climate variables along a traverse line in dronning maud land east antarctica temperature density and accumulation data were obtained from shallow firn cores drilled during an overland traverse through a previously unknown part of dronning maud land east antarctica the traverse area is characterised by high mountains that obstruct the ice flow resulting in a sudden transition from the polar plateau to the coastal region the spatial variations of potential temperature near surface firn density and accumulation suggest that katabatic winds are active in this region proxy wind data derived from firn density profiles confirm that annual mean wind speed is strongly related to the magnitude of the surface slope the high elevation of the ice sheet south of the mountains makes for a dry cold climate in which mass loss owing to sublimation is small and erosion of snow by the wind has a potentially large impact on the surface mass balance a simple katabatic wind model is used to explain the variations of accumulation along the traverse line in terms of divergence convergence of the local transport of drifting snow the resulting wind and snowdrift patterns are closely connected to the topography of the ice sheet ridges are especially sensitive to erosion while ice streams and other depressions act as collectors of drifting snow

spatial and temporal variability of snow accumulation using ground penetrating radar and ice cores on a svalbard glacier a 50 mhz ground penetrating radar was used to detect horizontal layers in the snowpack along a longitudinal profile on nordenskjoldbreen a svalbard glacier the profile passed two shallow and one deep ice core sites two internal radar reflection layers were dated using parameters measured in the deep core radar travel times were converted to water equivalent yielding snow accumulation rates along the profile for three time periods 1986 99 1963 99 and 1963 86 the results show 40 60 spatial variability in snow accumulation over short distances along the profile the average annual accumulation rate for 1986 99 was found to be about 12 higher than for the period 1963 86 which indicates increased accumulation in the late 1980s and 1990s

a century of accumulation and temperature changes in dronning maud land antarctica a mass balance program was initiated in the vestfjella heimefrontfjella area of western dronning maud land during the austral summer of 1988 1989 as a part of this program spatial and temporal variations in snow accumulation and temperature stable isotopes are measured using shallow firn cores in this paper we present surface accumulation data and discuss the climatic implications of the stable isotope records from two shallow firn cores one 30 m deep core obtained about 200 km from the coast at 700 m asl 73 36 s 12 26 w covers the period 1932 1991 the other core was drilled at about 500 km from the coast at 2900 m asl 75 00 s 2 00 e and covers the period 1865 1991 the recent accumulation increase that has been reported from several areas of the antarctic continent is not present in either of these records instead our coastal record suggests a significant decrease in accumulation with the strongest trend from about 1975 there is a positive trend in the oxygen isotope signal in both cores which in the coastal core corresponds to a temperature increase of about 1 8 c since the early 1930s and in the high altitude core to about 0 8 c since 1865 however it is likely that part of this increase in 18o is due to a change of moisture source

spatial distribution of snow in western dronning maud land east antarctica mapped by a ground based snow radar spatial distribution of snow in western dronning maud land east antarctica mapped by a ground based snow radar

the impact of the eruptions of mount pinatubo and cerro hudson on antarctic aerosol levels during the 1991 austral spring at the beginning of 1991 austral spring volcanic aerosols from mt pinatubo and cerro hudson were present in the polar stratosphere of the southern hemisphere satellite observations of aerosol extinction were used to identify and track the movement of these aerosols in the vicinity of the antarctic vortex during august through november 1991 a layer of mature mt pinatubo aerosols was identified near 21 km and a layer of fresh cerro hudson aerosols was identified near 12 km this altitude separation of the mt pinatubo and cerro hudson aerosols was observed throughout the period below 15 km the polar stratosphere was subject to episodes of strong wave activity which transported the cerro hudson aerosols poleward and after the middle of september they became a persistent feature beneath the vortex above 15 km signatures of mt pinatubo aerosols were observed near the vortex boundary but significant portions of the vortex interior remained free of any detectable intrusions of mt pinatubo aerosols until the final warming in mid november 13 refs 4 figs

