basal conditions beneath enhanced flow tributaries of slessor glacier east antarctica radio echo sounding data are used to investigate bed roughness beneath the three enhanced flow tributaries of slessor glacier east antarctica slow moving inter tributary areas are found to have rough beds while the bed of the northernmost tributary is relatively smooth a reconstruction of potential subglacial drainage routing indicates that water would be routed down this tributary and investigations of basal topography following isostatic recovery reveal that the bed would have been below sea level in preglacial times so marine sediments may have accumulated here together these factors are further support for the dominance of basal motion in this tributary reported elsewhere conversely although the other two slessor tributaries may have water routed beneath them they would not have been below sea level before the growth of the ice sheet so cannot be underlain by marine sediments they are also found to be rough and within the range of uncertainties it is likely that basal motion does not play a major role in the flow of these tributaries perhaps the most interesting area however is a deep trough where flow rates are currently low but the bed is as smooth as the northern slessor trough it is proposed that although ice deformation currently dominates in this trough basal motion may have occurred in the past when the ice was thicker

influence of subglacial conditions on ice stream dynamics seismic and potential field data from pine island glacier west antarctica 1 we interpret seismic reflection and airborne potential field data acquired on pine island glacier west antarctica and find variations in the subglacial geology which correlate with variations in ice dynamics immediately beneath the glacier is a mixture of soft deforming sediments and harder non deforming sediments beneath this a sedimentary basin lies under part of the main glacier with another under one of its slower moving tributaries a tectonic boundary underlies the main trunk of the glacier separating these sedimentary basins to the north from crystalline rocks to the south which also include a thick rift related magmatic intrusion the boundary correlates with changes in the basal roughness ice flow speed and basal drag smoother bed faster flow and lower basal drag characterize the thicker sedimentary sequences to the north but there is no corresponding lateral change in the acoustic properties of the bed changes in the sub bed i e deeper than the ice bed interface lithology appear to account for the contrasting basal drag and ice velocity patterns over the glacier subglacial erosion could remove a thin layer of soft sediments to the south of the geological boundary leading to increased basal drag and reduced ice flow in the future we conclude that the subglacial geology plays a significant role in controlling the spatial pattern of present day ice flow and that the consequences of subglacial erosion may be reflected in temporal changes to the ice dynamics in the past and perhaps also in the near future

quantifying subglacial bed roughness in antarctica implications for ice sheet dynamics and history abstract glaciated landscapes consist of complex assemblages of landforms resulting from ice flow dynamic regimes and ice sheet history superimposed over and in turn modifying preglacial topography lithology and geological structure insights into the formation of glaciated landscapes can in principle be obtained by analysing modern ice sheet beds but terrain analyses beneath modern ice sheets are restricted by the inaccessibility of the bed it is however possible to quantify roughness the vertical variation of the subglacial interface with horizontal distance along two dimensional images of the bed obtained from radio echo sounding res here we collate several case studies from antarctica where roughness calculations have been used as a glaciological tool to infer basal processes and ice sheet history over large 500 km 2 areas we present two examples from west antarctica which demonstrate the utility of bed roughness in determining the presence and extent of subglacial sediments glacial dynamics and former ice sheet size we also present two examples from east antarctica which illustrate how roughness provides knowledge of ice sheet dynamics in the interior and pre quaternary ice sheet histories in modern ice sheet settings characterising bed roughness along res tracks has the twin advantages of being relatively simple to calculate while producing informative subsurface data and is especially powerful at furthering understanding when coupled with knowledge of ice flow from field satellite and modelling investigations the technique also offers significant potential for the comparison of modern and former ice sheet terrains contributing to an improved understanding of the formation and evolution of glaciated landscapes

