ice flow velocities on rutford ice stream west antarctica are stable over decadal timescales surface ice flow velocities measured at stakes on rutford ice stream west antarctica covering a period of similar to 25 years are analysed for evidence of temporal variations in flow no indications of significant long term changes in flow are found earlier observations have shown significant tidally related variations in flow speed we conclude that temporal variability on rutford ice stream west antarctica appears limited to tidal periods of days and weeks and weaker interannual variation possibly related to long period tides or seasonal effects while long term decadal changes in flow speed are either absent or smaller than similar to 0 1 a 1

subsurface crevasse formation in glaciers and ice sheets 1 crevasses form in response to tensile stresses in glaciers and ice sheets it has been widely assumed that crevasses initiate at or near the surface of the ice from starter cracks up to a few centimeters long if the tensile stress is sufficient these cracks propagate downward into the ice to form a crevasse until the weight induced lithostatic stress prevents them penetrating deeper we present ground penetrating radar data acquired on the rutford ice stream antarctica which indicate that crevasses occur at depths of several meters beneath the ice surface and were formed in areas where surface crevassing is absent the data support the hypothesis that these are examples of subsurface crevasse formation using linear elastic fracture mechanics lefm we investigate the feasibility of crevasse initiation at depth we consider the initiation of an isolated crevasse from a subsurface crack subject to a dynamic tensile stress which results from deformation associated with ice movement and a weight induced lithostatic stress the lefm approach allows us to estimate a init the minimum length a crack must be before crack propagation will occur in earlier models of crevasse formation it was assumed that the dynamic tensile stress is constant with depth we consider a more realistic scenario where the dynamic tensile stress varies with depth in such a way that the tensile strain rate remains constant we show that in this scenario crevasse initiation from centimeter scale starter cracks is feasible at depths of 10 30 m as well as at the surface at present the formulation of a reliable predictive model is limited by an incomplete knowledge of the mechanical properties of firn in previous studies the depth of buried crevasses has been used to estimate the time elapsed since ice was exposed to higher stresses and different flow regimes in the light of the results presented here those estimates may need to be reviewed

observations of ice sheet motion in greenland using satellite radar interferometry we present interferometric observations of ice sheet motion in western greenland based on pairs of ers 1 synthetic aperture radar sar images these observations provide the first detailed regional view of ice motion associated with dynamically supported topography near the margin of an ice sheet the interferograms of this area are much more complicated than other interferograms of ice sheets presented to date we devote the largest part of this paper to explaining the source of the complexity in these interferograms a synthetic interferogram based on a simple model helps to illustrate the effects of different components of the ice velocity field in interferometric data and suggests a method for estimating the large scale ice velocity field from such data

titanium mobilization by hydrocarbon fluids related to sill intrusion in a sedimentary sequence scotland abstract an occurrence of vein hosted bitumen in carboniferous rocks central scotland exhibits unusual enrichments in titanium zirconium and chromium detected by electron microprobe these elements occur as mineral inclusions of titanium and titanium iron oxides a close association between titanium rich tuffs and a quartz dolerite sill suggests that metals were leached from igneous rocks by a hydrocarbon rich fluid generated by the heat of the intrusion into organic rich shales this occurrence supports other evidence for widespread titanium mobility under low temperature conditions inclusions of nickel arsenide may reflect regionally important mineralization including former ore deposits related to sills and dykes as sills are extensively intruded into petroleum prospective basins offshore they may have a significant influence upon sediment geochemistry

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

a tutorial on the use of control methods in ice sheet modeling control methods are recommended as an efficient means to estimate undetermined physical parameters and boundary conditions and in so doing to improve the fidelity of a given ice sheet flow model to specific ice sheet velocity observations to accomplish this task the underlying dynamics of the model are inverted this permits model tuning adjustments to be represented explicitly in terms of model observation misfit

flow switching and water piracy between rutford ice stream and carlson inlet west antarctica rutford ice stream and carlson inlet are neighbouring glaciers in west antarctica rutford ice stream flows at speeds greater than 350m a 1 whereas carlson inlet which has some similar dimensions and supports a similar driving stress flows 10 50 times slower we discuss a range of observations concerning carlson inlet and conclude that there is good indirect evidence that it is a relict ice stream which ceased streaming more than 240 years bp but sufficiently recently that its surface morphology basal water content and basal morphology still retain characteristics produced by streaming an analysis of expected subglacial drainage pathways indicates that carlson inlet is not streaming because it is currently starved of subglacial water which is currently directed beneath rutford ice stream this current state of water piracy by rutford ice stream is however sensitive to minor thickness changes on the ice streams a similar to 120 m 4 thickening of rutford ice stream would divert almost all the subglacial water in the system towards carlson inlet and could reactivate its flow the result highlights the importance of subglacial drainage in controlling ice stream evolution and the requirement for ice sheet models to couple ice flow with subglacial drainage

