density log of a 181 m long ice core from berkner island antarctica a 181 m long ice core was drilled at 79 36 51 s 45 43 28 w near the summit of berkner island antarctica 886 m a s l berkner island is located between the filchner and ronne ice shelves and the ice near the summit shows little lateral flow the density of the ice core was measured every 3 mm along its length using attenuation of a gamma ray beam which gave an absolute accuracy of 2 as expected there is a general density increase with depth the maximum densities of 900 kg m 3 being reached just above 100 m depth comparison with the electrical conductivity method ecm shows density variations with the same wavelength as the annual signals which can be seen in the ecm log higher acidity during summer in the shallowest part of the core the density of winter layers is higher than that of summer layers a relationship which is reversed at greater depth we assume that the densification rates for the two types of firn are different similar density phenomena were observed on ice cores from greenland showing that such phenomena are not a local effect

continuous methane measurements from a late holocene greenland ice core atmospheric and in situ signals abstract ancient air trapped inside bubbles in ice cores can now be analysed for methane concentration utilising a laser spectrometer coupled to a continuous melter system we present a new ultra high resolution record of atmospheric methane variability over the last 1800 yr obtained from continuous analysis of a shallow ice core from the north greenland eemian project neem 2011 s1 during a 4 week laboratory based measurement campaign our record faithfully replicates the form and amplitudes of multi decadal oscillations previously observed in other ice cores and demonstrates the detailed depth resolution 5 3 cm rapid acquisition time 30 m day 1 and good long term reproducibility 2 6 2 of the continuous measurement technique in addition we report the detection of high frequency ice core methane signals of non atmospheric origin firstly measurements of air from the firn ice transition region and an interval of ice core dating from 1546 1560 ad gas age resolve apparently quasi annual scale methane oscillations traditional gas chromatography measurements on discrete ice samples confirm these signals and indicate peak to peak amplitudes of ca 22 parts per billion ppb we hypothesise that these oscillations result from staggered bubble close off between seasonal layers of contrasting density during time periods of sustained multi year atmospheric methane change secondly we report the detection of abrupt 20 100 cm depth interval high amplitude 35 80 ppb excess methane spikes in the neem ice that are reproduced by discrete measurements we show for the first time that methane spikes present in thin and infrequent layers in polar glacial ice are accompanied by elevated concentrations of carbon and nitrogen based chemical impurities and suggest that biological in situ production may be responsible

shear wave processing of sonic log waveforms in a limestone reservoir sonic full waveforms were recorded in a shale limestone interval with an experimental 12 channel acoustic logging device well defined shear pseudo rayleigh waves were observed throughout most of the 142 m interval and were used to distinguish lithologic boundaries and zones of fracturing as interpreted by logs the high signal to noise ratio of the waveforms permitted meaningful shear velocities to be obtained by intervals in this well a correlation of changes in the vp vs ratio with depth aided in identifying some compositional changes in the well but such a correlation could not be used to distinguish fracturing in the limestone shear wave amplitudes however were effective for identifying lithologic changes as well as fractures from the sonic log shear amplitudes were lower in the shale than in the limestone and shear wave attenuation increased in fractured zones there was no strong correlation between the degree of fracturing and the attenuation of stoneley waves in general shear wave pr

a review of the bipolar see saw from synchronized and high resolution ice core water stable isotope records from greenland and east antarctica numerous ice core records are now available that cover the last glacial cycle both in greenland and in antarctica recent developments in coherent ice core chronologies now enable us to depict with a precision of a few centuries the relationship between climate records in greenland and antarctica over the millennial scale variability of the last glacial period stacks of greenland and antarctic water isotopic records nicely illustrate a seesaw pattern with the abrupt warming in greenland being concomitant with the beginning of the cooling in antarctica at the antarctic isotopic maximum aim in addition from the precise estimate of chronological error bars and additional high resolution measurements performed on the edc and taldice ice cores we show that the seesaw pattern does not explain the regional variability in antarctic records with clear two step structures occurring during the warming phase of aim 8 and 12 our antarctic high resolution data also suggest possible teleconnections between changes in low latitude atmospheric circulation and antarctic without any greenland temperature fingerprint

assessing a multilayered dynamic firn compaction model for greenland with asiras radar measurements a method to assess firn compaction using data collected with the airborne sar synthetic aperture radar interferometric radar altimeter system asiras is developed for this we develop a dynamical firn compaction model that includes meltwater retention based on the asiras data which show internal layers as annual horizons in the uppermost firn the method relies on inferring the age depth internal layers information from the radar data using a monte carlo inversion technique to tune in parallel both the firn model and the atmospheric forcing parameters temperature and accumulation the model is validated against two firn cores and it is shown that applying both firn densities and age depth information for the inversion gives the most accurate understanding of model biases the method is then applied to a 67 km section of the egig line forced by atmospheric output from a regional climate model using only age depth information in the inversion step the layers traced by the asiras data are modeled with a root mean square error of 9 cm which is within the estimated error of the layer tracing this gives us confidence in applying observed annual layering from firn radar data to assess firn compaction however the study also indicates that our firn model tuning parameters are site dependent and cannot be parameterized by temperature and accumulation alone

