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

precise analysis of icesat altimetry data and assessment of the hydrostatic equilibrium for subglacial lake vostok east antarctica summary based on the ice cloud and land elevation satellite icesat laser altimetry data the hydrostatic equilibrium he condition for the subglacial lake vostok east antarctica is evaluated a digital elevation model dem of the ice surface is derived by a regional crossover adjustment the analysis of the dem and its comparison with gps derived ice surface elevations and an ice surface dem based on radar altimetry data reveal an overall accuracy of better than 0 7 m for the lake area the dem is combined with an ice thickness model and a regional geoid model to determine the deviation of the local ice surface height from he for large parts of the lake the ice sheet fulfils the he our results reveal a strong positive deviation of about 10 m along the lake shoreline in addition positive deviations are found in the northern part of the lake which coincide with ice rumples detected by radio echo sounding in the southern part of the lake we find a linear negative deviation 4 0 m which coincides with the convoy route from vostok station to mirny base in addition to the dem relative biases for the icesat laser operational periods are determined in the regional crossover adjustment

ice flow sensitivity to boundary processes a coupled model study in the vostok subglacial lake area antarctica several hundred subglacial lakes have been identified beneath antarctica so far their interaction with the overlying ice sheet and their influence on ice dynamics are still subjects of investigation while it is known that lakes reduce the ice sheet friction towards a free slip basal boundary condition little is known about how basal melting and freezing at the lake ice interface modifies the ice dynamics thermal regime and ice rheology in this diagnostic study we simulate the vostok subglacial lake area with a coupled full stokes 3 d ice flow model and a 3 d lake circulation model the exchange of energy heat and mass at the lake ice interface increases decreases the temperature in the ice column above the lake by up to 10 in freezing melting areas resulting in a significant modification of the highly nonlinear ice viscosity we show that basal lubrication at the bottom of the ice sheet has a significant impact not only on the ice flow above the lake itself but also on the vicinity and far field while the ice flow crosses vostok subglacial lake flow divergence is observed and modelled the heterogeneous basal mass balance pattern at the lake ice interface intensifies this divergence instead of interactive coupling between the ice flow model and the lake flow model only a single iteration is required for a realistic representation of the ice water interaction in addition our study indicates that simplified parameterizations of the surface temperature boundary condition might lead to a velocity error of 20 for the area of investigation

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

the hydrochemistry of lake vostok and the potential for life in antarctic subglacial lakes our understanding of lake vostok the huge subglacial lake beneath the east antarctic ice sheet has improved recently through the identification of key physical and chemical interactions between the ice sheet and the lake the north of the lake where the overlying ice sheet is thickest is characterized by subglacial melting whereas freezing of lake water occurs in the south resulting in 210 m of ice accretion to the underside of the ice sheet the accreted ice contains lower concentrations of the impurities normally found in glacier ice suggesting a net transfer of material from meltwater into the lake the small numbers of microbes found so far within the accreted ice have dna profiles similar to those of contemporary surface microbes microbiologists expect however that lake vostok and other subglacial lakes will harbour unique species particularly within the deeper waters and associated sediments the extreme environments of subglacial lakes are characterized by high pressures low temperatures permanent darkness limited nutrient availability and oxygen concentrations that are derived from the ice that provides the meltwater copyright 2002 john wiley sons ltd

dielectric properties of jovian satellite ice analogs for subsurface radar exploration a review the first european mission dedicated to the exploration of jupiter and its icy moons jupiter icy moons explorer juice will be launched in 2022 and will reach its final destination in 2030 the main goals of this mission are to understand the internal structure of the icy crusts of three galilean satellites europa ganymede and callisto and ultimately to detect europa s subsurface ocean which is believed to be the closest to the surface among those hypothesized to exist on these moons juice will be equipped with the 9 mhz subsurface penetrating radar rime radar for icy moon exploration which is designed to image the ice down to a depth of 9 km moreover a parallel mission to europa which will host onboard reason radar for europa assessment and sounding ocean to near surface equipped with 9mhz and 60mhz antennas has been recently approved by nasa the success of these experiments strongly relies on the accurate prediction of the radar performance and on the optimal processing and interpretation of radar echoes that in turn depend on the dielectric properties of the materials composing the icy satellite crusts in the present review we report a complete range of potential ice types that may occur on these icy satellites to understand how they may affect the results of the proposed missions first we discuss the experimental results on pure and doped water ice in the framework of the jaccard theory highlighting the critical aspects in terms of a lack of standard laboratory procedures and inconsistency in data interpretation we then describe the dielectric behavior of extraterrestrial ice analogs like hydrates and icy mixtures carbon dioxide ice and ammonia ice building on this review we have selected the most suitable data to compute dielectric attenuation velocity vertical resolution and reflection coefficients for such icy moon environments with the final goal being to estimate the potential capabilities of the radar missions as a function of the frequency and temperature ranges of interest for the subsurface sounders we present the different subsurface scenarios and associated radar signal attenuation models that have been proposed so far to simulate the structure of the crust of europa and discuss the physical and geological nature of various dielectric targets potentially detectable with rime finally we briefly highlight several unresolved issues that should be addressed in near future to improve our capability to produce realistic electromagnetic models of icy moon crusts the present review is of interest for the geophysical exploration of all solar system bodies including the earth where ice can be present at the surface or at relatively shallow depths

