tephra layers in the siple dome and taylor dome ice cores antarctica sources and correlations 1 volcanic ash or tephra layers are found in the taylor dome siple dome a and siple dome b ice cores significant shard concentrations are found at a number of depths in all three cores electron and ion microprobe analyses indicate that the geochemical composition of most layers is basaltic basanitic or trachytic and the geochemical signatures of the layers suggest derivation from the pleiades volcanic center mt melbourne volcano or small mafic centers probably in the royal society range area presence of tephra layers suggests an episode of previously unrecognized antarctic volcanic activity between 1776 and 1805 a d from at least two volcanic centers a strong geochemical correlation d 3 49 and 3 97 with a value of 4 considered identical is observed between tephra layers at depth of 79 2 m in the taylor dome ice core and layers between 97 2 and 97 7 m depth in the siple b core this correlation and the highly accurate depth age scale of the siple b core suggest that the age of this horizon in the taylor dome ice core presented by steig et al 1998a 2000 should be revised downward to the younger age of 675 25 years before 1995 this revised chronology is consistent with vertical strain measurements presented by hawley et al 2003

potential atmospheric impact of the toba mega eruption 71 000 years ago an approx 6 year long period of volcanic sulfate recorded in the gisp2 ice core about 71 000 5000 years ago may provide detailed information on the atmospheric and climate impact in the toba mega eruption deposition of these aerosols occur beginning of an approx 1000 year long stadial event but not immediately before the longer glacial period beginning approx 67 500 years ago total stratospheric loading estimates over this approx 6 year period range from 2200 to 4400 mt of h sub 2 so sub 4 aerosols the range in values is given to compensate for uncertainties in aerosol transport magnitude and longevity of the atmospheric loading may have led directly to enhanced cooling during the initial two centuries of this approx 1000 year cooling event 25 refs 2 fig 1 tab

timing of millennial scale climate change at siple dome west antarctica during the last glacial period using atmospheric methane and the isotopic composition of o2 as correlation tools we place the dd record of ice from the siple dome west antarctica ice core on a precise common chronology with the gisp2 greenland ice core for the period from 9 to 57 ka the onset of major millennial warming events in siple dome preceded major abrupt warmings in greenland and the pattern of millennial change at siple dome was broadly similar though not identical to that previously observed for the byrd ice core also in west antarctica the addition of siple dome to the database of well dated antarctic paleoclimate records supports the case for a coherent regional pattern of millennial scale climate change in antarctica during much of the last ice age and glacial interglacial transition

evidence of the eldgja iceland eruption in the gisp2 greenland ice core relationship to eruption processes and climatic conditions in the tenth century glaciochemical studies and the evaluation of tephra in the gisp2 ice core provide information on the characteristics and potential environmental and climatic effects of the mid to late ad 930s voluminous fissure eruption of eldgja iceland the similarity in the chemical composition of basaltic glass shards found in a section of core dated at ad 938 4 compared to proximal glass from the eldgja eruption verifies the presence of eldgja debris a dacitic glass present in the same layer probably originated from eldgja as well in which case eldgja was the primary contributor of sulphur rich aerosols to the atmosphere in the late ad 930s we cannot completely exclude the possibility that another explosive eruption in the ad 930s produced this dacitic glass estimated maximum stratospheric loading is 100 x 1012 g h 2so4 over a 3 6 year period following the eruption but loading could be as low as half of that value a search of historical and proxy records for the late ad 930s to early 940s fail to show a co

role of conduit shear on ascent of the crystal rich magma feeding the 800 year b p plinian eruption of quilotoa volcano ecuador we have characterized pumice products belonging to the climactic phase of the 800 year b p quilotoa eruption bulk rock compositions petrography mineral and glass chemistry and textural investigations were performed on the three end member pumice types namely white gray and mingled pumices all the investigated pumice clasts are dacites characterized by the same bulk rock composition and mineralogical assemblage but glass compositions and bulk textures change according to different pumice types white pumice has higher crystallinity 48 wt abundant euhedral pheno microphenocrysts no groundmass microlites the most evolved glass compositions 74 78 wt sio2 and heterogeneous vesicle populations marked by deformed and highly coalesced vesicles with thin walls gray pumice exhibits lower crystallinity 29 36 wt abundant broken and or resorbed crystals ubiquitous groundmass phenocryst fragments and microlites the widest range of glass compositions 69 78 wt sio2 and quite homogeneous poorly deformed and coalesced vesicles with thicker walls mingled pumices are characterized by the alternation of bands or patches with white and gray pumice compositional and textural characteristics we attribute heterogeneities in glass compositions and crystal and vesicle textures to processes occurring within volcanic conduits as magma is ascending to the surface in particular the above observations and results are consistent with an origin of a gray magma by heating of the original white magma in a strongly sheared region of the conduit because of a mechanism of viscous dissipation and crystal grinding and resorption at the conduit walls the less viscous gray magma therefore would enable the onset and preservation of a high mass flux of the eruption otherwise difficult to explain for highly viscous crystal rich dacitic magmas

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

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

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

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

glaciological studies at siple station antarctica potential ice core paleoclimatic record the quality and utility of the records of oxygen isotopic abundances dust concentrations and anionic concentrations preserved in the ice at siple station 75 55 s 84 15 w are assessed from four shallow 20 m cores the combination of high accumulation 0 56 m a 1 w e and low mean annual temperature 24 c preserves the prominent seasonal variations in 18 which are very spatially coherent sulfate concentrations vary seasonally and in conjunction with 18 will allow accurate dating of deeper cores from siple station the concentrations of insoluble dust are the lowest measured in antarctica making siple station an excellent location to examine large increases in atmospheric tubidity the seasonal variations and annual fluxes of the anions are examined for the last two decades ad 1966 85 with regard to probable sources an unusually high sulfate flux in 1976 may reflect the february 1975 eruption of mount ngauruhoe new zealand no annual signal in nitrate concentration is confirmed and no unusually high nitrate fluxes support the suggestion of nitrate production by large solar flares however nitrate flux is higher for the latter half of the 1970s and early 1980s possibly reflecting the recent loss of stratospheric ozone finally comparison of the 18 o record with available surface temperature data ad 1957 85 reveals that multi year trends along the western coast of the antarctic peninsula are recorded at siple more importantly comparison with areally weighted temperature reconstructions suggests that the 18 record may reflect larger scale persistent trends in the high southern latitudes the strong spatial coherence of the preserved records the potential for accurate dating and possible relevance to larger scale processes make siple station an excellent site for paleoenvironmental reconstruction from ice cores

