rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

quantitative mineralogical characterization of sandstones by back scattered electron image analysis abstract methods are described for the quantitative analysis of both the composition of sandstones and the two dimensional morphology of their component mineral phases based on image analysis of back scattered electron bse images of flat sections mineral phases are distinguished largely by their gray levels intensities in the bse image where contrast derives almost entirely from the compositions of the phases although morphological criteria are applied where phases overlap in gray level the concentration of each phase in each image is then measured as proportional area and the average over many images gives an analysis of a significantly large area of the specimen morphological quantification is achieved in a totally objective way by operating a series of two dimensional opening t ansformations on segmented images of the component minerals and pores and the results are presented in the form of feature size histograms also summed over many image fields both the compositional and morphological analyses are capable of being fully automated

theoretical correlations between the elastic and electrical properties in layered porous rocks with cracks of varying orientations abstract cracks that are widely existing in geological formations play an important role in affecting the elastic and electrical rock properties which are remotely measured for detecting and characterizing cracked rocks joint interpretation of the complementary elastic and electrical data is expected to give a better assessment of the cracks however the correlations between the elastic and electrical rock properties which are the key to the successful joint interpretation remain poorly understood in layered porous rocks with cracks of varying orientations we reviewed and summarized the most recent advances in the theoretical models for the elastic and electrical properties of layered porous rocks with inclined and rotated cracks as well as with randomly orienting cracks the limitations of the models were identified by comparing the modeling results with available experimental data and we applied the models within their validity range to obtaining theoretically the correlations between the elastic and electrical properties in layered porous rocks with cracks of the above mentioned orientations in the horizontal and vertical directions respectively we showed that the elastic and electrical properties are systematically correlated with cracks of varying crack densities and aspect ratios different cracks orientations affect the correlations in varying ways the results not only illustrate the link between the elastic and electrical properties in cracked rocks but also have important practical applications when the seismic and electromagnetic exploration data are jointly interpreted to gain better knowledge about the subsurface earth although future work is required to extend the models to more realistic cracked formations and to experimentally test the validity of the models and the theoretically obtained joint correlations

sea ice and oceanic processes on the ross sea continental shelf we have investigated the spatial and temporal variability of antarctic sea ice concentrations on the ross sea continental shelf in relation to oceanic and atmospheric forcing sea ice data were derived from nimbus 7 scanning multichannel microwave radiometer smmr brightness temperatures from 1979 1986 ice cover over the shelf was persistently lower than above the adjacent deep ocean averaging 86 during winter with little month to month or interannual variability the large spring ross sea polynya on the western shelf results in a longer period of summer insolation greater surface layer heat storage and later ice formation in that region the following autumn newly identified pennell and ross passage polynyas near the continental shelf break appear to be maintained in part by divergence above a submarine bank and by upwelling of warmer water near the slope front warmer subsurface water enters the shelf region year round and will retard ice growth and enhance heat flux to the atmosphere when entrained in the strong winter vertical circulation temperatures at 125 m depth on a mooring near the ross ice shelf during july 1984 averaged 0 15 c above freezing sufficient to support a vertical heat flux above 100 w m2 monthly average subsurface ocean temperatures along the ross ice shelf lag the air temperature cycle and begin to rise several weeks before spring ice breakout the coarse smmr resolution and dynamic ice shelf coastlines can compromise the use of microwave sea ice data near continental boundaries

ice flow physical processes derived from the ers 1 high resolution map of the antarctica and greenland ice sheets accepted 1999 july 7 received 1999 june 7 in original form 1998 june 24 summary the ers 1 satellite launched in 1991 has provided altimetric observations of the greenland ice sheet and 80 per cent of the antarctica ice sheet north of 82 s it was placed in a geodetic 168 day repeat orbit between april 1994 and march 1995 yielding a 1 5 km across track spacing at latitude 70 with a higher along track sampling of 350 m we have analysed the waveform altimetric data from this period to compute maps with a 1 30 grid size data processing consists of correcting for environmental factors and editing and retracking the waveforms a further step consists of reducing the radial orbit error through crossover analysis and correcting the slope error to second order the high resolution topography of both ice sheets reveals numerous details a kilometre scale surface roughness running at 45 from the flow direction is the dominant topographic characteristic of both continents antarctica also exhibits many scars due to local flow anomalies several physical processes can be identified abrupt transitions from deformation to sliding and vice versa and impressive strike slip phenomena inducing en echelon folds

