snow grain size profiles deduced from microwave snow emissivities in antarctica spaceborne microwave radiometers are an attractive tool for observing antarctic climate because their measurements are related to the snow temperature however the conversion from microwave emission to snow temperature is not simple and strongly depends on the emissivity through snow properties this difficulty in predicting the snow property profile for antarctic conditions is the main bottleneck in the retrieval of accurate climate information from microwave radiometers we attempt to explain the vertically polarized emissivity at 19 3 and 37 ghz derived from brightness temperatures acquired by the special sensor microwave imager ssm i and physical temperature from the era 40 re analysis in antarctica the snow emissivities at 19 3 and 37 ghz are nearly equal although a decrease with frequency is expected to explain this we consider various profiles of snow grain size and density and predict their emissivity using a dense medium radiative transfer dmrt model the results show that the emissivities cannot be explained by constant profiles of grain size and density heterogeneous snowpacks need to be considered we first test random variations of snow density and grain radius with depth and then monotonic and continuous variations in the snow grain radius in both cases we show that an overall increase of the snow grain radius with depth is required to match the observed emissivity in antarctica in addition two parameters characterizing the snow grain profiles are retrieved and compared with 1 in situ measurements of grain size at various locations in east antarctica 2 grain size estimated using visible spaceborne radiometers and 3 a semi empirical relationship for grain growth

late carboniferous permian of nw europe an introduction to a new regional map this data set contains a set of shapefiles outlining the subsurface geology of nw europe for structures and strata of late carboniferous to permian age shapefiles can be loaded in different types of geographic information systems and other geological and geographical tools the projection of the data is utm3

generalized maxwell bodies and estimates of mantle viscosity summary three generalized maxwell bodies gmbs are discussed whose transient creep properties make them interesting alternatives to the classical maxwell body cmb in interpretations of post glacial uplift the first gmb is defined by its relaxation spectrum the second by its quality factor and the third by its stress strain relation in each case the gmb is characterized by three parameters only the unrelaxed modulus the steady state viscosity or a time constant and a dimensionless parameter representative of the transient creep properties this is one parameter less than needed for the burgers body which has mainly been used so far to model transient creep the gmb models are described in some detail and numerical results for their viscoelastic moduli relaxation spectra and relaxation and creep functions are given for practical applications it is most important that the viscoelastic moduli can be calculated at arbitrary frequencies in the second part of the paper post glacial uplift data from canada and fenno scandia are interpreted with the gmb rheologies described otherwise the earth model used and the assumptions on the form and history of the ice load are very simple effective viscosities of the successful models i e inverse creep rates at times representative of mantle convection fall in the range 1022 1024p 1021 1023pas and are in part considerably larger than mantle viscosities derived under the assumption of a cmb rheology hence post glacial uplift data constrain mantle viscosity less than has been believed until recently

the density distribution of the fractured asperities on the surfaces of a fault abstract it is shown how the density distribution of the stress field variations caused by the earthquakes occurring in a fault gives the density distribution of the fractured asperities on the sides of the fault it is then suggested that the fractal dimension of the faults is associated to that of the density distribution of the stress variations due to the earthquakes occurring on them the decrease of the exponent of the power law of the density distribution of the stress drops is then a signal of onset of instability three examples of decrease of the exponent of that power law followed by an earthquake are presented

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

radiation enhanced fission track annealing revisited and consequences for apatite thermochronometry apatite fission track aft analyses for granitoid and metamorphic bedrock samples from the western superior province ontario the churchill rae province melville peninsula and southampton islan

reconstructing thermal properties of firn at summit greenland from a temperature profile time series we have constrained the value for thermal diffusivity of near surface snow and firn at summit station greenland using a fourier type analysis applied to hourly temperature measurements collected from eight thermistors in a closed off air filled borehole between may 2004 and july 2008 an implicit finite difference method suggests that a bulk diffusivity of 25 3m2 a 1 is the most reasonable for representing macroscale heat transport in the top 30 m of firn and snow this value represents an average diffusivity and in a conduction only model generates temperature series whose phase shifts with depth most closely match those of the summit borehole data rms difference between measurements and model output is 6 days this bulk value derived numerically and corroborated analytically is useful over large tracts of the greenland ice sheet where density and microstructure are unknown

seismic coda q and scaling law of the source spectra at the aeolian islands southern italy the model developed by aki and chouet for the coda wave generation and propagation has been used to calculate the quality factor q for the zone of the aeolian islands southern italy in the frequency range of 1 to 12 hz and the scaling properties of the seismic spectrum in the magnitude range of 0 4 to 4 7 the q found for the aeolian area has a frequency dependence of the form q qfv the absolute values of q seem to be dependent on the station and location of the seismic events confirming the strong lateral heterogeneities in the geological structure beneath the aeolian arc a temporal variation has been noted in the q calculated at vulcano station vpl in a period of 3 weeks soon after the occurrence of a main shock of ml 5 5 located near the station the scaling behavior of this sequence is similar to that obtained in two areas of california and one portion of japan with a corner frequency that remains constant with an increasing seismic moment between magnitudes 1 and 4 it differs substantially from the scaling properties of the hawaian earthquakes that show a linear pattern without an increase of the stress drop with magnitude the fact that vulcano is an active volcano seems not to influence the scaling properties of the seismic sequence localized very near it it probably indicates that the aftershocks used for calculating the scaling law are generated out of the volcanic complex lipari vulcano in a zone with a good capability of accumulating the stress

modeling time series of microwave brightness temperature at dome c antarctica using vertically resolved snow temperature and microstructure measurements time series of observed microwave brightness temperatures at dome c east antarctic plateau were modeled over 27 months with a multilayer microwave emission model based on dense medium radiative transfer theory the modeled time series of brightness temperature at 18 7 and 36 5 ghz were compared with advanced microwave scanning radiometer eos observations the model uses in situ high resolution vertical profiles of temperature snow density and grain size the snow grain size profile was derived from near infrared nir reflectance photography of a snow pit wall in the range 850 1100 nm to establish the snow grain size profile from the nir reflectance and the specific surface area of snow two empirical relationships and a theoretical relationship were considered in all cases the modeled brightness temperatures were overestimated and the grain size profile had to be scaled to increase the scattering by snow grains using a scaling factor and a constant snow grain size below 3 m depth i e below the image derived snow pit grain size profile brightness temperatures were explained with a root mean square error close to 1 k most of this error is due to an overestimation of the predicted brightness temperature in summer at 36 5 ghz

