independence of sst skewness from thermocline feedback in the eastern equatorial indian ocean 1 the observed sea surface height ssh sea surface temperature sst in east equatorial indian ocean eeio shows a significant asymmetric relation between the positive and negative ssh anomalies during boreal autumn whether or not the thermocline sst feedback is responsible for the negative sst skewness in the eeio is explored by diagnosing various air sea feedback processes and a mixed layer heat budget our analysis based on observations suggests that the ssh subsurface temperature relation is approximately symmetric between the positive and negative episode which is significantly different from the asymmetric ssh sst relation this implies that the observed ssh sst asymmetry is not attributed to the ocean thermocline feedback a further analysis of the sst precipitation precipitation wind stress and wind stress ssh relations demonstrates that the asymmetry arises from asymmetric atmospheric heating wind responses to the sst anomaly a mixed layer heat budget analysis reveals that the ratio of the mixed layer temperature tendency between the positive and negative events keeps approximately unchanged with and without vertical temperature advection suggesting that the thermocline feedback is not crucial for generating the negative sst skewness in the eeio

magnetic fingerprinting of hydrodynamic variations and channel erosion across the turbidity maximum zone of the yangtze estuary china abstract magnetic measurements were conducted on surface sediments and suspended particles collected across the turbidity maximum zone of the yangtze estuary in order to examine the spatial distribution of magnetic mineral assemblages and the factors responsible for this distribution the results indicate that magnetic properties are dominated by ferrimagnetic grains bulk magnetic susceptibility and saturation isothermal remanent magnetization sirm values show positive correlations with the proportion of the 63 m fraction in the north channel while anhysteretic remanent magnetization arm is significantly correlated with the proportion of the arm sirm ratios which is consistent with the coarsest particle size due to strong hydrodynamics i e currents within each channel and sirm values are higher in sediments from shallower water depth due to energetic conditions resulting from waves compared with surface sediments suspended particles have lower and sirm values but higher arm sirm ratios due to lower sand fractions the increasing trend of arm sirm of suspended particles along the pathway of sediment transport indicates weakening hydrodynamics from the inner estuary to the outer estuary diagenesis is another factor influencing magnetic properties in addition to particle size channel erosion leads to local exposure of buried sediments on the channel bed as a result of a stronger diagenetic imprint they show magnetic properties different from the recently deposited sediments our results indicate that magnetic properties cannot only indicate spatial variations in hydrodynamics but also provide insight into sediment erosion deposition processes combined granulometric and magnetic methods can therefore be used to interpret hydrodynamics and track changes in estuary morphology

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

magnetic geochemical and mineralogical properties of sediments from karstic and flysch rivers of croatia and slovenia the aim of the present work was to investigate links between the low field magnetic susceptibility ms and chemical and mineral composition of sediments from several croatian and slovenian rivers as well as to determine possible anthropogenic influence on these sediments ms measurements are a fast and simple method which serves as a proxy for the estimation of pollution in different environmental systems the investigated rivers are predominantly unpolluted rivers from croatian and slovenian karstic and flysch areas which belong to the adriatic or the black sea watersheds the dragonja the mirna the rasa the ri ana the reka the rak the cerknisnica the unec and the ljubljanica rivers it was assumed that due to their mostly unpolluted status they could serve as a database for natural ms background values for this region for comparison several rivers and a lake from the celje old metallurgic industrial area slovenia were also investigated the savinja the hudinja the voglajna rivers and slivnisko lake they form a sub basin of the sava river drainage basin sediments of the clean karstic and flysch rivers showed extremely low ms values with mass susceptibility values ranging from 0 58 10 7 to 5 11 10 7 m3 kg and isothermal remanent magnetism irm values ranging from 0 71 to 7 88 a m in the celje industrial area river sediments showed much higher ms values with mass susceptibility values ranging from 1 31 10 7 to 38 3 10 7 m3 kg and irm values ranging from 0 91 to 100 42 a m the highest ms value was found in the voglajna river at teharje store a point which showed a significant number of anomalies of toxic metals in earlier investigations semiquantitative determination of relations between grain size and concentration of magnetite was performed using the thompson oldfield method x ray diffraction xrd mineralogical analysis showed that sediments of the celje area have mostly quartz as major mineral with relatively small amount of carbonate minerals while in sediments of karstic rivers carbonate minerals prevail statistically significant correlations were obtained between ms and cr mn fe co ni cu zn cd and ba in the slovenian karstic region and between ms and cr fe co ni and zn in flysch drainage basins on the contrary no correlation of ms and hg content was obtained

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

gas age ice age differences and the chronology of the vostok ice core 0 100 ka 1 gas is trapped in polar ice at depths of 50 120 m and is therefore significantly younger than the ice in which it is embedded the age difference is not well constrained for slowly accumulating ice on the east antarctic plateau introducing a significant uncertainty into chronologies of the oldest deep ice cores vostok dome fuji and dome c we recorrelate the gas records of vostok and greenland ice sheet project 2 gisp2 cores in part on the basis of new ch4 data and use these records to construct six vostok chronologies that use different assumptions to calculate gas age ice age differences we then evaluate these chronologies by comparing times of climate events at vostok with correlative events in the well dated byrd ice core west antarctica from this evaluation we identify two leading chronologies for the vostok core that are based on recent models of firn temperature firn densification and thinning of upstream ice one chronology involves calculating gas age ice age differences from these models the second new approach involves calculating ice depths in the core that are contemporaneous with depths in the same ice core whose gas ages are well constrained this latter approach circumvents problems associated with highly uncertain accumulation rates in the vostok core the uncertainty in vostok chronologies derived by correlating into the gisp2 gas record remains about 1 kyr and high precision correlations continue to be difficult

