extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

palaeoclimatological and chronological implications of the vostok core dust record the2 083 m vostok ice core recovered by the soviet antarctic expeditions has provided much information of climatic and environmental interest for a period covering a full glacial inter glacial cycle1 6 here we present and discuss the dust record obtained down to 2 202 m the final depth to which this core was extended in 1986 first we document the fact that major changes in aeolian deposits as recorded in the vostok core appear to be of global significance and confirm the existence of a link between high latitude aeolian deposits and the earth s orbital parameters7 8 second we propose atmospheric dust as a strati graphic marker to compare timing with other records of palaeocli mate and use the magnetic susceptibility profile measured along the rc11 120 indian ocean core9 for this purpose assuming that major dust events correspond to common aeolian inputs this approach indicates that the vostok and marine records were roughly in phase at the previous glacial interglacial transition

did glacials start with global warming abstract correlation of paleoclimatic evidence with orbital changes shows that the build up of polar ice accelerated when low obliquity coincided with perihelion in northern hemisphere winter under low obliquity the insolation was channeled to the tropics at the expense of both polar caps as perihelion moved from winter solstice toward spring equinox the solar beam in astronomic winter and spring became stronger than in summer and autumn this orbital configuration under climate conditions like today would lead to warming of tropical oceans but cooling of the polar regions the areally weighted global mean surface temperature which is dominated by the low latitudes would increase consequently during the first millennia the early glacial ice build up was most likely accompanied by global warming it was the associated increase of meridional insolation and temperature gradients which were instrumental in the transition to a glacial a significant part of the current global warming is due to the gradual temperature increase of the tropical oceans as the changing orbital configuration today resembles that of the last interglacial glacial transition the warming is likely to have a natural component

a 420 000 year deuterium excess record from east antarctica information on past changes in the origin of precipitation at vostok here we present and analyze the complete vostok ice cores deuterium excess record which spans the last four climatic cycles back to 420 000 years b p to extract paleoclimate information from this record we use isotopic modeling showing that changes in deuterium excess d d 8 18o of vostok precipitation reflect changes in the average temperature of oceanic moisture sources over the last 250 000 years the deuterium excess is strongly anticorrelated with changes in earth s obliquity this reflects changes in the relative contribution of low and high latitudes to the vostok precipitation resulting from changes in the latitudinal annual mean insolation gradient governed by the obliquity however this modulation by obliquity is not observed prior to 250 000 years b p we attribute this difference to the ice flow the deeper ice under vostok station having accumulated in a location upstream vostok receiving precipitation from different oceanic origins despite this difference between the earlier and the later portions of the record the deuterium excess changes during all the glacial inceptions are similar in amplitude and timing relative to the deuterium decrease the glacial inceptions are characterized by high deuterium excess indicating the significant role of the tropics in supplying moisture to the already cold poles

a 135 000 year vostok specmap common temporal framework the object of the present study is to introduce a means of comparing the vostok and marine chronologies our strategy has been to use the 18o of atmospheric o2 denoted 18oatm from the vostok ice core as a proxy for the 18o of seawater denoted 18osw our underlying premise in using 18oatm as a proxy for 18osw is that past variations in 18osw an indicator of continental ice volume have been transmitted to the atmospheric o2 reservoir by photosynthesizing organisms in the surface waters of the world s oceans we compare our record of 18oatm to the 18osw record which has been developed from studies of the isotopic composition of biogenic calcite 18oforam in deep sea cores we have tied our 18oatm record from vostok to the specmap timescale throughout the last 135 kyr by correlating 18oatm with a 18osw record from v19 30 results of the correlation indicate that 77 of the variance is shared between these two records we observed differences between the 18oatm and the 18osw records during the coldest periods which indicate that there have been subtle changes in the factors which regulate 18oatm other than 18osw our use of 18oatm as a proxy for 18osw must therefore be considered tentative especially during these periods by correlating 18oatm with 18osw we provide a common temporal framework for comparing phase relationships between atmospheric records from ice cores and oceanographic records constructed from deep sea cores our correlated age depth relation for the vostok core should not be considered an absolute vostok timescale we consider it to be the preferred timescale for comparing vostok climate records with marine climate records which have been placed on the specmap timescale we have examined the fidelity of this common temporal framework by comparing sea surface temperature sst records from sediment cores with an antarctic temperature record from the vostok ice core we have demonstrated that when the southern ocean sst and antarctic temperature records are compared on this common temporal framework they show a high degree of similarity we interpret this result as supporting our use of the common temporal framework for comparing other climate records from the vostok ice core with any climate record that has been correlated into the specmap chronology

visual stratigraphic dating of the gisp2 ice core basis reproducibility and application annual layers are visible in the greenland ice sheet project 2 ice core from central greenland allowing rapid dating of the core changes in bubble and grain structure caused by near surface primarily summertime formation of hoar complexes provide the main visible annual marker in the holocene and changes in cloudiness of the ice correlated with dustiness mark wisconsinan annual cycles both markers are evident and have been intercalibrated in early holocene ice layer counts are reproducible between different workers and for one worker at different times with 1 error over century length times in the holocene reproducibility is typically 5 in wisconsinan ice age ice and decreases with increasing age and depth cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50 000 years visible observations are not greatly degraded by brittle ice or many other core quality problems allowing construction of long consistently sampled time series high accuracy requires careful study of the core by dedicated observers

a comparison of the vostok ice deuterium record and series from southern ocean core md 88 770 over the last two glacial interglacial cycles taking advantage of the fact that the vostok deuterium d record now covers almost two entire climatic cycles we have applied the orbital tuning approach to derive an age depth relation for the vostok ice core which is consistent with the specmap marine time scale a second age depth relation for vostok was obtained by correlating the ice isotope content with estimates of sea surface temperature from southern ocean core md 88 770 both methods lead to a close correspondence between vostok and md 88 770 time series however the coherence between the correlated d and insolation is much lower than between the orbitally tuned 8d and insolation this reflects the lower accuracy of the correlation method with respect to direct orbital tuning we compared the ice and marine records set in a common temporal framework in the time and frequency domains our results indicate that changes in the antarctic air temperature quite clearly lead variations in global ice volume in the obliquity and precession frequency bands moreover the average phase we estimated between the filtered d and insolation signals at precessional frequencies indicates that variations in the southern high latitude surface temperature could be induced by changes in insolation taking place during a large period of the summer in northern low latitudes or winter in southern low latitudes the relatively large lag found between vostok d variations and obliquity driven changes in insolation suggests that variations in the local radiative balance are not the only mechanism responsible for the variability in surface temperature at those frequencies finally in contrast to the cross spectral analysis method used in previous studies the method we use here to estimate the phases can reveal errors in cross correlations with orbitally tuned chronologies

ice age variability from the vostok deuterium and deuterium excess records the four climatic cycles obtained from the vostok ice core offer a unique opportunity to study the high frequency paleoclimatic variability i e on time scales smaller than 15 kyr we focused our study on the deuterium d and deuterium excess d records which are proxies for local temperature and remote evaporation source temperature and hence give us access to spatial climatic variations spectral analyses of paleoclimatic records have shown that the last glacial period 110 15 kyr before present is characterized by large and fast temperature oscillations examples of such variations in the northern hemisphere are the so called dansgaard oeschger oscillations and heinrich events at vostok these oscillations are also imprinted in the ice with broadband periodicities between 5 and 8 kyr and between 1 4 and 1 8 kyr scenarios for this behavior have recently been developed and argued as well as connections with the northern hemisphere we now can investigate the stability of the fast spectral features in the previous ice ages recovered in the vostok isotopic records this allows us to document the different types of climatic behavior under glacial conditions and hence connect the fast variation statistics with the slower ones controlled by insolation and sea level change our results show that d and d do have a distinct spectral behavior we discuss the implications on the ocean circulation from such a difference