anomalous accumulation rates in the vostok ice core resulting from ice flow over lake vostok the accumulation rate of snow is crucial to the development of accurate age depth models for ice cores the dating of the vostok ice core assumes that accumulation rates generally vary linearly between the core site and the ice divide 250 km to the west jouzel et al 1996 lorius et al 1985 petit et al 1999 an assumption which impacts the timing of prominent climatic transitions we present evidence for a local accumulation rate anomaly at the ice surface above the western shoreline of lake vostok a significant thickening between isochronous layers results from this geographically fixed high accumulation zone which can be stratigraphically traced to a depth of 820 1100 m in the vostok ice core a portion known for its high accumulation rates and paleoclimate records that deviate from other antarctic ice core records this non climatic accumulation anomaly in the vostok ice core impacts the flow dependent age models and subsequent interpretations of sequencing of global climate shifts during the last glacial additional unrecognized accumulation anomalies are likely present at other depths in this and other cores these previously unreported geographically fixed accumulation rate anomalies are introduced into ice cores drilled away from ice domes e g byrd and vostok and should be considered in age depth models

circulation in lake vostok a laboratory analogue study 1 the waters of sub glacial lake vostok are thought to represent a unique biological habitat that has been out of contact with the atmosphere for millions of years although the water circulation within the lake will determine how nutrients are redistributed and hence where life may exist the handful of existing studies conflict regarding whether the lake is stratified or well mixed whether there is a clockwise or anti clockwise circulation or whether the sloping roof leads to a flow intensified along the eastern boundary here an experimental analogue model of lake vostok is used to show a qualitatively different mode of circulation than described previously the dominant mode of dispersion and hence bio and chemical redistribution is controlled by the presence of columnar vortex structures that arise from rotating convection this form of circulation does not occur in any other lake on earth we estimate that a water parcel takes 20 30 days to travel from the base to the roof of lake vostok and will experience minimal lateral mixing during this time as the nutrient supply to the lake via melting ice is predicted to be less than that required for active growth within the entire lake we speculate that this form of slow columnar convection would lead to the presence of thin biological boundary layers within the waters of the lake this has important implications for the interpretation of any direct water samples taken near the roof of lake vostok

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

the role of subglacial water in ice sheet mass balance subglacial water can significantly affect the velocity of ice streams and outlet glaciers of ice sheets depending on the geometry and capacity of the subglacial hydrologic system increased surface melting in greenland over the coming decades may influence the ice sheet s mass balance furthermore subglacial lakes in antarctica can modulate ice velocities and act as nucleation points for new fast flowing ice streams in the coming decades significant changes in the polar regions will increase the contribution of ice sheets to global sea level rise under the ice streams and outlet glaciers that deliver ice to the oceans water and deformable wet sediments lubricate the base facilitating fast ice flow the influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system water moving rapidly through a well connected system of conduits or channels will have little impact on ice sheet velocities but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet and thereby trigger increased ice sheet velocities in greenland the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice sheet mass balance in antarctica subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice flow tributaries climate models of ice sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics

investigating the stability of subglacial lakes with a full stokes ice sheet model despite the large amount of subglacial lakes present underneath the east antarctic ice sheet and the melt processes involved the hydrology beneath the ice sheet is poorly understood changes in subglacial potential gradients may lead to subglacial lake outbursts discharging excess water through a subglacial drainage system underneath the ice sheet such processes can eventually lead to an increase in ice flow in this paper a full stokes numerical ice sheet model was employed which takes into account the ice flow over subglacial water bodies in hydrostatic equilibrium with the overlying ice sensitivity experiments were carried out for small perturbations in ice flow and basal melt rate as a function of ice thickness general surface slope ice viscosity and lake size in order to investigate their influence on the subglacial potential gradient and the impact on subglacial lake drainage experiments clearly demonstrate that small changes in surface slope are sufficient to start and sustain episodic subglacial drainage events lake drainage can therefore be regarded as a common feature of the subglacial hydrological system and may influence to a large extent the present and future behavior of large ice sheets

dielectric signatures and evolution of glacier ice we analyzed the dielectric spectra 0 1 hz 1 mhz of 49 firn and ice samples from ice sheets and glaciers to better understand how differing ice formation and evolution affect electrical properties the dielectric relaxation of ice is well known and its characteristic frequency increases with the concentration of soluble impurities in the ice lattice we found that meteoric ice and firn generally possess two such relaxations indicating distinct crystal populations or zonation typically one population is consistent with that of relatively pure ice and the other is significantly more impure however high temperatures e g temperate ice long residence times e g ancient ice from mullins glacier antarctica or anomalously high impurity concentrations favor the development of a single relaxation these relationships suggest that annealing causes two dielectrically distinct populations to merge into one population the dielectric response of temperate ice samples indicates increasing purity with increasing depth suggesting ongoing rejection of impurities from the lattice separately subglacially lake frozen samples from the vostok antarctica 5g ice core possess a single relaxation whose variable characteristic frequency likely reflects the composition of the source water we conclude that multi frequency methods are essential to dielectric discrimination between different types of glacier ice

calculating the balance between atmospheric co2 drawdown and organic carbon oxidation in subglacial hydrochemical systems in order to constrain co2 fluxes from biogeochemical processes in subglacial environments we model the evolution of ph and alkalinity over a range of subglacial weathering conditions we show that subglacial waters reach or exceed atmospheric pco2 levels when atmospheric gases are able to partially access the subglacial environment subsequently closed system oxidation of sulfides is capable of producing pco2 levels well in excess of atmosphere levels without any input from the decay of organic matter we compared this model to published ph and alkalinity measurements from 21 glaciers and ice sheets most subglacial waters are near atmospheric pco2 values the assumption of an initial period of open system weathering requires substantial organic carbon oxidation in only 4 of the 21 analyzed ice bodies if the subglacial environment is assumed to be closed from any input of atmospheric gas large organic carbon inputs are required in nearly all cases these closed system assumptions imply that order of 10 g m 2 y 1 of organic carbon are removed from a typical subglacial environment a rate too high to represent soil carbon built up over previous interglacial periods and far in excess of fluxes of surface deposited organic carbon partial open system input of atmospheric gases is therefore likely in most subglacial environments the decay of organic carbon is still important to subglacial inorganic chemistry where substantial reserves of ancient organic carbon are found in bedrock in glaciers and ice sheets on silicate bedrock substantial long term drawdown of atmospheric co2 occurs