why baltic shield zircons yield late paleozoic lower intercept ages on u pb concordia in the baltic shield the paleozoic is known as a period of regional pb mobilization that resulted in new lead deposits and the addition of radiogenic pb to older deposits in addition u pb data from zircons in the baltic shield commonly yield late paleozoic lower intercepts on the u pb concordia regarded as geologically insignificant results from fission track studies reveal that the rocks that form the present bedrock surface in sweden and finland were heated at the same time this fact is explained by upper paleozoic sedimentary deposits much thicker than hitherto known that covered the basement for at least 200 m y these erosion products of the caledonides formed terrestrial or shallow water old red deposits in a foreland basin that covered sweden and to a lesser extent finland hydrothermal solutions leached metamict zircons in the basement rocks for a long time resulting in pb loss and paleozoic lower intercept ages on u pb concordia the radiogenic pb was redistributed and preferentially concentrated into fractures and veins or was added to older sulfide deposits

temperature measurements and heat transfer in near surface snow at the south pole to study near surface heat flow on the antarctic ice sheet snow temperatures were measured at south pole station to a depth of 3 m at 15 min intervals during most of 1992 solar heating and water vapor transport were negligible during the 6 month winter as was inter grain net thermal radiation leaving conduction as the dominant heat transport mechanism the rate of temperature change at depth over 15 min intervals was smaller than that at the surface by one order of magnitude at 20 cm depth and two orders of magnitude at 1 m depth a finite difference model with conduction as the only heat transfer mechanism and measured temperatures as the upper and lower boundary conditions was applied to foursets of three thermistors each the thermal conductivity was estimated as that which minimized the difference between modeled and measured 15 min changes in temperatures at the center thermistor the thermal conductivity obtained at shallow depths above 40 cm was lower than that given by existing parameterizations based on density probably because the snow grains were freshly deposited cold and poorly bonded a model using only vertical conduction explains on average 87 ofthe observed 15 min temperature changes at less than 60 cm depth and 92 below 60 cm the difference between modeled andmeasured temperature changes decreased with depth the discrepancies between model and observation correlated more strongly with the air snow temperature difference than with the product of that difference with the square of the wind speed suggesting that the residual errors are due more to non vertical conduction and to sub grid scale variabilis of the conductivity than to windpumping the residual heating rate not explained by the model of vertical conduction exceeds 0 2 w m 3 only in the top 60 cm of the near surface snow

relaxation and free modes of a self gravitating planet summary the relaxation and purely radial free modes of a planet subject to a non hydrostatic pre stress are studied the non hydrostatic pre stress considered is caused by gravity and is obviously present and relevant to a certain depth in the earth as the presence of large mountain ranges and abyssal plains imply the relaxation of this stress field is studied and it is shown that there is an infinite set of rheological models of the same type which have the same relaxation time only other information on the behaviour of the material such as the q 1 allows us to specify better the rheological model it is also shown that the pre stress shifts the period of each purely radial free mode of the planet however in the case of the earth this effect is not relevant with the present accuracy of determination of the periods of the free modes

snow metamorphism under alternating temperature gradients morphology and recrystallization in surface snow 1 the composition of the lower atmospheric boundary layer can be strongly influenced by snow photochemistry surface snow where air snow interactions take place is viewed as slowly changing quasi isothermal snow implied by the observation of mainly rounded snow crystals the role of snow for photochemistry is therefore expected to be purely geometric however large temperature gradients are often observed in these layers which would imply high recrystallization and faceting in controlled laboratory experiments we showed that temperature gradients on the order of 100 k m 1 do not lead necessarily to faceting if their sign changes with a daily cycle the shape of snow crystals does not reflect necessarily the metamorphic process with time lapse x ray tomography recrystallization rates as high as 60 of the total ice mass were observed during 12 hours the high recrystallization rates in apparently isothermal snow not only contradict the current understanding of snow metamorphism they also might influence chemical air snow interactions

the local insolation signature of air content in antarctic ice a new step toward an absolute dating of ice records an accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and to understand the relation between insolation and climate a new domain of research in this area has been stimulated by the work of m bender linking the record of n2 o2 ratio in the air trapped in the ice with the local insolation here we investigate the potential of the air content of polar ice v as another and complementary ice proxy of local insolation we propose that the long term changes in air content recorded in ice from the high antarctic plateau is dominantly imprinted by the local summer insolation the v measurements covering the last 440 000 yr and obtained along the epica dc edc ice core are presented 86 of the variance observed in the v record can be explained neither by air pressure nor by temperature changes and then should reflect properties influencing the porosity at close off other than temperature a wavelet analysis indicates a dominant obliquity period around 41 ka over the last 440 ka we propose a mechanism which can account for the observed anti correlation between local insolation and v and explain how the local insolation via the integrated summer insolation can affect the near surface snow structure and consequently the porosity at close off the v and the integrated summer insolation changes show high coherency over all the record and a variable phase relationship with a maximum phase difference of about 4000 yr around 200 ka ago the phase difference may reflect the difference between the edc2 chronology based on an inverse dating method and an accurately dated insolation curve our work by proposing a new and complementary ice proxy for local insolation should eventually contribute to the establishment of an absolute dating of the ice paleo record

spatial and temporal characterization of hoar formation in central greenland using ssm i brightness temperatures the summertime formation and burial of low density coarse grained hoar layers in the snow of central greenland can be mapped using satellite passive microwave data variations in a signal derived from special sensor microwave imager ssm i brightness temperature trends correlate temporally and spatially with hoar complex evolution over 120 000 km of the greenland ice sheet s dry firn facies observations at the greenland ice sheet project ii gisp2 site indicate that changes in surface conditions and brightness temperatures correspond to four hoar events over two summers as expected from theory following a snowfall the smooth high density surface reflects some emitted 37 ghz horizontally polarized h radiation but little vertically polarized v radiation progressive surface roughness increases and density decreases during hoar formation cause a gradual decrease in h reflection formation and burial of a hoar layer thus causes a slow decrease followed by an abrupt increase in the v h ratio hoar layers have been used to date the gisp2 ice core through the entire holocene archived microwave data now can be used to assess the timing and frequency of the formation of these stratigraphic markers in central greenland

orbital tuning chronology for the vostok climate record supported by trapped gas composition abstract we present data on the o2 n2 ratios of trapped gas samples for the entire length of the vostok climate record as in other cores o2 n2 ratios in these samples are less than the atmospheric ratio by a small and variable amount because o2 is selectively excluded during the gas trapping process and because o2 is also preferentially lost in poorly preserved core samples samples younger than 150 ka have large and variable o2 depletions samples older than 200 ka have o2 n2 ratios that replicate well and vary smoothly with depth we plot o2 n2 ratios of well replicated samples older than 160 ka using a chronology derived by matching the 18o of paleoatmospheric o2 18oatm to northern hemisphere june insolation on this timescale o2 n2 varies coherently with local 78 s summertime insolation based on time series analysis of the o2 n2 record and the dynamics of snow metamorphism at the surface we conclude that summertime insolation influences physical properties of ice grains that control the degree of o2 exclusion during bubble closeoff o2 n2 in vostok is thus arguably a property that records local summertime insolation and can be used to test independent chronologies for the core we show that the 18oatm chronology supported by the coincidence of o2 n2 ratios with insolation is also compatible with recent radiometric dating of corals from high sea stands we further successfully test the 18oatm tuning chronology by showing that it predicts a chronology for the gisp2 core which is essentially indistinguishable from the standard gisp2 chronology and therefore in excellent agreement with the radiometric chronology of hulu cave china an accurate chronology for the vostok ice core is now in place

attenuation parameters for friuli region from strong motion accelerogram spectra abstract by using the accelerometric data obtained during the heaviest earthquakes that occurred in friuli in 1976 an attempt was made to obtain a law of attenuation in the northeastern po river area as dependence on the frequency the study was carried out by comparison of power spectra of entire accelerograms at different distances in the frequency range of 0 1 to 10 hz a q value was found which was proportionally dependent on the frequency as f n with n 1 1 this result can be considered valid for that region and for distances of up to about 200 km from the epicentral area

