the carrington event not observed in most ice core nitrate records the carrington event of 1859 is considered to be among the largest space weather events of the last 150 years we show that only one out of 14 well resolved ice core records from greenland and antarctica has a nitrate spike dated to 1859 no sharp spikes are observed in the antarctic cores studied here in greenland numerous spikes are observed in the 40 years surrounding 1859 but where other chemistry was measured all large spikes have the unequivocal signal including co located spikes in ammonium formate black carbon and vanillic acid of biomass burning plumes it seems certain that most spikes in an earlier core including that claimed for 1859 are also due to biomass burning plumes and not to solar energetic particle sep events we conclude that an event as large as the carrington event did not leave an observable widespread imprint in nitrate in polar ice nitrate spikes cannot be used to derive the statistics of seps

a continuous 770 year record of volcanic activity from east antarctica a 100 m ice core from site g 15 accumulation rate 0 1 m water yr 1 mean annual temperature 38 c on the mizuho plateau dronning maud land east antarctica has been analysed using the dielectric profiling dep technique the capacitance and conductance of the core were measured at ac frequencies 20 hz 300 khz the high frequency conductivity profile shows variations that are primarily related to the strong acids derived from volcanic activity the tambora 1815 eruption can be identified with the aid of an approximate chronology based on the firn densification rate other historic eruptions can then be recognised beyond about 300 years historical observations are very few however if a constant overall accumulation rate is assumed a well known eruption of 1259 a d can be found near the bottom of the core other peaks in the conductivity profile can then be assigned dates accurate to within a few years using the conductivity profile it is possible to estimate the relative acid deposition fluxes produced by the main eruptions with reasonable accuracy the estimated acid deposisition fluxes realtive to the tambora 1815 eruption of agung 1963 is 27 krakatoa 1883 25 the signal of 1601 28 and that of 1259 53

inferring geothermal heat flux from an ice borehole temperature profile at law dome east antarctica geothermal heat flux ghf is an important control on the dynamics of antarctica s ice sheet because it controls basal melt and internal deformation however it is hard to estimate because of a lack of in situ measurements estimating ghf from ice borehole temperature profiles is possible by combining a heat transfer equation and the physical properties of the ice sheet in a numerical model in this study we truncate ice borehole temperature profiles to determine the minimum ratio of temperature profile depth to ice sheet thickness required to produce acceptable ghf estimations for law dome a temperature profile that is within 60 of the local ice thickness is sufficient for an estimation that is within approximately one median absolute deviation of the whole profile ghf estimation this result is compared with the temperature profiles at dome fuji and the west antarctic ice sheet divide which require a temperature profile that is 80 and more than 91 of the ice thickness respectively for comparable accuracy in deriving ghf median estimations from truncated temperature profiles it is possible to discriminate between available ghf models this is valuable for assessing and constraining future ghf models

the seafloor geomorphology of the windmill islands wilkes land east antarctica evidence of law dome ice margin dynamics abstract a high resolution multibeam sonar dataset covering an area of ca 33 km 2 was collected in the vicinity of the windmill islands 67 s 110 e wilkes land east antarctica the new data permit visualisation of the nearshore seafloor morphology in unprecedented detail providing invaluable insight into the ice sheet history of the region a range of geomorphic features are evident including prominent parallel northwest trending linear fault sets affecting mesoproterozoic metamorphic basement which appear to control the regional coastal physiography the fault systems probably formed during fragmentation of eastern gondwana during the mesozoic networks of sub glacial meltwater channels preserved on bedrock platforms and ridges indicate grounding of a thick ice sheet over the continental shelf during previous glaciations west trending subtle glacial lineations and streamlined landforms record evidence of the westward expansion of the grounded law dome ice sheet margin probably during the late pleistocene the direction of these features coincides with glacial striae on onshore crystalline bedrock outcrops perhaps the most striking glacial geomorphological features are sets of arcuate ridges confined mostly within glacially excavated u shaped troughs formed by erosion of the northwest trending bedrock fault sets these ridge sets are interpreted as push moraines or grounding zone features formed during episodic retreat of highly channelised topographically controlled ice streams following ice surging of the law dome margin this event was possibly triggered in response to local environmental forcing during the mid late holocene minor post glacial marine sedimentation is preserved in several small 1 km 2 isolated basins with shallow seaward sills