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

δ15n of n2 in air trapped in polar ice a tracer of gas transport in the firn and a possible constraint on ice age gas age differences with respect to gas transport the fim near the surface of an ice sheet can be divided into three zones the uppermost is a convective zone located just below the surface of the ice sheet in which the air is rapidly flushed by convective exchange with the overlying atmosphere below the convective zone there is a diffusive air column in which diffusion is rapid but there is no convection between the bottom of the diffusive air column and the bubble close off region there may be a nondiffusive zone in which diffusion is so slow that negligible gas transport occurs the diffusive air column is characterized by progressive enrichment with depth of 15n in n2 and heavy isotopes of gases in general as predicted using the barometric equation in this paper we present data on the 15n of n2 in recently trapped air samples from 12 ice cores along with numerous downcore samples from byrd vostok and dome c bubble close off depths for these cores calculated from a densification model ranged from 51 to 114 meters below the surface mbs we used these data and the barometric equation to calculate the thickness of the diffusive air column and found that it comprised 46 to 93 of the total firn thickness at our study sites paleo close off depths calculated from the densification model for glacial sections of byrd vostok and dome c are 15 25 m deeper than close off depths today diffusive column heights calculated from 15n varied in a more complex manner the diffusive column height at byrd appears to have decreased from 74 m during the last glacial period to 50 m during the holocene at vostok and dome c the diffusive column height calculated from 15n increase from about 65 m during the last glacial period to about 80 m in the holocene we use records of surface temperature and co2 at byrd and vostok along with their respective chronologies to constrain the ice age gas age difference age throughout the section of the vostok ice core corresponding to the last glacial termination in principle age values calculated from these data can be used to discriminate whether gas in the fim mixes to the bubble close off depth or to a depth equivalent to the diffusive column height in practice however uncertainties in the chronology of byrd and vostok are too great to allow us to distinguish between these two possibilities one can only say that at the time of the last termination age for vostok was between 3 and 10 5 kyr previous estimates fall within this range

densification of layered firn in the ice sheet at dome fuji antarctica in order to better understand the densification of polar firn firn cores from the three sites within 10 km of dome fuji antarctica were investigated using surrogates of density dielectric permittivities e v and e h at microwave frequencies with electrical fields in the vertical and horizontal planes respectively dielectric anisotropy e e v e h was then examined as a surrogate of the anisotropic geometry of firn we find that layered densification is explained as a result of complex effects of two phenomena that commonly occur at the three sites basically layers with initially smaller density and smaller geometrical anisotropy deform preferentially throughout the densification process due to textural effects second layers having a higher concentration of cl ions deform preferentially during a limited period from the near surface depths until smoothing out of layered cl ions by diffusion we hypothesize that cl ions dissociated from sea salts soften firn due to modulation of dislocation movement moreover firn differs markedly across the three sites in terms of strength of geometrical anisotropy mean rate of densification and density fluctuation we hypothesize that these differences are caused by textural effects resulting from differences in depositional conditions within various spatial scales

aerosol deposited in east antarctica over the last glacial cycle detailed apportionment of continental and sea salt contributions 1 the major ions sodium na calcium ca2 and chloride cl deposited in central antarctica and preserved in ice cores originate from both marine and continental sources they provide important proxy records helping to reconstruct past climatic processes however it is difficult to clearly separate the individual contributions from the two sources particularly the continental one during glacial periods on the basis of na and ca2 records at an unprecedented resolution from the european project for ice coring in antarctica epica dome c ice core back to the penultimate glacial period mean ion mass ratios were deduced for the continental and the sea salt aerosol body over east antarctica the sea salt ion mass ratios are in the range predicted for both wind induced bubble bursting of breaking waves on the open ocean and sea ice brine derived aerosols respectively thus allowing no clear decision on the contribution of sea ice to the central antarctic sea salt aerosol the continental ion mass ratios point to a substantial contribution by halide aerosols which is in agreement with the source properties in southern south america although these ratios do not rule out the continental shelf exposed during glacial stages as an additional source while during cold glacial periods continental sources accounted for more than 90 of the total ca2 input this contribution was highly variable during the remaining glacial periods covarying with the antarctic warm events during the holocene it was less than 50 but it was significantly higher during the last interglacial period the sea salt aerosol contribution to the total na input which was mostly dominant and higher than 90 was reduced to only two thirds during the last two glacial maxima and the period around 60 ka thus the glacial continental na contribution appears to be more important than previously assumed implying that na records not corrected for continental na do not represent a pure marine signal at the east antarctic plateau during glacial times

evidence of dynamic recrystallization in polar firn 1 microstructural analyses have been performed on polar firn from the european project for ice coring in antarctica drilling site in dronning maud land antarctica the results derived from images of the firn structure in microscopic resolution indicate that dynamic recrystallization is active in firn at all depths and it dominates the evolution of the microstructure when the firn density exceeds a critical value of 730 kg m3 overburden snow load 0 2 mpa at the firn ice transition density 820 kg m3 the microstructure is characterized by many small grains and bulged or irregularly shaped grain boundaries more than half of all grains show subgrain boundaries thus strain induced boundary migration is an essential feature to describe the irregular grain structure in agreement with previous studies significant grain growth has been observed with depth for the largest grains in the samples however our microscopic analysis reveals that the grain growth with depth in fact vanishes if all grains larger than 65 m in diameter are taken into account this result reflects the fact that the growth of the largest grains is counteracted by grain size reduction by shrinking and subdivision of old grains as well as production of new grains consequently previous conclusions that grain growth in polar firn is essentially analogous to normal grain growth in metallic and ceramic sinters and that the stored strain energy is small in comparison with grain boundary energy can no longer be supported additionally our observations show that the incipience of dynamic recrystallization in polar ice sheets is not as sensitive to temperature as supposed so far a discussion of the change of the mean grain size due to the measuring technique is imperative

thermophysical properties of the earth s crust in situ measurements from continental and ocean drilling knowledge of the variation of thermal conductivity and heat production with depth is critical to understanding the thermal state of the crust continental and oceanic drill holes provide unique opportunities for the calibration of empirical and theoretical models relating crustal thermal properties to physical and chemical properties these calibrations are based on more than 30 000 well log measurements of acoustic velocity both compressional and shear density porosity radioelement concentrations k u th and major element chemistry al si ca fe s mg na in formations ranging in age from 5 to 620 ma and in composition from granitic to gabbroic the mineralogical data available from induced gamma ray spectroscopy logs when combined with known mineral thermal conductivities in a model for the thermal conductivity of a crystalline aggregate enable the in situ application of a laboratory estimation technique and yield continuous conductivity profiles however mineralogy based conductivity models cannot account for the anisotropic conductivity observed in foliated metamorphic rocks a phonon conduction model which utilizes acoustic velocity and bulk density measurements is accurate within 15 in both isotropic and anisotropic formations of the upper continental crust and in oceanic crustal layers 2c and 3 in oceanic crustal layers 2a and 2b however the effects of fracturing on compressional and shear velocities lead to inaccurate results the heat flow heat production relationship which provides one method of determining subsurface heat production has well documented limitations allis 1979 and rybach and buntebarth 1982 1984 on the basis of laboratory measurements have proposed quantitative relationships between heat production and rock compositional and physical properties the well log k u and th data indicate that heat production can be predicted from compositional data within a factor of 2 or 3 predictions of heat production from acoustic velocity and bulk density measurements are only accurate to within an order of magnitude three factors account for these results 1 the natural variability of velocity and density for a given rock composition 2 the tendency of u and th to associate with secondary rather than primary minerals and 3 u and th redistribution through fluid flow and metamorphism thus seismic velocity based heat production profiles can at best be taken as first order estimates which may misrepresent the complexity of the continental crust however the correlation of formations of known heat production with subsurface structures when combined with a suite of existing techniques for estimating heat production may lead to more accurate results