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

temperatures heating rates and vapour pressures in near surface snow at the south pole a finite volume model is used to simulate 9 years 1995 2003 of snow temperatures at the south pole the upper boundary condition is skin surface temperature derived from routine upwelling longwave radiation measurements while the lower boundary condition is set to the seasonal temperature gradient at 6 5 m depth taken from prior measurements at the south pole we focus on statistics of temperature heat fluxes heating rates and vapour pressures in the top metre of snow but present results from the full depth of the model 6 5 m the monthly mean net heat flux into the snow agrees with results from previous studies performed at the south pole on shorter timescales the heating rates and vapour pressures show large variability the net heat flux into the snow which is between 5wm 2 in the monthly mean can be greater than 20 w m 2 on hourly timescales on sub daily timescales heating rates exceed 40 k d 1 in the top 10 cm of the snow subsurface temperatures and therefore heating rates are more variable during winter april september due to increased synoptic activity and the presence of a strong surface based atmospheric temperature inversion the largest vapour pressures 60 70 pa and vertical gradients of vapour pressure are found in the top metre of snow during the short summer december january in contrast during the long winter the low temperatures result in very small vapour pressures and insignificant vapour pressure gradients the high summertime vapour pressure gradients may be important in altering the isotopic composition of snow and ice on the antarctic plateau

multifrequency microwave emission fromthe dome c area on the east antarctic plateau temporal and spatial variability the antarctic plateau that extends for several hundred kilometers with an average altitude of close to 3000 m a s l is the highest part of the east antarctic ice cap this area provides unique opportunities for various scientific disciplines including glaciology and atmospheric and earth sciences in addition there is growing interest in using the antarctic plateau for calibrating and validating data of satellite borne microwave radiometers thanks to the size structure and spatial homogeneity of this area and the thermal stability of deeper snow layers in this paper we analyze the temporal and spatial variabilities of multifrequency microwave emission from the area surrounding the dome c scientific station using advanced microwave scanning radiometer data collected throughout 2005 moreover a multilayer coherent electromagnetic model is used for estimating the contribution of snow layers to emission at various frequencies the results are consistent with the physical structure of the ice sheet and with its seasonal and spatial variations

snow stratigraphic heterogeneity within ground based passive microwave radiometer footprints implications for emission modeling two dimensional measurements of snowpack properties stratigraphic layering density grain size and temperature were used as inputs to the multilayer helsinki university of technology hut microwave emission model at a centimeter scale horizontal resolution across a 4 5 m transect of ground based passive microwave radiometer footprints near churchill manitoba canada snowpack stratigraphy was complex between six and eight layers with only three layers extending continuously throughout the length of the transect distributions of one dimensional simulations accurately representing complex stratigraphic layering were evaluated using measured brightness temperatures large biases 36 to 68 k between simulated and measured brightness temperatures were minimized 0 5 to 0 6 k within measurement accuracy through application of grain scaling factors 2 6 to 5 3 at different combinations of frequencies polarizations and model extinction coefficients grain scaling factors compensated for uncertainty relating optical specific surface area to hut effective grain size inputs and quantified relative differences in scattering and absorption properties of various extinction coefficients the hut model required accurate representation of ice lenses particularly at horizontal polarization and large grain scaling factors highlighted the need to consider microstructure beyond the size of individual grains as variability of extinction coefficients was strongly influenced by the proportion of large hoar grains in a vertical profile it is important to consider simulations from distributions of one dimensional profiles rather than single profiles especially in sub arctic snowpacks where stratigraphic variability can be high model sensitivity experiments suggested that the level of error in field measurements and the new methodological framework used to apply them in a snow emission model were satisfactory layer amalgamation showed that a three layer representation of snowpack stratigraphy reduced the bias of a one layer representation by about 50

contact spectroscopy for determination of stratigraphy of snow optical grain size we present a technique for in situ measurement of the vertical and spatial stratigraphic distribution of snow optical grain size with a coupled contact illumination probe and field spectroradiometer accurate measurements of optical equivalent grain size are critical for modeling radiative properties of snow such as spectral albedo and microwave emission measurements of the spectral reflectance of the snow pit surface are made at 2 cm intervals in the vertical plane under constant illumination and view geometries we invert the integral of the continuum normalization of the ice absorption feature with maximum at 1 03 mm wavelength for optical equivalent grain size using the validated model of nolin and dozier 2000 that has accuracy of 10 50 mm across the grain size range 50 900 mm results are presented for an alpine site in southwest colorado usa across the ablation season and for a greenland ice sheet site at the onset of snowmelt these results suggest that traditional measurements of grain size using a hand lens are nearly accurate only for rounded grains r 2 0 41 rmse 160 mm for polycrystals and faceted grains the hand lens approach is very inaccurate r 2 0 03 and 0 24 rmse 1206 and 1010 mm respectively we demonstrate an order of magnitude improvement in modeling of shortwave spectral albedo and net shortwave flux with contact spectroscopy measurements of grain size stratigraphy over those from a hand lens

relation between grain size and correlation length of snow in the past it has often been difficult to compare results of different types of snow structural information grain size and correlation length are such parameters of granular media and there exist different definitions and different measurement methods for both of them the relation between these parameters is analyzed from theoretical and from experimental points of view considering optical and microwave properties for spherical ice grains the connecting formulas are simple but for other shapes the two parameters are not directly related care must be taken in the measurement procedure especially if grain size is regarded as the maximum extent of connected ice particles the results are likely to lead to extreme overestimates therefore it is concluded that grain size should be complemented by an additional size parameter namely the surface to volume ratio of equivalent spheres i e a measure of the correlation length methods to determine this quantity in the laboratory have been known for a long time methods to obtain such measurements in the field are described here

