internal layer tracing and age depth accumulation relationships for the northern greenland ice sheet clues to previous ice sheet structure and long term glaciological processes are preserved in the internal layering configuration of the greenland ice sheet information about these internal layers has been retrieved over many parts of the ice sheet with the university of kansas ice penetrating radar we report on the coherence of these layers over very large distances describe a method of tracing these layers along thousands of kilometers of flight line and do so for one flight during the 1999 program for arctic regional climate assessment parca aircraft campaign we determine the ages of these layers based on information at the grip ice core site and extend these ages along the flight line to camp century where they are compared to modeled derived age estimates these ages agree with each other to between 2 and 15 differences that can be substantially reduced with minor changes to the model parameters accumulation rate and shear layer depth finally we are able to derive estimates of accumulation rates along the flight line by fitting the age depth data from layer tracing to a dansgaard johnsen model with a minimization technique providing estimates that match recent accumulation patterns within a few centimeters per year

trace fossils biology and taphonomy 1990 special topics in palaeontology 3 280 pp e17 95 pbk e40 00 hbk unwin hyman london isbn 004445 6867 pbk 3035 hbk

modeling of sh wave propagation in an irregularly layered medium application to seismic profiles near a dome campillo m 1987 modeling of sh wave propagation in an irregularly layered medium application to seismic profiles near a dome geophysical prospecting 35 236249 an approach that relies on a discrete representation of seismic wavefields allows the computation of synthetic sh seismograms in a laterally varying medium with plane and curved interfaces in the two dimensional 2 d case the diffracting interfa is represented by an array of body forces located along the interfa at equal spacing the numerical treatment is limited to the irregular boundary while the propagation in fiat layered zones is obtained by the refiection transmission matrix method as an example we have studied the case of a dome in a stratified medium the solutions obtained verify the reciprocity theorem with good accuracy the computation of vertical profiles and of surface refiection profiles illustra tes the effects of diffraction and the importance of lateral propagation in such a structure

comments on the paper reconnaissance of upper jurassic morrison formation ichnofossils rocky mountain region usa paleoenvironmental stratigraphic and paleoclimatic significance of terrestrial and freshwater ichnocoenoses by stephen t hasiotis

reconstructing ice sheet accumulation rates at ridge b east antarctica understanding how ice sheets responded to past climate change is fundamental to forecasting how they will respond in the future numerical models calculating the evolution of ice sheets depend upon accumulation data which are principally available from ice cores here we calculate past rates of ice accumulation using internal layering the englacial structure of the east antarctic ice divide at ridge b is extracted from airborne ice penetrating radar the isochronous surfaces are dated at their intersection with the vostok ice core site where the depth age relationship is known the dated isochrons are used as input to a one dimensional ice flow model to investigate the spatial accumulation distribution the calculations show that ice accumulation rates generally increase from vostok lake towards ridge b the western flank of the ice divide experiences markedly more accumulation than in the east further ice accumulation increases northwards along the ice divide the results also show the variability of accumulation in time and space around the ridge b ice divide over the last 124 000 years

influence of ice crystal anisotropy on seismic velocity analysis in 2010 a reflection seismic survey was carried out on the alpine glacier colle gnifetti the processed and depth converted data could be compared to a nearby ice core drilled almost to the bed comparisons showed that the depth of the p wave bed reflection was too shallow while the depth of the sh wave bed reflection fitted the ice core length well we are now able to explain the major part of these differences using the existing crystal orientations of the ice at colle gnifetti we calculate anisotropic velocities for p and sh waves that are usually picked for stacking and compare them with zero offset velocities needed for the depth conversion here we take the firn pack at colle gnifetti into account for p and s wave analysis to incorporate the s wave analysis we first derive a new equation for the relationship between density and s wave velocity from diving waves we show that anisotropic fabrics observed at colle gnifetti introduce a difference of only 1 between stacking and depth conversion velocities for the sh wave but 7 for the p wave we suggest that this difference in stacking and depth conversion velocity for the p wave can be used to derive information about the existing anisotropy by combining our seismic data with for example radar data

