surface and bed topography of trapridge glacier yukon territory canada digital elevation models and derived hydraulic geometry measurements of ice thickness and surface elevation are prerequisite to many glaci ological investigations a variety of techniques has been develo ped for inter pret ation of these data including means of constructing regularly gridded digital eleva tion models dem s for use in numcrical studies here we present a simple yet stati sti cally sound method for processing ice pe netr ating radar data and descr ibe a tech nique for interpol ating these data onto a regular grid dems generatcd fort rapridge glacier yukon territory canada are used to derive geometric quantities lhal give pre liminary insights into the underlying basin scale hydrol ogical syste m this simple geo metric analysis suggests that at low water press ures a dendrilic drainage netw ork exists that evolves into a uniaxial morphology as water pressure approaches notation these pre dictions are compared to hydraulic connection probabilities based on bore hole drilling

desert pavements and associated rock varnish in the mojave desert how old can they be desert pavements are common features of arid landscapes and have been widely used as a relative age indicator of the geomorphic surfaces upon which they are developed in this study i examined the patterns of pavement development as a function of elevation in the mojave desert as well as the causes for the gradual disappearance of pavement at high elevations pavement density as measured by percentage of pebble coverage decreases systematically with elevation gain by 3 per 100 m from 95 coverage below 500 m to less than 60 at 1700 m plants appear to be the main agent of pavement disruption plant density decreases as pavement density increases burrowing by rodents and crusting by cryptobiota also disrupt pavement development at higher elevation during the last glacial maximum plant communities were displaced 1000 1400 m downward in the mojave desert pavements today generally do not survive above the blackbush coleogyne ramossisma sagebrush artemisia tridentata zone evidence from packrat middens shows that these and other plants typical of high elevations today grew as low as 300 400 m during the last glacial maximum i suggest that during the last glacial maximum desert pavements were confined to the lowest alluvial fans of death valley and adjoining low valleys no alluvial desert pavements above 400 m in the region are older than the latest pleistocene by the same reasoning desert varnish on desert pavements above 400 m may all be holocene in age except where developed on stable boulders

modeling the radio echo reflections inside the ice sheet at summit greenland 1 radio echo surveys to determine the thickness of ice sheets often record reflections from inside the ice to increase our understanding of these internal reflections we have used synthetic seismogram techniques from early seismic modeling to construct two models both models were one dimensional the first considered only primary reflections while the second included both primary and multiple reflections the inputs to both models were a radio pulse and data from the greenland ice core project grip core of length 3028 m the ice core data consisted of a profile of the high frequency conductivity calculated from dielectric profile dep measurements and a smooth profile of the real permittivity the models produced synthetic radargrams which are the energy reflected from conductivity variations as a function of the two way travel time both models gave similar results indicating that multiples do not alter the travel time of the reflections i e no o doherty anstey effect at our time resolution one of the results was then processed to simulate the reflected energy passing through the receiver circuit of a radio echo system and then compared with a recorded trace the processed result contained many of the larger reflections recorded below about 500 m including nearly all the features from depths greater than 1500 m in particular several interstadial events in the wisconsin age ice since high frequency conductivity variations are dominated by chemical changes which are caused by deposition on the surface of the ice sheet it is possible to conclude that the reflections deep inside the greenland ice sheet can be treated as isochrons

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

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

anomalous accumulation rates in the vostok ice core resulting from ice flow over lake vostok the accumulation rate of snow is crucial to the development of accurate age depth models for ice cores the dating of the vostok ice core assumes that accumulation rates generally vary linearly between the core site and the ice divide 250 km to the west jouzel et al 1996 lorius et al 1985 petit et al 1999 an assumption which impacts the timing of prominent climatic transitions we present evidence for a local accumulation rate anomaly at the ice surface above the western shoreline of lake vostok a significant thickening between isochronous layers results from this geographically fixed high accumulation zone which can be stratigraphically traced to a depth of 820 1100 m in the vostok ice core a portion known for its high accumulation rates and paleoclimate records that deviate from other antarctic ice core records this non climatic accumulation anomaly in the vostok ice core impacts the flow dependent age models and subsequent interpretations of sequencing of global climate shifts during the last glacial additional unrecognized accumulation anomalies are likely present at other depths in this and other cores these previously unreported geographically fixed accumulation rate anomalies are introduced into ice cores drilled away from ice domes e g byrd and vostok and should be considered in age depth models

regional variations of porosity and cement st peter and mount simon sandstones in illinois basin petrographic study of over 230 thin sections of cuttings cores and outcrop samples from the ordovician st peter and cambrian mount simon sandstones of the craton center illinois basin yielded a series of maps that show a fairly regular distribution of primary and secondary porosity and cements both primary and secondary porosity are present in the st peter sandstone primary porosity is dominant from outcrop to 4 000 ft 1 219 m whereas secondary porosity is dominant at depths greater than 4 000 ft the overall porosity decline with burial is best described by an exponential equation phgr 30 8 exp 0 00032 d where phgr equals porosity and d is depth in feet however two linear equations provide the best fit of primary above 4 000 ft 1 219 m and secondary porosity below 4 000 ft the chronology of porosity development appears to be closely related to the models proposed by p j c nagtegaal and includes early cementation leaching of cement and framework stabilized framework and framework collapse cements in the st peter are depth dependent they define distinct regions are mappable and include calcite dolomite silica overgrowths chert and chalcedony virtually everywhere in the mount simon sandstone porosity is secondary and results from dissolution of authigenic and replacement cements framework grains and fractures in the subsurface porosity reaches a maximum of 18 at 5 000 ft 1 524 m and drops rather sharply to 8 below 5 000 ft as with the st peter sandstone the overall decline is best described by an exponential equation of the form phgr 31 08 exp 0 00026 d cements in the mount simon include quartz and feldspar overgrowths hematite and kaolinite carbonate chlorite and microquartz chert basinwide maps show that they have a fairly regular distribution pattern in the basin we suggest that in the future basinwide maps of cement and porosity types will be abundant such maps should enhance understanding of diagenesis especially where map pattern can be related to fluid and burial history maps of cements and porosity types can also aid the calibration of wireline logs help find diagenetic traps and help the design of drilling fluid systems and well completion procedures the routine use of cuttings rather than cores will hasten the advent of such maps