a look at the surface based temperature inversion on the antarctic plateau data from radiosondes towers and a thermistor string are used to characterize the temperature inversion at two stations the amundsen scott station at the south pole and the somewhat higher and colder dome c station at a lower latitude ten years of temperature data from a 22 m tower at the south pole are analyzed the data include 2 and 22 m temperatures for the entire period and 13 m temperatures for the last 2 yr statistics of the individual temperatures and the differences among the three levels are presented for summer december and january and winter april september the relationships of temperature and inversion strength in the lowest 22 m with wind speed and downward longwave flux are examined for the winter months two preferred regimes one warming and one cooling are found in the temperature versus longwave flux data but the physical causes of these regimes have not been determined the minimum temperatures and the maximum inversions tend to occur not with calm winds but with winds of 3 5 m s 1 likely due to the inversion wind this inversion wind also explains why the near surface winds at south pole blow almost exclusively from the northeast quadrant temperature data from the surface to 2 m above the surface from south pole in the winter of 2001 are presented showing that the steepest temperature gradient in the entire atmosphere is in the lowest 20 cm the median difference between the temperatures at 2 m and the surface is over 1 0 k in winter under clear skies this difference increases to about 1 3 k monthly mean temperature profiles of the lowest 30 km of the atmosphere over south pole are presented based on 10 yr of radiosonde data these profiles show large variations in lower stratospheric temperatures and in the strength and depth of the surface based inversion the near destruction of a strong inversion at south pole durin g7ho n 8september 1992 is examined using a thermal conductivity model of the snowpack driven by the measured downward longwave flux the downward flux increased when a cloud moved over the station and it seems that this increase in radiation alone can explain the magnitude and timing of the warming near the surface temperature data from the 2003 04 and 2004 05 summers at dome c station are presented to show the effects of the diurnal cycle of solar elevation over the antarctic plateau these data include surface temperature and 2 and 30 m air temperatures as well as radiosonde air temperatures they show that strong inversions averaging 10 k between the surface and 30 m develop quickly at night when the sun is low in the sky but are destroyed during the middle of the day the diurnal temperature range at the surface was 13 k but only 3 k at 30 m

topography and its isostatic compensation as a cause of seismicity a revision abstract the maximum shear stress mss generated in a spherical shell by the load of a mountain range and the buoyancy of its isostatic compensation has been computed in a previous paper caputo et al 1984 by simulating the effect of the buoyant body force with a surface force applied to the inner surface of the shell in this paper the buoyant force is modeled more exactly with a body force in a multilayered earth model the results show that the previous model is only accurate when the load is above the buoyant mass case a and not when the two are displaced case b the more accurate modelling of this paper shows that in case a the mss is reduced to less than 25 of the load by half way down in the second layer while in case b the mss extends to a much greater depth for example for a surface load of 350 bar isostatically compensated with a second layer 80 km thick the mss is less than 70 bar at a depth of 70 km from the surface in case a in case b this depth is close to 210 km also the very large mss found for case b in the model of the previous paper caputo et al 1984 is greatly reduced with the more accurate model of this paper

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

reply to comment on apatite fission track and u th he data from fennoscandia an example of underestimation of fission track annealing in apatite by b w h hendriks and t f redfield abstract in the absence of any remnant sedimentary rocks or other tangible geological evidence apatite fission track aft data from fennoscandia have been interpreted in terms of deep burial beneath a caledonian foreland basin we rejected this interpretation of aft data from central finland in 2005 in favor of one incorporating radiation enhanced annealing over geologically extended periods of time the physics underlying our hypothesis have been discussed extensively during the past two decades by various peer reviewed studies in this reply we contend that in their comment larson et al incorrectly interpret published geological data to support deep burial beneath an aerially extensive caledonian foreland basin we show the avalonia baltica tectonic collision better explains data that intimate slightly elevated paleo temperatures and paleo pressures in southern sweden we demonstrate that most of the geological data cited by larson et al are geographically isolated from the area we discussed in our 2005 contribution and thus completely unrelated to our conclusions we consider the comment by larson et al as unfounded and consequently uphold our original interpretation

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

extending the time range of apatite u th he thermochronometry in slowly cooled terranes palaeozoic to cenozoic exhumation history of southeast sweden the use of u th he thermochronometry in old slowly cooled terranes has long been debated hence studies of natural setting are needed to verify the expected diffusivity behaviour of helium our results demonstrate that the u th he method can be applicable to samples older than 200 ma and that available helium diffusion models can reproduce the results obtained from the age vs depth trends in addition the results shed some light on the cross validation with the apatite fission track thermochronometer u th he thermochronometry on apatites has been applied to samples taken from drill cores in the precambrian basement in southeast sweden to unravel the time of exhumation of the uppermost 1 3 km of the crust much of the phanerozoic exhumation history in sweden is poorly constrained due to a large hiatus in the sediment record results from the drill cores yield he ages decreasing with increasing depth from similar to 270 ma at the surface down to similar to 120 ma at 1700 in depth the age vs depth trend shows an inflection point at similar to 1400 in depth which coincides with the upper boundary of the present helium partial retention zone a period of slow exhumation similar to 17 m my probably linked to the isostatic uplift of the caledonian foreland basin is revealed by the upper section of the trend in the data the results demonstrate that the area has not been reheated since the mid permian this argues against the existence of a thick mesozoic sedimentary cover in this region which if present at all cannot have exceeded 100 in in thickness furthermore the age vs depth trend below the inflection point allows dating the cessation of exhumation at approximately 100 ma the area has had no significant amount of sedimentation erosion or uplift since this time less

effect of atmospheric water vapor on modification of stable isotopes in near surface snow on ice sheets south pole are used to simulate the d 18 o of near surface snow as it evolves in time the sensitivity of d 18 o of near surface snow to wind speed surface temperature and accumulation rate is tested through model experiments a steady wind of 5 10 m s 1 results in annual mean d 18 o enrichment of 3 7 enrichment of the heavy isotope occurs predominantly in buried winter snow layers during summer however in many simulations there is a slight depletion of d 18 o summer layers that occurs as atmospheric water vapor is deposited within the snow during winter postdepositional modification of water stable isotopes in near surface snow also depends on the snow accumulation rate high accumulation rates quickly advect snow layers away from the influence of the atmosphere preventing significant modification low accumulation rates e g at vostok and dome c allow significant postdepositional modification because the near surface snow is exposed to forced ventilation for several annual cycles postdepositional modification during the last glacial maximum lgm at summit greenland is estimated to be greater than the present day postdepositional modification therefore the temperature difference for lgm may be larger than that previously inferred from the d 18 o record however because of the compensating effects of lower temperatures and smaller accumulation during the lgm in antarctica the postdepositional enrichment in east antarctica may be approximately the same for lgm as for the modern climate

on apatite fission track dating and the tertiary evolution of west greenland topography abstract combined with geological information apatite fission track aft data can impose valid thermal and temporal constraints however their uncritical interpretation may also lead to unsupported conclusions because fission tracks in apatite undergo measurable shortening even at surface temperatures model artefacts can potentially be mistaken for geological cooling events this problem can be especially acute when older fanning kinetic models are utilized instead of the newest curvilinear ones in any circumstances aft model results must be interpreted with considerable caution and should rarely be considered to supersede conventional geological wisdom the possibility that young cooling events are simply artefacts ought always to be entertained as an example this study considers aft data and model results that have been cited to suggest that today9s high mountains of west greenland are erosional remnants of a landmass uplifted during the neogene however in the best of circumstances the aft data in question are heavily contaminated and in the worst case they carry virtually no geological meaning although geological constraints require the faulted westward facing escarpment of west greenland9s disko region to have been erected after commencement of sea floor spreading in baffin bay the aft model based hypothesis that it was constructed in purely neogene time remains an unproven speculation