acoustic modes of propagation in the borehole and their relationship to rock properties acoustic waveform measurements in boreholes have important applications in fracture hydrology and radioactive waste disposal but ambiguities in existing interpretation techniques remain a problem we have addressed the problem by using residue theory to predict the relative excitation of various modes contained in experimental waveforms a plane geometry model involving a layer of fluid between two elastic half spaces is shown to provide velocity dispersion curves for propagating modes that are very similar to those for the fluid filled borehole we use the plane geometry model to illustrate the effects of the confined borehole fluid on surface and body waves traveling along the borehole in the elastic solid we also computed excitation functions for some of the lowest order symmetric modes calculated the time domain response of the trapped modes following the shear head waves and compared them to waveforms recorded in boreholes through several homogeneous formations the insight into the mode composit

core scale radioscopic imaging a new method reveals density calcium link in antarctic firn abstract a new radioscopic imaging technique has been developed to measure firn density in unprecedented resolution and accuracy even when the porosity is low or the geometry of a core or piece of core is not perfect the technique is based on an x ray microfocus computer tomograph ice ct designed especially for ice core applications applied on an archive piece of the antarctic firn core b32 drilled in dronning maud land in 1998 the obtained density profile shows a strong correlation with the calcium ion concentration as found previously in greenland given the impurity density relationship found previously in greenland our result suggests both improved accuracy of the new density measurements and an impurity density relationship with a similar magnitude in greenland to that on the antarctic plateau our measurements provide first evidence that the impurity density relationship is a universal feature of polar firn and that the calcium ion concentration can serve as a proxy to describe quantitatively the effect of the impurities on densification

unveiling the anatomy of termination 3 using water and air isotopes in the dome c ice core east antarctica abstract each glacial interglacial transition of the quaternary occurs in a different orbital context leading to various timing for the deglaciation and sequence of high vs low latitudes events termination 3 250 kyears before present ka is an unusual deglaciation in the context of the last 9 deglaciations recorded in the old epica dome c edc antarctic ice core it exhibits a three phase sequence two warming phases separated by a small cooling the last phase suggesting a particularly rapid temperature increase we present here new high resolution 15n and deuterium excess d excess data from the edc ice core to provide a detailed temperature change estimate during this termination then we combined the d and 18o to discuss the relationship between high and low latitude changes through the d excess we also provide the high vs low latitude sequence of events over this deglaciation without chronological uncertainty using low latitude ice core proxies in agreement with previous studies based on speleothem analyses we show that the first phase of termination 3 256 249 ka is associated with small heinrich like events linked to changes in itcz position monsoon activity and teleconnections with antarctica in a context of minimum northern hemisphere insolation this leads to a rather strong antarctic warming as observed in the 15n record in contrast to the relatively small d increase the second warming phase occurs during the rise of the northern hemisphere insolation with a large heinrich like event leading to the characteristic antarctic warming observed in the 15n and d increase as for the more recent terminations

natural and human induced landsliding in the garhwal himalaya of northern india after the march 28 1999 garhwal earthquake 338 active landslides including 56 earthquake induced landslides were mapped in a 226 km 2 study area in the garhwal himalaya northern india these landslides mainly comprised shallow failures in regolith and highly weathered bedrock involving avalanches slides and flows the total volume of active 33 landslide debris in the region was estimated to be 1 3 million m including 0 02 million m 2 of the total volume moved during and within a few days of the earthquake the denudation produced by the active landsliding within the study area is equivalent to a maximum landscape lowering of 5 7 mm if active landsliding persists for a duration of between 1 and 10 years then denudation due to landsliding is in the order of 0 6 6 mm a y1 approximately two thirds of the landslides in this region were initiated or accelerated by human activity mostly by the removal of slope toes at road cuts suggesting that human activity is accelerating denudation in this region three ancient catastrophic landslides each involving 1 million m 3 of debris were identified and two were dated to the early middle holocene using cosmogenic radionuclide 10 be and 26 al cosmogenic radionuclide 10 be and 26 al were also used to date strath terraces along the alaknanda river in lower garhwal himalaya to provide an estimate of 4m m a y1 for the rate of regional denudation throughout the holocene natural landsliding therefore contributes 5 50 of the overall denudation in this region and is important as a formative process in shaping the landscape q 2001 elsevier science b v all rights reserved

an empirical relation between overburden pressure and firn density two empirical equations for firn densification have been obtained considering firn porosity as a function of overburden pressure in the first equation thereduction ratio of porosity in firn is assumed to be proportional to the increasing ratioof overburden pressure and the mth power of the porosity the porosity exponent m should be close to 2 so as to have a best fit with 14 depth density profiles fromgreenland and antarctica in the second equation the reduction ratio of porosity wasassumed to increase proportionally to the increment of overburden pressure and thenth power of the porosity the most satisfactory values of the exponent range from 1 to 1 it has been suggested that firn density determined primarily by overburdenpressure and firn temperature contribute to a lesser degree