climate dependent contrast in surface mass balance in east antarctica over the past 216 ka documenting past changes in the east antarctic surface mass balance is important to improve ice core chronologies and to constrain the ice sheet contribution to global mean sea level change here we reconstruct past changes in the ratio of surface mass balance smb ratio between the epica dome c edc and dome fuji df east antarctica ice core sites based on a precise volcanic synchronization of the two ice cores and on corrections for the vertical thinning of layers during the past 216 000 a this smb ratio denoted smb edc smb df varied between 0 7 and 1 1 being small during cold periods and large during warm periods our results therefore reveal larger amplitudes of changes in smb at edc compared with df consistent with previous results showing larger amplitudes of changes in water stable isotopes and estimated surface temperature at edc compared with df within the last glacial inception marine isotope stages mis 5c and mis 5d the smb ratio deviates by up to 0 2 from what is expected based on differences in water stable isotope records moreover the smb ratio is constant throughout the late parts of the current and last interglacial periods despite contrasting isotopic trends

how fast does rock varnish grow rates of rock varnish accumulation have never been systematically documented owing to the difficulty in accurately determining both varnish thickness and age in this study we quantitatively assess varnish accumulation rates through thin sectioning and microscopic examination of rock varnish from radiometrically dated geomorphic features of late quaternary age in the western united states drylands our data indicate that rock varnish grows at rates ranging from 1 to 40 m k y on subaerially exposed rock surfaces and rarely reaches a thickness exceeding 200 m regardless of age our data also indicate that varnish accumulation rates vary greatly from sample to sample at a given site suggesting that varnish thickness does not correlate with the age of the associated geomorphic feature invalidating the potential use of varnish thickness as a relative age indicator in geomorphology and archaeology nevertheless being the slowest known accumulating terrestrial sedimentary deposit rock varnish constitutes a unique long term microscale sedimentary archive of past environmental changes in deserts

a time marker at 17 5 kyr bp detected throughout west antarctica deep radar soundings as part of the international trans antarctic scientific expedition us itase traverses in west antarctica have revealed a bright internal reflector that we have imaged throughout widespread locations across the ice sheet the layer is seen in traverses emanating from byrd station in four directions and has been traced continuously for distances of 535 km toward the weddell sea drainage 500 km toward south pole 150 km toward the executive committee range and 160 km toward kamb ice stream former ice stream c the approximate area encompassed by the layer identified in these studies is 250 000 km 2 if the layer identification can also be extended to siple dome where we have additional radar soundings jacobel and others 2000 the approximate area covered would increase by 50 in many locations echo strength from the layer rivals the bed echo in amplitude even though it generally lies at a depth greater than half the ice thickness at byrd station where the layer depth is 1260 m an age of 17 5 kyr bp has been assigned based on the blunier and brook 2001 chronology hammer and others 1997 note that the acidity at this depth is 20 times the amplitude of any other part of the core the depiction of this strong and widespread dated isochrone provides a unique time marker for much of the ice in west antarctica we apply a layer tracing technique to infer the depth time scale at the inland west antarctic ice sheet divide and use this in a simple model to estimate the average accumulation rate

a 220 year continuous record of volcanic h2so4 in the antarctic ice sheet continuous h2so4 profiles observed in snow from several antarctic locations reveal four major volcanic events of the past two centuries agung krakatoa tambora and another large scale event not recorded historically acid deposition and interhemispheric distribution mechanisms are quantified and then used to obtain an order of magnitude estimate for the h2so4 emissions from these eruptions

sulfate oxygen 17 anomaly in an oligocene ash bed in mid north america was it the dry fogs 1 the oxygen and sulfur isotope compositions of sulfate particularly the oxygen 17 anomaly provide clues to the origin of sulfate we report a variable oxygen 17 anomaly for water and acid leached sulfate from an oligocene volcanic ash bed in the northern high plains u s a we find no sulfate o 17 anomaly however in freshly collected ashes from recent eruptions around the world the oligocene paleoclimatic and sedimentary evidence argues against a hyperarid condition in the high plains thus a long term background atmospheric sulfate accumulation is less likely the origin combining sulfur isotope data we suggest that the anomalous sulfate was associated with volcanic eruptions in the west but was not directly carried by ash falls extreme dry fog sulfate haze events resulting from tropospheric oxidation of volcanic sulfur gases might provide a viable explanation for the sulfates in the ash bed that carry the oxygen 17 anomaly

multidecadal observations of the antarctic ice sheet from restored analog radar records airborne radar sounding can measure conditions within and beneath polar ice sheets in antarctica most digital radar sounding data have been collected in the last 2 decades limiting our ability to understand processes that govern longer term ice sheet behavior here we demonstrate how analog radar data collected over 40 y ago in antarctica can be combined with modern records to quantify multidecadal changes specifically we digitize over 400 000 line kilometers of exploratory antarctic radar data originally recorded on 35 mm optical film between 1971 and 1979 we leverage the increased geometric and radiometric resolution of our digitization process to show how these data can be used to identify and investigate hydrologic geologic and topographic features beneath and within the ice sheet to highlight their scientific potential we compare the digitized data with contemporary radar measurements to reveal that the remnant eastern ice shelf of thwaites glacier in west antarctica had thinned between 10 and 33 between 1978 and 2009 we also release the collection of scanned radargrams in their entirety in a persistent public archive along with updated geolocation data for a subset of the data that reduces the mean positioning error from 5 to 2 5 km together these data represent a unique and renewed extensive multidecadal historical baseline critical for observing and modeling ice sheet change on societally relevant timescales

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

res signatures of ice bottom near to dome c antarctica geophysical surveys have played a fundamental role in glaciology climatology and geology studies conducted at and around the site of the epica dome c ice core antarctica analysis of radio echo sounding res data collected during the 2009 and 2011 italian antarctic expeditions in the immediate vicinity 2 km of the core site reveals the presence of small scale bedrock structures data acquired during the 2011 campaign which applied the latest updates of our instrument show double echoes from the ice bottom separated by very small time intervals these reflections are distributed close to the topographic dome and do not always correspond to particular features of the bedrock structure but instead may correspond to small scale subglacial water storage the unprecedented spatial resolution of the basal environment for dome c from these recent surveys allows us to identify this and other features that have been missed by previous larger scale res surveys of this area