contributions of an ancient evaporitic type reservoir to subglacial lake vostok chemistry abstract we present here the first comprehensive study of the chemical composition of accretion ice from lake vostok ion chromatographic analyses were performed on samples obtained along the deeper part of the vostok ice core samples were taken from 3350 down to 3611 m depth both in glacier ice and subglacial lake ice the total ionic contents of two accretion ice layers a few meters thick and centered around 3540 and 3590 m depth are several times lower than those of glacier ice very low concentrations were also observed in the deeper part of accretion ice below 3609 m depth elsewhere the total ionic content is variable but remains 5 to 50 times higher than in glacier ice whatever its total ionic content the ionic composition of accretion ice is significantly different from what is observed in glacier ice it is dominated by sodium chloride homogeneously distributed throughout the ice lattice as well as calcium and magnesium sulfate likely located in solid inclusions or to a lesser extent at grain boundaries chemical considerations combined with additional studies of sulfur and oxygen isotopes in sulfate and iron measurements strongly suggest that glacier water recycling and bedrock hydrolysis do not play a prominent role in providing impurities to accretion ice it is more likely that nacl rich water carrying fine sulfate salt particles is sporadically incorporated in the ice accreting in a shallow bay upstream from vostok the origin of such salty water which should also contribute to lake salinity is discussed

new 3d bathymetry and sediment distribution in lake vostok implication for pre glacial origin and numerical modeling of the internal processes within the lake abstract a new distribution of water and unconsolidated sediments in subglacial lake vostok east antarctica was developed via inversion of airborne gravity data constrained by 60 seismic soundings a model was developed for host rock with a density of 2550 kg m 3 that was inferred from prior 2d modeling our 3d bathymetry model of lake vostok corresponds better with seismic data rms of 125 m than two previous models based on the same gravity dataset the good match in both water and sediment thicknesses between the gravity model and seismic measurements confirms two major facts about lake vostok 1 the lake is hosted by sedimentary rocks and 2 the bottom of the lake is covered with a layer of unconsolidated sediments that does not exceed 300 m in the southern basin and thickens almost to 400 m in the northern basin our new bathymetry model suggests much shallower water thicknesses up to twice the previous estimates in the middle and northern parts of the lake while the water layer is thicker in the southern basin numerical modeling of the internal processes in the lake reveals the relevance of our new bathymetry model to the basal mass balance a significant decrease in transport is observed in the shallower northern basin as well as a decrease of 33 in the turbulent kinetic energy however only minor differences were observed in the distribution of the calculated freezing and melting zones compared to previous models estimates for the sedimentation rates for six possible mechanisms were made possible sedimentation mechanisms are 1 fluvial and periglacial i e those that are active prior to the establishment of a large subglacial lake 2 deposition due to overlying ice sheet including melting out of the ice as well as bulldozering by the overriding ice and 3 suspended sediments from subglacial water flow including those deposited by periodical subglacial outbursts the estimates for these mechanisms show that unconsolidated sediments of the observed thickness are most consistent with a lake that existed before glaciation

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

millennially averaged accumulation rates for the vostok subglacial lake region inferred from deep internal layers accumulation rates and their spatio temporal variability are important boundary conditions for ice flow models the depths of radar detected internal layers can be used to infer the spatial variability of accumulation rates here we infer accumulation rates from three radar layers 26 35 and 41 ka old in the vostok subglacial lake region using two methods 1 the local layer approximation lla and 2 a combination of steady state flowband modeling and formal inverse methods the lla assumes that the strain rate history of a particle traveling through the ice sheet can be approximated by the vertical strain rate profile at the current position of the particle which we further assume is uniform the flowband model however can account for upstream strain rate gradients we use the lla to map accumulation rates over a 150 km 350 km area and we apply the flowband model along four flowbands the lla accumulation rate map shows higher values in the northwestern corner of our study area and lower values near the downstream shoreline of the lake these features are also present but less distinct in the flowband accumulation rate profiles the lla inferred accumulation rate patterns over the three time periods are all similar suggesting that the regional pattern did not change significantly between the start of the holocene and the last 20 ka of the last glacial period however the accumulation rate profiles inferred from the flowband model suggest changes during that period of up to 1 cm a 1 or 50 of the inferred values

constraints on hydrothermal processes and water exchange in lake vostok from helium isotopes lake vostok the largest subglacial lake in antarctica is covered by the east antarctic ice sheet which varies in thickness between 3 750 and 4 100 m ref 1 at a depth of 3 539 m in the drill hole at vostok station sharp changes in stable isotopes and the gas content of the ice delineate the boundary between glacier ice and ice accreted through re freezing of lake water2 unlike most gases helium can be incorporated into the crystal structure of ice during freezing3 making helium isotopes in the accreted ice a valuable source of information on lake environment here we present helium isotope measurements from the deep section of the vostok ice core that encompasses the boundary between the glacier ice and accreted ice showing that the accreted ice is enriched by a helium source with a radiogenic isotope signature typical of an old continental province this result rules out any significant hydrothermal energy input into the lake from high enthalpy mantle processes which would be expected to produce a much higher 3he 4he ratio based on the average helium flux for continental areas the helium budget of the lake leads to a renewal time of the lake of the order of 5 000 years

a microbial ecosystem beneath the west antarctic ice sheet liquid water has been known to occur beneath the antarctic ice sheet for more than 40 years but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial antarctic lake subglacial lake whillans slw lies beneath approximately 800 m of ice on the lower portion of the whillans ice stream wis in west antarctica and is part of an extensive and evolving subglacial drainage network the water column of slw contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component heterotrophic and autotrophic production data together with small subunit ribosomal rna gene sequencing and biogeochemical data indicate that slw is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea our results confirm that aquatic environments beneath the antarctic ice sheet support viable microbial ecosystems corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes that can mobilize elements from the lithosphere and influence southern ocean geochemical and biological systems