site information and initial results from deep ice drilling on law dome antarctica the aim of deep ice drilling on law dome antarctica has been to exploit the special characteristics of law dome summit i e low temperature and high accumulation near an ice divide to obtain a high resolution ice core for climatic environmental studies of the holocene and the last glacial maximum lgm drilling was completed in february 1993 when basal ice containing small fragments of rock was reached at a depth of 1196 m accurate ice dating obtained by counting annual layers revealed by fine detail 18 o peroxide and electrical conductivity measurements is continuous down to 399 m corresponding to a date of ad 1304 sulphate concentration measurements made around depths where conductivity tracing indicates volcanic fallout allow confirmation of the dating for agung in 1963 and tambora in 1815 or estimates of the eruption date from the ice dating for the kuwae vanuatu eruption 1457 the lower part of the core is dated by extrapolating the layer counting using a simple model of the ice flow at the lgm ice fabric measurements show a large decrease 250 to 14 mm 2 in crystal size and a narrow maximum in c axis verticality the main zone of strong single pole fabrics however is located higher up in a broad zone around 900 m oxygen isotope 18 o measurements show holocene ice down to 1113 m the lgm at 1133 m and warm 18 o about the same as holocene ice near the base of the ice sheet the lgm holocene 18 o shift of 7 0 only 1 larger than for vostok indicates that law dome remained an independent ice cap and was not overridden by the inland ice sheet in the glacial

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

sediment effect on tsunami generation of the 1896 sanriku tsunami earthquake the 1896 sanriku earthquake was one of the most devastating tsunami earthquakes which generated an anomalously larger tsunami than expected from its seismic waves previous studies indicate that the earthquake occurred beneath the accretionary wedge near the trench axis it was pointed out recently that sediments near a toe of an inner trench slope with a large horizontal movement due to the earthquake might have caused an additional uplift in this paper the effect of the additional uplift to tsunami generation of the 1896 sanriku tsunami earthquake is quantified we estimate the slip of the earthquake by numerically computing tsunamis and comparing their waveforms with those recorded at three tide gauges the estimated slip for the model without the additional uplift is 10 4 m and those with the additional uplift are 5 9 6 7 m this indicates that the additional uplift of the sediments near the trench has a large effect on the tsunami generation

modelled stress distributions at the dome summit south borehole law dome east antarctica a comparison of anisotropic ice flow relations in this study we compare the anisotropic flow relations for polycrystalline ice of azuma and goto azuma 1996 thorsteinsson 2002 placidi and others 2010 and budd and others 2013 observations from the dome summit south dss ice coring site at law dome east antarctica are used to model the vertical distribution of deviatoric stress components at the borehole site the flow relations in which the anisotropic rheology is parameterized by a scalar function so that the strain rate and deviatoric stress tensor components are collinear provide simple shear and vertical compression deviatoric stress profiles that are most consistent with laboratory observations of tertiary creep in combined stress configurations those flow relations where 1 the anisotropy is derived from the magnitude of applied stresses resolved onto the basal planes of individual grains and 2 the macroscopic deformation is obtained via homogenization of individual grain responses provide stress estimates less consistent with laboratory observations this is most evident in combined simple shear and vertical compression flow regimes where shear is dominant our results highlight the difficulties associated with developing flow relations which incorporate a physically based description of microdeformation processes in particular this requires that all relevant microdeformation recrystallization and recovery processes are adequately parameterized

beryllium 10 transport to antarctica results from seasonally resolved observations and modeling 1 cosmogenic 10be measured in polar ice cores has important application in the reconstruction of past solar activity however the processes controlling its atmospheric transport and deposition to the ice sheets are not fully understood here we use the seasonal changes in 10be concentrations in a 10 year monthly resolved ice core record from the law dome site east antarctica in conjunction with echam5 ham general circulation model gcm simulations of 10be and 7be deposition as tools to examine this problem maximum 10be concentrations are observed in the ice core during the austral late summer to early autumn summer autumn while minimum concentrations are observed during the austral winter the gcm simulations corroborated by earlier observations of 10be 7be ratios in antarctica from the georg von neumayer air sampling station suggest that the 10be concentration maximum is linked to direct input of stratospheric 10be from the antarctic stratosphere to the lower levels of the antarctic troposphere during the austral summer autumn this result contrasts with the modeled transport of 10be to greenland where the seasonal maximum in stratospheric input is seen in the late winter to spring synchronous with the timing of the seasonal maximum in midlatitude stratosphere to troposphere exchange our results suggest that a different combination of processes is responsible for the transport of 10be to the antarctic and greenland ice sheets