evidence of a hydrological connection between the ice divide and ice sheet margin in the aurora subglacial basin east antarctica subglacial hydrology in east antarctica is poorly understood yet may be critical to the manner in which ice flows data from a new regional airborne geophysical survey icecap have transformed our understanding of the topography and glaciology associated with the 287 000 km2 aurora subglacial basin in east antarctica using these data in conjunction with numerical ice sheet modeling we present a suite of analyses that demonstrate the potential of the 1000 km long basin as a route for subglacial water drainage from the ice sheet interior to the ice sheet margin we present results from our analysis of basal topography bed roughness and radar power reflectance and from our modeling of ice sheet flow and basal ice temperatures although no clear cut subglacial lakes are found within the aurora basin itself dozens of lake like reflectors are observed that in conjunction with other results reported here support the hypothesis that the basin acts as a pathway allowing discharge from subglacial lakes near the dome c ice divide to reach the coast via the totten glacier

consistent generation of ice streams via thermo viscous instabilities modulated by membrane stresses accurate computation of ice stream location and dynamics is a key aspiration for theoretical glaciology ice sheet models with thermo viscous coupling have been shown to exhibit stream like instabilities using shallow ice approximation mechanics but the location and width of these streams depends on the numerical implementation and are not unique we present results from thermo viscously coupled ice sheet models incorporating membrane stresses spontaneous generation of fast flowing linear features still occurs under certain parameter regimes with computed stream widths between 20 km to 100 km comparable with observations these features are maintained as the grid size is decreased the thermo viscous feedback mechanism that generates ice streams under the shallow ice approximation still operates now selecting a unique stream size computations of thermo viscous ice flows should include membrane stresses when the bed is approximately flat e g parts of antarctica and former ice sheets of the northern hemisphere previous calculations of spontaneous ice stream generation using the shallow ice approximation should be reassessed citation hindmarsh r c a 2009 consistent generation of ice streams via thermo viscous instabilities modulated by membrane stresses geophys res lett 36 l06502 doi 10 1029 2008gl036877

bedrock surface roughness and the distribution of subglacially precipitated carbonate deposits implications for formation at glacier de tsanfleuron switzerland two carbonate deposits are identified on the exposed bedrock surface in the forefield of glacier de tsanfleuron switzerland macrocrystalline sparite and microcrystalline micrite comparison of the distributions of these forms with lee side slope facets identified by high pass filtering of a flow parallel bedrock profile at a range of frequencies reveals two significant results first while the distribution of sparite is consistent with formation in the lee side of subglacial bedrock hummocks that of micrite is not this contrasts with previous investigations in which both sparite and micrite have been considered to form by mineral concentration and precipitation during the refreezing of regelation related basal meltwaters in the lee side of bedrock hummocks alternative mechanisms of micrite formation involving carbonate deposition and or precipitation within subglacial bedrock hollows are proposed second the distribution of sparite is most strongly correlated with the distribution of lee side slope facets identified by filtering at a frequency equivalent to a hummock wavelength of c 0 1 m this correspondence indicates empirically that pressure related melting and refreezing regelation operates most effectively around bedrock hummocks that are shorter than c 0 1 m 1998 john wiley sons ltd

weak bed control of the eastern shear margin of thwaites glacier west antarctica recent acceleration and thinning of thwaites glacier west antarctica motivates investigation of the controls upon and stability of its present ice flow pattern its eastern shear margin separates thwaites glacier from slower flowing ice and the southern tributaries of pine island glacier troughs in thwaites glacier s bed topography bound nearly all of its tributaries except along this eastern shear margin which has no clear relationship with regional bed topography along most of its length here we use airborne ice penetrating radar data from the airborne geophysical survey of the amundsen sea embayment antarctica agasea to investigate the nature of the bed across this margin radar data reveal slightly higher and rougher bed topography on the slower flowing side of the margin along with lower bed reflectivity however the change in bed reflectivity across the margin is partially explained by a change in bed roughness from these observations we infer that the position of the eastern shear margin is not strongly controlled by local bed topography or other bed properties given the potential for future increases in ice flux farther downstream the eastern shear margin may be vulnerable to migration however there is no evidence that this margin is migrating presently despite ongoing changes farther downstream