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

metamorphism of stratified firn at dome fuji antarctica a mechanism for local insolation modulation of gas transport conditions during bubble close off 1 the evolution of the structure of a 112 59 m long firn core recovered at dome fuji east antarctica was investigated in order to improve understanding of firn densification and bubble formation processes which are important for interpreting local insolation proxies used for astronomical dating of deep ice cores using selected samples we measured physical properties including 1 the relative dielectric permittivities in both the vertical and horizontal planes 2 the bulk density at a resolution of millimeters 3 the three dimensional geometric structure of pore space and 4 crystal orientation fabrics we found that the firn at dome fuji contains horizontal strata with thicknesses of several centimeters near the surface of the ice sheet these strata are characterized by contrasting bulk density earlier field studies suggest that summer insolation causes densification of surface firn down to 30 m density maxima exhibited a clear positive correlation with the strength of structural anisotropy and c axis clustering around the vertical in contrast the correlation is negative in deeper firn confirming previous findings that initially less dense firn became denser than initially dense firn in addition numerous examples of textures indicating that deformation preferentially occurred in weaker layers were found moreover the initially dense firn layers were more permeable for air near the bottom of firn we propose a model linking firn properties with conditions for the gas transport processes near the bottom of firn the model explains how stronger insolation can lead to bulk ice with a lower o2 n2 ratio and smaller total gas content

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

accumulation rates in dronning maud land antarctica as revealed by dielectric profiling measurements of shallow firn cores the european programme for ice coring in antarctica includes a comprehensive pre site survey on the inland ice plateau of dronning maud land antarctica the german glaciological programme during the 1997 98 field season was carried out along a 1200 km traverse on amundsenisen and involved sampling the snow cover in pits and by shallow firn cores this paper focuses on the accumulation studies the cores were dated by dielectric profiling and continuous flow analysis distinct volcanogenic peaks and seasonal signals in the profiles served to establish a depth time scale the eruptions of krakatoa tambora an unknown volcano kuwae and el chichon are well documented in the ice variations of the accumulation rates over different times were inferred from the depth time scales a composite record of accumulation rates for the last 200 years was produced by stacking 12 annually resolved records according to this accumulation rates decreased in the 19th century and increased in the 20th century the recent values are by no means extraordinary as they do not exceed the values at the beginning of the 19th century variations in accumulation rates are most probably linked to temperature variations indicated in 18o records from amundsenisen

location of cation impurities in ngrip deep ice revealed by cryo cell uv laser ablation icpms in polar ice sheets the average grain size varies with depth ice grain size increases due to several factors including ice temperature and impurity content which in turn varies with climate the effect of impurities on grain growth is thought to be crucial but has never been observed experimentally using a methodology recently developed at royal holloway university of london in situ chemical analysis of frozen ice at sub ppm concentrations with unprecedented spatial resolution 150 m is achievable using ultraviolet laser ablation inductively coupled plasma mass spectrometry uv la icpms featuring a two volume cryo la cell following surface cleaning with a custom built vice equipped with a ceramic blade ngrip ice slabs 86 ka before ad 2000 have been analysed using a series of one dimensional profiles and two dimensional maps of laser spots at a resolution of 200 300 m results demonstrate that cation impurities are not uniformly distributed in ice layers and show significant variations in concentration on a sub millimetre scale furthermore a different pattern of elemental distribution between clear ice and layers enriched in impurities cloudy bands has been identified while concentration differences for cloudy bands are not resolvable between boundaries and inner grain domains within clear ice grain boundaries and junctions are significantly up to 100 times impurity enriched relative to corresponding grain interiors

sulphate record from a northeast greenland ice core over the last 1200 years based on continuous flow analysis a 150 m deep ice core from the low accumulation area of northeast greenland was analyzed for sulphate calcium sodium and electrolytical meltwater conductivity at a depth resolution of approximately 1 cm by continuous flow analysis cfa the calcium and sodium profiles are used to establish a relatively precise ice core chronology by annual layer counting back to ad 830 inspection of the novel cfa method for sulphate revealed relative errors typically around 15 but at least 20 ng g 1 for concentrations 5130 ng g 1 and a current detection limit for routine ice core analyses of 40 ng g 1 annual sulphate peaks are shown to occur over almost the entire core with only a small shift in seasonality between the modern and pre industrial sections inspection of volcanic horizons allowed more accurate timing of these peaks and clear identification of calcium rich events disregarding clear volcanic peaks significant long term changes of sulphate are only seen over the industrial period however a higher frequency of important volcanic inputs was identified around ad 1200

visual stratigraphy of the north greenland ice core project northgrip ice core during the last glacial period 1 a continuous high resolution record of digital images has been obtained from the north greenland ice core project northgrip ice core 75 1 n 42 3 w in the depth interval from 1330 m to the bedrock at 3085 m the ice core stratigraphy is clearly visible throughout the glacial period with the most frequent and brightest visible layers appearing during the coldest events down to a depth of 2600 m the horizontal layering is very regular below this depth small irregularities in the layering start to appear and below 2800 m the visual stratigraphy becomes more uncertain perhaps because of penetration into climatically warmer ice comparison of the visual stratigraphy with high resolution continuous records of chemical impurities and dust reveals a high degree of correlation which indicates that the visible layers are caused by these impurities a new approach is used to automatically determine annual layer thicknesses from the visual stratigraphy record by carrying out a frequency analysis of the most prominent visible layers in the profile the result gives strong support for the northgrip timescale model

microstructure dependent densification of polar firn derived from x ray microtomography the densification of dry polar snow and firn results in a continuous increase of density with depth accompanied by significant density fluctuations within seasonal layers density measurements of high spatial resolution reveal a persistent minimum of density fluctuations in the vicinity of the snow firn transition 0 55 0 65 g cm 3 in firn core records in this study we give an explanation for the fluctuation minimum by applying a new method of x ray microtomography to obtain three dimensional 3 d structural data of a greenland firn core at 13 different depths between 10 and 78 m a set of 16 samples of 40 cm total length for each depth interval was measured a reconstructed firn segment of 40 cm covers 1 2 years of snow accumulation using digital image analysis techniques different structural parameters are estimated including 3 d pore and particle sizes and specific surface areas it is shown that the densification rates of snow and firn layers consisting of coarse particles are much higher than those consisting of fine particles within the same depth interval this causes a density crossing of fine and coarse grained layers with a minimum of density variations at the crossover point this crossing over implies that formerly dense layers in the seasonal density signal are not of the same origin as dense layers in the deeper part of the firn column and that the seasonal density signal will totally change shape with depth it is speculated that in coarse and fine grained firn the dominant mechanism of densification acts over different regimes of density

