structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

ice thickness effects on aquarius brightness temperatures over antarctica the dome c region in the east antarctic plateau is regarded as an ideal natural laboratory for calibration validation of space borne microwave radiometers at l band the thermal stability of this region has been confirmed by several experimental campaigns however its use as an independent external calibration target has recently been questioned due to some spatial inhomogeneities and seasonal effects revealed in the brightness temperatures t b acquired in this area this paper shows the observed relationship from exploratory research between the antarctic ice thickness spatial variations and the measured aquarius t b changes a 3 months no daylight period during the austral winter has been analyzed four transects have been defined over east antarctica covering areas with different ice thickness variations and ranges the theoretical l band penetration depth has been estimated to understand the possible contributions to the measured signal a good agreement has been observed between aquarius t b and ice thickness variations over the whole antarctica with correlations of approximate to 0 6 0 7 the two variables show a linear trend with slopes of approximate to 8 3 9 5 k km no correlation has been observed with the subglacial bedrock the maximum l band penetration depth has been estimated to be approximate to 1 1 5 km results are therefore consistent the spatial variations found on aquarius t b are not related to the emissivity of the bedrock which lies deeper this study provides evidence that new l band satellite observations could contribute to further our understanding of antarctic geophysical processes

ice flow sensitivity to boundary processes a coupled model study in the vostok subglacial lake area antarctica several hundred subglacial lakes have been identified beneath antarctica so far their interaction with the overlying ice sheet and their influence on ice dynamics are still subjects of investigation while it is known that lakes reduce the ice sheet friction towards a free slip basal boundary condition little is known about how basal melting and freezing at the lake ice interface modifies the ice dynamics thermal regime and ice rheology in this diagnostic study we simulate the vostok subglacial lake area with a coupled full stokes 3 d ice flow model and a 3 d lake circulation model the exchange of energy heat and mass at the lake ice interface increases decreases the temperature in the ice column above the lake by up to 10 in freezing melting areas resulting in a significant modification of the highly nonlinear ice viscosity we show that basal lubrication at the bottom of the ice sheet has a significant impact not only on the ice flow above the lake itself but also on the vicinity and far field while the ice flow crosses vostok subglacial lake flow divergence is observed and modelled the heterogeneous basal mass balance pattern at the lake ice interface intensifies this divergence instead of interactive coupling between the ice flow model and the lake flow model only a single iteration is required for a realistic representation of the ice water interaction in addition our study indicates that simplified parameterizations of the surface temperature boundary condition might lead to a velocity error of 20 for the area of investigation

500 2000 mhz brightness temperature spectra of the northwestern greenland ice sheet an ultra wideband radiometer has been developed to measure subsurface properties of the cryosphere including ice sheets and sea ice the radiometer measures brightness temperature spectra from 0 5 to 2 ghz using 12 channels each of which measures scene brightness temperatures over an 88 mhz bandwidth resolved into 0 24 mhz intervals the instrument was flown over northwestern greenland in september 2016 and acquired the first wideband low frequency brightness temperature spectra over the ice sheet and coastal region the results reveal strong spatial and spectral variations that correlate well with the physical properties of the surface encountered along the flight path which started over ocean then passed the rock near the coast and then up onto the ablation wet percolation and dry snow zones of the interior ice sheet in particular strong spectral responses in percolation and dry snow zones are observed and plausibly explained by varying the distribution of horizontal density layers and isolated icy bodies in the upper portion of the firn the success of the airborne deployment of the instrument and subsequent implementation of algorithms to limit radio frequency interference in unprotected bands is motivating continued airborne investigations as well as stimulating research into the feasibility of a spaceborne instrument

rupture parameters of the 2003 zemmouri mw 6 8 algeria earthquake from joint inversion of interferometric synthetic aperture radar coastal uplift and gps 1 we study the surface deformation associated with the 21 may 2003 mw 6 8 zemmouri algeria earthquake the strongest seismic event felt in the algiers region since 1716 the thrust earthquake mechanism and related surface deformation revealed an average 0 50 m coastal uplift along 55 km long coastline we obtain coseismic interferograms using envisat advanced synthetic aperture radar asar is2 and radarsat standard beam st4 data from both the ascending and descending orbits of envisat satellite whereas the radarsat data proved useful only in the descending mode while the two radarsat interferograms cover the earthquake area envisat data cover only the western half of the rupture zone although the interferometric synthetic aperture radar insar coherence in the epicenter area is poor deformation fringes are observed along the coast in different patches in the boumerdes area the maximum coseismic deformation is indicated by the high gradient of fringes visible in all interferograms in agreement with field measurements tape differential gps leveling and gps to constrain the earthquake rupture parameters we model the interferograms and uplift measurements using elastic dislocations on triangular fault patches in an elastic and homogeneous half space we invert the coseismic slip using first a planar surface and second a curved fault both constructed from triangular elements using poly3dinv program that uses a damped least square minimization the best fit of insar coastal uplift and gps data corresponds to a 65 km long fault rupture dipping 40 to 50 se located at 8 to 13 km offshore with a change in strike west of boumerdes from n60 65 to n95 105 the inferred rupture geometry at depth correlates well with the seismological results and may have critical implications for the seismic hazard assessment of the algiers region

regional isostatic response to messinian salinity crisis events abstract the salinity crisis of the mediterranean during messinian time was one of the most dramatic episodes of oceanic change of the past 20 or so million years resulting in the deposition of kilometer thick evaporitic sequences a large and rapid drawdown of the mediterranean water level caused erosion and deposition of non marine sediments in a large lago mare basin both the surface loading by the lower messinian evaporites and the removal of the water load resulted in isostatic flexural rebound that significantly affected river canyons and topographic slopes we use flexure models to quantitatively predict possible signatures of these events and verify these expectations at well studied margins the highly irregular shape of the reconstructed basin calls for a three dimensional model near basin margins plate bending effects are most pronounced which is why flexure is particularly important for a relatively narrow basin like the mediterranean we focus on one specific sea level scenario for the messinian salinity crisis where most of the evaporite load was deposited during a sea level highstand followed by a rapid desiccation evaporite loading at current sea level is expected to cause subsidence of the deep basins by hundreds of meters and simultaneous uplift of continental parts of the margins differential uplift may lead to significant slope angle changes and thus gravity flows the relative scarcity of lower evaporite sequences along the margins may be a result of these phenomena normal faulting of lower evaporite and older sediments and rocks is expected on the margins desiccation enhances erosion of the freshly exposed continental shelf and slope subsidence and riverbed sedimentation occurs on the continental margins and significant uplift towards the basin center reverse faulting is predicted at the margins finally regional isostatic uplift following zanclean flooding is predicted to destabilize margin slope deposits and to cause marginal uplift river down cutting and normal faulting

