an integrated lightweight ice penetrating radar system we describe a portable low frequency impulse radar system intended for ground based surveys that employs off the shelf hardware integrated with custom designed software the hardware comprises a 1 200 mhz transmitter digitizer computer and gps receiver which together weigh 1 5 kg the entire system including waterproof enclosures and batteries suited for 8 hours of continuous operation weighs 10 kg plus the weight of the antenna housing the system design is flexible permitting hardware components such as the digitizer or navigation device to be exchanged the software includes acquisition parameter control real time visual ice depth rendering and data management capabilities using a hierarchical data format the system described here has been successfully used to sound polythermal ice up to 220 m thick in ski based surveys in the yukon canada and temperate ice up to 550 m thick in machine based surveys in iceland

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

upper mantle seismic anisotropy beneath antarctica and the scotia sea region summary recent investigations on shear wave splitting from recordings of permanent and temporary antarctic seismological stations have lead to a greater understanding of the upper mantle dynamics of the scotia sea region and the continental margin in the eastern weddell sea in terms of their tectonic evolution the analysis of shear wave splitting from teleseismic core sks skks pks and direct s waves reveals the seismic anisotropy and the strain field of the upper mantle similar to the caribbean anisotropy structures in the antarctic peninsula and scotia sea regions are assumed to be influenced by mantle flows in easterly directions around the subducting nazca plate in general anisotropy polarization directions in the scotia sea do not contradict this hypothesis with polarizations oriented nearly e w and therefore aligning with the suggested mantle flow patterns anisotropy strengths decrease from delay times of dt 1 8 s pmsa palmer station in the west towards the east with delay times of dt 0 3 s beneath hope south georgia and cand candlemas south sandwich islands nevertheless a lithospheric and therefore fossil origin cannot be ruled out only the exceptionally high delay times at pmsa probably originate in part from recent asthenospheric flow around the subduction slab of the former phoenix plate beneath the northwestern margin of the antarctic peninsula the continental margin of western dronning maud and coats land plays a crucial role in understanding the early processes during the break up of gondwana upper mantle seismic anisotropy with delay times well over dt 1 s in this region gives new constraints on ancient deformation processes during break up and former episodes two layer modelling reveals archaean anisotropy in the upper layer corresponding well to polarization directions of the south african kaapvaal craton lower layer anisotropy is assumed to have been created during early gondwana rifting stages

a less humid climate since ca 3500 yr b p from marine cores off karwar western india abstract a marked change in the vegetation of the western ghats at ca 3500 yr b p has been observed from a study of two marine cores taken from the inner shelf off karwar karnataka western india at the mouth of the kalinadi river this change is indicated by a decrease in forest pollen particularly from evergreen forests and by a corresponding increase in savanna pollen as well as by a reduction in mangrove pollen at the same time the values of the stable isotope 13 c of sedimentary organic matter increased suddenly due to a higher contribution of organic matter of margine origin all these modifications were probably induced by a less humid climate the term drier can hardly be used for an area where the annual rainfall still attains 6 m in the hills above this clear limit the same trends steady but considerably weaker also resulting a reduction in the humid conditions were recorded up to ca 2200 yr b p reduction in forest vs increase in savannas decrease in the mangrove vegetation higher 13 c values from there onwards the pollen assemblages have remained uniform up to the present day it may be deduced that a climate quite similar to the present conditions was established about 2200 yr ago and still prevails the curves representing the percentages of marine microfossils dinoflagellates organic tests of foraminifera eggs of copepods show little variation at the 3500 yr b p boundary the marine assemblages were modified drastically only at about 2200 yr b p these sharp modifications are probably due to an increase in the marine influence as a result of a reduction in the fresh water supply from the kalinadi the stability in the representation of marine assemblages which has persisted from about 2200 yr b p to the present confirms the establishment of the present day climate around that date this paleoclimatic reconstruction is in conformity with the evidence for the beginning of drier conditions recorded at about the same time in the low latitudes in many parts of the world india northern arabian sea africa sahara tropical forest east african lakes australia and the carribbean

basal melting at the ekstrom ice shelf antarctica estimated from mass flux divergence we characterize the basal mass balance of the ekstr om ice shelf dronning maud land antarctica using interferometrically derived surface velocities and ice thickness measurements from radio echo sounding res the surface velocities are based on data from european remote sensing satellites 1 and 2 ers 1 2 during 1994 97 the ice thickness grid consists of 136 res profiles acquired between 1996 and 2006 mass fluxes are calculated along selected res profiles where possible to reduce uncertainties from ice thickness interpolation elsewhere large scale mass fluxes are calculated using interpolated ice thickness data themass flux into the ekstr om ice shelf from themain grounded drainage basins is estimated to be 3 19 0 4gt a 1 the mass flux near the ice shelf front is 2 67 0 3gt a 1 assuming steady state and based on the equation of continuity we interpret the residual mass flux as a combined effect of snow accumulation and subglacial melting refreezing using net snow accumulation rates from previous studies we link the mass flux divergence in irregular shaped polygons to processes beneath the ice shelf the highest subglacial melt rates of 1 1ma 1 are found near the grounding zone of two main inflow glaciers and around the german station neumayer iii the detection of unlikely refreezing in a small area 15 km west of neumayer iii is attributed to both dataset inaccuracies and a possibly past violation of the steady state assumption in general the method and input data allow mapping of the spatial distribution of basal melting and the results are in good agreement with several previous studies

