basal melting over subglacial lake ellsworth and its catchment insights from englacial layering deep water stable subglacial lakes likely contain microbial life adapted in isolation to extreme environmental conditions how water is supplied into a subglacial lake and how water outflows is important for understanding these conditions isochronal radio echo layers have been used to infer where melting occurs above lake vostok and lake concordia in east antarctica but have not been used more widely we examine englacial layers above and around lake ellsworth west antarctica to establish where the ice sheet is drawn down towards the bed and thus experiences melting layer drawdown is focused over and around the northwest parts of the lake as ice flowing obliquely to the lake axis becomes afloat drawdown can be explained by a combination of basal melting and the weertman effect at the transition from grounded to floating ice we evaluate the importance of these processes on englacial layering over lake ellsworth and discuss implications for water circulation and sediment deposition we report evidence of a second subglacial lake near the head of the hydrological catchment and present a new high resolution bed dem and hydropotential model of the lake outlet zone these observations provide insight into the connectivity between lake ellsworth and the wider subglacial hydrological system

estimating the depth and shape of subglacial lake vostok s water cavity from aerogravity data 1 we use aerogravity data to estimate the water depth of subglacial lake vostok in east antarctica the inversion produces the first bathymetry map covering the entire lake lake vostok consists of two sub basins separated by a ridge with very shallow water depths the deeper southern sub basin is approximately double the spatial area of the smaller northern sub basin the close correlation between the pattern of basal melting and freezing and the bathymetric structure has important ramifications for the water circulation and the sediment deposition we estimate the lake volume to be 5400 1600 km3

is vostok lake in steady state stable isotope d da ndd 18 o data from the vostok east antarctica ice core are used to explore whether or not subglacial vostok lake is in isotopic steady state a simple box model shows that the lake is likely to be in steady state on time scales of the order of 10 4 10 5 years three to four residence times of the water in the lake given our current knowledge of north south and east west gradients in the stable isotopic composition of precipitation in the vicinity of vostok station and ridge b however the lake may not be in perfect steady state depending on the precise location of the melting area which determines the source region of inflowing ice and on the magnitude of the east west gradient in isotopic compositions in the vicinity of vostok station and ridge b

a large deep freshwater lake beneath the ice of central east antarctica in 1974 75 an airborne radio echo survey of ice depths over central east antarctica led to the discovery of a sub ice lake of unknown depth and composition with an area of about 10 000km2 and lying beneath 4km of ice1 in 1993 altimetric data from satellite measurements2 provided independent evidence of the lake s areal extent thus confirming it to be the largest known sub ice lake by an order of magnitude here we analyse new altimetric and radio echo data along with existing seismic data3 to show that the lake is deep mean depth of 125 m or more and fresh and that it has an area that exceeds previous estimates by about 50 dimensions comparable with those of lake ontario we estimate that the residence time of the water in the lake is of the order of tens of thousands of years and that the mean age of water in the lake since deposition as surface ice is about one million years regional ice dynamics can be explained in terms of steady state ice flow along and over the lake

identification of subglacial lakes using ers 1 radar altimeter radar altimeter data from ers 1 allow detailed topographic mapping of antarctica to 82 degrees s to be carried out revealing several notable surface features among these is the large subglacial lake near vostok which is mapped here in detail the central part of the lake is found to have an exceptionally smooth surface with r m s elevation variations of less than 0 2 m a search for other large antarctic lakes in the data is made based on the smoothness and low gradient of the surface a number of other flat areas are identified with lake locations previously determined from radio echo sounding observations however radar altimeter observations show that a minimum lake size of 20 km is required for a surface above a lake to become flat numerous bowl like features can be seen in the surface topography and these may be associated with intermediate sized subglacial lakes it is determined that high spatial resolution radar altimetery could be used to identify subglacial lakes greater than 10 km in lateral extent flat regions of the ice sheet are particularly useful as they may be used as height reference surfaces to help fix the orbits of radar altimeter satellites

a decade of west antarctic subglacial lake interactions from combined icesat and cryosat 2 altimetry we use cryosat 2 interferometric satellite radar altimetry over the mercer and whillans ice streams west antarctica to derive surface elevation changes due to subglacial lake activity at monthly resolution for the period 2010 to 2013 we validate cryosat 2 elevation measurements trends and spatial patterns of change using satellite image differencing and in situ vertical movement from global positioning system gps data two subglacial lake discharge events occur in the same subglacial hydrological catchment within a 9 month period using gps measurements that are spanning the gap between the ice cloud and land elevation satellite and cryosat 2 missions we cross calibrate the two missions to establish the efficacy of cryosat 2 altimetry to measure dynamic changes on the ice sheets

