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

evolution of the antarctic ice sheet throughout the last deglaciation a study with a new coupled climate north and south hemisphere ice sheet model the aim of this paper is to assess through the understanding of deglaciation processes the contribution of the antarctic ice sheet to sea level rise during the last deglaciation to achieve this goal we use an earth system model in which the interactions between the atmosphere the ocean the vegetation and the northern and antarctic ice sheets are represented this new tool allows the simulation of the evolution of the antarctic ice volume which starts to decrease at around 15 ka at the end of deglaciation the melting of the antarctic ice sheet contributes to an ice equivalent sea level rise of 9 5 m in the standard experiment and 17 5 m in a more realistic sensitivity experiment accounting for a different bathymetry in the weddell sea which succeeds in producing both major ice shelves ross and ronne filchner in both experiments the melting of all ice sheets contributes to 121 5 m and 129 5 m respectively which is very consistent with data the new coupled model provides a timing and amplitude of the antarctic deglaciation different from those previously obtained by prescribing the temperature record from the vostok antarctic ice core 78 27 s 106 52 e as a uniform temperature forcing sensitivity experiments have also been performed to analyse the impact of the parameters at the origin of the deglaciation process insolation changes atmospheric co2 variation basal melting and sea level rise all those parameters have an influence on the timing of the deglaciation the prescribed global sea level rise is shown to be a major forcing factor for the evolution of the antarctic ice volume during the last deglaciation we quantify the direct effect of the sea level rise due to the northern hemisphere ice sheet melting on the grounding line retreat which in turn favours enhancement of grounded ice flow by lowering the buttressing effect of ice shelves

selective glacial erosion and weathering zones in the coastal mountains of marie byrd land antarctica in the coastal mountains of marie byrd land antarctica there is a juxtaposition of ice moulded landforms at lower altitudes and upstanding summits with weathered surfaces bearing tors this paper uses geomorphological mapping and exposure dating to test two hypotheses commonly used to explain such a landscape contrast either the pattern reflects contrasts in glacial erosion related to the basal thermal regime beneath a former ice sheet or it represents a periglacial trimline marking the upper limit of ice cover during the last glacial maximum lgm cosmogenic nuclide measurements on erratics show that the mountains were covered by ice on several occasions most recently during the lgm similar measurements on bedrock show that fragile landforms on weathered surfaces survived many glaciations nuclide concentrations in bedrock indicate both that subglacial erosion is insignificant and that ice free periods of periglacial weathering are longer at higher elevations we conclude that the pattern of landscape modification reflects both topographically controlled contrasts in the basal thermal regime of overriding ice and the longer exposure to periglacial conditions at higher elevations in addition the combination of nuclide data and the wider pattern of striations shows that the lgm ice cover was thinner than predicted by ice sheet models assuming equilibrium conditions that ice sheet thinning has occurred from 10 400 years ago to the present and that regional flow by overriding ice has been replaced by radial ice flow from local glaciers centred on individual mountain massifs

pleistocene deglaciation chronology of the amery oasis and radok lake northern prince charles mountains antarctica abstract the east antarctic ice sheet is the largest ice mass on earth with a capacity to raise global sea level by up to 65 m as the lambert glacier amery ice shelf drainage system is the largest to reach the coast of antarctica quantifying its evolution over the quaternary is a vital component in developing an understanding of the antarctic response to future climate change here we present a deglaciation chronology based on 10 be and 26 al in situ cosmogenic exposure ages of the northern prince charles mountains which flank the lambert glacier amery system and that records the progressive emergence of mcleod massif and radok lake basin from beneath the mac robertson land lobe of the east antarctic ice sheet the exposure ages monotonically decrease with both decreasing altitude and increasing proximity to the amery ice shelf at the antarctic coast exposure ages from the crests of mcleod massif near the edge the amery ice shelf and from fisher massif 75 km further inland each at 1200 m above sea level are 2 2 0 3 and 1 9 0 2 ma respectively suggesting their continuous exposure above the ice sheet at least since close to the plio pleistocene boundary an extensive plateau at 800 m altitude on mcleod massif above battye glacier records the massif s increased emergence above the ice sheet surface at about between 880 and 930 ka ago indicating 400 m of ice volume reduction in the mid pleistocene correcting these apparent ages for a reasonable choice in erosion rate would extend this event to 1 15 ma a period identified from prydz bay odp core 1167 when sedimentation composition alters and rates decrease 10 fold exposure ages from boulder mantled erosional surfaces above and beyond the northern end of radok lake at 220 m range from 28 to 121 ka independent of choice of model interpretation to explain this age spread the most recent major reoccupation of radok lake by battye glacier ice occurred during the last glacial cycle moraine ridges at the lower altitude of 70 125 m were deposited during the final withdrawal of battye glacier ice from the lake basin between 11 and 20 ka ago this new chronology indicates that the highest amery oasis peaks have not been overridden by the mac robertson land lobe of the east antarctic ice sheet for at least the past 2 ma since this time we document 3 major periods of regional reduction in ice sheet volume at 1 1 ma during the last glacial cycle 120 to 30 ka and through the last glacial maximum 20 to 10 ka that resulted in an overall 1000 m of ice lowering in the battye glacier radok lake region

