the apparent effects of the mt pinatubo eruption on the greenland ice sheet melt extent the indirect climatological effects of major volcanic eruptions can be of great importance because of the complex feedbacks that exist in the global climate system one such effect is the melt area reduction on the greenland ice sheet using passive microwave satellite data for the period 1979 1995 the melt conditions of the ice sheet before and after the 1991 mt pinatubo eruptions are examined statistical tests indicate that an observed drop following the eruptions has a 97 to 99 probability of being outside the limits of undisturbed variability furthermore this anomaly diminishes as the time from the eruption increases these characteristics in conjunction with an observed increasing melt trend prior to the eruptions indicate that mt pinatubo has had a significant effect on the melt conditions and consequently the energy balance characteristics of the greenland ice sheet

rise in frequency of surface melting at siple dome through the holocene evidence for increasing marine influence on the climate of west antarctica 1 a new melt layer history from siple dome west antarctica indicates notable late holocene summertime warming visual stratigraphic analyses of the 1004 m ice core identified 62 years with melt layers melting events began around 11 7 ka followed by a period of no melting from 8 8 6 6 ka melt layer frequency increased from 6 6 ka to the present with the 1000 year average melt layer frequency reaching a maximum of 2 at 0 8 ka we use our millennial scale archive of melt events as a unique seasonal paleothermometer to elucidate changes in west antarctic holocene summer climate our calibration suggests the change in melt frequency from 0 to 2 may represent a summer temperature increase of 2 c from the middle to late holocene this temperature change cannot be explained entirely by local change in ice elevation or summer insolation and is in contrast to east antarctic climate records which show peak warmth in the early holocene followed by stable or decreasing temperature we interpret the rise in melt frequency as evidence of an increasing marine influence on the ross sea sector of west antarctica although the surface elevation of siple dome has not changed greatly the continued lateral retreat of the west antarctic ice sheet from its last glacial maximum configuration across the outer continental shelf and the delayed drawdown in ice thickness from the adjacent coastal marie byrd land region in conjunction with periods of increased cyclogenesis perhaps related to variations in enso would allow a moderated maritime climate to more easily reach west antarctica

ultrashallow depth imaging of a channel stratigraphy with first arrival traveltime inversion and prestack depth migration a case history from bull creek oklahoma depth imaging in ultrashallow 50 m environments presents twofold challenge 1 coda available for depth migration is very limited and 2 conventional time processing with limited coda generally fails to estimate reliable velocity models for depth migration we studied the combining of first arrival traveltime inversion and prestack depth migration psdm for depth imaging of ultrashallow paleochannel stratigraphy associated with the bull creek drainage system oklahoma restricted by a limited number of geophones 24 we acquired data for inversion and migration through two coincident profiles the first profile for inversion has a wider survey aperture 115 m maximum shot receiver spacing and consequently sparse cmp spacing 2 5 m whereas the second profile for psdm has denser cmp spacing 1 m and consequently a narrower survey aperture 46 m maximum shot receiver spacing we also found that the velocity model from traveltime inversion of the wider aperture data set is more preferable for dep

ultrashallow seismic experiment on a trenched section of the chelunpu fault zone taiwan ultrashallow p wave seismic reflection experiments were conducted at a model test site and in a trenched shallow fault zone along the chelunpu fault line the field layout was designed to have the shallowest undistorted reflection from about 1 m depth with 0 5 m vertical resolution the smallest group interval tested in this study was 0 05 m with a 0 25 ms sample interval which can avoid spatial aliasing of ground roll if the target is very shallow and the velocities are low data processing was designed to be simple but consistent as the ultrashallow reflections may be contaminated with high amplitude coherent noise in many aspects first break muting and surgical muting were performed on each file as detailed as possible and f k filtering was applied mainly for the purpose of attenuating the aliasing energy and back scattered noise data acquired in this study show that the low p wave velocities 200 m s and high dominant frequencies 120 200 hz of near surface layers may have a potential vertical resolution of 0 4 m or even better comparing the test profile with the ground penetrating radar gpr control profile of the same test site and correlating the results obtained from the study site with those of the geologic cross section of the trench this experiment demonstrates the possibility of using seismic methods in investigating shallow structures at depths of less than a few meters with vertical resolution comparable to the gpr technique

the influence of hematite on the sorption of uranium vi onto granite filling fractures abstract continuous flow through column experiments have been performed to determine the sorption of uranium in granite hematite mixtures the results obtained have shown the importance that oxy hydroxy iron compounds present as fracture fillings can have in the uranium retardation in its migration through the geosphere the experimental results showed the reversibility of the sorption process and have been successfully fitted with a model combining both thermodynamic and kinetic terms

physical structural and isotopic characteristics and growth processes of fast sea ice in lutzow holm bay antarctica a sea ice ocean study was conducted off queen maud land and enderby land antarctica from 1990 to 1991 by the japanese antarctic research expedition observations of multiyear land fast sea ice were made in lutzow holm bay over a period of 2 years to determine the snow and ice characteristics and ice growth processes the snow depth in the bay reached large values of 1 0 to 1 5 m during the winter season at offshore locations from the analysis of ice thickness measurements it is confirmed that the fast ice with deep snow cover grew little in winter but substantially thickened during the summer months on the basis of ice core structure salinity and stable isotopic composition we conclude that the summer growth was caused by upward growth at the top of the ice to which snow ice and superimposed ice formation contribute these processes were the primary contributors to sea ice growth and characteristics only where the snow accumulation was large in areas of low snow accumulation there was no surface growth superimposed ice formation on sea ice in antarctica has not been reported previously evidence for snow cover melting which is a prerequisite for superimposed ice formation was also found

monitoring ice sheet behavior from space satellite remote sensing has revolutionized ice sheet research a variety of instruments sensitive to different parts of the electromagnetic spectrum take what the human eye detects as a flat white desert and provide data sets rich in scientific information image based maps of ice sheets are becoming commonplace and have become an integral component of field work more than a pretty picture the digital character of the satellite data from these instruments has become fundamental to the production of elevation motion accumulation and reflectance data sets visible imagery shows the scientist a wealth of features that offer clues to the history and current behavior of the ice sheet radar and microwave imagery provide information from beneath the surface and have been used to estimate snow accumulation rates interferometry principles have recently been applied to measure surface topography and ice motion with unparalleled precision nonimaging instruments also keep a watchful eye monitoring the ice sheet for indications of growth or shrinkage further expansion of the uses of satellite data is anticipated in the future

climate and surface mass balance of coastal west antarctica resolved by regional climate modelling west antarctic climate and surface mass balance smb records are sparse to fill this gap regional atmospheric climate modelling is useful providing that such models are employed at sufficiently high horizontal resolution and coupled with a snow model here we present the results of a high resolution 5 5 km regional atmospheric climate model racmo2 simulation of coastal west antarctica for the period 1979 2015 we evaluate the results with available in situ weather observations remote sensing estimates of surface melt and smb estimates derived from radar and firn cores moreover results are compared with those from a lower resolution version to assess the added value of the resolution the high resolution model resolves small scale climate variability invoked by topography such as the relatively warm conditions over ice shelf grounding zones and local wind speed accelerations surface melt and smb are well reproduced by racmo2 this dataset will prove useful for picking ice core locations converting elevation changes to mass changes for driving ocean ice sheet and coupled models and for attributing changes in the west antarctic ice sheet and shelves to changes in atmospheric forcing

distribution of uranium and thorium in core samples from the underground research laboratory lease area southeastern manitoba canada abstract petrographic examination of core samples from seven boreholes in the underground research laboratory lease area of the lac du bonnet batholith revealed that the granitic core can be divided into four sample groups 1 grey granite 2 pink granite 3 deep red granite and 4 cream coloured clay rich granite the order of these four groups represents an evolutionary sequence that can be related to the alteration of the grey granite u and th concentrations were determined for the four groups of granitic core samples the u concentration in the four groups of core samples showed a distinct variation whereas the th concentration showed little variation the distribution pattern of u in the four sample groups can be related to its mobility and concentration under various stages of rock alteration while the uniform distribution of th is interpreted to be due to its limited mobility