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

snowball earth a thin ice solution with flowing sea glaciers 1 the late neoproterozoic era 600 800 myr ago was marked by at least two intervals of widespread cold that left glacial deposits at low paleolatitudes both snowball solutions with global ice cover and slushball solutions with ice free tropical oceans have been proposed to explain the paleomagnetic data the snowball model is best able to explain the auxiliary geological evidence particularly the existence of cap carbonates but it implies drastic survival pressure on the photosynthetic biota if the ice cover was everywhere thick enough to prevent sunlight from reaching the underlying ocean a thin ice solution that avoids this problem has been proposed but is thought to be inconsistent with realistic optical properties of sea ice and with the equatorward flow of sea glaciers here we use a coupled energy balance climate sea glacier model to argue that these apparent difficulties can be overcome and that thin tropical ice may have prevailed during these remarkable glacial episodes we also suggest that 1 some processes beyond the scope of zonal mean energy balance models may significantly affect the solutions and 2 thin ice could have prevailed on low latitude seas or large lakes protected from large scale sea glacier flow by surrounding land even if most of the earth was in a hard snowball state

evidence of the contrasted fission track clock behavior of the apatites from in ouzzal carbonatites northwest hoggar the low temperature thermal history of an archean basement this fission track study is performed on the apatites from the in ouzzal northwest hoggar algeria carbonatite complex and permits us to present a complete thermal history of this archean core two types of apatites the pink ones early carbonatites and the green ones late carbonatites have been dated the temperature during the pan african orogeny would have reached 100 120 c in the in ouzzal core as both types of apatites from the carbonatites have recorded this event 500 630 m y a mild permian thermal event reset only the fission track clock of the green late apatites this permian thermal event is of quite a large extent in the hoggar shield it has also been detected in the pharusian belt and in central hoggar this event is related to the opening of the atlantic ocean the very high u th content of some of these apatites and consequently the amount of radiation damage in the mineral lattice has been shown to possibly influence the fission track clock behavior of these minerals the f cl content of the apatites does not show any correlation with the degree of age reductions

apatite fission track and u th he data from fennoscandia an example of underestimation of fission track annealing in apatite abstract apatite fission track aft data from cratons have commonly been interpreted in terms of major episodes of sedimentary burial and subsequent denudation often in the absence of any remnant sedimentary rocks or other supporting geological evidence reconciling these interpretations with geologically documented denudation events or outcropping regional stratigraphy can be problematic also u th he ages from cratonic igneous rocks that are older than paired aft data are commonly discarded as too old even when the former are repeatable at the 2 confidence level for example aft data from central fennoscandia have been interpreted to reflect first burial by a caledonian foreland basin several kilometres in thickness and subsequently its denudation however throughout fennoscandia there is no direct evidence that such a deep extensive foreland basin ever existed and indeed some geological evidence points to the contrary additionally a significant number of u th he ages from fennoscandia are older than their aft pairs but have been interpreted by their authors as too old relative to the aft ages and not geologically meaningful despite repeatable results here we propose a new interpretation of aft data from fennoscandia that closely reflects the observed data yet is compatible with the generally accepted geological history discarding the hypothesis of a thick caledonian foreland basin we suggest that 1 aft ages in finland are too young rather than that the u th he ages are too old 2 repeatable sequences of u th he ages are more likely to record the true denudation history of cratons 3 the importance of radiation enhanced annealing at low temperatures has been overlooked and 4 fennoscandian aft data may be divided into an eastern domain strongly affected by radiation enhanced annealing where current aft annealing models are invalid and a western domain much less affected by radiation enhanced annealing where current modelling methods may appropriately be used to extract thermal histories in principle radiation enhanced annealing is also pertinent to the interpretation of young aft ages from apatites rich in emitter actinides the construction of a properly calibrated annealing model that fully incorporates the effects of radiation enhanced annealing is fundamentally important

measurement of vertical profiles of snow specific surface area with a 1 cm resolution using infrared reflectance instrument description and validation the specific surface area ssa defined as the surface area of ice per unit mass is an important variable characterizing the complex microstructure of snow its application range covers the physical evolution of snow metamorphism photochemistry and optical and microwave remote sensing this paper presents a new device posssum profiler of snow specific surface area using swir reflectance measurement designed to allow the rapid acquisition of ssa profiles down to 20 m depth and with an effective vertical resolution of 10 20 mm posssum is based on the infrared ir reflectance technique a laser diode operating at 1310 nm illuminates the snow at nadir incidence angle along the face of a drilled hole the reflected radiance is measured at three zenith angles 20 40 and 60 each for two azimuth angles 0 and 180 a second laser operating at a shorter wavelength 635 nm which is almost insensitive to ssa allows the distance to the snow face to be estimated the reflected ir radiance and the distance are combined to estimate bidirectional reflectances these reflectances are converted into hemispherical reflectances and in turn into ssa using a theoretical formulation based on an asymptotic solution of the radiative transfer equation the evaluation and validation of posssum s ssa measurements took place in spring 2009 in the french alps the new method was compared with the methane adsorption technique and dufisss another well validated instrument based on the ir technique the overall measurement error is in the range 10 15

comment on apatite fission track and u th he data from fennoscandia an example of underestimation of fission track annealing in apatite by hendriks and redfield earth planet sci lett 236 443 458 abstract in a recent paper hendriks and redfield question the existence of major episodes of burial and subsequent denudation in old cratonic settings they use fennoscandia as an example a continental shield region once covered by foreland basin deposits related to the caledonian orogen but today characterized by an exposed precambrian basement hendriks and redfield argue against a significant caledonian foreland basin cover referring to a selection of the numerous thermal indicator studies that have been performed in the region furthermore they discern an inconsistency between previously published fission track and u th he results in the region and suggest an alternative interpretation of the apatite fission track data from fennoscandia here we present geological arguments and highlight the numerous studies only briefly mentioned or not referred to at all by hendriks and redfield that strongly support the former existence of thick and extensive deposits on the caledonian foreland furthermore we discuss the alleged inconsistency between the different data sets by examining the data referred to more closely finally we evaluate the significance of the suggested inverse correlation between fission track age and 238u concentration presented by hendriks and redfield there is in fact no published example of an inconsistency between the two methods concerning paleozoic cooling in fennoscandia at present and the inverse relationship stated by the authors is poorly constrained therefore although radiation enhanced lattice recovery may have an influence on the apatite fission track age and should be examined further we conclude that the study by hendriks and redfield is poorly constrained their argumentation weakly and sometimes wrongly founded and that the thermochronology data from fennoscandia indeed do reflect sedimentary loading