rock physics of organic shales several publications over the last 20 years have established that black organic shales are generally characterized by strong velocity anisotropy low velocity in the bedding normal direction and relatively low density and porosity e g vernik and nur 1992 vernik and liu 1997 these rock properties are of interest in seismic attribute studies but even more so in geomechanical applications related to reservoir characterization and hydraulic fracture stimulation organic shales typically but not necessarily express strong vertical transverse isotropy vti with axis of symmetry perpendicular to the bedding parallel lamination and clay particle preferred orientation high resolution sem imaging figure 1 immediately reveals all these textural features in addition to silt grains and the lenticular distribution of the solid organic matter kerogen which in turn is characterized by significant intraparticle porosity in mature shales any ti medium is described by the five independent elastic consta

bayesian glaciological modelling to quantify uncertainties in ice core chronologies abstract valuable information about the environment and climate of the past is preserved in ice cores which are drilled through ice sheets in polar and alpine regions a pivotal part of interpreting the information held within the cores is to build ice core chronologies i e to relate time to depth existing dating methods can be categorised as follows 1 layer counting using the seasonality in signals 2 glaciological modelling describing processes such as snow accumulation and plastic deformation of ice 3 comparison with other dated records or 4 any combination of these conventionally implementation of these approaches does not use statistical methods in order to quantify dating uncertainties in this paper we develop the approach of category 2 further first the sources of uncertainty involved in glaciological models are formalised feeding these into a statistical framework that we call bayesian glaciological modelling bgm allows us to demonstrate the effect that uncertainty in the glaciological model has on the chronology bgm may also include additional information to constrain the resulting chronology for example from layer counting or other dated records such as traces from volcanic eruptions our case study involves applying bgm to date an antarctic ice core a dyer plateau core working through this example allows us to emphasise the importance of properly assessing uncertain elements in order to arrive at accurate chronologies including valid dating uncertainties valid dating uncertainties in turn facilitate the interpretation of environmental and climatic conditions at the location of the ice core as well as the comparison and development of ice core chronologies from different locations

time dependence of the spatial pattern of accumulation rate in east antarctica deduced from isochronic radar layers using a 3 d numerical ice flow model 1 in east antarctica surface mass balance data can only be obtained from the sparsely distributed ice cores when considering time periods greater than a few decades observations of internal layers measured by airborne ice penetrating radar in principle permit extrapolation of mass balance information from these ice cores we use radar survey lines gathered in the 1970s and a three dimensional numerical model to investigate the feasibility of such extrapolation seeking to match the calculations of englacial layer geometry with observations first we justify the use of a three dimensional model by showing that simple vertical flow models cannot explain all the observations and that horizontal advection is a significant glacial process then we examine processes that affect calculations of layer geometry finding that spatial accumulation rate patterns are extremely important while geothermal heat flux and flow mode sliding or internal deformation are of substantially less importance where the layer is from the last glacial maximum 17 5 ka we find a very good match between the spatial pattern of accumulation rates inferred from this layer and the modern spatial pattern of accumulation rates when considering deeper layers from beyond the current interglacial we find that a different spatial accumulation rate pattern must have existed in addition to the known change in accumulation rate from ice cores the glacial spatial accumulation rate pattern would have had proportionally greater accumulation at the south pole than now compared with the vostok and dome c ice cores

evidence for two intervals of enhanced 10 be deposition in antarctic ice during the last glacial period we have previously reported concentration profiles of cosmic ray produced cosmogenic 10be in deep ice cores from dome c and vostok antarctica1 2 in both these cores we found a concentration of 10be approximately two times larger in ice from the late glacial period than in the holocene ice we interpreted this as probably resulting from a lower precipitation rate on the antarctic plateau during glacial periods compared to interglacial periods in the vostok profile there was one sample corresponding to 60 000 yr bp which gave an unusually large 10be concentration not correlated with any obvious climatic event we suggested that this sample might be reflecting increased 10be production as for example during a period of reduced solar modulation2 we have now measured a much more detailed concentration profile for 10be in the vostok core the results confirm a 10be peak lasting 1 000 2 000 years at 60 000 yr bp and show another similar peak at 35 000 yr bp we have also observed the latter peak in the dome c core we discuss possible sources for these peaks and their potential as stratigraphic markers

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

modeling the signal transfer of sea water δ18o to the δ18o of atmospheric oxygen using a diagnostic box model for the terrestrial and marine biosphere we make use of a simple diagnostic box model to determine the sensitivities of the influencing parameters for the isotopic signal transfer of seawater oxygen to atmospheric oxygen we calculate the 18o of atmospheric oxygen from prescribed oxygen fluxes of the living and dead biomes on land and in the ocean respectively the model is driven by an assumed experiment 1 or measured experiments 2 and 3 temporal seawater 18o signal and a land biomass estimation in experiment 1 we calculated the required changes of several model parameters in order to study fast variations of 18o of atmospheric oxygen as seen in the greenland ice core project grip ice at depths assigned to the eemian time period our calculations support evidence of stratigraphic problems at these depths in the grip ice core in experiment 2 we adjusted the model output which was driven by the benthic seawater 18o record from v19 30 to the measured greenland ice sheet project 2 18o record of atmospheric oxygen for the last 110 000 years by varying the model parameter single and multi parameter matchings were performed the results for single parameter runs exceed the uncertainty ranges for most of the parameters while multiparameter variations are well within these ranges the model calculations are most sensitive to the land respiration factor our results support the findings of van de water et al 1994 that the fractionations associated with biomes activities were most probably lower during cold periods which could point to a combination of fractionations with different temperature dependencies the model results indicate periods of higher marine biological activity during the ice age than today temporal variations of the model parameters show a double peak around 10000 and 8000 years ago which could be associated with meltwater pulses as shown in experiment 3 however they are hardly the well known fairbanks fairbanks et al 1992 pulses since these occur 3000 to 4000 years earlier

evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

gcm analysis of local influences on ice core δ signals a high resolution gcm is used to examine the effect of changes in local surface climate parameters on the ice sheets that can influence the interpretation of the isotopic signal of the ice from deep cores the model suggests that the 10 c difference between the lgm surface temperature deduced from borehole thermometry and that deduced from the water isotope analysis to a great extent may be due to a modification of the precipitation seasonality in central greenland for central east antarctica the model tends to suggest a weak opposite bias

atmospheric oxygen 18 and sea level changes past isotopic composition of atmospheric oxygen 18oatm can be inferred from the analysis of air bubbles trapped in ice caps the longest record covers the last 420 ka thousand of years at the vostok site in east antarctica it shows a strong modulation by the precession and striking similarities but also noticeable differences with the deep sea core oxygen 18 record from which changes in the oxygen content of sea water 18osw and in sea level can be derived indeed 18oatm is driven by complex fractionation processes occuring during respiration and photosynthesis both 18oatm and its difference with respect to 18osw the dole effect are influenced by factors such as the ratio of oceanic and terrestrial productivities which may have significantly changed between different climates also the response time of 18oatm to oceanic changes should be taken in consideration but this parameter itself depends on biospheric activity we review the various aspects of the link between the 18oatm and the 18osw signals we also examine the approach followed by shackleton science 2000 for deriving sea level change from the 18oatm vostok record assuming that the phase between this record and insolation changes is constant and that the dole effect is a fraction of the precessional component of the 18oatm signal glaciological constraints on the vostok chronology and the complexity of the dole effect show that those two assumptions are quite probably too simplistic

a volcanic marker 92 ka for dating deep east antarctic ice cores tephra layers recorded in east antarctic ice enable reliable linking over long distances and when correlated with well dated eruptions in the source area provide absolute ages for improving the accuracy of model based ice chronology we used chronostratigraphic information and grain specific geochemical data major elements by electron microprobe and trace elements by la icp ms to suggest that a tephra layer from the epica dome c and dome fuji ice cores is the distal counterpart of the mt berlin marie byrd land province west antarctica pyroclastic unit 40ar 39ar dated to 92 5 2 0 and 92 2 0 9 ka such one to one correlation which is proposed here for the first time for the east antarctic deep climatic archives provides independent age constraints for glaciological modelling of core timescales

microfracturing paleostress and the growth of faults abstract we have analyzed the microfractures in samples taken near one thrust fault and five normal faults of known displacement to test the dependence of microfracture density and distribution on fault slip we have also recorded the orientation of microfractures as a function of distance from the associated fault surface in order to control as many parameters as possible shallow faults with similar lithologies were chosen they showed the same kind of deformation namely microfracturing without block rotation recrystallization extensive granulation or crystal plasticity the results of over 8000 microfracture measurements suggest that maximum microfracture density is independent of net slip we interpret this relationship as indicating that the preponderance of microfracturing occurs in proximity to the propagating fault tip the angular relationship between the shear plane and microfractures was commonly found to be between 5 and 20 significantly less than the 30 expected between the far field maximum principal stress and the shear surface this low angle between microfracture orientation and shear plane orientation is predicted for a local stress field associated with a propagating mode ii fault tip other possible explanations for the small angle for tensional microfractures and the shear surface are 1 the effective confining pressure was very low or 2 shear strength at failure was much larger than expected