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

features of meteorological events preserved in a high resolution law dome east antarctica snow pit snow pitandshallow firn corerecordsofoxygenisotoperatios d 18 o and traceionspeciesweregeneratedatahigh accumulationsiteonlaw dome eastantarctica concordancebetweenaccumulationeventsidentifiedin recordsupto 7 7kmapartconfirms that the observed glaciochemical variations are the result of regional rather than local sur face effects this allows calibration of the snow pit records with measured meteorological parameters netaccumulationperiodsthatcomprisethesnow pitrecordareidentifiedusing hourly snow accumulation measurements from a co located automatic weather station aws particular focus isgiventothreenetaccumulationperiods preservedduringaustral summer 1999 2000 that correspond to the top 0 5m of the snow pit local meteorological conditions recorded during the summer accumulation periods by the aws are combined with regional and synoptic scale meteorology derived from casey station 110km away and advancedvery high resolution radiometer satellite imagery to identify potential source regions forchemical signals preserved in summer snowat law dome

a model of crystal size evolution in polar ice masses in the deep ice cores drilled at the grip ngrip and gisp2 sites in greenland and at byrd station and the summit of law dome in antarctica the mean crystal size increases with depth in the shallow subsurface and reaches steady values at intermediate depth this behaviour has been attributed to the competition between grain boundary migration driven crystal growth and crystal polygonization but the effects of changing crystal dislocation density and non equiaxed crystal shape in this competition are uncertain we study these effects with a simple model it describes how the mean height and width of crystals evolve as they flatten under vertical compression and as crystal growth and polygonization compete the polygonization rate is assumed to be proportional to the mean dislocation density across crystals migration recrystallization which can affect crystal growth via strain induced grain boundary migration but whose impact on the mean crystal size is difficult to quantify for ice at present is not accounted for when applied to the five ice core sites the model simulates the observed crystal size profiles well down to the bottom of their steady regions although the match for law dome is less satisfactory polygonization rate factors retrieved for the sites range from 10 5 to 10 2 a 1 we conclude that since crystal size and dislocation density evolve in a strongly coupled manner consistent modelling requires multiple differential equations to track both of these variables future ice core analysis should also determine crystal size in all three principal directions

post depositional movement of methanesulphonic acid at law dome antarctica and the influence of accumulation rate a series of ice cores from sites with different snow accumulation rates across law dome east antarctica was investigated for methanesulphonic acid msa movement the precipitation at these sites up to 35 km apart is influenced by the same air masses the principal difference being the accumulation rate at the low accumulation rate w20k site 0 17 m ice equivalent msa was completely relocated from the summer to winter layer moderate movement was observed at the intermediate accumulation rate site 0 7 m ice equivalent dome summit south dss while there was no evidence of movement at the high accumulation rate de08 site 1 4 m ice equivalent the main dss record of msa covered the epoch ad 1727 2000 and was used to investigate temporal post depositional changes co deposition of msa and sea salt ions was observed in the surface layers outside of the main summer msa peak which complicates interpretation of these peaks as evidence of movement in deeper layers a seasonal study of the 273 year dss record revealed msa migration predominantly from summer into autumn in the up core direction but this migration was suppressed during the tambora 1815 and unknown 1809 volcanic eruption period and enhanced during an epoch 1770 1800 with high summer nitrate levels a complex interaction between the gradients in nss sulphate nitrate and sea salts which are influenced by accumulation rate is believed to control the rate and extent of movement of msa

antarctic volcanic flux ratios from law dome ice cores 3 climatestudiescenter institutefor quaternarystudies universityofmaine orono me 04469 5717 u s a abstract explosivevolcanic eruptions can inject largequantitiesof sulphur dioxide intothe stratosphere theaerosolsthat result fromoxidationof thesulphur dioxidecanpro duce significant cooling of the troposphere by reflecting or absorbing solar radiation it is possibleto obtainanestimateoftherelativestratosphericsulphuraerosolconcentrationpro duced by different volcanoes by comparing sulphuric acid fluxes determined by analysis of polaricecores here weuseanon sea saltsulphatetimeseriesderivedfromthreewell dated law dome ice cores to investigate sulphuric acid flux ratios for major eruptions over the period ad1301 1995 weuseadditionaldata fromothercorestoinvestigatesystematicspa tial variability in the ratios only for the kuwae eruption law dome ice date ad1459 5 wasthe h2so4 flux largerthanthatdepositedbytambora law domeicedate ad1816 7

magnetotelluric evidence for crustal suture zones bounding the southern great valley california a geoelectric section inferred from a regional magnetotelluric study across the coast ranges the great valley and the sierra nevada reveals significant variations in electrical resistivity zones of lower resistivity interpreted at depths from 10 km to at least 30 km lie near mapped geologic boundaries between the coast ranges and the great valley and beneath the eastern side of the great valley the former boundary is inferred by others to separate the subduction complex of the coast ranges from the mafic basement of the great valley the lower resistivities are most likely associated with metasediments trapped between the coast ranges ophiolite and the former oceanic crust beneath the great valley the latter boundary is problematic but may be evidence for a deep metasedimentary section trapped between the ophiolites beneath the great valley and the granitic rocks of the sierra nevada the lack of change in the magnetotelluric phase across the great valley indicates that a suture zone marked by lower resistivities is unlikely to be present beneath the valley however this does not preclude the existence of a resistive suture zone