spatiotemporal variations of snowmelt in antarctica derived from satellite scanning multichannel microwave radiometer and special sensor microwave imager data 1978 2004 1 we derived the extent onset date end date and duration of snowmelt in antarctica from 1978 to 2004 using satellite passive microwave scanning multichannel microwave radiometer smmr and special sensor microwave imager ssm i data a wavelet transform based method was developed to determine and characterize melt occurrences about 9 12 of the antarctic surface experiences melt annually this is more than twice the surface melt extent measured in greenland seasonally surface melt primarily takes place in december january and february and peaks in early january regression analysis over the 25 year period of study reveals a negative interannual trend in surface melt nevertheless the trend inference is not statistically significant large year to year fluctuations characterize the interannual variability extremely high melt occurred in the 1982 1983 and 1991 1992 summers while extremely weak melt occurred in the 1999 2000 summer a strong correlation with air temperature suggests that the melt index can serve as a diagnostic indicator for regional temperature variations periodic melting has been observed over ross ice shelf ronne filchner ice shelf the west antarctic ice streams and outlet glaciers in the transantarctic mountains the antarctic peninsula west ice shelf shackleton ice shelf amery ice shelf and the ice shelf along the princess ragnhild coast experienced the most persistent and intensive melt and should be closely monitored for their stability in the future given the recent disintegration of the larsen ice shelf a and b

alteration of uraninite from the nopal i deposit pen a blanca district chihuahua mexico compared to degradation of spent nuclear fuel in the proposed u s high level nuclear waste repository at yucca mountain nevada abstract at the nopal i uranium deposit primary uraninite nominally uo 2 x has altered almost completely to a suite of secondary uranyl minerals the deposit is located in a basin and range horst composed of welded silicic tuff uranium mineralization presently occurs in a chemically oxidizing and hydrologically unsaturated zone of the structural block these characteristics are similar to those of the proposed u s high level nuclear waste hlw repository at yucca mountain nevada petrographic analyses indicate that residual nopal i uraninite is fine grained 5 10 m and has a low trace element content average about 3 wt these characteristics compare well with spent nuclear fuel the oxidation and formation of secondary minerals from the uraninite have occurred in an environment dominated by components common in host rocks of the nopal i system e g si ca k na and h 2 o and also common to yucca mountain in contrast secondary phases in most other uranium deposits form from elements largely absent from spent fuel and from the yucca mountain environment e g pb p and v the oxidation of nopal i uraninite and the sequence of alteration products their intergrowths and morphologies are remarkably similar to those observed in reported corrosion experiments using spent fuel and unirradiated uo 2 under conditions intended to approximate those anticipated for the proposed yucca mountain repository the end products of these reported laboratory experiments and the natural alteration of nopal i uraninite are dominated by uranophane nominally ca uo 2 2 si 2 o 7 6h 2 o with lesser amounts of soddyite nominally uo 2 2 sio 4 2h 2 o and other uranyl minerals these similarities in reaction product occurrence developed despite the differences in time and physical chemical environment between yucca mountain approximate laboratory experiments and yucca mountain approximate uraninite alteration at nopal i suggesting that the results may reasonably represent phases likely to form during long term alteration of spent fuel in a yucca mountain repository from this analogy it may be concluded that the likely compositional ranges of dominant spent fuel alteration phases in the yucca mountain environment may be relatively limited and may be insensitive to small variations in system conditions

surface melting derived from microwave radiometers a climatic indicator in antarctica this paper aims at presenting a new dataset including the melt events derived from microwave remote sensing occurring in antarctica from summer 1979 80 to 2005 06 the method for detecting melt events and sources of error is presented and then trends in melt duration for every pixel are extracted from the dataset mapped and analyzed the analysis focuses on two particular cases and the main results show that 1 the trends over the period 1980 2006 in the antarctic peninsula match with lengthening of the melt season on the ice shelves and surprisingly shortening of the melt season in the mountainous area of the peninsula and 2 the trends over the period 1996 2006 on the entire continent show a dipolar pattern with the western regions experiencing decreasing melt duration whereas east antarctica and the ross ice shelf experience increasing melt duration this pattern closely mirrors the temperature pattern expected when the southern annular mode is in a decreasing trend as it is over the period 1996 2006 for further analysis and validation the dataset has been made available at http www lgge obs ujf grenoble fr picard melting

azimuth variation in microwave scatterometer and radiometer data over antarctica while designed for ocean observation scatterometer and radiometer data have proven very useful in a variety of cryosphere studies over large regions of antarctica ice sheet and bedrock topography and the snow deposition drift and erosional environment combine to produce roughness on various scales roughness ranges from broad basin scale ice sheet topography at spl sim 100 km wavelengths to large spatially coherent dune fields at spl sim 10 km wavelength to erosional features on the meter scale known as sastrugi these roughness scales influence the microwave backscattering and emission properties of the surface combining to introduce azimuth angle dependencies in the satellite observation data in this paper the authors explore the use of nasa scatterometer nscat data european remote sensing ers advanced microwave instrument ami scatterometer mode data and special sensor microwave imager ssm i data to study surface roughness effects in antarctica all three sensors provide strong evidence of azimuth modulation which is correlated with the surface slope environment and results in a katabatic wind flow regime due to its broad azimuth coverage nscat data appears to be the best suited for azimuth angle observations a simple empirical model for the azimuth variation in the radar backscatter is developed and an algorithm for computing the parameters of the model from nscat data at a fine scale is presented results indicate relationships exist between the azimuthal variation of the data and the orientation of the surface slope and small scale roughness relative to the sensor look direction

constructing improved decadal records of antarctic ice shelf height change from multiple satellite radar altimeters abstract antarctica s ice shelves the floating extensions of the ice sheet exert an important dynamic constraint on the flow of ice from the grounded ice sheet to the ocean and therefore on changes in global sea level thinning of an ice shelf reduces its ability to restrain the ice discharge from the grounded ice sheet however our understanding of how ice shelf processes couple ice sheet changes to climate variability is still rudimentary in part this is due to the brevity and low temporal resolution of surveys of ice shelf thickness relative to the broad range of time scales on which ice sheet mass fluctuates here we present improved procedures to construct 18 year 1994 2012 time series of antarctic ice shelf surface height at high spatial resolution 30 km by merging data from three overlapping satellite radar altimeter missions ers 1 ers 2 and envisat we apply an averaging scheme to enhance the signal to noise ratio of height changes over the floating ice shelves and extract low order polynomial trends using a robust approach regularized regression with cross validation that accounts for both bias and variance in the fit we construct formal confidence intervals by bootstrap resampling of the residuals of the fit the largest source of height error arises from the interaction of the radar signal with the snow and firn surface on annual time scales changes in surface and sub surface scattering and radar penetration lead to apparent height changes that are larger than the true surface height change arising from densification our 18 year time series of surface height provide an insight into how ice shelves respond to the changing atmospheric and oceanic conditions our methods could also be applied to grounded portions of the ice sheets both in antarctica and greenland

evaluation of passive microwave melt detection methods on antarctic peninsula ice shelves using time series of sentinel 1 sar abstract passive microwave datasets have been used to quantify the extent and duration of surface melt in greenland and antarctica from 1978 on with daily and near daily intervals these results have important implications for climate analysis and may help evaluate ice shelf stability however the accuracy of passive microwave methods used to detect melt is difficult to quantify especially on the antarctic peninsula here four different melt detection methods are employed including a new formulation of a statistical analysis of brightness temperature time series using a k means clustering algorithm strikingly two of the most widely used passive microwave melt detection methods are found to vary by 48 mean days of melt per year across six different locations on the larsen c wilkins and george vi ice shelves in the absence of ground truth observations time series of sentinel 1 sar observations from 2016 on provide a comparison dataset in topographically flat regions where surface melt is spatially uniform the passive microwave melt detection method based on a k means analysis and the cross polarization gradient ratio method demonstrate the highest agreement and correlation with active radar melt detection methods one issue which has plagued passive microwave analysis is its coarse spatial resolution high resolution sar images are able to demonstrate and quantify the spatial variability of melt within individual passive microwave pixels melt is shown to be suitably uniform in space for passive microwave applications at the study sites on antarctic peninsula ice shelves but not so in other regions of the antarctic peninsula spatial heterogeneity of surface melt on the sub pixel scale is often related to varying surface topography