measurement of ice sheet topography using satellite radar interferometry detailed digital elevation models dems do not exist for much of the greenland and antarctic ice sheets radar altimetry is at present the primary in many cases the only source of topographic data over the ice sheets but the horizontal resolution of such data is coarse satellite radar interferometry uses the phase difference between pairs of synthetic aperture radar sar images to measure both ice sheet topography and surface displacement we have applied this technique using ers 1 sar data to make detailed i e 80 m horizontal resolution maps of surface topography in a 100 km by 300 km strip in west greenland extending northward from just above jakobshavns isbrae comparison with a 76 km long line of airborne laser altimeter data shows that we have achieved a relative accuracy of 2 5m along the profile these observations provide a detailed view of dynamically supported topography near the margin of an ice sheet in the final section we compare our estimate of topography with phase contours due to motion and confirm our earlier analysis concerning vertical ice sheet motion and complexity in ers 1 sar interferograms

ice sheet motion and topography from radar interferometry both topography and motion information are present in repeat pass ers 1 interferograms over ice sheets the authors demonstrate that the topography is separable from the surface displacement field when a sequence of radar images are available if the velocity field is constant over the time span of observation the topography can be derived from differential interferograms formed from sequential observations with this measurement a pure displacement field can then be obtained by removal of the topographic contribution to the interferometric phase at each pixel further they discuss how the vertical and horizontal components of displacement affect the interferometrically derived motion field they illustrate their approach with four successive 3 day repeat ers 1 images of a flow feature in northeastern greenland

garnet compositions in scottish and norwegian basement terrains a framework for interpretation of north sea sandstone provenance detrital garnets have proved to be useful discriminators of north sea sandstone provenance because they show a wide range of potential compositions and are relatively stable during burial diagenesis it has been less easy to use garnet data to provide a direct link between sediment and source because of the lack of a comprehensive database of garnet compositions in basement terrains forming the north sea hinterland this paper presents garnet compositional data from river sediments sourced from northern scotland and norway and demonstrates the presence of marked variations in garnet compositions from different regions related to fundamental differences in basement lithology the value of the river sediment database is demonstrated by comparing it with garnet compositions in paleocene sandstones from the north sea and more basins enabling the establishment of direct links between source and sediment paleocene sandstones in the gannet field area on the southwestern margin of the central north sea were derived from the dalradian of the grampian highlands those in the northern north sea were derived from the moine dalradian rocks of shetland and those along the more basin margin were derived from western norway by contrast paleocene sandstones in the nelson field central north sea and in the beryl embayment northern north sea have a garnet component that cannot be readily traced back to any basement terrain in either scotland or norway this component which was ultimately derived from granulite facies metasediments or charnockites is interpreted as being recycled from triassic sandstones which were themselves derived from an exotic source probably to the west of the british isles q 2004 elsevier ltd all rights reserved

distortion of isochronous layers in ice revealed by ground penetrating radar in addition to measuring ice sheet thickness ground penetrating radar can be used to delineate reflections in ice sheets1 2 3 these reflections are generally accepted to result from layers of isochronous deposition of snow and can reveal much about the dynamics of the ice flow here we present ground penetrating radar data from fletcher promontory antarctica which show arches and troughs in isochronous ice layers to a depth of 100 m we demonstrate that the origin of these features can be determined by their growth with depth and many features result from local anomalies in accumulation rate which can be correlated with the ice surface slope one arch appears to be the result of a local anomaly in vertical strain rate its proximity to the ice divide width and growth with depth indicate that this arch is one of a class of features postulated by raymond4 but not previously shown to exist in the field such a feature is an indication of the nonlinear rheology of ice and requires that palaeoclimate records from ice cores extracted from the vicinity of ice divides underlain by similar features should be specifically corrected for such effects on ice flow