characteristics of accumulation around the epica deep drilling site in dronning maud land antarctica based on ground penetrating radar profiles we analyze area wide spatial and temporal characteristics of accumulation rate in the vicinity of the epica european project for ice coring in antarctica deep drilling site in dronning maud land antarctica edml an area of 1600 km 2 is covered by 500 km of radar profiles organized in a star like pattern with eight 20 25 km legs and a 10 km grid with 1 3 km spacing each pattern being centred on the edml drilling location distributions of density cumulative mass age and the electromagnetic wave speed with depth are available from physical ice core records nine internal reflection horizons are continuously tracked within the upper 110 m of ice over the whole area yielding a spatial picture of accumulation rate history over 1000 years the mean accumulation rate over the last 153 years varies between 50 and 75 kg m 2 a 1 over 50 km perpendicular to the ice divide the spatial average is 61 kg m 2 a 1 this general pattern is overlain by small scale variations of accumulation rate on the order of 10 of the mean maximum local gradients in accumulation rate are 2 3 kg m 2 a 1 km 1 about five times the regional accumu lation rate gradient comparison of topography and accumulation rate along a 20 km profile in the direction of the mean winds indicates that variations in accumulation rate over short distances are linked to surface undulations our results show that advected spatial variations of accumulation rate are on the same order and even exceed temporal changes over the investigated periods ice flow and upstream effects therefore might influence accumulation rates reconstructed from the edml ice core

mechanistic links between the sedimentary redox cycle and marine acid base chemistry the redox state of earth s surface is controlled on geological timescales by the flow of electrons through the sedimentary rock cycle mediated largely by the weathering and burial of c s fe phases these processes buffer atmospheric po at the same time co influxes and carbonate burial control seawater acid base chemistry and climate over long timescales via the carbonate silicate cycle however these two systems are mechanistically linked and impact each other via charge balance in the hydrosphere here we use a low order earth system model to interrogate a subset of these connections with a focus on changes that occur during perturbations to electron flow through the sedimentary rock cycle we show that the net oxidation or reduction of the earth s surface can play an important role in controlling acid base processes in the oceans and thus climate and suggest that these links should be more fully integrated into interpretive frameworks aimed at understanding earth system evolution throughout precambrian and phanerozoic time

mapping greenland accumulation rates using observations of thermal emission at 4 5 cm wavelength accurate predictions of sea level rise over the coming century will require improved knowledge of the processes controlling accumulation on the great ice sheets the sparsity of accumulation rate observations both temporally and spatially hinder development of this understanding we introduce a new method to observe accumulation rates averaged over roughly a decade using satellite observations of microwave emission at 4 5 cm wavelength focusing in this paper on greenland at this wavelength scattering by the grain fabric in firn is unimportant relative to quasi reflection from density and thus dielectric permittivity stratification we show observationally a strong link between random firn density stratification on scales of millimeters to centimeters and accumulation rate we then show theoretically how the observed density stratification can produce and is consistent with observations of polarization of 4 5 cm wavelength emission we employ observations from the scanning multichannel microwave radiometer smmr and previously published ground observations of accumulation rates in greenland to complete specification of the relationship between accumulation rate and polarization the relationship is sufficiently accurate to serve as a basis for mapping accumulation rate fields we compare our satellite derived maps with previously published maps based on syntheses of ground data we find broad agreement between the two types of maps though the satellite derived map indicates more strongly the importance of topography and prevailing weather patterns in determining detailed accumulation rate patterns finally we discuss possible refinements and the prospects for improved satellite derived maps based on a new generation of sensors about to be launched

propagation of big island eddies using satellite altimetry data we have observed a series of anticyclonic eddies as they form at the big island of hawaii and have tracked them as they move away from the island while similar eddies have been observed near the hawaiian islands in previous studies the fate of the anticyclonic eddies has previously been unclear the eddies that we observed initially propagated to the southwest but consistently changed propagation direction to the northwest later in their lifetimes this was intriguing to us as theoretically the decay of isolated anticyclonic eddies on a plane should cause them to continually move toward the southwest such isolated eddy dynamics are unable to account for the observed change to northwestward eddy propagation and the presence of the westward flowing north equatorial current turns out to be important to the big island eddy dynamics the eddies are not passively advected by the north equatorial current rather the mean flow changes the propagation characteristics of the eddies an existing theory that includes meridionally varying purely zonal mean flow is shown to account for the observed propagation of the big island eddies if the zonal variation of the mean flow is considered