relationship between passive microwave derived snowmelt and surface measured discharge wheaton river yukon territory canada snow volume and melt timing are major factors influencing the water cycle at northern high altitudes and latitudes yet both are hard to quantify or monitor in remote mountainous regions twice daily special sensor microwave imager ssm i passive microwave observations of seasonal snow melt onset in the wheaton river basin yukon territory canada 60 08 05 n 134 53 45 w are used to test the idea that melt onset date and duration of snowpack melt refreeze fluctuations control the timing of the early hydrograph peaks with predictable lags this work uses the ssm i satellite data from 1988 to 2002 to evaluate the chronology of melt and runoff patterns in the upper yukon river basin the wheaton river is a small 875 km2 tributary to the yukon and is a subarctic partly glacierized heterogeneous basin with near continuous hydrographic records dating back to 1966 ssm i pixels are sensitive to melt onset due to the strong increase in snow emissivity and have a robust signal in spite of coarse 25 25 km2 pixel resolution and varied terrain results show that wheaton river peak flows closely follow the end of large daily variations in brightness temperature of pixels covering the wheaton river but the magnitude of flow is highly variable as might be expected from interannual snow mass variability spring rise in the hydrograph follows the end of high diurnal brightness temperature tb amplitude variations dav by 0 to 5 days approximately 90 of the time for this basin subsequent work will compare these findings for a larger 7250 km2 unglacierized tributary the ross river which is farther northeast 61 59 40 n 132 22 40 w in the yukon territory these techniques will also be used to try to determine the improvement in melt detection and runoff prediction from the higher resolution 15 15 km2 advanced microwave scanning radiometer for eos amsr e sensor copyright 2006 john wiley sons ltd

high resolution shallow seismic experiments in sand part ii velocities in shallow unconsolidated sand we conducted a shallow high resolution seismic reflection and refraction experiment on a sandy beach the depth of investigation was about 2 m we interpret the data using the hertz mindlin contact theory combined with gassmann s equation these were used to obtain the vertical velocity profile then the profile was computed from seismic data using the turning rays approximation the normal moveout nmo velocity at the depth of 2 m matches the velocity profile as a result we developed a method to invert measured velocity from first arrivals i e velocity versus distance into velocity versus depth using only one adjustable parameter this parameter contains all the information about the internal structure and elasticity of the sand the lowest velocity observed was about 40 m s it is noteworthy that the theoretical lower bound for velocity in dry sand with air is as low as 13 m s we find that modeling sand as a quartz sphere pack does not quantitatively agree with the measured data however the the

interaction of katabatic winds and near surface temperatures in the antarctic 1 a two dimensional mesoscale model was applied to simulate wintertime katabatic winds in the antarctic coastal region simulations were made for a constant slope angle with the slope height varying and for fixed slope heights with the slope angle varying thermal wind opposed the katabatic flow near the foot of the slope but enhanced it over the high plateau the steeper and higher the slope the stronger the effect on the plateau the 2 m potential temperature decreased down the slope toward sea ice because 1 the katabatic wind resulted in the accumulation of cold near surface air over the sea ice and the lower parts of the slope 2 over the flat sea ice zone the stratification was stronger and 3 the shallow slope was within the strong surface inversion from over the sea ice with a slope aspect ratio of 5 m km 1 and a slope height below 1000 m 2 m temperature t2m decreased down the slope but for slope heights of 1500 m and more t2m increased down the slope adiabatic warming and because of the stronger wind enhanced turbulent mixing of the warmer air from aloft contributed to the warming for slope angles ranging from 1 to 20 m km 1 with a small slope height of 500 m t2m decreased down the slope but not monotonically whereas with a slope height of 2000 m yielding stronger winds and larger adiabatic warming t2m increased monotonically down the slope the model results were supported by observations from several antarctic sites with different topographic conditions

surface melting on antarctic peninsula ice shelves detected by passive microwave sensors a 13 year time series of spaceborne passive microwave radiance measurements over the antarctic peninsula ice shelves reveals a systematic increase in the duration of the summer melt season combined with data from meteorological stations on the antarctic peninsula the annual motion and long term trends of the 0 c isotherm can be monitored

snow facies over ice sheets derived from envisat active and passive observations this paper aims to separate different snow regions over the terrestrial ice sheets based on their measured microwave signatures it takes advantage of coregistered data from passive and active sensors on the environmental satellite envisat to directly derive a snow facies indicator in a point by point basis this paper represents the first attempt of this kind in exploiting nadir viewing and dual frequency data from both altimeter and radiometer sensors the approach is based on a clustering method such representation of the data by means of fewer clusters necessarily loses fine details but achieves simplification in geographical representation and eases the description of the condition of the ice sheets in 2004 our approach broadens the description of the snow pack by taking into account characteristics such as surface roughness grain size stratification and snowmelt effects whereas the latter has often solely been considered in most previous work such partition of the ice sheets might help to better understand relationships between microwave signatures and snow morphology it could also be useful for estimating elevation uncertainty in altimeter data which in turn is essential to correctly interpret the significance of the rates of elevation change in a changing climate and to convert elevation change to snow mass change

shallow seismic investigation of a site with poor reflection quality a shallow seismic reflection experiment was performed on a construction site to determine the feasibility of using reflection seismology to investigate the shallow structure in a weathered sand gravel interlayered zone that was known to be a poor transmission of high frequency seismic energy field recording parameters were designed to fit the limited space of the urban construction survey area a 7 kg sledgehammer was used to generate p waves and sh waves single 100 hz geophones were deployed at 1 0 m 0 5 m group intervals and 200 100 hz low cut filters were applied prior to a to d conversion to attenuate ground roll for sh wave reflections single 14 hz geophones and a 70 hz low cut filter on the seismograph were used the dominant frequency bands ranged from 33 to 275 hz and were centered around 110 hz for p waves lower dominant frequency bands 20 to 160 hz with a dominant frequency of around 85 hz were observed on sh wave records four seismic lines three p wave recordings and one sh wave recordi

extent and duration of antarctic surface melting the extent and duration of surface melting on the antarctic ice shelves and margins of the antarctic ice sheet are derived from satellite passive microwave data for 1978 87 the occurrence of surface melting in daily maps of t b is indicated by a marked increase in microwave brightness temperature t b which is caused by moisture in the near surface firn t b increases of more than 30 deg above the annual mean t b are chosen to indicate melting most antarctic surface melting occurs during december and january the observed melting is correlated with regional air temperatures but some melt patterns also appear to be related to katabatic wind effects the correlations suggest that the surface melting in antarctica increases about 3 5 10 6 d km 2 per degree of summer temperature increase the surface melt index duration times area of melting calculated for antarctica is 24 10 6 d km 2 averaged over nine summers the observed inter annual and regional variability is large surface melting was most extensive during the 1982 83 summer 36 10 6 d km 2 and least extensive during the 1985 86 summer 15 10 6 d km 2 the data indicate a decline in surface melting over the 9 years but meaningful inferences regarding trends in surface melting are precluded by the large inter annual variability

insignificant change in antarctic snowmelt volume since 1979 1 surface snowmelt is widespread in coastal antarctica satellite based microwave sensors have been observing melt area and duration for over three decades however these observations do not reveal the total volume of meltwater produced on the ice sheet here we present an antarctic melt volume climatology for the period 1979 2010 obtained using a regional climate model equipped with realistic snow physics we find that mean continent wide meltwater volume 1979 2010 amounts to 89 gt y 1 with large interannual variability 41 gt y 1 of this amount 57 gt y 1 64 is produced on the floating ice shelves extending from the grounded ice sheet and 71 gt y 1in west antarctica including the antarctic peninsula we find no statistically significant trend in either continent wide or regional meltwater volume for the 31 year period 1979 2010