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

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

seismic anisotropy in sedimentary rocks part 1 a single plug laboratory method a single plug method for measuring seismic velocities and transverse isotropy in rocks has been rigorously validated and laboratory tested the method requires only one sample to measure the velocities needed to derive the five independent elastic constants for transversely isotropic materials in this method piezoelectric transducers are fitted to the top bottom and sides of the cylindrical sample laboratory velocity and anisotropy can be measured as functions of pressure temperature fluid saturation and fluid displacement because this method uses a horizontal core plug that has much higher permeability than a vertical core plug it is especially suitable for low permeability shale measurements it reduces the sample preparation and velocity measurement time by more than two thirds

the effect of tectonic environment on permeability development around faults and in the brittle crust abstract fluid flow in the brittle crust is strongly influenced by brittle deformation the tectonic environment in which brittle deformation occurs will dictate both the orientation and magnitude of the resulting permeability tensor the effect of the tectonic environment on permeability is considered conceptually and triaxial deformation experiments showing microfracture permeability development in westerly granite in the pre failure region prior to pervasive shear failure of the sample are used to illustrate the concept in the experiments the permeability changes are greatest in a simulated extensional tectonic regime and smallest in a compressional tectonic environment the results are most usefully considered in the context of effective mean stress p and differential stress q space where permeability may be contoured to allow an indication of permeability development under any experimental loading path

elastic anisotropy of source rocks implications for hydrocarbon generation and primary migration we combined acoustic velocities and anisotropy measurements with x ray diffraction mineralogy rock eval organic geochemical analyses vitrinite reflectance and scanning electron microscope observations on 69 cores of hydrocarbon source rocks collected from eight sedimentary basins the velocity data indicate the lamellar distribution of solid organic matter kerogen in compacted black shales and show a strong correlation between their elastic anisotropy and organic richness the experimental results are consistent with the two component anisotropic model of black shales with a continuous kerogen network in both bedding parallel and bedding normal directions beginning from relatively low toc values the strong elastic anisotropy of tight thermally mature source rocks i further enhanced by overpressure induced bedding subparallel microcrack development during the main stage of hydrocarbon hc generation and primary migration at r0 greater than 0 75 in agreement with published petrographic observations these microcracks significantly aid primary hc migration particularly horizontally elastic anisotropy of medium to high porosity illite smectite shales is weaker than in lower porosity predominantly illite shales however the overall positive trend of elastic anisotropy with kerogen content remains unchanged

organic carbon paleo pco2 and marine ice core correlations and chronology here we present evidence that marine organic matter 13 c measurements can closely reproduce the vostok ice core co 2 record and in addition can be used to evaluate the absolute vostok chronology and the transfer of that chronology between the marine and terrestrial realm our data supports recent speculations that the base of the vostok ice core 2755 m is still within oxygen isotope stage 7 in agreement with recent orbitallytuned ice core chronologies

age scale of the air in the summit ice implication for glacial interglacial temperature change the air occluded in ice sheets and glaciers has in general a younger age defined as the time after its isolation from the atmosphere than the surrounding ice matrix because snow is first transformed into open porous firn in which the air can exchange with the atmosphere only at a certain depth firn ice transition the pores are pinched off and the air is definitely isolated from the atmosphere the firn ice transition depth is at around 70 m under present climatic conditions at summit central greenland the air at this depth is roughly 10 years old due to diffusive mixing whereas the ice is about 220 years old this results in an age difference between the air and the ice of 210 years this difference depends on temperature and accumulation rate and did thus not remain constant during the past we used a dynamic firn densification model to calculate the firn ice transition depth and the age of the ice at this depth and an air diffusion model to determine the age of the air at the transition past temperatures and accumulation rates have been deduced from the 18o record using time independent functions we present the results of model calculations of two paleotemperature scenarios yielding a record of the age difference between the air and the ice for the greenland ice core project grip and the greenland ice sheet project two gisp2 ice cores for the last 100 000 years during the holocene the age difference stayed rather stable around 200 years while it reached values up to 1400 years during the last glaciation for the colder scenario the model results are compared with age differences obtained independently by matching corresponding climate events in the methane and 18o records assuming a very small phase lag between variations in the greenland surface temperature and the atmospheric methane the past firn ice transition depths are compared with diffusive column heights obtained from 15n of n2 measurements the results of this study corroborate the large temperature change of 20 to 25 k from the coldest glacial to holocene climate found by evaluating borehole temperature profiles

the effect of kerogen on the elastic anisotropy of organic rich shales abstractthe elastic properties of reservoir rocks are important for geomechanics applications the most important of which are analysis of stress changes due to production analysis of rock deformation and failure wellbore trajectory optimization and the design of hydraulic fractures organic rich shales are often observed to be strongly anisotropic due to the partial alignment of anisotropic clay minerals and the bedding parallel lamination of organic material within the shale neglecting shale anisotropy may lead to incorrect estimates of the in situ stress or stress changes resulting from production as a result isotropic models may fail to describe geomechanical behavior correctly the distribution of the organic phase plays an important role in determining the elastic properties of organic rich shales and this has a significant effect on production induced stress changes the presence of kerogen leads to a decrease in all of the elastic moduli and has a significant effect on the geomechanical b

texture and anisotropy analysis of qusaiba shales scanning and transmission electron microscopy synchrotron x ray diffraction microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried qusaiba shales from the rub alkhali basin saudi arabia kaolinite illite smectite illite mica and chlorite show strong preferred orientation with 001 pole figure maxima perpendicular to the bedding plane ranging from 2 4 6 8 multiples of a random distribution m r d quartz feldspars and pyrite crystals have a random orientation distribution elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution assuming a nonporous material the average calculated bulk p wave velocities are 6 2 km s maximum and 5 5 km s minimum resulting in a p wave anisotropy of 12 the calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample in the ultrasonic experiment which measures the effects of the shale matrix as well as the effects of porosity velocities are smaller p wave maximum 5 3 km s and minimum 4 1 km s the difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample which have not been taken into account in the matrix averaging

a tentative chronology for the epica dome concordia ice core a tentative age scale edc1 for the last 45 kyr is established for the new 788 m epica dome c ice core using a simple ice flow model the age of volcanic eruptions the end of the younger dryas event and the estimated depth and age of elevated 10be about 41 kyr ago were used to calibrate the model parameters the uncertainty of edc1 is estimated to 10 yr for 0 to 700 yr bp up to 200 yr back to 10 kyr bp and up to 2 kyr back to 41 kyr bp the age of the air in the bubbles is calculated with a firn densification model in the holocene the air is about 2000 yr younger than the ice and about 5500 yr during the last glacial maximum

estimation of temperature change and of gas age ice age difference 108 kyr b p at vostok antarctica air trapped in ice core bubbles provides our primary source of information about past atmospheres air isotopic composition 15n 14n and 40ar 36ar permits an estimate of the temperature shifts associated with abrupt climate changes because of isotope fractionation occurring in response to temperature gradients in the snow layer on top of polar ice sheets a rapid surface temperature change modifies temporarily the firn temperature gradient which causes a detectable anomaly in the isotopic composition of nitrogen and argon the location of this anomaly in depth characterizes the gas age ice age difference age during an abrupt event by correlation with the d or 18o anomaly in the ice we focus this study on the marine isotope stage 5d 5c transition 108 kyr b p a climate warming which was one of the most abrupt events in the vostok antarctica ice isotopic record petit et al 1999 a steplike decrease in 15n and 40ar 4 from 0 49 to 0 47 possibly a gravitational signal due to a change in firn thickness is preceded by a small but detectable 15n peak possibly a thermal diffusion signal we obtain an estimate of 5350 300 yr for age close to the model estimate of 5000 years obtained using the vostok glaciological timescale our results also suggest that the use of the present day spatial isotope temperature relationship slightly underestimates but by no more than 20 15 the vostok temperature change from present day at that time which is in contrast to the temperature estimate based on borehole temperature measurements in vostok which suggests that antarctic temperature changes are underestimated by up to 50 salamatin et al 1998