fortnightly variations in the flow velocity of rutford ice stream west antarctica ice sheets like that of antarctica lose much of their ice via fast flowing ice streams hilmar gudmundsson has monitored the flow in one such stream the rutford ice stream in west antarctica over a period of two months the findings are a surprise surface flow velocities here fluctuate by as much as 20 over a period of two weeks perhaps under the influence of the spring neap fortnightly tidal cycle although the mechanism that couples these tides to ice flow has yet to be elucidated these observations caution against the use of velocity measurements over limited periods to infer long term changes in flow rate monitoring of the flow of an ice sheet in antarctica finds that the surface velocity oscillates by as much as 20 per cent every two weeks the spring to neap tidal cycle seems to be the cause although the mechanism through which these tides couple to ice flow has yet to be elucidated these observations caution against the use of velocity measurements over limited periods to infer long term changes in flow rate most of the ice lost from the antarctic ice sheet passes through a few fast flowing and highly dynamic ice streams1 quantifying temporal variations in flow in these ice streams and understanding their causes is a prerequisite for estimating the potential contribution of the antarctic ice sheet to global sea level change2 3 here i show that surface velocities on a major west antarctic ice stream rutford ice stream vary periodically by about 20 per cent every two weeks as a result of tidal forcing tidally induced motion on ice streams has previously been thought to be limited to diurnal or even shorter term variations4 5 6 7 8 9 the existence of strong fortnightly variations in flow demonstrates the potential pitfalls of using repeated velocity measurements over intervals of days to infer long term change

a new approach to provenance studies electron microprobe analysis of detrital garnets from middle jurassic sandstones of the northern north sea reading provenance from heavy mineral suites is hampered by the depletion of diagnostic but unstable heavy minerals through intrastratal solution a common phenomenon in deep sedimentary basins such as the north sea this paper demonstrates the potential of electron microprobe analysis in overcoming this problem by concentrating on the compositional variations shown by detrital garnets which are relatively resistant to intrastratal solution studies of the garnets from the brent group middle jurassic of the murchison and tern oilfields in the northern north sea reveal that three distinct areas supplied detritus association 1 which characterizes the broom formation in both areas and recurs higher in the sequence in the tern field is ascribed to an orkney shetland source the location of the areas supplying the garnets of association 2 best represented in murchison and association 3 common to both fields is less clear their ultimate sources clearly include high grade metamorphics and therefore probably lie on the norwegian landmass the orkney shetland platform or conceivably the scottish landmass but the possibility of recycling makes it difficult to judge their immediate provenances nevertheless the presence of three garnet associations indicates that the most widely accepted model of brent sedimentation with sands derived from a domal uplift in the outer moray firth and channelled northward along the viking graben is untenable

stratigraphic correlation of late palaeocene sand deposits in the sogne basin area of the danish and norwegian central north sea a stratigraphic analysis of late palaeocene sands of the sogne basin and the western part of the norwegian danish basin shows that the sand bodies are of differenct ages the geographic distribution of the sand deposits shows that they are related to underlying mesozoic structures suggesting a controlling effect of tertiary tectonics on the deposition of sand during the late palaeocene however the structural setting of various sand bodies varies from reactivation of older faults and reactivation of salt structures the local character of the structures active during the late palaeocene introduces minor depressions with no lateral connection the sand bodies which are interpreted as having been deposited in these depressions are thus in general separate bodies with no lateral connection the fennoscandian shield and eroded mesozoic sediments along the fennoscandian border zone are suggested as source area for the late palaeocene sand deposits

glaciological studies on rutford ice stream antarctica rutford ice stream drains part of the west antarctic ice sheet into ronne ice shelf much of the drainage basin has a bed well below sea level and is therefore an area which could undergo substantial change if a climatic warming were to cause sustained thinning of ronne ice shelf snow accumulation data suggest that an accumulation rate of 0 51 0 12 mg m 2 yr 1 is required for balance an extensive ice movement survey network was established across the grounding line in 1978 1980 and was extended for more than 100 km upstream in 1984 1986 velocities at five sites have been calculated using doppler satellite position measurements when the velocities are combined with cross sectional areas of the ice stream measured by radio echo sounding mass flux figures show that drag at the sidewalls and on the base must decrease downstream toward the grounding line the increasing influence of buoyancy forces on ice stream motion is also shown by the steady rise in the ratio of bedrock depth to ice thickness going downstream along the network below the grounding line that was found to cross the middle part of the earlier network is a zone stretching for a further 100 km where it can now be shown that the ice stream is intermittently grounded in these grounded areas the glacier bed is raised with respect to the surrounding seabed and forms eskerlike features surface elevations over the grounded areas are less than 30 m above those needed for hydrostatic equilibrium

