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

progressive dissolution of fine carbonate particles in pelagic sediments abstract large systematic variations occur in the proportion of coccolith sized carbonate particles relative to other types of carbonate particles within the

spatial and temporal variability in isotope composition of recent snow in the vicinity of vostok station antarctica implications for ice core record interpretation continuous detailedisotope ddandd 18 o profileswereobtainedfrom eight snow pits dug in the vicinity of vostok station antarctica during the period1984 2000 in addition snow samples taken along the 1km long accumulation stake profile were measured to determine spatial variability in isotope composition of recent snow the stacked dd time series spanning the last 55years shows only weak correlation with the mean annual air temperature recorded at vostok station significant oscillations of both snow accumulation and snow isotope composition with the periods 2 5 5 20 and possibly 10 2 years observed at single points are interpreted in terms of drift of snow accumulationwaves of various scales onthe surface of the ice sheet

spatial and temporal variability of surface mass balance near talos dome east antarctica 1 predictions concerning antarctica s contribution to sea level change have been hampered by poor knowledge of surface mass balance snow accumulation is the most direct climate indicator and has important implications for paleoclimatic reconstruction from ice cores snow accumulation measurements stake core snow radar taken along a 500 km transect crossing talos dome east antarctica have been used to assess accumulation signals and the representativeness of ice core records stake readings show that accumulation hiatuses can occur at sites with accumulation rates below 120 kg m 2 yr 1 differences between cores and stakes can lead to statistical misidentification of annual layers determined from seasonal signals at sites with accumulation rates below 200 kg m 2 yr 1 because of nondetection of higher and lower values achieving 10 accuracy in the reconstruction of snow accumulation from single cores requires high accumulation 750 kg m 2 yr 1 low accumulation sites are representative if cumulative rates computed over several years are used to reach the 750 kg m 2 yr 1 threshold temporal variability of accumulation over the last two centuries shows no significant increase in accumulation wind driven processes are a fundamental component of surface mass balance spatial variations in accumulation are well correlated with surface slope changes along the wind direction and may exceed 200 kg m 2 yr 1 within 1 km wind driven sublimation rates are less than 50 kg m 2 yr 1 in plateau areas and up to 260 kg m 2 yr 1 in slope areas and account for 20 75 of precipitation whereas depositional features are negligible in surface mass balance

phase center of l band radar in polar snow and ice backscatter from an aggregate of inhomogeneities combine to form an apparent surface reflection particularly in relation to interferometric synthetic aperture radar the depth z of this reflection can reside well below the true surface when the transmissivity at the interface between air and the aggregate is high snow and ice provide good examples for which we calculate z with different accumulation history and physical properties using a 0 5 3 0 ghz ground penetrating radar we acquired our data along transects in antarctica and svalbard we find values of z 40 in low absorbing antarctic firn and 10 meters in glaciers and ice shelves where melt freeze cycles and lateral mass movement lead to an electrically more heterogeneous snow and ice column the heterogeneity reduces dielectric contrast more rapidly with depth thus z is found at shallower depth but still resides several meters beneath the snow surface

nine centuries of microparticle deposition at the south pole abstract the analysis of microparticles in a 101 m core from amundsen scott south pole station antarctica has revealed a substantial increase in total particle concentration between approximately 1450 and 1850 a d a period encompassing the latest neoglacial interval or little ice age it is likely that this reflects a simultaneous increase in the concentration of particulate material in the antarctic atmosphere this is important climatologically for the antarctic atmosphere may represent the closest approximation to the natural background aerosol thus cores from east antarctica may contain long and detailed records of the natural global background aerosol such records are unavailable from any other medium additionally a cyclical variation which appears to be annual has been detected in the south pole particle record these features allow construction of a relative time scale for ice cores older than 100 yr from regions of low accumulation 1 where many traditional techniques are not applicable this is especially significant as the comparison of climatic data extracted from ice cores with other records of proxy data depends upon the ability to assign an accurate time scale to the ice core an estimated nine century record of net annual accumulation at the south pole has been compiled and the calculated error in the time scale is 90 yr