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

carbon isotope records from pacific surface waters and atmospheric carbon dioxide we have stacked planktonic carbon isotope data from three cores in the western equatorial pacific in order to generate a new reconstruction of atmospheric carbon dioxide over the past 450 000 years our new reconstruction resembles that of shackleton et al 1983 based on data from east pacific core v19 30 which successfully predicted features that were subsequently verified by barnola et al 1987 in the record from the vostock ice core in addition the new data confirm the discovery of shackleton and pisias 1985 that changes in atmospheric co2 lead changes in ice volume and hence probably contributed to the glacial interglacial cycles our new reconstruction avoids some of the deficiencies of the previous reconstruction in particular the planktonic species neogloboquadrina dutertrei on which the earlier reconstruction depends does not calcify in truly nutrient free surface water as the model assumes whereas our new reconstruction uses globigerinoides sacculifer which is expected to be more reliable in addition the surface waters in the west pacific are closer to the nutrient free ideal on which the model broecker 1982 depends on the other hand the amplitude of the new reconstruction is significantly smaller than the amplitude observed by barnola et al 1987 it is not clear whether this smaller range is a better estimate of the amplitude of the biological pump effect or whether the true amplitude is reduced by bioturbation in the west pacific cores that we studied

consistent dating for antarctic and greenland ice cores we are hereby presenting a new dating method based on inverse techniques which aims at calculating consistent gas and ice chronologies for several ice cores the proposed method yields new dating scenarios simultaneously for several cores by making a compromise between the chronological information brought by glaciological modeling i e ice flow model firn densification model accumulation rate model and by gas and ice stratigraphic constraints this method enables us to gather widespread chronological information and to use regional or global markers i e methane volcanic sulfate beryllium 10 tephra layers etc to link the core chronologies stratigraphically confidence intervals of the new dating scenarios can be calculated thanks to the probabilistic formulation of the new method which takes into account both modeling and data uncertainties we apply this method simultaneously to one greenland ngrip and three antarctic epica dome c epica dronning maud land and vostok ices cores and refine existent chronologies our results show that consistent ice and gas chronologies can be derived for depth intervals that are well constrained by relevant glaciological data in particular we propose new and consistent dating of the last deglaciation for greenland and antarctic ice and gas records

glacial interglacial changes in ocean surface conditions in the southern hemisphere the stable isotope signatures of oxygen and hydrogen in the water of preserved ice and snow are both widely used to infer local temperatures of past environments a derived quantity based on these two signatures the deuterium excess 1 provides additional palaeoclimatic information2 3 4 as this parameter depends on the meteorological and oceanic characteristics of the water s source regions in particular their temperature2 3 and relative humidity4 published studies mainly focus on records from the past 40 000 years here we present a deuterium excess history obtained from ice cores from vostok east antarctica spanning the full glacial interglacial cycle of the past 150 000 years the deuterium excess record shows a strong anticorrelation with the earth s orbital obliquity 41 000 year periodicity and values are markedly higher during the cold stage 5d following the last interglacial than during the other cold stages we interpret the relationship with obliquity as resulting from changes in the latitudinal insolation gradient affecting ocean surface conditions and thus the delivery of moisture to the polar region we argue that the high 5d values relative to other cold stages are driven by relatively less moisture delivered from high latitudes and more from low latitudes the deuterium excess in antarctic precipitation thus provides long term spatially integrated information on ocean surface conditions and ocean atmosphere circulations in the southern hemisphere

trace elements in vostok antarctic ice during the last four climatic cycles li v cr mn co as rb sr ba bi and u were determined by inductively coupled plasma sector field mass spectrometry icp sfms in various sections of the 3623 m vostok deep antarctic ice core dated from 4600 to 410 000 years bp which corresponds to the last four climatic cycles back to isotopic stage 11 3 concentrations of all elements were found to be highly variable with low values during interglacial periods and warm interstadials and much higher values during the coldest periods of the last four ice ages crustal enrichment factors suggest various sources for the different elements rock and soil dust is the dominant source of v mn rb ba and u whatever the period and of li cr co sr and as during cold periods sea salt aerosol together with aeolian dust also contributes significantly to sr whereas volcanic emissions could provide a significant input for as and bi especially during warm periods

ultrasonic velocity and anisotropy of hydrocarbon source rocks an experimental study of the physical properties of black kerogen rich shales also including maturation analysis scanning electron microscope sem observations and physical modeling revealed fairly peculiar petrophysical parameters specifically these rocks have very low porosity and density but most importantly both p and s ultrasonic velocities normal to bedding are extremely low whereas they are much higher parallel to bedding giving rise to a strong anisotropy even at high confining pressures we found that these parameters primarily reflect kerogen content microstructure and maturation level of these rocks we found also that microcracks inferred from ultrasonic velocity measurements occur only in mature shales these microcracks are parallel to the bedding plane and further enhance strong intrinsic anisotropy notably at low effective pressure our results show that on a small scale kerogen rich shales are transversely isotropic rocks and can be effectively modeled using the thin laye

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

a large deep freshwater lake beneath the ice of central east antarctica in 1974 75 an airborne radio echo survey of ice depths over central east antarctica led to the discovery of a sub ice lake of unknown depth and composition with an area of about 10 000km2 and lying beneath 4km of ice1 in 1993 altimetric data from satellite measurements2 provided independent evidence of the lake s areal extent thus confirming it to be the largest known sub ice lake by an order of magnitude here we analyse new altimetric and radio echo data along with existing seismic data3 to show that the lake is deep mean depth of 125 m or more and fresh and that it has an area that exceeds previous estimates by about 50 dimensions comparable with those of lake ontario we estimate that the residence time of the water in the lake is of the order of tens of thousands of years and that the mean age of water in the lake since deposition as surface ice is about one million years regional ice dynamics can be explained in terms of steady state ice flow along and over the lake

introduction to special section vostok the russian vostok station is located on the high antarctic plateau at 78 29 s 106 49 e in one of the most remote parts of the world vostok station was established in 1957 during the international geophysical year igy and ice drilling activities started there in 1970 the environmental conditions at vostok station are very severe elevation 3490 m mean annual temperature 55 4 c and the working conditions are extremely difficult adding to the extreme climatic conditions delays in acquiring a complete climate record were related to problems with drilling i e stuck drills and the need to start a new hole when one drill became stuck and the infrastructure support needed from the station i e a fire over the winter in the power station delayed drilling for 1 year

past natural changes in cu zn and cd in vostok antarctic ice dated back to the penultimate interglacial period 1 improved ice core decontamination procedures have allowed us to obtain the first reliable data on cu zn and cd in ancient antarctic ice drilled in a fluid filled hole at vostok station dated back to the beginning of the next to last ice age 240 000 years ago cu zn and cd concentrations and fallout fluxes display very large natural variations by up to a factor of 35 with high values obtained during the coldest climatic stages and much lower values during warm climatic stages crustal dust was an important source of cu and zn during the coldest climatic stages and volcanic emissions were probably an important source of cd both during warm and cold periods