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

multiple oxygen and sulfur isotopic analyses on water soluble sulfate in bulk atmospheric deposition from the southwestern united states 1 sulfate is a major component of bulk atmospheric deposition including dust aerosol fog and rain we analyzed sulfur and oxygen isotopic compositions of water soluble sulfate from 40 sites where year round dust traps collect bulk atmospheric deposition in the southwestern united states average sulfur and oxygen isotopic compositions 34s and 18o are 5 8 1 4 cdt and 11 2 1 9 smow n 47 respectively samples have an oxygen 17 anomaly 17o with an average value of 1 0 0 6 except for a weak positive correlation between 18o and 17o values r2 0 4 no correlation exists for 18o versus 34s 17o versus 34s or any of the three isotopic compositions versus elevation of the sample site exceptional positive 17o values up to 4 23 are found in samples from sites in the vicinity of large cities or major highways and near zero 17o values are found in samples close to dry lakes comparison of isotopic values of dust trap sulfate and desert varnish sulfate from the region reveals that varnish sulfate has average isotopic values that are 4 8 lower for 18o 2 1 higher for 34s and 0 3 lower for 17o than those of the present day bulk deposition sulfate although other factors could cause the disparity this observation suggests a possibility that varnish sulfate may have recorded a long term atmospheric sulfate deposition during the holocene or pleistocene as well as the differences between sulfur and oxygen isotopic compositions of the preindustrial bulk deposition sulfate and those of the industrial era

radar imaging of glaciovolcanic stratigraphy mount wrangell caldera alaska interpretation model and results glaciological measurements and an airborne radar sounding survey of the glacier lying in mount wrangell caldera raise many questions concerning the glacier thermal regime and volcanic history of mount wrangell an interpretation model has been developed that allows the depth variation of temperature heat flux pressure density ice velocity depositional age and thermal and dielectric properties to be calculated some predictions of the interpretation model are that the basal ice melting rate is 0 64m yr 1 and the volcanic heat flux is 7 0 w m 2 by using the interpretation model to calculate two way travel time and propagation losses radar sounding traces can be transformed to give estimates of the variation of power reflection coefficient as a function of depth and depositional age prominent internal reflecting zones are located at depths of approximately 59 91 m 150 m 203 m and 230 m we attribute these internal reflectors to buried horizons of acidic ice possibly intermixed with volcanic ash that were deposited during past eruptions of mount wrangell the depositional dates corresponding to these reflecting zones are 1950 1924 1853 1770 and 1728 a d and we use this information to propose a volcanic history for mount wrangell

decoding ice sheet behavior using englacial layer slopes the complex flow fields of the antarctic and greenland ice sheets deform layers deposited as snow at the ice sheet surface leaving a record of the regional flow history and or local transitions in basal boundary conditions within the geometry of ice sheet layers ice penetrating radar reveals these layers but interpretations are limited by the challenges of quantitatively and reproducibly comparing observations with model output we present a conceptual framework that relates along track reflector slope to gradients in the steady state velocity field of ice sheets this method makes effective use of englacial reflectors in regions where it is challenging to image continuous layers and avoids the error propagation inherent to tracer transport methods developing the potential for formal radar data assimilation in future modeling studies we apply our method to radar data collected at the grounding line of whillans ice stream where enhanced bed friction produces characteristic reflector slopes reproducible using a higher order ice flow model

source and genesis of sulphate and phosphate sulphate minerals in a quartz sandstone cave environment gypsum caso4 2h2o alunite kal3 so4 2 oh 6 and rare phosphate sulphate sanjuanite al2 po4 so4 oh 9 h2o and rossiantonite al3 po4 so4 2 oh 2 h2o 14 have recently been identified as secondary mineral deposits in different quartz sandstone caves in the gran sabana region venezuela due to the extended time scale required for speleogenesis in the hard and barely soluble quartz sandstone lithology these caves are considered to be as old as 20 to 30 my the study of these peculiar secondary mineral deposits potentially reveals important insights for understanding the interaction between deep superficial and atmospheric processes over thousands to perhaps millions of years in this study chemical and petrographic analyses of potential host rock sources sulphur and oxygen isotope ratios and meteorological hydrological and geographical data are used to investigate the origin of sulphates and phospho sulphates the results suggest that the deposition of sulphates in these caves is not linked to the quartz sandstone host rock rather these mineral deposits originate from an external atmospheric sulphate source with potential contributions of marine non sea salt sulphates terrestrial dimethyl sulphide and microbially reduced h2s from the forests or peatbogs within the watershed air currents within the caves are the most plausible means of transport for aerosols driving the accumulation of sulphates and other secondary minerals in specific locations moreover the studied sulphate minerals often co occur with silica speleothems of biological origin although this association would suggest a possible biogenic origin for the sulphates as well direct evidence proving that microbes are involved in their formation is absent nonetheless this study demonstrates that these quartz sandstone caves accumulate and preserve allogenic sulphates playing a yet unrecognized role in the sulphur cycle of tropical environments

thermal convection in ice sheets we look but do not see un critere de rayleigh generalise de la convection thermique dans les solides polycristallins chauffes par en dessous a ete developpe et applique a la convection dans les calottes glaciaires une analyse du profil de temperature a l aval du forage de byrd station suggere qu environ mille metres de glace en dessous du point d inversion de la densite entretiendrait la convection

cause and implications of rock varnish microchemical laminations rock varnish is a dark coating composed mostly of clays and manganese and iron oxides1 that accretes on rock surfaces in all terrestrial environments2 perry and adams3 first observed micron scale manganese rich and manganese poor relatively iron rich layers in varnish and proposed that these may be related to unspecified environmental changes electron microprobe analyses reported here suggest that mn fe ratios vary systematically with depth in varnishes on k ar dated volcanic rocks from the coso and cima volcanic fields eastern california and on talus flatirons in the negev desert israel these microchemical laminations probably reflect past fluctuations in the level of aeolian alkalinity and possibly climatic change this new indicator of terrestrial environmental change may be of importance to research on geomorphology archaeology palaeoclimatology and quaternary studies in arid environments

internal structure of the ice sheet between kohnen station and dome fuji antarctica revealed by airborne radio echo sounding this study aims to demonstrate that deep ice cores can be synchronized using internal horizons in the ice between the drill sites revealed by airborne radio echo sounding res over a distance of 1000 km despite significant variations in glaciological parameters such as accumulation rate between the sites in 2002 03 a profile between the kohnen station and dome fuji deep ice core drill sites antarctica was completed using airborne res the survey reveals several continuous internal horizons in the res section over a length of 1217 km the layers allow direct comparison of the deep ice cores drilled at the two stations in particular the counterpart of a visible layer observed in the kohnen station edml ice core at 1054 m depth has been identified in the dome fuji ice core at 575 m depth using internal res horizons thus the two ice cores can be synchronized i e the ice at 1560 m depth at the bottom of the 2003 edml drilling is 49 ka old according to the dome fuji age depth scale using the traced internal layers presented in this study