detailed images of the shallow alpine fault zone new zealand determined from narrow azimuth 3d seismic reflection data previous high resolution seismic reflection investigations of active faults have been based on 2d profiles unfortunately 2d data may be contaminated by out of the plane reflections and diffractions that may be difficult to identify and eliminate although full 3d seismic reflection methods allow out of the plane events to be recognized and provide superior resolution to 2d methods they are only rarely applied in environmental and engineering studies because of high costs a narrow azimuth 3d acquisition and processing strategy is introduced to produce a high resolution seismic reflection volume centered on the alpine fault zone new zealand the shallow 3d images reveal late quaternary deformation structures associated with this major transpressional plate boundary fault the relatively inexpensive narrow azimuth 3d acquisition pattern consisting of inline source and receiver lines was easily implemented in the field to provide 2 by 4 m cmp coverage over an approximately 500 by 200 m area the narrow

mapping a bedrock surface under dry alluvium with shallow seismic reflections shallow seismic reflection techniques were used to image the bedrock alluvial interface near a chemical evaporation pond in the texas panhandle allowing optimum placement of water quality monitor wells the seismic data showed bedrock valleys as shallow as 4 m and accurate to within 1 m horizontally and vertically the normal moveout velocity within the near surface alluvium varies from 225 m s to 400 m s all monitor well borings near the evaporation pond penetrated unsaturated alluvial material on most of the data the wavelet reflected from the bedrock alluvium interface has a dominant frequency of around 170 hz low cut filtering at 24 db octave below 220 hz prior to analog to digital conversion enhanced the amplitude of the desired bedrock reflection relative to the amplitude of the unwanted ground roll the final bedrock contour map derived from drilling and seismic reflection data possesses improved resolution and shows a bedrock valley not interpretable from drill data alone

ice shelf disintegration by plate bending and hydro fracture satellite observations and model results of the 2008 wilkins ice shelf break ups abstract satellite remote sensing observations of three break up events in 2008 for the wilkins ice shelf 28 february to 6 march 27 may to 31 may and 28 june to mid july provide unprecedented detail of ice shelf calving during rapid break up the observations reveal that the wilkins break ups occur through a distinctive type of shelf calving which we term disintegration as well as more typical rifting and calving here we focus on the disintegration process which is characterized by repeated rapid fracturing that creates narrow ice edge parallel blocks with subsequent block toppling and fragmentation forming an expanding iceberg and ice rubble mass we use these data to develop and test a model of floating ice plate disintegration in which ice plate bending stresses at the ice front arising from buoyancy forces can lead to runaway calving when free mobile water is available high resolution satellite images and laser altimetry of the first break up event provide details of fracture spacings ice thicknesses and plate bending profiles that agree well with our model predictions we suggest that surface or near surface meltwater is the main pre condition for disintegration and that hydro fracture is the main mechanism brine layers from near waterline brine infiltration can support a similar process but this is less effective unless regional ice stress patterns contribute to the net stress available at the crack tip for fracturing a combination of brine enhanced fracturing and changing internal net extensional stresses was the likely mechanism behind the latter two wilkins events

greenland ice sheet melt extent 1979 1999 analysis of melt extent on the greenland ice sheet is updated to span the time period 1979 1999 and examined along with its spatial and temporal variability using passive microwave satellite data to acquire the full record the issue of continuity between the previous passive microwave sensors smmr ssm i f 8 and ssm i f 11 and the most recent ssm i f 13 sensor is addressed the f 13 cross polarized gradient ratio melt classification threshold is determined to be 0 0154 results show that for the 21 year record a positive melt trend of nearly 1 yr is observed but this trend falls just below the 90 significance level the observed melt increase does appear to be driven by conditions in the western portion of the ice sheet rather than the east where melt appears to have decreased slightly moreover the eruption of mount pinatubo in 1991 is likely to have had some impact on the melt but not so much as previously suspected the 1992 melt anomaly is 1 7 standard deviations from the mean finally the relationship between coastal temperatures and melt extent suggests an increase in surface runoff contribution to sea level of 0 31 mm yr for a 1 c temperature rise

multiyear accumulation and temperature history near the north greenland ice core project site north central greenland this paper presents a comparison of two independent methods of estimating subseasonal accumulation across the interior of greenland these methods high resolution snow pit studies and atmospheric modeling have differing spatial and temporal resolution but both can estimate net accumulation for subseasonal and shorter periods the snow pit approach is based on a documented relationship between high resolution snow pit profiles of oxygen stable isotope ratio 18o and multiyear special sensor microwave imager ssm i 37 ghz brightness temperature records comparison of ssm i data to profiles obtained during the 1995 alfred wegener institut north greenland traverse field season shows that 18o data from snow in north central greenland are a reliable high resolution temperature proxy this enables determination of accumulation amount rate and timing from approximately july 1991 through june 1995 across this 220 km long transect of the ice sheet precipitation estimates derived from early modeling based on european centre for medium range weather forecasts data show a similar average seasonal pattern but a diminished magnitude of accumulation 56 for these sites the slope of the multiyear t versus correlation was evaluated for each site on the basis of the observed and calculated temperature history from the nearby north greenland ice core project ngrip site automatic weather station these data should assist interpretation of the paleoclimatic record in the ngrip deep core

u series age and origin of two secondary uranium deposits central eastern desert egypt at two sites in the central eastern desert of egypt secondary uranium minerals are found at the surfaces of tabular fractured rock bodies which host primary uranium mineralization at depth at el atshan the host rock is a 28 m thick bostonite sill cutting siltstones and at el erediya the host rock is a 20 cm jasperoid vein cutting granite whereas the primary mineralization at depth is pre tertiary we obtain u series ages for the secondary mineralization at both sites of 80 000 to 140 000 yr we interpret this episode of uranium mobilization to have resulted from ground water saturation during humid oxygen isotope climatic stage 5 at both sites adsorbed uranium in the host rock immediately below the secondary ores is shown to have been the result of subsequent mobilization during the last 60 000 yr

seismic detection of overpressuring and fracturing an example from the qaidam basin people s republic of china abstract shallow hydrocarbon reserves were discovered in 1959 in the nan yi shan structure located in the qaidam basin about 2500 kms west of beijing p r c the first successful deep well encountered an overpressured zone at 3000 meters which resulted in a well blowout to improve the structural definition of the field and delineate the overpressured layer a 3d seismic survey was conducted a region of anomalous seismic time sag associated with fracturing and small quantities of oil and gas was identified on the northwest plunging nose of the nan yi shan anticline velocity dispersion effects were encountered and attributed to localized fracturing in a deeper interval seismic amplitudes were used to identify gas saturated fracture porosity and to describe the spatial limits of overpressuring within this layer this paper will discuss the seismic distortion and unusual velocity signature associated with a localized fracture zone it will demonstrate that with good quality data and sufficient lateral and vertical resolution thin fractured hydrocarbon bearing reservoirs can be delineated and overpressure zones predicted

amsr e melt patterns on the southern patagonia icefield passive microwave 37 ghz vertically polarized v brightness temperature tb measure ments from the advanced microwave scanning radiometer for earth observing system amsr e are used to monitor the extent and timing of snowmelt on the southern patagonia icefield spi in chile and argentina twice daily tb s for 2002 08 for high elevation 1200 m a s l pixels exhibit a bimodal histogram typical of snow covered regions in yukon alaskan icefields and the greenland ice sheet the low count between the two populations represents the tb threshold for melt 252 k this tb value with the 18 k diurnal amplitude variation threshold quantifies onset and duration of the spring melt refreeze period and is used to identify melt regimes and seasonal tb signals tb histograms for pixels west of the andean divide have a normal distribution above the melt threshold we interpret the tb histogram as controlled by surface moisture the shape and position with respect to tb are retained with changes in both latitude and elevation and the region is known to have a moist climate tb is not driven by seasonal temperature changes in the northwest sector of the icefield because the tb threshold is exceeded 75 of the time for all pixels the spring melt refreeze period has shortened by a mean of 10 days a 1 and a mean of 16 days a 1 for pixels with bimodal distributions between 2002 and 2008