impact of the cerro hudson and pinatubo volcanic eruptions on the antarctic air and snow chemistry atmospheric records of sulfate and msa in aerosols were obtained by year round samplings in the boundary layer at two coastal antarctic sites neumayer 1983 1995 and dumont d urville 1991 1997 at dumont d urville and neumayer the non sea salt sulfate nssso42 level observed from october 1991 to october 1993 exceeded by 44 and 48 ng m 3 respectively the mean level 150 ng m 3 observed during nonvolcanic years the neumayer and dumont d urville records first exhibit spring october to december 1991 nssso42 concentrations exceeding mean spring concentrations by some 100 to 150 ng m 3 caused by a significant poleward transport of the cerro hudson volcanic aerosol in the lower stratosphere beneath the polar vortex and possibly in the middle upper troposphere limited to 10 ng m 3 during winter 1992 the nssso42 perturbation reached 78 ng m 3 in fall 1993 at neumayer the latter enhancement corresponds to the input of the pinatubo volcanic aerosol advected through stratosphere troposphere air mass exchanges an enhancement of nssso42 concentrations is also recorded in snow layers deposited between 1991 and 1993 at various sites located over the high antarctic plateau on the basis of these firn data the relative impact of the three latest volcanic eruptions of global concern namely mount agung 1963 el chichon 1982 and pinatubo together with cerro hudson 1991 was evaluated in terms of sulfate input at high southern latitudes the fallout of sulfate in central antarctic snow following the cerro hudson pinatubo eruptions was slightly lower than fallout after the mount agung eruption sulfate fallout after el chichon was 2 to 3 times lower than that from either mount agung or pinatubo the enhancement of sulfate levels detected in central antarctic snow deposits during the 1991 1993 time period allows us to estimate a mean atmospheric sulfate perturbation of around 60 ng m 3 in the boundary layer of these regions i e at least 35 higher than that seen at coastal sites this observation suggests that coastal antarctic regions are less sensitive than the high plateau in detecting volcanic sulfate fallouts following eruptions of global concern atmospheric near surface year round sampling achieved at coastal antarctic sites reveals no significant enhancement of the nitrate level over 1992 and 1993 suggesting that volcanic aerosols have had a limited effect on the transfer of nitric acid from the lower antarctic stratosphere to the boundary layer in these regions

micrometre sized volcanic glasses in polar ices and snows explosive volcanic eruptions can follow long cycles of activity1 and the material that they inject into the atmosphere may affect the climate2 we report here the discovery of ultrathin micrometre sized glass shards from such eruptions extracted from both ancient antarctic ices and recent snow samples from greenland in which they have been well preserved by deep freezing when such shards have been preselected using a high voltage electron microscope microanalysis of their eight major constituent elements gives new clues about the origin of major volcanic acid fallout previously detected in the cores including important characteristics of their parent eruptions and reveals complex volcanic ash layers that could reflect periods of world wide enhanced volcanicity moreover the very small reynolds numbers of the micrometre sized shards make them promising tracers of dust transport processes in the ancient atmosphere

dielectric signatures and evolution of glacier ice we analyzed the dielectric spectra 0 1 hz 1 mhz of 49 firn and ice samples from ice sheets and glaciers to better understand how differing ice formation and evolution affect electrical properties the dielectric relaxation of ice is well known and its characteristic frequency increases with the concentration of soluble impurities in the ice lattice we found that meteoric ice and firn generally possess two such relaxations indicating distinct crystal populations or zonation typically one population is consistent with that of relatively pure ice and the other is significantly more impure however high temperatures e g temperate ice long residence times e g ancient ice from mullins glacier antarctica or anomalously high impurity concentrations favor the development of a single relaxation these relationships suggest that annealing causes two dielectrically distinct populations to merge into one population the dielectric response of temperate ice samples indicates increasing purity with increasing depth suggesting ongoing rejection of impurities from the lattice separately subglacially lake frozen samples from the vostok antarctica 5g ice core possess a single relaxation whose variable characteristic frequency likely reflects the composition of the source water we conclude that multi frequency methods are essential to dielectric discrimination between different types of glacier ice

kuwae 1425 a d the forgotten caldera in vanuatu tongoa and epi islands once formed part of a larger landmass kuwae which was partly destroyed during a cataclysmic seismo volcanic event that is recorded in local folklore it led to the formation of a 12 kmlong and 6 km wide oval shaped submarine caldera with two distinct basins and a total area of 60 km2 at the level of the rim the age ofthis eniption 1420 1430 a d and the structure of the related collapse are discussed and a composite log 143 m of the pyroclastics surrounding the caldera is presented they comprise thick hydromagmatic deposits belonging to a terminal hydromagmatic phase of the pre caldera edifice which grade upwards into two major sequences of pyroclastic flow deposits clearly related to the caldera event collapse near the caldera edge was at least in the range 650 to 950 m and may have been as much as 800 to 1100 m the volume of rocks engulfed during the caldera formation is 32 39 km3 suggesting the same volume of magma was erupted even if two coalescent collapse structures were formed it is worth noting that the kuwae caldera is not a reactivated structure but the result of a single event of short duration which occurred in the first half of the fifteenth century this event is one of the seven biggest caldera forming events during the last 10 000 years and is comparable with the santorini minoan eruption and the crater lake eruption

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

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

contributions of an ancient evaporitic type reservoir to subglacial lake vostok chemistry abstract we present here the first comprehensive study of the chemical composition of accretion ice from lake vostok ion chromatographic analyses were performed on samples obtained along the deeper part of the vostok ice core samples were taken from 3350 down to 3611 m depth both in glacier ice and subglacial lake ice the total ionic contents of two accretion ice layers a few meters thick and centered around 3540 and 3590 m depth are several times lower than those of glacier ice very low concentrations were also observed in the deeper part of accretion ice below 3609 m depth elsewhere the total ionic content is variable but remains 5 to 50 times higher than in glacier ice whatever its total ionic content the ionic composition of accretion ice is significantly different from what is observed in glacier ice it is dominated by sodium chloride homogeneously distributed throughout the ice lattice as well as calcium and magnesium sulfate likely located in solid inclusions or to a lesser extent at grain boundaries chemical considerations combined with additional studies of sulfur and oxygen isotopes in sulfate and iron measurements strongly suggest that glacier water recycling and bedrock hydrolysis do not play a prominent role in providing impurities to accretion ice it is more likely that nacl rich water carrying fine sulfate salt particles is sporadically incorporated in the ice accreting in a shallow bay upstream from vostok the origin of such salty water which should also contribute to lake salinity is discussed

biogeochemical weathering under ice size matters 1 the basal regions of continental ice sheets are gaps in our current understanding of the earth s biosphere and biogeochemical cycles we draw on existing and new chemical data sets for subglacial meltwaters to provide the first comprehensive assessment of sub ice sheet biogeochemical weathering we show that size of the ice mass is a critical control on the balance of chemical weathering processes and that microbial activity is ubiquitous in driving dissolution carbonate dissolution fueled by sulfide oxidation and microbial co2 dominate beneath small valley glaciers prolonged meltwater residence times and greater isolation characteristic of ice sheets lead to the development of anoxia and enhanced silicate dissolution due to calcite saturation we show that sub ice sheet environments are highly geochemically reactive and should be considered in regional and global solute budgets for example calculated solute fluxes from antarctica 72 130 t yr 1 are the same order of magnitude as those from some of the world s largest rivers and rates of chemical weathering 10 17 t km 2 yr 1 are high for the annual specific discharge 2 3 4 1 10 3 m our model of chemical weathering dynamics provides important information on subglacial biodiversity and global biogeochemical cycles and may be used to design strategies for the first sampling of antarctic subglacial lakes and other sub ice sheet environments for the next decade

