify and temporally constrain two acceleration events on pine island glacier pig these two events are separated by a period of at least seven years 1987 1994 the change in discharge between two flux gates indicates that the majority of the increase in discharge associated with the second acceleration originates well inland 80 km from the grounding line an analysis indicates that changes in driving stress consistent with observed thinning rates are sufficient in magnitude to explain much of the acceleration

river piracy and drainage basin reorganization led by climate driven glacier retreat river piracy the diversion of the headwaters of one stream into another one can dramatically change the routing of water and sediment with a profound effect on landscape evolution stream piracy has been investigated in glacial environments but so far it has mainly been studied over quaternary or longer timescales here we document how retreat of kaskawulsh glacier one of canada s largest glaciers abruptly and radically altered the regional drainage pattern in spring 2016 we use a combination of hydrological measurements and drone generated digital elevation models to show that in late may 2016 meltwater from the glacier was re routed from discharge in a northward direction into the bering sea to southward into the pacific ocean based on satellite image analysis and a signal to noise ratio as a metric of glacier retreat we conclude that this instance of river piracy was due to post industrial climate change rapid regional drainage reorganizations of this type can have profound downstream impacts on ecosystems sediment and carbon budgets and downstream communities that rely on a stable and sustained discharge we suggest that the planforms of slims and kaskawulsh rivers will adjust in response to altered flows and the future kaskawulsh watershed will extend into the now abandoned headwaters of slims river and eventually capture the kluane lake drainage river piracy the diversion of one stream s headwaters into another has occurred on long timescales an analysis of streamflow and digital elevation models documents river re routing in response to glacier retreat in yukon canada in may 2016

influence of tunneling methods on the strainburst characteristics during the excavation of deep rock masses abstract it is widely known that blasting and tbm are the general methods for the deep rock mass excavation and can respectively induce transient release of in situ stress tris and quasi static unloading of in situ stress qsuis on the excavation boundary as one of the most important triggers the unloading of in situ stress caused by excavation frequently induces strainbursts however little attention has been focused on the influence of the tunneling methods on the strainburst characteristics in this paper the cracking of surrounding rock masses and associated energy dissipation under the different tunneling methods was analyzed the influence of different tunneling methods on the evolution characteristics of strainburst was also discussed results show that compared with the tbm excavation the blasting excavation aggravates the cracking of surrounding rock masses and enlarges the energy dissipation during the cracking process during the unloading process of in situ stress the total energy and the releasable strain energy for the case of blasting excavation are much higher than that for the tbm excavation this makes that the intensity and frequency of immediate strainbursts induced by blasting excavation are much greater than that caused by tbm excavation while after the unloading of in situ stress as the surrounding rock masses dissipate larger energy during its cracking process the releasable strain energy for the case of blasting excavation is lower than that for the tbm excavation this brings down the risk of time delayed strainbursts for the blasting excavation in addition a case study at diversion tunnels in jinping ii hydropower project was presented as a verification

rothlisberger channel theory its origins and consequences the theory of channelized water flow through glaciers most commonly associated with the names of hans rothlisberger and ron shreve and their 1972 papers in the journal of glaciology was developed at a time when interest in glacier bed processes was expanding and the possible relationship between glacier sliding and water at the bed was becoming of keen interest the r channel theory provided for the first time a physically based conceptual model of water flow through glaciers the theory also marks the emergence of glacier hydrology as a glaciological discipline with goals and methods distinct from those of surface water hydrology