recent changes in the microwave scattering properties of the antarctic ice sheet time series satellite microwave data are used to monitor and quantify changes in the scattering properties of the antarctic ice sheet daily ers scatterometer escat and special sensor microwave imager ssm i image data acquired since 1992 are analyzed to understand the seasonal and interannual changes over the ice sheet for regions of the ice sheet where azimuthal modulation is negligible seasonal cycles are observed in both the escat amplitude spl sim 0 5 db and ssm i data amplitude spl sim 10 k these cycles are attributed to seasonal changes in surface temperature interannual variability in the time series signatures appears to be associated with accumulation there is also evidence to suggest that shifts in the wind direction can alter the backscatter through azimuthal modulation over the period 1992 97 large trends are observed in the escat 1 k yr sup 1 signatures over several regions in antarctica these changes typically occur over ice shelves and at the margins of the ice sheet where previous melt events have occurred and where accumulation is relatively high 300 mm yr sup 1 it is likely the large changes result from the successive burial of an efficient scattering layer formed by refreezing after a melt event prior to 1992 there is also evidence to suggest that similarly large changes can be observed in the interior of the ice sheet due to the burial of depth hear layers in order to monitor long term change in the properties of the antarctic ice sheet it is necessary to remove the seasonal cycle from time series microwave data such anomaly data can then be used to understand the link between escat and ssm i with accumulation and wind shifts

modeling time series of microwave brightness temperature in antarctica this paper aims to interpret the temporal variations of microwave brightness temperature at 19 and 37 ghz and at vertical and horizontal polarizations in antarctica using a physically based snow dynamic and emission model sdem sdem predicts time series of top of atmosphere brightness temperature from widely available surface meteorological data era 40 re analysis to do so it successively computes the heat flux incoming the snowpack the snow temperature profile the microwaves emitted by the snow and finally the propagation of the microwaves through the atmosphere up to the satellite since the model contains several parameters whose value is variable and uncertain across the continent the parameter values are optimized for every 50 km 50 km pixel simulation results show that the model is inadequate in the melt zone where surface melting occurs on at least a few days a year because the snowpack structure and its temporal variations are too complex in contrast the accuracy is reasonably good in the dry zone and varies between 2 and 4 k depending on the frequency and polarization of observations and on the location at the antarctic scale the error is larger where wind is usually stronger suggesting either that meteorological data are less accurate in windy regions or that some neglected processes e g windpumping surface scouring are important at dome c in calm conditions a detailed analysis shows that most of the error is due to inaccuracy of the era 40 air temperature 2 k finally the paper discusses the values of the optimized parameters and their spatial variations across the antarctic

melt detection in antarctic ice shelves using scatterometers and microwave radiometers ku band dual polarization radar backscatter measurements from the seawinds on quikscat scatterometer are used to determine periods of surface freeze and melt in the antarctic ice shelves the normalized horizontal polarization radar backscatter sigmao and backscatter polarization ratio are used in maximum likelihood estimation of the ice state this method is used to infer the daily ice surface conditions for 25 study locations located on the ronne ross larsen amery shackleton and other ice shelves the temporal and spatial variations of the radar response are observed for various neighborhood sizes surrounding each given location during the study period criteria for determining the dates of melt onset and freeze up for each austral summer are presented validation of the ice state and melt onset date estimates is performed by analyzing the corresponding brightness temperature tb measurements from special sensor microwave imager ssm i radiometers quikscat sigmao measurements from 1999 to 2003 are analyzed and found to be effective in determining periods of melt in antarctic ice sheets at high temporal and spatial resolutions these estimates can be used in studies of the climatic effects of the seasonal and interannual melting of the antarctic ice sheets

interannual variations of snowmelt and refreeze timing on southeast alaskan icefields u s a twice daily satellite observations from the special sensor microwave imager ssm i indicate melt onset and refreeze on southeast alaskan icefields melt and refreeze are based on 37 ghz vertically polarized brightness temperatures t b and diurnal amplitude variations dav two types of melt regime have different summer characteristics onset is characterized by increasing average daily t b and a switch from low to high amplitude dav melt timing calibrated using juneau icefield temperatures correlates well with nearby stream hydrographs some pixels maintain high t b throughout the melt season and return to low amplitude dav after melt onset refreeze on these pixels is identified by decrease in t b and accompanying high amplitude dav other pixels maintain high dav throughout the summer indicating nocturnal refrecze fall refreeze is determined by the end of high amplitude dav interannual variability in melt timing and ablation season length is high melt onset and refreeze timing show a regional tendency toward earlier glacier melt onset and longer ablation seasons from 1988 98

modeling the microwave emission of bubbly ice applications to blue ice and superimposed ice in the antarctic and arctic passive microwave remote sensing is extensively used in polar regions to study the cryosphere to better understand the measured signal above continental ice covered areas our objective is to estimate the microwave emission of bubbly ice surfaces using a physically based multilayer electromagnetic model i e the dense media radiative transfer multilayer model dmrt ml this model accounts for ice layers with variable amounts of bubbles each layer is fully described by its temperature density thickness and air bubble radius simulations are performed using in situ data from two distinct sites one in antarctica on a coastal blue ice area near the cap prud homme cph station in adelie land and the other on the barnes ice cap bic located on baffin island in the arctic on this ice cap superimposed ice with seasonal snow cover about 1 m thick was observed in both cases several ice parameters were measured or estimated and the others were optimized results of the dmrt ml simulations are compared with in situ surface based radiometer sbr measurements at 11 19 and 37 ghz at both horizontal and vertical polarizations results show that dmrt ml is able to reproduce the microwave emission of different ice types with good accuracy when accounting for ice bubbles final hbox rmse 7 37 hbox k and 8 42 k for cph and bic respectively compared with rmse ranging from 15 k to 40 k without bubbles comparisons between sbr measurements and satellite data for the bic also show good agreement hbox rmse 4 1 hbox k for 19 and 37 ghz both polarizations

mineral chemistry and oxygen isotopic analyses of uraninite pitchblende and uranium alteration minerals from the cigar lake deposit saskatchewan canada abstract the cigar lake unconformity type u deposit is one of the largest and highest grade u deposits in the proterozoic athabasca basin northern saskatchewan canada cigar lake has recently been the focus of an international 3 a collaborative program in which this u deposit was studied as a natural analogue for a spent nuclear fuel repository the deposit is located near the eastern margin of the athabasca basin 430 m below the surface at the intersection between hudsonian age faults and the unconformity between athabasca group sandstones and aphebian metasediments three stages of u mineralization have been identified based on cross cutting relationships and textures observed in thin section and back scattered electron bse images o isotope data and chemical compositions all stages of u mineralization have been variably altered to ca rich u hydrate minerals or uranyl oxide hydrate minerals and coffinite u pb chemical ages of the 3 stages of u mineralization from cigar lake coincide with the 3 major fluid events that precipitated clay and silicate minerals at 1500 ma 950 ma and 300 ma throughout the entire athabasca basin stage 1 and 2 uraninite and pitchblende have the lowest 18o values that range from 30 1 to 15 2 whereas stage 3 uraninite has 18o values ranging from 10 0 to 3 4 uranyl oxide hydrate minerals have 18o values that range from 11 3 to 8 2 whereas uranyl minerals have much higher 18o values based on u pb chemical ages 18o values and petrographic relationships of u alteration minerals associated with primary u mineralization the cigar lake u ore is similar to u ore from other unconformity type u deposits in the athabasca basin therefore the cigar lake ore deposit although surrounded by clay and sandstone barriers has been effected by the same fluid events that have altered other unconformity type u deposits in the athabasca basin the 3 stages of ore formation and associated alteration minerals permit the detailed study of fluids responsible for u deposition and alteration this information provides the necessary context for the evaluation of the cigar lake deposit as a natural analogue for the disposal of spent nuclear fuel in underground vaults in rocks of the canadian shield

geophones on a board we examined the feasibility of using seismic reflections to image the upper 10 m of the earth s surface quickly and effectively by rigidly attaching geophones to a wooden board at 5 cm intervals the shallow seismic reflection information obtained was equivalent to control test data gathered using classic single geophone plants with identical 5 cm intervals tests were conducted using both a 22 caliber rifle source and a 30 06 rifle source in both cases the results were unexpected in response to our use of small high resolution seismic sources at offsets of a few meters we found little intergeophone interference that could be attributed to the presence of the board furthermore we noted very little difference in a 60 ms intra alluvial reflection obtained using standard geophone plants versus that obtained using board mounted geophones for both sources amplitude spectra were nearly identical for data gathered with and without the board with the 30 06 source filtering at high frequency passbands