high precision dating of volcanic events a d 1301 1995 using ice cores from law dome antarctica a record of volcanic activity over the period a d 1301 1995 has been extracted from three law dome ice cores east antarctica the record dating is unambiguous at the annual level from a d 1807 to 1995 and has an uncertainty of 1 year at a d 1301 signals from 20 eruptions are preserved in the record including those of two unknown eruptions with acid deposition beginning in a d 1810 8 and a d 1685 8 the beginning of the ice core signal from the a d 1815 tambora eruption is observed in the austral summer of a d 1816 1817 the mean observed stratospheric transport and deposition time to law dome from the eruption site is 1 5 years 0 6 years from 11 well dated eruptions the largest eruption observed in the law dome record has its maximum in a d 1460 with volcanic sulfate deposition beginning in the austral winter of a d 1459 this event is also observed in other ice core records and is attributed to the volcano kuwae with an eruption date in the range a d 1455 9 1459 9 if all sources of error are considered this is at least three years later than the date previously ascribed by dendrochronological and historical studies

lead ba and bi in antarctic law dome ice corresponding to the 1815 ad tambora eruption an assessment of emission sources using pb isotopes lead ba and bi concentrations and pb isotopic compositions have been measured in antarctic law dome 66 8 s 112 4 e ice dated from 1814 ad to 1819 ad by thermal ionisation mass spectrometry to investigate the possible deposition of heavy metals from the 1815 ad eruption of tambora volcano 8 5 s 117 4 e in indonesia although volcanic s emissions from tambora observed as so42 are present in the antarctic ice core record there are grounds to question the origin of the pb and bi also deposited at law dome from late 1817 as the pb isotope data suggest this pb originated from mount erebus 77 5 s 167 2 e on ross island antarctica it is shown that at least 97 of any pb and bi emitted from tambora was removed from the atmosphere within the 1 6 year period required to transport aerosols from indonesia to antarctica consequently increased pb and bi concentrations observed in law dome ice about 1818 ad are attributed to either increased heavy metal emissions from mount erebus or increased fluxes of heavy metals to the antarctic ice sheet resulting from climate and meteorological modifications following the tambora eruption elevated ba concentrations observed from mid 1816 to mid 1818 indicate increased atmospheric loading of rock and soil dust also occurred at the time

holocene deglaciation sea level change and the emergence of the windmill islands budd coast antarctica a holocene deglaciation sequence for the windmill islands was determined from the 14c age of raised marine shorelines lakebottom sediments and adelie penguin remains found in abandoned rookeries a north south gradient in the elevation of the upper marine limit was observed with the highest marine limit 31 32 m observed on browning peninsula and hull island at the southern edge of the islands correspondingly the southern islands were found to have been deglaciated by 8000 corr yr b p while the northern islands were deglaciated by 5500 corr yr b p isostatic uplift rates were calculated as 0 5 to 0 6 m 100 yr with an estimated total uplift of around 53 m which indicates late pleistocene ice sheet thicknesses of 200 and 400 m over the islands and adjacent petersen bank respectively the margin of the late pleistocene grounded ice sheet extended an estimated 8 15 km offshore which coincides with the location of the 200 m isobath

origin and development of textures and fabrics in basal ice at summit central greenland abstract detailed textural and crystallographic characteristics of the bottom 6 m of the grip core summit central greenland are presented the results are discussed in the light of present day fabric analogues ice fabrics are shown to retain the mark from the entrainment of locally formed ice by the growing ice sheet this mark is only partly overprinted by the present day stress configuration at the ice divide these results corroborate the model put forward by souchez et al 1 on stable isotopes and gas composition grounds in which the basal silty ice appears as a remnant of a growing stage of the ice sheet during this stage which probably represents the original build up ice of local origin formed at the ground surface was overridden by the main ice sheet and incorporated into its base preservation of remnants of ancient fabric patterns and occurrence of annealing recrystallization fabrics just above the first layer of silty ice are used amongst other arguments to demonstrate that this basal ice is not presently subject to large cumulative strains the implications for flow and dating models are discussed

covariation of sea ice and methanesulphonic acid in wilhelm ii land east antarctica sea ice plays an important role in ocean atmosphere heat exchange global albedo and the marine ecosystem knowledge of variation in sea ice extent is essential in order to understand past climates and to model possible future climate scenarios this paper presents results from a short firn core spanning 15 years collected from near mount brown wilhelm ii land east antarctica variations of methanesulphonic acid msa at mount brown were positively correlated with sea ice extent from the coastal region surrounding mount brown 60 1208 e and from around the entire antarctic coast 0 3608 e previous results from law dome identified this msa sea ice relationship and proposed it as an antarctic sea ice proxy curran and others 2003 with the strongest results found for the local law dome region our data provide supporting evidence for the law dome proxy at another site in east antarctica but a deeper mount brown ice core is required to confirm the sea ice decline suggested by curran and others 2003 results also indicate that this deeper record may also provide a more circum antarctic sea ice proxy