the two step shape and timing of the last deglaciation in antarctica the two step character of the last deglaciation is well recognized in western europe in greenland and in the north atlantic for example in greenland a gradual temperature decrease started at the bolling b around 14 5 ky bp spanned through the allerod a and was followed by the cold younger dryas yd event which terminated abruptly around 11 5 ky bp recent results suggest that this ba yd sequence may have extended throughout all the northern hemisphere but the evidence of a late transition cooling is still poor for the southern hemisphere here we present a detailed isotopic record analyzed in a new ice core drilled at dome b in east antarctica that fully demonstrates the existence of an antarctic cold reversal acr these results suggest that the two step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences thus the coldest part of the acr which shows a temperature drop about three times weaker than that recorded during the yd in greenland may have preceded the yd antarctica did not experienced abrupt changes and the two warming periods started there before they started in greenland the links between southern and northern hemisphere climates throughout this period are discussed in the light of additional information derived from the antarctic dust record

homogeneous climate variability across east antarctica over the past three glacial cycles recent ice core studies have raised the disturbing possibility that glacial interglacial climate changes may be non uniform across antarctica1 2 these findings have been confined to records from the ross sea sector of the continent but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from vostok east antarctica on large spatial scales3 here we present an isotopic profile from a core drilled at dome fuji4 5 situated 1 500 km from vostok in a different sector of east antarctica the two records show remarkable similarities over the past three glacial cycles the extent of the dome fuji record in both large amplitude changes such as terminations interglacials and interstadials and more subtle glacial events even when the origin of precipitation is accounted for our results indicate that antarctic climate is essentially homogeneous at the scale of the east antarctic plateau possibly as a consequence of the symmetry of the plateau and the adjacent ocean

calibration of the 14c time scale to 40 ka by 234u 230th dating of lake lisan sediments last glacial dead sea a new comparison of 14c dates with 234u 230th ages is presented of aragonites from lake lisan the last glacial dead sea between 20 52 cal ka bp the lisan data are coincident with the coral based 14c calendar age calibration through the continuous portion of the curve to 23 5 cal ka bp and with the additional checkpoints at 30 and 40 cal ka bp the agreement with the corals provides evidence for the accuracy of the u th and 14c ages and indicates that lisan aragonites can potentially be used to generate a nearly continuous record of the atmospheric 14c variations through this crucial time interval the lisan data are compared with other records older than 25 cal ka bp from lake suigetsu japan north atlantic foraminifera south african cave deposits and tufa from spain over some age intervals the records show broad agreement over other intervals they diverge all agree that 14c ages were 2 5 0 5 ka younger than calendar ages between 20 32 cal ka bp for ages 32 cal ka bp the lake suigetsu data indicate small differences between 14c ages and calendar ages of less than 1 5 ka the other records broadly agree that 14c ages are too young by 3 1 ka from 32 39 cal ka bp at 40 cal ka bp the foraminifera show equal 14c and calendar ages while the corals lisan aragonites and the spanish tufa indicate a large age difference of 4 5 ka a recent paleomagnetic study of the lisan formation indicates that the high calendar 14c age difference at 40 cal ka bp may be associated with the laschamp paleomagnetic excursion

response of south atlantic deep waters to deglacial warming during terminations v and i abstract new deep sea core data from the atlantic sector of the southern ocean covering mis12 to mis10 and the last deglaciation show a clear lag of the changes in deep water properties with respect to changes in surface conditions the development of a chronology based on the correlation of southern ocean sea surface temperature with air temperature over antarctica allows the quantification and comparison of phase lags within the marine records during termination v tv and termination i ti deglacial changes in the south atlantic are interpreted as the response to changes in the state of the atlantic meridional ocean circulation amoc the warming of south atlantic surface waters and air temperature over antarctica at the beginning of both tv and ti is attributable to a reduction in interhemispheric heat transport due to the weakening of the amoc comparison of our results with climber 2 simulations indicates that the response of bottom waters seen in the benthic isotopic records delayed with respect to south atlantic surface warming can be explained by the increased inflow of north atlantic deep water nadw to the south atlantic site at the time of the amoc recovery reconstructed sea surface temperature at our south atlantic site exhibits a cold spell at the end of tv resembling the antarctic cold reversal of the last deglaciation the presence of cold spells during tv and ti may be explained by the fact that the recovery of the amoc took place early during the termination in both cases the sequence of events is similar during both terminations however the magnitude of the phase shifts between south atlantic surface and deep waters conditions differs from one termination to the other suggesting variations in the magnitude and duration of the amoc perturbation

stratigraphic correlations between the european project for ice coring in antarctica epica dome c and vostok ice cores showing the relative variations of snow accumulation over the past 45 kyr 1 high resolution chemistry analysis and electrical measurements performed on two ice core records european project for ice coring in antarctica epica dome c and vostok spanning the last 45 kyr allow stratigraphic correlations by matching volcanic events several common events were identified along the two ice cores on the basis of acidity and sulphate spikes in snow layers timescales were matched through comparison with isotope d profiles and using the antarctic cold reversal acr minimum a 10be peak and a dust spike as temporal checkpoints ratios of relative snow accumulation at the two sites during the holocene in the glacial interglacial transition and in the last part of the glacial period were reconstructed by finding the best fit between dome c and vostok depths recording the same events after accounting for thinning of the layers as they are buried within the glacier the dome c vostok accumulation ratio expected to be roughly constant from the conventional accumulation temperature isotope approach is 1 12 for the glacial period but increases to as much as 1 44 for a large part of the holocene glaciological effects mainly related to the geographic origin of the vostok ice along the ridge b vostok axis can account for only a minor fraction of this change instead we argue that accumulation variability between the cores stems from differential changes in atmospheric circulation during these respective climatic periods at the two sites regional changes in atmospheric circulation are proposed with a negative anomaly in dome c a positive accumulation anomaly in vostok or a combination of both during glacial climate our approach may help to improve ice core dating by 1 revealing anomalies in accumulation rate estimation based on the classical thermodynamic method and 2 supporting the necessity to take into account contributions due to changes in atmospheric circulation processes

characteristics and sources of tephra layers in the epica dome c ice record east antarctica implications for past atmospheric circulation and ice core stratigraphic correlations thirteen discrete air fall tephra layers were identified in the last 200 000 yr section of the epica dome c ice record drilled in the east antarctic plateau 75 06 s 123 21 e quantitative grain size glass particle morphology and the grain discrete major element composition of the glass fraction of these layers were investigated through comparison with literature data on the rock composition of quaternary volcanic centres located within and around antarctica five tephra layers were attributed to south sandwich volcanoes in the south atlantic ocean two to south shetland volcanoes northern antarctic peninsula two to andean volcanoes and four to antarctic marie byrd land and melbourne provinces the abundance of layers originating in the southern part of the atlantic confirms that westerly atmospheric circulation spiralling towards east antarctica prevailed over the last 200 ka moreover the record of events from antarctic centres suggests that atmospheric trajectories from west to east antarctica can also be significant a few ash layers are geochemically distinct and appear equivalent to levels from vostok and dome fuji deep ice records located ca 600 km and ca 2000 km respectively from dome c on the antarctic plateau these layers provide unambiguous markers for future correlation with other antarctic ice cores and circumpolar marine climatic records they also provide reliable constraints to get a common timescale by glaciological modelling and represent a first step towards absolute ice core dating

transferring radiometric dating of the last interglacial sea level high stand to marine and ice core records in order to derive a radiometric age marker for the end of the penultimate glacial interglacial transition we compiled published u series isotope measurements on corals from the period extending from stage 6 to the middle of the last interglacial and computed the corresponding open system ages using thompson et al model thompson w g spiegelman m w goldstein s l speed r c an open system model for u series age determinations of fossil corals earth planet sci lett 210 2003 365 381 we obtain a global mean age of 126 calendar kyr bp ka 1 7kyr 2 for the beginning of the last interglacial sea level high stand after showing that the phase relationships observed between changes in sea level north atlantic benthic and planktonic foraminifera oxygen isotopic records and atmospheric methane over the last deglaciation were likely also valid over the penultimate deglaciation we derive an age of 131 2ka 2kyr 2 for the abrupt increase in atmospheric ch4 and north atlantic surface temperature marking the end of the penultimate glacial interglacial transition this age is consistent with u th dates of the penultimate glacial interglacial transition recorded in speleothems from sites where speleothems isotopic records are synchronous with north atlantic temperature records over the last deglaciation finally we show that the phase obtained between the climatic response and northern hemisphere summer insolation is not constant from termination ii to termination i implying that northern hemisphere summer insolation alone cannot explain the timing of terminations