a method to reconstruct past accumulation rates in alpine firn regions a study on fiescherhorn swiss alps annual snow layers in the accumulation zone of glaciers become thinner by viscous deformation while moving to greater depth the reconstruction of the accumulation rate history requires the correction of the thickness of annual layers we apply a novel method to determine the vertical velocity by repeated survey with a caliper probe of grooves scratched into the wall of a borehole with this information and the assumptions of steady state velocity and density fields the correction of layer thicknesses can be determined without knowledge of the ice density profile and thus can be applied to boreholes without ice cores the method is applied to a borehole on fiescherhorn swiss alps resulting in a substantially larger correction than with the simpler method of nye 1963 copyright 2006 by the american geophysical union

a quantitative comparison of microfossil extraction methods from ice cores microfossil records from ice archives allow vegetation fire and land use activity reconstructions on broad spatial scales samples typically contain low microfossil concentrations therefore large ice volumes are often needed for palynology hence it is crucial to extract maximum microfossil numbers through appropriate physical chemical treatments we compare six methods covering the main water reduction procedures evaporation filtration and centrifugation with snow samples adding a known number of lycopodium marker spores prior to sample treatment and a second marker eucalyptus after laboratory processing allows a quantitative microfossil loss assessment during pollen extraction we applied the best performing method average loss of 22 to high alpine firn cores from colle gnifetti glacier for validation with a natural archive containing extremely low microfossil concentrations we conclude that samples processed with different microfossil extraction protocols may give different results for pollen concentrations percentages and ratios between different pollen types especially if vesiculate conifer pollen is an important pollen assemblage component we recommend a new evaporation based method which delivers the smallest and least variable losses among the tested approaches since microfossil losses are inevitable during laboratory procedure adding markers prior to sample processing is mandatory to achieve reliable microfossil concentration and influx estimates

multiwell study of seismic attenuation at the co2crc otway project geosequestration site comparison of amplitude decay centroid frequency shift and 1d waveform inversion methods

snow accumulation and ice flow at dome du gouter 4300 m mont blanc french alps glaciological experiments have been carried out at dome du gouter 4300 m a s l mont blanc in order to understand the flow of firn ice in this high altitude alpine glacierized area accumulation measurements from stakes show a very strong spatial variability and an unusual feature of mass balance fluctuations for the alps i e the snow accumulation does not show any seasonal patterns measured vertical velocities which should match with long term mean mass balance are consistent with observed accumulations therefore the measurement of vertical velocities seems a good way of quickly obtaining reliable mean accumulation values for several decades in such a region a simple flow model can be used to determine the main flowlines of the glacier and to propose snow ice age of core samples from the two boreholes drilled down t the bedrock in june 1994 these results coincide with radioactivity measurements made to identify the well known radioactive snow layers of 1963 and 1986 we can hope to obtain ice samples 55 60 years old about 20 or 30 m above the bedrock 110 m deep below the deformation of the ice layers is loo great to be dated accurately

