variations of the effective elastic thickness reveal tectonic fragmentation of the antarctic lithosphere abstract to this day little is known about thermal and rheological properties of the antarctic lithosphere we derive the effective elastic thickness t e as a proxy for these parameters by using ice thickness bedrock topography and a combination of new satellite and high resolution terrestrial gravity data cross spectral analysis based on the fan wavelet technique was employed to calculate t e variations by means of admittance and coherence techniques our results confirm a clear tectonic division of antarctica with predominantly high values in east antarctica eant t e 60 80 km and low values in west antarctica want t e 5 20 km for the transantarctic mountains separating these provinces we found t e to be around 10 km along the whole chain which is comparable to want apart from this general division we found fragmentation of the lithosphere within these provinces especially eant doesn t represent a single lithospheric block but shows strong variations of t e the highest values are found around the aurora subglacial basin t e 90 km and in dronning maud land t e 80 km the minimum value of t e within eant 15 km is found in the lambert graben such a low value can be associated with active rifting in the permian triassic strong localized erosion or possibly the effect of a cenozoic mantle plume according to the coherence calculations the weak zone extends to the gamburtsev subglacial mountains gsm showing a distinct decrease of t e to 25 30 km thus this weak channel divides the previously mentioned strong blocks however the admittance analysis gives relatively high values t e 70 km for the gsm based on the analysis of the wavelength dependent admittance and coherence results and misfits for several principal locations we give some preference to the coherence based values

sub ice topography and meteorite finds near the allan hills and the near western ice field victoria land antarctica we have investigated the glaciological causes of large meteorite concentrations on blue ice fields west and southwest of the allan hills in antarctica a sub ice topography map for the area was prepared from data of a radio echo sounding survey the map reveals a mesa type paleosurface it was formed prior to and modified by glacial processes during the initial stage of glaciation of antarctica ice flow toward mawson glacier north of the allan hills is largely confined to a n s trending depression between the allan hills ice field and the near western ice field blue ice at the margins of the ice stream flows over the mesas on both sides of this depression meteorites entrained in blue ice are uncovered by sublimation and ablation we present arguments showing that currently almost all of the blue ice flowing into the allan hills ice field is sublimated leaving meteorites on the ice surface we present evidence that windblown meteorites are trapped by snow bridges across crevasses resulting in a near surface meteorite concentration near the ice ridges of the allan hills ice field nevertheless most meteorites are exposed for only a short period of time to the atmosphere before they are blown by the wind across the ice toward the western foot of the allan hills from where they are slowly carried northward to mawson glacier and the ross sea

the thermomechanical response of the greenland ice sheet to various climate scenarios using a three dimensional numerical model for land based ice sheets in the shallow ice approximation simulations are performed to determine the velocity and temperature distributions within the greenland ice sheet through time for various climate scenarios the ice is treated as a rheologically nonlinear heat conducting viscous fluid and the substrate is a heat conducting rigid solid this system is fed from above by prescribing as the climatic inputs the atmospheric temperature and the accumulation ablation rate functions at the free surface and from below by the geothermal heat we present the governing equations in the shallow ice approximation discuss the parameterizations used in the descriptions of the ice surface temperature and accumulation ablation functions briefly state how the complicated initial boundary value problem is numerically solved and how the input data that are available from measurements are implemented results of preliminary calculations disclose how the model performs and delimit its validity we study the role played by basal sliding and make clear that sliding should be accounted for where ever the basal ice is temperate and that the frictional heat generated in this sliding is thermomechanically significant we also study the reaction of the greenland ice sheet to various climate scenarios and make clear that today s thermal regime depends significantly upon the prior climate history moreover the thermomechanical properties of the ice are equally significant as is the thermal interaction of the ice sheet with the rockbed beneath

a numerical study of plane ice sheet flow l ecoulement bidimensionnel stationnaire d une nappe de glace reposant sur le sol est analyse numeriquement au moyen du modele simplifie de morland et hutter la glace se comporte comme un fluide visqueux non lineaire dependant de la temperature la nappe de glace est supposee longue et mince

a persistent and dynamic east greenland ice sheet over the past 7 5 million years 10be and 26al isotopic evidence in quartz sand from the seafloor shows that a dynamic east greenland ice sheet has existed for the past 7 5 million years understanding the growth and stability of the greenland ice sheet is a long standing priority in palaeoclimate research and one that is at the heart of modern discussion of sea level rise paul bierman and colleagues present marine records of cosmogenic isotopes and conclude that an ice sheet in east greenland was continuously eroding sediments over the past 7 5 million years although the method could miss transient deglaciations and cannot firmly distinguish between remnant and larger ice sheets the results are consistent with model simulations of a waxing and waning but continuously present regional ice sheet climate models show that ice sheet melt will dominate sea level rise over the coming centuries but our understanding of ice sheet variations before the last interglacial 125 000 years ago remains fragmentary this is because terrestrial deposits of ancient glacial and interglacial periods1 2 3 are overrun and eroded by more recent glacial advances and are therefore usually rare isolated and poorly dated4 in contrast material shed almost continuously from continents is preserved as marine sediment that can be analysed to infer the time varying state of major ice sheets here we show that the east greenland ice sheet existed over the past 7 5 million years as indicated by beryllium and aluminium isotopes 10be and 26al in quartz sand removed by deep ongoing glacial erosion on land and deposited offshore in the marine sedimentary record5 6 during the early pleistocene epoch ice cover in east greenland was dynamic in contrast east greenland was mostly ice covered during the mid to late pleistocene the isotope record we present is consistent with distinct signatures of changes in ice sheet behaviour coincident with major climate transitions although our data are continuous they are from low deposition rate sites and sourced only from east greenland consequently the signal of extensive deglaciation during short intense interglacials could be missed or blurred and we cannot distinguish between a remnant ice sheet in the east greenland highlands and a diminished continent wide ice sheet a clearer constraint on the behaviour of the ice sheet during past and ultimately future interglacial warmth could be produced by 10be and 26al records from a coring site with a higher deposition rate nonetheless our analysis challenges the possibility of complete and extended deglaciation over the past several million years