ice and bedrock characteristics underneath dome c antarctica from radio echo sounding data analysis the radio echo sounding res system is one of the most widely used active remote sensing techniques for polar ice sheet exploration including bedrock morphology studies and subglacial lake investigations recently bedrock characterization has been improved through the analysis of radar echo strength in this paper the analysis of the res signal amplitude has been used to collect information about the controversial problem of electromagnetic ice absorption to highlight areas of high reflectivity variation ascribable to wet ice bedrock interfaces a method to distinguish a wet or dry bedrock ice interface using a model to describe the internal ice absorption is proposed and discussed moreover the comparison between the ice absorption rates from res measurements and from european project for ice coring in antarctica dome c antarctica ice core conductivity data the signal amplitude contributions of internal ice layers and different kinds of rock interface is evaluated encouraged by the results the data analysis led to obtaining a bedrock reflectivity variation map of the dome c area this map outlined a wide dispersion of wet dry rock interfaces in the studied area indicating the possibility of flowing water along both sides of the concordia trench

ice cover landscape setting and geological framework of lake vostok east antarctica abstract lake vostok located beneath more than 4 km of ice in the middle of east antarctica is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment melting and freezing at the base of the ice sheet which slowly flows across the lake controls the flux of water biota and sediment particles through the lake the influx of thermal energy however is limited to contributions from below thus the geological origin of lake vostok is a critical boundary condition for the subglacial ecosystem we present the first comprehensive maps of ice surface ice thickness and subglacial topography around lake vostok the ice flow across the lake and the landscape setting are closely linked to the geological origin of lake vostok our data show that lake vostok is located along a major geological boundary magnetic and gravity data are distinct east and west of the lake as is the roughness of the subglacial topography the physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake s circulation lake vostok is a tectonically controlled subglacial lake the tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small but significant amounts of thermal energy into the lake

ice flow field over lake vostok east antarctica inferred by structure tracking abstract here we present a flow field for the east antarctic ice sheet over lake vostok based on tracking structures across the lake inherited from the western upstream shoreline the structures distinctive peaks and troughs identified in the ice sheet internal layers are imaged in ice penetrating radar data collected in a systematic grid over the lake these structures are resolved in three distinct internal layers at depths between 900 and 3750 m ridges in the internal layers are associated with prominent topographic highs along the western shoreline and troughs are correlated with shoreline topographic lows lake vostok is bisected by a topographic ice divide south of this topographic divide the ice flow is dominantly nnw to sse and north of the divide the ice flow is w to e the flow over the lake is also deflected by the small 0 02 southward lake surface slope accretion ice lake water frozen to the bottom of the ice sheet is preferentially imaged along flowlines emanating from topographic ridges the coincidence of the accretion ice reflector with our flowlines both provides independent support for our new flow field and suggests focused accretion along the western shoreline global positioning system gps data provide additional independent support for our new flow field in the southern lake the new flow field will be crucial for subsequent analyses of mass exchange between the ice sheet and the lake identifying areas of melting above the lake and estimating residence times

ice flow physical processes derived from the ers 1 high resolution map of the antarctica and greenland ice sheets accepted 1999 july 7 received 1999 june 7 in original form 1998 june 24 summary the ers 1 satellite launched in 1991 has provided altimetric observations of the greenland ice sheet and 80 per cent of the antarctica ice sheet north of 82 s it was placed in a geodetic 168 day repeat orbit between april 1994 and march 1995 yielding a 1 5 km across track spacing at latitude 70 with a higher along track sampling of 350 m we have analysed the waveform altimetric data from this period to compute maps with a 1 30 grid size data processing consists of correcting for environmental factors and editing and retracking the waveforms a further step consists of reducing the radial orbit error through crossover analysis and correcting the slope error to second order the high resolution topography of both ice sheets reveals numerous details a kilometre scale surface roughness running at 45 from the flow direction is the dominant topographic characteristic of both continents antarctica also exhibits many scars due to local flow anomalies several physical processes can be identified abrupt transitions from deformation to sliding and vice versa and impressive strike slip phenomena inducing en echelon folds

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

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

exploring antarctic subglacial lakes with scientific probes a formal probabilistic approach for operational risk management since their discovery antarctic subglacial lakes have become of great interest to the science community it is hypothesized that they may hold unique forms of biological life and that they hold detailed sedimentary records of past climate change according to the latest inventory a total of 387 subglacial lakes have been identified in antarctica wright and siegert 2011 however exploration using scientific probes has yet to be performed we propose a generic formal approach to manage the operational risk of deploying probes during clean access to subglacial lake exploration a representation of the entire probe deployment process is captured in a markov chain the transition from one state to the next depends on several factors including reliability of components and processes we use fault trees to quantify the probability of failure of the complex processes that must take place to facilitate the transition from one state to another therefore the formal framework consists of integrating a markov chain fault trees component and subsystem reliability data and expert judgment to illustrate its application we describe how the approach can be used to address a series of what if scenarios using the intended ellsworth subglacial lake probe deployment as a case study