trace element mobility during sub seafloor alteration of basaltic glass from ocean drilling program site 953 off gran canaria trace element concentrations of altered basaltic glass shards layer silicates and zeolites in volcaniclastic sediments drilled in the volcanic apron northeast of gran canaria during ocean drilling program odp leg 157 document variable element mobilities during low temperature alteration processes in a marine environment clay minerals saponite montmorillonite smectite replacing volcanic glass particles are enriched in transition metals and rare earth elements ree the degree of retention of ree within the alteration products of the basaltic glass is correlated with the field strength of the cations the high field strength elements are preferentially retained or enriched in the alteration products by sorption through clay minerals most trace elements are enriched in a boundary layer close to the interface mineral altered glass this boundary layer has a key function for the physico chemical conditions of the subsequent alteration process by providing a large reactive surface and by lowering the fluid permeability the release of most elements is buffered by incorporation into secondary precipitates sodium rich zeolites phillipsite fe and mn oxides as shown by calculated distribution coefficients between altered glasses and authigenic minerals chemical fluxes change from an open to a closed system behavior during prograde low temperature alteration of volcaniclastic sediments with no significant trace metal flux from the sediment to the water column

atmospheric limitations to repeat track radar interferometry in its recent radar imaging mission the shuttle imaging radar satellite sir c devoted three days to repeat track interferometry we have analyzed the data from a test site in the mojave desert of california although good topography 10 m on 21 m postings was obtained most of the error was caused by turbulent water vapor in the lower atmosphere spatial structure of 6 km and all smaller sizes was observed the rms one way time delay was found to be 0 24 cm essentially identical results were obtained at two wavelengths 24 and 5 7 cm

rapid large area mapping of ice flow using landsat 8 abstract we report on the maturation of optical satellite image based ice velocity mapping over the ice sheets and large glacierized areas enabled by the high radiometric resolution and internal geometric accuracy of landsat 8 s operational land imager oli detailed large area single season mosaics and time series maps of ice flow were created using data spanning june 2013 to june 2015 the 12 bit radiometric quantization and 15 m pixel scale resolution of oli band 8 enable displacement tracking of subtle snow drift patterns on ice sheet surfaces at 1 m precision ice sheet and snowfield snow drift features persist for typically 16 to 64 days and up to 432 days depending primarily on snow accumulation rates this results in spatially continuous mapping of ice flow extending the mapping capability beyond crevassed areas our method uses image chip cross correlation and sub pixel peak fitting in matching landsat path row pairs high pass filtering is applied to the imagery to enhance local surface texture the current high image acquisition rates of landsat 8 725 scenes per day globally reduces the impact of high cloudiness in polar and mountain terrain and allows rapid compilation of large areas or dense temporal coverage of seasonal ice flow variations the results rival the coverage and accuracy of interferometric synthetic aperture radar insar mapping

synthetic aperture radar interferometry over rutford ice stream and carlson inlet antarctica we describe the calibration and interpretation of interferograms generated from ers i synthetic aperture radar single look complex sar slc images of the rutford ice stream area ground surveys provide over 100 tie points with which to optimise the interferometric baselines that separate nominally repeated satellite orbits covariant tie point errors are dealt with by constructing an error covariance matrix for the expected values of the unwrapped interferometric phases at the tie points with baseline parameters that minimise the weighted residual variance rms tie point residuals of less than i cm in slant range are obtained these are attributed to a combination of interferometric phase noise movement survey errors and inadequate slope information the image set used is inadequate for isolating the influences of topography and movement so the glaciological conclusions to be drawn are limited nevertheless the interferograms confirm that the whole of the upper 50 k m of carlson inlet flows at a speed less than a tenth of that of the neighbouring rutford ice stream also confirmed are the entry of faster moving ice into the lower reaches of carlson inlet and the position of part of the carlson inlet grounding line in general the distribution of the residuals suggests no significant differences in ice movement between 1978 and 1992 an exception is the neighbourhood of the shear margin between rutford ice stream and carlson inlet where inconsistencies between ground surveys over the periods 1984 86 and 1994 96 and interferograms from 1994 a n d 1996 suggest fluctuations in velocity of up to 10 m year 1