crustal block movements from holocene shorelines rhodes island greece abstract signs of up to eight stepped holocene shorelines which have been reported in a previous study on the east coast of rhodes island have been reinvestigated in detail on the basis of a new geomorphological survey identification and petrological analysis of many new samples of exposed marine organic crusts and over 30 radiocarbon datings confirmation was obtained of the view that the island can be charactered by considering small crustal blocks up to a dozen kilometres long with each block being affected by a specific tectonic history and a general trend towards an uplift increasing from south to north two successive phases of submergence emergence have been revealed by petrogenetic sequences in many samples which give evidence of the occurrence of positive and negative vertical movements this implies possible rejuvenation effects of the later submergence phase on the apparent age of pre existing algal crusts and those have been taken into account and estimated the most likely sequence of vertical crustal movements to have occurred has been specified for each block and a time range has been ascribed to each former shoreline independent up and down movements increasing in amplitude from south to north appear in most blocks there is a recurrent periodicity varying from a few hundred to one or at most two thousand years the largest vertical displacement observed during the late holocene a sudden uplift movement of about 3 8 m in the northernmost part of the island is likely to be linked with the earthquake which destroyed the colossus in 222 b c

extensive valley glacier deposits in the northern mid latitudes of mars evidence for late amazonian obliquity driven climate change understanding spin orbital parameter driven climate change on mars prior to 20 ma ago requires geological evidence because numerical solutions for that period are chaotic and non unique we show geological evidence that lineated valley fill at low midlatitudes in the northern hemisphere of mars 37 58 n originated through regional snow and ice accumulation and underwent glacial like flow breached upland craters and theater headed valleys reveal features typical of erosion in association with terrestrial glaciers parallel converging and chevron like lineations in potentially ice rich deposits on valley floors indicate that flow occurred through constrictions and converged from different directions at different velocities together these martian deposits and erosional landforms resemble those of intermontaine glacial systems on earth particularly in their major morphology topographic shape planform and detailed surface features an inferred late amazonian age combined with predictions of climate models suggest that the obliquity of mars exceeded a mean of 458 for a sustained period during this time significant transfer of ice occurred from icerich regions e g the poles to mid latitudes causing prolonged snow and ice accumulation there and forming an extensive system of valley glaciers d 2005 elsevier b v all rights reserved

in situquantification of ice rheology and direct measurement of the raymond effect at summit greenland using a phase sensitive radar 1 the glen exponent ncharacterizes the stress dependence of ice deformation directly influencing the rate at which ice masses respond to external forcing the slow deformation in large ice sheets makes laboratory rheometry at representative strain rates difficult we develop a new technique to estimaten in situ deploying a phase sensitive radar to measure vertical strain rates of around 10 4 yr 1within the top 1000 m of ice across ice divides at summit and neem greenland a fluid dynamical feature the raymond effect predicts strong vertical strain rate variation across divides over distances of a few ice thicknesses we achieve sufficient resolution to show this pattern enabling us to estimaten 4 5 by inverting our observations with flow modelling this is higher than values previously used but consistent with other indirect measurements implying laboratory measurements do not explore the full range of ice rheology and the consequent possibility of a greater sensitivity and responsiveness in ice sheet dynamics

ephemeral liquid water at the surface of the martian north polar residual cap results of numerical modelling abstract gypsum a mineral that requires water to form is common on the surface of mars most of it originated before 3 5 gyr when the red planet was more humid than now however occurrences of gypsum dune deposits around the north polar residual cap nprc seem to be surprisingly young late amazonian in age this shows that liquid water was present on mars even at times when surface conditions were as cold and dry as the present day a recently proposed mechanism for gypsum formation involves weathering of dust within ice e g niles p b michalski j 2009 nat geosci 2 215 220 however none of the previous studies have determined if this process is possible under current martian conditions here we use numerical modelling of heat transfer to show that during the warmest days of the summer solar irradiation may be sufficient to melt pure water ice located below a layer of dark dust particles albedo 0 13 lying on the steepest sections of the equator facing slopes of the spiral troughs within martian nprc during the times of high irradiance at the north pole every 51 ka caused by variation of orbital and rotational parameters of mars e g laskar j et al 2002 nature 419 375 377 this process could have taken place over larger parts of the spiral troughs the existence of small amounts of liquid water close to the surface even under current martian conditions fulfils one of the main requirements necessary to explain the formation of the extensive gypsum deposits around the nprc it also changes our understanding of the degree of current geological activity on mars and has important implications for estimating the astrobiological potential of mars