geomorphology and till architecture of terrestrial palaeo ice streams of the southwest laurentide ice sheet a borehole stratigraphic approach abstract a multidimensional study utilising geomorphological mapping and the analysis of regional borehole stratigraphy is employed to elucidate the regional till architecture of terrestrial palaeo ice streams relating to the late wisconsinan southwest laurentide ice sheet detailed mapping over a 57 400 km2 area of southwestern saskatchewan confirms previous reconstructions of a former southerly flowing ice stream demarcated by a 800 km long corridor of megaflutes and mega scale glacial lineations ice stream 1 and cross cut by three formerly southeast flowing ice streams ice streams 2a b and c analysis of the lithologic and geophysical characteristics of 197 borehole samples within these corridors reveals 17 stratigraphic units comprising multiple tills and associated stratified sediments overlying preglacial deposits the till thicknesses varying with both topography and distance down corridor reconciling this regional till architecture with the surficial geomorphology reveals that surficial units are spatially consistent with a dynamic switch in flow direction recorded by the cross cutting corridors of ice streams 1 2a b and c the general thickening of tills towards lobate ice stream margins is consistent with subglacial deformation theory and variations in this pattern on a more localised scale are attributed to influences of subglacial topography including thickening at buried valley margins thinning over uplands and thickening in overridden ice marginal landforms

episodic ice velocity fluctuations triggered by a subglacial flood in west antarctica height change anomalies in satellite altimeter data have been interpreted as the surface expressions of basal water moving into and out of subglacial lakes these signals have been mapped throughout antarctica on timescales of months to years but only broad connections have been made between active lakes and ice dynamics we present the first high frequency observations of ice velocity evolution due to a cascading subglacial lake drainage event collected over 5 years 2010 2015 using global positioning system data on whillans and mercer ice streams west antarctica we observed three episodic ice velocity changes over 2 years where flow speed increased by up to 4 as well as an 11 month disruption of the tidally modulated stick slip cycle that dominates regional ice motion our observations reveal that basal conditions of an antarctic ice stream can rapidly evolve and drive a dynamic ice response on subannual timescales which can bias observations used to infer long term ice sheet changes

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

gravity waves appearing in a high resolution gcm simulation global characteristics of gravity waves in the lower stratosphere are examined using a gcm with high resolution in both the horizontal t106 corresponding to about 120 km and the vertical 600 m the bottom boundary condition of the model is that of an aquaplanet with perpetual february sea surface temperature the simulated gravity waves are in good agreement with mesosphere stratosphere troposphere mst radar observations at a middle latitude on the gravity wave structure and on the frequency spectra as a function of height the frequency spectra of simulated wind and temperature fluctuations are also examined as a function of latitude large values of spectral density are observed at frequencies higher than the inertial frequency f in a weak wind region around 20 km which is consistent with the characteristics of internal gravity waves an isolated peak is observed near f for horizontal wind spectra at latitudes higher than 108 while the energy is distributed in a wide range of frequency at lower latitudes where f approaches zero further analysis is performed of those fluctuations having periods shorter than 24 h and those having vertical wavelengths smaller than 5 km these are frequently analyzed as gravity waves using observation data the distribution of energy and momentum fluxes in the latitude height section is examined the result indicates that short period waves mostly propagate upward and poleward from the equatorial region the wave energy reaches about 508 lat at the 27 km altitude a negative positive maximum of vertical flux of meridional momentum y9w9 is seen above the subtropical jet in the northern southern hemisphere for small vertical scale gravity waves this is consistent with the preferred equatorward propagation of the wave indicated by a statistical analysis based on mst radar observations the ratio of potential to kinetic energy maximizes over the equator and decreases poleward the eliassen palm flux divergence associated with gravity waves is decelerative above the subtropical jet albeit small

mass balance of the antarctic ice sheet the antarctic contribution to sea level rise has long been uncertain while regional variability in ice dynamics has been revealed a picture of mass changes throughout the continental ice sheet is lacking here we use satellite radar altimetry to measure the elevation change of 72 of the grounded ice sheet during the period 1992 2003 depending on the density of the snow giving rise to the observed elevation fluctuations the ice sheet mass trend falls in the range 5 85gt yr 1 we find that data from climate model reanalyses are not able to characterise the contemporary snowfall fluctuation with useful accuracy and our best estimate of the overall mass trend growth of 27 29 gt yr 1 is based on an assessment of the expected snowfall variability mass gains from accumulating snow particularly on the antarctic peninsula and within east antarctica exceed the ice dynamic mass loss from west antarctica the result exacerbates the difficulty of explaining twentieth century sea level rise