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

influx of meltwater to subglacial lake concordia east antarctica we present evidence for melting at the base of the ice that overlies lake concordia an 800 km2 subglacial lake near dome concordia east antarctica via a combination of glaciohydraulic melting associated with the tilted ice ceiling and its influence on lake circulation melting temperature and melting by extreme strain heating where the ice sheet is grounded an influx of water is necessary to provide nutrients material and biota to support subglacial lake ecosystems but has not been detected previously freezing is the dominant observed basal process at over 60 of the surface area above the lake the total volume of accreted ice above the lake surface is estimated as 50 60 km3 roughly 25 30 of the 200 40 km3 estimated lake volume estimated rates of melting and freezing are very similar 2 6 mm a 1 the apparent net freezing may reflect the present day response of lake concordia to cooling associated with the last glacial maximum or a large influx of water either via a subglacial hydrological system or from additional melting of the ice sheet lake concordia is an excellent candidate for subglacial exploration given active basal processes proximity to the dome concordia ice core and traverse resupply route

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

an inventory of active subglacial lakes in antarctica detected by icesat 2003 2008 through the detection of surface deformation in response to water movement recent satellite studies have demonstrated the existence of subglacial lakes in antarctica that fill and drain on timescales of months to years these studies however were confined to specific regions of the ice sheet here we present the first comprehensive study of these active lakes for the antarctic ice sheet north of 868 s based on 4 5 years 2003 08 of nasa s ice cloud and land elevation satellite icesat laser altimeter data our analysis has detected 124 lakes that were active during this period and we estimate volume changes for each lake the icesat detected lakes are prevalent in coastal antarctica and are present under most of the largest ice stream catchments lakes sometimes appear to transfer water from one to another but also often exchange water with distributed sources undetectable by icesat suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow thus these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds but also may withdraw water at other times to slow flow

deformation warming and softening of greenland s ice by refreezing meltwater when basal meltwater refreezes the resulting warm ice can influence the flow dynamics of the ice sheet above an analysis of airborne gravity and radar data identifies extensive basal ice units across the northern greenland ice sheet that coincide with areas of deformed ice and fast ice flow

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

spatial and temporal variability of snow accumulation in east antarctica from traverse data recent snow accumulation rate is a key quantity for ice core and mass balance studies several accumulation measurement methods stake farm fin core snow radar profiling surface morphology remote sensing were used compared and integrated at eight sites along a transect from terra nova bay to dome c east antarctica to provide information about the spatial and temporal variability of snow accumulation thirty nine cores were dated by identifying tritium b marker levels 1965 66 and non sea salt nss so4 2 spikes of the tambora indonesia volcanic event 1816 in order to provide information on temporal variability cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation stake farm and ice core accumulation rates are observed to differ significantly but isochrones snow radar correlate well with ice core derived accumulation the accumulation ablation pattern from stake measurements suggests that the annual local noise metre scale in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation with no accumulation or ablation for a 5 year period in up to 40 of cases the spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi decadal secular scale stake measurements and firn cores at dome c confirm an approximate 30 increase in accumulation over the last two centuries with respect to the average over the last 5000 years

widespread persistent thickening of the east antarctic ice sheet by freezing from the base an international polar year aerogeophysical investigation of the high interior of east antarctica reveals widespread freeze on that drives substantial mass redistribution at the bottom of the ice sheet although the surface accumulation of snow remains the primary mechanism for ice sheet growth beneath dome a 24 of the base by area is frozen on ice in some places up to half of the ice thickness has been added from below these ice packages result from the conductive cooling of water ponded near the gamburtsev subglacial mountain ridges and the supercooling of water forced up steep valley walls persistent freeze on thickens the ice column alters basal ice rheology and fabric and upwarps the overlying ice sheet including the oldest atmospheric climate archive and drives flow behavior not captured in present models

characterization of subglacial lake vostok as seen from physical and isotope properties of accreted ice deep drilling at the vostok station has reached the surface of subglacial lake vostok lv twice in february 2012 and january 2015 as a result three replicate cores from boreholes 5g 1 5g 2 and 5g 3 became available for detailed and revalidation analyses of the 230 m thickness of the accreted ice down to its contact with water at 3769 m below the surface the study reveals that the concentration of gases in the lake water beneath vostok is unexpectedly low a clear signature of the melt water in the surface layer of the lake which is subject to refreezing on the icy ceiling of lv has been discerned in the three different properties of the accreted ice the ice texture the isotopic and the gas content of the ice these sets of data indicate in concert that poor mixing of the melt and hydrothermal water with the resident lake water and pronounced spatial and or temporal variability of local hydrological conditions are likely to be the characteristics of the southern end of the lake the latter implies that the surface water may be not representative enough to study lv s behaviour and that direct sampling of the lake at different depths is needed in order to move ahead with our understanding of the lake s hydrological regime

insights into hydrological regime of lake vostok from differential behavior of deuterium and oxygen 18 in accreted ice 1 we use isotopic data deuterium and oxygen 18 of the recently recovered deepest vostok ice core section down to 3650 m depth to study processes leading to the formation of lake ice and the hydrological regime of subglacial lake vostok the significant variability of the lake ice isotopic content implies fluctuations in physical conditions of ice formation mainly volume and or growth rate of frazil ice crystals as well as variations of the isotope composition of the freezing water the latter implies a poor mixing of the source waters glacier melt and hydrothermal water with the water of the main lake body poor mixing within the lake may have important consequences for the lake s chemical and gas balance and particularly for its microbiological content a poorly mixed lake may provide ecological niches where microbial life can hide from high oxygen concentrations likely typical for the lake we also show that the isotopic content of the main lake s input meltwater significantly differs from that of the output lake ice which can be explained by the contribution of an additional hydrothermal source this latter conclusion is supported by the observed noncovariant behavior of deuterium and oxygen 18 isotopes in the lake ice