holocene glacier and deep water dynamics adelie land region east antarctica abstract this study presents a high resolution multi proxy investigation of sediment core md03 2601 and documents major glacier oscillations and deep water activity during the holocene in the adelie land region east antarctica a comparison with surface ocean conditions reveals synchronous changes of glaciers sea ice and deep water formation at milankovitch and sub milankovitch time scales we report 1 a deglaciation of the adelie land continental shelf from 11 to 8 5 cal ka bp which occurred in two phases of effective glacier grounding line retreat at 10 6 and 9 cal ka bp associated with active deep water formation 2 a rapid glacier and sea ice readvance centred around 7 7 cal ka bp and 3 five rapid expansions of the glacier sea ice systems during the mid to late holocene associated to a long term increase of deep water formation at milankovich time scales we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier sea ice ocean system throughout the holocene in the adelie land region in addition the orbitally forced seasonality seems to control the coastal deep water formation via the sea ice ocean coupling which could lead to opposite patterns between north and south high latitudes during the mid to late holocene at sub milankovitch time scales there are eight events of glacier sea ice retreat and expansion that occurred during atmospheric cooling events over east antarctica comparisons of our results with other peri antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier sea ice ocean interactions and their holocene evolutions reflect a more global antarctic holocene pattern

iron in ice cores from law dome a record of atmospheric iron deposition for maritime east antarctica during the holocene and last glacial maximum total dissolvable iron tdfe was measured in sections of ice cores recovered from law dome on the coast of wilkes land east antarctica these samples include ice dating from the last glacial maximum lgm the last deglaciation and the early and mid holocene as well as samples from the anthropocene that have been dated with seasonal to annual resolution combining our tdfe concentration data with estimates of the ice accumulation rate we estimate the atmospheric iron deposition for law dome and the adjacent southern ocean during these periods our results indicate that the atmospheric iron deposition flux to this region during the lgm 8 mol fe m 2 yr 1 was an order of magnitude higher than the average holocene deposition flux 0 8 mol fe m 2 yr 1 this holocene flux estimate is significantly higher than recent estimates of atmospheric iron deposition based on the analysis of iron in samples of the dome c epica ice core implying that there are significant meridional gradients in eolian iron flux to the antarctic region our data also suggest that there have been significant variations in atmospheric iron deposition to law dome and adjacent ocean waters over seasonal to decadal timescales during the past century analysis of ice samples dating from calendar years 1927 to 1928 indicates an anomalously high flux of tdfe to the law dome region amounting to around half the maximum lgm flux possibly as a result of severe drought conditions on the australian continent given that chronic iron deficiency is thought to limit phytoplankton production in much of the ocean around antarctica such large secular variations in atmospheric iron supply are likely to have had profound impacts on year to year primary production and ecosystem structure in antarctic waters

firn air δ15n in modern polar sites and glacial interglacial ice a model data mismatch during glacial periods in antarctica the phase lag between atmospheric composition air bubbles and temperature water isotopes can be quantified from ice cores provided that the age difference between entrapped air and the surrounding air can be correctly estimated this difference depends on the lock in depth lid when air no longer mixes with the atmosphere the lid can be estimated from firnification models or from the air isotopic composition 15n and 40ar both methods give consistent results for greenland and one coastal site in antarctica byrd new firn measurements in greenland northgrip and antarctica berkner island bas depot dome c confirm that firnification models correctly reproduce the present lid over a large range of surface conditions however a systematic mismatch is observed for the last glacial maximum lgm in east antarctic sites vostok dome c dome f questioning the model s validity here we use new 15n measurements from two coastal antarctic sites kohnen station and law dome providing depth estimates again distinct from firnification model calculations we show that this discrepancy can be resolved by revising the estimate of past accumulation rates 15n measurements can therefore help to constrain past accumulation rate and improve ice core dating

ice core evidence for antarctic sea ice decline since the 1950s the instrumental record of antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal antarctica here we report a significant correlation p