a continuum mechanical formulation for shallow polythermal ice sheets this paper is concerned with a new theoretical approach to model grounded ice sheets in three dimensions these are considered as polythermal i e there will be regions with temperatures below the

effects of spatial discretization in ice sheet modelling using the shallow ice approximation this paper assesses a two dimensional vertically integrated ice model for its numerical properties in the calculation of ice sheet evolution on a sloping bed using the shallow ice approxi mation we discuss the influence of initial conditions and individual model parameters on the model s numerical behaviour with emphasis on varying spatial discretizations the modelling results suffer badly from numerical problems they show a strong dependence on gridcell size and we conclude that the widely used gridcell spacing of 20 km is too coarse the numerical errors are small in each single time step but increase non linearly over time and with volume change as a result of feedback of the mass balance with height we propose a new method for the calculation of the surface gradient near the margin which improves the results significantly furthermore we show that we may use dimension analysis as a tool to explain in which situations numerical problems are to be expected

the surface accumulation and ablation of a coastal blue ice area near cap prudhomme terre adelie antarctica a record of accumulation and ablation from a network of 47 stakes at a coastal blue ice area in terre adelie antarctica is presented and analyzed the record covers early 2004 to early 2006 from 25 field surveys including some in austral winter the two years are very different with a virtually null surface mass balance during the 2004 winter but large accumulation during the 2005 winter a snow ice energy and mass balance model is used to reproduce the accumulation and ablation record a parameterization for snow erosion by wind is included input meteorology is from the european centre for medium range weather forecasts ecmwf analyses and forecasts corrected using 1 year of local meteorological observations from an automatic weather station model results agree reasonably well with the observations wind erosion is the largest contributor to ablation removing much of the precipitation sublimation and to a lesser extent melt runoff together account for 60 cm w e of ablation in 2 years mainly in summer although the record is short it confirms high interannual variability and thus high sensitivity to meteorology and climate monitoring and understanding the mass balance of such coastal blue ice areas may help monitor and detect climate change in the antarctic coastal regions

in situ cosmogenic radiocarbon production and 2 d ice flow line modeling for an antarctic blue ice area surface 14 c activity that differs by up to 25 from the activity calculated using an ablation only approximation which is used in all prior work and 3 that at high ablation margin sites solar modulation of the cosmic ray flux may change the strength of the dominant spallogenic production by up to 10 as part of this effort we model twodimensional ice flow along the central flow line of taylor glacier we present two methods for parameterizing vertical strain rates and assess which method is more reliable for taylor glacier finally we present a sensitivity study from which we conclude that uncertainties in published cosmogenic production rates are the largest source of potential error the results presented here can inform ongoing and future 14 c and ice flow studies at ice margin

polythermal three dimensional modelling of the greenland ice sheet with varied geothermal heat flux computations over 50 000 years into steady state with greve s polythermal ice sheet model and its numerical code are performed for the greenland ice sheet with today s climatological input surface temperature and accumulation function and three values of the geothermal heat flux 42 54 6 29 4 mw m 2 it is shown that through the thermomechanical coupling the geometry as well as the thermal regime in particular that close to the bed respond surprisingly strongly to the basal thermal heat input the most sensitive variable is the basal temperature field but the maximum height of the summit also varies by more than 100m furthermore some intercomparison of the model outputs with the real ice sheet is carried out showing that the model provides reasonable results for the ice sheet geometry as well as for the englacial temperatures

deglaciation of the northern hemisphere at the onset of the eemian and holocene high resolution tims u series dating of sea level events obtained from coral reef complexes suggests that global deglaciation from the saale penultimate glacial to the eem interglacial marine 18o stages 6 5 may have occurred earlier in relation to milankovitch insolation forcing than that from the wisconsinan glacial to the holocene interglacial marine 18o stages 2 1 however the interpretation of these data has been problematic because of the possibility of isotope exchange in order to investigate whether these different lead lag relations between milankovitch forcing and ice volume are feasible from the point of view of large scale ice sheet dynamics and thermodynamics the three dimensional polythermal ice sheet model sicopolis simulation code for polythermal ice sheets is applied to the entire northern hemisphere which gives the major contribution to global ice volume changes due to the relative stability of the antarctic ice sheet and simulations through the last two climatic cycles are conducted the simulations cover the interval from 250 kyr bp until today and are driven by surface temperature reconstructions of deep ice cores grip vostok and simple parameterizations for the change of precipitation with time discussion of the results is focused on the saale eem and the wisconsinan holocene transitions the amount and rate of deglaciation are in good agreement with the specmap record for both cases and the evidence of the data for an early start of the eem interglacial is supported

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

thermo mechanically coupled ice sheet response cold polythermal temperate classical mixture concepts are the appropriate vehicle for describing the dynamics of ice masses containing some water we review and derive respectively the theoretical formulations of cold polythermal and temperate ice masses emphasize the peculiarities of the model equations and point to difficulties that were encountered with the proposed models the focus is both on the adequate physical motivation of the models and the consistency of their mathematical representation

lithospheric structure of iberia and morocco using finite frequency rayleigh wave tomography from earthquakes and seismic ambient noise this research was funded by the u s national science foundation ear 0808939 the deployment of the iberarray broadband seismic network is part of the consolider ingenio 2010 topo iberia csd2006 00041 geosciences in iberia integrated studies on topography and 4 d evolution grant from the spanish ministry of science and innovation additional funding was provided by the spanish ministry under grants cgl2010 17280 cgl2006 01171 cgl2009 09727 and cgl2007 63889 and by generalitat de catalunya under grant 2009 sgr 6