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

application of scanning x ray analytical microscope to the petrographic characterization of a ductile shear zone an alternative method to image microstructures abstract a ductile shear zone within a metasomatic biotite band in the ryoke granite teshima sw japan has been studied using the scanning x ray analytical microscope sxam this enabled the quantitative distributions of major elements such as si k fe al and ca to be determined within the shear zone these element maps were processed to transform them into images showing the distribution of minerals such as quartz biotite plagioclase and k feldspar which form the major minerals within the biotite band and the granite protolith mineral profiles based on these mineral maps compared with the simple shear strain profile reveal that the shear zone is most intense where quartz and biotite have been substituted for the primary mineral assemblage of the granite protolith suggesting that the stresses imposed on the granite caused the shear strain to localize along the biotite band to produce the observed shear zone it appears that the rheological behavior changed around 50 60 of quartz modal composition

antarctica seasonal mass variations detected by grace abstract the newly available grgs eigen gl04 30day solutions computed by the grgs group in toulouse are used to study inter and intra annual mass variations in antarctica the series of gravity coefficients cover the period from july 2002 to march 2005 they are corrected for ocean tides ocean high frequencies and atmospheric pressure so the remaining signal mostly comes from ice mass variations and post glacial rebound the errors of these fields are estimated to be less than 2 4 cm of water height equivalent with punctual values of only 0 5 cm the polar antarctica zone benefits from a low error level which compensates for the weak gravity variations the temporal signal computed over the whole continent shows a clear seasonal cycle with a maximum of precipitation during winter months and a minimum during summer months the ratio between winter and summer snow precipitation is also estimated to be 2 75 which accords well with previous studies the gravity fields are developed to provide suitable information up to 666 km the study could therefore focus on regional areas the coastal zones exhibit higher variable signals with stronger snow accumulation rates than the central part in agreement with climatologic models and in situ observations the peninsula zone has the highest values with a clear semi annual component

ice discharge of eastern dome c drainage area antarctica determined from airborne radar survey and satellite image analysis eastern dome c southern talos dome and northern taylor dome are drained by the priestley reeves david mawson and mackay outlet glaciers which flow into the scott coast on the west side of the ross sea antarctica airborne radar surveys were conducted on these glaciers to determine ice thickness and bed morphology along transverse and longitudinal profiles of the grounded and floating segments a new analysis of a i andsat thematic mapper satellite image using a tracking technique was used to measure ice velocity at grounding lines and along ice tongues the integration of radar and satellite data helped to locate grounding lines and to calculate the ice discharge changes in ice fluxes of floating glaciers were used to determine basal melting and freezing rates the ice discharge calculated is less than half that required for a zero net surface mass balance according to the inputs given by the accumulation estimates widely adopted at present the basal melting rates of meteoric ice represent 50 of the net ablation rate