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

drilling to the beds of the greenland and antarctic ice sheets a review we give a review of drilling to the beds of the greenland and antarctic ice sheets with a history of just a century we use a chronological rather than a geographical ordering to emphasize the way drilling has developed the review is divided into two parts core drilling and hole only drilling for access to the beds or the deep interior of the ice sheets this is an overview not a comprehensive report on each project while we have endeavoured to include all projects that fit our selection criteria we have not provided all the technical details

late holocene east antarctic climate trends from ice core and lake sediment proxies a high resolution record of evaporation for the last 650 years was derived from the diatom salinity signal preserved in a sediment core taken from ace lake vestfold hills 68 28 s 78 11 e antarctica the seasonal oxygen isotope signal preserved in an ice core from law dome 66 44 s 112 50 e antarctica revealed a high resolution summer temperature record for the same time period the two proxies show highly correlated behaviour despite having significantly different climatic response mechanisms and a large geographic separation the correlation observed between proxies based on such differing processes and analytical method ologies provides not only a climate record for the past 650 years that is both robust and regionally representative of coastal east antarctica but also confirmation of the utility of reconstructions using these methods

the seneze maar french massif central hypothesis regarding a catastrophe occurring about 1 5 million years ago abstract a reconstruction based on direct observations in the form of borings and paleontological digs indicates repetitive catastrophes in the palaeo lake of the seneze depression long after formation of the maar this event is correlated with extensive slumping associated with erosion of the crater rim induced by a critical ring fault k ar dating gives a lower limit of around 2 48 million years for the initial formation but not the lapse of time between eruption and filling according to drilling sedimentology and palynological analysis the lake was functional between 2 3 and 1 3 million years ago i e throughout the tiglian and at the beginning of the eburonian the destruction of all animal life could only have been due to asphyxia but probably resulted from a co 2 release all classes of animals mainly mammals were affected and subsequently died they are found in the same levels in several fossiliferous beds at the top of the lacustrine deposits and also in reworked debris from the crater rim

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

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

a seasonal deuterium excess signal at law dome coastal eastern antarctica a southern ocean signature the snow isotopic composition 18o and d of two shallow cores from the high accumulation summit region of law dome east antarctica was measured at monthly resolution over the 1980 1992 period while the 18o or d signals clearly reflect the local temperature cycle the deuterium excess d d 8 18o is shifted with respect to 18o cycle by a 4 months lag interpretation of this phase lag is investigated using both an atmospheric general circulation model agcm which includes the water isotopic cycles and a simple isotopic model which better describes the microphysical processes within the cloud using this dual approach we show that the seasonality of 18o and d at law dome summit results from a combination of the southern ocean temperature cycle shifted by 2 3 months with respect to the local insolation and seasonal moisture origin changes due to a strong contribution of the local ocean when ice free both approaches are consistent with a dominant temperate to subtropical moisture origin we thus demonstrate from our present day subseasonal study that the record of d in the dome summit south dss deep ice core represents a potential tool for identifying changes in southern ocean temperatures and or sea ice cover at the scale of the past thousand years

relative timing of deglacial climate events in antarctica and greenland the last deglaciation was marked by large hemispheric millennial scale climate variations the bolling allerod and younger dryas periods in the north and the antarctic cold reversal in the south a chronology from the high accumulation law dome east antarctic ice core constrains the relative timing of these two events and provides strong evidence that the cooling at the start of the antarctic cold reversal did not follow the abrupt warming during the northern bolling transition around 14 500 years ago this result suggests that southern changes are not a direct response to abrupt changes in north atlantic thermohaline circulation as is assumed in the conventional picture of a hemispheric temperature seesaw

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

climatic and glaciological information inferred from air content measurements of a law dome east antarctica ice core the total air content v of ice has been measured along the dome summit south dss core from law dome east antarctica the main features of this record are the very well preserved sub annual fluctuations of v down to at least 900 m depth and the significant increase of the v values during the last deglaciation the sub annual variations reflect changes in close off porosity and we interpret the v seasonal peaks as tracers of depth hoar layers for the longer time scale the large v fluctuations observed are interpreted in terms of elevation and or close off porosity changes under different assumptions we analyze the possible influence of a different global pressure field and or a change in seasonal temperature and precipitation cycles during the last glacial period our estimates of surface elevation changes derived from the v data are then compared with independent reconstructions of past elevations

formaldehyde and peroxide concentrations in law dome antarctica firn and ice cores peroxide speciation and formaldehyde measurements have been made on ice cores retrieved from law dome antarctica measurements were made for ice deposited during four different periods modern pre industrial holocene early holocene and last glacial maximum lgm the data show modern peroxide levels 50 above pre industrial levels at 1 6 mol l 1 and an absence of methyl hydroperoxide down to a detection threshold of 0 003 mol l 1 formaldehyde levels show a 40 increase from pre industrial to modern times rising from 0 07 mol l 1 to 0 10 mol l 1 with a further increase and possible seasonality near the surface which we associate with post depositional processes peroxide levels in lgm ice are low but formaldehyde concentrations are high at 0 13 mol l 1 relative to modern levels similar high levels of formaldehyde are seen in early holocene ice 6900 years bp