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

permanent fast flow versus cyclic surge behaviour numerical simulations of the austfonna ice cap svalbard a large part of the ice flux within ice caps occurs through spatially limited fast flowing units some of them permanently maintain fast flow whereas others operate in an oscillatory mode characterized by short lived active phases followed by long quiescent phases this surge type behaviour results from intrinsic rather than external factors thus complicating estimates of glacier response to climate change here we present numerical model results from austfonna an ice cap on svalbard that comprises several surge type basins previous studies have suggested a thermally controlled soft bed surge mechanism for svalbard we systematically change the parameters that govern the nature of basal motion and thereby control the transition between permanent and oscillatory fast flow surge type behaviour is realized by a relatively abrupt onset of basal sliding when basal temperatures approach the pressure melting point and enhanced sliding of marine grounded ice irrespective of the dynamic regime the absence of considerable volumes of temperate ice both in the observed and simulated ice cap indicates that fast flow is accomplished by basal motion over a temperate bed given an idealized present day climate the equilibrium ice cap size varies significantly depending on the chosen parameters

melting at the base of the greenland ice sheet explained by iceland hotspot history basal melting is widespread in the north central greenland ice sheet geophysical data and numerical modelling suggest a geothermal anomaly in this region resulting from the earlier passage of greenland over the iceland mantle plume

interpreting ancient ice in a shallow ice core from the south yamato antarctica blue ice area using flow modeling and compositional matching to deep ice cores 1 we explore methods of dating a 101 m ice core from a bare ice ablation area in the yamato mountains dronning maud land east antarctica there are two unknowns the age of the ice at the surface and the age spanned by the core the ice crystal growth rate was used to estimate the age span of the core at about 5 kyr co2 ch4 and n2o data on the core were compared with well dated records from deep cores leading to two plausible matches both within isotope stage c detailed comparison of high resolution dep records from this core and the dome fuji core support the 55 61 kyr bp fit best oxygen isotope values in the core were then used to constrain the source elevation of the snow in the core and hence the velocities in a simple flow line model we inverted the ice core surface age age span and origin site and their confidence intervals in a sensitivity study of flow model parameter space the flow line model predicts good matches to the core by reducing glacial flow rates to 70 of present day accumulation rates by 45 with 10 confidence intervals the modeled surface age for the whole meteorite field yields maximum surface ages of about 90 kyr which is consistent with known but poorly constrained tephra dating meteorite terrestrial ages and the frequency of meteorite discoveries this approach can be used quite generally to link deep ice cores to surface outcrops on blue ice fields

geostatistics in glaciology implications of a study of scharffenbergbotnen dronning maud land east antarctica geostatistical methods are applied in the analysis of radio echo data from scharffenbergbotnen dronning maud land east antarctica in order to allow the following investigations detailed and reliable cartography of subglacial bed topography and ice thickness comparison of recent ice flow patterns and ice flow during earlier glacial maxima and mass balance studies in relation to climatic changes

application of a polythermal three dimensional ice sheet model to the greenland ice sheet response to steady state and transient climate scenarios abstract steady state and transient climate change computations are performed with the author s three dimensional polythermal ice sheet model simulation code for polythermal ice sheets for the greenland ice sheet the distinctive feature of this model is the detailed consideration of the basal temperate ice layer in which the water content and its impact on the ice viscosity are computed its transition surface to the cold ice region is accounted for by continuum mechanical jump conditions on this interface the simulations presented include steady states subject to a range of physical parameters and two different climates present and glacial conditions as well as three types of transient scenarios namely i sinusoidal milankovic period forcing ii paleoclimatic forcing from the greenland ice core project core reconstruction and iii future greenhouse warming forcing

the lithosphere asthenosphere boundary in the north west atlantic region abstract a detailed knowledge of the thickness of the lithosphere in the north atlantic is an important parameter for understanding plate tectonics in that region we achieve this goal with as yet unprecedented detail using the seismic technique of s receiver functions clear positive signals from the crust mantle boundary and negative signals from a mantle discontinuity beneath greenland iceland and jan mayen are observed according to seismological practice we call the negative phase the lithosphere asthenosphere boundary lab the seismic lithosphere under most of the iceland and large parts of central greenland is about 80 km thick this depth in iceland is in disagreement with estimates of the thickness of the elastic lithosphere 10 20 km found from postglacial rebound data in the region of flood basalts in eastern greenland which overlies the proposed iceland plume track the lithosphere is only 70 km thick about 10 km less than in iceland which is located directly above the proposed plume at the western greenland coast the lithosphere thickens to 100 120 km with no indication of the iceland plume track identified below jan mayen the lithospheric thickness varies between 40 and 60 km

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

radiometric 81kr dating identifies 120 000 year old ice at taylor glacier antarctica we present successful 81kr kr radiometric dating of ancient polar ice krypton was extracted from the air bubbles in four 350 kg polar ice samples from taylor glacier in the mcmurdo dry valleys antarctica and dated using atom trap trace analysis atta the 81kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 2 5 ka our experimental methods and sampling strategy are validated by i 85kr and 39ar analyses that show the samples to be free of modern air contamination and ii air content measurements that show the ice did not experience gas loss we estimate the error in the 81kr ages due to past geomagnetic variability to be below 3 ka we show that ice from the previous interglacial period marine isotope stage 5e 130 115 ka before present can be found in abundance near the surface of taylor glacier our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available greatly enhancing their scientific value as archives of old ice and meteorites at present atta 81kr analysis requires a 40 80 kg ice sample as sample requirements continue to decrease 81kr dating of ice cores is a future possibility

ice motion and mass balance at the allan hills blue ice area antarctica with implications for paleoclimate reconstructions we present a new surface balance and ice motion dataset derived from high precision gps measurements from a network of steel poles within three icefields of the allan hills blue ice area antarctica the surveys were conducted over a 14 year time period ice flow velocities and massbalance estimates for the main icefield mif are consistent with those from pre gps era measurements but have much smaller uncertainties the current study also extends these measurements through the near western icefield nwif to the eastern edge of the mid western icefield mwif the new dataset includes for the first time well constrained evidence of upward motion within the allan hills mif indicating that old ice should be present at the surface these data and terrestrial meteorite ages suggest that paleoclimate reconstructions using the surface record within the allan hills mif could potentially extend the ice core based record beyond the 800 000 years currently available in the epica