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

the relationship between sticky spots and radar reflectivity beneath an active west antarctic ice stream isolated areas of high basal drag or sticky spots are important and poorly understood features in the force balance and dynamics of west antarctic ice streams characterizing sticky spots formed by thin or drying subglacial till using ice penetrating radar is theoretically possible as high radar bed returned power brp is commonly related to an abundance of free water at the ice bed interface provided losses from englacial attenuation can be estimated in this study we use airborne radar data collected over evans ice stream to extract brp profiles and test the sensitivity of brp to the adopted englacial attenuation correction we analyse 11 20 km profiles in four fast flow areas where sticky spots have been inferred to exist on the basis of model and surface data inversions in the majority of profiles we note that the increase in basal drag is accompanied by a decrease in brp and suggest that this is evidence both for the presence of a sticky spot in those locations and that local variations in subglacial hydrology are responsible for their existence a comparison is made between empirical and numerical modelling approaches for deriving englacial attenuation and our findings generally support previous studies that advocate a modelling approach

the accuracy of digital elevation models of the antarctic continent abstract the accuracy of two widely used digital elevation models of antarctica was assessed using data from the geoscience laser altimeter system onboard icesat the digital elevation models were derived from satellite radar altimeter and terrestrial data sets the first termed jlb97 was produced predominantly from ers 1 data while the second termed rampv2 included other sources of data in areas of high relief and poor coverage by ers 1 the accuracy of the models was examined as a function of surface slope and original data source large errors in excess of 100 m were ubiquitous in both models in areas where terrestrially derived elevation data had been used but were more extensive in rampv2 elsewhere the systematic error bias was found to be a monotonic function of slope for jlb97 with a more complex less predictable bias for rampv2 the magnitude of the global slope dependent bias ranged from less than a metre to slightly over 10 m but with much larger regional deviations the random error ranged from about 1 m to over 100 m depending on the dem and slope the random error was consistently over a factor two larger for rampv2 compared to jlb97

rerouting of subglacial water flow between neighboring glaciers in west greenland investigations of the greenland ice sheet s subglacial hydrological system show that the connectivity of different regions of the system influences how the glacier velocity responds to variations in surface melting here we examine whether subglacial water flow paths can be rerouted beneath three outlet glaciers in the ablation zone of western greenland we use lamont doherty and center for remote sensing of ice sheets of university of kansas cresis ice penetrating radar data to create a new ice thickness map we then use a simple subglacial water flow model to examine whether flow paths can be rerouted and identify the topographic conditions that are sensitive to subglacial rerouting by varying water pressures within an observationally constrained range we show that moderate changes in pressure can cause flow paths to reroute and exchange water from one subglacial catchment to another flow across subglacial overdeepenings is particularly sensitive to rerouting these areas have low hydraulic gradients driving flow so subtle water pressure variations have a strong influence on water flow direction based on correlations between water flow paths and ice velocity changes we infer that water piracy between neighboring catchments can result in a different spatial pattern of hydrologically induced ice velocity speedup depending on the amount and timing of surface melt the potential for subglacial water to reroute across different catchments suggests that multiple hydrographs from neighboring glaciers are likely necessary to accurately ascertain melt budgets from proglacial point measurements the relationship between surface runoff ice dynamics and proglacial discharge can be altered by rerouting of subglacial water flow within and across outlet glaciers