highly deformed basal ice in the vostok core antarctica 1 our paper documents the build up of a highly deformed basal ice layer in the basal part of the vostok ice core this is done mainly on the basis of an isotopic composition investigation of the ice complex deformation in the lower 228 m of the ice sheet has resulted in folding and intermixing of ice at a submetric scale and for the upper part of this basal sequence in interbedding of ice layers from distinct origins at a larger scale this complex deformation occurred at a temperature largely below the pressure melting point the basal ice layer has built upwards and size selective incorporation of bed material into the ice has taken place the documentation of this complex basal deformation has implications for the maximum age of ice that will be useful in paleoclimate studies and for ice sheet dynamics

assessment of the record of the 1982 el chichon eruption as preserved in greenland snow variability in the so42 and cl time series for the 1980s from 12 shallow snow pits across the greenland ice sheet is used to evaluate the record of the 1982 el chichon eruption and the potential for recording a moderate northern equatorial eruption in a single greenland ice core composition of volcanic glass found in spring 1983 snow in one of the pits in the summit region matches that from el chichon glass thereby verifying the deposition of material from the eruption high na and cl concentrations in this same layer probably represent deposition of the reaction products of halite and h2so4 as observed in the stratosphere following the eruption these findings and the presence of a cl signal in five of the other pits indicate that the cl aerosol component of some eruptions has the potential to remain aloft for at least 1 year after the eruption some of these aerosols may be adsorbed onto tephra particles distinct so42 peaks that can be confidently linked to el chichon were found in only 50 of the records developed through subseasonal sampling however in several other pits an elevated baseline thought to represent more lengthy periods of el chichon aerosol deposition as opposed to deposition from a single snowfall event were observed smoothing of the original data by the calculation of annual so42 flux resulted in the presence of high flux values between 1982 and 1984 years thought to be affected by el chichon aerosol deposition in 9 of the 12 pits these results suggest that a single ice core from anywhere in greenland may record a signal from a northern equatorial eruption of magnitude similar to that of el chichon about 75 of the time this is despite the overall high levels of so2 4 deposition from anthropogenic sources that now make identification and quantification of the volcanic so2 portion of the record more difficult than obtaining the same data for preindustrial volcanism nevertheless composite records from all the pits sampled yielded stratospheric loading 20 mt and optical depth 0 13 estimates similar to stratospheric and satellite based measurements following the eruption equally high so42 concentration and flux values in snow from 1980 to 1982 reflect deposition from the series of middle to high northern latitude volcanic eruptions 1979 1981

ice cover landscape setting and geological framework of lake vostok east antarctica abstract lake vostok located beneath more than 4 km of ice in the middle of east antarctica is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment melting and freezing at the base of the ice sheet which slowly flows across the lake controls the flux of water biota and sediment particles through the lake the influx of thermal energy however is limited to contributions from below thus the geological origin of lake vostok is a critical boundary condition for the subglacial ecosystem we present the first comprehensive maps of ice surface ice thickness and subglacial topography around lake vostok the ice flow across the lake and the landscape setting are closely linked to the geological origin of lake vostok our data show that lake vostok is located along a major geological boundary magnetic and gravity data are distinct east and west of the lake as is the roughness of the subglacial topography the physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake s circulation lake vostok is a tectonically controlled subglacial lake the tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small but significant amounts of thermal energy into the lake

a 1500 year record of accumulation at amundsenisen western dronning maud land antarctica derived from electrical and radioactive measurements on a 120 m ice core during the nordic epica pre site survey in dronning maud land in 1997 1998 a 120 m long ice core was retrieved 76 00 s 08 03 w 2400 m above sea level the whole core has been measured using the electric conductivity measurement ecm and dielectric profiling dep techniques and the core chronology has been established by detecting major volcanic eruptions in a nearby shallow core radioactive traces from nuclear tests conducted during the 1950s and 1960s have been identified altogether 13 ecm and dep peaks in the long core are identified as originating from specific volcanic eruptions in addition two peaks of increased total activity are identified in the short core accumulation is calculated as averages over the time periods between these dated events accumulation rate is 62 millimetres w eq yr for the last 181 years 1816 a d to present and 61 mm w eq yr for the last 1457 years 540 a d to present our record shows an 8 decrease in accumulation between 1452 and 1641 a d i e part of the little ice age compared to the long term mean

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

constraints on hydrothermal processes and water exchange in lake vostok from helium isotopes lake vostok the largest subglacial lake in antarctica is covered by the east antarctic ice sheet which varies in thickness between 3 750 and 4 100 m ref 1 at a depth of 3 539 m in the drill hole at vostok station sharp changes in stable isotopes and the gas content of the ice delineate the boundary between glacier ice and ice accreted through re freezing of lake water2 unlike most gases helium can be incorporated into the crystal structure of ice during freezing3 making helium isotopes in the accreted ice a valuable source of information on lake environment here we present helium isotope measurements from the deep section of the vostok ice core that encompasses the boundary between the glacier ice and accreted ice showing that the accreted ice is enriched by a helium source with a radiogenic isotope signature typical of an old continental province this result rules out any significant hydrothermal energy input into the lake from high enthalpy mantle processes which would be expected to produce a much higher 3he 4he ratio based on the average helium flux for continental areas the helium budget of the lake leads to a renewal time of the lake of the order of 5 000 years

modeling the effects of frazil ice crystals on the dynamics and thermodynamics of ice shelf water plumes the seawater that comes into contact with the base of a floating ice shelf is modified as a result of the phase changes that occur melting is prevalent in the deepest parts of the subice cavity and this drives a buoyant flow of ice shelf water isw along the sloping ice shelf base the ascent of the isw toward the surface of the ocean causes supercooling because the freezing point rises with the falling pressure and this induces a change from melting to freezing assuming that seed crystals exist the isw now fulfills the condition for the rapid growth of disc shaped frazil ice crystals which may subsequently settle upward out of suspension under the action of gravity a simple numerical model of these processes has been developed based on the theory of inclined plumes the isw is treated as a turbulent particle laden gravity current ascending a reactive boundary and containing a suspended crystal load which evolves in response to the supercooling of the water and the inverted sedimentation of the crystals the frazil ice has two important effects on the behavior of the isw plume because the generation of crystals through out the plume provides such a large area over which phase changes can occur the conversion of supercooling into ice happens much more readily than is possible through turbulent transfer of heat and mass at the ice shelf base a suspended crystal load reduces the bulk density of the isw so that a growing suspension causes the plume to accelerate while deposition of crystals onto the ice shelf effects a deceleration there are positive feedbacks in that an acceleration of the plume induces more rapid crystal growth while a deceleration allows suspended crystals to settle out more easily