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

sensitivity of simulated cfc 11 distributions in a global ocean model to the treatment of salt rejected during sea ice formation we show that simulated oceanic absorption of an atmospheric gas is very sensitive to the representation of a process that occurs beneath sea ice as sea ice forms salt is rejected locally increasing surface sea water density this dense water can sink to the pycnocline at the base of the mixed layer previous studies have not considered the impact of this subgrid scale process on transient tracers in the ocean to assess the potential importance of this process to the oceanic absorption of atmospheric gases we performed two idealized simulations a control simulation in which salt rejected during sea ice formation is placed in the model s 25 m thick surface layer and a test simulation in which salt rejected during sea ice formation is distributed uniformly through the upper 160 m beneath the forming sea ice our treatment of rejected salt is highly idealized and is intended to demonstrate the need for a physically based parameterization of subgrid scale convection for use in ocean general circulation models that takes into account the subgrid scale heterogeneity of surface buoyancy forcing distributing rejected salt more deeply during periods of ice formation helps to maintain vertical density gradients inhibiting grid scale convection especially in the southern ocean this greatly diminishes simulated ocean uptake of cfc 11 and generally improves simulated cfc 11 and salinity fields the modeled global ocean inventory of cfc 11 for year 1990 is about 30 lower and modeled column inventories in the southern ocean are up to 90 lower in our test simulation relative to our control simulation we infer that a more detailed treatment of subgrid scale processes occurring beneath sea ice may diminish simulated oceanic absorption of anthropogenic co2 especially in the southern ocean

anisotropic elastocreep in glacial ice a mechanism for intergranular melt and recrystallization 1 bonded ice crystals under pressure are in a heterogeneous stress state because of the mechanical anisotropy of constituent grains this condition plays a role in intergranular melt and recrystallization which in turn influence properties such as permeability and biologic habitability to examine this we develop an anisotropic elastocreep model simulating subgrain scale stresses in polycrystalline ice choosing in particular the thermal and deformational regime of the lake vostok accretion ice a critical assumption with regard to localized melting is the macroscopic deviatoric stress our calculations indicate that for a macroscopic deviatoric stress of 50 kpa ice at 0 04 c below the bulk melting temperature would contain regions at scales 1 the grain size where the liquid phase is thermodynamically favored this translates to scales of 5 mm in the lower few meters of the vostok accretion under a deviatoric stress that is plausible near the lake perimeter less internal melting is indicated in analyses of ice relatively far from the lake margins due to the assumed presence of lower macroscopic deviatoric stress simulated strain energy jumps of 1 2 across grain boundaries of accretion ice near the lake boundaries are large relative to free surface energy indicating the importance of the former in boundary migration recrystallization collectively these findings are consistent with measured dislocation densities 107 1010 m 2 and irregular grain morphologies found in core samples the calculated melting point depressions associated with anisotropy fall short of experimental values by a factor of 2 while the calculated strain rates deviate by 20

radio echo layering in west antarctica a spreadsheet dataset of the various information recovered from radio echo sounding res of polar ice sheets internal layering is currently under utilized by glaciologists due in part to a lack of available data here res layering of the west antarctic ice sheet from the 1970s res survey of approximately 70 per cent of this ice mass is made available in a series of spreadsheets three types of internal layers are evident in the dataset the first is continuous layers that have a stratigraphic appearance and can often be traced easily for hundreds of kilometres the second is buckled layering which also resembles stratigraphy and can sometimes be traced over tens of kilometres although layer identification can often be difficult the roughness of these layers is often greater than the bed at the same wavelength the third is highly distorted or absent layering which is not possible to trace laterally despite debate concerning the origin of res layers they are thought by most glaciologists to represent isochronous surfaces the pattern of internal layering is potentially of importance to glaciologists for three reasons 1 the position of undeformed layers below the ice surface is a function of accumulation rate ice flow and basal melting conditions numerical modelling including new data assimilation techniques could be used to discriminate between these processes so revealing important information about the ice sheet and its environment 2 buckled layers are deformed by ice flow process and so their occurrence can be related to the flow dynamics of the ice sheet 3 very buckled layers are often associated with ice stream flow which allows their location to mark the positions of past and present fastflowing ice copyright 2005 john wiley sons ltd

brine micro droplets and solid inclusions in accreted ice from lake vostok east antarctica 1 lake vostok the largest antarctic sub glacial lake 14 000 km2 lies beneath nearly 4 km of ice sub glacial geophysical observations and studies of ice accreting at the lake glacier interface are the only means available to obtain information on the environment and dynamics of this huge water body formed several million years ago accretion ice has been studied using high resolution synchrotron x ray micro fluorescence for the first time liquid brine micro droplets 3 10 m are observed coexisting with large irregular sulfur rich aggregates 10 800 m containing gases and a mixture of very fine particles most of these objects are sequestered inside large crystals that grew slowly after ice formation their structure and composition support the existence of hydrothermal activity at the lake bottom and the occurrence of haline water pulses carrying fine solid debris and eventually biota from a deeper evaporitic reservoir into the lake