late pleistocene holocene paleoclimatic history of the southern kerala basin southwest india abstract the south kerala sedimentary basin sksb constitutes one of the most significant landward extensions of the southwest offshore sedimentary basins of india and is situated between 8o45 and 10o15 n latitudes with a maximum width of about 20 km and incorporating a 700 m thick sedimentary succession ranging in age from early miocene to holocene this belt lies almost entirely under water or alluvium covered coastal plains in this study we use two continuously cored bore holes at eruva 7 25m deep and muthukulam 3m deep separated by a distance of about 7km to investigate the depositional environment as well as paleo ecology of the depocentre and climatic aspects during the late pleistocene and holocene results from c14 dating of shell fragments from eruva depth zone 2 10 6 64m yielded ages in the range of 36 2 to 42 5 kybp corresponding to the late pleistocene wood fragments in the muthukulam core sample depth zone 1 27 3 00m gave c14 ages in the range of 3 7 to 7 2 kybp indicating a holocene history the lower half of the eruva bore hole indicates a marginal marine environment with an abundant supply of terrestrial carbonaceous debris probably corresponding to a period of abnormally high rainfall recorded in many parts of the globe covered by the asian summer monsoon the sediments in the upper part of this bore hole indicate a continuation of this environment but with much less input of terrestrial organic carbon the lower part of the bore hole from this locality corresponding to the holocene transgression is similar to the lower part of eruva bore hole in the case of toc deposition took place in water bodies with considerable marine influence but receiving high amounts of terrestrial plant debris mostly in the form of finely divided particles mixed with mud this transgressive sequence was also deposited during a time when the asian summer monsoon was abnormally high in intensity as indicated by many examples in india africa madagascar and elsewhere it is significant that during the deposition of this part the sea level was probably the same as present or higher suggesting possible lowering of the stream velocities and resultant deposition of only muddy sediments laden with terrestrial organic material along the coast the upper part of the section shows a progressively reduced rainfall pattern culminating in a period of very low precipitation with the development of a paleosol which is traceable all over the sksb where late holocene sediments are available this period also witnessed aeolian activity modifying the sand ridges in the ridge runnel systems formed by the holocene regression

a 1500 year record of accumulation at amundsenisen western dronning maud land antarctica derived from electrical and radioactive measurements on a 120 m ice core during the nordic epica pre site survey in dronning maud land in 1997 1998 a 120 m long ice core was retrieved 76 00 s 08 03 w 2400 m above sea level the whole core has been measured using the electric conductivity measurement ecm and dielectric profiling dep techniques and the core chronology has been established by detecting major volcanic eruptions in a nearby shallow core radioactive traces from nuclear tests conducted during the 1950s and 1960s have been identified altogether 13 ecm and dep peaks in the long core are identified as originating from specific volcanic eruptions in addition two peaks of increased total activity are identified in the short core accumulation is calculated as averages over the time periods between these dated events accumulation rate is 62 millimetres w eq yr for the last 181 years 1816 a d to present and 61 mm w eq yr for the last 1457 years 540 a d to present our record shows an 8 decrease in accumulation between 1452 and 1641 a d i e part of the little ice age compared to the long term mean

surface topography and ice flow in the vicinity of the edml deep drilling site antarctica interpretation of ice core records requires accurate knowledge of the past and present surface topography and stress strain fields the european project for ice coring in antarctica epica drilling site 75 00258 s 0 06848 e 2891 7 m in dronning maud land antarctica is located in the immediate vicinity of a transient and forking ice divide a digital elevation model is determined from the combination of kinematic gps measurements with the glas12 datasets from the icesat based on a network of stakes surveyed with static gps the velocity field around the drilling site is calculated the annual mean velocity magnitude of 12 survey points amounts to 0 74ma 1 flow directions mainly vary according to their distance from the ice divide surface strain rates are determined from a pentagonshaped stake network with one center point close to the drilling site the strain field is characterized by along flow compression lateral dilatation and vertical layer thinning

the initiation of particle movement by wind when air blows across the surface of dry loose sand a critical shear velocity fluid threshold ut must be achieved to initiate motion however since most natural sediments consist of a range of grain sizes fluid threshold for any sediment cannot be defined by a finite value but should be viewed as a threshold range which is a function of the size shape sorting and packing of the surface sediment in order to investigate the initiation of particle movement by wind a series of wind tunnel tests was carried out on a range of pre screened fluvial sands and commercially available glass beads with differing mean sizes and sorting characteristics a sensitive laser monitoring system was used in conjunction with a high speed counter to detect initial grain motion and to count individual grain movements test results indicate that when velocity is slowly increased over the sediment surface the smaller or more exposed grains are first entrained by the fluid drag and lift forces either in surface creep rolling or in saltation bouncing or hopping downwind as velocity continues to rise larger or less exposed grains may also be moved by fluid drag on striking the surface saltating grains impart momentum to stationary grains this impact may result in the rebound of the original grain as well as the ejection of one or more stationary grains into the air stream at shear velocities lower than that required to entrain a stationary particle by direct fluid pressure as a result there is a cascade effect with a few grains of varying size initially moving over a range of shear velocities the fluid threshold range and setting in motion a rapidly increasing number of grains results of the tests showed that the progression from fluid to dynamic threshold based on grain movement can be characterized by a power function the coefficients of which are directly related to the mean size and sorting characteristics of the sediment

shape effects in aeolian grain transport wind tunnel experiments are reported the results of which show that grain transport rate is responsive to characteristic grain shape it is relatively less sensitive to changes of sorting unless these involve the fraction smaller than 50 m a cubic relationship between transport rate and velocity gradient appears to be valid only for well worked natural grains having high sphericity