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

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

distortion of isochronous layers in ice revealed by ground penetrating radar in addition to measuring ice sheet thickness ground penetrating radar can be used to delineate reflections in ice sheets1 2 3 these reflections are generally accepted to result from layers of isochronous deposition of snow and can reveal much about the dynamics of the ice flow here we present ground penetrating radar data from fletcher promontory antarctica which show arches and troughs in isochronous ice layers to a depth of 100 m we demonstrate that the origin of these features can be determined by their growth with depth and many features result from local anomalies in accumulation rate which can be correlated with the ice surface slope one arch appears to be the result of a local anomaly in vertical strain rate its proximity to the ice divide width and growth with depth indicate that this arch is one of a class of features postulated by raymond4 but not previously shown to exist in the field such a feature is an indication of the nonlinear rheology of ice and requires that palaeoclimate records from ice cores extracted from the vicinity of ice divides underlain by similar features should be specifically corrected for such effects on ice flow

greenland snow accumulation estimates from satellite radar scatterometer data data collected by the c band ers 2 wind scatterometer escat the ku band adeos 1 nasa scatterometer nscat and the ku band seawinds on quikscat qscat satellite instruments are used to illustrate spatiotemporal variability in snow accumulation on the greenland ice sheet microwave radar backscatter images of greenland are derived using the scatterometer image reconstruction sir method at 3 day intervals over the periods 1991 1998 and 1996 1997 for escat and nscat respectively the backscatter coefficient normalized to 40 incidence a and gradient in backscatter b in the range 20 60 are compared with historical snow accumulation data and recent measurements made in the program for arctic regional climate assessment parca shallow snow pits empirical relationships derived from these comparisons reveal different exponential relationships between c and ku band a values and dry snow zone mean annual accumulation q frequency difference images between overlapping scatterometer images suggest that c band data are more sensitive to snow layering and buried inhomogeneities whereas ku band data are more sensitive to volume scattering from recently accumulated snow direct comparisons between nscat b values and in situ q measurements show a linear relationship between ln q and b with a negative rank correlation of r 0 8 the root mean square residual in fitting regression line equation ln q 3 08 17 83b to the data is 0 05 m snow water equivalent this simple ku band empirical relationship is exploited to investigate decadal changes in dry snow zone accumulation between seasat 1978 and nscat 1996 additional comparisons between nscat and recent qscat 1999 data reveal significant upslope shifts in the dry snow line along the southwestern flank of the ice sheet recent acceleration in the increase in intensity of scattering is observed in the percolation zone suggesting increased melting between 2000 and 3000 m elevation in the southern half of the ice sheet