height changes over subglacial lake vostok east antarctica insights from gnss observations height changes of the ice surface above subglacial lake vostok east antarctica reflect the integral effect of different processes within the subglacial environment and the ice sheet repeated gnss global navigation satellite systems observations on 56 surface markers in the lake vostok region spanning 11 years and continuous gnss observations at vostok station over 5 years are used to determine the vertical firn particle movement vertical marker velocities are derived with an accuracy of 1 cm yr or better repeated measurements of surface height profiles around vostok station using kinematic gnss observations on a snowmobile allow the quantification of surface height changes at 308 crossover points the height change rate was determined at 1 5 mm yr thus indicating a stable ice surface height over the last decade it is concluded that both the local mass balance of the ice and the lake level of the entire lake have been stable throughout the observation period the continuous gnss observations demonstrate that the particle heights vary linearly with time nonlinear height changes do not exceed 1 cm at vostok station and constrain the magnitude of spatiotemporal lake level variations icesat laser altimetry data confirm that the amplitude of the surface deformations over the lake is restricted to a few centimeters assuming the ice sheet to be in steady state over the entire lake estimates for the surface accumulation on basal accretion melt rates and on flux divergence are derived

nature of radio echo layering in the antarctic ice sheet detected by a two frequency experiment a two frequency radio echo sounding experiment was carried out at dome fuji the second highest dome in east antarctica and along a 1150 km long traverse line from the dome to the coast the goal was to determine the dominant causes of the radio echo internal reflections and to investigate their possible changes with depth ranges and regions from the two frequency 60 mhz and 179 mhz radio echo responses at various sites we distinguished four zones each of the zones is characterized by a dominant cause of radio echo internal reflection as follows in the pd zone changes in dielectric permittivity are mainly due to density fluctuations in the pcof zone changes in dielectric permittivity are mainly due to changes in crystal orientation fabrics and in the ca zone changes in electrical conductivity are mainly due to changes in acidity induced by past volcanic eruptions in each of these three zones the changes occur commonly along isochrones in addition a basal echo free zone the fourth zone was found to appear always below the pcof zone these four zones and their distribution suggested variations of the physical conditions within the ice sheet

large subglacial lakes in east antarctica at the onset of fast flowing ice streams water has been found to gather in lakes underneath the antarctic ice sheet and it can move between lakes and drain catastrophically despite this relatively little is known about how subglacial lakes influence ice sheet dynamics now satellite imagery has identified four subglacial lakes similar in total area to lake vostok right at the onset of the recovery glacier ice stream in east antarctica this suggests that subglacial lakes may initiate and maintain rapid ice flow a mechanism that will need to be considered in future ice sheet mass balance assessments satellite imagery is used to identify four subglacial lakes similar in total area to lake vostok right at the onset of the recovery glacier ice stream in east antarctica this suggests that the subglacial lakes can initiate and maintain rapid ice flow a mechanism that will need to be considered in future ice sheet mass balance assessments water plays a crucial role in ice sheet stability and the onset of ice streams subglacial lake water moves between lakes1 and rapidly drains causing catastrophic floods2 the exact mechanisms by which subglacial lakes influence ice sheet dynamics are unknown however and large subglacial lakes3 4 have not been closely associated with rapidly flowing ice streams here we use satellite imagery and ice surface elevations to identify a region of subglacial lakes similar in total area to lake vostok at the onset region of the recovery glacier ice stream in east antarctica and predicted by ice sheet models5 we define four lakes through extensive flat featureless regions of ice surface bounded by upstream troughs and downstream ridges using ice velocities determined using interferometric synthetic aperture radar insar we find the onset of rapid flow moving at 20 to 30 m yr 1 of the tributaries to the recovery glacier ice stream in a 280 km wide segment at the downslope margins of these four subglacial lakes we conclude that the subglacial lakes initiate and maintain rapid ice flow through either active modification of the basal thermal regime of the ice sheet by lake accretion or through scouring bedrock channels in periodic drainage events we suggest that the role of subglacial lakes needs to be considered in ice sheet mass balance assessments

microbiology of the subglacial lake vostok first results of borehole frozen lake water analysis and prospects for searching for lake inhabitants this article examines the question of the possible existence of microbial life inhabiting the subglacial lake vostok buried beneath a 4 km thick antarctic ice sheet it represents the results of analysis of the only available frozen lake water samples obtained upon the first lake entry and subsequent re coring the water frozen within the borehole for comparison results obtained by earlier molecular microbiological studies of accretion ice are included in this study with the focus on thermophiles and an unknown bacterial phylotype a description of two lake vostok penetrations is presented for the first time from the point of view of possible clean water sampling finally the results of current studies of lake vostok frozen water samples are presented with the focus on the discovery of another unknown bacterial phylotype w123 10 distantly related to the above mentioned unknown phylotype af532061 detected in vostok accretion ice both successfully passing all possible controls for contamination the use of clean room facilities and the establishment of a contaminant library are considered to be prerequisites for research on microorganisms from lake vostok it seems that not yet recorded microbial life could exist within the lake vostok water body in conclusion the prospects for searching for lake inhabitants are expressed with the intention to sample the lake water as cleanly as possible in order to make sure that further results will be robust

observational evidence on the stability of the hydro glaciological regime of subglacial lake vostok 1 combined geodetic geophysical and glaciological in situ measurements are interpreted regarding surface height changes over subglacial lake vostok and the local mass balance of the ice sheet at vostok station repeated gps observations spanning 5 years and long term surface accumulation data show that the height of the lake surface has not changed over the observation period the application of the mass conservation equation to purely observational data yields an ice mass balance for vostok station close to equilibrium