quantifying bed roughness beneath contemporary and palaeo ice streams bed roughness is an important control on ice stream location and dynamics the majority of previous bed roughness studies have been based on data derived from radio echo sounding res transects across antarctica and greenland however the wide spacing of res transects means that the links between roughness and flow are poorly constrained here we use digital terrain model dtm bathymetry data from a well preserved palaeo ice stream to investigate basal controls on the behaviour of contemporary ice streams artificial transects were set up across the minch palaeo ice stream nw scotland to mimic res flight lines over institute and moller ice streams antarctica we then explored how different data resolution transect orientation and spacing and different methods impact upon roughness measurements our results show that fast palaeo ice flow can occur over a rough hard bed not just a smooth soft bed which much previous work has suggested smooth areas of the bed occur over both bedrock and sediment covered regions similar trends in bed roughness values were found using fast fourier transform analysis and standard deviation methods smoothing of bed roughness results can hide important details we propose that the typical spacing of res transects is too wide to capture different landform assemblages and that transect orientation influences bed roughness measurements in both contemporary and palaeo ice stream setting

the evolution of the subglacial landscape of antarctica the aim is to investigate the evolution of the subglacial landscape of antarctica using an ice sheet and erosion model we identify different stages of continental glaciation and model the erosion processes associated with each stage the model links erosion to the basal thermal regime and indicates that much of the antarctic interior may have been subject to less than 200 m of erosion the depth of erosion reflects the presence or absence of warm based ice and the consistency of ice flow direction this information linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography is used to generate a map of the subglacial antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the laurentian and scandinavian shields near the continental margins selective linear erosion has overdeepened pre existing river valleys by as much as 2 8 km high elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold based ice high erosion rates result from steep thermal gradients in basal ice mountain regions such as the gamburtsev mountains uplands in dronning maud land and massifs in west antarctica are likely to bear features of local alpine glaciation such landscapes may have been protected under cold based ice for the last 34 myrs or possibly longer

radar derived bed roughness characterization of institute and moller ice streams west antarctica and comparison with siple coast ice streams 1 subglacial bed conditions exert a significant control on ice stream behavior and evolution and can be characterized by determining bed roughness from fft analysis of radar imaged basal reflectors here we assess bed roughness across institute and moller ice streams west antarctica and compare our findings with bed roughness determined across the siple coast ice streams we find that variations in bed roughness are spatially organized and attribute this to the varying efficacy of subglacial erosion and deposition with rougher inland slow flowing regions largely manifesting preglacial topography and smoother downstream fast flowing regions evincing significant postglacial modification to the subglacial landscape the observed similarities between bed roughness characteristics of iis mis and the siple ice streams suggest that iis and mis are largely underlain by wet poorly consolidated sediments and may therefore be vulnerable to the types of dynamical instabilities experienced by the siple ice streams

macro scale bed roughness of the siple coast ice streams in west antarctica subglacial bed conditions are key to understanding ice stream behaviour and evolution with bed roughness re ecting substrate composition and ow resistance here we present an analysis of bed roughness in the siple coast region of west antarctica from airborne radio echo sounding data the ice streams are associated generally with low bed roughness values which decrease downstream the bed of the slow owing ice stream c 10 000 km2 is also characterized by being smooth at all scales wavelengths ranging from 5 km to in excess of 40 km furthermore the bed is smooth either side of ice stream c this suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by bed morphology if the ice stream were encouraged to migrate laterally when active there would be little resistance offered by the subglacial morphology other inter ice stream regions are rough however indicating a subglacial topographic in uence on ice stream position bed roughness increases up ow of ice streams which unless the bed is modi ed may limit the inland migration of these systems copyright 2004 john wiley sons ltd