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

transient glacier response with a higher order numerical ice flow model in this paper a higher order numerical flowline model is presented which is numerically stable and fast and can cope with very small horizontal grid sizes 10 m the model is compared with the results from blatter and others 1998 on haut glacier d arolla switzerland and with the european ice sheet modelling initiative benchmarks huybrechts and others 1996 results demonstrate that the significant difference between calculated basal drag and driving stress profiles in a fixed geometry disappears when the glacier profile is allowed to react to the surface mass balance conditions and reaches a steady state dynamic experiments show that the mass transfer in higher order models occurs at a different speed in the accumulation and ablation areas and that the front position is more sensitive to migration compared to the shallow ice approximation

qanat hazard in iranian urban areas explanation and remedies this article explains the qanat hazard in iranian urban areas each qanat consists of an underground gallery tunnel which conveys groundwater to the surface and several to tens of vertical wells shafts which provide access to the gallery it is estimated that about 10 000 km qanats with 300 000 wells lie under iranian urban areas their number under urban areas of the other countries containing it seems to be significant as well in iran subsidence and other problems related to shafts and galleries of hidden qanats impose millions of dollars damage annually despite the importance of the qanat hazard it has not yet received enough attention from scholars in this article qanat hazard as a special kind of geological hazard is explained from such aspects as the causes the extents the impacts and the various remedies to combat this hazard remedies to abate this hazard should include hazard assessment risk assessment and risk reduction phases generally the most efficient strategy is to detect qanats using aerial photos maps or inquiring local people and construct the buildings in hazard prone areas with spread footing foundations however this is not applicable in all occasions so depending on conditions some other strategies which are provided in the text may be more effective

mapping blue ice areas in antarctica using etm and modis data blue ice areas bias and their geographical distribution in antarctica were mapped using landsat 7 etm images with 15 m spatial resolution obtained during the 1999 2003 austral summers and covering the area north of 82 58 s and a snow grain size image of the modis based mosaic of antarctica moa dataset with 125 m grid spacing acquired during the 2003 04 austral summer from 82 58 s to the south pole a map of bias was created with algorithms of thresholds based on band ratio and reflectance for etm data and thresholds based on snow grain size for the moa dataset the underlying principle is that blue ice can be separated from snow or rock by their spectral discrepancies and by different grain sizes of snow and ice we estimate the total area of bias in antarctica during the data acquisition period is 234 549 km 2 or 1 67 of the area of the continent blue ice is scattered widely over the continent but is generally located in coastal or mountainous regions the bia dataset presented in this study is the first map covering the entire antarctic continent sourced solely from etm and modis data this dataset can potentially benefit other studies in glaciology meteorology climatology and paleoclimate meteorite collection and airstrip site selection

measured horizontal temperature gradients constrain heat transfer mechanisms in greenland ice ice in the ablation zone of the greenland ice sheet is known to contain vertical temperature gradients that arise from conduction at the boundaries the addition of strain and latent heat and advective heat transport a three dimensional array of temperature measurements in a grid of boreholes reveals horizontal ice temperature gradients that challenge the present conceptualization of heat transfer we measure two distinct types of temperature variability in the horizontal direction one impacting a confined region where ice temperatures span a range of 5 c and another with temperatures consistently varying by approximately 2 c across the entire 3 d block we suggest the first demonstrates the localized and limited nature of latent heat input and the second demonstrates that vertical heat advection outpaces diffusion these findings imply that ice flow is highly variable over sub ice thickness length scales which in turn generates contrasts in ice temperature that may impact ice deformation and fracturing

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

inferences from stable water isotopes on the holocene evolution of scharffenbergbotnen blue ice area east antarctica we show that it is possible to extract a high resolution annual paleoclimate record from the surface of a blue ice area bia the variability of the surface stable isotope values suggests that almost all the surface ice in scharffenbergbotnen bia east antarctica is of holocene age the isotopic changes across the bia show that the modern climate there is warmer than the climate in the early holocene optimum 11 kyr bp a volume conserving ice flow model for the bia constrained by isotopic variability and layer thicknesses and a series of 14 c ages indicate both that the bia has been smaller than now and that the surface velocities were considerably smaller during the last glacial maximum changes in ice sheet thickness drive the bia towards present day conditions the relatively young age of the majority of the bia also explains the lack of meteorite finds in this area and may be typical for many bias in low elevation nunatak areas

radar attenuation and temperature within the greenland ice sheet 2015 american geophysical union all rights reserved the flow of ice is temperature dependent but direct measurements of englacial temperature are sparse the dielectric attenuation of radio waves through ice is also temperature dependent and radar sounding of ice sheets is sensitive to this attenuation here we estimate depth averaged radar attenuation rates within the greenland ice sheet from airborne radar sounding data and its associated radiostratigraphy using existing empirical relationships between temperature chemistry and radar attenuation we then infer the depth averaged englacial temperature the dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry where radar transects intersect boreholes radar inferred temperature is consistently higher than that measured directly we attribute this discrepancy to the poorly recognized frequency dependence of the radar attenuation rate and correct for this effect empirically resulting in a robust relationship between radar inferred and borehole measured depth averaged temperature radar inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice sheet model particularly in southern greenland this pattern suggests that past changes in surface boundary conditions temperature and accumulation rate affect the ice sheet s present temperature structure over a much larger area than previously recognized this radar inferred temperature structure provides a new constraint for thermomechanical models of the greenland ice sheet