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

mineral magnetic characterization of anthropogenic magnetic phases in the danube river sediments bulgarian part abstract magnetic methods have been widely used for delineation of environmental pollution of soils and sediments under certain conditions during the last decade a number of structure sensitive magnetic characteristics coercive force coercivity of remanence remanent magnetization were utilized for deduction of the grain size of the anthropogenic particulate matter which serves as a proxy for the evaluation of the distance from the pollution source possible health effects etc however up to now there is no detailed study on the influence of the morphology internal structure and phase composition of anthropogenic particles on the corresponding magnetic characteristics the aim of the present investigation is to obtain detailed microscopic magnetic and microchemical data on single grains from polluted river sediments and thus to check the validity of the classical grain size dependent trends of coercivity and remanence parameters obtained for natural and synthetic magnetites for the anthropogenic magnetic phases single anthropogenic particles from magnetic extracts have been separated from several sites along the bulgarian part of the danube river which show the strongest magnetic enhancement results from the combined magnetic thermomagnetic analysis and magnetic hysteresis microscopic optical and scanning electron microscopy sem and microchemical electron microprobe analysis empa study on single anthropogenic particles show that there is a general trend for significant underestimation of the physical size of the anthropogenic particles due to the following reasons 1 in most cases the spherules possess a complex internal structure in which the magnetic phase is presented as dendrites exsolved within a glassy non magnetic aluminosilicate matrix 2 the surface morphology is characterized by orange peel or dendritic structures or smaller strongly magnetic spherules are adhered to the surface magnetic mineralogy as deduced from single grain thermomagnetic k t analysis and further elucidated by microprobe data on the same particles shows that magnetite is the main ferromagnetic phase in isolated cases significant al substitution leads to a decrease of t c down to 500 c hysteresis parameters for all studied single grains of physical sizes varying from 39 m up to 1 5 mm fall mainly in the pseudo single domain psd range on the basis of the results from single grain magnetic measurements a new approach for semiquantitative estimation of the degree of anthropogenic pollution is proposed

suspended sediment characterization and tracing using a magnetic fingerprinting technique bassenthwaite lake cumbria uk robust identification of catchment suspended sediment sources is a prerequisite both for under standing sediment delivery processes and targeting of effective mitigation measures fine sediment delivery can pose universal management problems especially with regard to nutrient run off and lake siltation here 19 sus pended sediment samplers were located within the three main tributary inflows to lake bassenthwaite a key but vulnerable site of special scientific interest with water quality problems linked to accelerated delivery of fine sediment magnetic properties of contemporary suspended sediments collected on a monthly basis were measured on a particle size specific basis and compared with the lake sediment core tops ferrimagnetic grain size and magnetic hardness vary significantly between the suspended sediments collected from the different tributaries with the 8 31 m and 31 63 m clastic grain fractions displaying greatest magnetic contrasts post depositional formation of bacterial magnetosomes is evident in the 2 8 m and 2 m fractions of the lake sediments thus for comparison with the potential source suspended sediments we use only the detrital clas tic fractions 8 31 m and 31 63 m the lake sediment magnetic properties show little spatial variation indi cating through lake transport of sediment no evidence was found of postdepositional diagenetic sulphide formation magnetic comparisons between the potential sources and the lake surface sediments indicate that newlands beck providing only 10 of the lake s hydraulic load is the main contributor of sediment to the deep basin of the lake sediments from the river derwent subcatchment contributing 80 of the hydraulic load are possibly stored either on the floodplain or in shallower areas of the lake

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

individual and combined influences of enso and the indian ocean dipole on the indian summer monsoon the relative influences of the enso and indian ocean dipole iod events on the indian summer rainfall were studied using observational data and an atmospheric general circulation model agcm the composite analysis of rainfall anomalies demonstrates that the iod while significantly influencing the indian summer monsoon rainfall also significantly reduces the impact of enso on the indian summer rainfall whenever these events with the same phase co occur the agcm experiments have shown that during an el nino event the walker circulation over the tropical indo pacific region is modulated a low level anomalous divergence center over the western pacific and an anomalous convergence zone over the equatorial indian ocean are induced furthermore an anomalous zone of convergence over the myanmar and south china regions is induced during an el nino event these zones of anomalous convergence are complemented by anomalous divergence over the indian region causing anomalous subsidence and weakened rainfall when a strong positive iod event simultaneously occurs with el nino the latter s influence on the indian monsoon is reduced by both poles of the iod through the following mechanism an anomalous divergence center as compared to the summers when an el nino alone occurs is introduced in the eastern tropical indian ocean from this center the anomalous divergent flow crosses the equator and this air while weakening the el nino induced divergence over the western pacific also leads to convergence over the indian monsoon region this results in the reduction of the enso induced subsidence and the related rainfall deficit over the eastern flank of the indian monsoon trough region and adjoining regions to the east on the other hand over the western part of the tropical indian ocean sector part of the anomalous ascending motion from the warm pole of the positive iod event subsides just to the north of the equator moves northward ascends and causes surplus rainfall this reduces the enso induced rainfall deficit over western india the western part of the monsoon trough and parts of pakistan the agcm experiments also demonstrate that positive iod events amplify the enso induced dryness over the indonesian region

