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

propagation and the vertical structure of the madden julian oscillation abstract the madden julian oscillation mjo dominates tropical variability on time scales of 30 70 days during the boreal winter spring it is manifested as an eastward propagating disturbance with a strong convective signature over the eastern hemisphere the space time structure of the mjo is described using the national centers for environmental prediction national center for atmospheric research reanalysis advanced very high resolution radiometer outgoing longwave radiation observed sea surface temperature and the climate prediction center merged analysis of precipitation empirical orthogonal function analysis is used to identify the convective signature of the mjo and regression is used to identify key relationships with the convection compared to analyzing successive years of data the selection of years of strong mjo activity results in a more robust lead lag structure and an increase in explained variance the mjo exhibits a rich vertical structure with low level moisture convergence bein

an analysis of the ice sheet surface and subsurface topography above the vostok station subglacial lake central east antarctica radio echo sounding res and satellite radar altimeter data were analyzed in order to identify the surface and subsurface topography around the largest known subglacial lake at vostok station east antarctica named here as lake vostok in doing so a data set was established from which a qualitative description of the flow of ice across the lake was developed patterns of ice flow were constructed through consideration of 1 the ice sheet surface from the satellite altimeter and 2 internal layering from res it is concluded that lake vostok influences the dynamics of the overriding ice specifically although the flow of ice across the lake is dominated by the general eastward flow of the grounded ice sheet a southward velocity component caused by an ice shelf type ice flow mechanism is also present over the subglacial lake a further 67 smaller subglacial lakes exist within central regions of the antarctic ice sheet occupying 5 10 of the ice sheet base subglacial lakes may therefore exert a significant control on ice dynamics within central antarctica

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

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

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

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

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

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

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

response of subglacial sediments to basal freeze on 1 theory and comparison to observations from beneath the west antarctic ice sheet 1 we have constructed a high resolution numerical model of heat water and solute flows in sub ice stream till subjected to basal freeze on the model builds on quantitative treatments of frost heave in permafrost soils the full version of the clapeyron equation is used hence ice water phase transition depends on water pressure osmotic pressure and surface tension the two latter effects can lead to supercooling of the ice base this supercooling in turn induces hydraulic gradients that drive upward flow of pore water which feeds the growth of segregation ice onto the freezing interface this interface may progress into the till and form ice lenses if supercooling is sufficiently strong hence the ice segregation process develops a stratified basal ice layer in our model a high basal temperature gradient 0 054 c m 1 triggers ice stream stoppage and the loss of basal shear heating leads to relatively high basal freeze on rates 3 5 mm a 1 in response the subglacial till experiences comparatively rapid consolidation till porosity can decrease from 40 to 120 kpa approximately within one century basal supercooling arising from redistribution of solutes and ice water interfacial effects amounts to ca 0 35 c below the pressure melting point fine grained till is in our model associated with widely spaced thick ice lenses coarse grained till yields thinner ice lenses that are more closely spaced our model results compare favorably although not in all details with available observational evidence from borehole studies of west antarctic ice streams

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

structural analysis of cores and cuttings from the toa baja puerto rico borehole deformation structures in core samples and well cuttings from the toa baja borehole in puerto rico obtained from depths of 580 to 2700 meters can be divided into two major categories 1 structures resulting from compression and shear and 2 structures formed by extension generally the first ones are older and they are somewhat more abundant at horizons where fault zones occur as deduced from dipmeter readings and televiewer log these structures may have formed during an eocene thrusting event recognized regionally in puerto rico the extensional structures which almost always crosscut the compressional ones are filled with zeolite calcite prehnite or quartz there is poor correspondence between the abundance of these fractures and the position of the major fault zones the largest abundance of veins occurs between 1700 and 2100 meters depth they may be related to a phase of regional extension during the late paleogene

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

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

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

ice ocean interaction on ronne ice shelf antarctica detailed glaciological studies have been completed at 28 sites lying on an approximate flow line extending 760 km across ronne ice shelf parameters measured at each location include ice velocity thickness principal strain rates surface elevation temperature and accumulation rate the data have been used in a steady state model to derive the basal mass flux and the temperature profile with depth at each site from the principles of mass and energy conservation these calculations indicate basal melting in excess of 1 m yr 1 over the first 100 km of the flow line downstream of the grounding line where the ice shelf is between 1200 m and 1600 m thick the maximum melt rates in this region occur near the inland margin and exceed 4 m yr 1 melting continues at a lesser rate over the next 200 km before freezing commences freezing then dominates up to the final 100 km before the ice front resulting in the accumulation of a layer of basal sea ice up to 50 m thick this is rapidly removed as melt rates increase to over 6 m yr 1 at the ice front the cumulative effect of this pattern of basal accumulation and ablation is the wastage by melting of 85 of the mass discharged across the grounding line before it reaches the ice front supporting evidence for a layer of saline ice underlying the ice shelf is provided by the strength of basal radar reflections observed during radio echo sounding of ice thickness in the region where mass balance calculations suggest an accretion of basal sea ice reflection coefficients are consistently low ranging from 6 db to 38 db most of these weak reflections are believed to originate from the true base of the ice shelf the additional energy loss being the result of increased attenuation of the radar signal within the saline layer the derived pattern of basal melting and freezing is consistent with a simple model of sub ice shelf oceanic circulation involving a deep thermohaline convection cell dense saline water which is formed over the continental shelf during winter when the sea surface freezes drains into the deepest parts of the sub ice shelf cavity at the inland margin where this water mass comes into contact with the ice shelf its temperature is 1 c above the local pressure freezing point melting of ice results producing a buoyant outflow of cold relatively fresh water along the ice shelf base basal freezing occurs towards the ice front where the ascending water becomes supercooled this circulation has important implications for the production of antarctic bottom water and for the response of the ice shelf to driving stresses through the temperature dependent viscosity of ice