a new volcanic province an inventory of subglacial volcanoes in west antarctica abstract the west antarctic ice sheet overlies the west antarctic rift system about which due to the comprehensive ice cover we have only limited and sporadic knowledge of volcanic activity and its extent improving our understanding of subglacial volcanic activity across the province is important both for helping to constrain how volcanism and rifting may have influenced ice sheet growth and decay over previous glacial cycles and in light of concerns over whether enhanced geothermal heat fluxes and subglacial melting may contribute to instability of the west antarctic ice sheet here we use ice sheet bed elevation data to locate individual conical edifices protruding upwards into the ice across west antarctica and we propose that these edifices represent subglacial volcanoes we used aeromagnetic aerogravity satellite imagery and databases of confirmed volcanoes to support this interpretation the overall result presented here constitutes a first inventory of west antarctica9s subglacial volcanism we identified 138 volcanoes 91 of which have not previously been identified and which are widely distributed throughout the deep basins of west antarctica but are especially concentrated and orientated along the 3000 km central axis of the west antarctic rift system

glaciological investigations on union glacier ellsworth mountains west antarctica union glacier west antarctica was intensively mapped in december 2008 when an over snow traverse was conducted by cecs and ale with the aim to determine the ice dynamical characteristics of the glacier through mapping the crevasse fields and by providing a glaciological baseline for future studies a mean ice thickness of 1450 m was measured confirming the presence of a deep subglacial topography 900 m below sea level much deeper than previously estimated ice velocities were also measured at 21 stakes drilled into the ice at the narrowest gate of the glacier between december 2007 and december 2008 yielding a mean value of 22 6 m a 1 these velocities combined with the measured ice thicknesses and a numerical model yielded an ice flux of 0 10 0 03 km 3 a 1 w e considering the ice basin above this gate a mean surface mass balance of 0 18 0 05 m a 1 was estimated a value consistent with a mean snow accumulation for nearby ice streams these values indicate that the glacier is at present near equilibrium

glacial geomorphology of the neutral hills uplands southeast alberta canada the process form imprints of dynamic ice streams and surging ice lobes abstract the neutral hills uplands of southern alberta canada is an area of complex and varied glacial landforms dominated by glacitectonic compressional structures but also containing expansive areas of hummocky terrain and kame and kettle topography it lies between the strongly streamlined trunks of the former central alberta cais and maskwa palaeo ice streams of the sw laurentide ice sheet lis and hence comprises an inter ice stream regional moraine zone constructed at around 15 5 cal ka bp this study aimed to compile a regional map of the glacial geomorphology of central southeast alberta in order to decipher the landform sediment signatures of overprinted ice stream margins in terrestrial continental environments and to refine the palaeoglaciological reconstructions for the southwest lis detailed mapping from lidar and aerial imagery identifies distinctive glacial landsystems diagnostic of the partial overprinting of cross cutting ice stream trunks and fast flow lobes widespread evidence of surge diagnostic features indicates that the ice streams experienced repeated flow instabilities consistent with the broader scenario of a highly dynamic and unstable sw lis characterised by markedly transitory and cross cutting palaeo ice streams the inter ice stream moraine zone is characterised by spectacular glacitectonic compression of bedrock cupola hill construction and mega raft displacement but also displays evidence of multi phase stagnant ice melt out where partially overprinted surge lobes advanced into large areas of buried glacier ice contemporaneous ice melting led to the widespread development of glacier karst and the production of eskers at a range of scales the largest of which record deranged drainage patterns indicative of ice walled channel sedimentation controlled by the regional bedrock slope towards the northeast these process form regimes have created a significant local relief that is a product of not only glacitectonic compression of bedrock but also the creation and melting of a melange of ice and bedrock sediment blocks of variable ice volume which are representative of former buried snout ice with a glacier karst system that was repeatedly proglacially thrust due to surging widespread evidence for subglacial channel cutting is likely strongly linked to the transitory surging and cross cutting nature of the palaeo ice streams in the region whereby ice streams switched on and surged in response to the build up migration and marginal outbursts of subglacial water reservoirs in addition to the reduced basal friction caused by the low permeability of the cretaceous bedrock pressurized groundwater and potentially also shallow biogenic gas deposits were likely important to the process form regimes of surging lobes of soft bedded ice streams in a region where ice flow was against an adverse bed slope a scenario that gave rise to a variety of enigmatic landforms such as doughnuts doughnut chains apparent blow out features and possible till eskers as well as glacitectonic mega rafts