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

phase transition of the el nino southern oscillation a stationary sst mode a stationary sst mode is proposed to understand the physical mechanisms responsible for the phase transition of the el nino southern oscillation this stationary sst mode differs from the original delayed oscillator mode and the slow sst mode in the sense that it considers both balanced and unbalanced thermocline depth variations and does not take into account the zonal propagation of sst within this mode the walker circulation acts as a positive feedback mechanism to amplify and maintain an existing interannual sst anomaly whereas the hadley circulation acts as a negative feedback mechanism that dismisses the original anomaly and causes the phase shift from a warm cold to a cold warm episode the key to the cause of interannual oscillations in the stationary sst mode lies in the zonal mean thermocline depth variation that is not in equilibrium with the winds because of the nonequilibrium this part of the thermocline depth anomaly tends to have a phase lag with the wind or sst anomaly and therefore holds a key for the interannual oscillation the zonally asymmetric part of the thermocline depth anomaly on the other hand is always in sverdrup balance with the winds such a phase relationship agrees well with observations and with gcm simulations the stationary sst mode strongly depends on the basin width on the air sea coupling strength and on the seasonal cycle basic state for a reasonable parameter regime it depicts an interannual oscillation with a period of 2 7 years this stationary sst mode is also season dependent it has a maximum growth rate during the later part of the year and a negative growth rate during the northern spring which may explain the occurrence of the mature phases of the el nino in the northern winter and a rapid drop of the lagged correlation of the southern oscillation index in the boreal spring

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

late cenozoic paleomagnetism and chronology of andean basins of bolivia evidence for possible oroclinal bending new paleomagnetic and radioisotopic data are reported from two late tertiary high elevation non marine basins in the eastern cordillera of bolivia 1 quebrada honda located at 22 s lat consists of a 300 m thick section containing abundant santacrucian or friasian middle miocene fossil mammals this locality is constrained by mean 40 k 40 ar ages of 12 83 0 11 ma and 11 96 0 11 ma and the local magnetostratigraphy is correlated to chrons c5aa through c5a on the magnetic polarity time scale mpts the fossil mammals from quebrada honda have an extrapolated age of about 13 0 to 12 7 ma 2 micana located at 17 s lat consists of a 205 m thick section containing late miocene fossil mammals including a megatheriid sloth and the tiny mesothere microtypotherium cf m choquecotense this locality is constrained by a fission track age determination of 6 9 1 1 ma and the local magnetostratigraphy is correlated to chron 7 on the mpts the fossil mammals from this section have an extrapo

magnetic particle characterization in the seine river system implications for the determination of natural versus anthropogenic input 1 this study presents an innovative application of well established environmental magnetic proxy parameters on fluvial sediments with the aim to trace geological and human induced processes in the complex seine river drainage system in northern france we seek to identify environmental fingerprints of mechanical and chemical weathering processes the regional distribution of the suspended material and changes in the balance of natural input versus anthropogenic pollution in order to reach these goals we applied a combination of rock magnetic and advanced scanning electron microscopic techniques on a large number of sediment trap samples generally we observe an increase in magnetic concentration coupled with a coarsening in magnetic grain size downstream of the seine river system furthermore the dominant magnetomineralogy changes from high coercivity minerals upstream in more rural areas to magnetite dominated assemblages downstream each river segment shows its specific trend line depending on regional initial input weathering conditions drainage area and potential pollution sources one major outcome of this study is the observed significant correlation between anthropogenic antimony rich iron oxide particles and the magnetic concentration this shows the potential of magnetic remanence measurements as proxy parameters for specific heavy metal pollution concentrations hence the environmental magnetic study presented herein serves to identify major trends as well as local particularities and leads to quantitative analyses of the contributions of individual tributaries in the seine river system

biogenic magnetite as a primary remanence carrier in limestone deposits abstract studies on the microbial communities and magnetic phases of samples collected from carbonate oozes at sugarloaf key fl u s a and calcareous laminated sediments from laguna figueroa baja california mexico have revealed the existence of magnetotactic bacteria and ultrafine grained single domain magnetite in both environments magnetotactic bacteria were identified by light and electron microscopy the single domain magnetite was detected by coercivity spectra analysis with a squid magnetometer and examined under the transmission electron microscope the similarity in terms of size and shape between the single domain magnetite found in these sediments and the magnetite observed in the bacterial magnetosome from enriched cultures indicates the ultrafine grained magnetite in these two marine environments was biologically formed these results combined with the common occurrences of ultrafine grained magnetite in limestone deposits detected rock magnetically suggest biogenic magnetite may be present and contribute to the magnetic remanence in these rocks several cambrian limestone samples separately collected from siberia china and kazakhstan were examined for the presence of bacterial magnetite samples from the lower cambrian sinskian formation at siberia platform were found to contain both a large amount of apparently bacterial magnetite particles and a very stable primary magnetic component post cambrian diagenesis does not seem to affect the microgranulometry of these apparently bacterial magnetite crystals or the magnetic remanence carried by them assessing the potential role of biogenic magnetite as a primary remanence carrier in other phanerozoic limestone deposits ought to be further pursued

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

ice flow velocities over vostok subglacial lake east antarctica determined by 10 years of gnss observations repeated global navigation satellite systems gnss observations were carried out at 50 surface markers in the vostok subglacial lake east antarctica region between 2001 and 2011 the horizontal ice flow velocity vectors were derived with accuracies of 1 cma and 0 58 representing the first reliable information on ice flow kinematics in the northern part of the lake within the lake area ice flow velocities do not exceed 2ma the ice flow azimuth is southeast in the southern part of the lake and turns gradually to east northeast in the northern part in the northern part as the ice flow enters the lake at the western shore the velocity decreases towards the central lake axis then increases slightly past the central axis in the southern part a continued acceleration is observed from the central lake axis across the downstream grounding line based on the observed flow velocity vectors and ice thickness data mean surface accumulation rates are inferred for four surface segments between ridge b and vostok subglacial lake and show a steady increase towards the north

inclination shallowing in deep sea sediments from the north atlantic paleomagnetic data from miocene to recent deep sea sediments recovered during leg 94 of the deep sea drilling project dsdp in the north atlantic exhibit a systematic shallowing of inclinations with depth at some sites this shallowing is coincident with a downhole decrease in water content and is observed only in sediments with a carbonate content consistently greater than 80 compaction due to overburden pressure is believed to be responsible for the shallow inclinations observed in these unconsolidated sediments at sites where the carbonate content of the sediments is consistently below about 80 no significant downcore decreasing trends in the water content or inclination record are observed