a model computation of moisture content in polythermal glaciers measurements in boreholes and internal radar horizons confirm the existence of polythermal structures in polar and subpolar glaciers and ice sheets the occurrence of an intraglacial phase boundary makes it necessary to consider two layers and transition conditions between cold and temperate ice the governing field equations and constitutive relations for a two layer model are stated with emphasis on boundary and transition conditions a reduced plane flow model is introduced by using dimensionless variables and performing a scale analysis according to the stated aim of this paper a parallel sided slab model is suitable for rough analyses of borehole measurements its governing equations are deduced and their analytical and numerical treatment is discussed sensitivity tests reveal a strong dependence of moisture content profiles on the numerical value of the water diffusivity coefficient and especially on strain heating

weakened lithosphere beneath greenland inferred from effective elastic thickness a hot spot effect the effective elastic thickness t e of the lithosphere provides geophysical information about long term flexural strength and can be used to constrain thermorheological properties of the lithosph

high geothermal heat flow basal melt and the origin of rapid ice flow in central greenland age depth relations from internal layering reveal a large region of rapid basal melting in greenland melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet locally high melt rates indicate geothermal fluxes 15 to 30 times continental background the southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin

radar evidence of ponded subglacial water in greenland the thermal state at the bed of a large ice sheet is a critical boundary condition governing its future evolution radar surveys provide an opportunity for direct but remote observation of the ice sheet bed and therefore offer a means of constraining numerical ice sheet models at the ice bed interface here we have processed results of radar surveys of the greenland ice sheet undertaken by the program for arctic regional climate assessment parca between 1999 and 2003 to explore this opportunity we consider the robustness of the measurements in the context of uncertain dielectric losses in the ice sheet concluding that the observed radar signal characteristics reflect the character of the bed itself rather than that of uncertain englacial absorption however the identification of thaw is restricted to areas where subglacial water has sufficient depth to influence the radar reflection we derive a map of inferred areas of subglacial thaw and compare our results with other studies predicting regions with temperate bed we show that in many areas the radar inferences of ponded water lie within areas predicted to be thawed by modelling and radiostratigraphy there is clear disagreement in certain areas suggesting the presence of high geothermal flux anomalies

a synthesis of the basal thermal state of the greenland ice sheet the basal thermal state of an ice sheet frozen or thawed is an important control upon its evolution dynamics and response to external forcings however this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes here we synthesize spatially extensive inferences of the basal thermal state of the greenland ice sheet to better constrain this state existing inferences include outputs from the eight thermomechanical ice flow models included in the searise effort new remote sensing inferences of the basal thermal state are derived from holocene radiostratigraphy modern surface velocity and modis imagery both thermomechanical modeling and remote inferences generally agree that the northeast greenland ice stream and large portions of the southwestern ice drainage systems are thawed at the bed whereas the bed beneath the central ice divides particularly their west facing slopes is frozen elsewhere there is poor agreement regarding the basal thermal state both models and remote inferences rarely represent the borehole observed basal thermal state accurately near northgrip and dye 3 this synthesis identifies a large portion of the greenland ice sheet about one third by area where additional observations would most improve knowledge of its overall basal thermal state

physical modeling of the influence of bedrock topography and ablation on ice flow and meteorite concentration in antarctica 1 three dimensional laboratory physical experiments have been used to investigate the influence of bedrock topography and ablation on ice flow different models were tested in a plexiglas box where a transparent silicone simulating ice in nature was allowed to flow experimental results show how the flow field in terms of both flow lines and velocity and variations in the topography of the free surface and internal layers of the ice are strongly influenced by the presence and height of bedrock obstacles in particular the buttressing effect forces the ice to slow down rise up and avoid the obstacle the higher the bedrock barrier the more pronounced the process only limited uplift of internal layers is observed in these experiments in order to exhume deep material embedded in the ice ablation simulated by physically removing portions of silicone from the model surface to maintain a constant topographic depression must be included in the physical models in this case the analogue ice replenishes the area of material removal thereby allowing deep layers to move vertically to the surface and severely altering the local ice flow pattern this process is analogous to the ice flow model proposed in the literature for the origin of meteorite concentrations in blue ice areas of the antarctic plateau

a 14 year mass balance record of a blue ice area in antarctica accumulation and ablation rates over an antarctic blue ice area spanning the 14 year period 1988 2002are presented data were obtained by direct stakemeasurements large spatial and temporal variations in the net balance were observed without any clear trend over the entire period there are marginally significant increases in snow accumulation and in ablation in the blue ice area farthest from the equilibrium zone both at the 95 confidence level the snow blue ice transition zone shows no change over the entire period of observation andtheblue ice area near the zone showsno change inablation rate over the 14 year period the mass balance gradient in scharffenbergbotnen may have increased during the period 1988 2002 however the changes are small especially when compared with the changes observed elsewhere in antarctica even relatively close to the blue ice area this may indicate that the blue ice areas are relatively stable to changes in accumulation rate and possibly temperature

qanat is not a hazard comments are presented on the article by abbasnejad et al environ earth sci 75 1306 2016 dealing with qanat and hazards in iran my rebuttal starts from the direct attribution of the described hazards to qanat and addresses the importance in the correct use of terminology for geological hazards all of the problems pointed out in iran subsidence sinkholes pollution have to me an anthropogenic origin and cannot be directly ascribed to qanat eventually i present some additional elements to highlight the remarkable importance of qanat systems and their influence on the development of similar underground structures in many countries of the mediterranean basin this remarks the relevance of qanat as cultural heritage sites and the need for their preservation and valorization

