reassessment of net surface mass balance in antarctica abstract recent in situ measurements of surface mass balance and improved calculation techniques are used to produce an updated assessment of net surface mass balance over antarctica a new elevation model of antarctica derived from ers 1 satellite altimetry supplemented with conventional data was used to delineate the ice flow drainage basins across antarctica the areas of these basins were calculated using the recent digital descriptions of coastlines and grounding lines the delineation of drainage basins was achieved using an automatic procedure which gave similar results to earlier hand drawn catchment basins more than 1800 published and unpublished in situ measurements of net surface mass balance from antarctica were collated and then interpolated a net surface mass balance map was derived from passive microwave satellite data being employed as a forcing field to control the interpolation of the sparse in situ observations basinwide integrals of net surface mass balance were calculated using t

evidence for winter spring denitrification of the stratosphere in the nitrate record of antarctic firn cores a firn core from within the polar vortex in the weddell sea sector of antarctica shows nitrate peaks that occur in the spring or early summer they are far less prominent in two other cores from sites that are further north although other data are needed circumstantial evidence suggests that the peak may be due to sedimentation of polar stratospheric clouds from the stratosphere during winter and spring no change in the form of the peak is seen over the last three decades it may be possible to observe past stratospheric conditions over longer time scales from ice cores but other sources may obliterate the signal in ice from the glacial periods 34 refs 5 figs

a new scheme for the very deep geological disposal of high level radioactive waste a case is presented for reconsidering deep borehole disposal for high level radioactive waste hlw in the light of recent discoveries about the hydrogeology and hydrogeochemistry of the continental crust a new multi barrier concept is proposed for very deep elevated temperature disposal of vitrified hlw spent fuel and ex military and other fissile materials which involves melting and recrystallization of a granitic host rock utilizing the heat from the waste this scheme is fundamentally different from previously proposed borehole disposal scenarios in its key aspects particularly in utilizing only partial melting and a surviving container the perceived advantages of the scheme are discussed in general and in relation to previous deep disposal ideas particularly from the standpoint of safety it is concluded that the scheme offers a potentially safer and environmentally more acceptable option for the permanent disposal of high level waste

variability in accumulation rates from gpr profiling on the west antarctic plateau isochronal layers in firn detected with ground penetrating radar gpr and dated using results from ice core analyses are used to calculate accumulation rates along a 100 km across flow profile in west antarctica accumulation rates are shown to be highly variable over short distances elevation measurements from global positioning system surveys show that accumulation rates derived from shallow horizons correlate well with surface undulations which implies that wind redistribution of snow is the leading cause of this variability temporal changes in accumulation rate over 25 185 year intervals are smoothed to along track length scales comparable to surface undulations in order to identify trends in accumulation that are likely related to changes in climate results show that accumulation rates along this profile have decreased in recent decades which is consistent with core derived time series of annual accumulation rates measured at the two ends of the radar profile these results suggest that temporal variability observed in accumulation rate records from ice cores and gpr profiles can be obscured by spatial influences although it is possible to resolve temporal signals if the effects of local topography and ice flow are quantified and removed

spatial covariance of water isotope records in a global network of ice cores spanning twentieth century climate change 1 estimating the spatial extent of past climate changes has been an ongoing challenge for paleoclimatology for such estimates to be made with confidence it is important to establish an understanding of the spatial coherence of proxy records during an interval of known climate change we use water stable isotopes from high resolution ice cores and twentieth century observations of sea level pressures and sea surface temperatures to assess the covariance among isotopic records and its link to organized patterns of climate variability covarying signals in the cores are identified using empirical orthogonal function analysis results from regression analysis show that the leading signals are consistent with key climate patterns including the northern atlantic oscillation and southern annular mode and variability in tropical pacific sea surface temperatures associated with the el nino southern oscillation patterns that have recently been identified in instrumental data such as positive tropical pacific sst anomalies associated with the negative phase of the sam are evident in the ice cores these explanations for the variance of stable isotopes are consistent with recent studies using isotope enabled general circulation models and provide a physical basis for interpreting the observed isotopic signals while there is also a global change signal that is evident when analyzing the records collectively there are some limitations in reconstructing global temperatures due to the geographic coverage of the available records and the current lack of modeling studies to explain the observed global scale changes still water stable isotope ratios preserved in ice cores provide a sufficiently rich sampling of large scale climate variability that they can be more widely used in physically based paleoclimate reconstructions covering the last millennium and other periods

