subgrain boundaries in antarctic ice quantified by x ray laue diffraction ice in polar ice sheets undergoes deformation during its flow towards the coast deformation and recrystallization microstructures such as subgrain boundaries can be observed and recorded using high resolution light microscopy of sublimation edged sample surfaces microstructure mapping subgrain boundaries observed by microstructure mapping reveal characteristic shapes and arrangements as these arrangements are related to the basal plane orientation full crystallographic orientation measurements are needed for further characterization and interpretation of the subgrain boundary types x ray laue diffraction measurements validate the sensitivity of different boundary types with sublimation used by microstructure mapping for the classification x ray laue diffraction provides misorientation values of all four crystal axes line scans across a subgrain boundary pre located by microstructure mapping can determine the rotation axis and angle together with the orientation of the subgrain boundary this yields information on the dislocation types tilt and twist boundaries composed of dislocations lying in the basal plane and tilt boundaries composed of nonbasal dislocations were found a statistical analysis shows that nonbasal dislocations play a significant role in the formation of all subgrain boundaries

wave dispersion study for tsunami propagation in the sea of marmara in this paper the aim is to investigate whether there are differences between the dispersion and non dispersion solutions on tsunami propagation for this purpose two numerical models of tsunami propagation are compared one of these numerical models is a nondispersive model that uses saint venant equations and the other is a dispersive model that uses boussinesq equations the tsunamis resulting from a submarine mass failure smf which is settled at the bottom of the north eastern sea of marmara are examined an analytical solution considering wave dispersion is developed for obtaining near field tsunami amplitudes above the submarine mass failure numerical modeling is used at the sea surface from the common boundary called as liquid boundary with incident waves up to the coastal regions to get the tsunami amplitudes the output of the analytical model is taken as the disturbances for the numerical method in the numerical solutions telemac 2d software system is used for both dispersive and nondispersive modeling the results of the dispersive and nondispersive models are compared to each other both temporal and spatial differences in the amplitudes and wave shapes are examined the obtained results demonstrate that there are no noticeable differences between the dispersion and non dispersion solutions except some special cases and some special landslide velocities

tide model accuracy in the amundsen sea antarctica from radar interferometry observations of ice shelf motion 1 this study assesses the accuracy of tide model predictions in the amundsen sea sector of west antarctica tide model accuracy in this region is poorly constrained yet tide models contribute to simulations of ocean heat transfer and to the removal of tidal signals from satellite observations of ice shelves we use two satellite based interferometric synthetic aperture radar insar methods to measure the tidal motion of the dotson ice shelf at multiple epochs a single difference technique that measures tidal displacement and a double difference technique that measures changes in tidal displacement we use these observations to evaluate predictions from three tide models tpxo7 1 cats2008a opt and fes2004 all three models perform comparably well exhibiting root mean square deviations from the observations of 9 cm single difference technique and 10 cm double difference technique care should be taken in generalizing these error statistics because 1 the dotson ice shelf experiences relatively small semidiurnal tides and 2 our observations are not sensitive to all tidal constituents an error analysis of our insar based methods indicates measurement errors of 7 and 4 cm for the single and double difference techniques respectively a model based correction for the effect of fluctuations in atmospheric pressure yields an 6 improvement in the agreement between tide model predictions and observations this study suggests that tide model accuracy in the amundsen sea is comparable to other antarctic regions where tide models are better constrained these methods can be used to evaluate tide models in other remote antarctic waters

gps derived velocity and strain fields around dome argus antarctica knowledge of the surface topography velocity field and strain field at an ice core site is critical to the accurate interpretation of ice core records at dome argus dome a where a chinese deep ice core drilling project is being carried out we have produced an accurate surface digital elevation model from gps measurements in january 2013 at 47 sites we identify two peaks at dome a with the northern peak 7 cm higher than the southern peak repeat gps measurements at 12 sites in 2008 and 2013 provide a surface velocity field around the dome the surface velocity ranges from 3 1 2 6 to 29 4 1 2 cm a 1 with a mean of 11 1 2 4 cm a 1 the surface flow directions are near perpendicular to the surface elevation contours velocities from gps are lower than derived from satellite radar interferometry insar from gps velocities the accuracy of velocity from the existing insar velocity field is determined resulting in a standard deviation of 0 570 m a 1 in speed and 117 58 in direction this result is consistent with the reported accuracy of insar showing the value of in situ gps measurements for assessing and correcting remote sensing results a surface strain field for the drilling site over dome a is calculated from 24 strain triangles showing north south extension east west compression and vertical layer thinning