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

radiostratigraphy and age structure of the greenland ice sheet 2015 the authors several decades of ice penetrating radar surveys of the greenland and antarctic ice sheets have observed numerous widespread internal reflections analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections here we present a comprehensive deep radiostratigraphy of the greenland ice sheet from airborne deep ice penetrating radar data collected over greenland by the university of kansas between 1993 and 2013 to map this radiostratigraphy efficiently we developed new techniques for predicting reflection slope from the phase recorded by coherent radars when integrated along track these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing core intersecting reflections were dated using synchronized depth age relationships for six deep ice cores additional reflections were dated by matching reflections between transects and by extending reflection inferred depth age relationships using the local effective vertical strain rate the oldest reflections dating to the eemian period are found mostly in the northern part of the ice sheet within the onset regions of several fast flowing outlet glaciers and ice streams reflections typically do not conform to the bed topography disrupted radiostratigraphy is also observed in a region north of the northeast greenland ice stream that is not presently flowing rapidly dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly this radiostratigraphy provides a new constraint on the dynamics and history of the greenland ice sheet

basal seismicity of the northeast greenland ice stream seismic studies of glaciers yield insights into spatio temporal processes within and beneath glaciers on scales relevant to flow and deformation of the ice these methods enable direct monitoring of the bed in ways that complement other geophysical techniques such as geodetic or ground penetrating radar observations in this work we report on the analysis of passive seismic data collected from the interior of the north east greenland ice stream the greenland ice sheet s largest outlet glacier we record thousands of basal earthquakes many of which repeat with nearly identical waveforms we also record many long duration glacial tremor episodes that migrate across the seismic network with slow velocities e g 4 12 m s 1 analysis of the basal earthquakes indicates a transition between times of individual event activity and times of tremor activity we suggest that both processes are produced by shear slip at localized asperities along the bed the transition between discrete and quasi continuous slipping modes may be driven by pore water pressure transients or heterogeneous strain accumulation in the ice due to strength contrasts of the underlying till

solid earth heating glaciers from below climate change is affecting the cryosphere from above geothermal heat flux from below is also contributing to conditions at the base of greenland s ice sheet which sits atop a lithosphere of variable thickness

european ice sheet modelling initiative eismint model intercomparison experiments with first order mechanics 1 the european ice sheet modelling initiative eismint intercomparison experiments with thermomechanical coupling are repeated with an ice sheet model that applies the first order approximation for computing the flow field the experiments impose radially symmetric boundary conditions most of the previous results have shown the loss of implied radial symmetry i e the formation of distinct regularly spaced spokes of cold ice in the simulated basal temperatures a similar result is also observed in the presented first order model results the computed velocity components scatter widely along the marginal grid points this indicates that the spokes may be triggered by the poor representation of the margin with a regular grid where the steep gradients in the surface enhance the numerical errors additionally the generally applied second order discretization scheme tends to decouple even and odd numbered grid points thus leading to wavy solutions with a wavelength of two grid cells these patterns strongly suggest that the loss in radial symmetry is a numerical artifact

dynamics of ice mass deformation linking processes to rheology texture and microstructure 1 prediction of glacier and polar ice sheet dynamics is a major challenge especially in view of changing climate the flow behavior of an ice mass is fundamentally linked to processes at the grain and subgrain scale however our understanding of ice rheology and microstructure evolution based on conventional deformation experiments where samples are analyzed before and after deformation remains incomplete to close this gap we combine deformation experiments with in situ neutron diffraction textural and grain analysis that allows continuous monitoring of the evolution of rheology texture and microstructure we prepared ice samples from deuterium water as hydrogen in water ice has a high incoherent neutron scattering rendering it unsuitable for neutron diffraction analysis we report experimental results from deformation of initially randomly oriented polycrystalline ice at three different constant strain rates results show a dynamic system where steady state rheology is not necessarily coupled to microstructural and textural stability textures change from a weak single central c axis maxima to a strong girdle distribution at 35 to the compression axis attributed to dominance of basal slip followed by basal combined with pyramidal slip dislocation related hardening accompanies this switch and is followed by weakening due to new grain nucleation and grain boundary migration with decreasing strain rate grain boundary migration becomes increasingly dominant and texture more pronounced our observations highlight the link between the dynamics of processes competition and rheological and textural behavior this link needs to be taken into account to improve ice mass deformation modeling critical for climate change predictions

susceptibility mapping of instability related to shallow mining cavities in a built up environment anthropogenic activities and urbanization frequently spread over areas underlain by unstable karst ground or man made cavities leading to potential risk situations for buildings infrastructure and population the roof of the cavities may rapidly propagate upwards eventually resulting in progressive ground settlement and or sudden collapse these processes are frequently accelerated or triggered by various human activities e g overloading water recharge water table decline in this paper the susceptibility to instability of artificial cavity networks under an urban area in apulia region southern italy was assessed and evaluated here there is dense network of underground quarries excavated for the extraction of massive calcarenite for building and ornamental stone that are currently affected by severe instability problems identifying the zones of the cavities most prone to instability is of great practical importance susceptibility models have been developed analyzing the statistical relationships between the cavity sections with evidence of instability and a number of predisposing factors mainly related to the 3d geometry of the voids roof thickness and the presence of overloads the models produced by the discriminant analysis and the logistic regression approaches were independently and quantitatively evaluated through the construction of roc curves although the two models are characterized by different input data treatment as the logistic regression allows using continuous and discrete variables or any combination of both types even if they do not have a normal distribution the roc curves highlighted for both methods a satisfactory congruence between the model results and the observed data consequently from the model performance analysis the two models were evaluated comparable in terms of result reliability the methodology should be considered as a general first level analysis for near surface underground cavities aimed at identifying critical cave sectors that can be the focus of more detailed analyses especially those associated with sensitive zone related to the presence of buildings roads and frequent presence of human activity