influence of subglacial vostok lake on the regional ice dynamics of the antarctic ice sheet a model study we applied a newly developed three dimensional time dependent thermomechanical ice sheet model including higher order stress gradients to simulate the ice flow across subglacial vostok lake east antarctica simulations of both lake and no lake conditions by treating the ice lake interface as a stress free surface similar to an ice shelf demonstrate the effects of the subglacial lake such as pronounced surface flattening and ice flow turning on the overall ice dynamics in the vicinity although subglacial lake dynamics are not treated explicitly when buoyancy forces and hydrostatic equilibrium of the ice above the lake are taken into account the along lake surface slope is preserved and the ice flow pattern is in accord with sparse observations model experiments point to a local ice speed up in the northern part of the lake which can be associated with the onset of an enhanced ice flow feature more precisely the onset of the totten glacier catchment

new insights into late pleistocene glacial and postglacial history of northernmost ungava canada from pingualuit crater lake sediments abstract the pingualuit crater was formed by a meteoritic impact ca 1 4 million years ago in northernmost ungava canada due to its geographical position near the center of successive north american ice sheets and its favorable morphometry the pingualuit crater lake water depth 246 m promises to yield a unique continuous sedimentary sequence covering several glacial interglacial cycles in the terrestrial canadian arctic in this paper we suggest the existence of a subglacial lake at least during the last glacial maximum lgm by hydraulic potential modeling using lgm ice surface elevation and bed topography derived from a digital elevation model these results support the hypothesis that the bottom sediments of the crater lake escaped glacial erosion and may contain a long term continental sedimentary sequence we also present the stratigraphy of a 9 m long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history the base of the core is formed by very dense diamicton reflecting basal melt out environments marking the end of subglacial conditions at the coring site the overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity infra red stimulated luminescence and ams 14 c dating as well as biostratigraphic data indicate sediment mixing between recent e g holocene and much older pre to mid wisconsinan material reworked by glacier activity this process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake two finer grained and organic rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice free periods the lower organic interval corresponds to the early postglacial period 6850 5750 cal bp and marks the transition between proglacial and postglacial conditions during the holocene thermal maximum while the uppermost organic rich core section represents late holocene sediments 4200 600 cal bp the organic intervals are separated by a basin scale erosive slide occurring around 4200 cal bp and likely related to 1 a seismic event due to the glacio isostatic rebound following the last deglaciation or 2 slope instabilities associated with rapid discharge events of the lake

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

physiography and tectonic setting of the subglacial lake district between vostok and belgica subglacial highlands antarctica summary we present the interpretation of 11 radio echo sounding res missions carried out over the vostok dome concordia region during the italian antarctic expeditions in the period 1995 2001 the extension and the density of the radar data in the surveyed area allowed to reconstruct a reliable subglacial morphology and to identify four relevant morphological structures namely the aurora trench the concordia trench the concordia ridge and the south hills these structures show evidence compatible with the presence of tectonic features morphological considerations indicate their development in cenozoic time hybrid cellular automata hca based numerical modelling allowed to justify a possible role played by the tectonics of the aurora and concordia trench evolution this was accomplished by matching the bed profiles along opportunely projected sections with the modelled surfaces as derived by the activity of normal faults with variable surfaces within the continental crust the vostok dome c region is characterized by a large number of subglacial lakes from the analysis of basal reflected power echo we identified 14 new lakes and obtained information about their physiography as well as their possible relations with tectonics we propose a grouping of subglacial lakes on the base of their physiography and geological setting namely relief lakes basin lakes and trench lakes relief lakes located in the belgica subglacial highlands and are characterized by sharp and steep symmetric edges suggesting a maximum water depth of the order of 100 m their origin may well relate to localized positive geothermal flux anomalies basin lakes located in the vincennes subglacial basin and are characterized by wider dimension that allow the development of well defined flat ice surface anomalies trench lakes characterize the aurora and concordia trenches as the possible effect of normal fault activity

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

variability in the distribution of fast ice and the sub ice platelet layer near mcmurdo ice shelf variability in the volume of supercooled ice shelf water outflow in mcmurdo sound is reflected in the thickness and distribution of fast ice and the sub ice platelet layer beneath ground based electromagnetic induction and drill hole surveys of the distribution and thickness of ice shelf influenced fast ice and the sub ice platelet layer in mcmurdo sound were carried out in late spring of 2011 2013 2016 and 2017 in 2011 and 2017 thicker sub ice platelet layers of up to 7 5 and 6 m were observed respectively fast ice formation throughout the winters of 2011 and 2017 was influenced by a higher occurrence of strong southerly wind events and resultant activity of the ross sea polynya in contrast lower wind conditions in 2016 led to largely undisturbed sea ice growth and anomalously extensive fast ice coverage a thinner sub ice platelet layer of up to 4 m was observed in 2016 in 2011 and 2017 substantial and variable sub ice platelet layers were detected in a region of exchange of water masses between the ross sea and the mcmurdo ross ice shelf cavity which were not observed in 2013 and 2016 we hypothesize that a higher frequency of strong southerly wind events resultant polynya activity and high salinity shelf water production over winter accelerates circulation and increases melting in the proximal shallow mcmurdo ice shelf and the deeper ross ice shelf regions of the conjoined cavity the outflow of supercooled ice shelf water and sub ice platelet layer formation in mcmurdo sound are consequently promoted