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

antarctica stirring the icy waters lake vostok is a giant freshwater lake hidden below the east antarctic ice sheet there is some evidence that the lake may contain ancient life radar data now confirms that ice melts and refreezes at the base of the ice sheet in a way that encourages circulation of the water this has implications for the survival of life in 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

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

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

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

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

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

evidence for tides in the subglacial lake vostok antarctica the phenomenon of lake tides is investigated for the subglacial lake vostok east antarctica a model computation of equilibrium lake tides leads to a maximum lake level variation of about 18mm to verify the hypothesis of really existing lake tides data from two different observational techniques are analysed the re evaluation of old tidal gravity data from vostok station as well as satellite synthetic aperture radar interferometry insar reveal specific signals which are explained as lake tides the results of gravimetric tidal observations at vostok station from 1969 schneider 1971 schneider and simon 1974 show systematic deviations from the expected solid earth tide signal which correspond to a vertical tidal displacement of 12 and 2 mm amplitude for the waves k1 and m2 respectively the insar data show the areal pattern of a vertical motion at the southern lake tip which is analogous to the grounding zone of ice shelves

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

radio echo layering in polar ice sheets and past volcanic activity a recent study1 has shown how acidity profiles along dated greenland ice cores can reveal large volcanic eruptions in the northern hemisphere during the past 10 000 yr it has been suggested that these layers of acidic ice in the polar ice sheets may also be detected by airborne radio echo sounding res techniques as stratification echoes2 4 explosive volcanic eruptions eject large amounts of so2 into the stratosphere5 where it forms an h2so4 aerosol6 studies of antarctic snow7 and greenland ice cores2 show that this material can be deposited in layers of large areal extent on polar ice sheets calculations based on observations of these slightly acidic layers show that they should give rise to radar reflections of similar magnitude to those observed for stratification echoes new res data from the antarctic enables the present comparison to be made between observed layer power reflection coefficients prcs and calculated values for reflections from acidic ice layers and from layers of ice of changed density a gap in layering has been identified which seems to coincide with a similar gap reported in greenland at crete8 profiles of layer prc against age show a common pattern for many sites on the antarctic ice sheet this prc age profile may provide a record of explosive volcanic activity for the southern hemisphere over the past 150 000 yr

glacier meltwater hydrochemistry abstract glacierised areas present an ideal environment in which to study water rock interaction since chemical weathering rates are high and anthropogenic impacts are often minimal detailed investigations of meltwater quality variations have suggested the importance of these environments in estimates of terrestrial chemical erosion and global biogeochemical cycles most notably the role of meltwaters in co2 sequestration during episodes of deglaciation has attracted considerable attention since this may impact on climate at glacial interglacial timescales however there is still considerable uncertainty surrounding estimates of co2 drawdown by meltwaters which remains to be resolved water flow through glaciers exerts an important control on ice mass dynamics and influences the quantity and quality of water delivered to environments downstream of glacierised basins thus the study of the configuration and dynamics of subglacial drainage systems is important not only to enhance scientific understanding but also to allow effective water resource utilisation in glacierised headwater catchments bulk meltwater quality characteristics draining terrestrial ice masses also offer the potential to provide unique information on hydrological and hydrochemical processes operating in the inaccessible subglacial environment here significant advances have been made in understanding the controls on chemical weathering reactions based on the identification of key dissolved indicator species this has allowed water quality variations to be exploited as a tool for both subglacial hydrochemical and hydrological investigations as a result this area of glaciology has received considerable attention in recent years utilising an increasing range of dissolved ions and integrating field and laboratory studies however uncertainty still surrounds certain areas of meltwater quality science including the role of microorganisms in a system which to date has largely been viewed as abiotic a better understanding of the processes and rates of chemical weathering in glacierised environments has the potential to enhance our understanding of the environment and to facilitate the exploitation of water quality variations for both scientific and applied objectives in this paper the development and current state of meltwater quality science as a tool for investigating subglacial hydrology and geochemistry is detailed and problems and future directions identified this will hopefully stimulate wider interest in an important area of aquatic chemistry with significant applied implications