stratigraphic continuity in 400 mhz short pulse radar profiles of firn in west antarctica we track dated firn horizons within 400mhz short pulse radar profiles to find the continuous extent over which they can be used as historical benchmarks to study past accumulation rates in west antarctica the 30 40cm pulse resolution compares with the accumulation rates of most areas we tracked a particular set that varied from 30 to 90m in depth over a distance of 600 km the main limitations to continuity are fading at depth pinching associated with accumulation rate differences within hills and valleys and artificial fading caused by stacking along dips the latter two may be overcome through multi kilometer distances by matching the relative amplitude and spacing of several close horizons along with their pulse forms and phases modeling of reflections from thin layers suggests that the 37 to 50db range of reflectivity and the pulse waveforms we observed are caused by the numerous thin ice layers observed in core stratigraphy constructive interference between reflections from these close high density layers can explain the maintenance of reflective strength throughout the depth of the firn despite the effects of compaction the continuity suggests that these layers formed throughout west antarctica and possibly into east antarctica as well

annual accumulation over recent centuries at four sites in central greenland 1 accurate accumulation records are fundamental to understanding mass balance of the greenland ice sheet ice cores can provide multicentury high resolution ground based point estimates of water accumulation in 2003 and 2004 four new ice cores were collected in the central western d4 and d5 and summit sandy and katie regions of greenland annual layer counting based on multiple glaciochemical parameters primarily hydrogen peroxide sea salt and dust proxies was used to date the ice cores resulting in annual dating the bottom depth ages for d4 d5 sandy and katie were estimated at 1738 1673 1844 and 1934 a d with mean annual accumulation rates of 41 4 35 2 22 4 and 22 4 cmweq yr 1 respectively these new records were in good agreement with previous accumulation maps and four previously published records from nearby multicentury ice cores spatial variability was quantified through an analysis of variance thereby allowing for more meaningful comparisons to atmospheric processes more regionally representative accumulation records were constructed for the central western and summit regions spanning recent centuries using a principle component analysis of both the new and previously reported ice core measurements these regional records exhibited 6 7 interannual variability 1 standard deviation of the mean and had lower spatial variability uncertainties than individual accumulation records correlations indicate that 20 of the variance in the central western region was explained by the north atlantic oscillation nao and suggests that an array of more northern ice cores may correlate more closely with nao

recent increase in south pole snow accumulation this paper summarizes the 37 year history of net accumulation measurements at the geographic south pole obtained by numerous investigators using a variety of techniques these data lead to the conclusion that annual net snow accumulation has increased in the vicinity of south pole station sps since 1955 the records were examined for evidence of a station effect and it is concluded that not all of the observed increase can be attributed to snow drift associated with the presence of the station furthermore the accumulation increase at the south pole appears consistent with increases observed at other locations on the east antarctic plateau and in the peninsula region as well these data suggest that the recent accumulation increase at sps may be regionally extensive over the east antarctic plateau

accumulation variability and mass budgets of the lambert glacier amery ice shelf system east antarctica at high elevations the temporal and spatial variability of the annual accumulation rate and the mass budgets of five sub basins of the lambert glacier amery ice shelf system las east antarctica at high elevations are assessed using a variety of datasets derived from field measurements and modeling the annual temporal variations of the accumulation rate for four cores from the west and east sides of the las are around 34 decadal fluctuation of the accumulation from the dt001 firn core drops to 10 and the 30 year fluctuation to 5 which is assumed to contain the information about the regional and long term trend in accumulation the 15 point running mean of the annual accumulation rate derived from stake measurements can remove most of the high frequency spatial variation so as to better represent the local accumulation model simulations show that the spatial variability of erosion deposition of snow by the wind has a noticeable impact on the surface mass balance at the higher parts of the las mass budget estimates at high elevation sub basins of the las suggest drainage 9 has a negative imbalance of 0 7 0 4 gt a 1 lambert and mellor glaciers have a positive imbalance of 3 9 2 1 and 2 1 2 4 gt a 1 respectively and fisher glacier and drainage 11 are approximately in balance the higher elevation region as a whole has a positive mass imbalance of 4 4 6 3 gt a 1 which is consistent with the most recent radar altimetry assessment that shows an overall thickening over this region

late 20th century increase in south pole snow accumulation a compilation of the 37 year history of net accumulation at the south pole mosley thompson et al 1995 suggests an increase in net annual accumulation since 1965 this record is sporadic and its quality is compromised by spatially restricted observations and nonsystematic measurement procedures results from a new spatially extensive network of 236 accumulation poles document that the current 5 year 1992 1997 average annual net accumulation at the south pole is 84 5 8 9 mm water equivalent w e this accumulation rate reflects a 30 increase since the 1960s when the best although not optimal records indicate that it was 65 mm w e identification of two prominent beta radioactivity horizons 1954 1955 and 1964 1965 in six firn cores confirms an increase in accumulation since 1965 viewed from a longer perspective of accumulation provided by ice cores and a snow mine study the net accumulation of the 30 year period 1965 1994 is the highest 30 year average of this millennium limited data suggest this recent accumulation increase extends beyond the south pole region and may be characteristic of the high east antarctic plateau enhanced accumulation over the polar ice sheets has been identified as a potential early indicator of warmer sea surface temperatures and may offset a portion of the current rise in global sea level