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

the holocene giant lake chad revealed by digital elevation models abstract the chad basin is a closed basin in the central part of north africa a southern sub basin which is supplied by the humid tropics includes the present day lake chad the northern sub basin is presently dry as it only receives drainage from sahara rivers in these areas the existence of a giant lake known as the lake mega chad has been debated for a long time its level would be controlled by the mayo kebbi threshold in the southern part of the lake which joined the lake mega chad and the niger river via the benoue trough digital elevation models the topo6 and globe data sets are used to characterise a well defined shelf like morphology locally up to 50 km wide followed at a constant elevation over hundreds of kilometers this strictly horizontal geomorphic feature is interpreted as a wave cut lacustrine shoreline terrace it is associated with a sandridge that represents a barrier island system built by wave generated currents this study demonstrates that a holocene lake mega chad was present from 11 n to 18 n across the southern and northern sub basins the influence of such a water vapour source must be considered in palaeoclimatological reconstructions

entrainment threshold of natural grains in liquids determined empirically from dimensionless settling velocities and other measures of grain size abstract grain size plays a crucial role in sediment transport but different methods of size analysis do not yield comparable results particle diameters obtained by settling tube for example cannot be employed in equations based on sieve sizes although the majority of experiments on the initiation of sediment motion has been based on sieve data settling tube analysis is probably superior as both the settling rate and the entrainment threshold of grains are determined by the same factors of size shape and density in this paper empirical equations are provided which allow the determination of a non dimensional critical shear stress directly from the equivalent sedimentation diameter the equations apply to the entrainment of well sorted grains with a high sphericity on flat sediment beds and are valid for particles and liquids of different densities

holocene environmental changes as recorded in sediments of a paleodelta southwest coast of india abstract sedimentary record of a 40 m deep borehole drilled in a paleodelta region of southwest coast of india has been studied for sedimentary proxies texture clay minerals geotechnical parameters and pollens the sedimentary record spanning from 12 ka to recent in age exhibits two different sedimentary environments of deposition sediments record high values of moisture content organic carbon and plasticity index sediment texture and geotechnical properties indicate a distinct change in depositional environment from marine to fluvial during the sea level fall i e after 7 ka it also suggests that major rise of sea level from 11 to 7 ka and regression from 7 ka to 5 ka contributed to the changes in the environment of deposition the downcore increase of illite and decrease of kaolinite at 12 m depth 6 ka and an upward increase of smectite and kaolinite and decrease of illite concentration support the major fall in sea level in the region that accounted for the change of depositional environment the pollen records reveal the abundant occurrence of semi evergreen type of mangroves during early to mid holocene thus the multi proxy record provides an evidence of change in the environment of deposition from marine to fluvial which might have been influenced by neotectonics sea level variations and monsoonal intensity in the region

mass balance of the sor rondane glacial system east antarctica mass changes of polar ice sheets have an important societal impact because they affect global sea level estimating the current mass budget of ice sheets is equivalent to determining the balance between surface mass gain through precipitation and outflow across the grounding line for the antarctic ice sheet grounding line outflow is governed by oceanic processes and outlet glacier dynamics in this study we compute the mass budget of major outlet glaciers in the eastern dronning maud land sector of the antarctic ice sheet using the input output method input is given by recent surface accumulation estimates smb of the whole drainage basin the outflow at the grounding line is determined from the radar data of a recent airborne survey and satellite based velocities using a flow model of combined plug flow and simple shear this approach is an improvement on previous studies as the ice thickness is measured rather than being estimated from hydrostatic equilibrium in line with the general thickening of the ice sheet over this sector we estimate the regional mass balance in this area at 3 15 8 23 gt a 1 according to the most recent smb model results

temporal and spatial variation of stable isotope ratios and accumulation rates in the hinterland of neumayer station east antarctica four firn cores were retrieved in 2007 at two ridges in the area of the ekstrom ice shelf dronning maud land coastal east antarctica in order to investigate the recent regional climate variability and the potential for future extraction of an intermediate depth core stable water isotope analysis tritium content and electrical conductivity were used to date the cores for the period 1981 2006 a strong and significant correlation between the stable isotope composition of firn cores in the hinterland and mean monthly air temperatures at neumayer station was r 0 54 0 71 no atmospheric warming or cooling trend is inferred from our stable isotope data for the period 1962 2006 the stable isotope record of the ice firn cores could expand well beyond the meteoro logical record of the region no significant temporal variation of accumulation rates was detected however decreasing accumulation rates were found from coast to hinterland as well as from east halvfarryggen to west sorasen the deuterium excess d exhibits similar differences higher d at sorasen lower d at halvfarryggen with a weak negative temporal trend on halvfarryggen 0 04 a 1 probably implying increasing oceanic input we conclude that halvfarryggen acts as a natural barrier for moisture carrying air masses circulating in the region from east to west

geometric boundary conditions for modelling the velocity field of the antarctic ice sheet a comparison of the two dimensional horizontal velocity field obtained on the basis of conservation of mass balance velocity with the diagnostic velocityfield calculated with an ice sheet model dynamics velocity may yield information on shortcomings in the way the ice sheet model describes the ice flow thispaper presents improved geometric boundary conditions surface elevation and ice thickness required as input in such calculations in particular the surfaceelevation grid is described in detail as it has been generated specifically for such a study and represents a new standard in accuracy and resolution forcalculating surface slopes the digital elevation model was generated on a 10 km grid size from over 20 000 000 height estimates obtained from seven 35 dayrepeat cycles of ers 1 radar altimeter data for surface slopes less than 0 5i the relative elevation accuracy is better than 1 m in areas of high surface slope coastal and mountainous regions the altimeter measurements have been supplemented with data taken from the antarctic digital database south of 81 5i data from the spri folio map have been used the ice thickness grid was produced from a combination of a re digitisation of the spri folio and the originalradio echo sounding flight lines for areas of grounded ice the bedrock was estimated from surface elevation and ice thickness significant differences inexcess of 25 percent of ice thickness were obtained between an earlier digitisation of the folio bedrock map and the dataset derived here furthermore a newvalue of 26 6 x 106 km3 was obtained for the total volume of the ice sheet and shelves which is a reduction of 12 percent compared with the original estimatederived during the compilation of the spri folio these differences will have an important influence on the results obtained by numerical ice sheet models