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

holocene glacial history of antarctica and the sub antarctic islands abstract a history of holocene glaciation in the antarctic and sub antarctic affords insight into questions concerning present and future ice sheet and mountain glacier behavior and global climate and sea level change existing records permit broad correlation of holocene ice fluctuations within the region in several areas ice extent was less than at present in mid holocene time an important exception to this is the west antarctic ice sheet which has undergone continued recession throughout the holocene probably in response to internal dynamics the first neoglacial ice advances occurred at 5 0 ka although some sites e g western ross sea lack firm evidence for glacial expansion at that time glaciers in all areas underwent renewed growth in the past millennium and most have subsequently undergone recession in the past 50 years ranging from near catastrophic in parts of the antarctic peninsula to minor in the western ross sea region and sections of east antarctica this magnitude difference likely reflects the much greater warming that is taking place in the antarctic peninsula region today as compared to east antarctica

regional ice mass changes and glacial isostatic adjustment in antarctica from grace abstract we infer regional mass changes in antarctica using ca 4 years of gravity recovery and climate experiment grace level 2 data we decompose the time series of the stokes coefficients into their linear as well as annual and semi annual components by a least squares adjustment and apply a statistical reliability test to the stokes potential coefficients linear temporal trends mass changes in three regions of antarctica that display prominent geoid height change are determined by adjusting predictions of glacier melting at the tip of the antarctic peninsula and in the amundsen sea sector and of the glacial isostatic adjustment gia over the ronne ice shelf we use the gfz rl04 cnes rl01c jpl rl04 and csr rl04 potential coefficient releases and show that although all data sets consistently reflect the prominent mass changes differences in the mass change estimates are considerably larger than the uncertainties estimated by the propagation of the grace errors we then use the bootstrapping method based on the four releases and six time intervals each with 3 5 years of data to quantify the variability of the mean mass change estimates we find 95 of our estimates to lie within 0 08 and 0 09 mm a equivalent sea level esl change for the antarctic peninsula and within 0 18 and 0 20 mm a esl for the amundsen sea sector forward modelling of the gia over the ronne ice shelf region suggests that the antarctic continent was covered by 8 4 to 9 4 m esl of additional ice during the last glacial maximum ca 22 to 15 ka bp with regards to the mantle viscosity values and the glacial history used this value is considered as a minimum estimate the mass change estimates derived from all grace releases and time intervals lie within ca 20 amundsen sea sector 30 antarctic peninsula and 50 ronne ice shelf region of the bootstrap estimated mean demonstrating the reliability of results obtained using grace observations

cosmogenic nuclides 10be and 26al imply limited antarctic ice sheet thickening and low erosion in the shackleton range for 1 m y concentrations of the cosmogenic nuclides 1 0 be and 2 6 al on bedrock surfaces in the shackleton range antarctica indicate minimum exposure ages between 3 0 03 and 1 16 0 10 ma the isotope data indicate that the maximum long term erosion rate is 0 10 0 35 m m y and the ratios suggest no prolonged periods of burial by cold based ice the findings are important because of the location of the massif close to the junction of the east antarctic ice sheet and the landward extent of the filchner ice shelf these results point to three conclusions first the massif has not been overridden by the east antarctic ice sheet during the late quaternary rather moraines 200 340 m above outlet glaciers are likely to represent the maximum thickening of the filchner ronne ice shelf during the quaternary second the high radionuclide concentrations on bedrock surfaces one of which is striated suggest that some glacial landforms were created in at least pliocene or more likely miocene time third the exceptionally low erosion rates imply that the modern cold arid climate has persisted for millions of years these findings provide evidence of old stable landscapes over a wider area of antarctica than the mc murdo dry valleys