surface velocity and mass balance of ice streams d and e west antarctica over 75 000 surface velocity measurements are extracted from sequential satellite imagery of ice streams d and e to reveal a complex pattern of flow not apparent from previous measurements horizontal and vertical strain rates calculated from surface velocity indicate that the bed experiences larger basal shear where the surface of these ice streams is rougher ten airborne radar profiles and one surface based radar profile of ice thickness make possible the calculation of mass balance for longitudinal sections of each ice stream improved data collection methods increase data density substantially reducing random errors in velocity however systematic errors continue to limit the ability of the flux differencing technique used here to resolve local variations in mass balance nevertheless significant local variations in mass balance are revealed while overall ice streams d and e are in approximate equilibrium an earlier estimate of the net mass balance for ice stream d is improved

a model for flow in the chalk unsaturated zone incorporating progressive weathering summary groundwater from unconfined chalk aquifers constitutes a major water resource in the uk the unsaturated zone in such systems plays a crucial role in the hydrological cycle determining the timing and magnitude of recharge and the transport and fate of nutrients however despite more than three decades of study our physical understanding of this system is incomplete in this research state of the art instrumentation provided high temporal resolution readings of soil moisture status rainfall and actual evaporation from two sites in the pang and lambourn catchments berkshire uk for a continuous two year period 2004 5 a parsimonious physically based model for the flow of water through the chalk unsaturated zone including a novel representation of the soil and weathered chalk layers was developed the parameters were identified by inverse modelling using field measurements of water content and matric potential the model was driven by rainfall and evaporation data and simulated fluxes throughout the profile including the discrete matrix and fracture components down to the water table but not the water table response results showed that the model was able to reproduce closely the observed changes in soil moisture status recharge was predominantly through the matrix and the recharge response was strongly attenuated with depth however the activation of fast recharge pathways through fractures in the chalk unsaturated zone was highly sensitive to rainfall intensity relatively modest increases in rainfall led to dramatically different recharge patterns with potentially important implications for groundwater flooding the development and migration of zero flux planes with time and depth were simulated the simulations also provided strong evidence that for water table depths greater than 5 m recharge fluxes persist throughout the entire year even during drought conditions with important implications for the calculation of specific yield from baseflow estimates and the representation of recharge in groundwater models

studies of the grounding line location on ice streams d and e antarctica landsat thematic mapper tm images were used prior to the 1991 92 field season to infer the position of the grounding line at the mouths of ice streams d and e west antarctica our field plan for mass balance studies was based on this determination and thus the imagery played a central role in both the scientific and logistics planning a radar profile along the flow direction was made across the inferred grounding line at one location and ice thickness measurements together with surface surveying enable us to compare the hydrostatic surface and the actual topography to determine the point at which the ice becomes grounded the profile transits from floating to grounded ice at the same location as the grounding line inferred from the imagery changes in the radar echo strength also occur at this location giving further support to this interpretation tilt studies of the ice flexure caused by tidal variations at locations on either side of this grounding point give additional evidence that grounding is occurring close by the combination of these three measurements thus confirms the grounding line location derived from the satellite imagery and supports the use of this technique to determine grounding

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone a conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone was developed based on the results of lithological studies and a series of ponded infiltration tests conducted at the box canyon site near the idaho national engineering and environmental laboratory the infiltration tests included one 2 week test in 1996 three 2 day tests in 1997 and one 4 day test in 1997 for the various tests initial infiltration rates ranged from 4 1 cm d 4 75 10 7 m s to 17 7 cm d 2 05 10 7 m s and then decreased with time presumably because of mechanical or microbiological clogging of fractures and esicular basalt in the near surface zone as well as the effect of entrapped air the subsurface moisture redistribution was monitored with tensiometers neutron logging time domain reflectrometry and ground penetrating radar a conservative tracer potassium bromide was added to the pond water at a concentration of 3 g l to monitor water flow with electrical resistivity probes and water sampling analysis of the data shows evidence of preferential flow rather than the propagation of a uniform wetting front we propose a conceptual model describing the saturation desaturation behavior of the basalt in which rapid preferential flow occurs through the largest vertical fractures followed by a gradual wetting of other fractures and the basalt matrix fractures that are saturated early in the tests may become desaturated thereafter which we attribute to the redistribution of water between fractures and matrix lateral movement of water takes place within horizontal fracture and rubble zones enabling development of perched water bodies