ekstrom ice shelf antarctica in 1980 81 1983 84 and 1985 86 airborne surveys with the electromagnetic reflection emr system were made of ekstrom ice shelf antarctica the emr data were supplemented by measurements of surface elevation with radar altimetry during flights at a constant pressure altitude the accuracy measurements of ice thickness in areas with clearly developed bottom reflectors was used to generate a plot of surface elevation against ice thickness the effect of changing barometric pressure during flights could be reduced by this means elevations were calibrated over the open sea at the beginning and end of each flight on the basis of these data the surface elevation ice thickness and isostatic anomalies have been mapped over the ice shelf

nivlisen an antarctic ice shelf in dronning maud land geodetic glaciological results from a combined analysis of ice thickness ice surface height and ice flow observations extensive observations on nivlisen an ice shelf at antarctica s atlantic coast are analysed and combined to achieve a new quality description of its complex glaciological regime we generate models of ice thickness primarily from ground penetratingradar ellipsoidal ice surface height primarily from ers 1 satellite altimetry freeboard height by utilising precise sea surface information and ice flow velocity from ers 1 2 sar interferometry and gps measurements accuracy assessmentsare included exploiting the hydrostatic equilibrium relation we infer the apparent air layer thickness as a useful measure for a glacier s density deviation from a pure ice body this parameter exhibits a distinct spatial variation ranging from 2 m to 16 m which we attribute to the transition from an ablation areato an accumulation area we compute mass flux and mass balance parameters on a local and areally integrated scale the combined effect of bottom mass balance and temporal change averaged over an essential part of nivlisen is 654 170 kgm2a 1 which suggests bottom melting processes to dominate we discuss our results in view of temporal ice mass changes including remarks on historical observations basal processes near surface processes and ice flow dynamical features the questionfor temporal changes remains open from the data at hand and we recommendfurther observations and analyses for its solution

stratigraphical and palynological appraisal of the late quaternary mangrove deposits of the west coast of india the organic deposits derived from the mangrove swamps form reliable stratigraphic markers within the late quaternary sequence of kerala konkan basin three generations of such deposits have been identified the older one is dated to around 43 000 40 000 14c yr b p with a few dates beyond the range of radiocarbon the younger ones date from the middle holocene to latest pleistocene 10 760 4540 14c yr b p and the late holocene 4000 14c yr b p pollen analyses confirm that the deposits are mostly derived from the mangrove vegetation peat accumulation during the period 40 000 28 000 14c yr b p can be correlated with the excess rainfall 40 100 greater than modern values of the asian summer monsoon the low occurrence of mangrove between 22 000 and 18 000 14c yr b p can be attributed to the prevailing aridity and or reduced precipitation associated worldwide with last glacial maximum because exposure surfaces and ferruginous layers are commonly found in intervals representing this period the high rainfall of 11 000 4000 14c yr b p is found to be the most significant as the mangrove reached an optimum growth around 11 000 14c yr b p but with periods of punctuated weaker monsoons from the present and previous studies it has been observed that after about 5000 or 4000 14c yr b p the monsoons became gradually reduced leading to drying up of many of the marginal marine mangrove ecosystems a case study of hadi profile provided an insight to the relevance of magnetic susceptibility to record the ecological shift in late holocene

the temperature regime of fimbulisen antarctica numerical simulations of the temperature regime of the ice shelf fimbulisen antarctica are presented a vertical temperature profile s1 of fimbulisen has been measured at the extension of jutulstraumen in which the temperature decreases with depth the three dimensional steady state temperature field was computed by a finite element technique horizontal flow velocities and surface accumulation rates were derived from observations the basal melt rate distribution arose from an assumption of balance in the mass continuity equation the computed basal melt rate distribution a b indicates that the highest basal melt rates up to 15 m a 1 occur at the inflow gate of jutulstraumen and low basal melt rates 0 6 ma 1 occur in the slower moving parts where the ice shelf overhangs the continental shelf a b 1 2 m a 1 the resulting temperature field indicates that fimbulisen consists of a cold middle part built up by the extension of jutulstraumen and warmer ice masses in slow moving areas to the west and east furthermore model runs were set up in which the atmospheric temperatures increased in 1 k steps the results suggest that the warming effectively increases the temperatures throughout the ice column in the slower moving parts therefore enhancing shear at the margins of the extension of jutulstraumen

new maps of the ice thickness and subglacial topography in dronning maud land antarctica determined by means of airborne radio echo sounding since the austral summer 1994 95 the alfred wegener institute awi hascarried out airborne radio echo sounding measurements res in antarctica withits newly designed res system since 1995 96 an ongoing presite survey foran ice coring drill site in dronning maud land dml has been carried out this survey is part of the epica programme european project for ice coring inantarctica it covers an area of 948000 km2 with more than 49500 km ofairborne res obtained from more than 200 hours of flight operation flown from1994 1997 within this paper first results of the airborne res survey will begraphically summarized as newly derived maps of the ice thickness and thesubglacial topography as well as a 3d view of surface and subglacial bed andoutcrop topography revealing a total icevolume of 1 48 million km3

spatial distribution of surface mass balance on amundsenisen plateau antarctica derived from ice penetrating radar studies the distribution of surface mass balance on amundsenisen dronning maud land antarctica is investigated along a continous profile line ice penetrating radar is used to map variations in ice layer thickness within the upper 100 m of the ice sheet the route passes several firn and ice core drilling sites over a distance of 320 km dielectric profiling data of ice cores is used to calculate the depths of selected reflection horizons and the cumulative mass of the ice column the local surface mass balance is determined as a temporal average covering a time span of almost two centuries the findings indicate a complex accumulation pattern superimposed on a general low surface mass balance which is related to small scale surface undulations the results of the radar soundings are in general in good agreement with surface mass balance data derived from firn core studies discrepancies between these two datasets can be explained by spatial mismatch or by minor quality of either ice core profiles or radar data for regional comparison of radar based accumulation data we use an accumulation distribution interpolated from point measurements the surface mass balance varies up to 50 over short distances with correlation lengths of 10 km we conclude that the current utilization schemes of point sampling are only capable of reproducing local values and regional trends but provide no information on the small scale variability of surface mass balance