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

the antarctic dipole and its predictability this study investigates the nature of interan nualvariability ofantarcticseaiceanditsrelationshipwith the tropical climate we nd that the dominant interan nual variance structure in the sea ice edge and surface air temperature elds is organized as a quasi stationary wave which we call the antarctic dipole adp it is charac terized by an out of phase relationship between the ice and temperature anomalies in the central eastern pacic and atlantic sectors of the antarctic the dipole consists of a strong standing mode and a weaker propagating motion within each basin s ice eld it has the same wavelength as the antarctic circumpolar wave acw and dominates the acw variance the dipole is clearly associated with tropical enso events it can be predicted with moderate skill using linear regression involving surface temperature two to four months ahead the prediction performs better in extreme warm cold years and best in la ni na years

chemical analysis of ice vein microenvironments ii analysis of glacial samples from greenland and antarctica chemical constituents trapped within glacial ice provide a unique record of climate as well as repositories for biological material such as pollen grains fungal spores viruses bacteria and dissolved organic carbon past research suggests that the veins of polycrystalline ice may provide a liquid microenvironment for active microbial metabolism fueled by concentrated impurities in the veins despite these claims no direct measurements of impurity concentration in ice veins have been made using micro raman spectroscopy we show that sulfate and nitrate concentrations in the veins of glacial ice from greenland greenland ice sheet project 2 and antarctic newall glacier and a dominion range glacier core samples were 10 4 and 10 5 times greater than the concentrations measured in melted bulk core water methanesulfonate was not found in the veins consistent with its presence as particulate matter within the ice the measured vein concentration of molecular anions implies a highly acidic ph 3 vein environment with high ionic strength mm m we estimate that the vein volume provides 16 7 and 576 km 3 of habitable space within the greenland and antarctic ice sheets respectively which could support the metabolism of organisms that are capable of growing in cold high ionic strength solutions with low ph

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

electrical conductivity and temperature in the canadian cordilleran crust abstract high electrical conductivity and high heat flow coexist in much of the canadian cordillera a region of recent accretion of crustal terranes to north america the relationship between temperature and electrical conductivity in the crust is investigated by means of results from 251 heat flow determinations and 301 magnetotelluric mt soundings we first compared maps of mt phase at period 10 s and of heat flow larger phases correlate with higher heat flows in some areas but the relationship is complicated by other causes of variation in these two parameters to give a more focussed comparison we map the depth d 450 to the 450 c isotherm for two assumed distributions of reduced heat flow and the depth d c to the top of the lower crustal conductor at mt sites away from major fracture zones the map of d c visually resembles both of the maps of d 450 and readings at 76 points of a grid give correlation coefficient 0 80 this supports a relationship between high conductivity in the crust and temperatures above 450 c both the lower crustal conductor and the 450 c isotherm occur at depths near 30 km above the subducting oceanic plate under vancouver island at 15 20 km in the intermontane belt and of 10 15 km in the omineca belt if there is an upcurrent in the mantle beneath the continent behind the subduction as proposed elsewhere its axis may now be under the omineca belt this location is in harmony with evidence of recent extension and uplift there

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

solar forcing of the polar atmosphere we present highly resolved annually dated calibrated proxies for atmospheric circulation from several antarctic ice cores itase international trans antarctic scientific expedition siple dome law dome that reveal decadal scale associations with a south pole ice core 10 be proxy for solar variability over the last 600 years and annual scale associations with solar variability since ad 1720 we show that increased decreased solar irradiance is associated with increased decreased zonal wind strength near the edge of the antarctic polar vortex the association is particularly strong in the indian and pacific oceans and as such may contribute to understanding climate forcing that controls drought in australia and other southern hemisphere climate events we also include evidence suggestive of solar forcing of atmospheric circulation near the edge of the arctic polar vortex based on ice core records from mount logan yukon territory canada and both central and south green land as enticement for future investigations our identification of solar forcing of the polar atmosphere and its impact on lower latitudes offers a mechanism for better understanding modern climate variability and potentially the initiation of abrupt climate change events that operate on decadal and faster scales