a year long record of size segregated aerosol composition at halley antarctica 1 size segregated aerosol samples were collected with a cascade impactor at 2 week intervals for a year at the research station halley situated near the coast in the weddell sea region of antarctica sea salt is a major component of aerosol throughout the year and we estimate that at least 60 of the total sea salt arriving at halley is from brine and frost flowers on the sea ice surface rather than open water chloride in sea salt particles is depleted relative to sodium in summer consistent with loss of hcl as sea salt particles react with gaseous acidic species but is enhanced in large particles in winter because of fractionation occurring during the production of new sea ice non sea salt sulphate peaks in the summer with the majority being in small particles indicative of a gas phase origin the distribution of methane sulphonic acid closely follows that of non sea salt sulphate in the winter non sea salt sulphate is frequently negative especially on stages collecting large particle sizes consistent with the source of sea salt during the winter being predominantly the sea ice surface rather than open water nitrate peaks in the spring and summer and shows some association with sea salt particles

annually resolved southern hemisphere volcanic history from two antarctic ice cores the continuous sulfate analysis of two antarctic ice cores one from the antarctic peninsula region and one from west antarctica provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century the dating is accurate within 3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis the two sulfate records are consistent with each other a systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals the resulting volcanic chronology covering 1417 1989 a d resolves temporal ambiguities about several recently discovered events a number of previously unknown moderate eruptions during late 1600s are uncovered in this chronology the eruption of tambora 1815 and the recently discovered eruption of kuwae 1453 in the tropical south pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium a technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux for the same eruptions the variability of the volcanic sulfate flux between the cores is within 20 of the sulfate flux from the tambora eruption

insights into hydrological regime of lake vostok from differential behavior of deuterium and oxygen 18 in accreted ice 1 we use isotopic data deuterium and oxygen 18 of the recently recovered deepest vostok ice core section down to 3650 m depth to study processes leading to the formation of lake ice and the hydrological regime of subglacial lake vostok the significant variability of the lake ice isotopic content implies fluctuations in physical conditions of ice formation mainly volume and or growth rate of frazil ice crystals as well as variations of the isotope composition of the freezing water the latter implies a poor mixing of the source waters glacier melt and hydrothermal water with the water of the main lake body poor mixing within the lake may have important consequences for the lake s chemical and gas balance and particularly for its microbiological content a poorly mixed lake may provide ecological niches where microbial life can hide from high oxygen concentrations likely typical for the lake we also show that the isotopic content of the main lake s input meltwater significantly differs from that of the output lake ice which can be explained by the contribution of an additional hydrothermal source this latter conclusion is supported by the observed noncovariant behavior of deuterium and oxygen 18 isotopes in the lake ice

origin and fate of lake vostok water frozen to the base of the east antarctic ice sheet the subglacial lake vostok may be a unique reservoir of genetic material and it may contain organisms with distinct adaptations but it has yet to be explored directly the lake and the overlying ice sheet are closely linked as the ice sheet thickness drives the lake circulation while melting and freezing at the ice sheet base will control the flux of water biota and sediment through the lake here we present a reconstruction of the ice flow trajectories for the vostok core site using ice penetrating radar data and global positioning system gps measurements of surface ice velocity we find that the ice sheet has a significant along lake flow component persistent since the last glacial maximum the rates at which ice is frozen accreted to the base of the ice sheet are greatest at the shorelines and the accreted ice layer is subsequently transported out of the lake using these new flow field and velocity measurements we estimate the time for ice to traverse lake vostok to be 16 000 20 000 years we infer that most vostok ice analysed to date was accreted to the ice sheet close to the western shoreline and is therefore not representative of open lake conditions from the amount of accreted lake water we estimate to be exported along the southern shoreline the lake water residence time is about 13 300 years

limnological conditions in subglacial lake vostok antarctica subglacial lake vostok is located 4 km beneath the surface of the east antarctic ice sheet and has been isolated from the atmosphere for 15 million yr concerns for environmental protection have prevented direct sampling of the lake water thus far however an ice core has been retrieved from above the lake in which the bottom 85 m represents lake water that has accreted i e frozen to the bottom of the ice sheet we measured selected constituents within the accretion ice core to predict geomicrobiological conditions within the surface

correlation of a 3 200 year old tephra in ice cores from vostok and south pole stations antarctica tephra layers in two antarctic ice cores are correlated on the basis of their chemical compositions and estimated ages we believe the tephra was produced about 3 200 years ago from a major explosive eruption of candlemas island in the south sandwich islands this is the first time that tephra layers have been correlated between two widely separated ice cores and demonstrates that tephra layers may serve as stratigraphic markers for correlating and perhaps in some cases dating antarctic ice cores

the dimensions and topographic setting of antarctic subglacial lakes and implications for large scale water storage beneath continental ice sheets radio echo sounding res at 60 mhz has penetrated to the ice sheet bed on about 400 000 km of flight track covering more than 50 of the 13 5 x 106 km2 antarctic ice sheet about 70 subglacial lakes have been identified by characteristic strong mirror like and very flat res reflectors most are located in the ice sheet interior where numerical modeling predicts basal melting and 33 are within 100 km of the ice crest mean ice thickness above the lakes is about 3000 m about 75 of lakes have radio echo lengths of 30 km the largest is vostok lake which is 230 km long 14 000 km2 in area and has a water volume of about 2000 km3 more than 60 of lakes have maximum local bedrock elevations of 400 m and bed gradients of 0 1 adjacent to their margins extrapolating the observed side slope topography implies water depths from tens to several hundred meters in a few cases about 20 000 km2 of subglacial lakes are inferred from res which can be doubled for the entire ice sheet to yield an estimated total area of about 40 000 km2 excluding vostok lake assuming average lake depths between 50 and 250 m and including the 2000 km3 of water stored within vostok lake we calculate an envelope of about 4000 to 12 000 km3 for the likely volume of water stored in modern antarctic subglacial lakes equivalent to 10 35 mm of global sea level rise in these volume calculations it is assumed that no subglacial lakes the size of lake vostok remain to be discovered and that res length measurements along single transects are representative of overall lake dimensions our estimates of the total water volume of antarctic subglacial lakes which may be a suitable analogue for full glacial quaternary ice sheets do not necessarily conflict with the possible significance of large meltwater floods during the deglaciation of former midlatitude ice sheets

reassessing lake vostok s behaviour from existing and new ice core data abstract interpretation of new ice core data and reappraisal of existing data both from the basal part of the vostok ice core give strong support to a kind of thermohaline circulation in lake vostok although the salinity of the lake is considered as weak less than 1 the prominent influence of salinity at high pressure and low temperature on water density makes such a circulation possible as a consequence subglacial melting along the northern shores of the lake is balanced further south by frazil ice production in the upper water column its accretion and consolidation at the ice water interface followed by accreted ice export out of the system together with the southeasterly glacier flow the dynamics of the system is documented by a stable water isotope budget estimate by inferences concerning accreted ice formation and by an investigation of ice properties at the transition between meteoric ice and accreted ice this complex behaviour is the controlling factor on water biota and sediment fluxes in the lake environment