dynamics and mass balance of the ice sheet ice shelf regime at nivlisen antarctica as derived from a coupled three dimensional numerical flow model

reconstruction of the 30 40 ka bp enhanced indian monsoon climate based on geological records from the tibetan plateau abstract multi proxy records from ice caps lakes and pollen records from the tibetan plateau are used to reconstruct the palaeoclimate during the period 30 40 ka bp lake geomorphological and lacustrine sedimentological studies show that numerous high lake level stands and or freshwater lakes occurred in large areas of western china at this time including over the tibetan plateau where the area contains mostly shallow water and saline hypersaline water lakes under extremely dry conditions of today pollen based reconstruction of tibetan vegetation shows systematic differences from the present alpine steppe forests were shifted ca 400 km further north and the alpine conifer forest extended ca 400 800 km beyond their present western limits variations in 18 o curves from ice cores from the plateau suggest that the temperature was 2 4 c higher and precipitation was 40 to over 100 higher than today all of the evidence consistently suggests the existence of an exceedingly strong summer monsoon climate over the plateau the vigorous evaporation of the tropical ocean surface would also play an important role in promoting the penetration of moisture rich southwest monsoon over the tibetan plateau these climate patterns with strong summer monsoon circulation during the period 30 40 ka bp reflect the 20 ka earth orbital precessional cycle when the tibetan plateau region received greater solar radiation which thus enlarged the thermodynamical contrast between the plateau and the mid south portion of the indian ocean

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

formation and disintegration of the antarctic ice sheet a model of the antarctic ice sheet has been used to simulate the ice sheet in warmer climates in order to investigate what kind of ice sheet geometries one canreasonably expect under what kind of climatic conditions and to find out which physical mechanisms may be involved to explain them the results of theseexperiments reveal the large stability of in particular the east antarctic ice sheet it would require a temperature rise of between 17 and 20k above presentlevels to remove this ice sheet from the subglacial basins in the interior of the continent and of 25k to melt the antarctic ice sheet completely down for atemperature rise below 5k the model actually predicts a larger antarctic ice sheet than today as a result of increased snowfall whereas the west antarctic icesheet was found not to survive temperatures more than 8 10k above present values furthermore basal temperature conditions in these experiments point tothe problems involved to raise the base to the pressure melting point over the large areas necessary to consider the possibility of sliding instability theseresults bear on a lively debate regarding the late cenozoic glacial history of antarctica in particular based on these findings it appears difficult to reconcile ahighly variable east antarctic ice sheet up to the pliocene with the modest warmings recorded in for instance the deep sea records for the late neogene

accumulation studies on amundsenisen dronning maud land antarctica by means of tritium dielectric profiling and stable isotope measurements first results from the 1995 96 and 1996 97 field seasons the paper focuses on studies of snow pit samples and shallow firn cores taken during the 1995 96 and 1996 97 field seasons at amundsenisen dronning maud land antarctica the dating of the firn is based on the artificial tritium distribution in the snow cover and on several reference horizons identified by electrical measurements the early 1964 through 1965 horizon is marked by the deposition of sulfate released to the atmosphere during the eruption of the agung volcano in march 1963 this horizon was detected by dielectric profiling and electrical conductivity measurements the proof by chemical analysis has still to be seen at the ten investigated sites on amundsenisen the 1964 65 horizon was identified 4 1 5 7 m below the surface the accumulation rates on amundsenisen are 41 91kg ma the cores are up to 100 years old a relationship between isotope content and the mean air temperature on a regional scale can be based onmeasurements of firn temperature at10m depth at the drilling sites betweenneumayer station at the coast and heimefrontfjella the temperature gradient of the deuterium content is 9 6 k south of heimefrontfjella on the amundsenisen plateau it is only 5 5 k time series of yearly accumulation rates show no significant trend for the isotope records a significant trend to higher values with gradients of 0 1 0 2 dh a can be seen in five of the ten time series

simulation of the antarctic ice sheet with a three dimensional polythermal ice sheet model in support of the epica project ii nested high resolution treatment of dronning maud land antarctica

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

age estimates of isochronous reflection horizons by combining ice core survey and synthetic radar data 1 ice core records and ice penetrating radar data contain complementary information on glacial subsurface structure and composition providing various opportunities for interpreting past and present environmental conditions to exploit the full range of possible applications accurate dating of internal radar reflection horizons and knowledge about their constituting features is required on the basis of three ice core records from dronning maud land antarctica and surface based radar profiles connecting the drilling locations we investigate the accuracies involved in transferring age depth relationships obtained from the ice cores to continuous radar reflections two methods are used to date five internal reflection horizons 1 conventional dating is carried out by converting the travel time of the tracked reflection to a single depth which is then associated with an age at each core location and 2 forward modeling of electromagnetic wave propagation is based on dielectric profiling of ice cores and performed to identify the depth ranges from which tracked reflections originate yielding an age range at each drill site statistical analysis of all age estimates results in age uncertainties of 5 10 years for conventional dating and an error range of 1 16 years for forward modeling for our radar operations at 200 and 250 mhz in the upper 100 m of the ice sheet comprising some 1000 1500 years of deposition history final age uncertainties are 8 years in favorable cases and 21 years at the limit of feasibility about one third of the uncertainty is associated with the initial ice core dating the remaining part is associated with radar data quality and analysis