the layered evolution of fabric and microstructure of snow at point barnola central east antarctica snow fabric defined as the distribution of the c axis orientations of the ice crystals in snow is poorly known so far only one study exits that measured snow fabric based on a statistically representative technique this recent study has revealed the impact of temperature gradient metamorphism on the evolution of fabric in natural snow based on cold laboratory experiments on polar ice sheets snow properties are currently investigated regarding their strong variability in time and space notably because of their potential influence on firn processes and consequently on ice core analysis here we present measurements of fabric and microstructure of snow from point barnola east antarctica close to dome c we analyzed a snow profile from 0 to 3 m depth where temperature gradients occur the main contributions of the paper are 1 a detailed characterization of snow in the upper meters of the ice sheet especially by providing data on snow fabric and 2 the study of a fundamental snow process never observed up to now in a natural snowpack namely the role of temperature gradient metamorphism on the evolution of the snow fabric snow samples were scanned by micro tomography to measure continuous profiles of microstructural properties density specific surface area and pore thickness fabric analysis was performed using an automatic ice texture analyzer on 77 representative thin sections cut out from the samples different types of snow fabric could be identified and persist at depth snow fabric is significantly correlated with snow microstructure pointing to the simultaneous influence of temperature gradient metamorphism on both properties we propose a mechanism based on preferential grain growth to explain the fabric evolution under temperature gradients our work opens the question of how such a layered profile of fabric and microstructure evolves at depth and further influences the physical and mechanical properties of snow and firn more generally it opens the way to further studies on the influence of the snow fabric in snow processes related to anisotropic properties of ice such as grain growth mechanical response electromagnetic behavior

from orogen to passive margin constraints from fission track and u th he analyses on mesozoic uplift and fault reactivation in sw norway the post caledonian tectonic history and landscape evolution of southwestern norway are poorly understood primarily owing to the lack of onshore post devonian sediments to bridge this knowledge gap low temperature thermochronological techniques were applied to investigate vertical movements in the upper crust new apatite fission track and apatite and zircon u th he analyses on samples from southwestern norway yielded permian to jurassic triassic to cretac eous and carboniferous to triassic ages respectively thermal history modelling indicates rela tively high cooling rates 2 3 8 cm a 21 throughout permian to early jurassic times since the jurassic samples from coastal areas have remained close to the surface and were reheated to 30 50 8c during sedimentary burial in the cretaceous inland samples experienced lesser amounts of permo triassic exhumation continued to cool slowly 1 8 cm a 21 throughout the jurassic cretaceous and did not reach the surface until the cenozoic both fission track and u th he ages are offset across faults highlighting the importance of fault activity throughout the mesozoic in combination with previously published results the new data suggest that the geo morphological evolution of southwestern norway is closely connected to rift and post rift tec tonics related to north sea and north atlantic rifting the topographic relief was most likely repeatedly rejuvenated during periods of tectonic activity

thermal effects due to air flow and vapor transport in dry snow the thermal effects of air flow forced through a snow sample are investigated numerically a new method for calculating vapor transport in snow is presented which allows for the determination of the effects of sublimation in this method the snow is not assumed to be saturated with water vapor results of the model show very good agreement with analytical and experimental results

measuring specific surface area of snow by near infrared photography the specific surface area ssa is considered an essential microstructural parameter for the characterization of snow photography in the near infrared nir spectrum is sensitive to the ssa we calculated the snow reflectance from calibrated nir images of snow pit walls and measured the ssa of samples obtained at the same locations this new method is used to map the snow stratigraphy the correlation between reflectance and ssa was found to be 90 calibrated nir photography allows quantitative determination of ssa and its spatial variation in a snow profile in two dimensions within an uncertainty of 15 in an image covering 0 5 1 0 m 2 even layers of 1 mm thickness can be documented and measured spatial maps of ssa are an important tool in initializing and validating physical and chemical models of the snowpack

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

thermal conductivity of snow firn and porous ice from 3 d image based computations estimating thermal conductivity of snow firn and porous ice is key for modeling the thermal regime of alpine and polar glaciers whereas thermal conductivity of snow was widely investigated studies on firn and porous ice are very scarce this study presents the effective thermal conductivity tensor computed from 64 3 d images of microstructures of snow antarctic firn and porous ice at 3 20 and 60 c we show that in contrast with snow conductivity of firn and porous ice correlates linearly with density is approximately isotropic and is largely impacted by temperature we report that performances of commonly used estimates of thermal conductivity vary largely with density in particular formulas designed for snow lead to significant underestimations when applied to denser ice structures we present a new formulation to accurately estimate the thermal conductivity throughout the whole density range from fresh snow to bubbly ice and for any temperature conditions encountered in glaciers

microstructural change around a needle probe to measure thermal conductivity of snow the thermal conductivity of snow determines to a large extent ground heat flux and snow metamorphism one common method of measuring the thermal conductivity of snow is with a needle probe we measured the microstructural changes in the snow around a typical needle using micro computed tomography the insertion of the needle probe caused structural changes up to a radial distance of 0 5 1 mm using a commercial needle probe with short 30 s heating time we measured thermal conductivity values in snow that were 50 lower than the conductivity measured using a calibrated guarded hot plate apparatus numerically simulated time temperature curves with an introduced air gap that simulated the needle damage reproduced the observed needle probe results well confirming that poor contact resistance between the needle and the snow will lead to measurement discrepancies and a large bias while most measurements in snow have been done using a long heating time and are not subject to this error the thermal conductivity of snow measured with needle probes with short measurement times should be avoided this same effect is probably observed in other brittle and highly porous materials a condition that may not be widely appreciated

extreme snow metamorphism in the allan hills antarctica as an analogue for glacial conditions with implications for stable isotope composition understanding physical processes in near zero accumulation areas can help us to better understand polar ice core records particularly during periods when accumulation rates were lower than today we report measurements from a 5 m firn core from the allan hills antarctica which include physical properties using computer tomography stable isotope ratios d and 18 o and 210 pb activity the core shows a highly metamorphosed firn with homogeneous and stable structure but with discrete layers near the surface the observed firn structure is caused by a combination of unique depositional and post depositional processes the irregular d and 18 o signal does not follow the stratigraphic sequence and implies post depositional modification caused by microscopic pressure gradients in the firn that can result from either forced ventilation over rough surfaces in the presence of wind or alternating temperature gradients between the firn and the atmosphere our results also indicate impact snow deposition under high winds and with a high initial density and air exchange between the atmosphere and the snowpack 210 pb activity below 0 3 m falls below the detection limit implying that most of the core is more than 100 years old we conclude that the allan hills record provides a unique opportunity to investigate important processes that would have affected ice core records from glacial periods