reconnaissance of upper jurassic morrison formation ichnofossils rocky mountain region usa paleoenvironmental stratigraphic and paleoclimatic significance of terrestrial and freshwater ichnocoenoses seventy five types of ichnofossils documented during a four year reconnaissance study in the upper jurassic morrison formation demonstrate that highly diverse and abundant plants invertebrates and vertebrates occur throughout most of the morrison or equivalent strata invertebrate ichnofossils preserving the most environmentally and climatically sensitive in situ behavior of morrison organisms are in nearly all outcrops terrestrial ichnofossils record biotic processes in soil formation indicating soil moisture and water table levels freshwater ichnofossils preserve evidence of water depth salinity and seasonality of water bodies ichnofossils categorized as epiterraphilic terraphilic hygrophilic and hydrophilic new terms reflect the moisture regime where they were constructed the ichnofossils are vertically zoned with respect to physical chemical and biological factors in the environment that controlled their distribution and abundance and are expressed as surficial shallow intermediate and deep the sedimentologic stratigraphic and geographic distribution of morrison ichnofossils reflects the environmental and climatic variations across the basin through time marginal marine tidal to brackish water ichnofossils are mainly restricted to the windy hill member very large to small termite nests dominate the salt wash member similar size ranges of ant nests dominate the brushy basin member soil bee nests dominate in the salt wash decreasing in abundance through the brushy basin deeper and larger insect nests indicate more seasonal distribution of precipitation and rainfall shallower and smaller insect nests indicate either dry or wet substrate conditions depending on the nest architecture and paleopedogenic and sedimentologic character of the substrate trace fossil indicators of flowing or standing water conditions are dominant in the tidwell member and in fluvial sandstones of the salt wash and brushy basin members large communities of perennial freshwater bivalve traces are abundant in the tidwell and brushy basin members but to a lesser extent in the salt wash member shallow crayfish burrows indicating a water table level close to the surface 1 m are restricted to channel bank and proximal alluvial deposits in the salt wash recapture and brushy basin members sauropod theropod pterosaur and other vertebrate tracks occur throughout the morrison formation associated with alluvial lacustrine and transitional marine shoreline deposits ichnofossils and co occurring paleosols in the morrison reflect the local and regional paleohydrologic settings which record the annual soil moisture budget and were largely controlled by the climate in the basin contributions to near surface biologic systems by groundwater from distant sources were minor except where the water table perennially seasonally or ephemerally intersected the ground surface the jurassic morrison formation in the southern portion of the basin experienced a mosaic of seasonal climates that varied from a drier tidwell windy hill deposition to a wetter lower and middle salt wash deposition and slightly drier upper salt wash deposition tropical wet dry climate returning to a wetter tropical wet dry climate near the end of morrison deposition brushy basin deposition the northern part of the basin experienced similar trends across a mosaic of mediterranean climate types the range and mosaic pattern of wet dry morrison climates is analogous to the range of climates and their seasonal variability that dominates the african savanna today

penny ice cap cores baffin island canada and the wisconsinan foxe dome connection two states of hudson bay ice cover ice cores from penny ice cap baffin island canada provide continuous holocene records of oxygen isotopic composition 18 o proxy for temperature and atmospheric impurities a time scale was established with the use of altered seasonal variations some volcanic horizons and the age for the end of the wisconsin ice age determined from the grip and gisp2 ice cores there is pre holocene ice near the bed the change in 18 o since the last glacial maximum lgm is at least 12 5 per mil compared with an expected value of 7 per mil suggesting that lgm ice originated at the much higher elevations of the then existing foxe dome and foxe ridge of the laurentide ice sheet the lgm 18 o values suggest thick ice frozen to the bed of hudson bay

a review of the discrete wavenumber method we present a review of the discrete wavenumber dwn method the method introduced by bouchon and art 1977 allows the simple and accurate calculation of the complete green s functions for many problems in elastodynamics

high altitude accumulation and preserved climate information in the western pamir observations from the fedchenko glacier accumulation basin the accumulation region of fedchenko glacier represents an extensive snow reservoir in the pamir mountains feeding the longest glacier in central asia observed elevation changes indicate a continuous ice loss in the ablation region of fedchenko glacier since 1928 while the mass balance of the accumulation region is largely unknown in this study we show that accumulation varies considerably in the main accumulation basin with accumulation rates up to 2400 mm w e a 1 in the west decreasing to 1 in the center although the elevation difference is

north america s largest dinosaur trackway site implications for morrison formation paleoecology little known exposures of the upper jurassic morrison formation from the purgatoire valley of southeastern colorado have yielded the world s largest continuously mapped assemblage of dinosaur trackways body fossils include plant invertebrate and vertebrate remains indicative of predominantly fresh water conditions the tracks occur in a lacustrine sequence characterized by 1 shallow water shales 2 micritic shoreface limestones with ooids intraclasts ripple marks mud cracks and 3 minor quartzose sandstone with salt crystal casts analysis of these sedimentary facies suggests that in southeastern colorado lakes were larger and longer lived than in other morrison paleoenvironments trackway orientations and footprint depth contours pinpoint the location of the paleoshoreline at successive levels in the section detailed mapping of 1 300 footprints in bed 2 has revealed more than 100 trackways which testify to the activity of both quadrupedal and bipedal dinosaurs the respective ratio based on trackway counts is 40 60 the quadrupedal tracks are attributed to sauropods and represent the first ever discovered in north america they also exhibit the first known manus claw impressions and are in need of formal description more than 90 of the bipedal tridactyl prints lack claw impressions and are tentatively therefore referred to the ornithopoda cf gypsichnites possibly a camptosaurus the small proportion with distinct claw impressions may represent allosaurus resulting estimates of species diversity 5 and predator prey ratio 1 30 are in general agreement with the estimates of other authors based on skeletal remains and they suggest that the purgatoire river tracks may accurately reflect the composition of the dinosaur fauna distinctive groupings of parallel non overlapping trackways suggest gregarious behavior among sauropods and tridactylous forms