till beneath ice stream b 1 properties derived from seismic travel times seismic experiments conducted on ice stream b part of the marine ice sheet of west antarctica show a meters thick layer immediately beneath the 1000 m thick ice a seismic experiment consisting of wide angle reflection profiling along a line parallel to ice stream flow was conducted to determine the properties of this layer inversion of seismic travel times yields a compressional wave speed of less than 1700 m s 1 and a shear wave speed less than 160 m s 1 for the layer these very low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure based on wave speeds in other saturated unconsolidated sediments we believe that a porosity substantially greater than 0 32 probably around 0 4 and an excess of overburden pressure over pore pressure of only 50 kpa 0 5 bar characterize the layer at this location

groundwater flow under a paleo ice stream of the scandinavian ice sheet and its implications for the formation of stargard drumlin field nw poland

acoustic impedance and basal shear stress beneath four antarctic ice streams the acoustic impedance of the subglacial material beneath 7 2 km profiles on four ice streams in antarctica has been measured using a seismic technique the ice streams span a wide range of dynamic conditions with flow rates of 35 464 in a 1 the acoustic impedance indicates that poorly lithified or dilated sedimentary material is ubiquitous beneath these ice streams mean acoustic impedance across each profile correlates well with basal shear stress and the slipperiness of the bed indicating that acoustic impedance is a good diagnostic not only for the porosity of the subglacial material but also for its dynamic state deforming or non deforming beneath two of the ice streams lodged non deforming and dilated deforming sediment coexist but their distribution is not obviously controlled by basal topography or ice thickness their distribution may be controlled by complex material properties or the deformation history beneath rutford ice stream lodged and dilated sediment coexist and are distributed in broad bands several kilometres wide while on talutis inlet there is considerable variability over much shorter distances this may reflect differences in the mechanism of drainage beneath the ice streams the material beneath the slow moving carlson inlet is probably lodged but unlithified sediment this is consistent with the hypothesis that carlson inlet was once a fast flowing ice stream but is now in a stagnant phase which could possibly be revived by raised basal water content the entire bed beneath fast flowing evans ice stream is dilated sediment

cross coupled flow modeling of coincident streaming and electrochemical potentials and application to subglacial self potential data 1 this study aims to demonstrate that self potential measurements can yield unique information about subglacial drainage conditions which has so far been doubtful at the bed of warm based glaciers arborescent and distributed drainage systems interact and streaming and electrochemical potentials coincide a key secondary aim of this study is therefore the development of a mathematical framework for the analysis of self potentials generated by such interacting flow systems we consider cross coupling between hydraulic electrical and chemical driving forces and apply the resulting model solution to self potential data recorded beneath haut glacier d arolla switzerland we find that 1 the streaming and electrochemical contributions to the total self potential signal can be separated mathematically 2 streaming potentials directly reflect the direction of water flow at the glacier bed 3 combination of streaming potentials with hydraulic conductivity estimates from slug tests allows estimation of in situ subglacial water flow velocities 4 the subglacial zeta potential calculated from estimated values of the streaming coupling coefficient is small 0 022 v due to systematic flushing of clay minerals from the channel area during the melt season and 5 uncertainties in exact electrode location in the borehole are unlikely to produce self potential noise self potential measurements may therefore yield unique information about subglacial drainage conditions and especially the direction and velocity of in situ subglacial water flow are difficult to obtain by other methods we further anticipate that our mathematical framework will be applicable to other areas of subsurface hydrology especially where spatially distributed seepage feeds preferential flow pathways