observing and modeling the influence of layering on bubble trapping in polar firn interpretation of ice core trace gas records depends on an accurate understanding of the processes that smooth the atmospheric signal in the firn much work has been done to understand the processes affecting air transport in the open pores of the firn but a paucity of data from air trapped in bubbles in the firn ice transition region has limited the ability to constrain the effect of bubble closure processes here we present high resolution measurements of firn density methane concentrations nitrogen isotopes and total air content that show layering in the firn ice transition region at the west antarctic ice sheet wais divide ice core site using the notion that bubble trapping is a stochastic process we derive a new parameterization for closed porosity that incorporates the effects of layering in a steady state firn modeling approach we include the process of bubble trapping into an open porosity firn air transport model and obtain a good fit to the firn core data we find that layering broadens the depth range over which bubbles are trapped widens the modeled gas age distribution of air in closed bubbles reduces the mean gas age of air in closed bubbles and introduces stratigraphic irregularities in the gas age scale that have a peak to peak variability of 10 years at wais divide for a more complete understanding of gas occlusion and its impact on ice core records we suggest that this experiment be repeated at sites climatically different from wais divide for example on the east antarctic plateau

densification of layered firn of the ice sheet at neem greenland densification of firn at the north greenland eemian ice drilling neem camp is investigated using density surrogates dielectric permittivities v and h at microwave frequencies with electrical fields in the vertical and horizontal planes respectively dielectric anisotropy v h is then examined as a surrogate for the anisotropic geometry of firn its size fluctuations and mutual correlations are investigated in samples taken at depths from the surface to 90m the initial of 0 06appears within the uppermost 0 2 m after that decreases rapidly until 21 26 m depth below this decreases slowly layers with more ions of fluorine chlorine and some cations deposited between the autumn and the subsequent summer deform preferentially during all these stages this layered deformation is explained partly by the textural effects initially formed by the seasonal variation of metamorphism and partly by ions such as fluorine chlorine and ammonium which are known to modulate dislocation movement in the ice crystal lattice insolation sensitive microstructure appears to be preserved all the way to the pore close off within layers of the summer to autumn metamorphism like previous authors we hypothesize that calcium is not the active agent in the reported deformation calcium correlations

firn air δ15n in modern polar sites and glacial interglacial ice a model data mismatch during glacial periods in antarctica the phase lag between atmospheric composition air bubbles and temperature water isotopes can be quantified from ice cores provided that the age difference between entrapped air and the surrounding air can be correctly estimated this difference depends on the lock in depth lid when air no longer mixes with the atmosphere the lid can be estimated from firnification models or from the air isotopic composition 15n and 40ar both methods give consistent results for greenland and one coastal site in antarctica byrd new firn measurements in greenland northgrip and antarctica berkner island bas depot dome c confirm that firnification models correctly reproduce the present lid over a large range of surface conditions however a systematic mismatch is observed for the last glacial maximum lgm in east antarctic sites vostok dome c dome f questioning the model s validity here we use new 15n measurements from two coastal antarctic sites kohnen station and law dome providing depth estimates again distinct from firnification model calculations we show that this discrepancy can be resolved by revising the estimate of past accumulation rates 15n measurements can therefore help to constrain past accumulation rate and improve ice core dating

evidence for molecular size dependent gas fractionation in firn air derived from noble gases oxygen and nitrogen measurements we present elemental and isotopic measurements of noble gases he ne ar kr and xe oxygen and nitrogen of firn air from two sites the first set of samples was taken in 1998 at the summit of the devon ice cap in the eastern part of devon island the second set was taken in 2001 at ngrip location north greenland he and ne are heavily enriched relative to ar with respect to the atmosphere in the air near the close off depth at around 50 70 m the enrichment increases with depth and reaches the maximum value in the deepest samples just above the zone of impermeable ice where no free air could be extracted anymore similarly elemental ratios of o2 n2 o 2 ar and ar n2 are increasing with depth in contrast but in line with expectations isotopic ratios of 15 n 14 n 18 o 16 o and 36 ar 40 ar show no significant enrichment near the close off depth the observed isotopic ratios in the firn air column can be explained within the uncertainty ranges by the well known processes of gravitational enrichment and thermal diffusion to explain the elemental ratios however an additional fractionation process during bubble inclusion has to be considered we implemented this additional process into our firn air model the fractionation factors were found by fitting model profiles to the data we found a very similar close off fractionation behavior for the different molecules at both sites for smaller gas species mainly he and ne the fractionation factors are linearly correlated to the molecule size whereas for diameters greater than about 3 6 a the fractionation seems to be significantly smaller or even negligible an explanation for this size dependent fractionation process could be gas diffusion through the ice lattice

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

layering of surface snow and firn at kohnen station antarctica noise or seasonal signal the density of firn is an important property for monitoring and modeling the ice sheet as well as to model the pore close off and thus to interpret ice core based greenhouse gas records one feature which is still in debate is the potential existence of an annual cycle of firn density in low accumulation regions several studies describe or assume seasonally successive density layers horizontally evenly distributed as seen in radar data on the other hand high resolution density measurements on firn cores in antarctica and greenland showed no clear seasonal cycle in the top few meters a major caveat of most existing snow pit and firn core based studies is that they represent one vertical profile from a laterally heterogeneous density field to overcome this we created an extensive dataset of horizontal and vertical density data at kohnen station dronning maud land on the east antarctic plateau we drilled and analyzed three 90 m long firn cores as well as 160 one meter long vertical profiles from two elongated snow trenches to obtain a two dimensional view of the density variations the analysis of the 45 m wide and 1 m deep density fields reveals a seasonal cycle in density however the seasonality is overprinted by strong stratigraphic noise making it invisible when analyzing single firn cores our density dataset extends the view from the local ice core perspective to a hundred meter scale and thus supports linking spatially integrating methods such as radar and seismic studies to ice and firn cores