modelling the antarctic marine cryosphere at the last glacial maximum we estimate the sea ice extent and basal melt of antarctic ice shelves at the last glacial maximum lgm using a coupled ice shelf sea ice ocean model the shape of antarctic ice shelves ocean conditions and atmospheric surface conditions at the lgm are different from those in the present day these are derived from an ice shelf ice sheet model a sea ice ocean model and a climate model for glacial simulations respectively the winter sea ice in the lgm is shown to extend up to 7 of latitude further equatorward than in the present day for the lgm summer the model shows extensive sea ice cover in the atlantic sector and little sea ice in the other sectors these modelled sea ice features are consistent with those reconstructed from sea floor sedimentary records total basal melt of antarctic ice shelves in the lgm was 2147 gt a 1 which is much larger than the present day value more warm waters originating from circumpolar deep water could be easily transported into ice shelf cavities during the lgm because the full glacial grounding line extended to shelf break regions and ice shelves overhung continental slopes this increased transport of warm water masses underneath an ice shelf and into their basal cavities led to the high basal melt of ice shelves in the lgm

meteoritic event recorded in antarctic ice during systematic sampling of volcanic ash tephra layers at a well known antarctic meteorite collection site the allan hills main ice field a band of unusually dark and rounded many spheroidal particles was discovered this debris layer bit 58 extends parallel to the stratigraphy of the ice established from the tephra bands apparently marking a single depositional event the shapes internal texture major element composition and levels of cosmogenic nuclides of particles from within bit 58 all strongly suggest that this material represents ablation debris from the passage of a large h group ordinary chondrite preliminary cosmogenic isotope dating suggests an age of 2 8 ma implying that the east antarctic ice sheet has been stable since that time the relationship of the bit 58 layer to known impact events is not clear

a model of greenland ice sheet deglaciation constrained by observations of relative sea level and ice extent an ice sheet model was constrained to reconstruct the evolution of the greenland ice sheet gris from the last glacial maximum lgm to present to improve our understanding of its response to climate change the study involved applying a glaciological model in series with a glacial isostatic adjustment and relative sea level rsl model the model reconstruction builds upon the work of simpson et al 2009 through four main extensions 1 a larger constraint database consisting of rsl and ice extent data model improvements to the 2 climate and 3 sea level forcing components 4 accounting for uncertainties in non greenland ice the research was conducted primarily to address data model misfits and to quantify inherent model uncertainties with the earth structure and non greenland ice our new model termed huy3 fits the majority of observations and is characterised by a number of defining features during the lgm the ice sheet had an excess of 4 7 m ice equivalent sea level iesl which reached a maximum volume of 5 1 m iesl at 16 5 cal ka bp modelled retreat of ice from the continental shelf progressed at different rates and timings in different sectors southwest and southeast greenland began to retreat from the continental shelf by 16 to 14 cal ka bp thus responding in part to the bolling allerod warm event c 14 5 cal ka bp subsequently ice at the southern tip of greenland readvanced during the younger dryas cold event in northern greenland the ice retreated rapidly from the continental shelf upon the climatic recovery out of the younger dryas to present day conditions upon entering the holocene 11 7 cal ka bp the ice sheet soon became land based during the holocene thermal maximum htm 9 5 cal ka bp air temperatures across greenland were marginally higher than those at present and the gris margin retreated inland of its present day southwest position by 40 60 km at 4 cal ka bp which produced a deficit volume of 0 16 m iesl relative to present in response to the htm warmth our optimal model reconstruction lost mass at a maximum centennial rate of c 103 4 gt yr our results suggest that remaining data model discrepancies are affiliated with missing physics and sub grid processes of the glaciological model uncertainties in the climate forcing lateral earth structure and non greenland ice particularly the north american component finally applying the huy3 greenland reconstruction with our optimal earth model we generate present day uplift rates across greenland due to past changes in the ocean and ice loads with explicit error bars due to uncertainties in the earth structure present day uplift rates due to past changes are spatially variable and range from 3 5 to 7 mm a including earth model uncertainty

dating antarctic blue ice areas using a novel ice flow model 1 we present a new type of flow model suitable for antarctic blue ice areas with application to dating ice for paleoclimate purposes the volume conserving model uses field data for surface velocities mass balance and ice thickness along a flow line with parameterized variation of ice rheology with depth to produce particle trajectories and isochrones the model is tested on the contrasting allan hills near western ice field and the scharffenbergbotnen blue ice fields in antarctica by comparing predicted ages with ages inferred from meteorites and 14c data during the glacial periods ice surface velocities at the allan hills must have been 25 less and accumulation rates 50 less than present day values in order to match meteorite ages in contrast scharffenbergbotnen velocities have probably been fairly constant over time due to the atypical valley where it resides