a full stokes ice flow model to assist the interpretation of millennial scale ice cores at the high alpine drilling site colle gnifetti swiss italian alps the high alpine ice core drilling site colle gnifetti cg monte rosa swiss italian alps provides climate records over the last millennium and beyond however the full exploitation of the oldest part of the existing ice cores requires complementary knowledge of the intricate glacio meteorological settings including glacier dynamics here we present new ice flow modeling studies of cg focused on characterizing the flow at two neighboring drill sites in the eastern part of the glacier the3 d full stokes ice flow model is thermo mechanically coupled and includes firn rheology firn densification and enthalpy transport and is implemented using the finite element software elmer ice measurements of surface velocities accumulation borehole inclination density and englacial temperatures are used to validate the model output we calculate backward trajectories and map the catchment areas this constrains for the first time at this site the so called upstream effects for the stable water isotope time series of the two ice cores drilled in 2005 and 2013 the model also provides a 3 d age field of the glacier and independent ice core chronologies for five ice core sites model results are a valuable addition to the existing glaciological and ice core datasets this especially concerns the quantitative estimate of upstream conditions affecting the interpretation of the deep ice core layers

inference of accumulation rate patterns from deep layers in glaciers and ice sheets the spatial pattern of accumulation rate can be inferred from internal layers in glaciers and ice sheets non dimensional analysis determines where finite strain can be neglected shallow layer approximation or approximated with a local one dimensional flow model local layer approxima tion and where gradients in strain rate along particle paths must be included deep layers we develop a general geophysical inverse procedure to infer the spatial pattern of accumulation rate along a steady state flowband using measured topography of the ice sheet surface bed and a deep layer a variety of thermomechanical ice flow models can be used in the forward problem to calculate surface topography and ice velocity which are used to calculate particle paths and internal layer shapes an objective tolerance criterion prevents over fitting the data after making site specific simplifications in the thermomechanical flow algorithm we find the accumulation rate along a flowband through taylor mouth a flank site on taylor dome antarctica using a layer at approximately 100 m depth or 20 of the ice thickness accumulation rate correlates with ice surface curvature at this site gradients along flow paths critically impact inference of both the accumulation pattern and the depth age relation in a 100 m core

delineation of a complexly dipping temperate glacier bed using short pulse radar arrays we have defined the complex bed topography for a section of a small temperate glacier using 50 mhz monostatic short pulse radar data and a synthetic aperture array processing method the data were collected on a 100 m by 340 m array grid in the upper stem of gulkana glacier central alaska u s a the array processing was based on a modified three dimensional 3 d kirchhoff migration integral and implemented with a synthetic aperture approach that uses sequences of overlapping sub arrays to generate depth images in vertical planes typical sub array beam patterns are generally 5 at the 6 db level giving a flashlight like searching capability without distorting the wavelet shape the bed topography was constructed using normal reflections picked from 3 d array depth images in some instances reflections were imaged outside the data coverage area the bed surface dips steeply both parallel and transverse to the direction of ice flow the maximum observed depth is roughly 140 m the 3 d method resolved bed dips up to 45 in regions of steepest dip it improved depth accuracy by 36 compared with raw data and by 15 compared with standard two dimensional 2 d migration over 12 db of signal to noise improvement and improved spatial resolution was achieved compared to raw data and 2 d migration false bottom layering seen in the raw data and in 2 d migrations is not observed in the 3 d array results furthermore loss of bottom reflections is shown by the 3 d migration to be attributable to the dip and curvature of the reflector and not scattering losses or signal clutter from englacial inclusions