characteristics of accumulation around the epica deep drilling site in dronning maud land antarctica based on ground penetrating radar profiles we analyze area wide spatial and temporal characteristics of accumulation rate in the vicinity of the epica european project for ice coring in antarctica deep drilling site in dronning maud land antarctica edml an area of 1600 km 2 is covered by 500 km of radar profiles organized in a star like pattern with eight 20 25 km legs and a 10 km grid with 1 3 km spacing each pattern being centred on the edml drilling location distributions of density cumulative mass age and the electromagnetic wave speed with depth are available from physical ice core records nine internal reflection horizons are continuously tracked within the upper 110 m of ice over the whole area yielding a spatial picture of accumulation rate history over 1000 years the mean accumulation rate over the last 153 years varies between 50 and 75 kg m 2 a 1 over 50 km perpendicular to the ice divide the spatial average is 61 kg m 2 a 1 this general pattern is overlain by small scale variations of accumulation rate on the order of 10 of the mean maximum local gradients in accumulation rate are 2 3 kg m 2 a 1 km 1 about five times the regional accumu lation rate gradient comparison of topography and accumulation rate along a 20 km profile in the direction of the mean winds indicates that variations in accumulation rate over short distances are linked to surface undulations our results show that advected spatial variations of accumulation rate are on the same order and even exceed temporal changes over the investigated periods ice flow and upstream effects therefore might influence accumulation rates reconstructed from the edml ice core

comparison of elastic moduli from seismic diving wave and ice core microstructure analysis in antarctic polar firn we compared elastic moduli in polar firn derived from diving wave refraction seismic velocity analysis firn core density measurements and microstructure modelling based on firn core data the seismic data were obtained with a small electrodynamic vibrator source near kohnen station east antarctica the analysis of diving waves resulted in velocity depth profiles for different wave types p sh and sv waves dynamic elastic moduli of firn were derived by combining p and s wave velocities and densities obtained from firn core measurements the structural finite element method fem was used to calculate the components of the elastic tensor from firn microstructure derived from x ray tomography of firn core samples at depths of 10 42 71 and 99 m providing static elastic moduli shear and bulk moduli range from 0 39 to 2 42 gpa and 0 68 to 2 42 gpa respectively the elastic moduli from seismic observations and the structural fem agree within 8 5 for the deepest achieved values at a depth of 71 m and are within the uncertainty range our observations demonstrate that the elastic moduli of the firn can be consistently obtained from two independent methods which are based on dynamic seismic and static tomography and fem observations respectively for deeper layers in the firn below 10 m depth

surface topography and ice flow in the vicinity of the edml deep drilling site antarctica interpretation of ice core records requires accurate knowledge of the past and present surface topography and stress strain fields the european project for ice coring in antarctica epica drilling site 75 00258 s 0 06848 e 2891 7 m in dronning maud land antarctica is located in the immediate vicinity of a transient and forking ice divide a digital elevation model is determined from the combination of kinematic gps measurements with the glas12 datasets from the icesat based on a network of stakes surveyed with static gps the velocity field around the drilling site is calculated the annual mean velocity magnitude of 12 survey points amounts to 0 74ma 1 flow directions mainly vary according to their distance from the ice divide surface strain rates are determined from a pentagonshaped stake network with one center point close to the drilling site the strain field is characterized by along flow compression lateral dilatation and vertical layer thinning

magnitude based scaling of tsunami propagation 1 most current operational tsunami prediction systems are based upon databases of precomputed tsunami scenarios where some form of linear scaling is applied to the precomputed model runs in order to represent specific earthquake magnitudes this can introduce errors due to assumptions made about the rupture width and possible effects on dispersion in this paper we perform a series of numerical experiments on uniform depth domains using the method of splitting tsunamis most model and develop estimates of the maximum error that an assumed discrepancy in the width of a rupture will produce in the resulting field of maximum tsunami amplitude this estimate was produced from fitting the decay of maximum amplitude with normalized distance for various resolutions of the source widths to the grid size resulting in a simple power law whose coefficients effectively vary with wavelength resolution this provides a quantification of the effect that linear scaling of precomputed scenarios will have on forecasts of tsunami amplitude this estimate of scaling bias is investigated in relation to the scenario database that is currently in use within the joint australian tsunami warning centre