a record of uranium series transport at nopal i sierra pena blanca mexico implications for natural uranium deposits and radioactive waste repositories abstract studies of uranium series u series disequilibria within and around ore deposits provide valuable information on the extent and timing of actinide mobility via mineral fluid interaction over a range of spatial and temporal scales such information is useful in studies of analogs of high level nuclear waste repositories as well as for mining and mineral extraction sites locations of previous nuclear weapons testing and legacy nuclear waste contamination in this study we present isotope dilution mass spectrometry u series measurements for fracture fill materials hematite goethite kaolinite calcite dolomite and quartz from one such analog the nopal i uranium ore deposit situated at pena blanca in the chihuahua region of northern mexico the ore deposit is located in fractured unsaturated volcanic tuff and fracture fill materials from surface fractures as well as fractures in a vertical drill core have been analyzed high uranium concentrations in the fracture fill materials between 12 and 7700 ppm indicate uranium mobility and transport from the deposit uranium concentrations generally decrease with horizontal distance away from the deposit but in this deposit there is no trend with depth below the surface isotopic activity ratios 238u 234u 230th 232th linear age trends and u th pa model ages indicate an actinide mobility evolution that can be characterized as complex and varied there is evidence of both open and closed system behavior for uranium depending on both sample and time scale the 234u 238u activity ratios indicate u mobility from 1 2 0 2 ma in the last 0 2 ma there is isotopic evidence for some u mobility but mostly u immobility in almost all cases the th pa radionuclides studied here have been immobile for the past 200 ka radium appears to have been recently 0 1 8 ka mobile due to ongoing fluid flow in the fractures overall the mainly closed system behavior for u th pa over the past 200 ka provides an indicator of the geochemical immobility of these actinides over time scales relevant for potential nuclear waste repositories situated in fractured unsaturated tuff

meltwater pulse 1a from antarctica as a trigger of the bolling allerod warm interval meltwater pulse 1a mwp 1a was a prominent feature of the last deglaciation which led to a sea level rise of 20 meters in less than 500 years concurrent with mwp 1a was the onset of the bolling allerod interstadial event 14 600 years before the present which marked the termination of the last glacial period previous studies have been unable to reconcile a warm northern hemisphere with mwp 1a originating from the laurentide or fennoscandian ice sheets with the use of a climate model of intermediate complexity we demonstrate that with mwp 1a originating from the antarctic ice sheet consistent with recent sea level fingerprinting inferences the strength of north atlantic deep water nadw formation increases thereby warming the north atlantic region and providing an explanation for the onset of the bolling allerod warm interval the established mode of active nadw formation is then able to respond to subsequent freshwater forcing from the laurentide and fennoscandian ice sheets setting the stage for the younger dryas cold period the melting of continental ice sheets during the last deglaciation provided a freshwater source to the ocean that affected global sea level and the strength of the thermohaline circulation an exceptionally large melting event inferred from far field relative sea level records occurred

the last deglacial history of lutzow holm bay east antarctica past fluctuations of the antarctic ice sheet are poorly understood because of a lack of datable materials radiocarbon reservoir ages and severe environments direct evidence of the timing of ice retreat is important in order to understand the antarctic contribution to global sea level rise since the last glacial maximum here we report the first exposure ages constraining the timing of the last deglaciation from lutzow holm bay east antarctica our data suggest that the final retreat of the ice sheet in the region occurred rapidly in the early holocene and the reduction of the ice thickness in the region was at least 350 m this occurred after the major northern hemisphere deglaciation copyright 2011 john wiley sons ltd

dating of quaternary lake sediments from the schirmacher oasis east antarctica by infra red stimulated luminescence irsl detected at the wavelength of 560 nm abstract twelve samples from three antarctic lake cores in the schirmacher oasis east antarctica were selected for dating by a method using infra red stimulated luminescence irsl a spectral study of the luminescence signal from coarse grain plagioclase feldspars by a high sensitivity tl osl spectrometer using a ccd camera showed four wavelength maxima and the comparison of the equivalent doses d e measured at these wavelength namely 280 330 410 and 560 nm yielded different values the ages were calculated using d e obtained at 560 nm

on post glacial sea level i general theory summary modern analyses of sea level changes due to glacial isostatic adjustment gia are based on the classic sea level equation derived by farrell clark 1976 geophys j r astr soc 46 647 667 the connection between global sea level variations and changes to ocean height that is assumed within this equation breaks down in the presence of a time varying shoreline geometry we present a generalized sea level equation that overcomes this difficulty we also derive analytic expressions for and present schematic illustrations of the error in the ocean height change over finite time intervals introduced in published efforts to incorporate shoreline evolution into the theory of gia induced sea level change this comparison includes studies of shoreline migration due to either local sea level changes or the growth and ablation of marine based ice we conclude that the theories applied by johnston 1993 geophys j int 114 615 634 milne 1998 phd thesis university of toronto toronto and co workers are more accurate than the procedure advocated by peltier 1994 science 265 195 201 1998a geophys res lett 25 3955 3958 1998b rev geophys 114 615 634 although an improvement in the latter has recently been reported peltier drummond 2002 geophys res lett 29 10 1029 2001gl014273 our generalized theory is valid for any earth model in a companion paper we derive the equations necessary to treat the special case of a spherically symmetric linear viscoelastic and rotating earth and we quantify errors associated with previous work