non explosive constructional evolution of the ice filled caldera at volcan sollipulli chile a radar and gravity survey of the ice filled caldera at volcan sollipulli chile indicates that the intra caldera ice has a thickness of up to 650 m in its central part and that the caldera harbours a minimum of 6 km3 of ice reconnaissance geological observations show that the volcano has erupted compositions ranging from olivine basalt to dacite and have identified five distinct volcanic units in the caldera walls pre or syn caldera collapse deposits the sharkfin pyroclastic unit comprise a sequence which evolved from subglacial to subaerial facies post caldera collapse products which crop out along 17 of the 20 km length of the caldera wall were erupted almost exclusively along the caldera margins in the presence of a large body of intra caldera ice the alpehue crater formed by an explosive eruption between 2960 and 2780 a bp in the southwest part of the caldera is shown to post date formation of the caldera sollipulli lacks voluminous silicic pyroclastic rocks associated with caldera formation and the collapse structure does not appear to be a consequence of a large magnitude explosive eruption instead lateral magma movement at depth resulting in emptying of the magma chamber may have generated the caldera the radar and gravity data show that the central part of the caldera floor is flat but within a few hundred metres of the caldera walls the floor has a stepped topography with relatively low density rock bodies beneath the ice in this region this coupled with the fact that most of the post caldera eruptions have taken place along the caldera walls implies that the caldera has been substantially modified by subglacial marginal eruptions sollipulli caldera has evolved from a collapse to a constructional feature with intra caldera ice playing a major role the post caldera eruptions have resulted in an increase in height of the walls and concomitant deepening of the caldera with time

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

brine micro droplets and solid inclusions in accreted ice from lake vostok east antarctica 1 lake vostok the largest antarctic sub glacial lake 14 000 km2 lies beneath nearly 4 km of ice sub glacial geophysical observations and studies of ice accreting at the lake glacier interface are the only means available to obtain information on the environment and dynamics of this huge water body formed several million years ago accretion ice has been studied using high resolution synchrotron x ray micro fluorescence for the first time liquid brine micro droplets 3 10 m are observed coexisting with large irregular sulfur rich aggregates 10 800 m containing gases and a mixture of very fine particles most of these objects are sequestered inside large crystals that grew slowly after ice formation their structure and composition support the existence of hydrothermal activity at the lake bottom and the occurrence of haline water pulses carrying fine solid debris and eventually biota from a deeper evaporitic reservoir into the lake

historic eruptions of tambora 1815 krakatau 1883 and agung 1963 their stratospheric aerosols and climatic impact abstract decreases in surface temperatures after the eruptions of tambora 1815 krakatau 1883 and agung 1963 were of similar magnitude even though the amount of material dust and volatiles injected into the stratosphere by these three events differed greatly large amounts of fine ash and volatiles were dispersed into the upper atmosphere by krakatau and tambora the agung eruption in 1963 was a much smaller vulcanian type eruption which injected dust and volatiles into the stratospheric aerosol layer more directly analyses of magmatic volatiles indicate that the agung eruption was proportionately richer in so 2 and cl than either tambora or krakatau relative amounts of fine ash produced by the tambora krakatau and agung eruptions are estimated at about 150 20 1 whereas the masses of atmospheric sulfate aerosols produced were on the order of 7 5 3 1 decreases in surface temperature of a few tenths of a degree c for several years following volcanic eruptions are primarily a result of the sulfate aerosols rather than of the silicate dust the similarity in the atmospheric response after these three eruptions supports the idea of limiting mechanisms on volcanic stratospheric aerosol loading which is suggested by microphysical processes of aerosol particles fluctuations in stratospheric aerosol optical depth seem to be controlled to a large degree by high intensity sulfur rich eruptions e g agung 1963 which may however be relatively small in total ejecta volume such eruptions leave little geologic record but appear as acidity peaks in polar ice cores

mass balance and accumulation rate across siple dome west antarctica snow accumulation rates and rates of ice thickness change mass balance are studied at several sites on siple dome west antarctica accumulation rates are derived from analyses of grossbeta radioactivity in shallow firn cores located along a 60 km transect spanning both flanks and the crest of the dome there is a north south gradient in snow accumulation rate across the dome that is consistent with earlier radar mappingof internalstratigraphy orographicprocessesprobablycontrolthisdistribution mass balance is inferred from the difference between global positioning system gps derived vertical velocities and snow accumulation rates for sites close to the firn core locations results indicatethatthere is virtually no netthicknesschangeat fourof thefive sites the exception is at the northernmost site where a small amount of thinning is detected that appearstobe inconsistentwith other studies a possiblecause ofthisanom alousthinning is recent retreatof the grounding line of ice stream d

antarctic subglacial lakes abstract antarctic subglacial lakes were first identified by robin et al 1970 after airborne radio echo sounding res investigations of the ice sheet interior recently satellite altimetry was used to measure anomalous near flat regions on the ice sheet surface that represent a manifestation of the subglacial lake beneath using res and satellite altimetry the location and extent of antarctic subglacial lakes can be identified the largest subglacial lake exists beneath vostok station and is 14 000 km2 in area the combined area of additional subglacial lakes beneath dome c is 15 000 km2 and at least 15 000 km2 of lake surface lies beneath the remainder of the ice sheet the water depth of subglacial lakes can be estimated through seismic investigations although data exist only for lake vostok and consideration of the bedrock slopes that border subglacial lakes the depths of many subglacial lakes are of the order of 10 s 100 s of metres the total volume of water held beneath the ice sheet is estimated between 4000 and 12 000 km3 to date there are six known examples of radio echo reflections from the lake floors at a depth of no more than 20 m since e m attenuation through water is related to the salinity these data indicate that subglacial water is very pure and fresh some near flat surface regions that usually occur over lakes have been observed where no lakes exist such features are may be caused by water saturated basal sediments rather than subglacial lakes finally the spatial variation in geothermal heat flux around the central regions of antarctica can be established estimated by employing a simple thermal model of the ice sheet under an assumption that the basal ice temperature above subglacial lakes is equal to the pressure melting value calculations indicate that the geothermal heat flux varies spatially over the antarctic plate between 37 and 65 mw m 2

microbiology of the subglacial lake vostok first results of borehole frozen lake water analysis and prospects for searching for lake inhabitants this article examines the question of the possible existence of microbial life inhabiting the subglacial lake vostok buried beneath a 4 km thick antarctic ice sheet it represents the results of analysis of the only available frozen lake water samples obtained upon the first lake entry and subsequent re coring the water frozen within the borehole for comparison results obtained by earlier molecular microbiological studies of accretion ice are included in this study with the focus on thermophiles and an unknown bacterial phylotype a description of two lake vostok penetrations is presented for the first time from the point of view of possible clean water sampling finally the results of current studies of lake vostok frozen water samples are presented with the focus on the discovery of another unknown bacterial phylotype w123 10 distantly related to the above mentioned unknown phylotype af532061 detected in vostok accretion ice both successfully passing all possible controls for contamination the use of clean room facilities and the establishment of a contaminant library are considered to be prerequisites for research on microorganisms from lake vostok it seems that not yet recorded microbial life could exist within the lake vostok water body in conclusion the prospects for searching for lake inhabitants are expressed with the intention to sample the lake water as cleanly as possible in order to make sure that further results will be robust