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

formation and composition of rhabdophane bastnasite and hydrated thorium minerals during alteration implications for geochronology and low temperature processes abstract an investigation of accessory minerals in plutonic rocks from central madagascar reveals local very low grade alteration of the primary ree and th bearing phases monazite lree th po4 allanite careefe2 al2 sio7 sio4 o oh and thorite thsio4 all examples are found in relatively fresh looking samples in which alteration occurs on the micron to submicron scale the alteration occurs associated with micro fissures and predominantly affects the accessory minerals one type of alteration is replacement of thorite and monazite by thorogummite th u sio4 oh 4 and rhabdophane reepo4 h2o some of these secondary phases grow topotactically on the original magmatic crystals during development of rhabdophane pb and th can be transferred from the monazite precursor to rhabdophane resulting in similar apparent ages for both phases a second type of alteration has been investigated in two granites where bastnasite reeco3f forms at the expense of allanite which requires a fluid containing h2o co2 and f in either type of alteration mass transport of pb is deduced from galena development in the vicinity of the altered mineral in other examples mass transport of ree is assumed based on ree fractionation in secondary phases th rich minerals th rich monazite thorite are more affected by alteration than th poor phases this may be due to chemical disequilibrium at low temperatures or partial metamictization before alteration overlooking such alterations can lead to pitfalls during dating

ice shelf tidal motion derived from ers altimetry 1 ocean tides beneath floating ice shelves can affect heat and water circulations within the subshelf cavity which may influence patterns of basal melting accurate tidal predictions are essential to eliminate vertical tide motions when mapping the flow speeds and thickness changes of floating ice global ocean tide solutions are typically accurate to 2 3 cm in amplitude however their coarse resolution limits their utility in coastal regions moreover the absence of satellite and extensive gauge station data in the polar regions has resulted in significant differences between recent tide model solutions around the antarctic continent we use 9 years of high resolution european remote sensing ers satellite radar altimeter range measurements and a modified form of the orthotide method to generate tidal solutions for a series of ice shelves around the antarctic peninsula we compare our tidal solution at george vi ice shelf on the western coast of the antarctic peninsula to direct measurements from british antarctic survey tide gauge records and contrast the results with solutions from the fes99 and kantha2 0 global and the cats01 02 antarctic ocean tide models the average root mean square vector difference between the tide gauge and tide model predictions of amplitude and phase was 10 9 17 1 4 2 and 15 4 cm for the ers ice shelf kantha2 0 cats01 02 and fes99 models respectively tidal predictions derived from the ers ice shelf model are closer to the tide gauge recordings than those of the global models and the inclusion of ers altimeter data may lead to improved global model performance

spatial variability of snowmelt timing from amsr e and ssm i passive microwave sensors pelly river yukon territory canada spring snow melt run off in high latitude and snow dominated drainage basins is generally the most significant annual hydrological event melt timing duration and flow magnitude are highly variable and influence regional climate geomorphology and hydrology arctic and sub arctic regions have sparse long term ground observations and these snow dominated hydrologic regimes are sensitive to the rapidly warming climate trends that characterize much of the northern latitudes passive microwave brightness temperatures are sensitive to changes in the liquid water content of the snow pack and make it possible to detect incipient melt diurnal melt refreeze cycles and the approximate end of snow cover on the ground over large regions special sensor microwave imager ssm i and advanced microwave scanning radiometer for eos amsr e passive microwave brightness temperatures tb and diurnal amplitude variations dav are used to investigate the spatial variability of snowmelt onset timing in two stages dav onset and melt onset and duration for a complex sub arctic landscape during 2005 the satellites are sensitive to small percentages of liquid water and therefore represent incipient melt a condition somewhat earlier than a traditional definition of a melting snowpack incipient melt dates and duration are compared to topography land cover and hydrology to investigate the strength and significance of melt timing in heterogeneous landscapes in the pelly river a major tributary to the yukon river microwave derived melt onset in this region in 2005 occurred from late february to late april upland areas melt 1 2 weeks later than lowland areas and have shorter transition periods melt timing and duration appear to be influenced by pixel elevation aspect and uniformity as well as other factors such as weather and snow mass distribution the end of the transition season is uniform across sensors and across the basin in spite of a wide variety of pixel characteristics copyright 2007 john wiley sons ltd

spatial and temporal variability of antarctic ice sheet microwave brightness temperatures 1 annual and interannual variability of 21 years of passive microwave brightness temperatures on the antarctic ice sheet is documented through principal component analysis the leading modes show that brightness temperatures are dominantly forced by the annual temperature cycle with surface melting signals explaining about 5 of the total variance of the data analysis of the data with the annual cycle and melting signals removed results in two significant interannual modes the first is consistent with the antarctic oscillation and its influence on antarctic surface temperatures while the second reflects regional scale variability that appears to be linked to sea ice anomalies and the el nino southern oscillation the expression of these characteristic patterns of southern hemisphere climate variability on the antarctic continent provides a framework for interpreting modern climate records as well as a basis for reconstructing past climate variability with ice cores

snowmelt on the greenland ice sheet as derived from passive microwave satellite data abstract the melt extent of the snow on the greenland ice sheet is of considerable importance to the ice sheet s mass and energy balance as well as arctic and global climates by comparing passive microwave satellite data to field observations variations in melt extent have been detected by establishing melt thresholds in the cross polarized gradient ratio xpgr the xpgr defined as the normalized difference between the 19 ghz horizontal channel and the 37 ghz vertical channel of the special sensor microwave imager ssm i exploits the different effects of snow wetness on different frequencies and polarizations and establishes a distinct melt signal using this xpgr melt signal seasonal and interannual variations in snowmelt extent of the ice sheet are studied the melt is found to be most extensive on the western side of the ice sheet and peaks in late july moreover there is a notable increasing trend in melt area between the years 1979 and 1991 of 4 4 per year which came to an abrupt halt in 1

distribution of rare earth elements and oxyhydroxide phases within a weathered felsic igneous profile in hong kong abstract variation in type and abundance of oxyhydroxide phases and the fractionation of rare earth elements ree within a weathered felsic pyroclastic profile in hong kong were investigated in order to assess the key factors and micro environmental conditions controlling their distribution during weathering at rock and mineral scales three types of oxyhydroxide phases fe mn and ce rich were recognized based on their most abundant elements the fe rich types appeared in all samples at different stages of weathering the mn rich types however were limited to samples at advanced stages of weathering while the ce rich types were found solely in samples from oxyhydroxide rich zones fractionation of ree likely started at the early stages of weathering but became evident only at the advanced stages characteristics of ree patterns especially the direction negative or positive and extent of ce anomalies correlated very well with the appearance and abundance of mn oxyhydroxides and were attributed to the co existence of distinct micro environmental conditions within the profile these conditions resulted from two major competing processes leaching and fixation and oxidation precipitation and reduction dissolution which operated simultaneously within the profile at any given stage of weathering