ice motion over lake vostok antarctica constraints on inferences regarding the accreted ice ice motion over lake vostok antarctica is measured using repeat pass synthetic aperture radar sar interferometry the coverage of the lake and the components of the vector field are resolved using 10 overlapping data takes from ascending and descending look directions seventy day temporal baselines provide the sensitivity required to observe the range of ice motion 0 6 m a 1 over the lake and the adjacent ice sheet it is remarkable that the scattering field remained coherent over these time separations this is critical for interferometric analysis and can be attributed to the low surface accumulation and low air temperature at this elevation the regional flow of the ice sheet around lake vostok is from west to east perpendicular to the surface elevation contours as the ice flows past the grounding line a southward component of motion develops that is correlated with the north south surface slope along the length of the lake the surface velocity increases slowly from the northern tip of the lake and then more rapidly south of 77 s at vostok station the ice motion is 4 2 m a 1 across the lake and away from boundary effects the down lake flow pattern takes on a parabolic profile with maximum velocity close to the center line of the lake the overall influence of the subglacial lake is the addition of a down lake motion component to the prevailing west east motion of the ice sheet as a result we estimate 10 of the mass flowing onto the lake is diverted south reconstructions based on the vostok ice core indicate that the ice was grounded up glacier from the core site approximately 5000 years ago this suggests a minimum freezing rate of 40 mm a 1 for the subglacial accretion ice 10 times greater than that inferred from thermodynamic modeling of the upper 2 km of the ice core

salinity impact on water flow and lake ice in lake vostok antarctica 1 lake vostok isolated from direct exchange with the atmosphere for millions of years provides a unique so far inaccessible habitat by using a numerical model and recent geometry information the lake circulation was investigated for different salinites for freshwater thermally driven circulation occurs resulting from pressure dependent melting point differences at the inclined ice ceiling north to south ice pumping provides a steady supply of glacial water the weak circulation is driven by very small density contrasts but requires no unusual geothermal input for low salinity conditions however circulation intensifies occupying the entire lake the maximum amplitudes of melting freezing increase by about 50 and melting extends further south for both conditions approximately 200 m of refrozen ice accumulates beneath vostok station the lake habitat will be affected clearly by salinity it is essential to establish the specific chemistry for comprehending this unique environment and planning in situ experiments

the role of hydrochlorofluorocarbon densifiers in the formation of clathrate hydrates in deep boreholes and subglacial environments clear evidence for the formation of mixed clathrate hydrates of air and hydrochloro fluorocarbon densifier known as hcfc 141b sometimes also called r 141b is found by means of synchrotron x ray diffraction and raman spectroscopy on a sample recovered from the bottom of the epica dronning maud land deep borehole in antarctica subglacial water sgw appears to have reacted with the drilling liquid to build a large lump of clathrate hydrate the hydrate growth may well have been accelerated by the stirring of the sgw densifier mixture during drilling moreover dissolved air in the sgw appears to have participated in the formation of mixed hydrates of air and hcfc 141b as evidenced by the concomitant appearance of raman signals from both constituents our findings elucidate to some extent the meaning of earlier accounts of the formation of heavy chips that may sink to the bottom of the borehole possibly affecting or even impeding the drilling advance these observations raise concerns with respect to the use of hcfc 141b densifiers in ice core drilling liquids under warm ice conditions

origin and fate of lake vostok water frozen to the base of the east antarctic ice sheet the subglacial lake vostok may be a unique reservoir of genetic material and it may contain organisms with distinct adaptations but it has yet to be explored directly the lake and the overlying ice sheet are closely linked as the ice sheet thickness drives the lake circulation while melting and freezing at the ice sheet base will control the flux of water biota and sediment through the lake here we present a reconstruction of the ice flow trajectories for the vostok core site using ice penetrating radar data and global positioning system gps measurements of surface ice velocity we find that the ice sheet has a significant along lake flow component persistent since the last glacial maximum the rates at which ice is frozen accreted to the base of the ice sheet are greatest at the shorelines and the accreted ice layer is subsequently transported out of the lake using these new flow field and velocity measurements we estimate the time for ice to traverse lake vostok to be 16 000 20 000 years we infer that most vostok ice analysed to date was accreted to the ice sheet close to the western shoreline and is therefore not representative of open lake conditions from the amount of accreted lake water we estimate to be exported along the southern shoreline the lake water residence time is about 13 300 years