late quaternary climate driven environmental change in the larsemann hills east antarctica multi proxy evidence from a lake sediment core little is known about the response of terrestrial east antarctica to climate changes during the last glacial interglacial cycle here we present a continuous sediment record from a lake in the larsemann hills situated on a peninsula believed to have been ice free for at least 40 000 yr a mutli proxy data set including geochronology diatoms pigments and carbonate stable isotopes indicates warmer and wetter conditions than present in the early part of the record we interpret this as marine isotope stage 5e after application of a chronological age depth model and similar ice core evidence dry and cold conditions are inferred during the last glacial with lake level minima floristic changes towards a shallow water algal community and a greater biological receipt of ultraviolet radiation during the last glacial maximum and termination i the lake was perennially ice covered with minimal snowmelt in the catchment after ca 10 500 cal yr b p the lake became seasonally moated or ice free during summer despite a low accumulation rate the sediments document some holocene environmental changes including neoglacial cooling after ca 2450 cal yr b p and a gradual increase in aridity and salinity to the present

late quaternary evolution of reedy glacier antarctica abstract fresh deposits above the margins of reedy glacier show that maximum ice levels during the last glaciation were several hundred meters above present near the glacier mouth and converged to less than 60 m above the present day surface at the head of the glacier exposure ages of samples from five sites along its margin show that reedy glacier and its tributaries thickened asynchronously between 17 and 7 kyr bp at the quartz hills located midway along the glacier maximum ice levels were reached during the period 17 14 kyr bp farther up glacier the ice surface reached its maximum elevation more recently 14 7 10 2 kyr bp at the caloplaca hills 9 1 7 7 kyr bp at mims spur and around 7 kyr bp at hatcher bluffs we attribute this time transgressive behavior to two different processes at the glacier mouth growth of grounded ice and subsequent deglaciation in the ross sea embayment caused a wave of thickening and then thinning to propagate up glacier during the lateglacial and holocene increased snow accumulation on the east antarctic ice sheet caused transient thickening at the head of the glacier an important result of this work is that moraines deposited along reedy glacier during the last ice age cannot be correlated to reconstruct a single glacial maximum longitudinal profile the profile steepened during deglaciation of the ross sea thinning at the quartz hills after 13 kyr bp while thickening upstream near its confluence with mercer ice stream rapid thinning beginning prior to 7 8 kyr bp reduced the level of reedy glacier to close to its present level thinning over the past 1000 years has lowered the glacier by less than 20 m

first exposure ages from the amundsen sea embayment west antarctica the late quaternary context for recent thinning of pine island smith and pope glaciers dramatic changes acceleration thinning and grounding line retreat of major ice streams in the amundsen sea sector of the west antarctic ice sheet wais have been observed during the past two decades but the millennial scale context for these changes is not yet known we present the first surface exposure ages recording thinning of pine island smith and pope glaciers which all drain into the amundsen sea from these we infer progressive thinning of pine island glacier at an average rate of 3 8 0 3 cm yr 1 for at least the past 4 7 k y and of smith and pope glaciers at 2 3 0 2 cm yr 1 over the past 14 5 k y these rates are more than an order of magnitude lower than the similar to 1 6 m yr 1 recorded by satellite altimetry for pine island glacier in the period 1992 1996 similarly low long term rates 2 5 9 ern yr 1 since 10 ka have been reported farther west in the ford ranges marie byrd land but in that area the same rates of thinning continue to the present day our data provide the first evidence that puts into context recent rates of thinning of the wais in the amundsen sea embayment and demonstrates that these are unusually rapid the data also provide much needed constraints for ice sheet models which are the primary tool for predicting the future behavior of the wais and its likely contribution to sea level rise

deglacial history of the west antarctic ice sheet in the western amundsen sea embayment abstract the amundsen sea embayment ase drains approximately 35 of the west antarctic ice sheet wais and is one of the most rapidly changing parts of the cryosphere in order to predict future ice sheet behaviour modellers require long term records of ice sheet melting to constrain and build confidence in their simulations here we present detailed marine geological and radiocarbon data along three palaeo ice stream tributary troughs in the western ase to establish vital information on the timing of deglaciation of the wais since the last glacial maximum lgm we have undertaken multi proxy analyses of the cores core description shear strength x radiographs magnetic susceptibility wet bulk density total organic carbon nitrogen carbonate content and clay mineral analyses in order to 1 characterise the sedimentological facies and depositional environments and 2 identify the horizon s in each core that would yield the most reliable age for deglaciation in accordance with previous studies we identify three key facies which offer the most reliable stratigraphies for dating deglaciation by recording the transition from a grounded ice sheet to open marine environments these facies are i subglacial ii proximal grounding line and iii seasonal open marine in addition we incorporate ages from other facies e g glaciomarine diamictons deposited at some distance from the grounding line such as glaciogenic debris flows and iceberg rafted diamictons and turbates into our deglacial model in total we have dated 78 samples mainly the acid insoluble organic aio fraction but also calcareous foraminifers which include 63 downcore and 15 surface samples through careful sample selection prior to dating we have established a robust deglacial chronology for this sector of the wais our data show that deglaciation of the western ase was probably underway as early as 22 351 calibrated years before present cal yr bp reaching the mid shelf by 13 837 cal yr bp and the inner shelf to within c 10 12 km of the present ice shelf front between 12 618 and 10 072 cal yr bp the deglacial steps in the western ase broadly coincide with the rapid rises in sea level associated with global meltwater pulses 1a and 1b although given the potential dating uncertainty additional more precise ages are required before these findings can be fully substantiated finally we show that the rate of ice sheet retreat increased across the deep up to1600 m basins of the inner shelf highlighting the importance of reverse slope and pinning points in accelerated phases of deglaciation