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

stable isotopes in the basal silty ice preserved in the greenland ice sheet at summit environmental implications modelling ice sheet behaviour in the context of climatic changes depends on initial and boundary conditions which can be better defined by studying the composition of basal ice this study deals with basal ice reached by deep drilling at summit in central greenland grip core the isotopic composition of this ice indicates that ice formed at the ground surface in the absence of the ice sheet largely contributed to its formation the basal silty ice is a remnant of a growing stage of the ice sheet possibly the original build up

seasonality in late holocene climate from ice core records high resolution ice core 18o data from a site with well preserved seasonal cycles are used to extract seasonal temperature trends over the last 700 years with an effective resolution of a few mont

the lead pollution history of law dome antarctica from isotopic measurements on ice cores 1500 ad to 1989 ad abstract lead isotopic compositions and pb and ba concentrations have been measured in ice cores from law dome east antarctica covering the past 6500 years natural background concentrations of pb 0 4 pg g and ba 1 3 pg g are observed until 1884 ad after which increased pb concentrations and lowered 206pb 207pb ratios indicate the influence of anthropogenic pb the isotopic composition of natural pb varies within the range 206pb 207pb 1 20 1 25 and 208pb 207pb 2 46 2 50 with an average rock and soil dust pb contribution of 8 12 a major pollution event is observed at law dome between 1884 and 1908 ad elevating the pb concentration four fold and changing 206pb 207pb ratios in the ice to 1 12 based on pb isotopic systematics and pb emission statistics this is attributed to pb mined at broken hill and smelted at broken hill and port pirie australia anthropogenic pb inputs are at their greatest from 1900 to 1910 and from 1960 to 1980 during the 20th century ba concentrations are consistently higher than natural levels and are attributed to increased dust production suggesting the influence of climate change and or changes in land coverage with vegetation

seasonal variability in the input of lead barium and indium to law dome antarctica lead pb isotopic compositions and concentrations and barium ba and indium in concentrations have been determined at monthly resolution in five law dome coastal eastern antarctica ice core sections dated from 1757 ad to 1898 ad natural background pb concentrations in 1757 ad average 0 2 pg g 1 and can be attributed to mineral dust and volcanic emissions with 206pb 207pb ratios reaching up to 1 266 0 002 from 1887 ad to 1898 ad pb concentrations reached 5 pg g 1 and 206pb 207pb ratios decreased to 1 058 0 001 as a result of additional inputs of pb from anthropogenic sources seasonal variability in the late 1880s has been investigated by decoupling volcanic pb from the total measured pb concentrations revealing spring and autumn maxima and consistent winter minima in anthropogenic pb and mineral dust ba concentrations we link this variability to the annual cycle in the position and strength of the antarctic circumpolar trough and the southern ocean westerly winds to the north of the trough region during the autumn and spring seasons these systems increase in strength transporting more impurity laden air from the southern hemisphere continental regions to eastern antarctica and law dome as this pb is isotopically identical to that emitted from south eastern australia broken hill port pirie this implies a relatively direct air trajectory pathway from southern australia to law dome eastern antarctica

uncertainties in elevation changes and their impact on antarctic temperature records since the end of the last glacial period abstract this study presents a sensitivity analysis considering the influence of elevation changes associated with both ice thickness and land height changes on water stable isotope temperature proxies from antarctic ice cores we compare results from three different ice sheet models and three different earth viscosity models at a 10 ice core sites as expected the ice thinning signal at west antarctic sites is the largest contributor to elevation induced temperature changes the signal predicted by the ice models considered produced 100 200 of the total glacial to interglacial signal in d indicating that the deglacial ice thinning is overestimated by an amount approaching an order of magnitude at some locations this indicates that the total volume loss in these models is considerably overestimated furthermore the predicted rate of this change is not supported by the isotope data and so again most likely reflects inaccuracies in the adopted ice models estimates of contemporary ice mass changes inferred from satellite gravity data corrected using any of these models with therefore be biased as a result the isostatic signal acts to reduce the total elevation change at most sites and has a relatively small magnitude a few to 20 of that due to the ice thickness change so is secondary at most sites and for most of the time however our results indicate that it could be the dominant control on elevation at some west antarctic sites during the holocene resulting in a secular cooling signal of 10 20 in d none of the models capture the holocene isotopic depletion trend present at several sites in east antarctica