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

influence of bubbles on grain growth in ice abstract numerical static grain growth simulations of ice with air bubbles as a second phase show a significant drop in grain growth rate compared to bubble free ice the magnitude of this drop in growth rate is dependent on the bubble boundary mobility the volume fraction of air the average bubble size and the bubble size distribution the rate of grain growth decreases at first as the microstructure evolves towards a steady state only then does grain growth follow the expected linear increase of mean grain area with time in experiments this decrease in growth rate could erroneously be interpreted as growth with a deviating growth exponent

rate controlling processes in the creep of polar ice influence of grain boundary migration associated with recrystallization abstract information on the deformation modes and recrystallization processes in polar ice sheets was obtained thanks to the analysis of the ice structure along two deep ice cores from greenland and antarctica it is shown that the deformation of polar ice at low stresses is produced by intracrystalline slip accommodated by grain boundary migration gbm a deformation model based on an equilibrium between work hardening and recovery processes has been developed the decrease in dislocation density is due to both gbm associated with grain growth and the formation of boundaries by recrystallization the value of the dislocation density along the byrd and grip ice cores obtained thanks to the model is about 1 10 11 m 2 this value is in agreement with data from synchrotron x ray diffraction on samples taken along the core this deformation model can account for the deformation of polar ice at low stresses it is shown that the flow law with a stress exponent lower than 2 can be related to the efficiency of gbm as a recovery process

transient post glacial processes on mars geomorphologic evidence for a paraglacial period abstract on earth a transitional phase between glacial and interglacial periods is referred to as the paraglacial period this period immediately postdates glacial retreat and is characterized by ice removal glacial unloading and the exposure of steep slopes and large sediment stores these responses led to the development of a suite of morphologic units e g talus cones gullies sackungen and polygons which when observed together are indicative of the paraglacial period a similar period of transitional climate and deglaciation is identified on mars in the late amazonian characterized by the association of features in a glaciated 10 6 km diameter mid latitude crater this crater contains concentric crater fill ccf formed by debris covered glaciers as well as a suite of stratigraphically younger geomorphic units e g spatulate depressions washboard terrain gullies and polygonal terrain that are all indicative of the local environmental response to deglaciation these features are interpreted to represent a geologically recent martian paraglacial period within this crater the morphology and relative stratigraphic relationships among these paraglacial features are described in order to assess the processes operating during deglaciation and to document the recent history of glaciation on mars spatulate depressions formed by the differential sublimation of pure glacial ice near the base of the crater wall subsequently due to the loss of basal support and steepened slopes remnant ice on the crater wall began to flow downhill and formed transverse crevasses that created washboard terrain continuous thermal cycling of sediment mantled ice on crater walls created fractures that formed polygonal terrain during this time and after gullies formed by the transport of sediment downslope from crater rim alcoves analyses of modeled obliquity variations suggest that the paraglacial period could have operated within the last 5 myr and may still be ongoing suggesting that the current martian paraglacial period is much longer in duration than typical paraglacial periods on earth understanding the nature and sequence of paraglacial activity can help to identify variations in climate in recent mars history

a new device for the measurement of air content in polar ice a new device for measuring air content in polar ice has been designed built and tested with 22 samples of antarctic ice the new technique is based on the barometric method which implies 1 air extraction under vacuum by melting refreezing of the ice sample placed in a calibrated cell and 2 accurate air pressure and temperature measurements the new apparatus simplifies the experimental procedures decreases the duration of measurement and can eventually be used in the field it provides results with an accuracy equivalent to or better than other methods previously used

coastal staircase sequences reflecting sea level oscillations and tectonic uplift during the quaternary and neogene many coasts feature sequences of quaternary and neogene shorelines that are shaped by a combination of sea level oscillations and tectonics we compiled a global synthesis of sea level changes for the following highstands mis 1 mis 3 mis 5e and mis 11 also we date the apparent onset of sequences of paleoshorelines either from published data or tentatively extrapolating an age for the uppermost purported oldest shoreline in each sequence including the most documented mis 5e benchmark we identify 926 sequences out of which 185 also feature holocene shorelines six areas are identified where elevations of the mis 3 shorelines are known and 31 feature elevation data for mis 11 shorelines genetic relationships to regional geodynamics are further explored based on the elevations of the mis 5e benchmark mean apparent uplift rates range from 0 01 0 01 mm yr hotspots to 1 47 0 08 mm yr continental collision passive margins appear as ubiquitously uplifting while tectonic segmentation is more important on active margins from the literature and our extrapolations we infer ages for the onset of formation for 180 coastal sequences sea level fingerprinting on coastal sequences started at least during mid miocene and locally as early as eocene whether due to the changes in the bulk volume of seawater or to the temporal variations in the shape of ocean basins estimates of eustasy fail to explain the magnitude of the apparent sea level drop thus vertical ground motion is invoked and we interpret the long lasting development of those paleoshore sequences as the imprint of glacial cycles on globally uplifted margins in response to continental compression the geomorphological expression of the sequences matches the amplitude and frequency of glacial cyclicity from middle pleistocene to present day moderately fast 100 000 yrs oscillating sea levels favor the development of well identified strandlines that are distinct from one another pliocene and lower pleistocene strandlines associated with faster cyclicity 40 000 yrs are more compact and easily merge into rasas whereas older cenozoic low frequency eustatic changes generally led to widespread flat lying coastal plains

goringe alboran tell tectonic zone a transpression system along the africa eurasia plate boundary neotectonic structures distributed from the goringe bank to the tell atlas mountains show that the africa eurasia plate boundary in the western mediterranean corresponds to an east west trending deforming zone goringe alboran tell main pliocene and quaternary tectonic structures of the northern atlas mountains are northeast southwest striking fault related folds similar to that of el asnam and are related to north south to northwest southeast compressional movements active tectonics in agreement with the main seismicity distribution and focal mechanisms also support an oblique plate convergence and the existence of a 50 100 km wide transpression zone from goringe across alboran to the tell atlas mountains a kinematic model shows the interaction between dextral transcurrent faults and left lateral faults with block rotations and no lateral extension pinned model shortening and lateral movement rates during the quaternary are estimated to be 1 0 2 3 mm yr and block rotation rate is estimated as 2 5 3 9 m y the plate boundary may correspond to a transpression zone active thrust faults being controlled by deep seated dextral transcurrent faults

periglacial weathering and headwall erosion in cirque glacier bergschrunds glaciers produce cirques by scouring their beds and sapping their headwalls but evidence to constrain models of these processes has been elusive we report a suite of environmental measurements from three cirque glacier bergschrunds including the first temperature series recorded at depth throughout most of an annual cycle compared to the ambient air the bergschrunds were colder in summer and warmer in winter freeze thaw cycles were rare and relatively stable subfreezing temperatures persisted from november until may using a model for rock fracturing driven by ice segregation we demonstrate that favorable conditions for fracturing occur not only on the headwall above the glacier but also within the bergschrund where periglacial weathering and glacial transport can act together to drive cirque headwall retreat a small 3 c year round decrease in temperatures to conditions more typical of the pleistocene would likely intensify the weathering process though so far ignored in all glacial landscape evolution models the bergschrund likely plays an essential role in the sculpting of alpine landscapes