spatio temporal variability in volcanic sulphate deposition over the past 2 kyr in snow pits and firn cores from amundsenisen antarctica in the framework of the european project for ice coring in antarctica epica a comprehensive glaciological pre site survey has been carried out on amund senisen dronning maud land east antarctica in the past decade within this survey four intermediate depth ice cores and 13 snow pits were analyzed for their ionic compos ition and interpreted with respect to the spatial and temporal variability of volcanic sul phate deposition the comparison of the non sea salt nss sulphate peaks that are related to the well known eruptions of pinatubo and cerro hudson in ad1991 revealed sulphate depositions of comparable size 15 8 3 4 kg km 2 in 11 snow pits there is a tendency to higher annual concentrations for smaller snow accumulation rates the combination of seasonal sodium and annually resolved nss sulphate records allowed the establishment of a time scale derived by annual layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition using a robust outlier detection algo rithm 49 volcanic eruptions were identified between ad165 and 1997 the dating uncer tainty is 3 years between ad1997 and 1601 around 5 years between ad1601 and 1257 and increasing to 24 years at ad165 improving the accuracy of the volcanic chronology during the penultimate millennium considerably abstract in the framework of the european project for ice coring in antarctica epica a comprehensive glaciological pre site survey has been carried out on amund senisen dronning maud land east antarctica in the past decade within this survey four intermediate depth ice cores and 13 snow pits were analyzed for their ionic compos ition and interpreted with respect to the spatial and temporal variability of volcanic sul phate deposition the comparison of the non sea salt nss sulphate peaks that are related to the well known eruptions of pinatubo and cerro hudson in ad1991 revealed sulphate depositions of comparable size 15 8 3 4 kg km 2 in 11 snow pits there is a tendency to higher annual concentrations for smaller snow accumulation rates the combination of seasonal sodium and annually resolved nss sulphate records allowed the establishment of a time scale derived by annual layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition using a robust outlier detection algo rithm 49 volcanic eruptions were identified between ad165 and 1997 the dating uncer tainty is 3 years between ad1997 and 1601 around 5 years between ad1601 and 1257 and increasing to 24 years at ad165 improving the accuracy of the volcanic chronology during the penultimate millennium considerably

regional and temporal variation of accumulation around northgrip derived from ground penetrating radar during the summer of 2003 a ground penetrating radar survey around the north greenland icecore project northgrip deep ice core drilling site 75806 0 n 42820 0 w 2957 m a s l was carried out using a shielded 250 mhz radar system the drill site is located on an ice divide roughly 300 km north northwest of the summit of the greenland ice sheet more than 430 km of profiles were measured covering a 10 km by 10 km area with a grid centered on the drilling location and eight profiles extending beyond this grid seven internal horizons within the upper 120 m of the ice sheet were continuously tracked containing the last 400 years of accumulation history based on the age depth and density depth distribution of the deep core the internal layers have been dated and the regional and temporal distribution of accumulation rate in the vicinity of northgrip has been derived the distribution of accumulation shows a relatively smoothly increasing trend from east to west from 145 kg m 2 a 1 to 200 kg m 2 a 1 over a distance of 50 km across the ice divide the general trend is overlain by small scale variations on the order of 2 5 kg m 2 a 1 km 1 i e around 1 5 of the accumulation mean the temporal variations of the seven periods defined by the seven tracked isochrones are on the order of 4 of the mean of the last 400 years i e at northgrip 7k g m 2 a 1 if the regional accumulation pattern has been stable for the last several thousand years during the holocene and ice flow has been comparable to today advective effects along the particle trajectory upstream of northgrip do not have a significant effect on the interpretation of climatically induced changes in accumulation rates derived from the deep ice core over the last 10 kyr

snow megadunes in antarctica sedimentary structure and genesis 1 megadune fields occupy large areas in the interior of the east antarctic ice sheet and are the result of unusual snow accumulation and redistribution processes they therefore are important to surface mass balance and ice core interpretation field observations gps gpr and surface measurements have provided a detailed description of megadune sedimentation and morphology over a 70 km2 area located 200 km east of dome c a combination of remote sensing analysis using landsat and satellite radar altimetry and field measurements indicate that slope in the prevailing wind direction spwd and climatic conditions play a crucial role in megadune genesis the megadune areas tend to be characterized by slightly steeper regional slope and the presence of highly persistent katabatic winds the megadunes represent 2 to 4 m amplitude waves of 2 to 5 km wavelength formed by variable net accumulation ranging between 25 leeward faces to 120 windward faces of the accumulation in adjacent nonmegadune areas leeward faces are characterized by glazed sastrugi free surfaces and extensive depth hoar formation windward faces are covered by large rough sastrugi up to 1 5 m in height

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

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