holocene deglaciation of marie byrd land west antarctica surface exposure ages of glacial deposits in the ford ranges of western marie byrd land indicate continuous thinning of the west antarctic ice sheet by more than 700 meters near the coast throughout the past 10 000 years deglaciation lagged the disappearance of ice sheets in the northern hemisphere by thousands of years and may still be under way these results provide further evidence that parts of the west antarctic ice sheet are on a long term trajectory of decline west antarctic melting contributed water to the oceans in the late holocene and may continue to do so in the future

a deglacial model for antarctica geological constraints and glaciological modelling as a basis for a new model of antarctic glacial isostatic adjustment abstract we present a new reconstruction of the antarctic ice sheets between 20 ka bp and the present day our reconstruction is derived using a numerical model to generate a physically consistent ice surface across the whole of the continent we define the extent of the ice sheet at five time slices 20 15 10 5 and 0 ka bp assuming an equilibrium state for the 20 ka bp time slice and a transient state for the deglacial time slices the evolution of the ice sheet within the numerical model is driven by variations in temperature accumulation rate and relative sea level in order to reconstruct the concave profile of the ice sheet in marine grounded regions such as the ross and weddell seas we force our model to develop channels of faster flow by defining greater basal sliding along the trajectory of former ice streams we find a strong dependence upon the basal sliding parameters and also the position of the grounding line we use an extensive data base of geological and glaciological data to constrain our ice sheet reconstruction grounding line extent is prescribed from marine geological data and we test ice sheet thickness against onshore geological data at 62 sites of the five time slices considered our 20 ka bp reconstruction is the best constrained by data and has an rms misfit of 147 6 m when compared to observations of ice thickness change between 20 ka bp and the present day across all time slices there are large regions of the ice sheet which are poorly constrained especially after 20 ka bp we estimate the spatial distribution of uncertainty in our ice sheet reconstruction and note that the solutions are least reliable in regions of complex topography we predict that the antarctic ice sheets contributed 9 1 5 m of eustatic sea level to the global ocean between 20 ka bp and the present and our reconstruction with minimum misfit contributes 8 m eustatic sea level during this period these values which we argue are an upper bound are lower than many previous estimates the reconstructed pattern of ice unloading can serve as a new input for glacial isostatic models

fluctuations of the east antarctic ice sheet margin since the last glaciation from the stratigraphy of raised beach deposits along the soya coast

decoding the dipstick thickness of siple dome west antarctica at the last glacial maximum ice thickness in west antarctica at the last glacial maximum lgm is poorly known yet is key information for understanding ice streams and interpreting ice cores although trim lines moraine limits and exposure age dating provide geologic constraints on ice thickness near the transantarctic mountains and in marie byrd land lack of exposed bedrock hampers traditional geologic methods in a central 2 3 10 6 km 2 region here we infer ice sheet thickness changes in the central ross sea embayment by using a tran sient ice flow model to find combinations of accumulation rate and ice sheet thickness histories that match the depth age relationship and the measured layer thickness pattern in the siple dome ice core after we reject unreasonable accumulation rate histories the remaining history pairs indicate thinning of 200 400 m since the lgm our estimate is lower than previous reconstructions that were constrained by geologic evidence from the transantarctic mountains and by marine data from the ross sea floor which indicate that a grounded ice sheet extended to the continental shelf margin during the last glacial period low surface elevations in the central ross sea embayment during the lgm do not preclude thicker ice along its boundaries however if this grounded ice sheet came over 1000 km from interior west antarctica as is usually assumed then it had very low surface slope requiring a very slippery bed alternatively the grounded ross sea ice might have flowed from the transantarctic mountains and western marie byrd land