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

spatial and temporal variability in snow accumulation at the west antarctic ice sheet divide over recent centuries mean annual accumulation rates of 0 200 0 204 and 0 221 mweq a 1 respectively small scale spatial variability ssv was determined using an analysis of variance of accumulation in the ice core array thereby quantifying the uncertainty in individual accumulation records results indicate that the spatial variability was 0 030 mweq a 1 o r approximately 15 of the average annual accumulation an accumulation record representative of the wais divide local area over recent centuries was developed using a principal component analysis to identify the coherent accumulation signal the wais divide local record exhibited 14 interannual variability 1 standard deviation of the mean with the ssv reduced to 0 017 mweq a 1 correlations of the wais divide local accumulation record with atmospheric indices e g antarctic oscillation exhibited periods when the records oscillate in and out of phase thus reconstructing local and global atmospheric indices from wais divide accumulation records over recent centuries may prove problematic

occurrence frequency of thickness of annual snow accumulation layers at south pole this paper describes the frequency analysis of 2000 annual snow accumulation layers at the south pole it proposes application of this analysis to objective extraction of meteorological parameters from the south pole snow accumulation record we have compared the 200 year snow mine accumulation record of giovinetto and schwerdtfeger and a 2000 layer pit and core record obtained in 1982 frequency analysis of the number of occurrences of layers with respect to thickness or mass of the layer showed the logarithms of thickness or mass to be normally distributed this lognormality is quite robust arbitrary partitioning of the data by depth or systematic partition of the data by densification or firn ice transition does not destroy the lognormality of the accumulation series the geometric standard deviation of the mass of annual layers was the same as the geometric standard deviation of the thickness of these same layers as the layers densified from firn to ice this agrees with kapteyn s theory of transformability of lognormal distributions we have also compared the snow accumulation and marine aerosol sodium accumulation in recent annual layers with the station meteorological record and the surface aerosol record the amounts of snow and sodium accumulated are proportional to the number of warmings salt storms in most years of this short record the accumulation record may be transformable to provide an index of this meridional transport we propose that the magnitude of snow accumulation with respect to frequency of that accumulation provides an objective criterion for comparing individual years of meteorological history and that the geometric standard deviation of accumulation provides an objective index for estimation of climatic fluctuation during the period of accumulation

model based constraints on interpreting 20th century trends in ice core 10be 1 beryllium 10 ice core records are useful for understanding solar magnetic field changes over time and in particular over the 20th century during which there are a variety of relevant observations however differences between 10be snow concentration records from different locations complicate the process of developing a coherent understanding of changes in cosmogenic isotope production we use the goddard institute for space studies modele general circulation model to simulate the production and transport of beryllium isotopes for this time period we compare our results with surface air observations and with ice core records from dye 3 taylor dome and south pole we find that unforced weather related internal variability causes modeled trends in 10be snow concentration to vary from the ensemble mean by 50 and greater at all three ice core locations lower levels of internal variability at taylor dome and south pole relative to dye 3 make the simulated 10be values at these locations better estimates of the ensemble mean trend in 10be snow concentration in addition the ensemble mean concentration trend at dye 3 was significantly different from the expected modeled trend based on applied production changes alone overall the results imply that during the 20th century 10be data from multiple cores are likely to be required to make meaningful inferences about 10be production changes the model simulations imply that data from antarctica are likely to be more robust

topographic control of regional accumulation rate variability at south pole and implications for ice core interpretation snow accumulation rates are known to be sensitive to local changes in ice sheet surface slope because of the effect of katabatic winds these topographic effects can be preserved in ice cores that are collected at non ice divide locations the trajectory of an ice core site at south pole is reconstructed using measurements of ice sheet motion to show that snow was probably deposited at places of different surface slope during the past 1000 years recent accumulation rates derived from shallow firn cores vary along this trajectory according to surface topography so that on a relatively steep flank mean annual accumulation is 18 smaller than on a nearby topographic depression these modern accumulation rates are used to reinterpret the cause of accumulation rate variability with time in the long ice core record as an ice dynamics effect and not a climate change signal the results highlight the importance of conducting ancillary ice dynamics measurements as part of ice coring programs so that topographic effects can be deconvolved from potential climate signals