propagation of distant tsunamis over slowly varying topography 1 a new two dimensional finite difference numerical scheme is developed to simulate the propagation of distant tsunamis over slowly varying topography with improved dispersion effect of waves the new scheme solves the shallow water equations on a uniform grid system however the actual computation is made on a hidden grid system whose grid size is adjustable according to the condition required to satisfy local dispersion relationships of waves for varying water depth the present model is tested for the cases of two dimensional propagation of an initial gaussian hump over various uniform water depth regions for a varying topography a one dimensional test is conducted the tests show that accuracy of the numerical model is improved significantly over that of the conventional finite difference models finally the present model is applied to the simulation of a historical tsunami event the numerical result shows that the submerged rise and ridge play an important role of a waveguide for the tsunamis propagating over that topography

computation of tsunami amplitudes resulting from a predicted major earthquake in the shumagin seismic gap a time dependent two dimensional numerical model was developed to study the generation and propagation of a tsunami resulting from a major earthquake predicted to occur in the shumagin seismic gap area of the eastern part of the aleutian island chain the grid size is approximately 28 km in the latitudinal direction and 36 km in the longitudinal direction the leading wave of the tsunami took only about three hours to arrive at the southern british columbia coast and the northern part of the coast of the state of washington on the other hand it took about eight hours to propagate into the bering sea two important results emerged from this study the tsunami waves show very strong directionality and the presence of the so called lateral waves can be inferred in the deep ocean tsunami amplitudes up to one meter appear to occur to deduce the detailed distribution of the tsunami amplitudes at the coast the present large area model has to be coupled to a coastal model which uses either finer rectangular grids or irregular triangular grids

application of a continuum mechanical model for the flow of anisotropic polar ice to the edml core antarctica we present an application of the newly developed caffe model continuum mechanical anisotropic flow model based on an anisotropic flow enhancement factor to the epica ice core at kohnen station dronning maud land antarctica referred to as the edml core a one dimensional flow model for the site is devised which includes the anisotropic flow law and the fabric evolution equation of the caffe model three different solution methods are employed 1 computing the ice flow based on the flow law of the caffe model and the measured fabrics 2 solving the caffe fabric evolution equation under the simplifying assumption of transverse isotropy and 3 solving the unrestricted caffe fabric evolution equation method 1 demonstrates clearly the importance of the anisotropic fabric in the ice column for the flow velocity the anisotropic enhancement factor produced with method 2 agrees reasonably well with that of method 1 even though the measured fabric shows a girdle structure which breaks the transverse isotropy in large parts of the ice core for method 3 we find that the measured fabric is reproduced well by the model down to 2100 m depth systematic deviations at greater depths are attributed to the disregard of migration recrystallization in the model

motion of an antarctic glacier by repeated tidally modulated earthquakes subglacial seismicity reveals information about glacier behaviour analysis of repeated seismic events beneath an antarctic outlet glacier is consistent with sliding of debris laden ice over a bedrock asperity with an event frequency that is modulated by the ocean tides

relative hydraulic conductivity in the vadose zone from magnetic resonance sounding brooks corey parameterization of the capillary fringe the magnetic resonance sounding mrs method is used for noninvasive one dimensional assessment of aquifer structures i e for estimating the vertical water content and hydraulic conductivity distributions in the saturated zone so far mrs interpretation schemes for estimating the hydraulic conductivity as a function of the saturation degree in the vadose zone have not been developed in this study we developed a new inversion scheme for mrs to estimate the relative hydraulic conductivity krel which is the ratio of the unsaturated and saturated conductivities the new approach is based on the brooks corey parameterization bcp of the capillary fringe that is the water content distribution of the capillary fringe is considered to be equivalent to the water retention curve in equilibrium state the bcp inversion directly provides estimates of brooks corey parameters from mrs data which allows for the calculation of krel as a function of the saturation degree in doing so the water table must be gi