a review of possible eustatic isostatic and tectonic contributions in eight late holocene relative sea level histories from the mediterranean area abstract this paper consists of a comparison between eight late holocene sea level histories investigated by the author in different mediterranean areas and sea level predictions in the same areas made by global isostatic models the areas include three regions that are generally considered as tectonically relatively stable 1 the southern coast of france 2 sardinia and 3 the southern coasts of tunisia where late holocene evidence may be either of submergence or of emergence also considered are 4 a subsidence region in the northern adriatic and actively uplifting areas 5 in calabria and 6 in nisyros island greece lastly case studies in areas affected by repeated coseismic vertical displacements include 7 western crete and antikythira island in the hellenic arc and 8 the levant coasts of turkey syria and the lebanon in each case the question of whether the evidence available may or may not be consistent with gradual isostatic or eustatic displacements has been explored it appears that in non tectonic areas the hydro isostatic effects have been overestimated sardinia or underestimated southern tunisia by the same models in the northern adriatic the closest mediterranean area to the former scandinavian ice sheet glacio eustatic effects are suspected to be almost absent our analysis failed to quantify isostatic effects in areas of rapid tectonic uplift calabria and nisyros but rejected predictions of significant isostatic subsidence in the hellenic arc and on the levant coast finally several data from tectonic and non tectonic areas are consistent with nearly stable global eustasy since 6000 bp thus challenging the assertion of significant additional melting of antarctica after the complete melting of the former northern hemisphere ice caps

analyzing and modeling the smos spatial variations in the east antarctic plateau abstract the smos brightness temperature t b collected on the east antarctic plateau revealed spatial signatures at l band that have never before been observed when only higher frequency passive microwave observations were available and this has opened up a new field of research because of the much greater penetration depth modeling the microwave ice sheet emission requires taking into account not only snow conditions on the surface but should also include glaciological information even if the penetration depth of the l band is not well known due to the uncertainty on the imaginary part of the ice permittivity it is likely to be of the order of several hundreds of meters which means that the temperature of the ice over a depth of nearly 1000 m influences the emission over such a depth the temperature is related to both the surface conditions and to the ice sheet thickness which in turn depends on the bedrock topography and on other glaciological variables the present paper aims to provide a thorough theoretical explanation of the observed t b spatial variation close to the brewster angle at vertical polarization in order to limit the effect of surface and vertical density variability in the firn in order to provide reliable inputs to the microwave emission models used for simulating t b data an in depth analysis of the temperature profiles was performed by means of glaciological models the comparison between simulated and observed data over three transects totalling 2000 km in east antarctica pointed out that whereas the emission models are capable of explaining the t b spatial variations of several kelvins 0 7 and 2 9 k they are unable to predict its absolute value correctly this study also shows that the main limiting factor in simulating low frequency microwave data is the uncertainty in the currently available imaginary part of the ice permittivity

late holocene shoreline changes related to palaeoseismic events in the ionian islands greece a systematic multidisciplinary survey on the coasts of the ionian islands founded on 26 new radiocarbon accelerator mass spectrography ams dates has revealed the occurrence of sectors which were uplifted seismo tectonically during the late holocene in corfu two uplift movements of about 0 8m each took place in the central part of the island one of them around 790 400 cal bc and also at a more recent undetermined date in levkas up and down tectonic movements of metric order governed late holocene relative sea level changes at least in the northern part of the island submergence of at least 2 5 m occurred since 2400 years ago with a possible spasmodic subsidence around cal ad 500 700 in cephalonia two vertical displacements affected most of the island around cal ad 350 710 and in ad 1953 both movements resulted in uplift in the southeastern part of the island submergence seems to predominate round ithaca lastly in zante clear evidence of a holocene crustal block movement is limited

the 1953 earthquake in cephalonia western hellenic arc coastal uplift and halotectonic faulting summary geomorphological marine biological and radiometric data in combination with earlier reports reveal that the m 7 2 1953 cephalonia earthquake the most destructive but least studied earthquake in greece this century was associated with a 0 3 0 7m quasi rigid body uplift and westward tilting of the central part of the island another palaeoseismic event around 1500 yr bp associated with coastal uplifts was also identified structural data indicate that the 1953 uplift is bounded by two subparallel east dipping major reverse faults and corresponds to a piston like motion this structurally unusual pattern of seismic deformation is detached from the deformation of the basement conspicuously a thrust and different from the long term deformation pattern of the area it is probably due to the particularities of salt tectonics a 1500m thick salt layer acts as a regional dccollement while thinner layers are sandwiched between the carbonate thrust sheets that compose the overburden and reduce their friction during fault movement this crustal anisotropy is responsible for the observed anomalous attenuation of seismic waves during the 1953 and historical earthquakes the 1953 seismic surface deformation mimics long term halotectonic patterns but is not directly indicative of the regional stress field for it reflects uplift induced stresses only

bubbly ice densification in ice sheets i theory dry snow on the surface of polar ice ice sheets is first densified and metamorphosed to produce firn bubbly ice is the next stage of the transformation process which takes place below the depth of pore closure this stage extends to the transition zone where due to high pressures and low temperatures air trapped in bubbles and ice begins to form the mixed air clathrate hydrates while the gas phase progressively disappears here we develop a model of bubbly ice rheology and ice sheet dynamics taking into account glacier ice compressibility the interaction between hydrostatic compression of air bubbles deviatoric uniaxial compressive deformation of the ice matrix and global deformations of the glacier body is considered the ice matrix pressure and the absolute load pressure are distinguished similarity theory and scale analysis are used to examine the resultant mathematical model of bubbly ice densification the initial rate of bubble compression in ice sheets appears to be relatively high so that the pressure density relaxation process takes place only 150 200 m in depth below pore close off to reach its asymptotic phase wherein the minimal drop between bubble and ice pressures is governed by the rate of loading ice accumulation this makes it possible to consider densification under stationary present day conditions of ice formation as a special case of primary interest the computational tests performed with the model indicate that both ice porosity and bubble pressure profiles in ice sheets are sensitive to variations of the rheological parameters of pure ice however only the bubble pressure profile distinguishes between the rheological properties at low and high stresses the porosity profile at the asymptotic phase is mostly determined by the air content in the ice in the companion paper lipenkov and others 1997 we apply the model to experimental data from polar ice cores and deduce through an inverse procedure the rheological properties of pure ice as well as the mean air content in holocene and glacial ice sediments at vostok station antarctica