measurements of past ice sheet elevations in interior west antarctica a lateral moraine band on mount waesche a volcanic nunatak in marie byrd land provides estimates of past ice sheet surface elevations in west antarctica helium 3 and chlorine 36 surface exposure ages indicate that the proximal part of the moraine up to 45 meters above the present ice surface was deposited about 10 000 years ago substantially later than the maximum ice extent in the ross embayment the upper distal part of the moraine may record multiple earlier ice sheet high stands a nonequilibrium ice sheet model predicts a delay of several thousand years in maximum ice levels at mount waesche relative to the maximum ice extent in the ross sea the glacial geologic evidence coupled with the ice sheet model indicates that the contribution of the ross sea sector of the west antarctic ice sheet to holocene sea level rise was only about 3 meters these results eliminate west antarctic ice as the principle source of the large meltwater pulse during the early holocene

rapid deglaciation of marguerite bay western antarctic peninsula in the early holocene glacial geological evidence of rapid ice stream retreat is important for the potential insight it can bring to understanding of contemporary rapid ice sheet change here we report new chronological constraints on the deglacial history of the marguerite trough ice stream which formerly drained part of the western margin of the antarctic peninsula this ice stream has been previously identified on geomorphological grounds as an example of an outlet that underwent rapid retreat following the last glacial maximum but the precise timing of this retreat has not been conclusively determined we obtained cosmogenic surface exposure dates on erratic boulders that record the thinning history of ice flowing into the ice stream these dates show that the ice stream underwent 270 m of thinning very rapidly at 9 6 ka bp the timing of ice stream thinning agrees closely with previously published data on ice shelf retreat the age of the first post glacial beaches and minimum constraining ages for the onset of lacustrine sedimentation and post glacial sedimentation in inner shelf fjords we compare the timing of retreat to the similarly sized anvers trough ice stream further north and find that retreat in marguerite bay was more rapid and earlier than in the anvers trough we argue that the intrusion of circumpolar deep water is the most likely forcing mechanism for retreat in marguerite bay a key finding of this study is that rapid retreat occurred in deep water with reverse continent dipping slope but also in relatively shallow water with a positive slope this may have implications for understanding of oceanographically forced ice sheet change in other parts of west antarctica

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

sea level fingerprinting as a direct test for the source of global meltwater pulse ia the ice reservoir that served as the source for the meltwater pulse ia remains enigmatic and controversial we show that each of the melting scenarios that have been proposed for the event produces a distinct variation or fingerprint in the global distribution of meltwater we compare sea level fingerprints associated with various melting scenarios to existing sea level records from barbados and the sunda shelf and conclude that the southern laurentide ice sheet could not have been the sole source of the meltwater pulse whereas a substantial contribution from the antarctic ice sheet is consistent with these records

holocene sea level change and ice sheet history in the vestfold hills east antarctica abstract a new holocene sea level record from the vestfold hills antarctica has been obtained by dating the lacustrine marine and marine lacustrine transitions that occur in sediment cores from lakes which were formerly connected to the sea from an elevation of 7 5 m 8000 yr ago relative sea level rose to a maximum 9 m above present sea level 6200 yr ago since then sea level has fallen monotonically until the present the precision of the new record makes it suitable for constraining the recent history of the ice sheet in that region using numerical models of glacio hydro isostasy simplified regional models suggest that the ice sheet margin has retreated 30 40 km since the last glacial maximum with 600 700 m of thinning occurring at the present coastline

deep sea floor evidence of past ice streams off the antarctic peninsula the past existence of a giant ice stream off the northern end of the antarctic peninsula is suggested by a convex upward elongated sediment body now at a mean water depth of 1000 m because of its morphological characteristics i e a set of parallel to subparallel ridges and grooves to 100 km long with an overall width of 25 km we call this depositional body a bundle structure we hypothesize that bundle structures form by accumulation of basal deformation till under their parent ice streams from its location size and overall characteristics the bundle structure described here constitutes the best preserved largest deepest and relatively low latitude evidence of giant ice streams that flowed offshore antarctica during glacial maxima bundle structures reveal the very dynamic behavior of ice caps in the northern antarctic peninsula during the last glacial maximum with catchment areas draining rapidly under marine based critical subglacial conditions bundle structures represent a new megascale streamlined glacial landform