linear and nonlinear inverse rheologies of rocks abstract the generalized constitutive equations of anelastic media are considered and discussed in three dimensions 3d and in terms of two material functions as a generalized standard linear solid sls the inverse problem is considered and it is seen that one may not determine the material functions using the data of one standard creep or relaxation experiment data from both experiments would be needed if the medium is a generalized viscoelastic one then the material function can be determined with one experiment only the creep is determined in the generalized viscoelastic 3d case simulating a 3d experiment using the creep compliance obtained from the relaxation modulus determined from constant strain rate uniaxial experiments caputo 1983 it is seen that the one dimensional 1d model mostly used to model rock mechanics laboratory experiments which in practice are 3d experiments and not rigorously 1d gives the same value of the creep rate obtained using as load the difference between 1 and the confining pressure 3 the case of nonlinear viscoelastic stress strain relation is also discussed and a relation is found to determine the creep rate from 3d experiments at constant strain rate a check made with polycrystalline halite at high pressure and large strain rate gives satisfactory results

radionuclide mobility in thucholitic hydrocarbons in fractured quartzite radioactive hydrocarbons thucholites fill joints and fissures in presvecokarelian quartzites around the town of vastervik southeastern sweden uranium series nuclides including stable end members and carbon isotopes have been measured in surface samples and in drill core material originating down to 60 m below the surface uranium both is adsorbed onto noncrystalline hydrocarbonaceous material and forms different mineral phases the amount of hydrocarbons and uranium rapidly decreases with depth below 60 m the accumulations were too scanty for sampling uranium series nuclides show distinct gradients the surface samples with uranium contents up to 50 wt have been enriched in uranium lead and particularly thorium in geologically recent time probably during the last glaciation along the drill cores thorium has been immobile whereas 226ra and 222rn have migrated uranium has been distinctly migratory at and close to the surface but more or less immobile below 20 m depth almost no foreign rad

extreme firn metamorphism impact of decades of vapor transport on near surface firn at a low accumulation glazed site on the east antarctic plateau snow and firn properties control the transport of vapor gases and water between the atmosphere and the underlying strata an understanding of this transport and the properties that control it is important for predicting air snow transfer of chemical species and for interpreting ice cores remote sensing images of east antarctica show large areas of alternating light and dark bands these low amplitude long wavelength features have glazed downwind faces and rough upwind faces and are called megadunes the first linked measurements of the permeability and the associated microstructure for a glazed area within a well defined megadune area are reported in this paper permeability and density were measured along with grain scale properties derived from digital image processing of preserved thick sections at this cold low accumulation glazed site a clear layering pattern exists in the top meter the firn density ranges from 0 24 to 0 50 g cm 3 permeability measurements range from 50 x 10 10 to 200 x 10 10 2 several times greater than corresponding profiles from warmer higher accumulation sites like siple dome antarctica it is shown that buoyancy driven natural convection may be important in post depositional processes in very cold low accumulation sites like this

density specific surface area and correlation length of snow measured by high resolution penetrometry precise measurements of snow structural parameters are crucial to understand the formation of snowpacks by deposition and metamorphism and to characterize the stratigraphy for many applications and remote sensing in particular the area wide acquisition of structural parameters at high spatial resolution from state of the art methods is however still cumbersome since the time required for a single profile is a serious practical limitation as a remedy we have developed a statistical model to extract three major snow structural parameters density correlation length and specific surface area ssa solely from the snowmicropen smp a high resolution penetrometer which allows a meter profile to be measured with millimeter resolution in less than 1 min the model was calibrated by combining smp data with 3 d microstructural data from microcomputed tomography which was used to reconstruct full depth snow profiles from different snow climates alpine arctic and antarctic density correlation length and ssa were derived from the smp with a mean relative error of 10 6 16 4 and 23 1 respectively for validation we compared the density and ssa derived from the smp to traditional measurements and near infrared profiles we demonstrate the potential of our method by the retrieval of a two dimensional stratigraphy at kohnen station antarctica from a 46 m long smp transect the result clearly reveals past depositional and metamorphic events and our findings show that the smp can be used as an objective high resolution tool to retrieve essential snow structural parameters efficiently in the field

imaging of firn and bubbly ice in coaxial reflected light a new technique for the characterization of these porous media a new technique for characterizing the structure of firn and bubbly ice is presented this technique based on observation of etched sublimation surfaces in coax ial reflected light enables one to see simultaneously the pore network of the firn or bubbles in the ice and the crystal boundaries at the same time the main stages of image proces sing used to transform the initial photographs into clean binary images are described

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

reply to comment on compositional and structural control of fission track annealing in apatite by j barbarand a carter i wood and a j hurford chemical geology 198 107 137 2003

emplacement mechanism of the great whin and midland valley dolerite sills the great whin and midland valley dolerite sill complexes appear to have been emplaced laterally from the walls of feeder dykes the overall thickness of each sill increases with depth as would be expected if the magma finally reached a state of hydrostatic equilibrium variations in the thickness of the sills with estimated intrusion depth imply that the head of magma was about 100 m below the contemporary ground surface in the areas of the present day outcrops at the end of the intrusive episodes before hydrostatic equilibrium was established the magma pressure would probably have been somewhat greater so it is likely that intrusion of the sills was accompanied by the extrusion of flood basalts step and stair transgressions of the bedding are commonly found within the sills mostly stepping downwards in the direction of bedding dip the reason for this directionality is that the weight of sediments floating on an intruding sill has a downdip component that applies a tensile stress to intersecting fractures below the sill when magma is moving downdip and to intersecting fractures above the sill when magma is moving updip

effect of snow surface metamorphism on aquarius l band radiometer observations at dome c antarctica the antarctic plateau presents ideal characteristics to study the relationship between microwave observations and snow ice properties it is also a promising target for radiometer calibration and sensor intercalibration which are critical for applications requiring subkelvin accuracy such as sea surface salinity retrievals this paper presents the spaceborne aquarius l band radiometric observations collected since august 2011 over the antarctic plateau and it focuses on their temporal evolutions at dome c 75 1 circ hbox s 123 35 circ hbox e aquarius operates three radiometers with a sensitivity of 0 15 k over the oceans allowing us to analyze small variations in brightness temperature tb and changes with incidence angles over the antarctic plateau aquarius tbs have a relatively low annual standard deviation 0 2 0 9 k where melting never occurs however the analysis of the tb time series at dome c revealed significant variations up to 2 5 k in summer first these variations are compared with a remote sensing grain index gi based on high frequency 89 and 150 ghz shallow penetration tb channels variations in the ratio of tbs observed at horizontal and vertical polarizations are synchronous with gi changes second aquarius tb variations are compared with the presence of hoar crystals on the surface identified using surface based near infrared photographs the largest and longest changes in tbs correspond to periods with hoar crystals on the surface therefore in spite of the deep penetration of the l band radiation evolutions of the snow properties near the surface which usually change rapidly and irregularly do influence l band observations collection of accurate snow surface measurements and thorough analyses of the l band observations are thus needed to use the antarctic plateau as a calibration inter calibration target