height changes over subglacial lake vostok east antarctica insights from gnss observations height changes of the ice surface above subglacial lake vostok east antarctica reflect the integral effect of different processes within the subglacial environment and the ice sheet repeated gnss global navigation satellite systems observations on 56 surface markers in the lake vostok region spanning 11 years and continuous gnss observations at vostok station over 5 years are used to determine the vertical firn particle movement vertical marker velocities are derived with an accuracy of 1 cm yr or better repeated measurements of surface height profiles around vostok station using kinematic gnss observations on a snowmobile allow the quantification of surface height changes at 308 crossover points the height change rate was determined at 1 5 mm yr thus indicating a stable ice surface height over the last decade it is concluded that both the local mass balance of the ice and the lake level of the entire lake have been stable throughout the observation period the continuous gnss observations demonstrate that the particle heights vary linearly with time nonlinear height changes do not exceed 1 cm at vostok station and constrain the magnitude of spatiotemporal lake level variations icesat laser altimetry data confirm that the amplitude of the surface deformations over the lake is restricted to a few centimeters assuming the ice sheet to be in steady state over the entire lake estimates for the surface accumulation on basal accretion melt rates and on flux divergence are derived

on the potential of coupling air content and o2 n2 from trapped airfor establishing an ice core chronology tuned on local insolation the potential to access an ice core chronology tuned on local insolation has been demonstrated for the first time in the work of m bender 2002 linking the variations of o2 n2 ratios in the air trapped in the vostok ice with local 78 s summertime insolation more recently it has been shown that the long term changes in air content v recorded in ice from the high antarctic plateau are also dominantly imprinted by the local summer insolation raynaud et al 2007 this paper presents a new v record from vostok which is compared with the published vostok o2 n2 record for the same period of time 160 390 ka bp by using the same spectral analysis methods the spectral differences between the two properties and the possible mechanisms linking them with insolation through the surface snow structure and the close off processes are discussed the main result of our study is that the two experimentally independent local insolation proxies lead to absolute orbital timescales which agree together within less than 1 ka on average this result strongly adds credibility to the total content and the o2 to n2 ratio of the air trapped in ice as reliable and complementary tools for accurate dating of existing and future deep ice cores

characteristics of the bergschrund of an avalanche cone glacier in the canadian rocky mountains etude sur le terrain de la rimaye d un petit glacier dans les rocheuses canadiennes en particulier on analyse les effets de la topographie du lit rocheux les effets de la fonte des ecoulements et des taux de depot et de metamorphisme de la neige

reply to the comment of pedoja et al by maouche s meghraoui m morhange c belabbes s bouhadad y and haddoum h on the published paper maouche s meghraoui m morhange c belabbes s bouhadad y and haddoum h 2011 active coastal thrusting and folding and uplift rate of the sahel anticline and zemmouri earthquake area tell atlas algeria tectonophysics 509 2011 69 80 reply to the comment of pedoja et al by maouche s meghraoui m morhange c belabbes s bouhadad y and haddoum h on the published paper maouche s meghraoui m morhange c belabbes s bouhadad y and haddoum h 2011 active coastal thrusting and folding and uplift rate of the sahel anticline and zemmouri earthquake area tell atlas algeria tectonophysics 509 2011 69 80 said maouche mustapha meghraoui christophe morhange samir belabbes youcef bouhadad hamid haddoum

bubbly ice densification in ice sheets ii applications a mathematical model for simulating the densification of bubbly glacier ice is used to interpret the following experimental data from the vostok central antarctica ice core two ice porosity profiles obtained by independent methods and a bubble pressure profile obtained by direct measurements of air pressure within individual bubbles the rheological properties of pure polycrystalline ice are deduced from the solution of the inverse problem the model and the inferred ice flow law are then validated using porosity profiles from seven other ice cores drilled in antarctica and greenland in the temperature range from 55 to 20 c the following expression is adopted for the constitutive law 2e 1 2 exp q 1 t s 1 t r s where e and are the effective strain rate and stress respectively is the creep exponent taken as 3 5 r s is the gas constant and t t s is the temperature standard temperature the numerical values obtained for the linear and non linear viscosities are 1 2 9 1 3 mpayear and 2 0 051 0 019 mpa year and the apparent activation energy q is confirmed to be 60 kj mole 1 the corresponding flow law is in good agreement with results of both mechanical tests and independent estimations based on the analysis of different natural phenomena associated with glacier ice deformation when the model is constrained by the porosity and bubble pressure profiles from vostok the mean air content in holocene ice is inferred to be about 0 088 cm 3 g 1 the corresponding mean air pressure in bubbles at the end of pore closure is about 0 083 mpa whereas the atmospheric pressure at this depth level would be 0 063 mpa the influence of the climatic change on the ice porosity profile is discussed it resulted in an increased air content in ice at vostok during the last glacial maximum 0 096 cm 3 g 1