basal conditions beneath enhanced flow tributaries of slessor glacier east antarctica radio echo sounding data are used to investigate bed roughness beneath the three enhanced flow tributaries of slessor glacier east antarctica slow moving inter tributary areas are found to have rough beds while the bed of the northernmost tributary is relatively smooth a reconstruction of potential subglacial drainage routing indicates that water would be routed down this tributary and investigations of basal topography following isostatic recovery reveal that the bed would have been below sea level in preglacial times so marine sediments may have accumulated here together these factors are further support for the dominance of basal motion in this tributary reported elsewhere conversely although the other two slessor tributaries may have water routed beneath them they would not have been below sea level before the growth of the ice sheet so cannot be underlain by marine sediments they are also found to be rough and within the range of uncertainties it is likely that basal motion does not play a major role in the flow of these tributaries perhaps the most interesting area however is a deep trough where flow rates are currently low but the bed is as smooth as the northern slessor trough it is proposed that although ice deformation currently dominates in this trough basal motion may have occurred in the past when the ice was thicker

potential mechanisms for anisotropy in ice penetrating radar data radar data center frequency 150 mhz collected on the antarctic plateau near the epica deep drilling site in dronning maud land vary systematically in backscattered power depending on the azimuth antenna orientation backscatter extrema are aligned with the principal directions of surface strain rates and change with depth in the upper 900 m backscatter is strongest when the antenna polarization is aligned in the direction of maximal compression while below 900m the maxima shift by 90 pointing towards the lateral flow dilatation we investigate the backscatter from elongated air bubbles and a vertically varying crystal orientation fabric cof using different scattering models in combination with ice core data we hypothesize that short scale variations in cof are the primary mechanism for the observed anisotropy and the 900m boundary between the two regimes is caused by ice with varying impurity content observations of this kind allow the deduction of cof variations with depth and are potentially also suited to map the transition between holocene and glacial ice

kaolin deposits at melthonnakkal and pallipuram within trivandrum block southern india abstract the kaolin deposits at melthonnakkal and pallipuram mines form part of the warkalli formation belonging to the tertiary sequence in southern kerala and occur at the boundary between the tertiary sequence and precambrian granulite facies metapelites khondalites the sedimentary clays are composed mainly of kaolinite quartz and gibbsite xrd and sem studies have revealed that kaolinite is well crystallized variety and the platy crystals are scarcely broken in the sedimentary clays these sedimentary kaolins are considered to have been formed by intense tropical weathering of the khondalites and subsequently transported and deposited with high organic input into lakes near the weathering crust over the basement rock besides the surficial parts of the sedimentary deposits are extensively lateritized with the formation of goethite and hematite by quaternary tropical weathering processes

unraveling weathering episodes in tertiary regoliths by kaolinite dating western ghats india abstract secondary minerals in soils can record climatic changes affecting continental surfaces over geological times their dating should refine our present knowledge about their potential periods of formation as well as their relations with the ongoing change of climate and erosion weathering regimes in the present study twenty kaolinite samples from two lateritic profiles of the karnataka plateau an intensively studied area in the southern india have been dated using electron paramagnetic resonance epr spectroscopy kaolinite ages vary between 0 229 0 24 ma to 40 73 15 37 ma four different groups of age can be identified with ages clustered around 1 0 3 5 9 0 and 39 0 ma these groups of age indicate local preferential weathering periods that coincide with distinct indian climatic events described in independent studies such as monsoon strengthening thus regional or subcontinental factors likely prevailed over global forcing in the imprint of climatic events in the regolith profiles these results confirm that despite their simple mineralogy laterites can contain several relictual and coexisting generations of secondary minerals and that epr dating of kaolinite contributes to unraveling the complex history of continental surfaces over geological periods

geological geophysical and inherited tectonic imprints on the climate and contrasting coastal geomorphology of the indian peninsula abstract the indian subcontinent comprises accreted cratonic fragments that underwent subsequent rifting subduction collision processes along major mobile belts it is also a storehouse of a prolonged history of crustal evolution involving repeated episodes of magmatism volcanism sedimentation and metamorphism and the formation of intracratonic and foreland basins the geologic geomorphic evolution of the peninsula is recorded in relic faults suture zones that confine paleozoic mesozoic and cenozoic sedimentary basins and landforms in addition escarpments plateaus waterfalls deltas planation surfaces and strandlines are either aligned parallel and or formed over them asymmetric relief across the western eastern parts of the peninsula orographic effect on the precipitation pattern and climatic zones provide important constrains on the geologic and geomorphic evolution of the region though extensive continental and coastal deposition occurred during permo triassic and early cretaceous only the downwarped grabens of gondwana basins preserved the sedimentary records occurrences of extensive cenozoic deposits offshore and neogene holocene deltaic deposits along the entire east coast as opposed to the absence of comparable deltaic sequences in the west coast are linked to intense and recurrent episodes of denudation indicating first order control of basement structures over landscape evolution inheritance and continuum of basement structures over climate and landscape evolution of peninsular india can also be witnessed by the unique and diverse drainage patterns of major rivers while most of the major rivers follow a general easterly direction the landscape morphology of their catchments indicates youthful character and tectonically active nature the east flowing rivers show an asymmetry between the areal extents of drainage basin size and delta whereas the west flowing rivers are short and straight and their catchments are miniscule in comparison with the rivers flowing toward east the western ghats escarpment forms an orographic barrier and acts as the main divide between these two drainage systems there is a disparity between the quanta of sediment discharge as well in addition the eastern and western parts of india across the western ghats escarpment show significant differences in terms of climatic zones humid to per humid on the west while it is arid to subhumid on the east the west coast is characterized by 3000 mm year annual rainfall that often reaches 5000 mm year dominance of sw monsoon winds occurrence of narrow here we propose a conceptual tectono geomorphic model demonstrating the inheritance and continuum of gondwanan structural trends on the transient landscape of peninsular india