a comparison of radio echo sounding data and electrical conductivity of the grip ice core the depth of reflecting layers in arctic ice sheets has been determined by electromagnetic echo sounding using a varying distance between transmitter and receiver to determine the radar wave velocity the depth of the radar reflecting layers is compared with a profile of electrical conductivity measurements ecms from the greenland ice core project grip ice core in order to determine the velocity of the radar waves in the ice cap by using several reflecting layers it is possible to isolate the firn correction of the wave velocity and to estimate the accuracy of the calculated electromagnetic wave velocity the measured firn correction is compared with the correction calculated from the density profile and a comparison between the depth profiles of ecm and radar based on the corrected electromagnetic wave velocity is presented this profile shows that acid layers which originate from major volcanic eruptions show up as reflecting radar horizons

sulfate oxygen 17 anomalies in desert varnishes rock varnishes are ubiquitous in arid regions on earth and are believed to be commonly present on mars here we report high water soluble sulfate and nitrate contents in desert varnishes from the death valley region of southwestern u s a and that sulfate in varnishes possess 17o 18o ratios that do not fall on terrestrial mass dependent fractionation line sulfate from wet and dry atmospheric deposition is probably the source of the 17o anomalies the anomalies are only moderately lower than that of aerosol sulfates collected from the greater los angeles area indicating probably more than half of the sulfate in desert varnish is supplied by atmospheric deposition this finding suggests that earth surface environments are constantly accumulating 17o anomalous sulfate from the atmosphere arid and stable conditions facilitate the preservation of these atmospheric signatures this finding also indicates that different 17o 18o ratios found in different components in the martian meteorites may result from atmospheric chemical processes

note on the maximum upward migration of pore water in response to sediment compaction abstract a simplified model of compaction shows the maximum vertical upward pore water migration that can be expected as a result of sediment compaction this occurs when overpressuring lateral escape or fault related flow are absent in such a model the water that is expelled from a given sedimentary layer must be accommodated in the overlying layer s both sediment and water move downward with respect to the water sediment interface water however migrates downward at a slower pace than the sediment and hence appears to be expelled upward relative to a given sedimentary horizon burial history diagrams provide a convenient means of representing the time depth evolution of 1 sedimentary layers and 2 selected levels of water contained in the sediment above basement two major points are revealed by this approach firstly water generally does not escape a basin undergoing deposition however water can escape a basin through the water sediment interface when a thick layer of mud is blanketed by a thin sandy unit secondly a significant portion of a given sedimentary basin as modelled is saturated with water that was incorporated into it with its oldest sediments

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

deep radiostratigraphy of the east antarctic plateau connecting the dome c and vostok ice core sites several airborne radar sounding surveys are used to trace internal reflections around the european project for ice coring in antarctica dome c and vostok ice core sites thirteen reflections spanning the last two glacial cycles are traced within 200 km of dome c a promising region for million year old ice using the university of texas institute for geophysics high capacity radar sounder this provides a dated stratigraphy to 2318 m depth at dome c reflection age uncertainties are calculated from the radar range precision and signal to noise ratio of the internal reflections the radar stratigraphy matches well with the multichannel coherent radar depth sounder mcords radar stratigraphy obtained independently we show that radar sounding enables the extension of ice core ages through the ice sheet with an additional radar related age uncertainty of approximately 1 3 1 2 that of the ice cores reflections are extended along the byrd totten glacier divide using university of texas technical university of denmark and mcords surveys however core to core connection is impeded by pervasive aeolian terranes and lake vostok s influence on reflection geometry poor radar connection of the two ice cores is attributed to these effects and suboptimal survey design in affected areas we demonstrate that while ice sheet internal radar reflections are generally isochronal and can be mapped over large distances careful survey planning is necessary to extend ice core chronologies to distant regions of the east antarctic ice sheet

anomalous 17o compositions in massive sulphate deposits on the earth the variation of 18o that results from nearly all physical biological and chemical processes on the earth is approximately twice as large as the variation of 17o this so called mass dependent fractionation is well documented in terrestrial minerals1 2 evidence for mass independent fractionation 17o 17o 0 52 18o where deviation from this tight relationship occurs has so far been found only in meteoritic material and a few terrestrial atmospheric substances3 in the rock record it is thought that oxygen isotopes have followed a mass dependent relationship for at least the past 3 7 billion years ref 4 and no exception to this has been encountered for terrestrial solids5 here however we report oxygen isotope values of two massive sulphate mineral deposits which formed in surface environments on the earth but show large isotopic anomalies 17o up to 4 6 these massive sulphate deposits are gypcretes from the central namib desert and the sulphate bearing miocene volcanic ash beds in north america the source of this isotope anomaly might be related to sulphur oxidation reactions in the atmosphere and therefore enable tracing of such oxidation these findings also support the possibility of a chemical origin of variable isotope anomalies on other planets such as mars6

a chronology for the dome c deep ice core site through radio echo layer correlation with the vostok ice core antarctica ice at the new dome c drill site is correlated directly with the vostok ice core record using internal radio echo layering in the antarctic ice sheet layering observed on 60 mhz radar records at ice depths greater than 1000 m is a result of electro magnetic wave reflections from acidic ice layers formed it is assumed by volcanic eruption derived aerosols these acidic layers represent isochronous surfaces within the ice sheet we are able to trace five prominent layers for over 500 km across the antarctic ice sheet between vostok and the new ice core site at dome c this correlates the stratigraphy and depth age relationship between the two sites the thickness of ice deposited over the last glacial cycle 120 000 years at dome c is 300 m greater than at vostok and at comparable depths the ice at dome c is between about 10 000 and 25 000 years younger than at vostok

a framework for attenuation method selection evaluated with ice penetrating radar data at south pole lake all radar power interpretations require a correction for attenuative losses moreover radar attenuation is a proxy for ice column properties such as temperature and chemistry prior studies use either paired thermodynamic and conductivity models or the radar data themselves to calculate attenuation but there is no standard method to do so and before now there has been no robust methodological comparison here we develop a framework meant to guide the implementation of empirical attenuation methods based on survey design and regional glaciological conditions we divide the methods into the three main groups 1 those that infer attenuation from a single reflector across many traces 2 those that infer attenuation from multiple reflectors within one trace and 3 those that infer attenuation by contrasting the measured power from primary and secondary reflections to assess our framework we introduce a new ground based radar survey from south pole lake comparing selected empirical methods to the expected attenuation from a temperature and chemistry dependent arrhenius model based on the small surveyed area lack of a sufficient calibration surface and low reflector relief the attenuation methods that use multiple reflectors are most suitable at south pole lake