ice formation in subglacial lake vostok central antarctica abstract the investigation of chemical and isotopic properties in the lake ice from the vostok ice core gives clues to the mechanisms involved in ice formation within the lake a small lake water salinity can be reasonably deduced from the chemical data possible implications for the water circulation of lake vostok are developed the characteristics of the isotopic composition of the lake ice indicate that ice formation in lake vostok occurred by frazil ice crystal generation due to supercooling as a consequence of rising waters and a possible contrast in water salinity subsequent consolidation of the developed loose ice crystals results in the accretion of ice to the ceiling of the lake

solute acquisition in glacial melt waters i fjallsjokull south east iceland bulk melt waters with closed system characteristics l etude de la composition des eaux de surface cations alcalinite sulfates et ph montre des modifications par rapport aux precipitations par l acquisition de substances dissoutes provenant de l alteration et de la dissolution de debris rocheux dans un systeme ouvert aux gaz carbonique atmospherique les eaux resurgentes ont des compositions variables calcite qui peuvent provenir de l eau de surface

ice cores as an index of global volcanism from 1850 to the present to evaluate an important cause of past climate change climate researchers need reliable estimates of volcanic aerosol loading in the atmosphere previous indices the dust veil index volcanic explosivity index and those by mitchell 1970 sato et al 1993 and khmelevtsov et al unpublished manuscript 1993 all have drawbacks ice core acidity and sulfate records because they contain physical evidence of atmospheric loading are a promising source of information on past volcanic aerosols but these records contain large nonvolcanic signals as well we have compared northern hemisphere nh and southern hemisphere sh annual average versions of five indices with eight nh and six sh ice core records for the period 1850 to the present in an attempt to identify the volcanic signal common to all records the indices are all highly correlated with each other for the nh although the individual ice core records are in general not well correlated with each other or with any of the indices a composite derived from averaging the cores the ice core volcano index ivi shows promise as a new index of volcanic aerosol loading this new index correlates well with the existing non ice core volcanic indices and with high frequency temperature records for the sh the individual ice cores and indices are better correlated the shivi is again highly correlated with all indices and individual ice cores but not with high frequency temperature records for both hemispheres the southern oscillation index shows no significant correlation with the volcanic indices ice cores or the ivi thus providing no evidence for the impact of volcanic eruptions on el nino southern oscillation events

patagonian origin of glacial dust deposited in east antarctica vostok and dome c during glacial stages 2 4 and 6 abstract the source area of continental dust deposited at both vostok and dome c sites east antarctica during the glacial stages stage 2 18 ka last glacial maximum stage 4 60 ka and stage 6 160 ka of the last two climatic cycles has remained constant the isotopic composition 87 sr 86 sr and 143 nd 144 nd of the ice core dust has been compared with the isotopic composition of the potential source areas antarctica new zealand southern africa australia and south america this comparison reveals the southern south american provenance of the dust for all three glacial periods as has already been shown for the lgm 1 we show that the patagonian loess and the marine shelf sediments from the argentine continental shelf which was variably emerged during glacial periods display different isotopic compositions and that the composition of the patagonian loess best matches the signature of the ice core dust the identification of the patagonian region as the source of the windblown dust deposited over east antarctica during all the latest glacial periods permits a better understanding of paleo atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models

accumulation studies on amundsenisen dronning maud land antarctica by means of tritium dielectric profiling and stable isotope measurements first results from the 1995 96 and 1996 97 field seasons the paper focuses on studies of snow pit samples and shallow firn cores taken during the 1995 96 and 1996 97 field seasons at amundsenisen dronning maud land antarctica the dating of the firn is based on the artificial tritium distribution in the snow cover and on several reference horizons identified by electrical measurements the early 1964 through 1965 horizon is marked by the deposition of sulfate released to the atmosphere during the eruption of the agung volcano in march 1963 this horizon was detected by dielectric profiling and electrical conductivity measurements the proof by chemical analysis has still to be seen at the ten investigated sites on amundsenisen the 1964 65 horizon was identified 4 1 5 7 m below the surface the accumulation rates on amundsenisen are 41 91kg ma the cores are up to 100 years old a relationship between isotope content and the mean air temperature on a regional scale can be based onmeasurements of firn temperature at10m depth at the drilling sites betweenneumayer station at the coast and heimefrontfjella the temperature gradient of the deuterium content is 9 6 k south of heimefrontfjella on the amundsenisen plateau it is only 5 5 k time series of yearly accumulation rates show no significant trend for the isotope records a significant trend to higher values with gradients of 0 1 0 2 dh a can be seen in five of the ten time series

micro investigation of epica dome c bottom ice evidence of long term in situ processes involving acid salt interactions mineral dust and organic matter abstract the epica dome c ice core edc reached a final depth of 3260 m at a maximum height of about 15 m above the ice bedrock interface in december 2004 we present here data gained from a detailed investigation of selected samples of the deeper part of the core located below 3200 m and referred to as bottom ice this part of the core has been poorly investigated so far mainly because there are significant challenges in interpreting paleo records that were very likely modified by long term in situ processes our study combines high resolution ion chromatography high resolution synchrotron x ray micro fluorescence micro xrf scanning and transmission electron microscopy our aim was to identify the long term physico chemical processes at work close to the bedrock to determine how they have altered the initial registers and ultimately to extract information on the very ancient antarctic environment the ubiquitous presence of nanometer iron oxide crystals at the surface of wind borne dust aggregates containing also large amount of organic matter raises the possibility that the consolidation of windborne dust clusters formed during ice recrystallization could be related to microbial iron reduction and thus to the progressive reactivation of dormant bacterial activity in warming ice inclusions of size and number density increasing with depth observed in the 12 last meters 3248 3260 m contain liquid and solid species among them marine biogenic acids numerous wind borne dust aggregates and clusters of large reversible calcium carbonate particles precipitated once the inclusion was formed and often covered by secondary gypsum the refreezing of slush lenses is discussed as a potential cause of the formation of such heterogeneous and complex mixtures in addition to the very fine micrometer size minerals windborne from extra antarctic continental sources and often accreted in large aggregates single medium size particles a few to ca 20 m and among them organic debris are commonly encountered their size surface shape and mineralogy suggest that aerosol transport from antarctic ice free areas played a significant role at the time edc bottom ice was formed concentrations and concentration ratios of biogenic sulfur species also advocate for the strengthening of peri antarctic meteorological patterns that favor the inland penetration of disturbed flow carrying local material very large well preserved mineral particles several tens of micrometers in diameter and biotope relics in deeper ice close to 3260 m likely come from the sub glacial environment

a 10 century comparison of prominent bipolar volcanic events in ice cores measurements of key chemical and physical parameters made along continuous and selected long sections of polar ice cores provide reliable past snow accumulation rates and other environmental records the prime accumulation indicators include variations found in the stable isotopes ionic constituents and acidity concentration levels and physical changes in the strata and structure cross correlations of the time series curves resulting from multiparameter analyses of ice cores from antarctica nby89 sp78 bs68 and greenland cr74 d3 81 d3 18c have been made the results permit construction of a bipolar chemical stratigraphy chronology of volcanic events that is coherent with the 18 o and electrical conductivity method data sets and consistent back in time with historically recorded volcanic activity a bihemispheric comparison of high non sea salt so 4 2 peaks shows strong correlation at 1885 1836 1816 1810 1459 1346 1287 1278 1259 1228 and 1168 a d at time of snow deposit the prominent 1259 a d volcanic signal appears to be a significant bipolar ice core index horizon