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

recent sediment flux and erosional processes in a welsh upland lake catchment based on magnetic susceptibility measurements abstract single sample magnetic susceptibility measurements are used to correlate synchronous levels in 16 cores of dated 210 pb 137 cs recent sediment taken from the deep and oligotrophic llyn peris n wales in order to provide a basis for calculating total sediment and chemical influx through time results show that sediment influx has steadily increased since c 1750 a d to reach peak levels in the period 1966 1976 a d equivalent to a rise in erosion in the catchment from c 5 t km 2 yr 1 to c 42 t km 2 yr 1 comparison of down core susceptibility fluctuations with sediment pollen and organic pigment data indicates that maximum susceptibility values relate to periods of channel erosion and minimum susceptibility values relate to periods of slate debris inwash from spoil tips in the catchment a study of historical records reveals that pre twentieth century peak levels of erosion were due to the effects of extractive industries while twentieth century erosion has been caused by overgrazing increased trampling pressure and heavy construction works in the catchment

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

tectonically controlled subglacial lakes on the flanks of the gamburtsev subglacial mountains east antarctica 1 the morphology of surface lakes strongly influences their ecology and limnology wetzel 2001 this morphology is a result of both the geologic processes that produce topographic basins and the regional climatic and local hydrologic processes that control water depth and sediment infilling carroll and bohacs 1999 although basin forming processes range from glacial scour to meteorite impacts cohen 2003 the deepest oldest surface lakes are tectonically controlled meybeck 1995 and contain diverse exotic ecosystems rossiterm and kawanabe 2000 subglacial lakes are also thought to be ancient systems that may contain exotic biota bulat et al 2004 karl et al 1999 priscu et al 1999 here we present evidence for the scale and configuration of 2 large subglacial lakes in east antarctica that together with lake vostok define a province of major lakes on the flanks of the gamburtsev subglacial mountains spatially defined in the new moderate resolution imaging spectroradiometer modis imagery of antarctica t scambos et al a modis based mosaic of antarctica moa submitted to remote sensing of environment 2005 hereinafter referred to as scambos et al submitted manuscript 2005 these lakes are aligned parallel to lake vostok other data shows that they are distinguished by distinct gravity lows flat ice surface slopes and have estimated water depths of at least 900 m surface elevation data indicates that large deep subglacial lakes have a profound influence on the regional ice sheet topography and probably ice sheet flow these deep subglacial lakes with elongate rectilinear morphology are tectonically controlled features unlike the shallow lakes in west antarctica and beneath dome concordia these deep subglacial lakes remained stable environments through many glacial cycles since their origin 10 35 ma enabling the development of novel ecosystems

geochemistry of dissolved and suspended loads of the seine river france anthropogenic impact carbonate and silicate weathering this study focuses on the chemistry of the seine river system one of the major rivers in europe and constitutes the first geochemical investigation of both suspended and dissolved loads of this river the seine river drains a typical mesozoic cenozoic sedimentary basin the paris basin constituted of limestones mixed or interbedded with terrigenous sediments derived from the paleoreliefs bordering the mesozoic and cenozoic seas in the context of quantifying the global influence of carbonate and silicate weathering on atmospheric co2 consumption the seine river offers the possibility of examining weathering rates in a flat sedimentary environment under temperate climatic conditions one of the major problems associated with the seine river as with many temperate rivers is pollution we propose in this paper 2 approaches in order to correct the dissolved load of the seine river for anthropogenic inputs and to calculate weathering rates of carbonates and silicates the first uses the dissolved load of rivers and tries to allocate the different solutes to different sources a mixing model based on elemental ratios is established and solved by an inversion technique the second approach consists in using the suspended load geochemistry under steady state conditions we show that the geochemistry of suspended sediments makes it possible to estimate the amount of solutes released during the chemical weathering of silicates and thus to calculate weathering rates of silicates the total dissolved load of the seine river at paris can be decomposed into 2 of solutes derived from natural atmospheric sources 7 derived from anthropogenic atmospheric sources 6 derived from agriculture 3 derived from communal inputs and 82 of solutes derived from rock weathering during high floods the contribution of atmospheric and agriculture inputs predominates the weathering rate of carbonates is estimated to be 48 t km2 yr 25 mm 1000 yr only 10 of carbonates are transported in a solid form the rest being transported in solution co2 consumption by carbonate weathering approaches 400 103 mol km2 yr in the seine river at paris about 2 3 mg l of dissolved cations are found to originate from the chemical weathering of silicates by taking dissolved silica into accounts the total dissolved load derived from silicate weathering is about 6 7 mg l this value is minimal because biological uptake of silica probably occur in the seine river the chemical weathering rate of aluminosilicates is estimated to be 2 t km2 yr the ratio of physical over chemical weathering of silicates range between 1 and 3 and the total chemical and physical erosion rates of sedimentary silicates are about 2 3 mm kyr the co2 consumption by silicate weathering 15 24 103 mol km2 yr and is independent of dissolved silica concentration silicate consumption is thus 20 times less than carbonate consumption in the paris basin compared to the neighboring granitic areas the sedimentary region drained by the seine river has 2 to 3 times lower co2 consumption rates we attribute this difference to the cation depleted nature of the seine basin aluminosilicates which are of sedimentary origin at a world scale the chemical denudation rates found for the seine basin are very low and comparable to those given for tropical lowland rivers draining silicates such as the rivers of the congo and amazon basins in spite of huge climatic differences we attribute this similarity to the low mechanical denudation that characterizes these two types of regions