can high temperature high heat flux hydrothermal vent fields be explained by thermal convection in the lower crust along fast spreading mid ocean ridges we present numerical models to explore possible couplings along the axis of fast spreading ridges between hydrothermal convection in the upper crust and magmatic flow in the lower crust in an end member category of models corresponding to effective viscosities m lower than 1013 pa s in a melt rich lower crustal along axis corridor and permeability k not exceeding 10 16 m2 in the upper crust the hot melt rich gabbroic lower crust convects as a viscous fluid with convection rolls parallel to the ridge axis in these models we show that the magmatic hydrothermal interface settles at realistic depths for fast ridges i e 1 2 km below seafloor convection cells in both horizons are strongly coupled and kilometer wide hydrothermal upflows plumes spaced by 8 10 km arise on top of the magmatic upflows such magmatic hydrothermal convective couplings may explain the distribution of vent fields along the east epr and south east pacific rise sepr the lower crustal plumes deliver melt locally at the top of the magmatic horizon possibly explaining the observed distribution of melt rich regions pockets in the axial melt lenses of epr and sepr crystallization of this melt provides the necessary latent heat to sustain permanent 100 mw vents fields our models also contribute to current discussions on how the lower crust forms at fast ridges they provide a possible mechanism for focused transport of melt rich crystal mushes from moho level to the axial melt lens where they further crystallize feed eruptions and are transported both along and off axis to produce the lower crust

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

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

an inter hemispheric volcanic time marker in ice cores from greenland and antarctica a strong volcanic acid signal is clearly registered using an acidity measuring technique in the a d 1259 ice layer in four different greenland ice cores camp century milcent crete and dye 3 this signal is similar in amplitude to the laki iceland a d 1783 volcanic event as recorded in the central and south greenland ice cores measurement of ice layers from corresponding age levels in antarctic ice cores byrd station south pole and j 9 on the ross ice shelf provides similar strong acid signals there is no historical record of a significant volcanic eruption for the period around a d 1260 in the northern hemisphere subsequent chemical analyses of all a d 1259 ice layers show similar compositions we suggest that the a d 1259 signals registered in both greenland and antarctica were caused by the same volcanic disturbance and that its epicenter was located at the earth s equatorial zone which enabled global distribution of the acid gases these results indicate that inter hemispheric dating of ice sheets is possible by the chemical identification of major eruptive volcanic events in the equatorial zone

accumulation at south pole comparison of two 900 year records two 900 year records of annual accumulation at south pole are compared to evalu ate the origin and significance of observed variations despite difficulties establishing absolute timescales due to problems identifying annual layer markers the two records can be correlated with confidence after moderate smoothing this correlation shows that over the time period considered 1050 1956 a d no climatically significant changes in accumulation occurred in stead fluctuations preserved in the two cores reflect spatial variations in snow accumulation as sociated with nonuniform deposition induced by surface relief on the scale of several kilometers

past precipitation rates derived from ice core measurements methods and data analysis ice cores in which annual layers can be identified or particular horizons dated provide a record of past precipitation rates if measured layer thicknesses can be corrected for thinning by flow since deposition total strain is usually calculated from steady state flow models because of lack of information about the ice cap s history an assumption of uniform vertical strain rate is valid at best in the upper half of the ice column complex models are needed to take account of uneven bedrock and variations in precipitation rate upstream of the borehole drilling at an ice divide avoids these complications new data analyses suggest that precipitation at camp century has fluctuated by only plus or minus 10 for the past 8500 years whereas at devon island on the opposite side of baffin bay precipitation has been uniform only for the past 1300 years with significantly higher values before that estimation of pre holocene precipitation rates is especially difficult because that ice may have an effective viscosity different from holocene ice three published estimates of pre holocene precipitation at camp century are unreliable the authors did not allow for thinning and their time scales differ appreciably data from three antarctic stations show some inconsistencies measuring concentrations of 10be in ice cores may be an alternative method of determining past precipitation rates

four climate cycles in vostok ice core author s petit jr basile i leruyuet a raynaud d lorius c jouzel j stievenard m lipenkov vy barkov ni kudryashov bb davis m saltzman e kotlyakov v