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

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

a new spatial distribution map of δ18o in antarctic surface snow 1 we developed a gridded map of surface antarctic snow isotopic composition using a recently compiled database and the modified bowen and wilkinson 2002 model using latitude and elevation as the primary predictors while also incorporating regional and local deviations based on available isotopic data the map was generated using a 1 km digital elevation model grid data as the model input the average of the absolute deviations between observations and predictions was about 0 8 and the standard deviation is 0 9 the resulting 18o patterns reproduced correctly spatial isotopic gradients with respect to geographical characteristics as well as climatic features

glacio isostasy and glacial ice load at law dome wilkes land east antarctica abstract the holocene sea level high stand or marine limit in wilkes land east antarctica reached 30 m above present sea level at a few dispersed sites the most detailed marine limit data have been recorded for the windmill islands and budd coast at the margin of the law dome ice cap a dome of the east antarctic ice sheet eais relative sea level lowering of 30 m and the associated emergence of the windmill islands have occurred since 6900 14c corr yr b p numerical modeling of the earth s rheology is used to determine the glacio isostatic component of the observed relative sea level lowering glaciological evidence suggests that most of eais thickening occurred around its margin with expansion onto the continental shelf consequently a regional ice history for the last glacial maximum lgm was applied in the glacio isostatic modeling to test whether the observed relative sea level lowering was primarily produced by regional ice sheet changes the results of the modeling indicate that the postglacial 13 000 to 8000 14c yr b p removal of an ice load of between 770 and 1000 m from around the margin of the law dome and adjacent eais have produced the observed relative sea level lowering such an additional ice load would have been associated with a 40 to 65 km expansion of the law dome to near the continental shelf break together with a few hundred meters of ice thickening on the adjoining coastal slope of the eais up to 2000 m elevation whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes the glacio isostatic response at the windmill islands results from a combination of regional and to a lesser extent antarctic wide effects the correspondence between the holocene relative sea level lowering interpreted at the margin of the law dome and the lowering interpreted along the remainder of the wilkes land and oates land coasts 105 160 e suggests that a similar ice load of up to 1000 m existed along the eais margin between wilkes land and oates land

the effect of volcanic aerosols on global climate abstract the surface temperature decrease after major volcanic eruptions has been demonstrated by a number of groups to be the order of a few tenths of a degree at first the stratospheric aerosol is usually restricted to a narrow range of latitudes and the volcanically induced temperature decrease is found to be nonuniform over the surface of the earth in fact because of the differential cooling of land and ocean there should always be volcanically induced temperature gradients these temperature gradients will induce a redistribution of air mass and anomalous sea level pressure gradients anomalous winds and anomalous climate on a global scale in this paper a hypothesis is presented which assumes that volcanic aerosols by reducing the solar radiation induces surface temperature gradients and sea level pressure gradients between the land and the oceans since cooling of the land occurs before the oceans there will be at first an increase of sea level pressure over land relative to the oceans conservation of total air mass on a global scale requires the sea level pressure over the ocean to be reduced because the majority of the land area is in the northern hemisphere the volcanically induced cooling will transfer air mass from the oceanic anticyclones in both the northern and southern hemisphere to the continents and especially to southern eurasia the anomalous sea level pressure pattern slp which would be obtained higher slp over southern eurasia and lower slp over the southern oceans is very close to the pattern first named by sir gilbert walker called the negative phase of the southern oscillation the positive phase of the southern oscillation can occur when no volcanic aerosols are present and the stratosphere is clear then the additional radiation and heating of the land increases the transfer of air mass from the northern hemisphere land mass to the world s oceans the positive phase of the global southern oscillation in this paper it will be shown that this hypothesis has the potential to explain the observed association between low latitude volcanic aerosols and the el nino southern oscillation it also has the potential to explain why el chichon s eruption induced a very strong el nino compared to the weaker el nino events induced by the eruptions of agung and krakatau it also explains why almost all monsoon countries experience below normal precipitation just prior to the maximum of the el nino warming the hypothesis also has the potential to explain why low and high latitude aerosols will affect the global climate system differently this hypothesis represents a return to the ideas of sir gilbert walker who first defined the southern oscillation as a global scale anomaly rather than an index between just two stations

a revised 1000 year atmospheric δ13c co2 record from law dome and south pole antarctica 1 we present new measurements of 13c of co2 extracted from a high resolution ice core from law dome east antarctica together with firn measurements performed at law dome and south pole covering the last 150 years our analysis is motivated by the need to better understand the role and feedback of the carbon c cycle in climate change by advances in measurement methods and by apparent anomalies when comparing ice core and firn air 13c records from law dome and south pole we demonstrate improved consistency between law dome ice south pole firn and the cape grim tasmania atmospheric 13c data providing evidence that our new record reliably extends direct atmospheric measurements back in time we also show a revised version of early 13c measurements covering the last 1000 years with a mean preindustrial level of 6 50 finally we use a kalman filter double deconvolution to infer net natural co2 fluxes between atmosphere ocean and land which cause small 13c deviations from the predominant anthropogenically induced 13c decrease the main features found from the previous 13c record are confirmed including the ocean as the dominant cause for the 1940 a d co2 leveling our new record provides a solid basis for future investigation of the causes of decadal to centennial variations of the preindustrial atmospheric co2 concentration those causes are of potential significance for predicting future co2 levels and when attempting atmospheric verification of recent and future global carbon emission mitigation measures through coupled climate carbon cycle models