magnetic fingerprint of the sediment load in a meander bend section of the seine river france abstract this study aims to evaluate the potential of magnetic methods to determine the composition of the sediment load in a cross section of an unmanaged meander in the upstream stretch of the seine river marnay sur seine suspended particulate matter spm was collected based on a regular sampling scheme along a cross section of the river at two different depth levels during a low water stage may 2014 and a high water stage february 2015 riverbed sediments rbs were collected during the low water stage and supplementary samples were taken from the outer and inner banks magnetic properties of the dry bulk spm and sieved rbs and bank sediments were analysed after characterizing the main magnetic carrier as magnetite hysteresis parameters were measured giving access to the grain size and the concentration of these magnetite particles the results combined with sedimentary grain size data were compared to the three dimensional velocity profile of the river flow in the rbs where the magnetic grain size is rather uniform the concentration of magnetite is inversely proportional to the mean grain size of the total sediment indicating that magnetite is strongly associated with the fine sedimentary fraction the same pattern is observed in the samples from the outer and inner banks during the low water stage the uniformly fine spm grain size distribution characterizes the wash load the magnetic fraction is also relatively fine within the pseudo single domain range with concentration similar to that of the fine rbs fraction during the high water stage spm samples correspond to mixtures of wash load and resuspended sediment from the bedload and riverbanks here the grain size distribution is heterogeneous across the section showing coarser particles compared to those in the low water stage and more varying magnetite concentrations while the magnetic grain size is like that of the low water stage the magnetite concentration in the high water spm can be modelled based on a mixing of the magnetite concentrations of the different grain size fractions thus quantifying the impact of resuspension in the cross section

unusual early morning development of the equatorial anomaly in the brazilian sector during the halloween magnetic storm 1 the solar events that occurred at the end of october 2003 gave rise to very strong geomagnetic disturbances that peaked twice with dst values reaching 345 nt around 0000 ut on 30 october and 400 nt around 2300 ut on the same day disturbances in several ionospheric parameters were observed over brazil this work will focus on the ionospheric response to the initial westward prompt penetration electric field and on the strong intensification of the equatorial ionization anomaly that occurred because of the electric field polarity reversal that followed in the early morning hours of 29 october the f layer peak height over the equator first decreased under the strong prompt penetration westward electric field which was followed by significant height increase under eastward electric field we have used sheffield university plasmasphere ionosphere model supim with an intensified westward disturbed electric field in the presunrise hours presumably due to prompt penetration from the magnetosphere in order to study the effect of such a field in the ionosphere the simulation results showed that prompt penetration of magnetospheric electric fields of westward polarity to the nightside equatorial region seems to be the most probable cause of the initial f layer height decreases the intensification of the equatorial ionization anomaly and the unusual enhancement on f layer peak density which was not modeled by the supim are explained as caused by the strong eastward electric field that followed the initial phase in combination with a highly variable disturbed meridional transequatorial wind system as inferred from the f2 layer peak height variations the highly dynamic wind pattern with a short term response 2 4 hours is compatible with the predictions of some previous theoretical model calculations reported in the literature

relative role of dynamic and thermodynamic processes in the development of the indian ocean dipole an ogcm diagnosis 1 the relative role of oceanic dynamics and surface heat fluxes in the initiation and development of the indian ocean dipole was investigated by analyzing results from an oceanic general circulation model the model was forced by observed surface wind stress and heat flux fields for 1958 1997 the results show that it was capable of reproducing observed dipole events over the tropical indian ocean the diagnosis of the mixed layer heat budget indicates that the sst anomaly ssta in the east pole is primarily induced by anomalous surface latent heat flux and vertical temperature advection whereas in the west pole it is mainly caused by meridional and vertical temperature advection anomalies in both regions shortwave radiation anomalies tend to damp the ssta the ocean rossby waves are essential in linking the anomalous wind and sst off sumatra and subsurface temperature variations in southwest indian ocean

the unusual summer of 1994 in east asia iod teleconnections 1 an extremely hot and dry summer of 1994 was reported in east asian countries using observational data we have demonstrated that the indian ocean dipole iod is at least one possible cause of the abnormal east asian summer climate an anomalous cyclonic circulation over the western pacific and the southern china weakened the monsoonal northward flow in the lower troposphere an anomalous anticyclonic circulation with the equivalent barotropic structure around japan korea and the northeastern part of china caused the hot and dry summer of 1994 this accumulation of the lower potential vorticity in the far east is related to the wave activity from the mediterranean sahara region the monsoon desert mechanism connects a rossby wave source with the iod induced diabatic heating around the bay of bengal another rossby wave train pattern was generated in the upper troposphere and propagates northeastward from the southern china both the rossby wave patterns influenced the circulation changes over east asia