a comparison of the volcanic records over the past 4000 years from the greenland ice core project and dye 3 greenland ice cores since 1980 the electrical conductivity method ecm has been used to infer volcanic acid signals in greenland ice cores the method reveals the great majority of major volcanic eruptions including several known from historic records subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition i e the concentration of the volcanic acids h2so4 hci and hf plus e g the nonvolcanically derived hno3 while ecm data are available from a large number of shallow depth greenland ice cores covering the past 500 1500 years only the greenland ice core project grip greenland ice sheet project 2 gisp2 and dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in greenland ice cores representing several thousand years comparison of the volcanic signals registered in the grip and gisp2 cores will be presented elsewhere the latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature snow accumulation and chemical composition of the air here we present a comparison between the major volcanic signals over the past 4000 years in the grip core from central greenland and the dye 3 core from se greenland in order to investigate the depositional differences many of the major signals are detected in both cores but some of the differences in the records can be used to infer the latitudinal band of some eruption sites furthermore the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed

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

ultra low rare earth element content in accreted ice from sub glacial lake vostok antarctica this paper reports the first rare earth element ree concentrations in accreted ice refrozen from sub glacial lake vostok east antarctica ree were determined in various sections of the vostok ice core in order to geochemically characterize its impurities samples were obtained from accreted ice and for comparison from the upper glacier ice of atmospheric origin undisturbed disturbed and glacial flour ice ree concentrations ranged between 0 8 56 pg g 1 for ce and 0 0035 0 24 pg g 1 for lu in glacier ice and between 0 1 24 pg g 1 for ce and 0 0004 0 02 pg g 1 for lu in accreted ice interestingly the ree concentrations in the upper accreted ice ac1 characterized by visible aggregates containing a mixture of very fine terrigenous particles and in the deeper accreted ice ac2 characterized by transparent ice are lower than those in fresh water and seawater respectively we suggest that such ultra low concentrations are unlikely to be representative of the real ree content in lake vostok but instead may reflect phase exclusion processes occurring at the ice water interface during refreezing in particular the uneven spatial distribution on the order of a few cm and the large range of ree concentrations observed in ac1 are consistent with the occurrence absence of the aggregates in adjacent ice and point to the presence of solid phase concentration exclusion processes occurring within separate pockets of frazil ice during ac1 formation interestingly if the lree enrichment found in ac1 was not produced by chemical fractionation occurring in lake vostok water this may reflect a contribution of bedrock material possibly in combination with aeolian dust released into the lake by melting of the glacier ice collectively this valuable information provides new insight into the accreted ice formation processes the bedrock geology of east antarctica as well as the water chemistry and circulation of lake vostok

a 12 000 year record of explosive volcanism in the siple dome ice core west antarctica 1 air mass trajectories in the southern hemisphere provide a mechanism for transport to and deposition of volcanic products on the antarctic ice sheet from local volcanoes and from tropical and subtropical volcanic centers this study extends the detailed record of antarctic south american and equatorial volcanism over the last 12 000 years using continuous glaciochemical series developed from the siple dome a sdma ice core west antarctica the largest volcanic sulfate spike 280 g l occurs at 5881 b c e other large signals with unknown sources are observed around 325 b c e 270 g l and 2818 b c e 191 g l ages of several large equatorial or southern hemisphere volcanic eruptions are synchronous with many sulfate peaks detected in the sdma volcanic ice chemistry record the microprobe fingerprinting of glass shards in the sdma core points to the following antarctic volcanic centers as sources of tephra found in the sdma core balenny island pleiades mount berlin mount takahe and mount melbourne as well as mount hudson and possibly mount burney volcanoes of south america identified volcanic sources provide an insight into the poorly resolved transport history of volcanic products from source volcanoes to the west antarctic ice sheet

holocene electrical and chemical measurements from the epica dome c ice core the comparison between electric electric conductivity measurement ecm and dielectric profiling dep and chemical sulphate and chloride depth profiles along the first 400 m of the epica dome c ice core revealed a very good fit especially for peaks related to volcanic emissions from the comparison between these profiles a dominant contribution of sulphuric acid to the ionic balance of antarctic ice for the holocene was confirmed a progressive increase with depth was observed for chloride concentrations showing a change of relative contribution between sulphate and chloride a higher increase of chloride was evident between 270 and 360 m depth probably due to a change in source or transport processes or to an increase of the annual snow accumulation rate the dep ecm and sulphate ice signatures of tambora ad 1816 and el chichon ad 1259 eruptions are described in detail a characteristic peak series due to hcl deposition was identified at 103 109 m depth from the ecm dep and chloride profiles

evidence of glacial flour in the deepest 89 m of the vostok ice core the 3623 m long vostok ice core is divided into two main parts 1 from the surface to a depth of 3310 m the ice layers are undisturbed and may be used to reconstruct the climatic record over the past 420 kyr 2 from 3538 m to the bottom the core is made up of accreted ice formed by freezing of the lake in between the glacier ice is disturbed by ice dynamics as shown for example by inclined volcanic ash layers microparticle concentrations and distributions as well as ionic and isotopic content were used to subdivide this third section the identification of layers with bedrock material provides clues as to the entrainment processes at sub freezing temperatures dust concentration and size distribution as well as ionic content are comparable with values found in ice of glacial and interglacial periods below 3450 m depth however the mode of the volume size distribution clearly shifts from 2 1 m to 3 4 m in diameter particles as large as 30 m in diameter are observed and cannot have an aeolian origin from microscopic observations we suggest that they originate from the bedrock and represent glacial flour entrained in a shear layer up to 89 m from the glacier sole this process most likely occurred when the ice sheet was grounded before flowing over the lake

physicochemical properties of bottom ice from dome fuji inland east antarctica the deepest ice in inland antarctica is expected to preserve the oldest ice records and to potentially contain microorganisms however little is known about the physicochemical conditions in the deepest part of ice sheets this study investigates the physicochemical properties of the bottom section 3000 3035 m of the dome fuji inland ice core which is located immediately above unfrozen bedrock the ubiquitous presence of air hydrates and the water isotope composition of ice comparable to the upper main ice core show that the bottom ice is meteoric however ion concentrations exhibit abnormal drops at the greatest depths approximately below 3033 m in the same depth range microscopic investigations reveal that considerable relocation of air hydrates and micro inclusions water soluble impurities occurs suggesting that the observed reduction in ion concentration results from the segregation of inclusions to ice grain boundaries and the subsequent discharge of chemicals through liquid water veins principal component analysis of ion data supports the meteoric ice hypothesis suggesting that the bottom ice had similar original chemistry through all depths statistical analyses of chemical data suggest that the water soluble impurities attached to hydrates or dust water insoluble the ice soluble chemical species such as chlorine and solid particles are less affected by this chemical displacement phenomenon it is also noteworthy that in the bottom ice impurity chemicals which are limiting nutrients for ice dwelling microorganisms are concentrated largely to ice hydrate interfaces where oxygen another vital matter for aerobic microorganisms is also enriched