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

some sh wave seismic reflections from depths of less than three metres shallow sh wave reflections are far from routine although their study can provide insights into important properties of near surface materials that cannot be inferred from p wave data alone difficulties in separating sh wave reflections from love waves are generally considered the major obstacle to progress in shallow sh wave seismic reflection this may be the case in surveys undertaken at great depths but it is not necessarily true for reflection data gathered at shallow and ultra shallow depths this paper shows that when sh wave data possess wavelengths greater than the thickness of the superficial layer love waves are not greatly dispersed in this case misinterpretation between parts of reflection hyperbolae and waveguide arrivals is sufficiently limited in a one layer model earth which well approximates typical situations of the near surface underground the most energetic modes the lowermost modes of the dispersed surface waves have a dominant frequency band that falls below the wavelet spectrum of the shallow reflections therefore they can be filtered out in the frequency domain higher modes although their spectral content overlaps that of the reflections exhibit small amplitudes on seismograms and leave strong reflections unaffected we present field examples from three different sites where we were able to obtain ultra shallow reflections 3 m in unconsolidated sediments the high level of resolution vertical resolution up to 15 cm suggests that sh wave reflection imaging has the potential to complement other high resolution techniques such as p wave reflection and ground penetrating radar gpr imaging allowing a better and more complete characterization of the near surface environments

avoiding pitfalls in shallow seismic reflection surveys acquiring shallow reflection data requires the use of high frequencies preferably accompanied by broad bandwidths problems that sometimes arise with this type of seismic information include spatial aliasing of ground roll erroneous interpretation of processed airwaves and air coupled waves as reflected seismic waves misinterpretation of refractions as reflections on stacked common midpoint cmp sections and emergence of processing artifacts processing and interpreting near surface reflection data correctly often requires more than a simple scaling down of the methods used in oil and gas exploration or crustal studies for example even under favorable conditions separating shallow reflections from shallow refractions during processing may prove difficult if not impossible artifacts emanating from inadequate velocity analysis and inaccurate static corrections during processing are at least as troublesome when they emerge on shallow reflection sections as they are on sections typical of petroleum

ice sheet elevation changes caused by variations of the firn compaction rate induced by satellite observed temperature variations 1982 2003 changes in the surface elevation of the greenland and antarctic ice sheets and ice shelves caused by variations in the rate of firn compaction are calculated with a time dependent firn densification model driven by two decades 1982 2003 of satellite observed monthly surface temperatures the model includes the effects of melting and refreezing both the direct changes in density and the subsequent effects on the densification rate as previously shown the temperature dependent rate of densification is largest in summer but changes in winter temperatures also have a significant effect over the last decade climate warming has enhanced the rate of compaction and lowered the average surface elevation of greenland by 1 8 cma 1 and most of west antarctica by 1 9 cma 1 in east antarctica a small cooling raised the average surface elevation by 0 14 cma 1

near surface seismic reflection profiling of the matanuska glacier alaska several common midpoint seismic reflection profiles collected on the matanuska glacier alaska clearly demonstrate the feasibility of collecting high quality high resolution near surface reflection data on a temperate glacier the results indicate that high resolution seismic reflection can be used to accurately determine the thickness and horizontal distribution of debris rich ice at the base of the glacier the basal ice thickens about 30 over a 300 m distance as the glacier flows out of an overdeepening the reflection events ranged from 80 to 140 m depth along the longitudinal axis of the glacier the dominant reflection is from the contact between clean englacial ice and the underlying debris rich basal ice but a strong characteristic reflection is also observed from the base of the debris rich ice bottom of the glacier the p wave propagation velocity at the surface and throughout the englacial ice is 3600 m s and the frequency content of the reflections is in excess of 800 hz supporting d

genesis of kasolite associated with aplite pegmatite at jabal sayid hijaz region kingdom of saudi arabia abstract in this study we report kasolite pb uo 2 sio 4 h 2 o for the first time as a main uranyl mineral in the mineralized aplite pegmatite of jabal sayid hijaz region it commonly forms clusters of yellow acicular crystals in the voids and fractures the mineral chemistry and mineralogical characteristics of kasolite were investigated using different techniques calcium iron and phosphorus are detected in kasolite in addition to its major constituents uranium lead and silicon lead does not exist as a radiogenic product and not even as a substitute for uranium in the mineral structure alternatively galena mineralization could be considered as a source for lead the fluoride and carbonate complexes played a significant role in the formation of kasolite high temperature hydrothermal solutions reacted with pre existing uranium bearing metamictized accessory minerals such as pyrochlore u rich thorite and zircon to form uranous fluoride complexes these complexes are predominant in reducing environment and at ph 4 when the fluids approached the surface passing through fracture system the oxygen fugacity f o 2 and the ph increased because of the loss of volatile components at these conditions uranous fluorides would convert to uranyl fluoride complexes uo 2 f 3 further decrease in temperature was associated with the decay of the activity of fluorine ion by the dilution of hydrothermal solutions and precipitation of fluorite at this condition uranyl carbonate complexes are favoured these complexes were combined later with silica and lead to form kasolite

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

assessment and development of snowmelt retrieval algorithms over antarctica from k band spaceborne brightness temperature 1979 2008 abstract results from several previously published algorithms for wet snow detection in antarctica from k band spaceborne brightness temperature are compared and evaluated vs estimates of wet snow conditions from ground measurements in addition a new physically driven algorithm in which the detectable liquid water content is assumed constant is proposed and assessed all algorithms are also evaluated by analyzing their results during collapses of ice shelves two algorithms are selected for deriving updated trends of melting index mi the number of melting days times the area subject to melting between 1979 and 2008 over the whole antarctica and at sub continental scales in the first algorithm wet snow is identified when brightness temperature exceeds the mean of winter brightness temperature plus 30 k and the second is the new model based approach described here both negative and positive mi trends are obtained depending on the algorithm used a high number of melting days up to 100 days are detected over the wilkins ice shelf the peninsula and the george vi ice shelf over east antarctica the west and amery ice shelves are subject to melting for a maximum of approximately 50 days positive trends of number of melting days are detected over most of the west antarctica with peak values up to 1 2 days year over the larsen c ice shelf 1 8 days year over the george vi ice shelf and 0 55 days year over the wilkins ice shelf area the correlation between mi values and december january dj averaged air surface temperature over selected locations show values ranging between 0 8 and 0 4 results suggest that a 1 c increase in the monthly averaged dj air surface temperature corresponds to an average mi increase of approximately 2 106 km2 day

large near surface velocity gradients on shallow seismic reflection data extreme velocity gradients occasionally present within near surface materials can inhibit optimal common midpoint cmp stacking of near surface reflection arrivals for example abrupt increases in velocity are observed routinely at the bedrock surface and at the boundary between the vadose and the saturated zone when a rapid increase in near surface velocity is found nmo correction artifacts manifested on cmp gathers as sample reversion sample compression or duplication of reflection wavelets can reduce s n ratio on stacked data or can stack coherently elimination of these nonstretch related artifacts using conventional nmo stretch muting requires near vertically incident reflection arrivals and allowable stretch ratios as small as 5 in some shallow environments radical allowable stretch mutes are not a feasible means to subdue these artifacts if high amplitude coherent noise on near offset traces inhibits identification and digital enhancement of shallow reflections on most shallow seismic refl

seismic reflections from depths of less than two meters three distinct seismic reflections were obtained from within the upper 2 1 m of flood plain alluvium in the ar kansas river valley near great bend kansas reflections were observed at depths of 0 63 1 46 and 2 10 m and confirmed by finite difference wave equation modeling the wavefield was densely sampled by placing geophones at 5 cm intervals and near source nonelastic deformation was minimized by us ing a very small seismic impulse source for the reflections to be visible within this shallow range low seismic p wave ve locities 300 m s and high dominant frequency content of the data 450 hz were essential the practical implementa tion of high resolution seismic imaging at these depths has the potential to complement ground penetrating radar gpr chiefly in areas where materials exhibiting high electrical con ductivity such as clays prevent the effective use of gpr potential applications of these results exist in hydrogeology and environmental quaternary and neotectonic geology