modeling the densification of polar firn including heat diffusion application to close off characteristics and gas isotopic fractionation for antarctica and greenland sites 1 modeling the densification of polar firn is essential to estimate variations of close off characteristics density close off depth delta age in relation with past climate parameters temperature and accumulation rates furthermore the air composition in the firn is modified by gravitational and thermal fractionation and stable isotope measurements of permanent gases like nitrogen or argon can provide information on the amplitude of these fractionations in this work we propose a new model coupling firn densification and heat diffusion in addition to the determination of the firn thickness and gas ice age differences the model allows a reconstruction of the time evolution of the temperature for different sites in antarctica vostok and greenland gisp2 and therefore the evolution of gravitational and thermal isotopic fractionations in firn under present day conditions the modeled profiles are in good agreement with the available temperature measurements in firn for sites with low accumulation rates such as vostok the results show the existence of temperature gradients in the firn column even when no rapid climatic changes occur the comparison of the modeled 15n results to measurements allows to better constrain the 18o temperature relationship used to infer the surface temperature history and for gisp2 the model validates the long term borehole based temperature

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

seasonal and interannual variations of firn densification and ice sheet surface elevation at the greenland summit seasonal and interannual variations in surface elevation at the greenland summit are modeled using a new temperature dependent formulation of firn densification and are compared with elevations from european remote sensing satellite ers 1 2 radar altimetry the rate constant and activation energy usually set as constants in the arrhenius type relation are strongly temperature dependent based on measurements of crystal growth rates a multiplicative factor in the densification rate accounts for differences between densification and grain growth rates and is chosen to match the modeled and measured density profiles from 0 to 40 m the stronger temperature dependence produces a significant seasonal cycle in the densification rate in the upper firn much of the densification and consequent surface lowering occur within 3 months in late spring early summer followed by a build up from accumulation modeled elevation changes using automatic weather station measurements of temperature and accumulation and modeled precipitation agree well with observations the respective seasonal amplitudes are 18 and 25 cm peak to peak with minima in mid summer the minimum elevation in 1995 is driven mainly by a temporary accumulation decrease and secondarily by warmer temperatures increased compaction driven by a summer warming trend decreases the modeled elevation 1992 99 by 20 cm but accumulation increases in latter years dominate the overall 4 2 cm a 1 trend

lacustrine chronology links late pleistocene climate change and mass movements in northern new mexico well dated lacustrine deposits in northern white rock canyon new mexico record damming of the rio grande by at least four separate failures of a slump complex between about 17 5 and 12 4 ka sup 14 c linking mass movements to a period of rapid climate change in the western united states failure of metastable slumps probably resulted from removal of lateral support during down cutting and erosion by the rio grande and from a decrease in resisting forces due to increased pore pressures our chronology suggests that the lake that formed between 17 5 and 15 0 ka may record effects of both glacial melt and pluvial activity mainly enhanced rainfall the youngest lake neary 12 4 ka may record pluvial runoff and the intermediate lakes 13 7 to 13 1 ka may record pluvial and minor melt water activity we have not found lacustrine deposits younger than about 12 4 ka the record of geomorphic response along the rio grande suggests that late pleistocene climatic changes may have triggered similar mass movements elsewhere in the southwest 27 refs 4 figs

greenland temperature response to climate forcing during the last deglaciation greenland ice core water isotopic composition 18 o provides detailed evidence for abrupt climate changes but is by itself insufficient for quantitative reconstruction of past temperatures and their spatial patterns we investigate greenland temperature evolution during the last deglaciation using independent reconstructions from three ice cores and simulations with a coupled ocean atmosphere climate model contrary to the traditional 18 o interpretation the younger dryas period was 4 5 2 c warmer than the oldest dryas due to increased carbon dioxide forcing and summer insolation the magnitude of abrupt temperature changes is larger in central greenland 9 to 14 c than in the northwest 5 to 9 c fingerprinting a north atlantic origin simulated changes in temperature seasonality closely track changes in the atlantic overturning strength and support the hypothesis that abrupt climate change is mostly a winter phenomenon

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

temporal patterns of arid humid transitions in the south eastern arabian peninsula based on optical dating abstract the rub al khali aeolian system of the arabian peninsula is the world s largest erg while the region is presently hyper arid evidence for multiple past humid periods has been documented in previous studies radiocarbon dating of lacustrine travertine and palaeogroundwater deposits suggests that the climate was humid at 10 6 and 35 25 ka these phases have been associated with summer rainfall increases occurring in tandem with an intensification and northward migration of the monsoon system during northern hemisphere precessional maxima published optical dating studies have focused on preserved sand dune and aeolianite deposits to establish ages for the intervening arid phases here we present a summary of this work and additional optical dating results for samples of aeolian sediment from a deep drill core which provides insights into the style of barchan dune accretion in the liwa region of the united arab emirates the large dune accreted rapidly during the mid late holocene the results suggest that the transitions from humid to arid conditions and resulting accumulation of aeolian sediment in the form of large bedforms occurred abruptly at around 6 ka further aeolian sedimentation has not been constant since that time with initial gradual dune growth followed by rapid vertical accretion and possible termination of accumulation around c 2 ka

on the impact of impurities on the densification of polar firn abstract understanding polar firn densification is crucial for reconstructing the age of greenhouse gas concentrations extracted from ice cores and for the interpretation of air in ice as a dating tool or as a climate proxy firn densification is generally modeled as a steady burial and sintering process of defined layers where the structure of the layering is maintained along the whole firn and ice column however available high resolution density data as well as firn air samples question this picture and point to a lack of understanding of firn densification based on analysis of high resolution density and calcium concentration records from antarctic and greenland ice cores we show for the first time that also impurities may have a significant impact on the densification analysis of firn cores shows a correlation between density and the calcium ion ca concentration and this correlation increases with depth the existence of this relationship is independent of the local climatic conditions at the core sites analyzed the strong positive correlation between the density and the logarithm of ca concentration indicates that impurities induce softening and lead to faster densification over a wide range of concentrations in one core the impurity effect manifests itself so strongly that the density develops a seasonal cycle closely following the seasonal cycle of ca our results clearly show that the structure of the firn layering changes with depth and suggest that the increased variability in density observed in deep firn recently described as a universal feature of polar firn may arise from the influence of ca and or other impurities the impurity effect is likely to have direct implications on our understanding of glacial firn densification and on glacial gas age estimates