trace fossil analysis of lacustrine facies and basins abstract two ichnofacies are typical of lacustrine depositional systems the scoyenia ichnofacies characterizes transitional terrestrial nonmarine aquatic substrates periodically inundated or desiccated and therefore is commonly present in lake margin facies the mermia ichnofacies is associated with well oxygenated permanent subaqueous fine grained substrates of hydrologically open perennial lakes bathymetric zonations within the mermia ichnofacies are complicated by the wide variability of lacustrine systems detected proximal distal trends are useful within particular lake basins but commonly difficult to extrapolate to other lakes other potential ichnofacies include the typically marine skolithos ichnofacies for high energy zones of lakes and substrate controlled still unnamed ichnofacies associated to lake margin deposits trace fossils are useful for sedimentologic analysis of event beds lacustrine turbidites are characterized by low diversity suites reflecting colonization by opportunistic organisms after the turbidite event underflow current beds record animal activity contemporaneous with nearly continuous sedimentation ichnologic studies may also help to distinguish between marine and lacustrine turbidites deep marine turbidites host the nereites ichnofacies that consists of high diversity of ornate grazing traces and graphoglyptids recording highly specialized feeding strategies developed to solve the problem of the scarcity of food in the deep sea deep lacustrine environments contain the mermia ichnofacies which is dominated by unspecialized grazing and feeding traces probably related to the abundance and accessibility of food in lacustrine systems the lower diversity of lacustrine ichnofaunas in comparison with deep sea assemblages more likely reflects lower species diversity as a consequence of less stable conditions increase of depth and extent of bioturbation through geologic time produced a clear signature in the ichnofabric record of lacustrine facies paleozoic lacustrine ichnofaunas are typically dominated by surface trails with little associated bioturbation during the mesozoic bioturbation depth was higher in lake margin facies than in fully lacustrine deposits while significant degrees of bioturbation were attained in lake margin facies during the triassic major biogenic disruption of primary bedding in subaqueous lacustrine deposits did not occur until the cretaceous

joint interpretation of explosive and vibroseismic surveys on cold firn for the investigation of ice properties two seismic surveys were carried out on the high altitude glacier saddle colle gnifetti monte rosa italy switzerland explosive and vibroseismic sources were tested to explore the best way to generate seismic waves to deduce shallow and intermediate properties 100 m of firn and ice the explosive source sissy excites strong surface and diving waves degrading data quality for processing no englacial reflections besides the noisy bed reflector are visible however the strong diving waves are analyzed to derive the density distribution of the firn pack yielding results similar to a nearby ice core the vibrator source elvis used in both p and sh wave modes produces detectable laterally coherent reflections within the firn and ice column we compare these with ice core and radar data the sh wave data are particularly useful in providing detailed high resolution information on firn and ice stratigraphy our analyses demonstrate the potential of seismic methods to determine physical properties of firn and ice particularly density and potentially also crystal orientation fabric

determining the age distribution of colle gnifetti monte rosa swiss alps by combining ice cores ground penetrating radar and a simple flow model ice cores from cold alpine glaciers may provide unique paleoclimate information fromnon polar latitudes we explore the three dimensional internal age distribution of the small cold glaciersaddle colle gnifetti monte rosa italy switzerland to compare the age depth relations from fourlocal deep ice cores tracking isochronous refection horizons detected by ground penetrating radar gpr among the core locations reveals consistent dating up to 80 yearsbp this approach is confned torecent ages duetothelackofclearrefectionsbelowthefrn icetransition weattempttoovercomethislimitation by including a two dimensional fow model adapted to the gpr derived surface accumulationand ice thickness distribution modeled and gpr isochrones are compared indicating agreement inshape but featuring a potential offset of 0 3 5m the modeled isochrones are interpolated to the corearray with ages assigned according to the ice core datings the resulting age distribution is consistentup to 110 yearsbp with age uncertainties increasing from 7 to 80 years in the lower half of the ice this combination of methods is novel for alpine sites and may be adapted for spatial extrapolation ofice properties other than age