origin of the first global meltwater pulse following the last glacial maximum well dated sea level records show that the glacioeustatic rise following the last glacial maximum was characterized by two or possibly three brief intervals of rapid sea level rise separating periods with much lower rates these very high rates of sea level rise indicate periods of exceptionally rapid deglaciation of remaining ice sheets the laurentide ice sheet is commonly targeted as the source of the first and largest of the meltwater pulses mwp ia between 14 200 12 200 14c years b p and 13 700 years ago 11 700 14c years b p in all oceanic records of deglaciation of the former northern hemisphere ice sheets that we review only those from the gulf of mexico and the bermuda rise show evidence of low 18o values at the time of mwp ia identifying the southern laurentide ice sheet as a potential source for mwp ia we question this source for mwp ia however because 1 ice sheet models suggest that this sector of the ice sheet contributed only a fraction 10 of the sea level needed for mwp ia 2 melting this sector of the ice sheet at the necessary rate to explain mwp ia is physically implausible and 3 ocean models predict a much stronger thermohaline response to the inferred freshwater pulse out of the mississippi river into the north atlantic than is recorded this leaves the antarctic ice sheet as the only other ice sheet capable of delivering enough sea level to explain mwp ia but there are currently no well dated high resolution records to document this hypothesis these conclusions suggest that reconstructions of the laurentide ice sheet in the ice 4g model which are constrained to match the sea level record may be too low for time periods younger than 15 000 years ago furthermore 18o records from the gulf of mexico show variable fluxes of meltwater from the southern margin of the laurentide ice sheet which can be traced to the opening and closing of eastward draining glacial lake outlets associated with surging ice sheet behavior these variable fluxes through eastern outlets were apparently sufficient to affect formation of north atlantic deep water thus underscoring the sensitivity of this process to changes in freshwater forcing

holocene deglacial history of the northeast antarctic peninsula a review and new chronological constraints the northeast antarctic peninsula neap region is currently showing signs of significant environmental change evidenced by acceleration of glacial retreat and collapse of both larsen a and b ice shelves within the past 15 years however data on the past extent of the eastern margin of the antarctic peninsula ice sheet apis and its holocene retreat history are sparse and hence we cannot yet put the recent changes into a long term context in order to investigate the timing of deglaciation we present 16 new cosmogenic 10be surface exposure ages from sites on northern james ross island cape lachman johnson mesa and terrapin hill and seymour island the majority of the ages cluster around 6e10 ka with three significantly older 25e31 ka we combine these ages with existing terrestrial and marine radiocarbon deglaciation ages and a compilation of existing swath bathymetry data to quantify the temporal and spatial character of the regional glacial history ice had begun to retreat from the outer shelf by 18 3 ka reaching seymour island by w8 ka northern james ross island began to deglaciate around the time of the early holocene climatic optimum c 11e9 5 ka deglaciation continued and a transition from grounded to floating ice in prince gustav channel occurred around 8 ka separating the james ross island ice cap from the apis this occurred shortly before prince gustav channel ice shelf began to disintegrate at 6 2 ka our results suggest there may be a bathymetric control on the spatial pattern of deglaciation in the neap

a comparison of different ways of dealing with isostasy examples from modelling the antarctic ice sheet during the last glacial cycle the bedrock isostatic response exerts a strong control on ice sheet dynamics and is therefore always taken into account in ice sheet models this paperreviews the various methods normally used in the ice sheet modeling community to deal with the bedrock response and compares these with a moresophisticated full earth model each of these bedrock treatments five in total are coupled with a three dimensional thermomechanical ice sheet model underthe same forcing conditions to simulate the antarctic ice sheet during the last glacial cycle the outputs of the simulations are compared on the basis of thetime dependent behavior for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over antarctica thiscomparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns it furthermoredemonstrates the deficiencies inherent to the diffusion equation in modeling the complex deformation within the mantle nevertheless when characteristicparameters are varied within their range of uncertainty differences within one single method are often of the same order as those between the variousmethods this overview finally tries to point out the main advantages and drawbacks of each of these methods and to determine which one is mostappropriate depending on the specific modeling requirements

mechanical damage of a crystalline rock having experienced ultra high deviatoric stress up to 1 7 gpa 1 introductiondamage induced by high mechanical stress often leads todrastic changes in the physical and mechanical properties of rocks in the last decades damage mechanisms have been extensivelyinvestigated under different loading conditions 1 4 theconsequences of damage on rock properties such as strengthand permeability have also been analyzed in several papers 5 6 special attention has been paid to the damage developed inultra high stressed rock masses in relation to different situations such as faulting and earthquakes 7 mining at great depth 8 9 and rock masses subjected to a burst or to a blast 10 in a porous weak rock damage is mainly related to porecollapse and compaction 11 12 whereas damage mechanisms inhard ma c rock subjected to high stresses are less clear and notwell documented this scarcity of results is mainly due totechnical limitations for applying the ultra high stresses thatcould damage these types of rocks the present research is part of an ongoing project to study thefeasibility of earthquake prediction within this project anexperimental program has been carried out to investigate themechanical and thermal damage of hard crystalline rocks 13 this paper focuses on the mechanical damage of a gabbroinduced by an ultra high deviatoric stress for this purpose twotypes of triaxial tests were performed following a compressionstress path one test with a medium con ning pressure 200 mpa was undertaken to determine the mechanical strength of therock and another one with a high level of con ning pressure 650 mpa was performed to understand the mechanical damagethat occurred in the rock specimen damage to a rock specimen tested at 650 mpa con ningpressure was con rmed by subsequent measurements the changesin the elastic wave velocity as well as in the acoustic emissionswere recorded during a uniaxial uncon ned compressive testperformed on the pre damaged specimen additionally microscopicinvestigations were undertaken to highlight at the crystal scale thedeformation mechanism responsible for the observed damage 2 experimental device and testing procedure2 1 the high capacity giga triaxial pressultra high con ning pressure tests were carried out using the giga press this high capacity triaxial vessel was originallydesigned in the university of grenoble to test concrete specimensunder ultra high pressure the maximum capacity of the vessel is850 mpafor the con ning pressure minor principal stress