shear wave velocity structure in the northern basin and range province from the combined analysis of receiver functions and surface waves a new method based on the joint inversion of receiver functions and surface wave phase velocities results in well determined shear velocity structures that are consistent with the compressional wave structure gravity heat flow and elevation data in the northern basin and range this new inversion method takes advantage of average velocity information present in the surface wave method and differential velocity information contained in the receiver function method thus min imizing the nonuniqueness problem that results from the velocity depth trade off an unusually thick 38 kin and relatively faster crust and upper mantle are found in central and eastern nevada compared to the thin 28 to 34 km and slower crust and upper mantle of the western basin and range we interpret the regions of thicker and faster crust and upper mantle as zones that have undergone less cenozoic ex tension relative to the surrounding regions to the west and north the thick crust and consequently greater depth to the dense mantle material is consistent with the gravity low pattern in central and eastern nevada simple gravity modeling shows both local and regional isostatic compensation occur within 40 km of the surface indicating a near classical airy type of compensation in the province we analyze in detail the shear wave s wave velocity model derived from the receiver functions at station bmn and compressional wave p wave velocity models derived from the 1986 passcal experiment in northwestern nevada the most interesting feature of these models is the presence of negative velocity gradients in the s wave model with no corresponding velocity decrease in the p wave models between depths of 10 and 24 km this combined velocity model may be explained by high pore fluid pressures at these depths this model favors a layered fluid porosity model proposed in the literature to explain extensive middle to lower crust conti nental seismic reflections and high electrical conductivity an upper mantle grada tional low velocity zone is present between 32 and 38 km in the s wave model this upper mantle shear wave low velocity zone is consistent with partial melt which may be the source material for magmatic underplating in this region

climate since ad 1510 on dyer plateau antarctic peninsula evidence for recent climate change a 480 year record of the oxygen isotope ratios dust content chemical species and net accumulation from ice cores drilled in 1989 90 on dyer plateau in the antarctic peninsula is presented the continuous analyses of small sub annual samples reveal well preserved annual variations in both sulfate content and 18o thus allowing an excellent time scale to be established this history reveals a recent pronounced warming in which the last two decades have been among the warmest in the last five centuries furthermore unlike in east antarctica on dyer plateau conditions appear to have been fairly normal from ad 1500 to 1850 with cooler conditions from 1850 to 1930 and a warming trend dominating since 1930 reconstructed annual layer thicknesses suggest an increase in net accumulation beginning early in the 19th century and continuing to the present this intuitive conflict between increasing net accumulation and depleted 18o cooler climate in the 19th century appears widespread in the peninsula region and challenges our understanding of the physical relationships among moisture sources air temperatures and snow accumulation the complex meteorological regime in the antarctic peninsula region complicates meaningful interpretation of proxy indicators and results in a strong imprint of local high frequency processes upon the larger scale climate picture

volcanic aerosol layers observed by lidar at south pole september 1991 june 1992 during 1991 the terrestrial stratosphere went through a substantially increased aerosol load due mainly to the eruptions of mt pinatubo in the philippines and to a lesser extent to those of mt hudson in chile this paper reports lidar observations of the stratospheric aerosols at south pole two layers were present at different altitudes during the austral summer but only the higher one persisted in the stratosphere until the onset of the polar stratospheric cloud psc phenomenon data have been analyzed in terms of the integrated backscattering coefficient and the aerosol mass content has been estimated

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

glaciological and climatic significance of hercules dome antarctica an optimal site for deep ice core drilling 1 we present glaciological and climatological characteristics of hercules dome antarctica 86 s 105 w which demonstrate its potential as a deep ice core site annual layering in d ratios from a 72 m ice core collected by the us itase 2002 traverse indicate accumulation rates of 0 16 0 20 m yr ice equivalent over the last 300 years age control from stratigraphy seen in the radio echo sounding data collected during the same traverse suggests a rate of 0 09 0 11 m yr averaged over the past 18 000 years ice stratigraphy also indicates that the ice divide position has been stable through at least this period comparison of satellite derived temperature anomalies with atmospheric reanalysis data show that the site is sensitive to the two dominant patterns of climate variability in the high latitude southern hemisphere climate proxy data from a deep ice core at hercules dome would be indicative of changes in pacific southern hemisphere climate variability and may provide new information on rapid climate change events in antarctica the sensitivity of the site and the combination of relatively high accumulation rates low temperatures mean annual 35 c to 40 c and simple ice flow suggest that hercules dome is an ideal site for a future deep ice core

the 1500m south pole ice core recovering a 40 ka environmental record supported by the us national science foundation a new 1500 m approximately 40 ka old ice core will be recovered from south pole during the 2014 15 and 2015 16 austral summer seasons using the new us intermediate depth drill the combination of low temperatures relatively high accumulation rates and low impurity concentrations at south pole will yield detailed records of ice chemistry and trace atmospheric gases the south pole ice core will provide a climate history record of a unique area of the east antarctic plateau that is partly influenced by weather systems that cross the west antarctic ice sheet the ice at south pole flows at approximately 10m a exp 1 and the south pole ice core site is a significant distance from an ice divide therefore ice recovered at depth originated progressively farther upstream of the coring site new ground penetrating radar collected over the drill site location shows no anthropogenic influence over the past approximately 50 years or upper 15 m depth age scale modeling results show consistent and plausible annual layer thicknesses and accumulation rate histories indicating that no significant stratigraphic disturbances exist in the upper 1500m near the ice core drill site