temperature and accumulation of high altitude firn in the alps data on temperature and accumulation of high altitude firn in the alps are compiled and discussed firn temperature varies with incoming radiation slope aspect at a given altitude the altitudinal gradient of temperature in highly permeable firn bodies appears to be about twice as high as the mean lapse rate of air temperature cold infiltration takes place above about 3500 m a s firn temperatures on the highest peaks are around 15 c accumulation net balance also decreases with increasing altitude from about 3m h20 at 3500 m a s to around 0 5 m h20 at wind exposed sites between 4300 and 4800 m a s l probably this is strongly due to wind erosion and topographical effects however temperature and accumulation not only appear to be interrelated but also seem to be positively correlated to the heat applied to the surface assuming the observed altitudinal gradients have remained constant in time it can be estimated that high altitude firn bodies have become considerably warmer since the last century co2 induced atmospheric warming could lead to a drastic change in the mass turnover and flow activity of high glaciers in wind exposed places where wind erosion of the snowpack becomes a controlling factor of accumulation introduction studies on mass and heat exchange at the surface of alpine firn have usually been carried out at altitudes below about 3500 m a s where firn is temperate and accumulation is high eg lang and others 1977 muller 1977 access to firn regions of higher altitudes is difficult however rather unusual construction work eg refuge lenkins on mont blanc and a number of tunnels dug into the firn of the monte rosa region by j e fisher in the 1950s furnished some information which indicated that at high altitudes firn is cold and accumulation does not further increase with altitude interest in temperature and accumulation of high altitude firn has grown recently in connection with i englacial temperatures 2 ice avalanches and 3 alpine core drilling temperature distribution in the tongue of grenzgletscher one of the largest ice bodies in the alps must be caused by advection of cold ice from high altitudes blatter and haeberli 1984 the frequency of ice avalanches ultimately depends on the accumulation of firn alean 1985 and the stability of steep mountain glaciers seems to depend on firn and ice temperatures rothlisberger 198 1 alean 1984 finally core drilling projects in cold high alpine firn and ice provide important information about the evolution of the composition of the atmosphere in heavily industrialized regions over past decades and centuries eg wagenbach and others in press but require knowledge about the distribution of accumulation in space and time the aims of the present study are to compile information available and point to possible effects of recent atmospheric warming firn temperature temperature measurements from deep pits tunnels and shallow bore holes in high altitude firn of the alps have been compiled by haeberli 1976 cf also hooke and others 1983 new information is available from chli titlis jungfraujoch sphinxgrat and monte rosa colle gnifetti all swiss alps at chli titlis 3070 m a s i 15 m temperature in the summit s 22 m thick firn and ice was 0 7 c 1979 80 cf haeberli and others 1979 temperatures in the sphinxgrat crest were measured in a 70 m borehole through firn ice and perennially frozen rocks in connection with recent construction work at the jungfraujoch the ice rock interface 10 m below the surface at 3525 m a s had a temperature close to 6 c 198 1 temperatures around 14 c at 15 m depth were registered in all core drilling boreholes made so far on colle gnifetti 4450 m a s the fim ice transition in this cold firn saddle occurs about 40 m below the surface schotterer and others 1981 when presently known firn temperatures are compiled figure i two groups seem to exist group i incorporates summits crests and probably also very steep slopes 45 which mainly consist of impermeable ice or high density firn with high concentrations of ice layers temperatures in such ice bodies decrease with increasing altitude at a rate about i c ioo m which is slightly higher than the assumed lapse rate of mean annual air temperature 0 65 c ioo m no temperate firn bodies are known in such situations in contrast more gentle slopes and basins group 2 where highly permeable firn accumulates are temperate up to about 3600 m a s above this upper boundary of the warm infiltration zone of the alps percolating meltwater cannot