modelling of kealey ice rise antarctica reveals stable ice flow conditions in east ellsworth land over millennia flow at ice divides their shape size and internal structure depend not only on local conditions but also on the flow regimes and past histories of the surrounding ice masses here we use field data from kealey ice rise ellsworth land west antarctica in combination with flow modelling to investigate any possible signs of transients in the flow of the surrounding ice masses kealey ice rise shows linear surface features running parallel to its ridge in satellite imagery and a conspicuous layering in the ground penetrating radar data known as double peaked raymond bumps through numerical modelling by using an anisotropic full stokes thermomechanical flow solver we analyse the evolution of kealey ice rise and the timescales involved we conclude that the features observed in the stratigraphy of kealey ice rise require at least 3 ka of near stationary flow conditions however we cannot exclude the possibility of a recent flow reorganization in the last century we stress that the signs of stationary flow in radar stratigraphy observed in kealey ice rise have been observed in other ice divides in the east ellsworth land area suggesting stationary flow conditions over a millennial timescale in the region

microearthquakes and subglacial conditions 1 ten passive seismic recording stations were deployed in a 9 km by 6 km array on rutford ice stream west antarctica to detect microearthquakes from the ice stream bed the array covered an area where a varying distribution of basal sedimentary conditions had been identified from seismic reflection surveys and interpreted as areas of both basal sliding and subglacial sediment deformation the passive seismic experiment was designed to give an independent confirmation of this interpretation as basal sliding is believed to be associated with the release of more acoustic energy than a deforming bed the results show that this is the case basal sliding producing six times more events this confirms that the spatial pattern of basal conditions does indeed reflect the distribution of different ice flow mechanisms it also shows that microearthquake monitoring can be a valuable new technique for mapping ice stream basal conditions over wide areas

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

comparison of a large scale inertia gravity wave as seen in the ecmwf analyses and from radiosondes 1 the location characteristics and evolution of a large scale inertia gravity wave that occurred in the lower stratosphere over the north of the british isles on february 6 1997 are studied numerous high resolution radiosondes were available at that time and in that region as part of the fastex database they reveal an intense large scale inertia gravity wave igw propagating upwards above the tropopause maps of the divergence of the horizontal wind on isentropic surfaces were obtained from the ecmwf analyses and showed a clear pattern of alternating bands of convergence and divergence at the lower stratospheric heights in the same geographical region and starting at the same time the comparison of the characteristics of this igw in the analyses and in the observations suggests that the ecmwf analyses can be used for qualitative indications regarding the locations most favorable to large scale igw generation and the corresponding orientation of the waves

ice flow structure and ice dynamic changes in the weddell sea sector of west antarctica from radar imaged internal layering recent studies have aroused concerns over the potential for ice draining the weddell sea sector of west antarctica to figure more prominently in sea level contributions should buttressing from the filchner ronne ice shelf diminish to improve understanding of how ice stream dynamics there evolved through the holocene we interrogate radio echo sounding res data from across the catchments of institute and moller ice streams iis and mis focusing especially on the use of internal layering to investigate ice flow change as an important component of this work we investigate the influence that the orientation of the res acquisition track with respect to ice flow exerts on internal layering and find that this influence is minimal unless a res flight track parallels ice flow we also investigate potential changes to internal layering characteristics with depth to search for important temporal transitions in ice flow regime our findings suggest that ice in northern iis draining the ellsworth subglacial highlands has retained its present ice flow configuration throughout the holocene this contrasts with less topographically constrained ice in southern iis and much of mis whose internal layering evinces spatial changes to the configuration of ice flow over the past 10 000 years our findings confirm siegert et al s 2013 inference that fast flow was diverted from bungenstock ice rise during the late holocene and suggest that this may have represented just one component of wider regional changes to ice flow occurring across the iis and mis catchments as the west antarctic ice sheet has thinned since the last glacial maximum