sources and transport pathways of marine aerosol species into west antarctica sixteen high resolution marine aerosol na so4 records from spatially distributed international trans antarctic scientific expedition itase ice cores spanning the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine sources sea spray and frost flowers and transport pathways of marine aerosols into west antarctica factors contributing to the amount of marine aerosols transported inland include sea ice extent the presence of open water features polynyas leads wind strength and direction and the strength and positioning of low pressure systems analysis of so4 na ratios indicates that frost flowers can contribute significantly 40 to the na budget of antarctic ice cores higher na concentrations in the ross drainage system may result from greater production of marine aerosols related to frost flowers in the ross sea region in association with greater sea ice extent and larger open water areas significant positive correlations of sea ice extent and the na time series exist in some regions of west antarctica higher wind speeds in winter and higher na concentrations when slp is

physically based modeling of atmosphere to snow to firn transfer of h2o2 at south pole quantitative interpretation of ice core chemical records requires a detailed understanding of the transfer processes that relate atmospheric concentrations to those in the snow firn and ice a unique 2 year set of year round surface snow samples at south pole and snow pits with associated accumulation histories were used to test a physically based model for atmosphere to firn transfer of h2o2 the model which extends our previous transfer modeling at south pole into the snowpack is based on the advection dispersion equation and spherical diffusion within representative snow grains required physical characteristics of the snowpack such as snow temperature and ventilation were estimated independently using established physical models the surface snow samples and related model simulations show that there is a repeatable annual cycle in h2o2 in the surface snow at south pole it peaks in early spring and surface snow concentration is primarily determined by atmospheric concentration and temperature with some dependence on grain size the snow pits and associated model simulations point out the importance of accumulation timing and annual accumulation rate in understanding the deposition and preservation of h2o2 and 18o at south pole long term snowpack simulations suggest that the firn continues to lose h2o2 to the atmosphere for at least 10 12 years 3 m after burial at current south pole temperatures and accumulation rates

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

a 200 year sub annual record of sulfate in west antarctica from 16 ice cores sixteen high resolution ice core records from west antarctica and south pole are used to examine the spatial and temporal distribution of sulfate for the last 200 years the preservation of seasonal layers throughout the length of each record results in a dating accuracy of better than 1 year based on known global scale volcanic events a dual transport source for west antarctic sea salt ss so4 2 and excess xs so4 2 is observed lower tropospheric for areas below 1000 m elevation and mid upper tropospheric stratospheric for areas located above 1000 m our xsso4 2 records with volcanic peaks removed do not display any evidence of an anthropogenic impact on west antarctic so4 2 concentrations but do reveal that a major climate transition takes place over west antarctica at 1940 global scale volcanic eruptions appear as significant peaks in the robust spline residual xsso 4 2 records from sites located above 1000 m elevation but do not appear in the residual records from sites located below 1000 m

climate variability in west antarctica derived from annual accumulation rate records from itase firn ice cores thirteen annually resolved accumulation rate records covering the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine climate variability over west antarctica accumulation is controlled spatially by the topography of the ice sheet and temporally by changes in moisture transport and cyclonic activity a comparison of mean accumulation since 1970 at each site to the long term mean indicates an increase in accumulation for sites located in the western sector of the pine island thwaites drainage system accumulation is negatively associated with the southern oscillation index soi for sites near the ice divide and periods of sustained negative soi 1940 42 1991 95 correspond to above mean accumulation at most sites correlations of the accumulation rate records with sea level pressure slp and the soi suggest that accumulation near the ice divide and in the ross drainage system may be associated with the mid latitudes the post 1970 increase in accumulation coupled with strong slp accumulation rate correlations near the coast suggests recent intensification of cyclonic activity in the pine island thwaites drainage system

dating the siple dome antarctica ice core by manual and computer interpretation of annual layering the holocene portion of the siple dome antarctica ice core was dated by interpreting the electrical visual and chemical properties of the core the data were interpreted manuallyandwith acomputeralgorithm the algorithm interpretation was adjusted to be consistent with atmospheric methane stratigraphic ties to the gisp2 greenland ice sheet project 2 ice core 10 be stratigraphic ties to the dendrochronology 14 c recordandthedatedvolcanic stratigraphy thealgorithm interpretation ismorecon sistent andbetter quantifiedthanthe tedious and subjective manual interpretation