multiple oxygen 16o 17o and 18o and sulfur 32s 33s 34s and 36s isotope signatures of the dissolved sulfate from deception island antarctic peninsula implications on sulfate formation transportation and deposition in the antarctic region abstract oxygen 16 o 17 o and 18 o and sulfur 32 s 33 s 34 s and 36 s isotope ratios of and major ion na ca 2 cl no 3 and so 4 2 concentrations in lakes ponds and creeks from deception island antarctic peninsula were analyzed to study the sources of sulfate its oxidation and the surficial processes of the dissolved sulfate the positive relationship between the 34 s sulfate 8 1 to 17 3 and the cl so 4 2 molar ratio suggests mixing of sulfate from atmospheric deposition and from oxidation of sulfide minerals the average sea salt fraction 28 and 34 s nss values from 5 6 to 15 9 indicate that a combination of sea salt and marine biogenic sulfide provide the high 34 s end member of the dissolved sulfates the relatively low 18 o sulfate from 4 6 to 0 7 of deception island water suggests a role of local water in the formation of sulfate slightly negative but mass dependent 17 o sulfate values imply that atmospheric oxidation by o 3 and h 2 o 2 are negligible while these values might suggest a significant role of oxidation by molecular oxygen and oh the distinctly low 34 s sulfate value of two samples dcw 2 and dcw 3 suggests the input of sulfate from sulfide oxidation slight elevation of 34 s sulfate values up to 17 3 compared to a typical atmospheric value indicates a minimal role for dissimilatory microbial sulfate reduction of deception island water and sediments both 33 s sulfate and 36 s sulfate values are homogeneous and near zero implying that the dominant atmospheric oxidation process is tropospheric and that there are minimal to no contributions of stratospheric sulfate to deception island water

a comparison of deep antarctic ice cores and their implications for climate between 65 000 and 15 000 years ago abstract three ice cores drilled in the central part of the antarctic continent extend back to the last glacial period one from west antarctica byrd and two from east antarctica vostok and dome c this period is also partly covered by a few cores from the coastal areas in these cores climatic information is mostly derived from the isotopic profiles d or 18 o from which surface temperature and more indirectly precipitation rate can be estimated the main objective has been to compare thoroughly the three deep ice cores for the main part of the last glacial period from ca 65 000 15 000 yr b p the time scales have been examined in detail and a new 40 000 yr chronology for the dome c core adopted special emphasis is placed on the link between the concentration of 10 be and past accumulation changes and on the use of peaks in the concentration of this cosmogenic isotope as stratigraphic markers elevation changes of the ice sheet derived from gas content and isotopic data bear directly on interpretations of past temperature and precipitation rate changes

internal ice sheet radar layer profiles and their relation to reflection mechanisms between dome c and the transantarctic mountains causes of ice sheet layering at ice depths greater than about 900 m in a transect between dome c and the transantarctic mountains are examined using 60 mhz radar data collected in the 1970s by the u k u s danish collaboration normally a dual frequency technique is required for accurate determination of internal reflection mechanisms however by extracting the depth related features of 60 mhz radar profiles and comparing them with the dual frequency data collected by the japanese antarctic research expedition we have identified a simple method to estimate internal reflection mechanisms two zones can be distinguished 1 the c a zone where change in electrical conductivity due to variation in acidity is the major cause of internal reflection and 2 the p cof zone where change in dielectric permittivity due to crystal orientation fabrics is the major cause of internal reflections our analysis shows that the radar data reveal the development of p cof zones in regions where large amounts of ice shearing are expected this analysis shows how a similar interpretation of the full radar data archive may reveal information on internal reflection mechanisms across a large part of the east antarctic ice sheet

significance of secondary porosity in interpreting sandstone composition secondary porosity resulting from dissolution of unstable framework grains such as feldspar and rock fragments including chert is common in sandstones extensive dissolution of framework grains may result in misinterpreting the original composition of a sandstone and hence in misinterpreting its provenance to avoid these problems secondary porosity caused by grain dissolution must be recognized sandstone composition may be properly evaluated by including the dissolved portion of a framework grain as a grain rather than as porosity while point counting this should be useful in interpreting original composition of sandstones and in paleogeographic reconstruction of prospect areas

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

recent glacier variations and volcanic eruptions the injection of volcanic dust and gases into the atmosphere during major eruptions has been advanced to explain short term variations of climate1 4 a calculated global cooling of 1k during episodes of intense volcanic activity3 could lead to a snowline depression sufficient to cause glacier advances equivalent to those of the last several centuries the hypothesis would therefore be strengthened if a close relationship could be demonstrated between global volcanicity and the pattern of recent glacier variations glacier activity in the northern hemisphere during much of the past 100 yr shows a lack of synchrony with that in the southern hemisphere but in each hemisphere the sequence of glacier variations matches the acidity record in polar ice cores and the frequency of volcanic eruptions in successive latitude belts this suggests that glaciers fluctuate in response to atmospheric build up of volcanic aerosols produced during large eruptions and that explosive volcanism may therefore be a major factor in modulating climate on the decadal scale

microparticle concentration variations linked with climatic change evidence from polar ice cores the microparticle concentrations in three deep ice cores reveal a substantial increase in the concentration of insoluble particles in the global atmosphere during the latter part of the last major glaciation the ratio of the average particle concentration in the late glacial strata to that in the holocene strata is 6 1 for the core from dome c antarctica 3 1 for the core from byrd station antarctica and 12 1 for the core from camp century greenland whether this temporal correlation between increased atmospheric particle load and the lower surface temperatures is directly causal is unknown however the variations in these two parameters must be satisfactorily resolved in any successful hypothesis that addresses the causes of climatic change

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

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

improved method to determine radio echo sounding reflector depths from ice core profiles of permittivity and conductivity we present a technique that modifies and extends down hole target methods to provide absolute measures of uncertainty in radar reflector depth of origin we use ice core profiles to model wave propagation and reflection and then cross correlate the model results with radio echo sounding res data to identify the depth of reflector events stacked traces recorded with res near the epica drill site in dronning maud land antarctica provide reference radargrams and dielectric properties along the deep ice core form the input data to a forward model of wave propagation that produces synthetic radargrams cross correlations between synthetic and res radargrams identify differences in propagation wave speed they are attributed to uncertainties in pure ice permittivity and are used for calibration removing conductivity peaks results in the disappearance of related synthetic reflections and enables the unambiguous relation of electric signatures to res features we find that i density measurements with attenuation or dielectric profiling are too noisy below the firn ice transition to allow clear identification of reflections ii single conductivity peaks less than 0 5 m wide cause the majority of prominent reflections beyond a travel time of about 10 s 900 m depth and iii some closely spaced conductivity peaks within a range of 1 2m cannot be resolved within the res or synthetic data our results provide a depth accuracy to allow synchronization of age depth profiles of ice cores by res modeling of isochronous internal structures and determination of wave speed and of pure ice properties the technique successfully operates with dielectric profiling and electrical conductivity measurements suggesting that it can be applied at other ice cores and drill sites