the dimensions and topographic setting of antarctic subglacial lakes and implications for large scale water storage beneath continental ice sheets radio echo sounding res at 60 mhz has penetrated to the ice sheet bed on about 400 000 km of flight track covering more than 50 of the 13 5 x 106 km2 antarctic ice sheet about 70 subglacial lakes have been identified by characteristic strong mirror like and very flat res reflectors most are located in the ice sheet interior where numerical modeling predicts basal melting and 33 are within 100 km of the ice crest mean ice thickness above the lakes is about 3000 m about 75 of lakes have radio echo lengths of 30 km the largest is vostok lake which is 230 km long 14 000 km2 in area and has a water volume of about 2000 km3 more than 60 of lakes have maximum local bedrock elevations of 400 m and bed gradients of 0 1 adjacent to their margins extrapolating the observed side slope topography implies water depths from tens to several hundred meters in a few cases about 20 000 km2 of subglacial lakes are inferred from res which can be doubled for the entire ice sheet to yield an estimated total area of about 40 000 km2 excluding vostok lake assuming average lake depths between 50 and 250 m and including the 2000 km3 of water stored within vostok lake we calculate an envelope of about 4000 to 12 000 km3 for the likely volume of water stored in modern antarctic subglacial lakes equivalent to 10 35 mm of global sea level rise in these volume calculations it is assumed that no subglacial lakes the size of lake vostok remain to be discovered and that res length measurements along single transects are representative of overall lake dimensions our estimates of the total water volume of antarctic subglacial lakes which may be a suitable analogue for full glacial quaternary ice sheets do not necessarily conflict with the possible significance of large meltwater floods during the deglaciation of former midlatitude ice sheets

in situ stress orientations in the uk southern north sea regional trends deviations and detachment of the post zechstein stress field the orientation of the maximum horizontal compressive stress shmax in the uk southern north sea has been determined using data derived from borehole breakout analysis of four arm caliper logs the results agree with existing stress models for nw europe confirming that horizontal stresses in the region have an approximately nw se orientation of shmax this is interpreted as being a result of plate boundary convergence local deviations in the shmax orientations are observed spatially and also vertically within some wells some of these deviations are attributed to rotations of the stress field adjacent to faults or between different fault blocks the data also suggest detachment of the stress regime in the post permian cover rocks caused by the presence of a thick underlying permian aged evaporite sequence and associated halokinesis analyses of borehole resistivity image logs have been used to verify the shmax orientations in some wells these image logs validate some of the stress indicators whilst highlighting a number of deficiencies in the use of four arm caliper data to characterise borehole breakouts from the available data it is difficult to unambiguously define the nature of variations from the mean shmax orientations observed further analyses of image log data over greater depth ranges are therefore required in order to investigate more fully the effects of stress rotations near faults and apparent stress detachment above salt cored anticlinal structures

sensitivity of subglacial lake vostok s flow regime on environmental parameters abstract subglacial lakes provide unique habitats but the exact nature of physical and geochemical conditions are still a matter of debate and await direct sampling of water due to its isolation from external atmospheric forcing other environmental parameters influence the flow characteristics within the lake in this study we use an improved treatment of the physical processes at the ice water boundary interface to identify and quantify the impact of 1 the geothermal heat flux 2 the heat flux from the lake into the ice 3 the influence of the salinity of the lake water and 4 the ice thickness on the size of the freezing area and the freeze melt rates we show that the modelled basal mass imbalance that is the produced melt water minus the re frozen water depends on the geothermal heating as well as the heat flux into the ice the circulation and the temperature distribution within subglacial lake vostok are rather stable against variations of geothermal heat flux heat flux into the ice sheet salinity of the lake and small changes of the ice thickness above the lake however the flow regime for any subglacial lake with less than 2000 m ice thickness above will be substantially different from those that experience higher pressures this is because the buoyancy temperature relationship reverses at this depth

numerical modelling of ice sheet dynamics across the vostok subglacial lake central east antarctica a numerical model of the ice sheet ice shelf transformation was used to investigate ice sheet dynamics across the large subglacial lake beneath vostok station central east antarctica european remote sensing satellite ers 1 altimetry of the ice surface and 60 mhz radio echo sounding res of the ice sheet base and internal ice sheet layering were used to develop a conceptual flowline across the ice sheet which the model used as input the model calculates horizontal and vertical velocities and stresses from which particle flow paths can be obtained and the ice sheet temperature distribution an inverse approach to modelling was adopted where particle flow paths were forced to match those identified from internal res layering results show that ice dynamics across the inflow grounding line are similar to an ice sheet ice shelf transition model particle flow paths match internal res layering when ice is a taken away from the ice base across the first 2 km of the flowline over the lake and b added to the base across the remainder of the lake we contend that the process causing this transfer of ice is likely to be melting of ice and freezing of water at the ice water interface other explanations such as enhanced rates of accumulation over the grounding line of three dimensional convergent divergent flow of ice are inconsistent with available measurements such melting and refreezing would be responsible for circulation and mixing of at least the surface layers of the lake water our model suggests that several tens of metres of refrozen basal ice would accrete from lake water to the ice sheet before the ice regrounds

ice formation in subglacial lake vostok central antarctica abstract the investigation of chemical and isotopic properties in the lake ice from the vostok ice core gives clues to the mechanisms involved in ice formation within the lake a small lake water salinity can be reasonably deduced from the chemical data possible implications for the water circulation of lake vostok are developed the characteristics of the isotopic composition of the lake ice indicate that ice formation in lake vostok occurred by frazil ice crystal generation due to supercooling as a consequence of rising waters and a possible contrast in water salinity subsequent consolidation of the developed loose ice crystals results in the accretion of ice to the ceiling of the lake