spectral roughness of glaciated bedrock geomorphic surfaces implications for glacier sliding a microroughness meter mrm was used to measure the high frequency roughness of a number of geomorphic surfaces in the forefield of glacier de tsanfleuron switzerland resulting spectral power densities are added to low frequency spectra measured by electro optical distance meter edm to generate composite roughness spectra that include almost 5 orders of magnitude of roughness in the frequency domain these are used to define two roughness indices a general index of bed roughness is defined as the integral of the raw spectral power densities and a sliding related index of bed roughness is defined as the integral of the spectral power densities weighted to account for the optimum dependence of glacier sliding speed on hummock wavelength results indicate that mrm measured geomorphic components vary in roughness by 3 orders of magnitude principally depending on the surface microenvironment measured and profile orientation relative to the direction of former ice flow both mrm and edm measured roughnesses are lower parallel to the direction of former ice flow than perpendicular to it composite roughness spectra consequently indicate that the glacier bed is smoothed in the direction of former ice flow at all horizontal scales from 1 mm to 40 m typically resulting in an order of magnitude decrease in sliding related roughness relative to that measured perpendicular to ice flow comparison of data from two survey sites located adjacent to and 1 2 km from the current glacier margin indicates that postglacial subaerial weathering homogenizes bedrock roughness in particular reducing high frequency flow orthogonal roughness accounting for the effect of 28 ice bedrock separation over one of the profiles reduces net sliding dependent roughness by between 27 and 43 depending on the transition wave number used

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

draping or overriding the effect of horizontal stress gradients on internal layer architecture in ice sheets internal isochronic layers in ice sheets sensed by radar show two characteristic relationships to the basal topography either they override it with layers above the crests of rises lying essentially flat or they drape over it with the layers following rises and falls in basal topography a mechanical theory is presented which shows that overriding is the expected behavior when topographic wavelengths are comparable with or less than the ice thickness while draping occurs at longer wavelengths this is shown with analytical perturbation solutions for newtonian fluids numerical perturbation solutions for nonlinear fluids and finite element solutions for nonlinear fluids and large amplitude variations bed variation from topography and changes in the basal boundary condition are considered for fixed bed and sliding beds as well as three dimensional flows and thermomechanically coupled flows in all cases the dominant effect on draping overriding is the wavelength of the topography or variation in basal boundary conditions results of these full mechanical system calculations are compared with those from the shallow ice approximation and the longitudinal stress approximation some calculations are carried out for zero accumulation where the age of the ice and therefore isochrone geometry is not defined it is shown that there is a close relationship between isochrones and streamlines and that they behave similarly when bed wavelength divided by the ice thickness is small compared with the ratio of ice velocity and accumulation rate which is a useful approximation numerical comparisons of isochrones and streamlines show them to be virtually coincident

polar radar for ice sheet measurements prism abstract we provide an overview of a project to develop and demonstrate radars for imaging the ice bed interface mapping shallow and deep internal layers and measuring ice thickness we developed an ultra wideband very high frequency vhf radar 120 to 300 mhz for simultaneously measuring ice thickness mapping internal layers at depth and imaging the ice bed interface and an ultra high frequency uhf ultra wideband radar 500 to 2000 mhz for fine resolution mapping of near surface internal layers we used these radars to collect data at summit camp greenland during july 2005 and the west antarctic ice sheet wais deep drill core site during january 2006 these results provide us with an unprecedented view of basal characteristics and internal layers we also developed an outreach program a communications system and rovers to facilitate geophysical measurements in the future

characterization of subglacial landscapes by a two parameter roughness index previous studies using fourier transformation ft methods to analyze subglacial roughness have shown promise for distinguishing between different types of subglacial landscape from raw subglacial elevation data we derive a two parameter ft roughness index whereis based on the ft of elevation as previously considered in isolation andis based on both the ft of elevation and the ft of bed slope profile in this way we take account of both vertical and horizontal irregularities in subglacial surfaces we demonstrate the statistical veracity of using to consider roughness in terms of obstacle amplitudes and spacing and consider the use of in studies of ice dynamics and subglacial geomorphological interpretation we show that can be linked to basal sliding rates on the metre scale and can be used to differentiate further than single parameter roughness indices between different classes of subglacial landscape in particular between erosional and depositional settings