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

modelling flow and accreted ice in subglacial lake concordia antarctica more than 150 subglacial lakes have been discovered in antarctica so far due to obvious challenges with exploration numerical modelling remains one of the major tools to acquire information about those hard to access objects until now only the huge lake vostok has been investigated in detail this paper focuses on lake concordia the second largest subglacial lake in antarctica over which substantial geophysical data has been collected this lake is covered by about 4000 m ice and is located near dome c in order to apply numerical models to the hard to access antarctic subglacial lakes decent geometries and boundary conditions are required in this study we present the results of airborne gravity inversion suggesting that this lake has an area of 617 km2 a volume of 31 km3 and a maximum water column thickness of 126 m this bathymetry is used as geometry input for an established 3d numerical lake flow model to simulate the circulation and basal mass balance compared to our model studies of subglacial lake vostok we obtain a general circulation pattern that is significantly weaker due to the smaller size of the lake and of reversed orientation due to the reversed ice surface tilt the modelled mean horizontal and vertical velocities are in the order of 0 2 mm s and 0 5 m s respectively the larger molecular convective velocity estimations 1 35 0 13 mm s and 0 81 0 08 mm s are similar to lake vostok s the modelled average melting and freezing rates are 4 3 1 1 mm a and 1 1 0 3 mm a respectively and the corresponding fresh water gain is 58 27 dm3 s integration of the modelled freezing and melting along prescribed ice flow lines allows us to calculate the distribution and thickness of accreted ice at the ice sheet bottom we estimate a volume of 2 6 2 0 km3 8 3 8 2 of the total lake volume occupying the north eastern corner of the lake covering an area of 159 48 km2 26 9 of the total lake area with about 16 800 7600 yr the residence time of the lake s water is significantly shorter than lake vostok s

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

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

development of an antarctic digital elevation model by integrating cartographic and remotely sensed data a geographic information system based approach we present a high resolution digital elevation model dem of the antarctic it was created in a geographic information system gis environment by integrating the best available topographic data from a variety of sources extensive gis based error detection and correction operations ensured that our dem is free of gross errors the carefully designed interpolation algorithms for different types of source data and incorporation of surface morphologic information preserved and enhanced the fine surface structures present in the source data the effective control of adverse edge effects and the use of the hermite blending weight function in data merging minimized the discontinuities between different types of data leading to a seamless and topographically consistent dem throughout the antarctic this new dem provides exceptional topographical details and represents a substantial improvement in horizontal resolution and vertical accuracy over the earlier continental scale renditions particularly in mountainous and coastal regions it has a horizontal resolution of 200 m over the rugged mountains 400 m in the coastal regions and approximately 5 km in the interior the vertical accuracy of the dem is estimated at about 100 130 m over the rugged mountainous area better than 2 m for the ice shelves better than 15 m for the interior ice sheet and about 35 m for the steeper ice sheet perimeter the antarctic dem can be obtained from the authors

magnetic minerals in three asian rivers draining into the south china sea pearl red and mekong rivers the use of the marine sedimentary magnetic properties as tracers for changes in precipitation rate and in oceanic water masses transport and exchanges implies to identify and to characterize the different sources of the detrital fraction this is of particular importance in closed and or marginal seas such as the south china sea we report on the magnetic properties of sedimentary samples collected in three main asian rivers draining into the south china sea the pearl red and mekong rivers the geological formations as well as the present climatic conditions are different from one catchment to another the entire set of performed magnetic analyses low field magnetic susceptibility arm acquisition and decay irm acquisition and decay back field acquisition thermal demagnetization of three axes irm hysteresis parameters forc diagrams and low temperature magnetic measurements allow us to identify the magnetic mineralogy and the grain size distribution when magnetite is dominant some degree of variability is observed in each basin illustrating different parent rocks and degree of weathering on average it appears that the pearl river is rich in magnetite along the main stream while the mekong river is rich in hematite the red river is a mixture of the two compared to clay mineral assemblages and major element contents previously determined on the same samples these new findings indicate that the magnetic fraction brings complementary information of great interest for environmental reconstructions based on marine sediments from the south china sea

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

radiostratigraphy and age structure of the greenland ice sheet 2015 the authors several decades of ice penetrating radar surveys of the greenland and antarctic ice sheets have observed numerous widespread internal reflections analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections here we present a comprehensive deep radiostratigraphy of the greenland ice sheet from airborne deep ice penetrating radar data collected over greenland by the university of kansas between 1993 and 2013 to map this radiostratigraphy efficiently we developed new techniques for predicting reflection slope from the phase recorded by coherent radars when integrated along track these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing core intersecting reflections were dated using synchronized depth age relationships for six deep ice cores additional reflections were dated by matching reflections between transects and by extending reflection inferred depth age relationships using the local effective vertical strain rate the oldest reflections dating to the eemian period are found mostly in the northern part of the ice sheet within the onset regions of several fast flowing outlet glaciers and ice streams reflections typically do not conform to the bed topography disrupted radiostratigraphy is also observed in a region north of the northeast greenland ice stream that is not presently flowing rapidly dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly this radiostratigraphy provides a new constraint on the dynamics and history of the greenland ice sheet

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

spatial variation of englacial radar attenuation modeling approach and application to the vostok flowline 1 constraining the spatial variation of englacial radar attenuation is critical for accurate inference of the spatial variation of the englacial and basal properties of ice sheets from radar returned power here we evaluate attenuation models that account for spatial variations in ice temperature and chemistry and test them along the flowline that passes through the vostok ice core site antarctica the simplest model often used but rarely valid assumes a uniform attenuation rate everywhere along the flowline so that total attenuation is proportional to ice thickness the next simplest model uses spatially varying temperatures predicted by an ice flow model and assumes uniform chemistry additional models account for spatially varying chemistry using englacial stratigraphy we find that the roundtrip attenuation to the bed can easily differ by 10 db or more between the uniform attenuation rate model and models that account for variable ice temperature such differences are sufficient to confound the delineation of dry and wet beds also including spatial variations in chemistry produces smaller differences 10 db but the magnitude of these differences depends on the relative importance of dry and wet deposition of impurities in the past accounting for dry deposited impurities requires ice flow modeling and results in larger differences from all other models which assume uniform chemistry or wet deposition only these results indicate that modeling the spatial variation of attenuation requires a spatially varying temperature model in order to infer bed conditions from bed returned power accurately and that both ice core data and radar stratigraphy are also strongly desirable