a new three dimensional higher order thermomechanical ice sheet model basic sensitivity ice stream development and ice flow across subglacial lakes 1 a new three dimensional thermomechanically coupled ice sheet model is developed contrary to the majority of three dimensional ice sheet models shallow ice approximation higher order stress gradients longitudinal and transverse are accounted for in the force balance equations the horizontal velocity field is determined from the force balance equations in their derivative form elliptical equation using the method presented by pattyn 2000 2002a the model is solved on a regular grid in the horizontal and an irregular grid in the vertical and is numerically stable basic experiments include the european ice sheet modeling initiative eismint benchmarks for largescale ice sheet models and a comparison with the saito blatter ice sheet model including higher order stress gradients saito et al 2003 detailed calculations of ice flow over three dimensional bedrock perturbations showed the validity of the higher order solution the model is capable of simulating the evolution of an ice stream within the ice sheet and shows important aspects of observed ice stream features such as the surface flattening and the importance of side drag the simulation of the ice flow over a subglacial lake results in a flattening of the surface a local velocity increase over the lake and a deviation of the ice flow from the main flow direction features which are also observed at lake vostok antarctica index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3230 mathematical geophysics numerical solutions keywords higher order ice sheet model thermomechanical ice stream subglacial lake citation pattyn f a new three dimensional higher order thermomechanical ice sheet model basic sensitivity ice stream development and ice flow across subglacial lakes j geophys res 108 b8 2382 doi 10 1029 2002jb002329 2003

wissard at subglacial lake whillans west antarctica scientific operations and initial observations a clean hot water drill was used to gain access to subglacial lake whillans slw in late january 2013 as part of the whillans ice stream subglacial access research drilling wissard project over 3 days we deployed an array of scientific tools through the slw borehole a downhole camera a conductivity temperature depth ctd probe a niskin water sampler an in situ filtration unit three different sediment corers a geothermal probe and a geophysical sensor string our observations confirm the existence of a subglacial water reservoir whose presence was previously inferred from satellite altimetry and surface geophysics subglacial water is about two orders of magnitude less saline than sea water 0 37 0 41 psu vs 35 psu and two orders of magnitude more saline than pure drill meltwater 0 002 psu it reaches a minimum temperature of 0 558c consistent with depression of the freezing point by 7 019 mpa of water pressure subglacial water was turbid and remained turbid following filtration through 0 45 mm filters the recovered sediment cores which sampled down to 0 8 m below the lake bottom contained a macroscopically structureless diamicton with shear strength between 2 and 6 kpa our main operational recommendation for future subglacial access through water filled boreholes is to supply enough heat to the top of the borehole to keep it from freezing

modelling accreted ice in subglacial lake vostok antarctica 1 the distribution and thickness of accreted ice at the ice lake interface of subglacial lake vostok east antarctica is calculated conflating various sources 1 the modelled basal mass balance at the ice lake interface based on two different bathymetry models 2 different ice flow trajectories obtained from satellite interferometry and ice penetrating radar measurements and 3 reasonable ice flow velocity our results show that the accreted ice distribution is highly sensitive to the ice draft and to the used flow line directions the volume and thickness of the accreted ice depends significantly on the ice flow velocity according to our modelling we estimate the accreted ice area volume and mean thickness to be 10 800 500 km2 980 200 km3 and 90 45 m respectively for an ice flow velocity of 3 6 m a only about 36 2 of lake vostok s surface is in contact with meteoric ice melted by about 2 65 0 10 cm a this has impacts on the sedimentation rate and the supply of nutrients oxygen and or other components only present in meteoric ice but not in accreted lake ice we estimate the residence time of the lake water at about 32 000 4000 years

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

clathrate formation and the fate of noble and biologically useful gases in lake vostok antarctica 1 lake vostok is a large lake located 4 km beneath the east antarctic ice sheet that should be supersaturated with dissolved gases in equilibrium with clathrate present in the water column here we show that if the age of the lake is such that the lake water mass has been cycled over 30 times then the total dissolved gas equilibrates at about 2 5 liters stp of gas per kg of water high enough to have important implications for drilling into this deep subglacial lake different air gases are preferentially incorporated into the clathrate and thus the molar ratios in the water column will reflect the presence of clathrate and indicate a more precise age of the lake preferential incorporation of co2 into the clathrate would result in the clathrate sinking if the carbon input is 1 of the air input and the lake water is fresh water the redox state of the lake is set by the high oxygen concentration which is 50 times more than air equilibrated water and may be a severe biological stress