in situ high frequency p wave velocity measurements within 1 m of the earth s surface seismic p wave velocities in near surface materials can be much slower than the speed of sound waves in air normally 335 m s or 1100 ft s difficulties often arise when measuring these low velocity p waves because of interference by the air wave and the air coupled waves near the seismic source at least when gathering data with the more commonly used shallow p wave sources additional problems in separating the direct and refracted arrivals within 2 m of the source arise from source generated nonlinear displacement even when small energy sources such as sledgehammers small caliber rifles and seismic blasting caps are used using an automotive spark plug as an energy source allowed us to measure seismic p wave velocities accurately in situ from a few decimeters to a few meters from the shotpoint we were able to observe three distinct p wave velocities at our test site 130m s 180m s and 300m s even the third layer which would normally constitute the first detected layer in a shallow seismic

an ultrashallow sh wave seismic reflection experiment on a subsurface ground model an sh wave seismic reflection experiment was conducted to evaluate the feasibility and cost effectiveness of reflection imaging ultrashallow targets commonly encountered in engineering groundwater and environmental investigations it was carried out on a purpose built subsurface ground model consisting of a concrete layer at a depth from 2 85 5 m and a low velocity overburden 80 and 150 m s for s and p waves respectively constituted of filling material with the water table 2 60 m deep high quality cdp data acquired by using a 10 kg sledgehammer and newly designed horizontal detectors allowed us to obtain an extremely detailed stacked section with a minimal amount of processing uncertainty in determining the depth and horizontal dimensions of the concrete model was estimated to be 0 2 and 0 3 m respectively however the dominant frequencies lower than 150 hz the low transmission coefficient at the upper interface and the relatively high velocity 900 m s of the concrete layer prevented

muting the noise cone in near surface reflection data an example from southeastern kansas a 300 m near surface seismic reflection profile was collected in southeastern kansas to locate a fault s associated with a recognized stratigraphic offset on either side of a region of unexposed bedrock a substantial increase in the s n ratio of the final stacked section was achieved by muting all data arriving in time after the airwave methods of applying traditional seismic data processing techniques to near surface data 200 ms of data or less often differ notably from hydrocarbon exploration scale processing 3 4 s of data or more the example of noise cone muting used is contrary to normal exploration scale seismic data processing philosophy which is to include all data containing signal the noise cone mute applied to the data removed more than one third of the total data volume some of which contains signal in this case however the severe muting resulted in a higher s n ratio in the final stacked section even though some signal could be identified within the muted data this example supports the suggestion that nontraditional techniques sometimes need to be considered when processing near surface seismic data

passive microwave ssm i satellite predictions of valley glacier hydrology matanuska glacier alaska 1 we advance an approach to use satellite passive microwave observations to track valley glacier snowmelt and predict timing of spring snowmelt induced floods at the terminus using 37 v ghz brightness temperatures tb from the special sensor microwave imager ssm i we monitor snowmelt onset when both tb and the difference between the ascending and descending overpasses exceed fixed thresholds established for matanuska glacier melt is confirmed by ground measured air temperature and snow wetness while glacier hydrologic responses are monitored by a stream gauge suspended sediment sensors and terminus ice velocity measurements accumulation area snowmelt timing is correlated r2 0 61 to timing of the annual snowmelt flood peak and can be predicted within 5 days

fate of trace elements during alteration of uraninite in a hydrothermal vein type u deposit from marshall pass colorado usa alteration of uraninite from a hydrothermal vein type u deposit in marshall pass colorado has been examined by electron microprobe analysis in order to investigate the release and migration of trace elements w as mo zr pb ba ce y ca ti p th fe si al during alteration under both reducing and oxidizing conditions the release of trace elements from uraninite is used to establish constraints on the release of fission product elements from the uo2 in spent nuclear fuels uraninite occurs with two different textures 1 colloform uraninite and 2 fine grained uraninite the colloform uraninite contains 1 04 1 75 wt of wo3 0 16 1 70 wt of as2o3 0 06 0 88 wt of moo3 whereas the fine grained uraninite retains 2 25 4 93 wt of wo3 up to 5 76 wt of moo3 and 0 26 0 60 wt of as2o3 the near constant concentration of incompatible w in the colloform uraninite suggests w incorporation into the uraninite structure or homogeneous distribution of w rich nano domains incorporation of w and mo into the uraninite and subsequent precipitation of uranyl phases bearing these elements are critically important to understanding the release and migration of cs during the corrosion of spent nuclear fuel as there is a strong affinity of cs with w and mo zoning in the colloform texture is attributed to variation in the amount of impurities in uraninite for unaltered zones the calculated amount of oxygen ranges from 2 08 to 2 32 apfu atom per formula unit and defines the stoichiometry as uo2 x and u4o9 whereas for the altered zones of the colloform texture the oxygen content is 2 37 2 48 apfu which is probably due to the inclusion of secondary uranyl phases mainly schoepite the supergene alteration resulted in precipitation of secondary uranyl minerals at the expense of uraninite four stages of colloform uraninite alteration are proposed i formation of an oxidized layer at the rim ii corrosion of the oxidized layer iii precipitation of u6 phases with well defined cleavage and iv fracture of the uraninite surface along the cleavage planes of the u6 phases

mobility of uranium during weathering mineralogical and geochemical mechanisms of u fixation under oxidizing conditions in the vicinity of the secondary u ore deposit at koongarra australia were examined using transmission and scanning electron microscopy and thermodynamic calculations the formation of saleeite mg uo 2 2 po 4 2 1oh 2 o is the predominant mechanism for u fixation upstream from the deposit where saleeite replaces sklodowskite and granular apatite within the deposit and further downstream u is fixed in microcrystals 10 50 nm of saleeite and meta torbernite scattered within veins of fine grained 2 50 nm fe super 3 minerals primarily goethite and hematite thermodynamic calculations indicate the groundwater is undersaturated with respect to saleeite and metatorbernite and that these minerals should precipitate at higher u or p concentrations than observed this suggests that the upstream saleeite precipitated at the reaction interfaces of dissolving sklodowskite and apatite under local saturation conditions observed textural relationships of saleeite and meta torbernite microcrystals with the fe minerals combined with thermodynamic calculations suggest surface precipitation as the formation mechanism for saleeite and meta torbernite microcrystals within and downstream from the secondary ore deposit phosphorous released during the aging of ferrihydrite and u adsorbed onto fe minerals are probably the sources of the major components of the microcrystals downstream the microcrystals exist where groundwater u concentrations are as low as 10 30 mu g l once released from the ore deposit u is fixed in uranyl phosphates even where measured groundwater is undersaturated with respect to uranyl phosphates the surface precipitation is an important example of long term post adsorption u fixation in a natural system the fully crystalline and radiation damaged microstructures of saleeite indicate uranyl phosphates have formed continuously or intermittently for the last few million years

persistent surface snowmelt over antarctica 1987 2006 from 19 35 ghz brightness temperatures 1 persistent melting e g continuing for more than three days or for one consecutive day and night is mapped in antarctica 1987 2006 using night and day time special sensor microwave imager brightness temperatures tb at 19 35 ghz horizontal polarization snowmelt is indicated when tb and relative daily difference exceed threshold values respectively tc and t computed for each pixel and year or when both daytime and nighttime tb exceed tc results from an electromagnetic model suggest that the minimum detectable liquid water content ranges between 0 2 and 0 5 in volume we find that melting areas have been moving inland since 1987 a first time extensive melting 1987 2006 is detected over the transantarctic mountains on january 2005 875 km inland and 2000 m above sea level melting extent and index have been decreasing over antarctica since 1987 although either positive and negative trends are observed from a sub continental scale analysis

migration of shallow seismic reflection data we present an analysis of migration effects on seismic reflection images of very shallow targets such as those that are common objectives of engineering groundwater and environmental investigations we use an example of seismic reflection data from depths of 5 to 15 m that show negligible effect from migration despite the apparent steep dip on the seismic section our analysis of the question of when to migrate shallow reflection data indicates it is critical to take into account the highly variable near surface velocities and the vertical exaggeration on the seismic section a simple set of calculations is developed as well as a flow chart based on the migrator s equation that can predict whether migration of an arbitrary shallow seismic section is advisable because shallow reflection data are often processed on personal computers unnecessary migration of a large data set can be prohibitively time consuming and wasteful