on the retrieval of internal temperature of antarctica ice sheet by using smos observations abstract internal temperature is an essential parameter for understanding ice sheet dynamics glaciological models provide estimations of temperature profiles over antarctica and few boreholes are also available but at present no measurement exists at the scale of the whole continent the analysis of passive l band observations from the soil moisture and ocean salinity smos satellite shows that thanks to the high penetration depth i e up to 1500 m it is possible to infer information on in depth glaciological properties of the ice sheet including temperature in this study the temperature profile is retrieved from smos observations using jointly glaciological and emission models the developed methodology is valid in the inner part of antarctica where the ice sheet is almost stable i e its velocity is limited to 10 m yr 1 this analysis points out that in several cases differences are observed between retrieved temperature profiles and those predicted by glaciological models in particular some geophysical parameters namely the geothermal heat flux and the mean annual accumulation need to be modified with respect to their prior values in order to simulate smos brightness temperatures results also clearly show that the reliability of the retrieved profile in depth decreases with increasing ice thickness due to the limited penetration of microwaves in the ice the obtained results prove the capability of l band 1 4 ghz passive microwave sensors for investigating the internal temperature of the ice sheet

observational evidence on the stability of the hydro glaciological regime of subglacial lake vostok 1 combined geodetic geophysical and glaciological in situ measurements are interpreted regarding surface height changes over subglacial lake vostok and the local mass balance of the ice sheet at vostok station repeated gps observations spanning 5 years and long term surface accumulation data show that the height of the lake surface has not changed over the observation period the application of the mass conservation equation to purely observational data yields an ice mass balance for vostok station close to equilibrium

l band ice sheet brightness temperatures at dome c antarctica spectral emission modelling temporal stability and impact of the ionosphere the temporal thermal stability size structure and spatial uniformity of antarctic plateau regions such as dome c make them ideal candidates for external calibration and validation or radiometric performance monitoring of planned space borne l band radiometers such as the soil moisture and ocean salinity smos radiometer as experimental observations do not exist at this frequency a combination of historical ka xand c band data are used together with electromagnetic and ionospheric models to extrapolate to this longer wavelength dome c is demonstrated to exhibit negligible seasonal variability 0 1k and may prove to be a suitable candidate provided the effects of atmospheric and ionospheric perturbations can be mitigated

earthquake induced flooding and paleoseismicity of the el asnam algeria fault related fold late quaternary activity of the el asnam thrust fault responsible for the october 10 1980 ms 7 3 earthquake and 36 km coseismic faulting is explored through diverse paleoseismological field methods we trenched through the main and secondary 1980 coseismic scarps made an analysis of earthquake induced flood deposits conducted a geomorphic study of leveling profiles and offset geological units across thrust and normal scarps and considered the geomorphology of the active fold twenty five radiocarbon ages from colluvial and alluvial deposits along with conventional fossils and artefacts dating of geological units show the timing of successive net vertical displacements on the thrust related fold and bending moment faults previous work showed that eight pre 1980 earthquakes occurred in clusters during the late holocene cumulative net vertical slip that amounts to 3 times the 1980 displacement is observed on multiple thrust fault scarps and offsets of geological units on bending moment faults maximum cumulative vertical displacements which are visible in different zones along the fault segments can reach 10 to 25 times the 1980 coseismic displacements the late quaternary uplift rate on the el asnam fault is 0 6 mm yr and taking into account slip variation along the fault this rate may range between 0 25 1 6 mm yr from which we obtain a shortening rate of 0 17 1 2 mm yr because the tell atlas mountains exhibit comparable seismogenic fault related folds with parallel and sequential structures of active faults a total average shortening rate of 2 05 mm yr during the late quaternary represents part of the convergence accommodated along the africa eurasia plate boundary

spatial variation of englacial radar attenuation modeling approach and application to the vostok flowline 1 constraining the spatial variation of englacial radar attenuation is critical for accurate inference of the spatial variation of the englacial and basal properties of ice sheets from radar returned power here we evaluate attenuation models that account for spatial variations in ice temperature and chemistry and test them along the flowline that passes through the vostok ice core site antarctica the simplest model often used but rarely valid assumes a uniform attenuation rate everywhere along the flowline so that total attenuation is proportional to ice thickness the next simplest model uses spatially varying temperatures predicted by an ice flow model and assumes uniform chemistry additional models account for spatially varying chemistry using englacial stratigraphy we find that the roundtrip attenuation to the bed can easily differ by 10 db or more between the uniform attenuation rate model and models that account for variable ice temperature such differences are sufficient to confound the delineation of dry and wet beds also including spatial variations in chemistry produces smaller differences 10 db but the magnitude of these differences depends on the relative importance of dry and wet deposition of impurities in the past accounting for dry deposited impurities requires ice flow modeling and results in larger differences from all other models which assume uniform chemistry or wet deposition only these results indicate that modeling the spatial variation of attenuation requires a spatially varying temperature model in order to infer bed conditions from bed returned power accurately and that both ice core data and radar stratigraphy are also strongly desirable

coastal uplift and thrust faulting associated with the mw 6 8 zemmouri algeria earthquake of 21 may 2003 1 a shoreline uplift marked by a continuous white band visible at rocky headlands occurred during the 21 may 2003 earthquake mw 6 8 in northern algeria we measured the amount of coastal uplift on a white band emerged algae and harbors quays between boumerdes and dellys most of measured points were collected using tape and differential gps on rocky headlands with 0 15 m error bar tidal prism leveling lines running parallel and orthogonal to the coast also provide the precise amount of uplift in the epicentral area the uplift distribution shows an average 0 55 m along the shoreline with a maximum 0 75 m east of boumerdes and a minimum close to 0 near cap djinet the active deformation related to a thrust fault is modeled along the 55 km coastline the dislocation model predicts surface slip on a n 54 e trending reverse fault dipping 50 se in agreement with cmt solution and coastal uplift the faulting characteristics imply a fault geometry with possible sea bottom ruptures between 5 to 10 km offshore