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

magnetic properties of sediments of the red river effect of sorting on the source to sink pathway and its implications for environmental reconstruction we conducted a mineral magnetic study of river bank and subaqueous delta sediments from the red river in order to examine the role of sedimentary sorting on the variation of sedimentary magnetic properties from source to sink the magnetic mineralogy mainly consists of magnetite and hematite bulk sediment particle size variations have a strong influence on magnetic properties with the frequently used magnetic parameters fd arm arm and arm sirm exhibiting positive correlations with the 5 m water depth part of the subaqueous delta have lower and sirm values a finer ferrimagnetic grain size and higher proportions of hematite consistent with selective loss of coarse ferrimagnetic grains on the source to sink pathway we suggest that variations in magnetic properties in response to particle size compositions and therefore depositional environment changes should be carefully addressed when magnetic proxies such as arm sirm are used in the study of coastal and marine environmental changes e g sea level change in such cases the combined use of magnetic properties and geochemical indicators such as al ti ratio may provide better results for paleoenvironmental reconstruction

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

evidence of glacial flour in the deepest 89 m of the vostok ice core the 3623 m long vostok ice core is divided into two main parts 1 from the surface to a depth of 3310 m the ice layers are undisturbed and may be used to reconstruct the climatic record over the past 420 kyr 2 from 3538 m to the bottom the core is made up of accreted ice formed by freezing of the lake in between the glacier ice is disturbed by ice dynamics as shown for example by inclined volcanic ash layers microparticle concentrations and distributions as well as ionic and isotopic content were used to subdivide this third section the identification of layers with bedrock material provides clues as to the entrainment processes at sub freezing temperatures dust concentration and size distribution as well as ionic content are comparable with values found in ice of glacial and interglacial periods below 3450 m depth however the mode of the volume size distribution clearly shifts from 2 1 m to 3 4 m in diameter particles as large as 30 m in diameter are observed and cannot have an aeolian origin from microscopic observations we suggest that they originate from the bedrock and represent glacial flour entrained in a shear layer up to 89 m from the glacier sole this process most likely occurred when the ice sheet was grounded before flowing over the lake

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

errors in acoustic doppler profiler velocity measurements caused by flow disturbance acoustic doppler current profilers adcps are commonly used to measure streamflow and water velocities in rivers and streams this paper presents laboratory field and numerical model evidence of errors in adcp measurements caused by flow disturbance a state of the art three dimensional computational fluid dynamic model is validated with and used to complement field and laboratory observations of flow disturbance and its effect on measured velocities results show that near the instrument flow velocities measured by the adcp are neither the undisturbed stream velocity nor the velocity of the flow field around the adcp the velocities measured by the adcp are biased low due to the downward flow near the upstream face of the adcp and upward recovering flow in the path of downstream transducer which violate the flow homogeneity assumption used to transform beam velocities into cartesian velocity components the magnitude of the bias is dependent on the deployment configuration the diameter of the instrument and the approach velocity and was observed to range from more than 25 at 5 cm from the transducers to less than 1 at about 50 cm from the transducers for the scenarios simulated

subglacial lake vostok not expected to discharge water the question whether antarctica s largest lake subglacial lake vostok exchanges water is of interdisciplinary relevance but has been undecided so far we present the potential pathway outlet location and threshold height of subglacial water discharge from this lake based on a quantitative evaluation of the fluid potential if water left lake vostok it would flow toward ross ice shelf discharge would occur first to the east of the southern tip of the lake at this location the bedrock threshold is 91 23 m higher than the hydrostatic equipotential level of lake vostok it is concluded that lake vostok is not likely to reach this level within climatic timescales and that no discharge of liquid water is to be expected we show that in absence of the ice sheet the lake vostok depression would harbor a lake significantly deeper and larger than the present aquifer

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

a comment on the equation of state and the freezing point equation with respect to subglacial lake modelling the empirical equation of state eos allows the calculation of the density of water in dependence of salinity temperature and pressure water density is an important quantity to determine the internal structure and flow regime of ocean and lakes hence its exact representation in numerical models is of utmost importance for the specific simulation results the three parameters namely salinity temperature and pressure have a complex interdependency on the eos whether warmer water parcels sink or rise therefore depends on the surrounding salinity and pressure the empirical equation of freezing point eofp allows to calculate the pressure and salinity dependent freezing point of water both equations are necessary to model the basal mass balance below antarctic ice shelves or at the ice water interface of subglacial lakes this article aims three tasks first we comment on the most common formulations of the eos and the eofp applied in numerical ocean and lake models during the past decades then we describe the impact of the recent and selfconsistent gibbs thermodynamic potential formulation of the eos and the eofp on subglacial lake modelling finally we show that the circulation regime of subglacial lakes covered by at least 3000 m of ice in principle is independent of the particular formulation in contrast to lakes covered by a shallower ice sheet like e g subglacial lake ellsworth however as modelled values like the freezing and melting patterns or the distribution of accreted ice at the ice lake interface are sensitive to different eos and eofp we present updated values for subglacial lake vostok and subglacial lake concordia c 2010 elsevier b v all rights reserved