p wave attenuation measurements from laboratory resonance and sonic waveform data we computed compressional wave velocity vp and attenuation 1 qp from sonic log waveforms recorded in a cored 30 m thick dolostone reservoir using cores from the same reservoir laboratory measurements of vp and qp were also obtained we used a resonant bar technique to measure extensional and shear wave velocities and attenuations in the laboratory so that the same frequency range as used in sonic logging 5 25 khz was studied having the same frequency range avoids frequency dependent differences between the laboratory and in situ measurements compressional wave attenuations at 0 mpa confining pressure calculated on 30 samples gave average qp values of 17 experimental and geometrical errors were estimated to be about 5 percent measurements at elevated effective pressures up to 30 mpa on selected dolostone samples in a homogeneous interval showed mean qp and qs to be approximately equal and consistently greater than 125 at effective stress of 20 mpa and at room temperature the mean qp over

northern hemisphere forcing of climatic cycles in antarctica over the past 360 000 years the milankovitch theory of climate change proposes that glacial interglacial cycles are driven by changes in summer insolation at high northern latitudes the timing of climate change in the southern hemisphere at glacial interglacial transitions which are known as terminations relative to variations in summer insolation in the northern hemisphere is an important test of this hypothesis so far it has only been possible to apply this test to the most recent termination because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined here we present a new chronology of antarctic climate change over the past 360 000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the dome fuji and vostok ice cores this ratio is a proxy for local summer insolation5 and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter the accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation our results indicate that orbital scale antarctic climate change lags northern hemisphere insolation by a few millennia and that the increases in antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of northern hemisphere summer insolation these results support the milankovitch theory that northern hemisphere summer insolation triggered the last four deglaciations

glacial interglacial changes in mineral dust and sea salt records in polar ice cores sources transport and deposition 1 sea salt and mineral dust records as represented by na and ca2 concentrations respectively in greenland and antarctic ice cores show pronounced glacial interglacial variations for the last glacial maximum lgm mineral dust sea salt concentrations in greenland show an increase of a factor of approximately 80 15 compared to the holocene and significant shifts by a factor of 15 5 during dansgaard oeschger events in antarctica the dust sea salt flux is enhanced by a factor of 15 3 during the lgm compared to the holocene and variations by approximately a factor of 8 1 2 exist in parallel to antarctic warm events primary glacial dust sources are the asian deserts for greenland and patagonia for antarctica ice core evidence and model results show that both changes in source strength as well as atmospheric transport and lifetime contributed to the observed changes in greenland ice cores in antarctica changes in ice core fluxes are in large parts related to source variations both for sea salt and dust where the formation of sea salt aerosol from sea ice may play a pivotal role summarizing our latest estimates on changes in sources transport and deposition these processes are roughly able to explain the glacial increase in sea salt in both polar regions while they fall short by at least a factor of 4 7 for mineral dust future improvements in model resolution and in the formulation of source and transport processes together with new ice core records e g on dust size distributions will eventually allow convergence of models and observations

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

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

glacio chemical study spanning the past 2 kyr on three ice cores from dronning maud land antarctica 2 seasonally resolved chemical records the ammonium calcium and sodium concentrations from three intermediate depth ice cores drilled in the area of dronning maud land east antarctica have been investigated since all measurements were performed by a high resolution continuous flow analysis system for the first time seasonal signals of chemical trace species could be obtained from the interior of central antarctica over a period of approximately 2 millennia although the elevation as well as the accumulation rate differ between the drilling sites similar values were obtained by comparing mean concentrations spanning the last 900 years however a distinct lack of intersite correlation was found on decadal timescales despite a noticeable accumulation change apparent in one core no significant concentration change of all three species has occurred all the measured ions show clear seasonal signals over the whole records while the sea salt related component sodium peaks simultaneously with calcium the maximum ammonium concentration occurs in the snow with a time lag of 2 months after the sea salt peak more than 60 of the calcium concentration can be attributed to an ocean source elevated sodium concentrations were found within this millennium compared to mean values of the whole records but the spatially varying shape of the increase suggests that a possible climatic signal is biased by local deposition effects

high resolution variations in size number and arrangement of air bubbles in the epica dml antarctica ice core abstract we investigated the large scale 10 1000m and small scale mm cm variations in size number and arrangement of air bubbles in the epica dronning maud land edml antarctica ice core down to the end of the bubble hydrate transition bht zone on the large scale the bubble number density shows a general correlation with the palaeo temperature proxy d18o and the dust concentration which means that in holocene ice there are fewer bubbles than in glacial ice small scale variations in bubble number and size were identified and compared above the bht zone there exists a strong anticorrelation between bubble number density and mean bubble size in glacial ice layers of high number density and small bubble size are linked with layers with high impurity content identified as cloudy bands therefore we regard impurities as a controlling factor for the formation and distribution of bubbles in glacial ice the anticorrelation inverts in the middle of the bht zone in the lower part of the bht zone bubble free layers exist that are also associated with cloudy bands the high contrast in bubble number density in glacial ice induced by the impurities indicates a much more pronounced layering in glacial firn than in modern firn