geometric boundary conditions for modelling the velocity field of the antarctic ice sheet a comparison of the two dimensional horizontal velocity field obtained on the basis of conservation of mass balance velocity with the diagnostic velocityfield calculated with an ice sheet model dynamics velocity may yield information on shortcomings in the way the ice sheet model describes the ice flow thispaper presents improved geometric boundary conditions surface elevation and ice thickness required as input in such calculations in particular the surfaceelevation grid is described in detail as it has been generated specifically for such a study and represents a new standard in accuracy and resolution forcalculating surface slopes the digital elevation model was generated on a 10 km grid size from over 20 000 000 height estimates obtained from seven 35 dayrepeat cycles of ers 1 radar altimeter data for surface slopes less than 0 5i the relative elevation accuracy is better than 1 m in areas of high surface slope coastal and mountainous regions the altimeter measurements have been supplemented with data taken from the antarctic digital database south of 81 5i data from the spri folio map have been used the ice thickness grid was produced from a combination of a re digitisation of the spri folio and the originalradio echo sounding flight lines for areas of grounded ice the bedrock was estimated from surface elevation and ice thickness significant differences inexcess of 25 percent of ice thickness were obtained between an earlier digitisation of the folio bedrock map and the dataset derived here furthermore a newvalue of 26 6 x 106 km3 was obtained for the total volume of the ice sheet and shelves which is a reduction of 12 percent compared with the original estimatederived during the compilation of the spri folio these differences will have an important influence on the results obtained by numerical ice sheet models

changes in west antarctic ice stream velocities observation and analysis 1 we have produced a map of velocity covering much of the siple coast ice streams the map confirms earlier estimates of deceleration on whillans ice stream comparison with bed elevation data indicates that subglacial topography and the location of consolidated sediment play a strong role in determining the location of the tributaries feeding the ice streams force balance estimates based on these data indicate that the tributaries have beds nearly an order of magnitude stronger than those beneath many of the ice streams we have used a theoretical analysis to examine the controls on fast flow this analysis suggests that ice plains very wide ice streams are inherently unstable this instability may be responsible for the current deceleration on the ice plain of whillans ice stream and the shutdown of ice stream c 150 years ago thinning induced reductions in driving stress may also explain some of the observed deceleration particularly in upstream areas the active portions of ice stream c coincide well with the areas where we estimate that melt should be taking place current topography and inferences of large thickening following a shutdown suggest the upstream migration of a stagnation front that initiated at the ice plain uncertainty remains about the basal conditions on ice stream d while the basal resistance on ice stream e is large enough to ensure basal melting

basal friction of ice stream e west antarctica we use surface velocity derived from sequential landsat imagery and a control method to estimate the basal friction distribution of a major west antarctic ice stream the area averaged basal stress is approximately 1 4 10 4 pa or about 29 of the area averaged driving stress of 4 9 10 4 pa uncertainty of the derived area averaged basal stress is difficult to assess and depends primarily on spatial variation of the flow law rate factor in the constitutive law spatial variation associated with depth averaged temperature variation gives an uncertainty of approximately 10 3 pa approximately 60 of the ice stream has a basal stress magnitude less than 10 4 pa and approximately 30 has less than 10 3 pa these characteristics suggest the presence of a mechanically weak water charged subglacial till small scale sticky spots where basal friction exceeds the area averaged driving stress are scattered irregularly across the subglacial regime and comprise approximately 15 of the ice stream area sticky spots cluster in regions where landsat imagery suggests structural features in the underlying bedrock

new maps of the ice thickness and subglacial topography in dronning maud land antarctica determined by means of airborne radio echo sounding since the austral summer 1994 95 the alfred wegener institute awi hascarried out airborne radio echo sounding measurements res in antarctica withits newly designed res system since 1995 96 an ongoing presite survey foran ice coring drill site in dronning maud land dml has been carried out this survey is part of the epica programme european project for ice coring inantarctica it covers an area of 948000 km2 with more than 49500 km ofairborne res obtained from more than 200 hours of flight operation flown from1994 1997 within this paper first results of the airborne res survey will begraphically summarized as newly derived maps of the ice thickness and thesubglacial topography as well as a 3d view of surface and subglacial bed andoutcrop topography revealing a total icevolume of 1 48 million km3

icesat antarctic elevation data preliminary precision and accuracy assessment 1 since first light on february 20th 2003 nasa s ice cloud and land elevation satellite icesat has derived surface elevations from 86 n to 86 s latitude these unique altimetry data have been acquired in a series of observation periods in repeated track patterns using all three geoscience laser altimeter system glas lasers here we focus on antarctic ice sheet elevation data that were obtained in 2003 2004 we present preliminary precision and accuracy assessments of selected elevation data and discuss factors impacting elevation change detection we show that for low slope and clear sky conditions the precision of gla12 laser 2a release 21 data is 2 1 cm and the relative accuracy of icesat elevations is 14 cm based on crossover differences