late oligocene bunch grassland and early miocene sod grassland paleosols from central oregon usa abstract fossil soils burrows and mammals of the upper john day formation in central oregon are evidence of bunch grasses and open semiarid vegetation as old as late oligocene earliest arikareean 30 ma root traces in these paleosols include both stout tapering tubes like roots of trees as well as sinuous filamentous tubes similar to roots of grasses paleosol structure is fine subangular blocky with patchy distribution of grass like roots as in wooded grassland and sagebrush steppe with bunch grasses cursoriality in horses mesohippus miohippus and hypsodonty in rhinos diceratherium is also evidence for open grassy vegetation trace fossils of pallichnus dung beetle boli and edaphichnium earthworm chimneys are characteristic of wooded grassland paleosols whereas taenidium cicada burrows dominates desert shrubland paleosols as has also been found in quaternary paleosols and soils of eastern washington in both oligocene and quaternary paleosol sequences arid shrubland and semiarid grassland paleosols alternate on milankovitch frequencies 23 41 100 ka the oldest known paleosols in oregon with crumb structure and abundant fine fossil root traces characteristic of sod grasslands are dated by mammalian biostratigraphy as hemingfordian early miocene ca 19 ma wooded grassland habitats are indicated by scattered chalcedony calcite rhizoconcretions from large woody plants and by fossil chalicotheres moropus camels gentilicamelus paratylopus and horses parahippus silty texture and silcrete horizons are evidence of semiarid to arid paleoclimate and are in striking contrast to highly calcareous and clayey underlying paleosols of the john day formation these silcrete paleosols may represent the miocene onset of summer dry mediterranean seasonality as opposed to a summer wet monsoonal pattern of seasonality found in this region during the oligocene oregon s early rangelands can be compared with those in the north american great plains granular structured calcareous paleosols of the brule formation of south dakota are evidence of dry bunch grasslands as old as 33 ma early orellan early oligocene and crumb structured paleosols of the anderson ranch formation of nebraska are evidence of sod grasslands as old as 19 ma late arikareean early miocene although grasses were a conspicuous part of dry rangelands well back into the oligocene early and middle miocene sod grasslands in north america were restricted to regions estimated to have had less than 400 mm mean annual precipitation

a novel radiocarbon dating technique applied to an ice core from the alps indicating late pleistocene ages ice cores retrieved from high altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions because of the specific flow behavior of ice their age depth relationship is nonlinear preventing the application of common dating methods such as annual layer counting in the deepest and oldest part here we present a new approach and technique allowing dating of any such ice core at arbitrary depth for the age range between 500 years b p and the late pleistocene this new complementary dating tool has great potential for numerous ice core related paleoclimate studies since it allows improvement and extension of existing and future chronologies using small to ultrasmall sample size 100 g carbon content 5 g accelerator mass spectrometry we take advantage of the ice included water insoluble organic carbon fraction of carbonaceous aerosols for radiocarbon 14c dating analysis and dating of the bottom ice of the colle gnifetti glacier swiss italian alps 45 55 50 n 7 52 33 e 4455 m asl has been successful in a first application and the results revealed the core to cover most of the holocene at the least with indication for late pleistocene ice present at the very bottom

measurements of attenuation from vertical seismic profiles by iterative modeling we present a numerical simulation of vertical seismic profiles vsp using the discrete horizontal wavenumber representation of seismic wave fields the theoretical seismograms are computed in the acoustic case for flat layered media and they include the effects of absorption and velocity dispersion a study using the synthetic seismograms was conducted to investigate the accuracy and resolution of attenuation measurements from vsp data it is shown that in finely layered media estimates of the anelastic attenuation obtained by use of the reduced spectral ratio method are usually inaccurate when the attenuation is measured over a small vertical extent an iterative method is presented which improves the resolution of the measurements of intrinsic dissipation this method allows determination for synthetic data of the quality factor over depth intervals of about one wavelength of the dominant seismic frequency

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

synthetic seismograms for marine sediments and determination of porosity and permeability we present numerical simulations of vertical seismic profiles vsps of marine sediments the theoretical seismograms which are computed for vertically incident waves in flat layered poroelastic media include the effects of dispersion and attenuation predicted by biot theory according to biot theory fast and slow compressional waves are excited and there is mode conversion at the interfaces we include this effect in the calculation of reflection and transmission coefficients as an energy loss mechanism through the slow compressional waves finally we examine the spectral ratio method for determining porosity and permeability from synthetic seismogram data analytical expressions for the velocity and specific attenuation are found based on the weak frame approximation once the frequency dependent velocity and specific attenuation are calculated the porosity and permeability of marine sediments can be determined by using the proposed weak frame approximations spectral ratio calculations on syntheti