a topographic origin for double ridge features in visible imagery of ice divides in antarctica the appearance of double ridge features on visible imagery of the ice divides of antarctic ice rises has often been noted but largely due to a lack of adequate ground truth their origins have remained enigmatic we present several examples of ice rises and other isolated ice flow centres that apparently show double ridges we investigate one of these in particular fletcher promontory antarctica a digital elevation model dem of the summit region is derived from surface profiles obtained using the global positioning system gps and this is correlated with landsat mss satellite imagery precise registration is achieved by correlating image brightness values with surface slope calculated along the direction of the sun azimuth in the image using a simple bi directional relation the dem data are used to model the landsat image we therefore demonstrate that the double ridge is a product of a subtle concavity parallel to the ridge and is unlikely to be dependent on other factors this concavity is not predicted by steady state models of ice divides and so we suggest that the ridge may not be in a steady state but responding to changes in the glaciological boundary conditions we speculate that this may be an indication of ongoing migration of the ice divide

glacier mass balance determination by remote sensing and high resolution modelling an indirect methodology for determining the distribution of mass balance at high spatial resolution using remote sensing and ice flow modelling is presented the method based on the mass continuity equation requires two datasets collected over the desired monitoring interval i the spatial pattern of glacier surface elevation change and ii the mass flux divergence field at haut glacier d arolla valais switzerland the mass balance distribution between september 1992 and september 1993 is calculated at 20 m resolution from the difference between the pattern of surface elevation change derived from analytical photogrammetry and the mass flux divergence field determined from three dimensional numerical flow modelling constrained by surface velocity measurements the resultant pattern of mass balance is almost totally negative showing a strong dependence on elevation but with large localized departures the computed distribution of mass balance compares well r 2 0 91 with mass balance measurements made at stakes installed along the glacier centre line over the same period despite the highly optimized nature of the flow modelling effort employed in this study the good agreement indicates the potential this method has as a strategy for deriving high spatial and temporal resolution estimates of mass balance

topographic mapping from interferometric synthetic aperture radar observations interferometric synthetic aperture radar observations provide a means for obtaining high resolution topographic terrain maps from data acquired simultaneously at two slightly displaced antennas calculation of the three dimensional coordinates of all the points in a radar image can be made from the combination of along track slant range and interferometer fringe measurements thus the result compensates for the layover exhibited by conventional radar maps and removes the false targets generated by multiple signal paths to a given object in the scene we have derived a topographic map of a portion of the san francisco bay area utilizing data that were recorded by a radar system mounted on a nasa cv990 aircraft and processed by a general purpose digital computer this map displays the height above sea level of a region approximately 11 km by 10 km in size sampled on an 11 m pixel grid uncertainties in the estimated height result from imprecise knowledge of the observational geometry radar bandwidth limitations and finite signal to noise ratios for our system each factor contributed approximately 3 4 m to a relative rms error of about 6 m additional global errors of the order of 10 m can result from inaccurate monitoring of aircraft attitude the statistical variation of the height measurements from the ocean portion of the map which we can presume to be quite flat is 2 10 m rms which is consistent with the theoretical estimate comparison of our results with u s geological survey contour maps indicates a high degree of correlation between the two sets of altitude data

discrimination of density flow deposits using elemental geochemistry implications for subtle provenance differentiation in a narrow submarine canyon palaeogene danish north sea abstract elemental geochemistry of 1131 sandstone samples has been used to characterise five palaeogene sandstone members in a system of density flow deposits within an incised submarine canyon danish north sea diagenetic overprinting has complicated the use of most main and trace elements but a group of heavy mineral bound elements with low mobility ti y zr nb and th has proved highly potential for correlation the individual sandstone members exhibit very consistent relations between the heavy mineral elements along the canyon and based on zr ti plots two families of sandstone members can be distinguished the families are recognised on variations in inclination and intersection of linear regression lines which are related to subtle variations in provenance source area the inclination is believed to be controlled by the detrital heavy mineral hm suite and composition whereas the intersections are controlled by the background contribution such as hm inclusions in detrital rock forming minerals e g quartz and or feldspar as well as substituted and or adhered elements in glauconite the correlation pattern has been used to suggest a re interpretation of the stratigraphic relation of some of the sands