physical analysis of an antarctic ice core towards an integration of micro and macrodynamics of polar ice microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail ice core parameters crystal lattice preferred orientation lpo grain size grain shape mesostructures visual stratigraphy as well as borehole deformation were measured in a deep ice core drilled at kohnen station dronning maud land dml antarctica these observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the edml ice core drilling site european project for ice coring in antarctica in dml the results suggest a division of the core into five distinct sections interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock parallel shear region 1 uppermost approx 450 m depth with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization region 2 approx 450 textendash 1700 m depth shows a girdle type lpo with the girdle plane being perpendicular to grain elongations which indicates triaxial deformation with dominating horizontal extension in this region approx 1000 m depth the first subtle traces of shear deformation are observed in the shape preferred orientation spo by inclination of the grain elongation region 3 approx 1700 textendash 2030 m depth represents a transitional regime between triaxial deformation and dominance of shear which becomes apparent in the progression of the girdle to a single maximum lpo and increasing obliqueness of grain elongations the fully developed single maximum lpo in region 4 approx 2030 textendash 2385 m depth is an indicator of shear dominance region 5 below approx 2385 m depth is marked by signs of strong shear such as strong spo values of grain elongation and strong kink folding of visual layers the details of structural observations are compared with results from a numerical ice sheet model pism isotropic for comparison of strain rate trends predicted from the large scale geometry of the ice sheet and borehole logging data this comparison confirms the segmentation into these depth regions and in turn provides a wider view of the ice sheet this article is part of the themed issue textquoteleft microdynamics of ice textquoteright

observations of the surface properties of the ice sheets by satellite radar altimetry by comparing modelled and averag ed satellite altimeter return it is demonstra ted that time profiles of altimeter return can be used to provide important information on the surface proper ties of the ice sheets alt imeter ice sheet radar echoes from low altit udes and or rela tively low latitudes are in gene ral domin ated by surface scat tering and in greenl and the area of surface d ominated return broadly coi ncides with the zone of summer melting seasonal variations in the echo wave form shapes are negligible in all regions studied with the possib le exception of an area near the margin of the greenland dry snow zone in general the model expla ins well the observed variations in mean wave form shape but small discrepances between the model wave forms and the recorded wave forms indicate that sub sur face layers may be influ encing the shape of the return the poss ibility of deriving quantitative estima tes of surface proper ties is explored by fitting model returns to averaged altimeter wave forms from the wilkes land plateau in anta rctica surface roug hness can be meas ured unambig uously from the wave form data but estim ations of other parameters such as gra in size snow density and snow temperature are found to be ambiguous because different surface para meters have a similar infl uence on the shape of the retur n despite this the derived estimates compare well with ground b ased observations and suggest that the satellite alti meter may have an important role to play in providing info rmation on the surface properties of the ice sheets

unsteady flow inferred for thwaites glacier and comparison with pine island glacier west antarctica we present a comparison of surface velocities in 1996 derived from interferometric synthetic aperture radar with an estimate of the long term depth averaged velocity based on the assumption of steady state flow for both pine island glacier and its neighbour thwaites glacier west antarctica the results show that the former was close to balance conditions in 1996 within 9 the ice flux and velocity of the latter is significantly different in magnitude and distribution from that required to maintain the basin in a state of mass balance over the long term the balance flux was found to be 32 19 less than the measured outgoing flux we conclude that the mass imbalance and dramatic difference in the pattern of flow is most likely due to a substantial change in the flow regime of thwaites glacier in the recent past

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

potential mechanisms for anisotropy in ice penetrating radar data radar data center frequency 150 mhz collected on the antarctic plateau near the epica deep drilling site in dronning maud land vary systematically in backscattered power depending on the azimuth antenna orientation backscatter extrema are aligned with the principal directions of surface strain rates and change with depth in the upper 900 m backscatter is strongest when the antenna polarization is aligned in the direction of maximal compression while below 900m the maxima shift by 90 pointing towards the lateral flow dilatation we investigate the backscatter from elongated air bubbles and a vertically varying crystal orientation fabric cof using different scattering models in combination with ice core data we hypothesize that short scale variations in cof are the primary mechanism for the observed anisotropy and the 900m boundary between the two regimes is caused by ice with varying impurity content observations of this kind allow the deduction of cof variations with depth and are potentially also suited to map the transition between holocene and glacial ice