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

high sensitivity of subglacial hydrological pathways in antarctica to small ice sheet changes 1 the flow of water beneath the antarctic ice sheet has recently been shown to involve drainage from and exchange between subglacial lakes with flow routing over distances of 100km as subglacial water is known to be important to ice sheet dynamics changes to the flow routing of basal water may yield an ice sheet response here we show that the directions of subglacial hydrological flowpaths are highly sensitive to the ice sheet surface topography at certain sites in antarctica surface elevation changes of between 5 and 15 m are found to be sufficient to produce significant changes to the subglacial water flowpaths which affect the potential drainage routes of large subglacial lakes we identify the reasons for this high sensitivity and recognise several locations in east antarctica where changes to the drainage regime could have important effects on large scale basal water distribution

inertia gravity wave generation by the tropospheric midlatitude jet as given by the fronts and atlantic storm track experiment radio soundings 1 generation of inertia gravity waves by the midlatitude tropospheric jet is studied on the basis of the data obtained from the radio soundings over the north atlantic during the fronts and atlantic storm track experiment campaign a sample of 224 radio soundings is used to analyze the wave activity as a function of the distance to the jet it is shown that radio soundings displaying the most intense gravity wave activity both in the stratosphere and in the troposphere are the ones closest to the jet axis thus the jet region is the dominant source of gravity waves in this region far from orography further examination allows for identification of two specific regions of the flow that are associated with intense gravity wave activity the vicinity of the maximum of the jet velocity and the regions of strong curvature of the jet the detailed case studies we provide suggest that geostrophic adjustment is the dynamical mechanism responsible for the generation of large amplitude inertia gravity waves in the regions of the strong curvature of the wind the generation of waves in the vicinity of the regions where the wind veers in the deep troughs of the geopotential appears to be systematic

rapid recent warming on rutford ice stream west antarctica from borehole thermometry 1 the antarctic peninsula has warmed faster than the global average rate of warming during the last century due to limited availability of long term meteorological records the geographical extent of this rapid warming is poorly defined we collected borehole temperature measurements in the upper 300 m of rutford ice stream west antarctica and employed an inverse modeling scheme with a heat diffusion advection equation to determine the recent surface temperature history of the borehole position our results reveal recent warming of 0 17 0 07 c decade 1 since 1930 this result suggests that at least in an attenuated form the rapid warming observed over the antarctic peninsula extends as far south as rutford ice stream this result agrees with other recent results that show a warming trend across much of the west antarctic ice sheet

basal conditions on rutford ice stream west antarctica from seismic observations a seismic reflection profile perpendicular to the ice flow direction has been acquired on rutford ice stream antarctica an interpretation of both the amplitude and phase of the seismic reflections from the ice bed interface has been made to investigate the properties of the sub ice material the interpretation assumes that acoustic impedance can be used to imply subglacial sediment porosity multiple reflections from the ice bed interface on a number of seismic wide angle lines allowed a calibration of the reflection coefficient at the bed this enabled the acoustic impedance of the bed material to be calculated from the seismic reflection data mean acoustic impedance in the different sections of the bed ranges from 2 70 106 kg m 2 s 1 to 4 31 106 kg m 2 s 1 almost three quarters of the ice stream bed at this site appears to be saturated deforming sediments the rest of the bed is probably also saturated sediments but they are not deforming to any significant degree ice flow could include a combination of subglacial deformation and basal sliding localized regions which support disproportionately high amounts of basal shear stress may also occur from the seismic data it is not possible to apportion relative amounts of restraint to these different processes there does not appear to be any correlation between the different sections identified on the ice stream bed with either satellite images or nearby surface velocity data a feature which is interpreted as a subglacial drumlin is seen on the seismic section