acoustic impedance and basal shear stress beneath four antarctic ice streams the acoustic impedance of the subglacial material beneath 7 2 km profiles on four ice streams in antarctica has been measured using a seismic technique the ice streams span a wide range of dynamic conditions with flow rates of 35 464 in a 1 the acoustic impedance indicates that poorly lithified or dilated sedimentary material is ubiquitous beneath these ice streams mean acoustic impedance across each profile correlates well with basal shear stress and the slipperiness of the bed indicating that acoustic impedance is a good diagnostic not only for the porosity of the subglacial material but also for its dynamic state deforming or non deforming beneath two of the ice streams lodged non deforming and dilated deforming sediment coexist but their distribution is not obviously controlled by basal topography or ice thickness their distribution may be controlled by complex material properties or the deformation history beneath rutford ice stream lodged and dilated sediment coexist and are distributed in broad bands several kilometres wide while on talutis inlet there is considerable variability over much shorter distances this may reflect differences in the mechanism of drainage beneath the ice streams the material beneath the slow moving carlson inlet is probably lodged but unlithified sediment this is consistent with the hypothesis that carlson inlet was once a fast flowing ice stream but is now in a stagnant phase which could possibly be revived by raised basal water content the entire bed beneath fast flowing evans ice stream is dilated sediment

ice flow modulated by tides at up to annual periods at rutford ice stream west antarctica 1 for over 2 years we have collected gps data 40 km upstream of the grounding line on rutford ice stream west antarctica here we examine deviations from mean downstream flow although the record is incomplete during winter there is clear modulation of flow at semi diurnal diurnal two weekly semi annual and annual ocean tidal frequencies this is the first observation of ice stream flow variations over such a long time period and such a wide range of frequencies the ice stream flows fastest at equinoxes when there are two semi diurnal tides of equal magnitude and slowest at solstices when one of the semi diurnal tides has lower amplitude the sensitivity of the downstream flow is greatest to the long period forcing which suggests that ice stream velocity may be affected by future changes in sea level if so this effect would provide a feedback whereby rising sea levels could increase ice stream velocity and hence discharge

estimation of ice sheet motion using satellite radar interferometry method and error analysis with application to humboldt glacier greenland satellite radar interferometry provides glaciologists with an important new tool for determining the motion and topography of large ice sheets we examine the sources of error in interferometrically derived ice motion measurements including those errors due to inaccurate estimates of the interferometric baseline several simulations are used to assess baseline accuracy in terms of tie point error and the number and distribution of tie points these results give insight into how best to select tie points and also demonstrate the level of accuracy that can be achieved examination of two representative cases likely to occur in mapping ice sheet motion leads to the conclusion that with adequate tie point information ice velocity can be measured accurately to within a few meters per year a method to correct horizontal velocity estimates for the effect of vertical displacement using surface slopes is also developed finally we estimate the single component velocity field for an area on humboldt glacier northern greenland using interferograms formed from ers i sar images we estimate that these velocity measurements are accurate to within 2 3 m year 1

observation of ocean tides below the filchner and ronne ice shelves antarctica using synthetic aperture radar interferometry comparison with tide model predictions tides near and under floating glacial ice such as ice shelves and glacier termini in fjords can influence heat transport into the subice cavity mixing of the under ice water column and the calving and subsequent drift of icebergs free surface displacement patterns associated with ocean variability below glacial ice can be observed by differencing two synthetic aperture radar sar interferograms each of which represents the combination of the displacement patterns associated with the time varying vertical motion and the time independent lateral ice flow we present the pattern of net free surface displacement for the iceberg calving regions of the ronne and filchner ice shelves in the southern weddell sea by comparing sar based displacement fields with ocean tidal models the free surface displacement variability for these regions is found to be dominated by ocean tides the inverse barometer effect i e the ocean s isostatic response to changing atmospheric pressure also contributes to the observed vertical displacement the principal value of using sar interferometry in this manner lies in the very high lateral resolution tens of meters obtained over the large region covered by each sar image small features that are not well resolved by the typical grid spacing of ocean tidal models may contribute to such processes as iceberg calving and cross frontal ventilation of the ocean cavity under the ice shelf

ice flow dynamics of the greenland ice sheet from sar interferometry synthetic aperture radar sar interferograms produced from esa s ers 1 satellite provide the first synoptic view of ice flow dynamics of the western sector of the greenland ice sheet glacial motion is detected in the radar ranging direction at millimetric scales across a complete sequence of snow accumulation and melting regimes despite significant variations in their radar scattering properties ice flow evolves from a slow regular motion at the higher elevations at lower elevations motion is strongly convoluted by meter scale undulations in surface topography which have a unique interferometric signature that enables a novel approach for retrieving flow direction inferred flow directions combined with surface displacements in the radar ranging direction yield ice velocity estimates that are within 6 of in situ measurements gathered along a 40 km survey line application of repeat pass sar interferometry to the entire greenland ice sheet should enable precise mapping of its ice flow dynamics at an unprecedented level of spatial detail