combining shock barometry with numerical modeling insights into complex crater formation the example of the siljan impact structure sweden siljan central sweden is the largest known impact structure in europe it was formed at about 380 ma in the late devonian period the structure has been heavily eroded to a level originally located underneath the crater floor and to date important questions about the original size and morphology of siljan remain unanswered here we present the results of a shock barometry study of quartz bearing surface and drill core samples combined with numerical modeling using isale the investigated 13 bedrock granitoid samples show that the recorded shock pressure decreases with increasing depth from 15 to 20 gpa near the present surface to 10 15 gpa at 600 m depth a best fit model that is consistent with observational constraints relating to the present size of the structure the location of the downfaulted sediments and the observed surface and vertical shock barometry profiles is presented the best fit model results in a final crater rim to rim diameter of 65 km according to our simulations the original siljan impact structure would have been a peak ring crater siljan was formed in a mixed target of paleozoic sedimentary rocks overlaying crystalline basement our modeling suggests that at the time of impact the sedimentary sequence was approximately 3 km thick since then there has been around 4 km of erosion of the structure

generalized rheology and geophysical consequences abstract in some portions of the earth crust one finds stresses and creeps which are incompatible with the local geologic history and or the generally accepted rheological models of voigt or maxwell or standard linear solid also there is no reason to accept that the rheology of the earth is represented by mathematical formulae modeling combinations of simplicistic springs and dash pots which lead to represent the phenomenon by means of first order time derivatives of stress and or strains we describe here an attempt to obtain a rheological model for the lithosphere which is more realistic and flexible than the voigt the maxwell and the standard linear solid models which are generally used in geophysics and geology in this model the first order derivatives of maxwell stress strain relations are replaced by z order derivatives the resulting creep rates are variable functions of time as indicated by laboratory observations in the one dimensional case as well as in the case of the sphere the relaxation rate after a given time is a decreasing function of time a small value of z could explain the residual deviatoric stress present in the fennoscandia and canadian shields herget 1980 leijon et al 1981 and the deviatoric stress present in the rocky mountains and in the appalachian range caputo et al 1985 which seem stable and were formed many tens of millions of years ago a small value of z would also explain why the seismicity is decreasing with lithospheric age stein 1979 bergman and solomon 1980 but is still present 100 millions of years after the origin of the lithosphere which implies a relevant residual shear stress after long time if one wants to take into account the effect of temperature then one should consider that there is evidence that in some materials the creep rate is linearly increasing with temperature in the range between 100 c to 400 c caputo 1983 and that it is independent of the confining pressure then one would infer that the new viscosity parameter introduced with the model is decreasing with depth which would account for the deformation rates observed on the surface of the earth which should therefore be caused by the fast creep of the lower layers the rheological model gives more realistic values for the q of the mantle the variation of the node of lageos and that of ut1 are also discussed it is suggested that these variations may be caused by the cumulative rebounds due to several deglaciations and not by the last one only

orogeny and metamorphism a model for deformation and pressure temperature time paths with applications to the central and southern appalachians a model is presented for deformation uplift and exhumation in convergent orogens based on the following premises 1 foreland basin subsidence monitors the distribution in time and space of overthrust loads added to an orogen 2 the presence of an inherited rifted margin plays an important role in the subsequent history of an orogen by forming a basement ramp or buttress that must be surmounted in order for thrusts to advance on the craton on the seaward side of this transition up to 20 km of overthrusts can be accumulated without creating topography 3 critical shape theory can be applied to orogens as a whole allowing predictions to be made concerning dynamic balance between mass addition and loss uplift exhumation and growth of topography and 4 pressure temperature time p t t data can be used to reconstruct particle paths within the deforming orogen three states of overthrust orogens can be defined based on the relative rates of mass loss and mass addition as monitored by the foreland rapid exhumation of metamorphic terranes is most likely in the steady state where erosion balances accretion a constructive state where mass addition is greater than mass loss results in crustal thickening and initially little exhumation a destructive state where mass loss outweighs mass addition results in slow exhumation or subsidence of metamorphic rocks in the orogen depending on whether mass is removed by erosion or by extension p t t data on peak metamorphism pluton emplacement uplift exhumation and cooling can be used in conjunction with data from the foreland to distinguish among these various states the topography and strength of the inherited rifted margin play an important role in localizing zones of exhumation and uplift within the orogen application of this model to the central and southern appalachians suggests that during the constructive phases of the taconian and acadian orogenies overthrust loads accumulated mainly on the seaward side of the ocean continent transition as marked by the bouguer gravity gradient between the acadian and alleghanian orogenies the appalachian orogen was probably in a steady state with uplift and exhumation of rocks in the orogen but little subsidence of the foreland or advance of thrusts toward the craton the constructive stage of the alleghanian orogeny achieved the critical topography necessary to drive crystalline thrust sheets over the craton this resulted in widespread uplift and westward transport of older metamorphic rocks post orogenic unroofing of the southern appalachians is compatible with the predictions of flexural models the post orogenic unroofing history of the central appalachians and ouachitas probably reflects mesozoic extension in these areas

the tornquist sea and baltica avalonia docking early ordovician late arenig limestones from the sw margin of baltica scania bomholm have multicomponent magnetic signatures but high unblocking components predating folding and the corresponding palaeomagnetic pole latitude 19degreesn longitude 051degreese compares well with arenig reference poles from baltica collectively the arenig poles demonstrate a midsoutherly latitudinal position for baltica then separated from avalonia by the tomquist sea tornquist sea closure and the baltica avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for avalonia and baltica during the mid late ordovician by the caradoc avalonia had drifted to palaeolatitudes compatible with those of sw baltica and subduction beneath eastern avalonia was taking place we propose that explosive vents associated with this subduction and related to andean type magmatism in avalonia were the source for the gigantic mid caradoc c 455 ma ash fall in baltica i e the kinnekulle bentonite avalonia was located south of the subtropical high during most of the ordovician and this would have provided an optimum palaeoposition to supply baltica with large ash falls governed by westerly winds in scama we observe a persistent palaeomagnetic overprint of late ordovician ashgill age pole latitude 4degreess longitude 012degreese the remagnetisation was probably spurred by tectonic derived fluids since burial alone is inadequate to explain this remagnetisation event this is the first record of a late ordovician event in scania but it is comparable with the shelveian event in avalonia low grade metamorphism in the north sea basement of ne germany 440 450 ma and sheds new light on the baltica avalonia docking c 2002 elsevier science b v all rights reserved less