geomagnetic modulation of the 36cl flux in the grip ice core greenland geomagnetic field strength is expected to affect the production rate of cosmogenic isotopes such as beryllium 10 carbon 14 or chlorine 36 chlorine 36 data from the greenland ice core project grip ice core agree well with a production rate calculation based on a paleomagnetic reconstruction for the past 100 000 years over both long and short term variations a chlorine 36 peak at 38 000 years ago previously found in the beryllium 10 record from the vostok ice core can be explained by a period of low geomagnetic field intensity

firn processes and δ15n potential for a gas phase climate proxy abstract in order to quantify the sequence of events between changes in atmospheric composition and climate changes recorded in ice cores we must accurately account for the age difference between ice and gas at a given depth this gas age ice age difference depends on the age of the ice at the bottom of the firn layer where the bubbles are closed off firn densification models are used to calculate how this age difference varied in the past but have an uncertainty on the order of 1000 years for central antarctic sites here we explore the possibility that 15 n of n 2 is a gas phase proxy of climate which can be used to synchronize gas and ice records we present the 15 n record from the epica dome c edc ice core covering the last three glacial terminations and five glacial interglacial cycles between 300 and 800 ka previous studies have shown that gravitational settling enriches 15 n as a function of the diffusive column height in the firn if densification models prediction of deeper firn close off under glacial conditions is correct then we would expect heavier 15 n during glacial periods and a negative correlation with temperature instead edc 15 n is positively correlated with the ice deuterium content a proxy for temperature as previously reported at vostok dome fuji and epica dronning maud land we propose a mechanism that links accumulation rate firn permeability and convective mixing in the top meters of the firn to explain this correlation between 15 n and ice deuterium content the tightest correlation is observed over glacial terminations supporting the idea that 15 n is a property in the gas phase that records changes in surface conditions linked to deglacial warming

what was the surface temperature in central antarctica during the last glacial maximum abstract the temperature increase at vostok antarctica from the last glacial maximum to the present warm period is about 8 c based on the deuterium isotope profile the bore hole temperature temperature profile in the ice sheet indicates that the temperature difference may have been much larger about 15 c the temperature dependent gas occlusion process is the key to evaluate the two scenarios atmospheric air penetrates the porous firn layer of the ice sheet and gets trapped at the firn ice boundary consequently the air is younger than the surrounding ice when it gets enclosed in bubbles this age difference age between ice and enclosed gas is temperature and accumulation rate dependent therefore it is possible to estimate paleotemperatures from a known age we use the linkage between chronologies of ch 4 and water isotopes from byrd station and vostok to obtain an experimental age for vostok this experimental age is then compared to modeled age for the two temperature scenarios our results indicate that the temperature reconstruction deduced from the water isotopic composition is the more probable one

climate related variations in lead concentrations and sources in vostok antarctic ice from 65 000 to 240 000 years bp 1 pb has been measured in various sections of the 3 623 m vostok deep antarctic ice core dated from 65 000 to 240 000 years bp i e back to the beginning of the penultimate ice age and the preceding interglacial isotopic stage 7 5 pb concentrations were highly variable during this time interval with low values down to 0 5 pg g during warm climatic stages and much higher values up to 20 pg g during cold climatic stages especially isotopic stages 4 2 and 6 2 to 6 6 rock and soil dust accounts for virtually 100 of pb measured in the ice during cold climatic stages while the contribution from volcanoes might be significant during warm stages

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

new modeling of the vostok ice flow line and implication for the glaciological chronology of the vostok ice core 1 we have used new spaceborne elevation and airborne ice thickness data to constrain a 2d1 2 model of snow accumulation and ice flow along the ridge b vostok station ice flow line east antarctica we show that new evaluations of the ice flow line geometry from the surface elevation ice thickness from low frequency radar data and basal melting and sliding change significantly the chronology of the vostok ice core this new vostok dating model reconciles orbital and glaciological timescales and is in good agreement with the dome fuji glaciological timescale at the same time the new model shows significantly older ages than the previous gt4 timescale for the last glacial part being thus in better agreement with the grip and gisp2 chronologies

resolving milankovitch consideration of signal and noise milankovitch climate theory provides a fundamental framework for the study of ancient climates although the identification and quantification of orbital rhythms are commonplace in paleoclimate research criticisms have been advanced that dispute the importance of an astronomical climate driver if these criticisms are valid major revisions in our understanding of the climate system and past climates are required resolution of this issue is hindered by numerous factors that challenge accurate quantification of orbital cyclicity in paleoclimate archives in this study we delineate sources of noise that distort the primary orbital signal in proxy climate records and utilize this template in tandem with advanced spectral methods to quantify milankovitch forced paced climate variability in a temperature proxy record from the vostok ice core vimeux and others 2002 our analysis indicates that vostok temperature variance is almost equally apportioned between three components the precession and obliquity periods 28 a periodic 100 000 year cycle 41 and the background continuum 31 a range of analyses accounting for various frequency bands of interest and potential bias introduced by the saw tooth shape of the glacial interglacial cycle establish that precession and obliquity periods account for between 25 percent to 41 percent of the variance in the 1 10 kyr 1 100 kyr band and between 39 percent to 66 percent of the variance in the 1 10 kyr 1 64 kyr band these results are approximately two to four times greater than those published by wunsch 2004 for the same vostok time series in all cases most of the remaining variance is accounted for by the 100 000 year cycle which is distinct from a background continuum that resembles autoregressive red noise our analysis high lights the importance of a comprehensive assessment of the climate signals in geologic records and underscores the significance of orbital forcing pacing as a primary agent of pleistocene climate change

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

ice microstructure and fabric an up to date approach for measuring textures automatic c axes analyzers have been developed over the past few years leading to a large improvement in the data available for analysis of ice crystal texture such an increase in the quality and quantity of data allows for stricter statistical estimates the current textural parameters i e fabric crystallographic orientations and microstructure grain boundary networks are presented these parameters define the state of the polycrystal and give information about the deformation undergone by the ice to reflect the findings from automatic measurements some parameter definitions are updated and new parameters are proposed moreover a matlab toolbox has been developed to extract all the textural parameters this toolbox which can be downloaded online is briefly described

atmospheric methane during the last four glacial interglacial cycles rapid changes and their link with antarctic temperature 1 atmospheric methane ch4 recorded in antarctic ice cores represents the closest ice proxy available for greenland temperature changes beyond times when greenland climate records are available the record over four climatic cycles from the vostok ice core offers the opportunity to study the phase relationship between greenland and antarctic climate changes through detailed ch4 profiles combining american and french analytical efforts we have improved the time resolution of the existing ch4 record from petit et al 1999 spectral analyses reveal high and low frequency variability including a strong precessional component the phase relationship between ch4 and the antarctic temperature proxy d shows a systematic lag of ch4 versus temperature by 1100 200 years on long timescales 50 400 kyr and a more complex behavior over shorter timescales i e 25 kyr suggesting that dansgaard oeschger type of climatic variability and associated interhemispheric linkage are robust features of late quaternary climate

surface water temperature changes in the high latitudes of the southern hemisphere over the last glacial interglacial cycle a set of numerical equations is developed to estimate past sea surface temperatures sst from fossil antarctic diatoms these equations take into account both the biogeographic distribution and experimentally derived silica dissolution the data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments factor analysis of 166 samples 124 holocene core top and 42 artificial samples resolved four factors three of these factors depend on the water mass distribution one subantarctic and two antarctic assemblages factor 4 corresponds to a dissolution assemblage inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of sst over a wide range of biosiliceous dissolution a transfer function dtf 166 34 4 is derived from the distribution of these factors versus summer sst its standard error is 1 c in the 1 to 10 c summer temperature range this transfer function is used to estimate sst changes in two southern ocean cores 43 s and 55 s which cover the last climatic cycle the time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios the reconstructed sst records present strong analogies with the air temperature record over antarctica at the vostok site derived from changes in the isotopic ratio of the ice this similarity may be used to compare the oceanic isotope stratigraphy and the vostok time scale derived from ice flow model the oceanic time scale if taken at face value would indicate that large changes in ice accumulation rates occurred between warm and cold periods