sedimentary facies analysis mineralogy and diagenesis of the mesozoic aquifers of the central perth basin western australia abstract assessment and successful exploration for and exploitation of aquifers in the perth basin require knowledge of their petrophysical and sedimentological characteristics and geometries this study provides a sedimentological and lithofacies analysis of core from the mesozoic yarragadee formation cadda formation cattamarra coal measures eneabba formation and lesueur sandstone of western australia recovered from pinjarra 1 cockburn 1 gingin 1 and gingin 2 wells provide insights into changes in depositional environment over time and space in the central perth basin in studied sections nine different fluvial dominated lithofacies have been identified in the yarragadee formation cadda formation and cattamarra coal measures that occur in similar proportions whereas the lesueur sandstone is dominated by coarse grained deposits of high energy fluvial systems vertical variation in lithofacies on the order of 10 cm to approximately 2 m vertical scale is observed in all formations and wells changes in the lithofacies linked to local depositional environments are probably associated with fluvial alluvial to fluvio deltaic systems that have complex 3d architecture including braided and to probably meandering systems and are affected by channel avulsion point counting and automated mineral analysis of thin sections of core showed detrital mineralogy dominated by monocrystalline quartz with rare polycrystalline quartz a moderate amount of alkali feldspar and very minor amounts of garnet organic fragments muscovite and biotite these data show a lithofacies dependence of the proportion of minerals with little variation between equivalent lithofacies from different depths formations or wells grain size and sorting that have a first order control on porosity are strongly lithofacies dependent individual lithofacies types show a trend of decreasing porosity with depth due to the increasing effects of compaction quartz overgrowth cementation and authigenic clay mineral development lithofacies and depth are the main controls on permeability and so lithofacies distribution exerts a key control on hydraulic behaviour

satellite image derived velocity field of an antarctic ice stream the surface velocity of a rapidly moving ice stream has been determined to high accuracy and spatial density with the use of sequential satellite imagery variations of ice velocity are spatially related to surface undulations and transverse velocity variations of up to 30 percent occur such large variations negate the concept of plug flow and call into question earlier mass balance calculations for this and other ice streams where sparse velocity data were used the coregistration of images with the use of the topographic undulations of the ice stream and the measurement of feature displacement with cross correlation of image windows provide significant improvements in the use of satellite imagery for ice flow determination

the effects of basal melting on the present flow of the ross ice shelf antarctica on utilise un modele mixte aux elements finis et differences finies de l ecoulement et du transfert de chaleur avec deux hypotheses fusion nulle partout et fusion equilibrant tout epaississement a grande echelle

rapid climate driven changes in outlet glaciers on the pacific coast of east antarctica multidecadal trends in the terminus position of outlet glaciers along the margin of the east antarctic ice sheet reveal three epochal patterns of glacier retreat or advance consistent with a rapid and coherent response to air temperature and sea ice trends it is widely known that glaciers in west antarctica and greenland have been discharging ice into the oceans in response to warming in recent years and that sea levels have risen as a result by contrast we hear little about the much larger east antarctic ice sheet which has been viewed as being less vulnerable to climate change owing to its location in an extremely cold climate chris stokes and colleagues have used satellite imagery to map a large sample of glaciers along the pacific coast of east antarctica and show that in fact they are responding to decadal climate variability in concert with climate glaciers retreated in the 1970s and 1980s advanced in the 1990s and approximately split between advance and retreat since the 2000s the authors conclude that parts of the world s largest ice sheet may be more responsive to external forcing than previously recognized observations of ocean terminating outlet glaciers in greenland and west antarctica1 2 3 4 5 6 indicate that their contribution to sea level is accelerating as a result of increased velocity thinning and retreat7 8 9 10 11 thinning has also been reported along the margin of the much larger east antarctic ice sheet1 but whether glaciers are advancing or retreating there is largely unknown and there has been no attempt to place such changes in the context of localized mass loss7 9 or climatic or oceanic forcing here we present multidecadal trends in the terminus position of 175 ocean terminating outlet glaciers along 5 400 kilometres of the margin of the east antarctic ice sheet and reveal widespread and synchronous changes despite large fluctuations between glaciers linked to their size three epochal patterns emerged 63 per cent of glaciers retreated from 1974 to 1990 72 per cent advanced from 1990 to 2000 and 58 per cent advanced from 2000 to 2010 these trends were most pronounced along the warmer western south pacific coast whereas glaciers along the cooler ross sea coast experienced no significant changes we find that glacier change along the pacific coast is consistent with a rapid and coherent response to air temperature and sea ice trends linked through the dominant mode of atmospheric variability the southern annular mode we conclude that parts of the world s largest ice sheet may be more vulnerable to external forcing than recognized previously