dating firn cores by vertical strain measurements we have developed a system for measuring a vertical strain rate profile in the firn on polar ice sheets using a readily available video camera to detect metal bands inserted in an air filled hole we used this system in 1995 and 1996 at taylor dome antarctica we use density measurements combined with our strain rates to infer vertical velocities from our velocities we calculate a steady state depth age scale for the firn at taylor dome the age of a visible ash layer from 79 1 m is 675 25 years this ash can be correlated with ash found at 97 2 m in a recent ice core at siple dome west antarctica

microstructure and electrical properties of marine ice and its relationship to meteoric ice and sea ice a 215 m ice core has penetrated the central part of the ronne ice shelf 76 59 s 52 16 w the core consisted of meteoric ice above 152 8 m depth below this the ice was bubble free and of seawater origin the salinity of the layer below 152 8 m depth is less than 0 05 ppt very much lower than typical sea ice the ice represents an unusual source of ice intermediate in salinity and some physical properties between meteoric ice and sea ice the structure of the ice from four different depths where salinities vary by a factor of 4 has been investigated using a scanning electron microscope sem the fabric and grain structures are unusual and seem to depend on the impurity concentration in the ice chemical impurity localization has also been investigated the dielectric properties of the ice show that the ice has a transitional behavior from the linear dependence of conductivity on chloride concentration found in meteoric ice to the less predictable sea ice behavior the behavior may be interpreted in terms of the structure of the ice the higher salinity samples show convoluted grain boundaries small grain size and brine inclusions there are indications that the brine inclusions were liquid at temperatures between 10 c and 30 c by contrast the lower salinity samples possess larger grain sizes and show no evidence of brine inclusions all samples show brine concentrated at triple grain junctions and also along two grain boundaries in higher salinity samples the dielectric properties of the lower salinity samples are well described by a jaccard mechanism with l defects created in proportion to salinity that also describes the behavior of meteoric ice higher salinity samples exhibit lower conductivity than would be seen if l defects continued to be created in proportion to salinity the dielectric and structural data are consistent with a solubility limit of about 300 m for cl in the ice lattice

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

radar detection of accreted ice over lake vostok antarctica abstract airborne radar data collected over lake vostok east antarctica show a reflection close to the vostok ice core below the depth of the meteoric accreted ice boundary maib and near the boundary between impurity rich 1 and impurity poor 2 accreted ice a12b the spatial pattern of detection of this reflection is aligned with ice flow over the southern half of the lake ice core data from the accreted ice show large variations in the number density of inclusions soluble chloride ion concentration cl charge balance derived acidity h cb and crystal orientation fabric here we investigate the existing hypothesis that this reflection is due to the maib and seek possible reflection causes that explain the radar derived reflectivity 51 8 db the likely maximum reflectivity due to an insoluble mineral inclusion contrast is 125 db if none of the cl or h ions are trapped within inclusions then ice conductivity models predict a reflectivity of 50 db near the maib and 58 db near the a12b both primarily due to large h cb changes if some of those ions are trapped within inclusions then those values are smaller fabric contrasts at either boundary can produce significant reflectivities 62 db these results indicate that the mineral inclusion contrast near the maib does not cause the observed reflection because of uncertainty in the in situ location of the soluble impurities and because impurity rich accreted ice 1 is believed to only originate in the small bay in the southwestern corner of the lake yet the reflection is observed over a much wider area we argue that a fabric contrast at the a12b is the probable reflection cause both predicted spatial variations in accretion rates near the upstream shoreline or lower ice temperatures along flowbands that originate at bedrock ridges near the upstream shoreline may explain why the reflection is not detected everywhere that accretion is predicted

eight centuries of volcanic signal and climate change at talos dome east antarctica 1 during the 1996 programma nazionale di ricerche in antartide international trans antarctic scientific expedition traverse two firn cores were retrieved from the talos dome area east antarctica at elevations of 2316 m td 89 m long and 2246 m st556 19 m long cores were dated by using seasonal variations in non sea salt nss so42 concentrations coupled with the recognition of tritium marker level 1965 1966 and nss so42 spikes due to the most important volcanic events in the past pinatubo 1991 agung 1963 krakatoa 1883 tambora 1815 kuwae 1452 unknown 1259 the number of annual layers recognized in the td and st556 cores was 779 and 97 respectively the d record obtained from the td core has been compared with other east antarctic isotope ice core records dome c epica south pole taylor dome these records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries which might be related to the little ice age lia cold period because of the high degree of geographical variability the strongest lia cooling was not temporally synchronous over east antarctica and the analyzed records do not provide a coherent picture for east antarctica the accumulation rate record presented for the td core shows a decrease during part of the lia followed by an increment of about 11 in accumulation during the 20th century at the st556 site the accumulation rate observed during the 20th century was quite stable

spatial variation of englacial radar attenuation modeling approach and application to the vostok flowline 1 constraining the spatial variation of englacial radar attenuation is critical for accurate inference of the spatial variation of the englacial and basal properties of ice sheets from radar returned power here we evaluate attenuation models that account for spatial variations in ice temperature and chemistry and test them along the flowline that passes through the vostok ice core site antarctica the simplest model often used but rarely valid assumes a uniform attenuation rate everywhere along the flowline so that total attenuation is proportional to ice thickness the next simplest model uses spatially varying temperatures predicted by an ice flow model and assumes uniform chemistry additional models account for spatially varying chemistry using englacial stratigraphy we find that the roundtrip attenuation to the bed can easily differ by 10 db or more between the uniform attenuation rate model and models that account for variable ice temperature such differences are sufficient to confound the delineation of dry and wet beds also including spatial variations in chemistry produces smaller differences 10 db but the magnitude of these differences depends on the relative importance of dry and wet deposition of impurities in the past accounting for dry deposited impurities requires ice flow modeling and results in larger differences from all other models which assume uniform chemistry or wet deposition only these results indicate that modeling the spatial variation of attenuation requires a spatially varying temperature model in order to infer bed conditions from bed returned power accurately and that both ice core data and radar stratigraphy are also strongly desirable

borehole evidence for a thick layer of basal ice in the central ronne ice shelf the ronne ice shelf floating between berkner island and the antarctic peninsula is the biggest ice shelf in antarctica it drains an estimated 1 2 106km2 of the antarctic ice sheet much of it resting on bedrock below sea level consequently the balance and dynamics of this ice shelf is of importance to antarctic glaciology especially with regard to the integration of this part of the cryo sphere into the global processes that control the climate of the earth extensive radio echo sounding res by robin and others revealed reflections in the central part of the ronne ice shelf at the relatively shallow depth of 100 200 m below surface1 the interpretation of these echoes which varied in strength was ambiguous and the possibility of internal reflecting horizons was thoroughly discussed but after surface elevation measurements by radar altimeter from drifting balloons appeared to fit the presence of thin ice it was decided to base a thickness map of the ronne ice shelf on these res echoes1 4 we now present direct observational evidence from boreholes that the total ice thickness is much greater than mapped and that the shallow res reflections therefore do come from internal horizons