beryllium 10 in the greenland ice core project ice core at summit greenland concentrations of the cosmogenic isotope 10be have been measured in more than 1350 samples from the greenland ice core project grip ice core drilled at summit greenland although a dust associated component of 10be retained by 0 45 m filters in some of the samples complicates the interpretations the results confirm that the first order origin of 10be concentration variations is changes in precipitation rate associated with different climate regimes this effect is seen not only between glacial and interglacial periods but also during the shorter dansgaard oeschger interstadials by contrast the 10be data do not support the interpretation of rapidly varying accumulation i e climate during the last interglacial they can however be used to help place limits on the origin of the ice in these events after taking into account variable snow accumulation effects variations in the 10be flux are observed probably caused by solar and geomagnetic modulation but possibly also by primary cosmic ray variations the most dramatic is a 10be peak 40 000 years ago similar to that found in the vostok ice core thus permitting a very precise correlation between climate records from arctic and antarctic ice cores the 36cl 10be ratio considering either total or only ice associated 10be shows significant variability over the whole core depth thus confirming the difficulty in using this parameter for dating ice cores

flow properties of the ice from the greenland ice core project ice core the reason for folds long term deformation tests on ice from the greenland ice core project grip deep ice core show that ice from the different climate zones in the ice core has flow properties correlated with the concentrations of impurities in the sample the deformation tests are performed by uniaxial unconfined compression at 16 degrees c with an octahedral compression stress of 3 bars the ice samples are compressed for 1 2 to 3 years until the tertiary strain rate is reached it is believed that by the end all downhole flow conditions are forgotten and that the ice sample has settled in a state determined by the applied stress and temperature conditions all samples are tested under the same stress and temperature conditions so the resulting deformation rates and final ice crystal size and fabrics can only differ due to varying impurity concentrations the results show that ice from cold climatic periods with high concentrations of impurities deforms more slowly than ice from warm climatic periods in compression when tertiary creep is reached the crystal size is smaller in the cold ice than in the warm the ice from warmer climatic periods with lower concentrations of impurities deforms at a factor of 2 3 times more rapidly in compression the tertiary steady state crystal size is increased by 50 and the ice crystals have oriented more favorably for the applied compression in the warm ice which is believed to be the reason why the strain rates are greater here than in the cold ice in the bottom 200 m of the grip ice core zones are observed with folds on the scale of 1 8 cm an investigation of the ice layers in and around the folds shows that the layers are composed of ice from different climatic zones the folding is believed to result from the different flow and rheological properties of the layers involved in the folding structures

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

chronology of the vostok ice core constrained by o2 n2 ratios of occluded air and its implication for the vostok climate records abstract we present a timescale for the vostok ice core that is derived by orbitally tuning to o 2 n 2 ratios in occluded air for depths deeper than 1550 m 112 ka and by gas correlation to the gisp2 chronology for the section shallower than 1422 m 2 exclusion and hence the o 2 n 2 ratio in trapped gases the newly derived o 2 n 2 chronology is consistent with absolutely dated speleothem records the o 2 n 2 chronology differs from previously published orbital tuning chronologies ch 4 and 18 o atm by up to 6 kyr and from the original gt4 chronology by up to 15 kyr the difference between the o 2 n 2 chronology and the 18 o atm chronology varies in time with strong signals centered at 1 100 and 1 41 kyr 1 the ages for the last four glacial terminations in vostok correspond to high obliquity 23 7 at terminations midpoints they also correspond with decreasing precession index corresponding to increasing boreal summer insolation the vostok temperature record boreal summer insolation and the rate of change of the specmap property reflecting planktonic foram 18 o with respect to time are highly coherent at precession and obliquity periods these three properties vary almost synchronously with the possibility that vostok temperature lags behind the other two our new timescale supports the widespread view that boreal summer insolation played an important role in glacial interglacial cycles

the dole effect and its variations during the last 130 000 years as measured in the vostok ice core we review the current understanding of the dole effect the observed difference between the delta sup 18 o of atmospheric o sub 2 and that of seawater and its causes extended the record of variations in the dole effect back to 130 kyr before present using data on the delta sup 18 o of o sub 2 obtained from studying the vostok ice core and discuss the significance of temporal variations the dole effect reflects oxygen isotope fractionation during photosynthesis respiration and hydrologic processes evaporation precipitation and evapotranspiration our best prediction of the present day dole effect 20 8 per thousand is considerably lower than the observed value 23 5 per thousand and we discuss possible causes of this discrepancy during the past 130 kyr the dole effect has been 0 05 per thousand lower than the present value on average the standard deviation of the dole effect from the mean has been only per thousand and the dole effect is nearly unchanged between glacial maxima and interglacial periods the small variability in the dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant most periodic variability in the dole effect is in the precession band suggesting that changes in this global biogeochemical termmore reflects variations in low latitude land hydrology and productivity or possibly variability in low latitude oceanic productivity 65 refs 4 figs 3 tabs less

measurements and full field predictions of deformation heterogeneities in ice we have made creep experiments on columnar grained ice and characterised the microstructure and intragranular misorientations over a range of length scales a fft full field model was used to predict the deformation behaviour using the experimentally characterised microstructure as the starting material this is the first time this combination of techniques has been used to study the deformation of ice the microstructure was characterised at the cm scale using an optical technique the automatic ice texture analyser aita and at the micron scale using electron backscattered diffraction ebsd the crystallographic texture and intragranular misorientations were fully characterised by ebsd 3 angles the deformed microstructure frequently showed straight subgrain boundaries often originating at triple points these were identified as kink bands and for the first time we have measured the precise misorientation of the kink bands and deduced the nature of the dislocations responsible for them these dislocations have a basal edge nature and align in contiguous prismatic planes enabling deformation along the c axis in addition non uniform grain boundaries and regions of recrystallization were seen we present coupling between fine scale characterization of intragranular misorientations from experiments and prediction of internal stresses that cause it the model predicts the morphology of the observed local misorientations within the grains however it over predicts the misorientation values this is because the annealing and recrystallization mechanisms are not taken into account in the model ice is excellent as a model material for measuring predicting and understanding deformation behaviour for polycrystalline materials specifically for ice this knowledge is needed to improve models of ice sheet dynamics that are important for climatic signal interpretation

electrical conductivity method ecm stratigraphic dating of the byrd station ice core antarctica a continuous ecm profile strong acid concentration has been measured along the 2191 m of ice core recovered at byrd station antarctica in 1968 the ecm profile reveals continuous and systematic seasonal changes which are used for dating the ice core back to 50 000 bp hammer and others ecm stratigraphic dating of byrd station ice core antarctica

dating the vostok ice core by an inverse method using the chronological information available in the vostok records we apply an inverse method to assess the quality of the vostok glaciological timescale the inversion procedure provides not only an optimized glaciological timescale and its confidence interval but also a reliable estimate of the duration of successive events our results highlight a disagreement between orbitally tuned and glaciological timescales below 2700 m i e 250 kyr b p thousands of years before present this disagreement could be caused by some discontinuity in the spatial variation of accumulation upstream of vostok moreover the stratigraphic datings of central greenland ice cores grip and gisp2 appear older than our optimized timescale for the late glacial this underlines an unconsistency between the physical assumptions used to construct the vostok glaciological timescale and the stratigraphic datings the inverse method allows the first assessment of the evolution of the phase between vostok climatic records and insolation this phase significantly varies with time which gives a measure of the nonlinear character of the climatic system and suggests that the climatic response to orbital forcing is of different nature for glacial and interglacial periods we confirm that the last interglacial as recorded in the vostok deuterium record was long 16 2 2 kyr thousands of years however midtransition of termination ii occurred at 133 4 2 5 kyr bp which does not support the recent claim for an earlier deglaciation finally our study suggests that temperature changes are correctly estimated when using the spatial present day deuterium temperature relationship to interpret the vostok deuterium record