evidence of recent climatic warming on the eastern antarctic peninsula air temperatures at the stations marambio esperanza and matienzo have been analysed to investigate recent climate change on the eastern part of the antarctic peninsula the data are compared with the station orcadas on the south orkney islands the longest record available in antarctica and with faraday on the western coast of the peninsula though the interannual variability is comparatively high and the stations are located in different climatic regimes a pronounced warming trend shows up in all records at marambio a temperature increase of 1 5 c has been observed since the beginning of the record in 1971 this is of similar magnitude as the increase at the station faraday on the west coast with 2 5 c for the longer period since 1945 the steady retreat and collapse of the northern larsen ice shelf coincided with this warming trend of particular importance for the ice shelf mass balance in this region are the summer temperatures which show a statistically significant warming trend at the stations marambio and esperanza the representativity of the summer temperatures of marambio for northern larsen ice shelf is confirmed by intercomparison with the parallel measurements at matienzo which is located on the ice shelf

ice shelf advance and retreat rates along the coast of queen maud land antarctica we mapped ice shelf margins along the queen maud land coast antarctica in a study of ice shelf margin variability over time our objective was to determine the behavior of ice shelves at similar latitudes but different longitudes relative to ice shelves that are dramatically retreating along the antarctic peninsula possibly in response to changing global climate we measured coastline positions from 1963 satellite reconnaissance photography and 1997 radarsat synthetic aperture radar image data for comparison with coastlines inferred by other researchers who used landsat data from the mid 1970s we show that these ice shelves lost 6 8 of their total area between 1963 and 1997 most of the areal reduction occurred between 1963 and the mid 1970s since then ice margin positions have stabilized or even readvanced we conclude that these ice shelves are in a near equilibrium state with the coastal environment

marine controls on modern sedimentation on the antarctic continental shelf abstract the extreme depth and rugged topography of the antarctic continental shelf its seasonal to perennial sea ice cover and its large slowly calving ice shelves exert major influences on the adjacent ocean and sediments regionally variable exchanges of heat and momentum between the atmosphere and ocean result in net off shelf transport of sea ice and net downward salt flux this buoyancy partitioning drives a vertical convection that is followed by westward and northward flows of ventilated dense water across the continental shelves shelf waters meet mix with and modify circumpolar deep water at a dynamic slope front near the continental shelf break locally or periodically forming antarctic bottom water nutrient rich deep water upwells along this front regionally intruding onto the continental shelf in long thermally attenuated filaments these intrusions are frequently linked to mass balance processes at the base of ice tongues and ice shelves melting freezing and tidal currents beneath glacial ice are related to the larger scale circulation and to the fate of basal debris in the ice sheet the ocean circulation near ice fronts and decadal variability in ice front positions may account for several features of the sediment record time series 1 yr current measurements in the ross and weddell seas have revealed moderate to strong currents that are seasonally variable vertically coherent and dominated by the diurnal tide and longer term events few long term current measurements exist in the shelf and slope bottom boundary layers that are most important to sediment deposition and erosion icebergs may frequent certain routes e g in association with currents and fronts near the edge of the continental shelf and are capable of scouring and resuspending sediments down to shelf break depths sea ice plays a role in shelf sedimentation by rafting eolian and bottom debris away from the nearshore regions in addition generally offshore winds produce numerous leads and polynyas along the coastline and within the sea ice fields higher biological productivity in these polynyas may be linked to higher local sedimentation rates biogenic marine sediments apparently comprise a major percentage of the regionally variable modern shelf deposits despite the impressive glacial setting and polar environment

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change