airborne radar survey above vostok region east central antarctica ice thickness and lake vostok geometry during the 1999 2000 italian expedition an airborne radar survey was performed along 12 transects across lake vostok antarctica and its western and eastern margins ice thickness subglacial elevation and the precise location of lake boundaries were determined radar data confirm the geometry derived from previous surveys but with some slight differences we measured a length of up to 260 km a maximum width of 81 km and an area of roughly 14 000 km 2 along the major axis from north to south the ice thickness varies from 3800 to 4250 m with a decreasing gradient from west to east the ice thickness is fairly constant except for two narrow strips located on the western and eastern margins where it increases with high thickening rate over the lake the surface elevation increases from 3476 m a s l south to 3525 north with a decreasing gradient while the lake surface elevation decreases from 315 to 750 m a s l with a decreasing gradient absolute value the ice surface and lake ceiling slopes suggest that the lake is in a state of hydrostatic equilibrium

application of a three dimensional numerical model to lake vostok an antarctic subglacial lake the circulation in two water column thickness scenarios for lake vostok a subglacial lake in central east antarctica is investigated using a three dimensional numerical model in a scenario with a constant water column thickness the distance between the sloping ice sheet which caps the lake and the lake bed the circulation is barotropic but with a more realistic water column thickness the flow is baroclinic the different circulations result from the geothermal heat flux warming shallow regions of the realistic lake more efficiently thus forming a different horizontal density structure the differences and uncertainties between the two scenarios highlight the importance that the largely unknown water column thickness and geothermal heat flux have in determining the circulation in the lake

dynamics of active subglacial lakes in recovery ice stream recovery ice stream has a substantial number of active subglacial lakes that are observed with satellite altimetry to grow and drain over multiple years these lakes store and release water that could be important for controlling the velocity of the ice stream we apply a subglacial hydrology model to analyze lake growth and drainage characteristics together with the simultaneous development of the ice stream hydrological network our outputs produce a good match between modeled lake location and those identified using satellite altimetry for many of the lakes the modeled subglacial system demonstrates development of pressure waves that initiate at the ice stream neck and transit to within 100 km of the terminus these waves alter the hydraulic potential of the ice stream and encourage growth and drainage of the subglacial lakes lake drainage can cause large r channels to develop between basal overdeepenings that persist for multiple years the pressure waves along with lake growth and drainage rates do not identically repeat over multiple years due to basal network development this suggests that the subglacial hydrology of recovery ice stream is influenced by regional drainage development on the scale of hundreds of kilometers rather than local conditions over tens of kilometers

incorporation of particulates into accreted ice above subglacial vostok lake antarctica the nature of microscopic particulates in meteoric and accreted ice from the vostok antarctica ice core is assessed in conjunction with existing ice core data to investigate the mechanism by which particulates are incorporated into refrozen lake water melted ice samples from a range of ice core depths were filtered through 0 2 mm polycarbonate membranes and secondary electron images were collected at 500 magnification using a scanning electron microscope image analysis software was used to characterize the size and shape of particulates similar distributions of major axis lengths surface areas and shape factors aspect ratio and compactness for particulates in all accreted ice samples suggest that a single process may be responsible for incorporating the vast majority of particulates for all depths calculation of stokes settling velocities for particulates of various sizes implies that 98 of particulates observed could float to the ice water interface with upward water velocities of 0 0003 m s 1 where they could be incorporated by growing ice crystals or by rising frazil ice crystals the presence of particulates that are expected to sink in the water column 2 and the uneven distribution of particulates in the ice core further implies that periodic perturbations to the lake s circulation involving increased velocities may have occurred in the past

subglacial lake ellsworth a candidate for in situ exploration in west antarctica radio echo sounding reveals a 10 km long lake beneath 3 4 km of ice near the ellsworth mountains in west antarctica 20 km from the ice divide subglacial lake ellsworth is located within a distinct topographic hollow which is 1 5 km deeper than the surrounding bed judging by bed slopes flanking the lake the water depth is at least 10s of metres calculations of basal temperature reveal the ice base to be warm both now and during full glacial periods as the environments of subglacial lakes are broadly similar life may be expected in lake ellsworth as in any other given this its physical characteristics and the fact that the west antarctic ice sheet has been accessed on several occasions lake ellsworth is an excellent candidate for in situ examination