dynamic recrystallization and texture development in ice as revealed by the study of deep ice cores in antarctica and greenland the preferred c axis orientation of ice from polar ice sheets develops essentially as a result of intracrystalline slip but dynamic recrystallization appears to alter the kinetics of the development of deformation textures and is at high temperature at the origin of recrystallization textures the purpose of this work is to obtain a better understanding of recrystallization processes that occur in polar ice sheets and to clarify the relationship between dynamic recrystallization and textures the study was based on two deep ice cores from greenland and antarctica the greenland ice core project grip and vostok ice cores the structure along the grip core displays normal grain growth in the first 100 m of the ice sheet and rotation recrystallization and migration recrystallization near the bottom only grain growth and rotation recrystallization appear to occur in the vostok ice core the transition between these recrystallization regimes was studied estimating for interglacial ice the evolution with depth of the dislocation density this calculation has shown the efficiency of grain boundary migration for the absorption of dislocations at vostok the highest value of the dislocation density is found at a depth of about 1000 m and the continuous decrease in the dislocation density below this depth is related to the increase of the grain boundary migration rate it is shown that the driving force required to initiate migration recrystallization is not reached in interglacial ice at vostok the observed textures were compared with those predicted by the self consistent approach recrystallization textures are interpreted by assuming that the less stressed grains i e the best oriented for basal slip are favored by the size advantage of subgrains the recrystallization textures are compared with those of other materials

subaerial salt extrusions in iran as analogues of ice sheets streams and glaciers abstract ice h20 and salt halite nacl share many physical properties and resemble each other in hand specimens and subaerial gravity driven flows however while most significant bodies of ice accumulate in cold highlands and gravity spread where and soon after they form most significant bodies of salt accumulate in tropical marine basins and have to be buried by 1 km of other rocks before they flow buried salt is driven by differential loading into various categories of piercing structures known as diapirs many diapirs extrude onto the surface as sheets of allochthonous out of place salt thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years mainly in the toes of passive continental margins and in orogenic belts where some are 103 km2 in area most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in iran these were compared to ice glaciers soon after they were introduced to western science a comparison that has been neglected since here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists the profiles internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss however whereas snow merely compacts where it accumulates salt sheets are fed from below by already deformed salt when salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier like flows known as namakiers after locally exhausting their deep source layers salt fountains spread to the profiles of viscous droplets normal for ice caps ice typically deforms at 80 usually 90 of its absolute melting temperature while most salt deforms at

active coastal thrusting and folding and uplift rate of the sahel anticline and zemmouri earthquake area tell atlas algeria abstract major uplifts of late quaternary marine terraces are visible along the coastline of the tell atlas of algeria located along the africa eurasia convergent plate boundary the active tectonics of this region is associated with large shallow earthquakes m 6 5 numerous thrust mechanisms and surface fault related fold we conducted a detailed levelling survey of late pleistocene and holocene marine notches in the algiers region that experienced 0 50 m coastal uplift during the 2003 zemmouri earthquake mw 6 8 east of algiers holocene marine indicators show three pre 2003 main notch levels formed in the last 21 9 ka west of algiers on the sahel anticline the levelling of uplifted marine terraces shows a distinct staircase morphology with successive notches that document the incremental folding uplift during the late pleistocene and holocene the timing of successive uplifts related to past coseismic movements along this coastal region indicates episodic activity during the late holocene modelling of surface deformation in the zemmouri earthquake area implies a 50 km long 20 km wide ne sw trending se dipping fault rupture and an average 1 3 m coseismic slip at depth further west the 70 km long sahel fold is subdivided in 3 sub segments and shows 0 84 1 2 mm yr uplift rate in the last 120 140 ka the homogeneous holocene uplift of marine terraces and the anticline dimensions imply the possible occurrence of large earthquakes with mw 7 in the past the surface deformation and related successive uplifts are modelled to infer the size and characteristics of probable future earthquakes and their seismic hazard implications for the algiers region

physical and climatic parameters which influence the air content in polar ice abstract under present day climatic conditions the air content of polar ice v generally shows a high sensitivity to the atmospheric pressure and hence to the surface elevation of the ice sheet wherethe ice is formed the results presented here are from sixteen different sites fourteen in antartica one in greenland and one in the yukon territories canada and they allow a better understanding of the parameters which influence the air content in ice it is demonstrated the v can be expressed very simply as a function of the atmospheric pressure p i the temperature t i and the porous volume of ice v i at which the air in the firn becomes isolated in terms of pressure from the atmosphere during the process of pore close off our results confirm a v i increase with temperature and show no clear v i dependence on snow accumulation rate the possible non linearity of the v i t i relation we obtain could be due to a wind influence on v i and or to a second order effect of the accumulation rate our v i results are compared to measurements of the volume of closed pores versus depth in the firn to close we discuss the parameterization that we can obtain to interpret the air content variations observed in deep ice cores over periods covering glacial interglacial transitions in terms of paleoclimatic conditions prevailing at the surface of the ice sheet

fractionation of gases in polar ice during bubble close off new constraints from firn air ne kr and xe observations gas ratios in air withdrawn from polar firn snowpack show systematic enrichments of ne n2 o 2 n2 and ar n2 in the firn ice transition region where bubbles are closing off air from the bubbles in polar ice is correspondingly depleted in these ratios after accounting for gravitational effects gas in the bubbles becomes fractionated during the process of bubble close off and fractionation may continue as ice cores are stored prior to analysis we present results from firn air studies at south pole and siple dome antarctica which add ne kr and xe measurements to the suite of observations ne o2 and ar appear to be preferentially excluded from the shrinking and occluding bubbles and these gases therefore accumulate in the residual firn air creating a progressive enrichment with time and depth in firn air early sealing of gases by thin horizontal impermeable layers into a nondiffusive zone or lock in zone greatly enhances this enrichment a simple model of the bubble close off fractionation and lock in zone enrichment fits the data adequately the model presumes that fractionation is caused by selective permeation of gas through the ice lattice from slightly overpressured bubbles the effect appears to be size dependent because ne o2 and ar have smaller effective molecular diameters than n2 and fractionation increases strongly with decreasing size ne is fractionated 34 2 times more than o2 in south pole firn air and reaches an enrichment of 90 in the deepest sample the large atoms kr and xe do not appear to be fractionated by this process despite the large size difference between the two gases suggesting a threshold atomic diameter of 3 6a above which the probability becomes very small that the gas will escape from the bubble these findings have implications for ice core and firn air studies that use gas ratios to infer paleotemperature chronology and past atmospheric composition