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

evidence for a large surface ablation zone in central east antarctica during the last ice age abstract internal isochronous ice sheet layers recorded by airborne ice penetrating radar were measured along an ice flowline across a large 1 km high subglacial hill in the foreground of the transantarctic mountains the layers dated through an existing stratigraphic link with the vostok ice core converge with the ice surface as ice flows over the hill without noticeable change to their separation with each other or the ice base a two dimensional ice flow model that calculates isochrons and particle flowpaths and accounts for ice flow over the hill under steady state conditions requires net ablation via sublimation over the stoss face for the predicted isochrons to match the measured internal layers satellite remote sensing data show no sign of exposed ancient ice at this site however given the lack of exposed glacial ice surface balance conditions must have changed recently from the net ablation that is predicted at this site for the last 85 000 years to accumulation

east antarctic ice core sulfur isotope measurements over a complete glacial interglacial cycle 1 both sulfur and oxygen isotopes of sulfate preserved in ice cores from greenland and antarctica have provided information on the relative sources of sulfate in the ice and their chemical transformation pathways in the atmosphere over various time periods the mass independent fractionation in the oxygen isotopes of sulfate from the vostok ice core from east antarctica suggests that gas phase oxidation by the hydroxyl radical oh was relatively greater than aqueous phase oxidation by o3 and h2o2 during the last glacial period than during the eemian and preindustrial holocene the complete sulfur isotopic composition 33s 34s 36s from the same vostok ice core samples along with 34s measurements from the dome c east antarctic ice core from this study lend support to these conclusions and reveal significant isotopic fractionation of 34s during chemical transformation and transport to east antarctica these findings reveal that conservation of sulfur isotopic signatures upon transport cannot be assumed for the east antarctic plateau over the time periods considered

electrical resistivity of ice from the antarctic peninsula antarctica l objectif etait de determiner le comportement electrique de la glace dans une zone ou existe une fonte estivale substantielle ainsi que des regimes thermiques contrastes des mesures electriques effectuees en trois sites le long d une ligne de courant sur le george vi ice shelf montrent que a la resistivite de la glace en profondeur est semblable a celle des autres shelfs antarctiques b la resistivite de la glace a la surface de la glace du shelf qui est soumise a la percolation et au regel de l eau de fusion est semblable a celle de la glace en profondeur et donc la glace a un caractere polaire

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

different sulfate sources and their post depositional migration in atacama soils abstract sulfate is one of the major salts accumulated in the hyperarid atacama desert chile its origin has been attributed to local weathering volcanic source sea salt and atmosphere deposition previous studies concluded that atmospheric sulfate is present in the desert but this term was poorly defined in terms of chemical origin and its contribution to the total sulfate budget in soil is debated the contribution of each potential sulfate source is expected to vary geographically due to different source locations efforts to quantify the contribution from each source have been hampered by the lack of well defined isotopic compositions for its end members in this study we discard the vague term of atmospheric sulfate by recognizing two major sulfate sources on the basis of their formation pathways primary and secondary sulfate primary sulfate including those from rock weathering sea salt and volcanic ash leachates do not have an 17o anomaly secondary sulfate derived from the oxidation of reduced sulfur gases biological or volcanic emissions by atmospheric ozone or hydrogen peroxide however has an 17o anomaly we developed a method to extract water soluble anions sequentially or entirely from bulk soil samples and analyzed the sulfate concentrations and 17o anomalies for four geographically representative soil profiles in the central atacama desert 23 s to 25 5 s we found that sequential sulfate extractions on the same soil sample produce sulfate with decreasing 17o values except for a positive bulge at 20 to 50 cm in depth there is a general increase in the 17o value for total sulfate with soil depth for all the four soil profiles that we examined these findings are consistent with the hypothesis that secondary sulfates 17o anomalous sulfates are more soluble and thus preferentially leached in liquid water than primary sulfate the finding also warns that incomplete sulfate extraction from sulfate rich soils yields unpredictable results we infer a 17o value of 4 6 for secondary sulfate based on data from partial sulfate extraction experiments total contribution of secondary sulfate in the central atacama desert is estimated to range from 9 to 24 with the highest percentage in the central depression

determining basal ice sheet conditions in the dome c region of east antarctica using satellite radar altimetry and airborne radio echo sounding large subglacial lakes manifest themselves as flat regions on the ice surface ers 1 satellite radar altimetry of the dome c region of east antarctica was analyzed to correlate unusually flat areas on the ice surface with known locations of subglacial lakes identified from airborne radio echo sounding res data the mean length of subglacial lakes which have an expression in the ice sheet surface was 8 3 km whilst those that did not exhibit a surface morphological manifestation had a mean length of 3 3 km thus lakes up to about 4 km in length are unlikely to be detected from satellite radar altimetry of the ice surface given that the spacing of radio echo flight tracks within the spri nsf tud antarctic database is 50 100 km in many areas a number ofsubglacial lakes probably lie undetected beneath the ice sheet res information from two large flat surface regions within dome c and a further flat area located at 80 s 127 e indicates the absence ofsubglacial lakes beneath the ice surface features however these areas are characterised by relatively strong radio echo returns which may indicate the presence of water saturated basal sediments we suggest that 1 blankets of water saturated basal sediments may cause similar surface morphological features to those produced by subglacial lakes and 2 misidentification ofsubglacial lakes from satellite altimeter observations of the ice sheet surface is possible without the support of res information relating to the ice sheet base furthermore our study indicates a lack of sub glacial lake signals from res data over relatively thick regions of east antarctica such as the adventure subglacial trough we conclude that subglacial water produced in such regions may be transported by a basal hydrological system driven by overburden pressure to less thick regions of the ice sheet where subglacial lakes have been identified