exposure ages from mountain dipsticks in mac robertson land east antarctica indicate little change in ice sheet thickness since the last glacial maximum past changes in east antarctic ice sheet eais volume are poorly known and diffi cult to measure yet are critical for predicting the response of the ice sheet to modern climate change in particular it is important to identify the sources of sea level rise since the last glacial maximum lgm and ascertain the present day stability of the world s largest ice sheet we present altitudinal transects of 10 be and 26 al exposure ages across the framnes mountains in mac robertson land that allow the magnitude and timing of eais retreat to be quantifi ed our data show that the coastal eais thinned by at most 350 m in this region during the past 13 k y this reduction in ice sheet volume occurred over a 5 k y period and the present icesheet profi le was attained ca 7 ka in contrast to the west antarctic ice sheet which continues to retreat today combined with regional offshore and terrestrial geologic evidence our data suggest that the reduction in eais volume since the lgm was smaller than that indicated by contemporary ice sheet models and added little meltwater to the global oceans stability of the ice margin since the middle holocene provides support for the hypothesis that eais volume changes are controlled by growth and decay of northern hemisphere ice sheets and associated global sea level changes

reconstruction of the west antarctic ice sheet in pine island bay during the last glacial maximum and its subsequent retreat history abstract marine geological and geophysical studies were conducted to determine the late quaternary glacial history of the west antarctic ice sheet in pine island bay antarctica the data set includes sea floor imagery in the form of multibeam swath bathymetry and deep tow side scan sonar surveys distribution of sedimentary deposits and basal surface conditions are revealed through intermediate resolution seismic data and chirp 3 5 khz sub bottom profiles sedimentary deposits were sampled with piston cores and calcareous material was dated using ams radiocarbon techniques results from the study indicate the ice sheet was grounded on the outer shelf during its maximum extent sometime in the past thick ice flowing slowly and resting on crystalline bedrock was influenced by significant amounts of subglacial meltwater on the inner shelf thinner but more rapidly flowing ice characterized the seaward extent of the ice sheet which was grounded on a sedimentary substrate deglaciation occurred in two phases beginning soon after the last glacial maximum the outer most extension of the ice sheet retreated gradually pausing on a bathymetric high on the middle shelf by 16 000 14c years ago between 16 000 and 12 000 14c years ago ice sheet retreat resumed and may have proceeded rapidly to reach a present day position by 10 000 14c years ago

new relative sea level curves for the southern scott coast antarctica evidence for holocene deglaciation of the western ross sea here we present new relative sea level rsl curves developed from holocene aged raised beaches along the southern scott coast of the western ross sea antarctica fifty four dates of marine shells seal skin and elephant seal remains incorporated within raised beaches during storms afford a chronology for these curves all of the curves show the same pattern and timing of rsl change within a small range of error the best dated curve suggests that final unloading of grounded ross sea ice from the southern scott coast and mcmurdo sound region occurred shortly before 6500 14c yr bp this age is consistent with glacial geological evidence that places deglaciation between 5730 and 8340 14c yr bp our data strongly suggest that grounding line retreat of the ross sea ice sheet southward through the mcmurdo sound region occurred in mid and late holocene time if this is correct then rising sea level could not have driven ice recession to the present day grounding line on the siple coast because global deglacial sea level rise was essentially accomplished by mid holocene time copyright 1999 john wiley sons ltd

air content paleo record in the vostok ice core antarctica a mixed record of climatic and glaciological parameters under present day climatic conditions the air content of ice shows a high sensitivity to the atmospheric pressure and hence to the elevation at the surface of the ice sheet this observation has been used to infer past ice sheet thickness variations of antarctica and greenland a high resolution air content profile more than 1000 measurements covering approximately the last 200 000 years was obtained along the 2546 m long vostok ice core three analytical techniques were used leading to consistent results which show large amplitude and rapid air content variations the vostok results support thicker thinner ice in the central part of east antarctica during warm cold periods