inland thinning of the amundsen sea sector west antarctica 1 together with the pine island glacier pig the thwaites tg and smith sg glaciers are the principal drainage systems of the amundsen sea as sector of western antarctica here we use satellite radar altimetry and interferometry to show that a rapid thinning of ice has occurred within the fastest flowing sections of all as outlet glaciers the pattern of thinning extends to distances greater than 150 km inland between 1991 and 2001 the tg and sg thinned by more than 25 and 45 m at their grounding lines and a total of 154 16 km 3 of ice or 0 43 mm of eustatic sea level rise was lost from the as sector glaciers to the ocean we show that the thickness changes may have caused the pig tg and sg to retreat inland by over 8 4 and 7 km respectively in line with independent estimates of grounding line migration

the deuterium excess records of epica dome c and dronning maud land ice cores east antarctica new high resolution deuterium excess d data from the two epica ice cores drilled in dronning maud land edml and dome c edc are presented here the main moisture sources for precipitation at edc and edml are located in the indian ocean and atlantic ocean respectively the more southward moisture origin for edml is reflected in a lower present day d value compared to edc the edml and edc isotopic records 18o and d show the main climate features common to the east antarctic plateau and similar millennial scale climate variability during the last glacial period however quite large 18o and d differences are observed during mis5 5 and the glacial inception with a long term behaviour a possibility for this long term difference could be related to uncertainties in past accumulation rate which are used in the glaciological models regional climate anomalies between the two sites during mis5 5 could also be consistent with the observed edml edc 18o and d gradient anomalies simulations performed with the general circulation model echam4 for different time slices provide a temporal temperature isotope slope for the edml region in fair agreement to the modern spatial slope tsite and tsource records are extracted from both ice cores using a modelling approach after corrections for past 18o seawater and elevation changes a limited impact of d on antarctic temperature reconstruction at both edml and edc has been found with a higher impact only at glacial inception the aim antarctic isotope maximum events in both ice cores are visible also after the source correction suggesting that these are real climate features of the glacial period the different shape of the aim events between edc and edml as well as some climate features in the early holocene points to a slightly different climate evolution at regional scale a comparison of our temperature reconstruction profiles with the aerosol fluxes show a strong coupling of the nssca fluxes with antarctic temperatures during glacial period and a tighter coupling of 18o and tsite with ssna flux at edml compared to edc during the glacial period and mis5 5

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

past and present accumulation rate reconstruction along the dome fuji kohnen radio echo sounding profile dronning maud land east antarctica we used internal ice layers from a radio echo sounding profile between the kohnen and dome fuji deep drilling sites to infer the spatio temporal pattern of accumulation rate in this sector of dronning maud land east antarctica continuous internal reflection horizons can be traced to about half of the ice thickness and have a maximum age of approximately 72 7 ka bp to infer palaeo accumulation rates from the dated layers we derived the thinning functions from a flow calculation with a high resolution higher order model of dronning maud land embedded into a three dimensional thermomechanical model of the antarctic ice sheet the method takes into account complex ice flow dynamics and advection effects that cannot be dealt with using traditional local approaches we selected seven time intervals over which we determine the average accumulation rate and average surface temperature at the place and time of origin of the layer particles our results show lower accumulation rates along eastern parts of the profile for the late holocene 0 5 ka bp than are shown by existing maps which had no surface control points during the last glacial period we find a substantially lower accumulation rate than predicted by the usual approach linking palaeo accumulation rates to the condensation temperature above the surface inversion layer these findings were used to fine tune the relation between accumulation rate and temperature

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

simulation of andaman 2004 tsunami for assessing impact on malaysia mistakenly perceived as safe from the hazards of tsunami malaysia faced a rude awakening by the 26 december 2004 andaman tsunami since the event malaysia has started active research on some aspects of tsunami including numerical simulations of tsunami and the role of mangrove as a mitigation measure against tsunami hazards an in house tsunami numerical simulation model tuna has been developed and applied to the 26 december 2004 andaman tsunami to simulate the generation propagation and inundation processes along affected beaches in malaysia mildly nonlinear bottom friction term in the deeper ocean is excluded as it is insignificant to the simulation results consistent with theoretical expectation on the other hand in regions with shallow depth near the beaches friction and nonlinearity are significant and are included in tuna simulation results with tuna indicate satisfactory performance when compared with comcot and on site survey results