synthetic aperture radar interferometry over rutford ice stream and carlson inlet antarctica we describe the calibration and interpretation of interferograms generated from ers i synthetic aperture radar single look complex sar slc images of the rutford ice stream area ground surveys provide over 100 tie points with which to optimise the interferometric baselines that separate nominally repeated satellite orbits covariant tie point errors are dealt with by constructing an error covariance matrix for the expected values of the unwrapped interferometric phases at the tie points with baseline parameters that minimise the weighted residual variance rms tie point residuals of less than i cm in slant range are obtained these are attributed to a combination of interferometric phase noise movement survey errors and inadequate slope information the image set used is inadequate for isolating the influences of topography and movement so the glaciological conclusions to be drawn are limited nevertheless the interferograms confirm that the whole of the upper 50 k m of carlson inlet flows at a speed less than a tenth of that of the neighbouring rutford ice stream also confirmed are the entry of faster moving ice into the lower reaches of carlson inlet and the position of part of the carlson inlet grounding line in general the distribution of the residuals suggests no significant differences in ice movement between 1978 and 1992 an exception is the neighbourhood of the shear margin between rutford ice stream and carlson inlet where inconsistencies between ground surveys over the periods 1984 86 and 1994 96 and interferograms from 1994 a n d 1996 suggest fluctuations in velocity of up to 10 m year 1

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

thirteen years of subglacial lake activity in antarctica from multi mission satellite altimetry the ability to detect the surface expression of moving water beneath the antarctic ice sheet by satellite has revealed a dynamic basal environment with implications for regional ice dynamics grounding line stability and fluxes of freshwater and nutrients to the southern ocean knowledge of subglacial activity on timescales important for near term prediction of ice sheet fluctuations decadal to century is limited by the short observational record of nasa s ice cloud and land elevation satellite icesat laser altimetry mission used to generate the last continent wide survey 2003 08 here we use synthetic aperture radar interferometric mode data from esa s cryosat 2 radar altimetry mission 2010 present which samples 45 of the icesat derived subglacial lakes to extend their time series to the end of 2016 the extended time series show that there have been surface height changes at 20 of the 45 lakes since 2008 indicating that some of these features are persistent and potentially cyclic while other features show negligible changes suggesting these may be transient or nonhydrological features continued monitoring of active lakes for both height and velocity changes as well as developing methods for identifying additional lakes is critical to quantifying the full distribution of active subglacial lakes in antarctica

what controls the location of ice streams ice streams influence ice sheet mass balance and stability but key aspects of their behaviour remain poorly understood this paper reviews and discusses one very important aspect what controls their location in an ice sheet seven potential controls on ice stream location are identified from the literature topographic focusing topographic steps macro scale bed roughness calving margins subglacial geology geothermal heat flux and subglacial meltwater routing for each control the theoretical basis for its link to rapid ice flow is introduced followed by discussion of the evidence of its influence on the location of both contemporary and palaeo ice streams based on this new synthesis topographic focusing subglacial geology meltwater routing and calving margins appear to be most commonly associated with fast ice flow it is clear that rather than a single control however there exist a number of potential controls of varying influence we propose a hierarchy of factors with those occurring at the top of the hierarchy exerting a stronger influence on ice stream location and where present beneath an ice sheet are very likely to be associated with fast flow those factors occurring lower down the hierarchy are less commonly associated with ice streaming but appear to be influential in the absence of more common controls in such a hierarchy topographic focusing in the presence of a calving margin is the primary control in the absence of this ice streams will preferentially occur in areas with favourable subglacial meltwater routing and subglacial geology in the absence of these bed roughness geothermal heat flux and topographic steps may promote ice streaming significantly the primary controls on a given ice stream location are likely to influence its spatial and temporal dynamics ice streams governed by the presence of meltwater routing and or calving processes might exhibit more variable behaviour because these controls can vary over relatively short time scales compared to controls that vary over longer time scales e g geothermal heat flux subglacial roughness geology and topography identifying the controls on ice stream location is therefore of paramount importance when understanding ice stream longevity and their past and future activity