ultra low rare earth element content in accreted ice from sub glacial lake vostok antarctica this paper reports the first rare earth element ree concentrations in accreted ice refrozen from sub glacial lake vostok east antarctica ree were determined in various sections of the vostok ice core in order to geochemically characterize its impurities samples were obtained from accreted ice and for comparison from the upper glacier ice of atmospheric origin undisturbed disturbed and glacial flour ice ree concentrations ranged between 0 8 56 pg g 1 for ce and 0 0035 0 24 pg g 1 for lu in glacier ice and between 0 1 24 pg g 1 for ce and 0 0004 0 02 pg g 1 for lu in accreted ice interestingly the ree concentrations in the upper accreted ice ac1 characterized by visible aggregates containing a mixture of very fine terrigenous particles and in the deeper accreted ice ac2 characterized by transparent ice are lower than those in fresh water and seawater respectively we suggest that such ultra low concentrations are unlikely to be representative of the real ree content in lake vostok but instead may reflect phase exclusion processes occurring at the ice water interface during refreezing in particular the uneven spatial distribution on the order of a few cm and the large range of ree concentrations observed in ac1 are consistent with the occurrence absence of the aggregates in adjacent ice and point to the presence of solid phase concentration exclusion processes occurring within separate pockets of frazil ice during ac1 formation interestingly if the lree enrichment found in ac1 was not produced by chemical fractionation occurring in lake vostok water this may reflect a contribution of bedrock material possibly in combination with aeolian dust released into the lake by melting of the glacier ice collectively this valuable information provides new insight into the accreted ice formation processes the bedrock geology of east antarctica as well as the water chemistry and circulation of lake vostok

cryosphere bottom up restructuring of ice water at the base of ice sheets can lead to faster ice flow radar sounding of the greenland ice sheet reveals that refreezing of this water can also induce large changes in ice flow and structure

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

subaerial salt extrusions in iran as analogues of ice sheets streams and glaciers abstract ice h20 and salt halite nacl share many physical properties and resemble each other in hand specimens and subaerial gravity driven flows however while most significant bodies of ice accumulate in cold highlands and gravity spread where and soon after they form most significant bodies of salt accumulate in tropical marine basins and have to be buried by 1 km of other rocks before they flow buried salt is driven by differential loading into various categories of piercing structures known as diapirs many diapirs extrude onto the surface as sheets of allochthonous out of place salt thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years mainly in the toes of passive continental margins and in orogenic belts where some are 103 km2 in area most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in iran these were compared to ice glaciers soon after they were introduced to western science a comparison that has been neglected since here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists the profiles internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss however whereas snow merely compacts where it accumulates salt sheets are fed from below by already deformed salt when salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier like flows known as namakiers after locally exhausting their deep source layers salt fountains spread to the profiles of viscous droplets normal for ice caps ice typically deforms at 80 usually 90 of its absolute melting temperature while most salt deforms at

geodetic observations of ice flow velocities over the southern part of subglacial lake vostok antarctica and their glaciological implications summary in the austral summer seasons 2001 02 and 2002 03 global positioning system gps data were collected in the vicinity of vostok station to determine ice flow velocities over lake vostok ten gps sites are located within a radius of 30 km around vostok station on floating ice as well as on grounded ice to the east and to the west of the lake additionally a local deformation network around the ice core drilling site 5g 1 was installed the derived ice flow velocity for vostok station is 2 00 m a 1 0 01 m a 1 along the flowline of vostok station an extension rate of about 10 5 a 1 equivalent to 1 cm km 1 a 1 was determined this significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline with these lower velocities compared to earlier studies and hence larger transit times the basal accretion rate is estimated to be 4 mm a 1 along a portion of the vostok flowline an assessment of the local accretion rate at vostok station using the observed geodetic quantities yields an accretion rate in the same order of magnitude furthermore the comparison of our geodetic observations with results inferred from ice penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years

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

uncertainties in elevation changes and their impact on antarctic temperature records since the end of the last glacial period abstract this study presents a sensitivity analysis considering the influence of elevation changes associated with both ice thickness and land height changes on water stable isotope temperature proxies from antarctic ice cores we compare results from three different ice sheet models and three different earth viscosity models at a 10 ice core sites as expected the ice thinning signal at west antarctic sites is the largest contributor to elevation induced temperature changes the signal predicted by the ice models considered produced 100 200 of the total glacial to interglacial signal in d indicating that the deglacial ice thinning is overestimated by an amount approaching an order of magnitude at some locations this indicates that the total volume loss in these models is considerably overestimated furthermore the predicted rate of this change is not supported by the isotope data and so again most likely reflects inaccuracies in the adopted ice models estimates of contemporary ice mass changes inferred from satellite gravity data corrected using any of these models with therefore be biased as a result the isostatic signal acts to reduce the total elevation change at most sites and has a relatively small magnitude a few to 20 of that due to the ice thickness change so is secondary at most sites and for most of the time however our results indicate that it could be the dominant control on elevation at some west antarctic sites during the holocene resulting in a secular cooling signal of 10 20 in d none of the models capture the holocene isotopic depletion trend present at several sites in east 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

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

analytical solutions for the effect of topography accumulation rate and lateral flow divergence on isochrone layer geometry the effect of spatial variations in ice thickness accumulation rate and lateral flow divergence on radar detected isochrone geometry in ice sheets is computed using an analytical method under assumptions of a steady state ice sheet geometry a steady state accumulation pattern and a horizontally uniform velocity shape function by using a new coordinate transform we show that the slope of the isochrones with a normalized vertical coordinate depends on three terms a principal term which determines the sign of the slope and two scale factors which can modify only the amplitude of the slope the principal term depends only on a local characteristic time ice thickness divided by accumulation rate minus melting rate between the initial and final positions of the ice particle for plug flow only the initial and final values have an influence further applications are a demonstration of how the vertical velocity profile can be deduced from sharp changes in isochrone slopes induced by abrupt steps in bedrock or mass balance along the ice flow we also demonstrate ways the new coordinate system may be used to test the accuracy of numerical flow models