a 3 d model for the antarctic ice sheet a sensitivity study on the glacial interglacial contrast on the longer climatic time scales changes in the elevation and extent of the antarctic ice sheet have an important role in modulating global atmospheric and oceanographic processes and contribute significantly to world wide sea levels in this paper a 3 d time dependent thermomechanical model for the entire ice sheet is presented that is subsequently used to examine the effects of glacial interglacial shifts in environmental boundary conditions on its geometry the model takes into account a coupled ice shelf grounding line dynamics basal sliding and isostatic bed adjustment and considers the fully coupled velocity and temperature fields ice flow is calculated on a fine mesh 40 km horizontal grid size and 10 layers in the vertical for grounded and floating ice and a stress transition zone in between at the grounding line where all stress components contribute in the effective stress in the flow law there is free interaction between ice sheet and ice shelf so that the entire geometry is internally generated a simulation of the present ice sheet reveals that the model is able to yield realistic results a series of sensitivity experiments are then performed in which lower temperatures reduced accumulation rates and lower global sea level stands are imposed either singly or in combination by comparing results of pairs of experiments the effects of each of these environmental changes can be determined in agreement with glacial geological evidence we found that the most pronounced changes show up in the west antarctic ice sheet configuration they appear to be essentially controlled by variations in eustatic sea level whereas typical glacial interglacial changes in temperature and ice deposition rates tend to balance one another these findings support the hypothesis that the antarctic ice sheet basically follows glacial episodes in the northern hemisphere by means of sea level teleconnections grounding occurs more readily in the weddell sea than in the ross sea and long time scales appear to be involved it may take up to 30 40000 years for these continental shelf areas to become completely grounded after an initial stepwise perturbation in boundary conditions according to these reconstructions a steady state antarctic ice sheet may contribute some 16 m to global sea level lowering at maximum glaciation

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

sharp decrease in summer monsoon strength 4000 3500 cal yr b p in the central higher himalaya of india based on pollen evidence from alpine peat age constrained pollen data and magnetic susceptibility of an alpine peat profile from the garhwal higher himalaya display a continuous record of climate and monsoon trends for the past 7800 yr about 7800 cal yr b p dominance of evergreen oak quercus semecarpifolia alder alnus and grasses in the pollen record reflect a cold wet climate with moderate monsoon precipitation from 7800 to 5000 cal yr b p vegetation was progressively dominated by conifers indicating ameliorated climate with a stronger monsoon a warm humid climate with highest monsoon intensity from 6000 4500 cal yr b p represents the mid holocene climatic optimum between 4000 and 3500 cal yr b p the abundance of conifers sharply decreased with the greatest increase in evergreen oak this trend suggests progressive cooling with a decrease in the monsoon to its minimum about 3500 cal yr b p two relatively minor cold dry events at ca 3000 and 2000 cal yr b p marked step wise strengthening of the monsoon until ca 1000 cal yr b p after a cold dry episode that culminated ca 800 cal yr b p the monsoon again strengthened and continued until today a sharp decrease in temperature and rainfall at 4000 3500 cal yr b p represents the weakest monsoon event of the holocene record this cold dry event correlates with proxy data from other localities of the indian subcontinent arabian sea and western tibet

balance velocities and measured properties of the antarctic ice sheet from a new compilation of gridded data for modelling this paper presents a new compilation of gridded data sets for three dimensional modeling of the antarctic ice sheet these are for surface elevation icethickness bedrock elevation and accumulation rate as interpolated on a 281 x 281 mesh with 20 km spacing and encompass all of the ice sheet and thesurrounding continental shelf data sources include the bamber digital elevation model from ers 1 radar altimeter data a redigitization of available ice thicknessdata the giovinetto accumulation data recent ice thickness data from british and german expeditions as well as accumulation data from german and norwegianexpeditions in particular new data were incorporated for the filchner ronne schelfeis and for dronning maud land arising from the epica pre site survey special attention was devoted to carefully match the various data sources both among themselves as across the grounding line and below the ice shelves toenable ice sheet expansion and retreat in dynamic situations as an application the balance flow is calculated over the entire ice sheet using a two dimensionalfinite difference scheme and compared with a previous assessment this brought to light the existence of ice streaming features extending well inland of the icesheet a detailed zoom over dronning maud land exhibits the general flow characteristics of interest for locating a future deep drilling site as a by product anupdated value of 26 4 x 106 km3 was obtained for the total volume of the ice sheet and ice shelves or equivalent to 61 1 m of global sea level rise after removalof the ice sheet and subsequent oceanic invasion and isostatic rebound the total accumulation over the grounded ice sheet including the antarctic peninsula is1924 gta 1 or between 5 and 20 higher than earlier estimates including all of the ice shelves the value is 2344 gta 1

basal topography and ice flow in the bailey slessor region of east antarctica an airborne radio echo sounding campaign carried out in the upper reaches of bailey ice stream and slessor glacier in coats land east antarctica has revealed that tributaries of enhanced flow lie within well defined basal troughs and are separated from each other by bed highs these new data indicate significant differences in ice thickness compared with those estimated in the bedmap database a numerical modeling study has revealed that driving stresses are high enough to account for flow by ice deformation alone in intertributary areas most flow in the enhanced flow tributaries of slessor glacier may also be explained by ice deformation alone however although ice deformation is also significant in the bailey ice stream tributary a large amount of basal motion is also required to fully explain flow velocities here it is proposed that the trough in which bailey tributary lies is sufficiently deep that marine sediments may have accumulated here in preglacial times along with water produced by geothermal heating frictional heating and through a reduction in the pressure melting point basal motion may therefore be facilitated by the presence of a deformable saturated till layer at the bed