climatic interpretation of the recently extended vostok ice records a new ice core drilled at the russian station of vostok in antarctica reached 2755 m depth in september 1993 at this depth the glaciological time scale provides an age of 260 ky bp 25 we refine this estimate using records of dust and deuterium in the ice and of 18o of o2 in the entrapped air 18o of o2 is highly correlated with insolation over the last two climatic cycles if one assumes that the egt chronology overestimates the increase of age with depth by 12 for ages older than 112 ky bp this modified age depth scale gives an age of 244 ky bp at 2755 m depth and agrees well with the age depth scale of walbroeck et al in press derived by orbital tuning of the vostok d record we discuss the temperature interpretation of this latter record accounting for the influence of the origin of the ice and using information derived from deuterium excess data we conclude that the warmest period of stage 7 was likely as warm as today in antarctica a remarkable feature of the vostok record is the high level of similarity of proxy temperature records for the last two climatic cycles stages 6 and 7 versus stages 1 5 this similarity has no equivalent in other paleorecords

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

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

modeling anisotropic elasticity in an unconventional reservoir abstract during the last two decades several studies have shown that organic rich shales are characterized by strong velocity anisotropy it is well known that these types of rocks exhibit strong polar anisotropy also known as vertical transverse isotropy vti with vertical or bedding perpendicular velocities being much slower than horizontal or bedding parallel velocities however the amount of elastic anisotropy can vary significantly from one formation to another because the individual clay minerals the volume concentration and geometric distribution of organic matter and other geologic characteristics such as texture and nonclay mineralogy vary by geologic formation it is therefore important to quantify the amount of elastic anisotropy in our formations of interest for various geophysical and geomechanical applications related to reservoir characterization strongly anisotropic compressional and shear velocities in two formations of interest in an unconventional reservoir are analyzed

hemispheric roles of climate forcings during glacial interglacial transitions as deduced from the vostok record and lln 2d model experiments the vostok ice contains fingerprints of atmospheric greenhouse trace gases antarctic temperature northern hemisphere temperature and global ice volume sea level changes during the last glacial interglacial cycles and thus allows us to investigate the sequences of these climatic events in particular during the transitions from full glacial to interglacial conditions the use of the updated co2 record presented here and a reexamination of the sea level proxy confirm that the succession of changes has been similar through each of the four marked transitions found at vostok antarctic air temperature and co2 increase in parallel and almost synchronously while the rapid warmings over greenland take place during the last half of their change and coincide with the marked decay in continental ice volume the vostok results thus emphasize a fundamental difference between south and north in terms of climate dynamics our results confirm the role of co2 as an important amplifier of the glacial interglacial warming in the south it appears also that the marked warming observed at high northern latitudes lagging behind the co2 increase by several thousand years is roughly synchronous with the decay of the northern ice sheets suggesting a major role of climatic feedback due to this decay such a climatic scenario is supported by sensitivity experiments performed with the lln 2 d model forced by the northern hemisphere insolation and co2 model results indicate that the decay of the northern ice sheets and the northern hemisphere temperature depend primarily on the northern summer insolation these results nevertheless could be affected if mechanisms specific to the southern hemisphere appear to play a major role in driving the northern hemisphere climate the model also helps to constrain the time response of ice volume to insolation and co2 changes

sequence of events from the onset to the demise of the last interglacial evaluating strengths and limitations of chronologies used in climatic archives the last interglacial lig represents an invaluable case study to investigate the response of components of the earth system to global warming however the scarcity of absolute age constraints in most archives leads to extensive use of various stratigraphic alignments to different reference chronologies this feature sets limitations to the accuracy of the stratigraphic assignment of the climatic sequence of events across the globe during the lig here we review the strengths and limitations of the methods that are commonly used to date or develop chronologies in various climatic archives for the time span 140 100 ka encompassing the penultimate deglaciation the lig and the glacial inception climatic hypotheses underlying record alignment strategies and the interpretation of tracers are explicitly described quantitative estimates of the associated absolute and relative age uncertainties are provided recommendations are subsequently formulated on how best to define absolute and relative chronologies future climato stratigraphic alignments should provide 1 a clear statement of climate hypotheses involved 2 a detailed understanding of environmental parameters controlling selected tracers and 3 a careful evaluation of the synchronicity of aligned paleoclimatic records we underscore the need to 1 systematically report quantitative estimates of relative and absolute age uncertainties 2 assess the coherence of chronologies when comparing different records and 3 integrate these uncertainties in paleoclimatic interpretations and comparisons with climate simulations finally we provide a sequence of major climatic events with associated age uncertainties for the period 140 105 ka which should serve as a new benchmark to disentangle mechanisms of the earth system s response to orbital forcing and evaluate transient climate simulations

ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at vostok station east antarctica an interpretation of the deuterium profile measured along the vostok east antarctica ice core down to 2755 m has been attempted on the basis of the borehole temperature analysis an inverse problem is solved to infer a local geophysical metronome the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of milankovich periods by correlating the smoothed isotopic temperature record to the metronome a chronostratigraphy of the vostok ice core is derived with an accuracy of 3 0 4 5 kyr the developed timescale predicts an age of 241 kyr at a depth of 2760 m the ratio 13d 13t i between deuterium content and cloud temperature fluctuations at the top of the inversion layer is examined by fitting simulated and measured borehole temperature profiles the conventional estimate of the deuterium temperature slope corresponding to the present day spatial ratio 9 per mil oc is confirmed in general however the mismatch between modeled and measured borehole temperatures decreases noticeably if we allow surface temperature responsible for the thermal state of the ice sheet to undergo more intensive precession oscillations than those of the inversion temperature traced by isotope record with this assumption we obtain the long term temporal deuterium temperature slope to be 5 8 6 5 per mil oc which implies that the glacial interglacial temperature increase over central antarctica was about 15oc in the surface temperature and 10oc in the inversion temperature past variations of the accumulation rate and the corresponding changes in the ice sheet surface elevation are simultaneously simulated

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

glacial interglacial variations in central east antarctic ice accumulation rates past rates of ice accumulation in central east antarctica are defined poorly for the last glacial period ice cores from which current estimates are based are limited in number there is one deep ice core at vostok station one at dome f and two others currently being extracted at dome c and dronning maud land and are restricted spatially they are one dimensional here spatial variations in ice accumulation rates during the last glacial are calculated from isochronous internal ice sheet layering measured by airborne ice penetrating radar data the layers are used to identify the stratigraphy around five east antarctic ice domes isochrons are dated by linking them to the vostok ice core and in one case the epica dome c ice core this chronostratigraphy allows the depth age function to be identified across the ice sheet a simple ice flow model using the depth age measurements as input is then used to determine the spatial and temporal variation in east antarctic ice accumulation over the last glacial cycle the lowest rates of ice accumulation were predicted in the full glacial period to the south of dome a and ridge b there are two possible explanations for this 1 the ice divide topographies may have caused a precipitation shadow in the ice age 2 with the expansion of the ross ice shelf the area to the south of dome a and ridge b would be at the very centre of the ice sheet and hence at a maximum distance from the ocean moisture source r 2002 elsevier science ltd all rights reserved

validity of the isotopic thermometer in central antarctica limited impact of glacial precipitation seasonality and moisture origin the classical interpretation of water stable isotopes deuterium or oxygen 18 retrieved from ice cores into past local temperature relies on the use of the spatial isotope temperature slope as a surrogate of the temporal slope whereas this assumption has been challenged by independent methods in central greenland it is still considered as valid in central antarctica we use an atmospheric general circulation model gcm to study two parameters highlighted by previous studies as being among the most important with respect to this assumption we show that in the gcm between present day and last glacial maximum the change in precipitation seasonality and the cooling of the moisture sources have limited and opposite effects on the isotopic record of the antarctic local temperature this conclusion strengthens the validity of the classical interpretation of isotope records in central antarctica