atmospheric decadal variability from high resolution dome c ice core records of aerosol constituents beyond the last interglacial along the epica dome c ice core we measured concentrations of different water soluble aerosol constituents and deduced total depositional flux records here we present high resolution sodium calcium ammonium and nitrate data covering the last 173 000 years the first three of these species are passive tracers and reveal source and long range transport changes whereas nitrate is deposited reversibly however it can be used to check isotope derived accumulation rate estimates a prerequisite to calculate total depositional fluxes during the last two transitions from glacial to interglacial periods changes in the total depositional flux differ strongly for different aerosol species the largest changes are observed in the terrestrial aerosol proxy non sea salt calcium only moderate changes occur in the marine sea salt indicator sodium while ammonium a proxy for marine bioproductivity remains rather constant in agreement with previous studies we find that only considerable glacial interglacial changes at both the terrestrial and the marine sea salt aerosol source can explain the observed pronounced changes the unprecedented high resolution of our data allows for the first time the examination of decadal variability back to the penultimate glacial period on the one hand we find occasional fast shifts occurring within a few years here we present such an event in the calcium record from the penultimate glacial period on the other hand we examine variation coefficients and pairwise correlation coefficients both determined in 200 year windows they generally reveal only moderate changes during glacial periods slightly lower variation coefficients are found concurrent with slightly higher correlation coefficients which points to a more uniform and stronger coupled atmospheric long range transport of the different aerosol species to the east antarctic plateau and less influence of cyclonic activities during cold periods the opposite is observed for interglacial periods with probably even reinforced importance of cyclonic influences during the last interglacial period the marine isotope stage 5 5 this period reveals no evidence for abrupt climatic changes in any of the species however the marine sea salt aerosol indicator sodium shows a distinct minimum followed by a pronounced increase this pattern is explained by significantly reduced sea ice production in the indian southern ocean sector which is believed to be the dominant source of sodium deposited in dome c during warm periods

late quaternary intensified monsoon phases control landscape evolution in the northwest himalaya the intensity of the asian summer monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes terrestrial environments and marine sedi ment records however the mechanisms of long lived 2 5 k y intensified monsoon phases the related changes in precipitation distribution and their effect on landscape evolution and sedimen tation rates are not yet well understood the arid high elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal i e strength ened monsoon seasons analogous to present day rainfall anom alies enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure we as sociate landslide triggering during intensified monsoon phases with enhanced precipitation discharge and sediment flux leading to an increase in pore water pressure lateral scouring of rivers and ov ersteepening of hillslopes eventually resulting in failure of slopes and exceptionally large mass movements here we use lacustrine deposits related to spatially and temporally clustered large land slides 0 5 km 3 in the sutlej valley region of the northwest him alaya to calculate sedimentation rates and to infer rainfall patterns during late pleistocene 29 24 ka and holocene 10 4 ka inten sified monsoon phases compared to present day sediment flux measurements a fivefold increase in sediment transport rates re corded by sediments in landslide dammed lakes characterized these episodes of high climatic variability these changes thus em phasize the pronounced imprint of millennial scale climate change on surface processes and landscape evolution

water isotope diffusion in the wais divide ice core during the holocene and last glacial we use a high resolution water isotope record from the west antarctic ice sheet divide ice core wdc to evaluate the effects of water isotope diffusion for the last 29 ka b p using spectral analysis of the data we determine diffusion lengths in depth and time domains the diffusion length quantifies the mean cumulative diffusive displacement of water molecules relative to their original location at time of deposition we simulate the observed signal with models and find that our understanding of processes and conditions in the ice sheet is incomplete with the effects of ice deformational thinning removed portions of the holocene record show total diffusion lengths smaller than predicted for a lower limit case of diffusion through a single ice crystal such reduced diffusion is probably due to structural features such as crusts and tortuous porosity that inhibit vapor transport in the firn in the late glacial portion of the record diffusion lengths double between 19 5 and 17 ka b p known dependencies of diffusion on climatic variables do not account for this enhancement in models and we hypothesize that it could arise from thermal gradients in the firn column impurity driven enhancement of solid ice diffusion or changes in firn grain properties that alter vapor access to open pores despite model uncertainties the wdc diffusion length chronology will be an essential input to future studies of high frequency variability in the water isotope climate record as it allows for the effects of diffusion to be removed

impurity controlled densification a new model for stratified polar firn a new densification model which simulates the effect of impurities on the densification of polar firn is presented the classical densification models of herron and langway 1980 and pimienta and barnola barnola and others 1991 are modified by assuming that the activation energy for deformation is reduced by the impurities motivated by recent observations the impurity effect is formulated on an empirical basis using the seasonally varying ca2 ion concentration excellent agreement between simulated and measured high resolution density profiles confirms the new approach the same parameterization applies for greenland and antarctica despite the one order of magnitude difference in impurity concentration the new models allow us for the first time to simulate the density layering in firn down to the firn ice transition our results emphasize the importance of impurities and density layering for the air entrapment and for dating gas records of deep ice cores in particular for glacial climate conditions where the impurity concentrations are 10 100 fold higher than in modern firn

reconstruction of late quaternary monsoon oscillations based on clay mineral proxies using sediment cores from the western margin of india abstract in order to reconstruct the variations in the intensity of summer monsoon precipitation during the late quaternary two sediment cores from the southwestern continental margin of india were studied for their clay mineral composition and grain size parameters kaolinite illite and gibbsite were dominant in a core off cochin illite with increasing kaolinite content towards the core top was found to dominate in a core from the continental slope off goa major sources of clays at both the core sites were from the hinterland rocks and soils careful evaluations of several factors that could complicate the clay distribution in marine environment indicate that the clay mineral parameters can be used as proxies for the intensity of summer monsoon precipitation in the past the relatively low values of humidity proxies kaolinite content k c and k i ratios and higher illite crystallinity with significant variations indicate that the summer monsoons in general were weaker during the late glaciation with distinct events of intensification at 28 000 and 22 000 yr bp the last deglaciation was characterised by an increased terrigenous input with high values of humidity proxies during 15 700 14 800 cal yr bp indicating an early strengthening of summer monsoon activity in the region the most remarkable increase in kaolinite content k c and k i ratios associated with much reduced values of chlorite and illite and illite crystallinity however occur between 8800 and 6400 cal yr bp it appears that the holocene precipitation maxima occurred after 9000 cal yr bp and lagged behind the precessional forcing the late holocene witnessed reduced rainfall activity and resultant decrease in hydrolysis starting at 5600 cal yr bp