a user friendly anisotropic flow law for ice sheet modelling for accurate ice sheet flow modelling the anisotropic behaviour of ice must be taken fully into account however physically based micro macro m m models for the behaviour of an anisotropic ice polycrystal are too complex to be implemented easily in large scale ice sheet flow models an easy and efficient method to remedy this is presented polar ice is assumed to behave as a linearly viscous orthotropic material whose general flow law golf depends on six parameters and its orthotropic fabric is described by an orientation distribution function odf depending on two parameters a method to pass from the odf to a discrete description of the fabric and vice versa is presented considering any available m m model the parameters of the golf that fit the response obtained by running this m m model are calculated for any set of odf parameters it is thus possible to tabulate the golf over a grid in the space of the odf parameters this step is performed once and for all ice sheet flow models need the general form of the golf to be implemented in the available code once then during each individual run to retrieve the golf parameters from the table by interpolation as an example author i have changed from application ok the golf is tabulated using three different m m models and used to derive the rheological properties of ice along the grip ice core

modelling of the densification of polar firn characterization of the snow firn transition the transformation of dry snow to firn is described by the transition between densification by deformationless restacking and densification by power law creep the observed decrease with temperature of the density at the snow firn transition seems to result from the competition between grain boundary sliding and power law creep these two densification processess occur concurrenlly in snow although there are probably micro regions in which sliding alone occurs validation ofa geometrical densifi cation model developed for ceramics has been obtained from densification data from several antarctic and greenland sites and from the characterization of the structure of polar firn

radiometric approach for estimating relative changes in intraglacier average temperature we investigate the degree to which ultrahigh frequency radio emission can be used to estimate subsurface physical temperature in the polar ice sheets we combine electromagnetic emission forward models with plausible models of depth dependent physical properties in the ice sheet temperature models are parameterized with variables including accumulation rate geothermal heat flux and surface temperature scattering is parameterized using empirical observations of grain growth combined with measured densities electromagnetic absorption is modeled using dielectric dispersion processes and semiempirical models based on observations our models illustrate that information about east antarctic ice sheet temperature from near the surface to near the base can be gleaned from ultrawideband radiometer data based on our modeling study we illustrate an instrument concept to measure ice sheet temperature profiles comprising a novel ultrawideband radiometer

air bubbles and clathrate hydrates in the transition zone of the ngrip deep ice core abstract field studies of air bubble and clathrate inclusions in the ngrip ice core reveal two stages of clathrate formation in the transition zone translucent primary clathrates with rough surfaces and irregular shapes formed from individual bubbles split up and form smaller specimens deeper down in the transition zone 1100 m clathrate metamorphosis sets in giving rise to the formation of transparent secondary clathrates with smooth and regular often poly hedral or faceted shapes rod like crystals of great length 2 mm often show signs of separation into smaller units that fragment into smaller specimens these findings imply that the simplified picture of one bubble forming one clathrate has to be modified

short term velocity variations and basal coupling near a bergschrund storglaciaren sweden distance measurements using an automated electronic distance measurement system in the north cirque of storglaciaren sweden during the summer of 1989 revealed a diurnal variation in glacier speed amplitude and timing of the diurnal cycle correlate well with the timing and intensity of the diurnal temperature cycle indicating that speed responds to variations in daily melt with a lag of approximately 4 h one 2 d period of non diurnal velocity variations corresponded with a large rainfall event finite element modeling suggests that these velocity variations must be closely related to water inputs in the cirque rather than to longitudinal coupling with lower parts of the glacier

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

air content paleo record in the vostok ice core antarctica a mixed record of climatic and glaciological parameters under present day climatic conditions the air content of ice shows a high sensitivity to the atmospheric pressure and hence to the elevation at the surface of the ice sheet this observation has been used to infer past ice sheet thickness variations of antarctica and greenland a high resolution air content profile more than 1000 measurements covering approximately the last 200 000 years was obtained along the 2546 m long vostok ice core three analytical techniques were used leading to consistent results which show large amplitude and rapid air content variations the vostok results support thicker thinner ice in the central part of east antarctica during warm cold periods

flow at ice divide triple junctions 1 three dimensional full stokes modeling 1 ice domes are either axisymmetric high points along ridges or ridge triple junctions we model time dependent isothermal flow near triple junctions solving the full set of mechanical equations with a nonlinear power law rheology forcing is applied through the boundary conditions which affect flow patterns at outlets where such forcing is purely axisymmetric an axisymmetric dome is formed if a threefold symmetry in the forcing is applied the axisymmetric dome breaks up into three ridges subtending angles of 120 sets of experiments where the forcing was not exactly threefold symmetric by angle or by amplitude caused the triple junction to migrate to a new steady state here in steady state the ridges join the triple junction at nearly 120 but one ridge curves to satisfy the boundary forcing the slope pattern in the immediate dome vicinity depends only on a dimensionless parameter which is a function of the ice consistency the accumulation and the rheological power law index attempts to replicate the topography around summit greenland obtained a good fit with n 3 at a triple junction the dome is really distinct from the surrounding ridges contrary to the highest point of a single ridge divide as a consequence the raymond effect is at its strongest at the dome and weakens considerably over one ice thickness as one moves away from the flow center along the ridges leaving the dome the raymond effect is still present and decreases with the ratio of the flow across and along the ridge in the vicinity of the dome horizontal strain rates vary strongly from uniaxial to biaxial large scale effects represented in our model as fluxes at boundaries seem to be the primary controls on dome position and shape

simple relations for the close off depth and age in dry snow densification a physical model for the snow firn densification process salamatin and others 2006 and martinerie and others 1992 1994 correlation for the firn density at the pore closure are employed to perform a scale analysis and computational experiments in order to deduce simplified relations for the close off depth and ice age in quasi stationary ice formation conditions the critical snow density at which ice grain rearrangement stops is used to take into account variability of snow structures subjected to densification the results obtained are validated on a representative set of ice core data from 22 sites which covers wide ranges of present day temperatures and ice accumulation rates a simple analytical approximation for the density depth profile is proposed