first sulfur isotope measurements in central greenland ice cores along the preindustrial and industrial periods 1 sulfur isotopes of sulfate have been measured in a discontinuous set of polar ice core samples from summit central greenland covering the preindustrial from the fourteenth to the eighteenth century and industrial from 1872 to 1969 a d periods results have been used to estimate the different source contributions to the deposited sulfate and their evolution along the last centuries they indicate that the preindustrial background sulfate budget is slightly dominated on a year round average by marine biogenic emissions amounting to close to half of the non sea salt sulfate 49 the second contribution is provided by continental sources of secondary sulfate including background volcanism and to a lesser extent continental biota 44 of the non sea salt sulfate sulfur emitted by relatively weak eruptions is found to be largely depleted in 34s compared to bulk volcanic s suggesting an efficient washout of the heavier isotope during the tropospheric transport the impact of human driven emissions on the sulfate deposited in central greenland ice is visible in isotope data as early as 1870 a d the isotopic signature of anthropogenic sulfur deposited during the twentieth century is found to be constant 34s 3 0 1 5 regardless of the changes of dominant source regions and emission processes this signature is slightly but measurably lighter than the one reported for arctic haze pollution events

penetration of antarctic subglacial lakes by vhf electromagnetic pulses information on the depth and electrical conductivity of basal water bodies owing to the high level of absorption of very high frequency radio waves in water previous investigators of airborne radio echo sounding res data from antarctica have assumed that the depth of subglacial lakes cannot be measured directly by this method however we have identified a number of res returns from beneath the ice water interface at the surface of eight subglacial lakes that we have interpreted as being reflected from the lake floor the returns allow us to measure the depth of subglacial lakes since the velocity of radio waves in water 33 4 m s 1 is relatively unaffected by electrical conductivity attenuation of radio waves within water is controlled largely by its electrical conductivity consequently by examining the decay of the radio wave amplitude with depth we can gain information about the conductivity of subglacial water bodies our results indicate that the minimum water depths of eight subglacial lakes vary between 8 and 21 m the lakes from which our depth measurements were taken are distributed widely around the ice sheet thus it may be concluded for the first time that antarctic subglacial water bodies are generally at least several meters in depth by examining the attenuation of radio waves through subglacial water the electrical conductivity of the water is estimated to be extremely low i e fresh pure water

a stratigraphic link across 1100 km of the antarctic ice sheet between the vostok ice core site and titan dome near south pole isochronous internal ice sheet layering measured from airborne 60 mhz radar was traced between lake vostok and the titan ice dome 100 km from south pole station antarctica three layers were selected between ridge b and titan dome and between ridge b and lake vostok this layering can be used to correlate the existing vostok ice core across 1100 km of the ice sheet interior our correlation is also matched to the new epica ice core site by using an existing radar link between vostok and dome c stations thus three east antarctic ice domes are linked stratigraphically for the first time through internal ice sheet radar layering our results indicate that the basal layers of ice at titan dome are around 165 000 years old suggesting that this location and by inference the south pole station are prime sites for a high resolution ice core from the last glacial interglacial cycle

radio echo layering in polar ice sheets and past volcanic activity a recent study1 has shown how acidity profiles along dated greenland ice cores can reveal large volcanic eruptions in the northern hemisphere during the past 10 000 yr it has been suggested that these layers of acidic ice in the polar ice sheets may also be detected by airborne radio echo sounding res techniques as stratification echoes2 4 explosive volcanic eruptions eject large amounts of so2 into the stratosphere5 where it forms an h2so4 aerosol6 studies of antarctic snow7 and greenland ice cores2 show that this material can be deposited in layers of large areal extent on polar ice sheets calculations based on observations of these slightly acidic layers show that they should give rise to radar reflections of similar magnitude to those observed for stratification echoes new res data from the antarctic enables the present comparison to be made between observed layer power reflection coefficients prcs and calculated values for reflections from acidic ice layers and from layers of ice of changed density a gap in layering has been identified which seems to coincide with a similar gap reported in greenland at crete8 profiles of layer prc against age show a common pattern for many sites on the antarctic ice sheet this prc age profile may provide a record of explosive volcanic activity for the southern hemisphere over the past 150 000 yr

isotopic composition of sulfur in size resolved marine aerosols above the atlantic ocean sulfur isotope measurements were performed on size segregated aerosols collected during the albatross oceanographic campaign from 61 n to 35 s above the atlantic ocean in october and november 1996 results obviously showed the dependence of the sulfur isotope ratio upon particle size the finest particles being depleted in 34s compared to coarse particles suggesting a heavier continental influence in the fine mode in the coarse mode 50 90 of the excess sulfate in both hemispheres was found to be of biogenic origin in the fine mode a different picture was obtained in the northern hemisphere the contribution of biogenic sulfur was found to be less than 35 of the excess sulfur even in relatively clean air masses on the other hand in the southern hemisphere the participation of biogenic sulfur was about 60 of the excess sulfur in purely marine air the contribution of continental sulfur to the fine fraction in the southern hemisphere was up to 40 25 even under pure oceanic conditions and far more in the northern hemisphere these results attest to the possible importance of long range transport of fine sulfate particles or so2 possibly through the free troposphere or the importance of anthropogenic emissions due to shipping

oxygen 17 excesses of the central namib gypcretes spatial distribution abstract we present here sulfate oxygen isotopic data 72 samples with both 18o and 17o systematically collected from the central namib desert surface soils from two shore inland west east transects exhibit a gradual increase in the sulfate oxygen 17 excess 17o 17o 0 52 18o until at ca 70 km inland where no continuous gypcrete deposit is observed further east inland the oxygen isotopic compositions for water soluble sulfates extracted from soils and gypcretes range from 8 3 to 13 3 and 0 06 to 1 11 for 18o and 17o respectively the lateral pattern is similar to what has been seen in the cold deserts of the antarctic dry valleys however unlike the dry valleys no discernible correlation is found between 18o and 17o or between the depth of soil horizon and 17o in the namib possible explanations include a relatively smaller component of dimethylsulfide dms derived sulfate in the total gypsum deposits and or more active surface processes e g flooding and leaching in the central namib desert than in the antarctic cold deserts although current state of knowledge is insufficient to delineate quantitatively the sulfate contributions from different sources and reactions the measurement of sulfate 17o does identify an unmistakable atmospheric sulfate component and provides additional independent information regarding sources and reactions