re establishment of ice surface velocity field and snow surface elevation change around dome argus east antarctica in january 2016 static gps measurements were carried out in a 30 30 km2 area centered around kunlun station at dome argus dome a east antarctica to acquire high precision 3 d geodetic coordinates at 49 sites by comparing the coordinates with previous gps measurements in 2008 and 2013 at the same sites we constructed a detailed and long term record of the ice surface velocity field 2008 2016 around dome a during this time span the estimated ice surface velocity ranges from 0 8 0 3 to 28 7 1 6 cm a 1 with a mean of 10 4 0 3 cm a 1 from 2013 to 2016 the surface elevation of most dome a areas exhibits a rising trend and the maximum increase of snow surface elevation is 84 8 cm the mean snow surface elevation change rate at dome a is estimated to be 6 6 0 7 cm a 1 the difference of 1 0 cm a 1 between the snow surface change rate derived from gps and pole height change rate from surface mass balance is suspected to be a result of a combination of firn densification and basal melt under dome a

observations and numerical modeling of the 2012 haida gwaii tsunami off the coast of british columbia a major mw 7 7 earthquake occurred on october 28 2012 along the queen charlotte fault zone off the west coast of haida gwaii formerly the queen charlotte islands the earthquake was the second strongest instrumentally recorded earthquake in canadian history and generated the largest local tsunami ever recorded on the coast of british columbia a field survey on the pacific side of haida gwaii revealed maximum runup heights of up to 7 6 m at sites sheltered from storm waves and 13 m in a small inlet that is less sheltered from storms leonard and bednarski2014 the tsunami was recorded by tide gauges along the coast of british columbia by open ocean bottom pressure sensors of the neptune facility at ocean networks canada s cabled observatory located seaward of southwestern vancouver island and by several dart stations located in the northeast pacific the tsunami observations in combination with rigorous numerical modeling enabled us to determine the physical properties of this event and to correct the location of the tsunami source with respect to the initial geophysical estimates the initial model results were used to specify sites of particular interest for post tsunami field surveys on the coast of moresby island haida gwaii while field survey observations leonard and bednarski2014 were used in turn to verify the numerical simulations based on the corrected source region

subgrain boundaries and related microstructural features in edml antarctica deep ice core subgrain boundaries revealed as shallow sublimation grooves on ice sample surfaces are a direct and easily observable feature of intracrystalline deformation and recrystallization statistical data obtained from the epica dronning maud land edml deep ice core drilled in east antarctica cannot detect a depth region of increased subgrain boundary formation grain boundary morphologies show a strong influence of internal strain energy on the microstructure at all depths the data do not support the classical view of a change of dominating recrystallization regimes with depth three major types of subgrain boundaries reflecting high mechanical anisotropy are specified in combination with crystal orientation analysis

three dimensional simulation of tsunami generation and propagation application to intraplate events 1 a parallel finite difference numerical simulation program based on the navier stokes ns equations is developed for simulating 3 d tsunami generation and propagation we can simulate tsunami propagation over more than 1000 km using this program although such tsunami propagation over long distances has usually been conducted on the basis of on 2 d simulations some 2 d simulations have assumed that the initial tsunami distribution is identical to the sea bottom deformation caused by the earthquake the 3 d simulations however indicate that this assumption is inappropriate when the source width 2ax is less than 10 times the sea depth h 2ax 10h for a source process time of 20 s dispersion of tsunami appears when the source is of small size and the dispersion is more apparent in a direction perpendicular to the fault strike we also conduct tsunami simulations for two intraplate events the 2004 off kii peninsula m 7 4 and the 2007 off kuril islands m 8 1 events the 3 d tsunami simulation has successfully simulated the offshore tsunami and we obtained good agreement between the observations and the calculations for both events in particular for the 2004 off kii peninsula event although the 2 d linear long wave theory cannot simulate important characteristics in the record such as the arrival time of the peak amplitude and the dispersive tsunami the 3 d ns simulation is well able to model those characteristics

gpr reflection profiles of clark and commonwealth glaciers dry valleys antarctica englacial horizons deeper than 100 m are absent within 100 mhz ground penetrating radar gpr surface profiles we recorded on clark and commonwealth glaciers in the antarctic dry valleys region both glaciers show continuous bottom horizons to 280 m with bottom signal to noise ratios near 30 db density horizons should fade below 50 m depth because impermeable ice occurred by 36 m folding within commonwealth glacier could preclude radar strata beneath about 80 m depth but there is no significant folding within clark glacier strong sulfate concentrations and contrasts exist in our shallow ice core however it appears that high background concentration levels and possible decreased concentration contrasts with depth placed their corresponding reflection coefficients at the limit of or below our system sensitivity by about 77 m depth further verification of this conclusion awaits processing of our deep core chemistry profiles