spatial and temporal variability of antarctic ice sheet microwave brightness temperatures 1 annual and interannual variability of 21 years of passive microwave brightness temperatures on the antarctic ice sheet is documented through principal component analysis the leading modes show that brightness temperatures are dominantly forced by the annual temperature cycle with surface melting signals explaining about 5 of the total variance of the data analysis of the data with the annual cycle and melting signals removed results in two significant interannual modes the first is consistent with the antarctic oscillation and its influence on antarctic surface temperatures while the second reflects regional scale variability that appears to be linked to sea ice anomalies and the el nino southern oscillation the expression of these characteristic patterns of southern hemisphere climate variability on the antarctic continent provides a framework for interpreting modern climate records as well as a basis for reconstructing past climate variability with ice cores

an emerging technique multi ice core multi parameter correlations with antarctic sea ice extent using results stemming from the international trans antarctic scientific expedition itase ice core array plus data from ice cores from the south pole and siple dome we investigate the use of sodium na non sea salt sulfate nssso4 2 and methylsulfonate ms as proxies for antarctic sea ice extent sie maximum and mean annual chemistry concentrations for these three species correlate significantly with maximum mean and minimum annual sie offering more information and clarification than single ice core and single species approaches significant correlations greater than 90 exist between na and maximum sie nssso4 2 with minimum and mean sie and ms with mean sie correlations with sie within large geographic regions are in the same direction for all ice core sites for na and nssso4 2 but not ms all ice cores display an sie correlation with nssso4 2 and ms but not all correlate with na this multi core multi parameter study provides the initial step in determining which chemical species can be used reliably and in which regions as a building block for embedding other ice core records once established the resulting temporal and spatial matrix can be used to relate ice extents atmospheric patterns biological productivity and site conditions

recent southern indian ocean climate variability inferred from a law dome ice core new insights for the interpretation of coastal antarctic isotopic records stable isotopes in water have been measured along a very high accumulation ice core from law dome on the east antarctic coast these enable a detailed comparison of the isotopic records over sixty years 1934 1992 with local antarctic station data and remote meteorological observations atmospheric reanalyses and sea surface temperature estimates on a seasonal to inter annual time scale using both observations and isotopic atmospheric general circulation model gcm results we quantify the relationships between stable isotopes 18o d and deuterium excess d d 8 18o with site and source temperature at seasonal and decadal time scales showing the large imprint of source conditions on law dome isotopes these calibrations provide new insights for the quantitative interpretation of temporal isotopic fluctuations from coastal antarctic ice cores an abrupt change in the local meridional atmospheric circulation is clearly identified from law dome deuterium excess during the 1970s and analysed using gcm simulations

advanced microstructural characterization of four east antarctic firn ice cores the microstructures and microchemistry of four us international trans antarctic scientific expedition ice cores were examined at three depths 30 60 90m each using scanning electron microscopy including electron backscattered patterns and energy dispersive spectroscopy eds in order to assess the relationship between chemical and physical properties the physical characteristics grain size porosity density internal surface volume and crystallographic orientation at the four sites were inhomogeneous as expected on the basis of differences in the moisture content of deposited snow and the accumulation rate at their respective locations evidence of shallow subgrain boundary formation and trends in internal surface volume having implications for the study of firn densification and ice sheet modeling were also found chemical characterization revealed that site specific variations in particulate concentration and source could accurately be determined using eds analysis it was also found that the combination of elements predominant within the sample controls the morphology and microstructural location of the impurities

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

abrupt climate change around 22 ka on the siple coast of antarctica a new ice core from siple dome antarctica suggests the surface temperature increased by 6 c in just several decades at approximately 22 ka bp this abrupt change did not occur 500 km away in the byrd ice core or in climate proxy records in the siple dome core indicative of the mid latitude pacific this demonstrates there was significant spatial heterogeneity in the response of the antarctic climate during the last deglaciation and draws attention to unexplained mechanisms of abrupt climate change in antarctica