unravelling the high altitude nansen blue ice field meteorite trap east antarctica and implications for regional palaeo conditions abstract antarctic blue ice zones the most productive locations for meteorite recovery on earth contain old ice that is easily accessible and available in large quantities however the mechanisms behind these meteorite traps remain a topic of ongoing debate here we propose an interdisciplinary approach to improve our understanding of a meteorite trap in dronning maud land east antarctica on the nansen blue ice field meteorite trap 2600 3100 m above sea level where more than half of the asuka meteorites have been collected based on 185 surface blue ice samples one of the largest observed spatial patterns in oxygen isotopic variation to date is found relying on meteorites for which the terrestrial ages are determined using 14c and 36cl this surface ice is interpreted to date from the last interglacial up to the present day by combining state of the art satellite derived surface velocities surface mass balance modelling and ice flow modelling we estimate that about 75 85 of the meteorites found on the ice field were supplied by ice flow after entering the ice sheet in an accumulation area of a few hundred square kilometres located south upstream of the ice field less than 0 4 new meteorites per year are supplied to the ice field through ice flow suggesting that the hundreds of meteorites found 25 years after the first visit to this ice field mostly represent meteorites that were previously not found rather than newly supplied meteorites by combining these findings the infall rate of meteorites from space is estimated which is in line with values from the literature but situated at the higher end of the range a comparison of the oxygen isotopic variation of the surface blue ice to that of the european project for ice coring in antarctica epica dronning maud land edml ice core located 750 km to the west at the same elevation suggests that the regional changes in topography have been relatively limited since the last interglacial supporting theories of an overall stable east antarctic ice sheet eais over this time period

meteorites constrain the age of antarctic ice at the frontier mountain blue ice field northern victoria land abstract we show that meteorites can provide chronological constraints upon the age of the ice cropping out at the frontier mountain meteorite trap antarctica when their terrestrial age is placed in a glaciological context amongst the over 700 meteorites found so far frontier mountain fro 84001 99028 93005 and 93054 were most likely not wind drifted across the ice field since their masses 772 1665 g are much heavier than the local 200 g wind transport threshold the four meteorites were found along a stretch of ice where a representative section of the frontier mountain blue ice crops out based on the bedding of englacial tephra layers the structure of the ice along the section appears to be essentially an up glacier dipping monocline the 14 c terrestrial age of fro 8401 99028 and 93005 are 13 2 21 3 and 27 2 ky respectively the 41 ca 36 cl age of fro 93054 is 40 10 ky the terrestrial ages of the four meteorites increase from the top to the bottom layers of the monocline this geographic distribution is best explained by delivery of meteorites at the ice surface through the ice flow model i e englacial transport from the snow accumulation zone and exhumation in the blue ice area through ablation rather than direct fall since the effect of ablation in decoupling terrestrial ages of meteorites and the age of the ice on which they sit must have been minor most likely 7 ky based on the local ice dynamics we conclude that the age of the bulk of the ice body currently under ablation at frontier mountain is up to 50 ky old this result has implications on both the meteorite concentrations mechanism at frontier mountain and the regional ice dynamics

palaeoclimate into an ice age analyses of a new ice core from greenland yield the first high resolution picture of the start of the last ice age in the northern hemisphere and of the onset of climate instability as our planet cooled

heat flux variations beneath central greenland s ice due to anomalously thin lithosphere the thermal state of the earth s surface is usually influenced more by climate than by heating from the earth s interior numerical models show that in the oldest and thickest part of the greenland ice sheet geothermal heat flux through an anomalously thin lithosphere leads to strong regional variations in basal melting

evolution of the east antarctic ice sheet a numerical study of thermo mechanical response patterns with changing climate an efficient numerical ice sheet model including time dependence and full thermo mechanical coupling has been developed in order to investigate the thermal regime and overall configuration of a polar ice sheet with respect to changing environmental conditions from basic sensitivity experiments in which a schematic east antarctic ice sheet is forced with a typical glacial interglacial climatic shift it is found that i the mutual interaction of temperature and deformation has a stabilizing effect on its steady state configuration ii in the transient mode this climatic transition initially leads to increased ice thickness due to enhanced accumulation after which this trend is reversed due to a warmer base timescales for this reversal are of the order of 103 years in marginal zones and of 104 years in interior regions iii horizontal heat advection plays a major role in damping possible runaway behaviour due to the dissipation strain rate feed back suggesting that creep instability is a rather unlikely candidate to initiate surging of the east antarctic ice sheet the model is then applied to four east antarctic flow lines only the flow line passing through wilkes land appears to be vulnerable to widespread basal melting due to enhanced basal warming following climatic warming time dependent modelling of the vostok flow line indicates that the vostok station area has risen about 95 m since the beginning of the present interglacial due to thermomechanical effects which is of particular interest in interpreting the palaeoclimatic signal of the ice core obtained there

numerical modelling of the ice sheet in western dronning maud land east antarctica impacts of present past and future climates time dependent ice sheet modelling of a 176 000 km2 area in western dronning maud land east antarctica provided information on the ice sheet s response to six climate change scenarios another experiment was done to study changes in ice thickness flow and basal temperature conditions between the present ice configuration and a simulated maximum palaeo ice sheet the input to the model included new datasets of bed and surface topography compiled for this study the results of the six climate change experiments including a 0 5 c per century global warming scenario show that the ice sheet has a robust behaviour with respect to the different climate changes the maximum change in ice volume was

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

catch a falling star meteorites and old ice a model for the process of meteorite concentration in blue ice regions of the antarctic ice sheet is proposed based on data from near the allan hills and the assumptions that both meteorite influx and glacial flow have been constant the meteorite influx is calculated to be 60 x 10 6 kilogram per square kilometer per year and the age of the exposed ice to be 0 to 600 000 years varying with distance from the allan hills these results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites providing support for the assumption of steady flow and meteorite influx this may be the oldest sequence of ice in stratigraphic order yet discovered and the results imply that this part of the east antarctic ice sheet has been approximately steady during this time interval

seismic attenuation in glacial ice a proxy for englacial temperature 1 seismic attenuation or internal friction q 1 in glacial ice is highly sensitive to temperature particularly near the melting point here we detail a technique to estimate q and apply it to active source seismic data from jakobshavn isbrae greenland we compare our results to measured and modeled temperature profiles of the ice in the region we find an excellent match with differences between seismically estimated and modeled temperatures of less than 2 c mapping variations in seismic q through glacial ice thus is shown to allow detailed estimation of englacial temperature profiles which may be of special value in regions where in situ measurements are logistically difficult