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

direct major and trace element analyses of rock varnish by high resolution laser ablation inductively coupled plasma mass spectrometry la icpms laser ablation inductively coupled plasma mass spectrometry la icpms was used to determine major and trace element concentrations in rock varnish samples from the lahontan range near fallon nv and from a remote wilderness area near the san juan river in southeastern utah the data indicate that rapid la icpms analyses provide ample analytical resolution for semi quantitative compositional determinations of both trace and major elements in the varnish despite the presence of a rock substrate component in most analyses the overall major element contents of rock varnish from the two localities are grossly similar to rock varnish from other locations analyzed by solution icpms electron microprobe and energy dispersive scanning electron microscopy sem differences between microprobe and la icpms analyses may stem from different sampling scales and different degrees of substrate involvement it was possible to detect significant variations in trace element contents in the rock varnish samples the lahontan range is situated within a belt of w mineralization and varnish from that locality contained significantly higher w and mo contents than varnish from localities outside the w belt lead tl bi cd and as contents of varnish coated pebbles from near the san juan river in southeastern utah varied by an order of magnitude as a function of the position of the sampling site on the pebble elevated heavy element contents on the skyward facing varnish surfaces indicate that heavy elements may be preferentially scavenged at the locations most likely to receive direct inputs of atmospherically deposited airborne particulates the source of metal rich airborne particulates in this case is probably any one of several large coal fired power plants in the four corners region proximal to the san juan study area these patterns indicate that rock varnish chemistry is influenced by atmospherically derived fluxes of both dissolved and particulate constituents and that rock varnish can be used as a passive environmental indicator for a wide variety of elements in much the same manner as moss and lichens

parameters influencing porosity in sandstones a model for sandstone porosity prediction thirteen parameters were reviewed for their influence on porosity in sandstone core material during compaction in basins of average geothermal gradients the first order parameters are age time of burial detrital quartz content maximum depth of burial and sorting overpressure may slow the compaction process depending on onset of overpressure during burial approximately 2 primary porosity may be preserved for every 1 000 psi 6 9 mpa above hydrostatic pressure depth related temperature and median grain size were found to be only second order parameters on the basis of 428 cases function coefficients were calculated for the relationship between porosity and the first order parameters this function permits porosity prediction with a high degree of accuracy th equation is valid for sandstones older than 3 ma with little or no cement no leaching depth of burial in excess of 500 m and little or no shear stresses secondary porosity is excluded and estimations will therefore be conservative where leaching occurred due to interrelationship of compaction and cementation the porosity reduction by cement is usually only a small fraction of the total reduction the function can therefore also be applied to little cemented sandstones

volcanic sulfate aerosol formation in the troposphere the isotopic composition of volcanic sulfate provides insights into the atmospheric chemical processing of volcanic plumes first mass independent isotopic anomalies quantified by 17o and to a lesser extent 33s and 36s in sulfate depend on the relative importance of different oxidation mechanisms that generate sulfate aerosols second the isotopic composition of sulfate 34s and 18o could be an indicator of fractionation distillation condensation processes occurring in volcanic plumes here we present analyses of o and s isotopic compositions of volcanic sulfate absorbed on very fresh volcanic ash from nine moderate historical eruptions in the northern hemisphere most of our volcanic sulfate samples which are thought to have been generated in the troposphere or in the tropopause region do not exhibit any significant mass independent fractionation mif isotopic anomalies apart from those from an eruption of a mexican volcano coupled to simple chemistry model calculations representative of the background atmosphere our data set suggests that although h2o2 a mif carrying oxidant is thought to be by far the most efficient sulfur oxidant in the background atmosphere it is probably quickly consumed in large dense tropospheric volcanic plumes we estimate that in the troposphere at least more than 90 of volcanic secondary sulfate is not generated by mif processes volcanic s bearing gases mostly so2 appear to be oxidized through channels that do not generate significant isotopically mass independent sulfate possibly via oh in the gas phase and or transition metal ion catalysis in the aqueous phase it is also likely that some of the sulfates sampled were not entirely produced by atmospheric oxidation processes but came out directly from volcanoes without any mif anomalies

glaciological reconnaissance of an ice core drilling site penny ice cap baffin island analyse climatique sur 10 4 ans d une carotte de glace de 20 m prelevee dans l ile de baffin on a etudie les teneurs en oxygene en tritium le ph la conductivite electrolytique la concentration en ions majeurs et en particules une carotte proche a ete analysee de son contenu en pollen l epaisseur et la morphologie de la couche ont ete mesurees par echo radar

analytical solutions for the effect of topography accumulation rate and lateral flow divergence on isochrone layer geometry the effect of spatial variations in ice thickness accumulation rate and lateral flow divergence on radar detected isochrone geometry in ice sheets is computed using an analytical method under assumptions of a steady state ice sheet geometry a steady state accumulation pattern and a horizontally uniform velocity shape function by using a new coordinate transform we show that the slope of the isochrones with a normalized vertical coordinate depends on three terms a principal term which determines the sign of the slope and two scale factors which can modify only the amplitude of the slope the principal term depends only on a local characteristic time ice thickness divided by accumulation rate minus melting rate between the initial and final positions of the ice particle for plug flow only the initial and final values have an influence further applications are a demonstration of how the vertical velocity profile can be deduced from sharp changes in isochrone slopes induced by abrupt steps in bedrock or mass balance along the ice flow we also demonstrate ways the new coordinate system may be used to test the accuracy of numerical flow models

mass independent isotopic signatures of volcanic sulfate from three supereruption ash deposits in lake tecopa california abstract hundreds to thousands of megatons of sulfur dioxide released by supereruptions can change chemical and physical properties of the atmosphere and thus induce climate perturbations we present oxygen and sulfur isotope analyses of sulfate in 48 volcanic ash samples and 26 sediment samples from dry lake beds in the tecopa basin california usa these ash layers represent three supereruptions including the 0 64 ma lava creek tuff 2 04 ma huckleberry ridge tuff and 0 76 ma bishop tuff mass independent oxygen signatures 17o up to 2 26 that are present in these ash units and not in associated sediments indicate oxidation of volcanic so2 by mass independent ozone and its products in this study we consider the formation deposition preservation and dilution of mass independent volcanic sulfate mivs using the isotopic compositions of the sulfates we construct a mixing model that demonstrates that the main source of sulfate in lake tecopa is mass dependent sediment derived sulfate mdsds 77 however ash beds still preserve up to 23 of mivs that initially had undiluted 17o value around 8 and 33s as low as 0 35 and 36s up to 1 08 therefore despite potential dilution by mdsds the mivs signatures can be preserved in the geologic record for few million years if deposited as gypsum in arid environments alkaline or saline lake the oxygen and sulfur mass independent signatures of the volcanic sulfates indicate that photolysis and oxidation of volcanic so2 has been achieved in the upper atmosphere since only supervolcanic eruptions were shown to generate massive amount of mass independent sulfate it requires that up to 20 60 of the global ozone layer is consumed as a result of supervolcanic so2 released this may occur as a result of a strong physical and chemical degradation of the tropopause we speculate that the distinction between the high troposphere and the low stratosphere at least locally could be erased by supereruptions and recorded by mivs