density temperature and rheological models for the southeastern canadian cordillera implications for its geodynamic evolution two dimensional density temperature and rheological models are constructed for a 350 km northeast trending transect of the southeastern canadian cordillera all models highlight several major physical differences between foreland and hinterland lithosphere significant features of the density model are the presence of an anomalously low density 3 10 103 kg m 3 layer with a maximum thickness of 12 km beneath the moho in the hinterland the similar densities of the monashee terrane and the cratonic crust of the foreland and an increase in crustal thickness beneath the southern rocky mountain trench the temperature model shows steeper gradients and higher moho temperatures beneath the hinterland than beneath the foreland in the rheological model the hinterland is characterized by a thin brittle upper crust beneath which the entire lithosphere is hot weak and ductile in contrast the foreland is composed of a thick brittle upper crust with an additional brittle zone in the upper mantle the

high resolution ice core stable isotopic records from antarctica towards interannual climate reconstruction ice core records are a key resource for reconstructing antarctic climate however a number of physical processes preclude the simple interpretation of ice core properties such as oxygen isotopic ratios in terms of climate variables like temperature or sea level pressure we show that well dated sub annually resolved stable isotopic records from the united states international trans antarctic scientific expedition us itase traverses and other sources have a high correlation with local seasonal temperature variation however this temporal relationship cannot be simply extended to quantitative interannual resolution reconstructions of site temperature we suggest that a consistent and important target for ice core calibrations is a composite of annual mean temperature records from antarctic weather stations which covaries strongly with the dominant mode from principal component analysis of temperature variability in the antarctic significant correlations with this temperature index are found with individual ice core records with a composite of the ice cores and through a multiple linear regression model with the ice cores as predictors these results imply that isotopic signals like the instrumental temperature mode itself have a strong response to large scale atmospheric circulation variability which in the antarctic region is dominated by the southern annular mode

instrument and tree ring based estimates of the antarctic oscillation abstract an estimate of the strength of the austral summer antarctic oscillation using station sea level pressure records for the period 1878 2000 is presented the first to the authors knowledge the reconstruction was obtained by relating the antarctic oscillation aao intensity derived from ncep ncar reanalysis data to the leading principal components of station records using multiple regression analysis particular effort has been made to fit the model in a way that is robust to the questionable trends in the ncep ncar data in the southern hemisphere the trends in the reconstruction are derived from the station data not from the ncep data cross validation with the ncep data and comparison with other analyses of the aao over the late instrumental period give confidence that this station based reconstruction can be regarded as trustworthy with regard to the whole reconstruction period some unquantifiable uncertainty stems from potential instability of the statistical relationships to extend this

coincident conductive and reflective middle and lower crust in southern british columbia summary processing and interpretation of magnetotelluric data recorded as part of the lithoprobe southern cordillera transect studies across the boundary of the intermontane and omineca morphogeological belts reveals a high electrical conductivity in the middle and lower parts of the crust everywhere and b a depth dependency of geoelectric strike the data have been modelled using two different inversion algorithms and different methods for correcting static shifts the two different approaches gave similar results the depth to the top of a conductive layer decreases from 15 17km in the west across the intermontane belt to 8 10km across the transition to the omineca belt the top of this conductive layer is closely coincident with a layer of increased seismic reflectivity as shown by reprocessing of collocated lithoprobe seismic reflection data the eastward shallowing is associated with an increase in heat flow such that the top of the conductive and reflective zones remains at 400 450 c this coincidence suggests that the increased reflectivity and the high electrical conductivity observed in the middle crust may have a common cause and that their presence is limited to where the present temperature exceeds a critical value one explanation that meets these conditions is that both the conductivity and reflectivity are produced by a small amount of aqueous fluid porosity we propose that fluids are trapped in the middle crust by a ductile shear zone previously interpreted from the seismic sections as the okanagan valley fault to the west of okanagan lake the geoelectrical strike varies from n25 w for the first 5 10 km of the crust to n20 e for the middle lower crust and to n60 e for the upper mantle this variation indicates that the exotic terrane material is concentrated in the uppermost part of the crust and that the remainder of the crust is composed of ancestral north american rocks

high resolution ice cores from us itase west antarctica development and validation of chronologies and determination of precision and accuracy shallow ice cores were obtained from widely distributed sites across the west antarctic ice sheet as part of the united states portion of the international trans antarctic scientific expedition us itase program the us itase cores have been dated by annual layer counting primarily through the identification of summer peaks in non sea salt sulfate nssso4 2 concentration absolute dating accuracy of better than 2 years and relative dating accuracy better than 1 year is demonstrated by the identification of multiple volcanic marker horizons in each of the cores tambora indonesia 1815 being the most prominent independent validation is provided by the tracing of isochronal layers from site to site using high frequency ice penetrating radar observations and by the timing of mid winter warming events in stable isotope ratios which demonstrate significantly better than 1 year accuracy in the last 20 years dating precision to 1 month is demonstrated by the occurrence of summer nitrate peaks and stable isotope ratios in phase with nssso4 2 and winter time sea salt peaks out of phase with phase variation of 1 month dating precision and accuracy are uniform with depth for at least the last 100 years