radar detection of accreted ice over lake vostok antarctica abstract airborne radar data collected over lake vostok east antarctica show a reflection close to the vostok ice core below the depth of the meteoric accreted ice boundary maib and near the boundary between impurity rich 1 and impurity poor 2 accreted ice a12b the spatial pattern of detection of this reflection is aligned with ice flow over the southern half of the lake ice core data from the accreted ice show large variations in the number density of inclusions soluble chloride ion concentration cl charge balance derived acidity h cb and crystal orientation fabric here we investigate the existing hypothesis that this reflection is due to the maib and seek possible reflection causes that explain the radar derived reflectivity 51 8 db the likely maximum reflectivity due to an insoluble mineral inclusion contrast is 125 db if none of the cl or h ions are trapped within inclusions then ice conductivity models predict a reflectivity of 50 db near the maib and 58 db near the a12b both primarily due to large h cb changes if some of those ions are trapped within inclusions then those values are smaller fabric contrasts at either boundary can produce significant reflectivities 62 db these results indicate that the mineral inclusion contrast near the maib does not cause the observed reflection because of uncertainty in the in situ location of the soluble impurities and because impurity rich accreted ice 1 is believed to only originate in the small bay in the southwestern corner of the lake yet the reflection is observed over a much wider area we argue that a fabric contrast at the a12b is the probable reflection cause both predicted spatial variations in accretion rates near the upstream shoreline or lower ice temperatures along flowbands that originate at bedrock ridges near the upstream shoreline may explain why the reflection is not detected everywhere that accretion is predicted

magnetic fingerprinting of fluvial suspended particles in the context of soil erosion example of the canche river watershed northern france in northern france land use is dominated by agriculture erosion by runoff results in heavy loss of fertile soil into surface waters there is a need for cost effective tools to trace the sediment flux in catchments this study highlights the potential of environmental magnetism to provide rapid non destructive parameters to characterize the spatiotemporal runoff versus bedload signal in a watershed between 2015 and 2017 within the canche river watershed several spatiotemporal sampling campaigns of suspended particulate matter spm were undertaken and two distinct snapshot campaigns of flood events were conducted at key locations acquiring in addition hydrodynamical observations discharge turbidity sediment load etc agricultural soils and spm within the watershed have similar values for bulk magnetic concentration isothermal remanent magnetization irm the magnetic mineral assemblage of the spm is dominated by soft ferromagnetic sensu lato minerals during low water conditions and is enriched in high coercivity phases during high water stages associated with rainfall events low temperature remanence experiments identified goethite and hematite as the high coercivity phases irm acquisition component analysis of the room temperature results quantify the relative input of high versus low coercivity components focused on a given confluence site results from snapshot campaigns highlight the link between the enhanced runoff input of high coercivity particles during flood events and show that the s ratio parameter is an effective tool to trace erosion of topsoils

mass gains of the antarctic ice sheet exceed losses during 2003 to 2008 the mass gain of the antarctic ice sheet from snow accumulation exceeded the mass loss from ice discharge by 49 gt yr 2 5 of input as derived from icesat laser measurements of elevation change the net gain 86 gt yr over the west antarctic wa and east antarctic ice sheets wa and ea is essentially unchanged from revised results for 1992 to 2001 from ers radar altimetry imbalances in individual drainage systems ds are large 68 to 103 of input as are temporal changes 39 to 44 the recent 90 gt yr loss from three ds pine island thwaites smith and marie bryd coast of wa exceeds the earlier 61 gt yr loss consistent with reports of accelerating ice flow and dynamic thinning similarly the recent 24 gt yr loss from three ds in the antarctic peninsula ap is consistent with glacier accelerations following breakup of the larsen b and other ice shelves in contrast net increases in the five other ds of wa and ap and three of the 16 ds in east antarctica ea exceed the increased losses alternate interpretations of the mass changes driven by accumulation variations are given using results from atmospheric model re analysis and a parameterization based on 5 change in accumulation per degree of observed surface temperature change a slow increase in snowfall with climate warming consistent with model predictions may be offsetting increased dynamic losses

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

magnetic stratigraphy of cenozoic terrestrial sediments and mammalian dispersal the existing literature on the correlation of the magnetic polarity timescale to vertebrate mammalian chronology for the cenozoic is reviewed for all continents except the soviet union the magnetostratigraphic data from north america is the most complete followed by the indian sub continent ten criteria for rating magnetostratigraphic studies are established and the papers reviewed are rated from 1 10 with 10 being the maximum score the timing of mammalian dispersal is examined against the background of information from magnetostratigraphic studies allied with radiometric dating north american land mammal ages are partly defined on immigrant taxa and the boundaries of the nalma are based on dispersal events it has been suggested that dispersal and evolutionary episodes observed in siwalik sediments were correlative to sea level change deduced from delta 18 o data from benthic foraminifera to test this possibility in the general case dispersal events into north america were determined by us

mineral magnetic properties of artificial samples systematically mixed from haematite and magnetite summary detailed rock magnetic investigations were carried out on a set of samples with defined ratios of haematite and magnetite the measured parameters provide a reference for interpreting common rock magnetic parameters in investigations of sediments the contribution of haematite to the magnetic fraction must exceed 95 wt of the magnetic fraction when mixed with magnetite in order to visibly influence grain size and coercitivity indicative magnetic parameters coercivity of remanence bcr and coercive force bc do not change in the same way with increasing haematite content which results in a peak bcr bc value at around 99 5 wt haematite variations in haematite content can be ignored when interpreting most rock magnetic parameters especially grain size indicative parameters for samples where haematite contents range from 0 to 98 wt the s ratio is still the most sensitive parameter for estimating the relative amount of haematite in magnetite haematite mixtures a combination of s ratio the saturation isothermal remanent magnetization divided by the low field magnetic susceptibility sirm lf and bcr is the most effective way to identify haematite in natural samples our results agree with literature data and fill the gap between results obtained either from pure magnetite or haematite with comparable grain sizes