a numerical model for an alternative origin of lake vostok and its exobiological implications for mars in connection with recent galileo images of the jovian satellite europa there has been a significantly increased interest in the subglacial lake vostok in central east antarctica since the theoretical prediction by zotikov 1961 of the existence of lakes one of which later was named vostok under 4 km of ice in antarctica and its confirmation by radar measurements from aircraft in 1974 robin et al 1977 and from the ers 1 satellite in 1993 it was tacitly assumed that the lake originated from the basal melting of ice e g zotikov 1961 1977 1986 kapitsa et al 1996 recently zotikov and duxbury 2000 proposed an alternative hypothesis that if lake vostok had existed on the surface before the antarctic perennial glaciation began 5 30 myr ago then it was buried under the thermally protecting ice and never froze all the way to the bottom in this study we support our hypothesis by comprehensive numerical modeling and evaluate its interesting implications for mars and exobiology our numerical experiments on the sensitivity of the freezing depth to different upper boundary temperatures and different internal heat flows and the recent mars global surveyor mars orbiter laser altimeter mola data support our model of the origin of possible subpolar water on mars versus the old basal melting hypothesis we also propose here experimental tests for our hypothesis as a result of our computations we conclude that lake vostok has survived the antarctic glaciation without freezing completely if it were initially an open lake with a surprisingly small water depth greater than 53 m the current water depth at a single point is as much as 500 m verkulich et al 1996 this maximum freezing depth of 53 m was reached in only 3300 years when the total upper ice cover was only 600 m the computed critical water depth is applicable to other antarctic lakes under a thick ice cover for the martian internal heat flow we have computed the critical water depth to be 63 m the existence of the lake before the accumulation of ice in antarctica implies that possible microorganisms and their remnants in the lake can be older than the antarctic ice sheet i e older than 5 30 myr if future observations find water under the martian polar caps this subpolar water according to our model has originated from lakes that were on the martian surface before the formation of mars polar caps and have not completely frozen such environments would be ideal candidates for extant or extinct life on the red planet this argues for a drilling mission at the martian polar caps

the microstructure of polar ice part i highlights from ice core research polar ice sheets play a fundamental role in earth s climate system by interacting actively and passively with the environment active interactions include the creeping flow of ice and its effects on polar geomorphology global sea level ocean and atmospheric circulation and so on passive interactions are mainly established by the formation of climate records within the ice in form of air bubbles dust particles salt microinclusions and other derivatives of airborne impurities buried by recurrent snowfalls for a half century scientists have been drilling deep ice cores in antarctica and greenland for studying such records which can go back to around a million years experience shows however that the ice sheet flow generally disrupts the stratigraphy of the bottom part of deep ice cores destroying the integrity of the oldest records for all these reasons glaciologists have been studying the microstructure of polar ice cores for decades in order to understand the genesis and fate of ice core climate records as well as to learn more about the physical properties of polar ice aiming at better climate record interpretations and ever more precise models of ice sheet dynamics in this part i we review the main difficulties and advances in deep ice core drilling in antarctica and greenland together with the major contributions of deep ice coring to the research on natural ice microstructures in particular we discuss in detail the microstructural findings from camp century byrd dye 3 grip gisp2 northgrip vostok dome c edml and dome fuji besides commenting also on the earlier results of some pioneering ventures like the jungfraujoch expedition and the norwegian british swedish antarctic expedition among others in the companion part ii of this work faria et al 2014 the review proceeds with a survey of the state of the art understanding of natural ice microstructures and some exciting prospects in this field of research

determining basal ice sheet conditions in the dome c region of east antarctica using satellite radar altimetry and airborne radio echo sounding large subglacial lakes manifest themselves as flat regions on the ice surface ers 1 satellite radar altimetry of the dome c region of east antarctica was analyzed to correlate unusually flat areas on the ice surface with known locations of subglacial lakes identified from airborne radio echo sounding res data the mean length of subglacial lakes which have an expression in the ice sheet surface was 8 3 km whilst those that did not exhibit a surface morphological manifestation had a mean length of 3 3 km thus lakes up to about 4 km in length are unlikely to be detected from satellite radar altimetry of the ice surface given that the spacing of radio echo flight tracks within the spri nsf tud antarctic database is 50 100 km in many areas a number ofsubglacial lakes probably lie undetected beneath the ice sheet res information from two large flat surface regions within dome c and a further flat area located at 80 s 127 e indicates the absence ofsubglacial lakes beneath the ice surface features however these areas are characterised by relatively strong radio echo returns which may indicate the presence of water saturated basal sediments we suggest that 1 blankets of water saturated basal sediments may cause similar surface morphological features to those produced by subglacial lakes and 2 misidentification ofsubglacial lakes from satellite altimeter observations of the ice sheet surface is possible without the support of res information relating to the ice sheet base furthermore our study indicates a lack of sub glacial lake signals from res data over relatively thick regions of east antarctica such as the adventure subglacial trough we conclude that subglacial water produced in such regions may be transported by a basal hydrological system driven by overburden pressure to less thick regions of the ice sheet where subglacial lakes have been identified

glaciology ice sheet plumbing in antarctica it s not easy to work out what is going on beneath four kilometres of ice but remote imaging has enabled the discovery of the long distance discharge of water from one subglacial lake to another in antarctica

lakes beneath the ice sheet the occurrence analysis and future exploration of lake vostok and other antarctic subglacial lakes abstract airborne geophysics has been used to identify more than 100 lakes beneath the ice sheets of antarctica the largest lake vostok is more than 250 km in length and 1 km deep subglacial lakes occur because the ice base is kept warm by geothermal heating and generated meltwater collects in topographic hollows for lake water to be in equilibrium with the ice sheet its roof must slope ten times more than the ice sheet surface this slope causes differential temperatures and melting freezing rates across the lake ceiling which excites water circulation the exploration of subglacial lakes has two goals to find and understand the life that may inhabit these unique environments and to measure the climate records that occur in sediments on lake floors the technological developments required for in situ measurements mean however that direct studies of subglacial lakes may take several years to happen

ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at vostok station east antarctica an interpretation of the deuterium profile measured along the vostok east antarctica ice core down to 2755 m has been attempted on the basis of the borehole temperature analysis an inverse problem is solved to infer a local geophysical metronome the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of milankovich periods by correlating the smoothed isotopic temperature record to the metronome a chronostratigraphy of the vostok ice core is derived with an accuracy of 3 0 4 5 kyr the developed timescale predicts an age of 241 kyr at a depth of 2760 m the ratio 13d 13t i between deuterium content and cloud temperature fluctuations at the top of the inversion layer is examined by fitting simulated and measured borehole temperature profiles the conventional estimate of the deuterium temperature slope corresponding to the present day spatial ratio 9 per mil oc is confirmed in general however the mismatch between modeled and measured borehole temperatures decreases noticeably if we allow surface temperature responsible for the thermal state of the ice sheet to undergo more intensive precession oscillations than those of the inversion temperature traced by isotope record with this assumption we obtain the long term temporal deuterium temperature slope to be 5 8 6 5 per mil oc which implies that the glacial interglacial temperature increase over central antarctica was about 15oc in the surface temperature and 10oc in the inversion temperature past variations of the accumulation rate and the corresponding changes in the ice sheet surface elevation are simultaneously simulated

subglacial floods beneath ice sheets subglacial floods jokulhlaups are well documented as occurring beneath present day glaciers and ice caps in addition it is known that massive floods have occurred from ice dammed lakes proximal to the laurentide ice sheet during the last ice age and it has been suggested that at least one such flood below the waning ice sheet was responsible for a dramatic cooling event some 8000 years ago we propose that drainage of lakes from beneath ice sheets will generally occur in a time periodic fashion and that such floods can be of severe magnitude such hydraulic eruptions are likely to have caused severe climatic disturbances in the past and may well do so in the future

new modeling of the vostok ice flow line and implication for the glaciological chronology of the vostok ice core 1 we have used new spaceborne elevation and airborne ice thickness data to constrain a 2d1 2 model of snow accumulation and ice flow along the ridge b vostok station ice flow line east antarctica we show that new evaluations of the ice flow line geometry from the surface elevation ice thickness from low frequency radar data and basal melting and sliding change significantly the chronology of the vostok ice core this new vostok dating model reconciles orbital and glaciological timescales and is in good agreement with the dome fuji glaciological timescale at the same time the new model shows significantly older ages than the previous gt4 timescale for the last glacial part being thus in better agreement with the grip and gisp2 chronologies

water exchange between the subglacial lake vostok and the overlying ice sheet it has now been known for several years that a 200 km long lake called lake vostok lies beneath the ice sheet on which sits vostok station in antarctica the conditions at the base of the ice sheet above this subglacial lake can provide information about the environment within the lake including the likelihood that it supports life here we present an analysis of the ice sheet structure from airborne 60 mhz radar studies which indicates that distinct zones of basal ice loss and accretion occur at the ice water interface subglacial melting and net ice loss occur in the north of the lake and across its 200 km long western margin whereas about 150 m of ice is gained by subglacial freezing in the south this indicates that significant quantities of water are exchanged between the base of the ice sheet and the lake waters which will enrich the lake with gas hydrates cause sediment deposition and encourage circulation of the lake water

glacial interglacial variations in central east antarctic ice accumulation rates past rates of ice accumulation in central east antarctica are defined poorly for the last glacial period ice cores from which current estimates are based are limited in number there is one deep ice core at vostok station one at dome f and two others currently being extracted at dome c and dronning maud land and are restricted spatially they are one dimensional here spatial variations in ice accumulation rates during the last glacial are calculated from isochronous internal ice sheet layering measured by airborne ice penetrating radar data the layers are used to identify the stratigraphy around five east antarctic ice domes isochrons are dated by linking them to the vostok ice core and in one case the epica dome c ice core this chronostratigraphy allows the depth age function to be identified across the ice sheet a simple ice flow model using the depth age measurements as input is then used to determine the spatial and temporal variation in east antarctic ice accumulation over the last glacial cycle the lowest rates of ice accumulation were predicted in the full glacial period to the south of dome a and ridge b there are two possible explanations for this 1 the ice divide topographies may have caused a precipitation shadow in the ice age 2 with the expansion of the ross ice shelf the area to the south of dome a and ridge b would be at the very centre of the ice sheet and hence at a maximum distance from the ocean moisture source r 2002 elsevier science ltd all rights reserved

four climate cycles in vostok ice core author s petit jr basile i leruyuet a raynaud d lorius c jouzel j stievenard m lipenkov vy barkov ni kudryashov bb davis m saltzman e kotlyakov v