global surface temperatures over the past two millennia 1 we present reconstructions of northern and southern hemisphere mean surface temperature over the past two millennia based on high resolution proxy temperature data which retain millennial scale variability these reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the northern hemisphere conclusions for the southern hemisphere and global mean temperature are limited by the sparseness of available proxy data in the southern hemisphere at present

a 700 year record of southern hemisphere extratropical climate variability annually dated ice cores from west and east antarctica provide proxies for past changes in atmospheric circulation over antarctica and portions of the southern ocean temperature in coastal west and east antarctica and the frequency of south polar penetration of el nino events during the period ad 1700 1850 atmospheric circulation over the antarctic and at least portions of the southern hemisphere underwent a mode switch departing from the out of phase alternation of multi decadal long phases of eof1 and eof2 modes of the 850 hpa field over the southern hemisphere as defined in the recent record by thompson and wallace 2000 thompson and solomon 2002 that characterizes the remainder of the 700 year long record from ad 1700 to 1850 lower tropospheric circulation was replaced by in phase behavior of the amundsen sea low component of eof2 and the east antarctic high component of eof1 during the first phase of the mode switch both west and east antarctic temperatures declined potentially in response to the increased extent of sea ice surrounding both regions at the end of the mode switch west antarctic coastal temperatures rose and east antarctic coastal temperatures fell respectively to their second highest and lowest of the record polar penetration of el nino events increased during the mode switch the onset of the ad 1700 1850 mode switch coincides with the extreme state of the maunder minimum in solar variability late 20th century west antarctic coastal temperatures are the highest in the record period and east antarctic coastal temperatures close to the lowest since ad 1700 extratropical regions of the southern hemisphere have experienced significant climate variability coincident with changes in both solar variability and greenhouse gases

little ice age neoglacial paleoenvironmental conditions at siple station antarctica the 550 year records of 18 o and dust concentrations from siple station antarctica suggest warmer and less dusty atmospheric conditions from 1600 to 1830 a d which encompasses much of the northern hemisphere little ice age lia dust and 18 o data from south pole station indicate that the opposite conditions e g cooler and more dusty were prevalent there during the lia meteorological data from 1945 85 show that the lia temperature opposition between amundsen scott and siple inferred from 18 o is consistent with the present spatial distribution of surface temperature there is some observational evidence suggesting that under present conditions stronger zonal westerlies produce a temperature pattern similar to that of the lia these regional differences demonstrate that a suite of spatially distributed high resolution ice core records will be necessary to characterize the lia in antarctica

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

frequency dependence in seismoacoustic imaging of shallow free gas due to gas bubble resonance shallow free gas is investigated in seismoacoustic data in 10 frequency bands covering a frequency range between 0 2 and 43 khz at the edge of a gassy patch in the bornholm basin baltic sea compressional wave attenuation caused by free gas is estimated from reflection amplitudes beneath the gassy sediment layer imaging of shallow free gas is considerably influenced by gas bubble resonance because in the resonance frequency range attenuation is significantly increased at the resonance frequency of the largest bubbles between 3 and 5 khz high scattering causes complete acoustic blanking beneath the top of the gassy sediment layer in the wider resonance frequency range between 3 and 15 khz the effect of smaller bubbles becomes dominant and the attenuation slightly decreases this allows acoustic waves to be transmitted and reflections can be observed beneath the gassy sediment layer for higher frequencies above resonance beginning at 19 khz attenuation is low and the presence of free gas can be inferred from the decreased reflection amplitudes beneath the gassy layer below the resonance frequency range 1 khz attenuation is generally very low and not dependent on frequency using the geoacoustic model of anderson and hampton the observed frequency boundaries suggest gas bubble sizes between 1 and 4 6 mm and gas volume fractions up to 0 02 in a 2 m thick sediment layer whose upper boundary is the gas front with the multifrequency acoustic approach and the anderson and hampton model quantification of free gas in shallow marine environments is possible if the measurement frequency range allows the identification of the resonance frequency peak the method presented is limited to places with only moderate attenuation where the amplitudes of a reflection can be analyzed beneath the gassy sediment layer