the gamburtsev mountains and the origin and early evolution of the antarctic ice sheet the manner in which the antarctic ice sheet first formed at a time of rapid global climate change about 34 million years ago has been the subject of considerable speculation several lines of evidence point to central antarctic mountain ranges as the site of the initial ice sheet but our knowledge of the present ice sheet topography is highly restricted in the very zone where ice sheet initiation is most likely along the subglacial gamburtsev mountain range at the centre of the present ice sheet now a detailed survey and analysis of the morphology of the gamburtsev mountains has been performed based on an ice penetrating radar study conducted over two seasons the data reveal a mountain landscape initially incised by rivers then over deepened by ice movement the topography beneath up to 3 000 metres of ice resembles an exploded version of classic alpine valley topography and seems to have developed more than 34 million years ago when mean summer temperatures were about 3 c the nature of initial glaciation on antarctica about 34 million years ago is a mystery results from an intensive radar survey now show that the gamburtsev mountains at dome a at the centre of the present ice sheet were initially incised by rivers and then subsequently overdeepened by ice movement this is suggestive of topographical development before 34 million years ago when mean summer temperatures were about 3 c ice sheet development in antarctica was a result of significant and rapid global climate change about 34 million years ago1 ice sheet and climate modelling suggest reductions in atmospheric carbon dioxide less than three times the pre industrial level of 280 parts per million by volume that in conjunction with the development of the antarctic circumpolar current led to cooling and glaciation paced by changes in earth s orbit2 based on the present subglacial topography numerical models point to ice sheet genesis on mountain massifs of antarctica including the gamburtsev mountains at dome a the centre of the present ice sheet2 3 our lack of knowledge of the present day topography of the gamburtsev mountains4 means however that the nature of early glaciation and subsequent development of a continental sized ice sheet are uncertain here we present radar information about the base of the ice at dome a revealing classic alpine topography with pre existing river valleys overdeepened by valley glaciers formed when the mean summer surface temperature was around 3 c this landscape is likely to have developed during the initial phases of antarctic glaciation according to antarctic climate history estimated from offshore sediment records the gamburtsev mountains are probably older than 34 million years and were the main centre for ice sheet growth moreover the landscape has most probably been preserved beneath the present ice sheet for around 14 million years

3d modeling and monitoring of karst system as a base for its evaluation and utilization a case study from eastern serbia beljanica mountain in eastern serbia is a part of the carpathian balkan arch northern alpine branch it covers an area of about 300 km2 and consists mostly of jurassic and cretaceous limestones numerous surface karst features long caves and several large karstic springs located in beljanica s piedmont along the contact of karstic and non karstic rocks are all indicators of an intense karstification currently the large karstic water reserves of beljanica mountain are not properly utilized because of their distance from main consumers the objection by national water managers that the springs lack a stable and sufficient discharge particularly during recession periods due to its unpolluted and high quality water the area is a great prospect for future water supply and provides an opportunity for artificial regulation and for the design and implementation of specific tapping structures this paper includes an analysis of the created 3d arcgis model of karst interior and its correlation with historical and newly collected data of spring discharges and groundwater physico chemical characteristics the results of karst aquifer monitoring both quantitative and qualitative are linked with the results of extensive field geological and speleological survey of the upper non saturated part of the karst such as sinkholes pits and caves and with the investigation of the permanently saturated deeper part of the aquifer including the diving methods the model of karst interior is based on the data from the 69 caves 15 sinks and 1 682 dolines sinkholes surveyed the total length of the karst channels network calculated using the gis model and presented in a 3d environment is 647 km the catchment areas of five major springs that drain the areas are estimated to range from only 7 km2 malo vrelo spring to 124 km2 vrelo mlave spring the groundwater exploitable reserves of beljanica karst aquifer are estimated to be over 4 m3 s the waters are low mineralized unpolluted and have a great potential for water supply