stable isotope records from dronning maud land antarctica the european project for ice coring in antarctica epica includes a comprehensive pre site survey on the inland ice plateau of dronning maud land this paper focuses on the investigation of the o 18 content of shallow firn and ice cores these cores were dated by profiles derived from dielectric profiling and continuous flow analysis measurements the individual records were stacked in order to obtain composite chronologies of o 18 contents and accumulation rates with enhanced signal to noise variance ratios these chronologies document variations in the last 200 and 1000 years the o 18 contents and accumulation rates decreased in the 19th century and increased during the 20th century using the empirical relationships between stable isotopes accumulation rates and the 10 in firn temperature the variation of both parameters can be explained by the same temperature history but other causes for these variations such as the build up of the snow cover cannot be excluded a marked feature of the 1000 year chronology occurs during the period ad 1180 1530 when the o 18 contents remains below the long term mean cross correlation analyses between five cores from the weddell sea region and dronning maud land show that o 18 records can in some periods be positively correlated and in others negatively correlated indicating a complex climatic history in time and space

the epica ice core from dronning maud land first results from stable isotope measurements the european project for ice coring in antarctica epica focuses on the drilling of two deep ice cores the first at dome c and the second at kohnen station 75 00 s 0 04 e in dronning maud land dml this paper deals with stable isotope records from ice cores drilled in dml in the first season the deep epica dml core reached a depth of 450 m recovering ice approximately 7000 years old generally the d 18 o record indicates a stable holocene climate and shows low variability however during the last 4000 years based on a preliminary time scale the d 18 o values decrease continuously by about 0 6 and the deuterium excess values increase by about 0 5 t he correlation between d 18 o and the deuterium excess d is investigated for a 50 m long core section and the near surface snow high pass filtered profiles are positively correlated whereas the correlation between low pass filtered profiles is negative a post depositional effect due to diffusion processes can be seen in a sub annually resolved profile from snow pit samples changes in the seasonality of the evolution of the snow cover and the consequences for stable isotope content are demonstrated with data from ice core b31

characterizing the glaciological conditions at halvfarryggen ice dome dronning maud land antarctica we present a comprehensive approach including field data remote sensing and an anisotropic ice flow model to characterize halvfarryggen ice dome in coastal dronning maud land antarctica this is a potential drill site for the international partnerships in ice core sciences which has identified the need for ice cores covering atmospheric conditions during the last few millennia we derive the surface topography the ice stratigraphy from radar data and accumulation rates which vary from 400 to 1670 kg m 2 a 1 due to preferred wind directions and changing surface slope the stratigraphy shows anticlines and synclines beneath the divides we transfer dansgaard johnsen age depth scales from the flanks along isochrones to the divide in the upper 20 50 of the ice thickness and show that they compare well with the results of a full stokes anisotropic ice flow model which predicts 1 11 ka bp ice at 90 of the ice thickness 2 a temporally stable divide for at least 2700 4500 years 3 basal temperatures below the melting point 12 degrees c to 5 degrees c and 4 a highly developed crystal orientation fabric cof we suggest drilling into the apices of the deep anticlines providing a good compromise between record length and temporal resolution and also facilitating studies of the interplay of anisotropic cof and ice flow

transport by wind of granular materials of different grain shapes and densities aeolian transport rates were measured for three sands a quartz sand relative density 2 68 sphericity 0 73 a shelly sand relative density 2 64 sphericity 0 59 carbonate content 67 and granular aluminium oxide relative density 3 95 sphericity 0 67 low sphericity depresses the transport rate particularly at high wind speeds high density also does so but the effect is more marked at low transporting wind speeds the sand of low sphericity undergoes longer saltations than the other materials but is dislodged less frequently than they are and is transported less freely in a given wind of the more spherical materials the denser was the least effective at extracting energy from the wind for grain transport in the range of our experiments both of the more spherical materials showed evidence of a fairly sudden transition of transport behaviour at modest wind speed it is inferred that this marks the transfer of the function of grain dislodgement from direct wind action to inter granular collision the transition did not occur in experiments on the material of lower sphericity for a given transport rate wind speed near the bed is highest for the grains of low sphericity by a considerable margin and lowest for the more compact quartz grains propensity for transport by wind is greatest for the quartz sand less so for the heavy material and least for the material of low sphericity

a search in north greenland for a new ice core drill site a new deep ice core drilling site has been identified in north greenland at 75 12 n 42 30 w 316 km north northwest nnw of the grip drill site on the summit of the ice sheet the ice thickness here is 3085 m the surface elevation is 2919 m the north grip ngrip site is identified so that ice of eemian age 115 130 ka bp calendar years before present is located as far above bedrock as possible and so the thickness of the eemian layer is as great as possible an ice flow model similar to the one used to date the grip ice core is used to simulate the flow along the nnw trending ice ridge surface and bedrock elevations surface accumulation rate distribution and ratio echo sounding along the ridge have been used as model input the surface accumulation rate drops from 0 23 m ice equivalent year 1 at grip to 0 19 m ice equivalent year 1 50 km from grip over the following 300 km the accumulation is relatively constant before is starts decreasing again further north ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure melting point 100 250 km from grip the ngrip site is located 316 km from grip in a region where the bedrock is smooth and the accumulation rate is 0 19 m ice equivalent year 1 the modeled basal ice here has always been a few degrees below the pressure melting point internal radio echo sounding horizons can be traced between the grip and ngrip sites allowing us to date the ice down to 2300 m depth 52 ka bp an ice flow model predicts that the eemian age ice will be located in the depth range 2710 2800 m which is 285 m above the bedrock this is 120 m further above the bedrock and the thickness of the eemian layer of ice is 20 m thicker than at the grip ice core site