observed antarctic interannual climate variability and tropical linkages abstractthis study reviews the mechanisms associated with antarctic tropical climate linkages and presents new analyses of the seasonality and spatial patterns of tropical climate signals in the antarctic for the late 1950s to the present tropical climate signals are primarily communicated to the antarctic via the pacific south america psa pattern and the southern annular mode sam the impacts of these circulation patterns and their tropical linkages are evident in regressions of seasonally stratified antarctic station temperature data and annually resolved ice core records on global fields of sea surface temperature sea level pressure and precipitation temperature and ice core anomalies in the antarctic peninsula region and adjoining areas of west antarctica are significantly impacted by the psa interpreted as a rossby wave train driven by anomalous tropical deep convection during enso events this pattern is most evident in the austral spring consistent with recent studies suggesting that atm

phase structure of radar stratigraphic horizons within antarctic firn we have recorded reflection profiles of firn through large areas of west antarctica and part of the east antarctic plateau using 400 mhz short pulse radar the locations show accumulation rates that vary from well above to well below the vertical radar resolution most reflection horizons have extensive lateral continuity and are composed of distinctive wavelets with a consistent phase polarity sequence within their successive half cycles we modeled these waveforms and conclude that they arise from thin double layers of ice over hoar which is consistent with the standard model of firn stratification in addition we conclude that ice hoar layers are extensive throughout west antarctica and also present although more sparsely beneath the antarctic plateau

isotopic diffusion in polar firn implications for interpretation of seasonal climate parameters in ice core records with emphasis on central greenland if it were possible to properly extract seasonal information from ice core isotopic records paleoclimate researchers could retrieve a wealth of new information concerning the nature of climate changes and the meaning of trends observed in ice core proxy records it is widely recognized however that the diffusional smoothing of the seasonal record makes a proper extraction very difficult in this paper we examine the extent to which seasonal information specifically the amplitude and shape of the seasonal cycle is irrecoverably destroyed by diffusion in the firn first we show that isotopic diffusion firn is reasonably well understood we do this by showing that a slightly modified version of the whillans and grootes 1985 theory makes a tenable a priori prediction of the decay of seasonal isotopic amplitudes with depth at the gisp2 site though a small adjustment to one parameter significantly improves the prediction further we calculate the amplitude decay at various other ice core sites and show that these predictions compare favorably with published data from south pole and locations in southern and central greenland and the antarctic peninsula we then present numerical experiments wherein synthetic ice core records are created diffused sampled reconstituted and compared to the original these show that alter diffusive mixing in the entire fini column seasonal amplitudes can be reconstructed to within about 20 error in central greenland but that all information about sub annual signals is permanently lost there furthermore most of the error in the amplitude reconstructions is due to the unknowable variations in the sub annual signal finally we explore how these results can be applied to other locations and suggest that dye 3 has a high potential for meaningful seasonal reconstructions while siple dome has no potential at all an optimal ice core site for seasonal reconstructions has a high accumulation rate and a low temperature

sea level pressure variability in the amundsen sea region inferred from a west antarctic glaciochemical record using european center for medium range weather forecasts ecmwf numerical operational analyses sea ice extent records and station pressure data we investigate the influence of sea level pressure variability in the amundsen sea region on a west antarctic siple dome glaciochemical record empirical orthogonal function analysis of the high resolution siple dome multivariate ice core chemical time series record sdeof1 documents lower tropospheric transport of sea salt aerosols to the site during 1985 1994 the sdeof1 record of high low aerosol transport corresponds to anomalously low high sea level pressure slp in the amundsen sea region spatial correlation patterns between ecmwf monthly slp fields and the annual sdeof1 record suggest that a majority of sea salt aerosol is transported to siple dome during spring september october and november analysis of zonal and meridional wind fields supports the slp sdeof1 correlation and suggests the sdeof1 record is sensitive to changes in regional circulation strength no relationship is found between sea ice extent and the sdeof1 record for the period 1973 1994 to investigate the sdeof1 record prior to ecmwf coverage a spring transpolar index stpi is created using normalized slp records from the new zealand and south america antarctic peninsula sectors and is significantly correlated at least 95 c l with the sdeof1 record on an annual r 5 0 32 p 0 001 and interannual 3 years r 5 0 51 p 0 001 basis dominant periodicities 3 3 and 7 1 years in the annual sdeof1 record 1890 1994 a d suggest that a portion of the recorded interannual variability may be related tropical extratropical enso teleconnections changes in the periodic structure of the full 850 1994 a d siple dome record suggests a shift in slp forcing during the little ice age 1400 1900 a d interval