the climatology of zonal wave numbers 1 and 2 planetary wave structure in the mlt using a chain of northern hemisphere superdarn radars the zonal wave components 1 and 2 were extracted from the meridional wind along the latitude band of 51 66 n for the years 2000 2008 using eight super dual auroral radar network superdarn radars spanning longitudes from 25 e to 150 w each extracted zonal component represents the superposition of all temporal periods with that zonal structure and indicates the total planetary wave energy available with that wave number the hovmoller diagrams show stationary as well as eastward and westward traveling planetary waves propagating in the background wind the method used to detect the zonal planetary wave components in the superdarn data are detailed and validated using uk meteorological office data which allows the evolution of s1 and s2 planetary wave energy between the stratosphere and mesosphere to be assessed the climatology of zonal wave number 1 and 2 planetary wave activity in the mesosphere lower thermosphere mlt is presented and compared to the activity in the stratosphere the mlt climatology of the mean wind anomalies shows stronger planetary wave activity during winter and weaker activity during summer with enhancement around midsummer and autumn equinox the climatology of the mean wind displays similar amplitudes apart from very strong s1 planetary wave amplitudes during summer in addition planetary wave activity during winters with major and minor stratospheric warming events are examined and contrasted

middle miocene southern ocean cooling and antarctic cryosphere expansion magnesium calcium data from southern ocean planktonic foraminifera demonstrate that high latitude similar to55degreess southwest pacific sea surface temperatures ssts cooled 6degrees to 7degreesc during the middle miocene climate transition 14 2 to 13 8 million years ago stepwise surface cooling is paced by eccentricity forcing and precedes antarctic cryosphere expansion by similar to60 thousand years suggesting the involvement of additional feedbacks during this interval of inferred low atmospheric partial pressure of co2 pco 2 comparing ssts and global carbon cycling proxies challenges the notion that episodic pco2 drawdown drove this major cenozoic climate transition sst salinity and ice volume trends suggest instead that orbitally paced ocean circulation changes altered meridional heat vapor transport triggering ice growth and global cooling

neogene vegetation of the meyer desert formation sirius group transantarctic mountains antarctica a tundra vegetation consisting of at least 18 plant species is described from the meyer desert formation which outcrops along the beardmore glacier in the transantarctic mountains about 500 km from the south pole the fossils include pollen seeds fruits flowers leaves wood and in situ plants of which wood and leaves of nothofagus and a pollen assemblage had been previously reported the plants include a cryptogamic flora of mosses and liverworts conifers and angiosperms in the families gramineae cyperaceae nothofagaceae ranunculaceae hippuridaceae caryophyllaceae and chenopodiaceae or myrtaceae the plants grew in a weakly developed soil formed within a complex periglacial environment that included moraines glacial outwash streams well drained gravel ridges and poorly drained depressions in which peat and marl were being deposited d 2004 elsevier b v all rights reserved

the ellsworth subglacial highlands inception and retreat of the west antarctic ice sheet antarctic subglacial highlands are where the antarctic ice sheets first developed and the pinning points where retreat phases of the marine based sectors of the ice sheet are impeded due to low ice velocities and limited present day change in the ice sheet interior west antarctic subglacial highlands have been overlooked for detailed study these regions have considerable potential however for establishing the locations from which the west antarctic ice sheet originated and grew and its likely response to warming climates here we characterize the subglacial morphology of the ellsworth subglacial highlands west antarctica from ground based and aerogeophysical radio echo sounding res surveys and the moderate resolution imaging spectroradiometer modis mosaic of antarctica we document well preserved classic landforms associated with restricted dynamic marine proximal alpine glaciation with hanging tributary valleys feeding a significant overdeepened trough the ellsworth trough cut by valley tidewater glaciers fjord mouth threshold bars down ice of two overdeepenings define both the northwest and southeast termini of paleo outlet glaciers which cut and occupied the ellsworth trough satellite imagery reveals numerous other glaciated valleys terminating at the edge of deep former marine basins e g bentley subglacial trench throughout the ellsworth subglacial highlands these geomorphic data can be used to reconstruct the glaciology of the ice masses that formed the proto west antarctic ice sheet the landscape predates the present ice sheet and was formed by a small dynamic ice field s similar to those of the present day antarctic peninsula at times when the marine sections of the west antarctic ice sheet were absent the ellsworth subglacial highlands represent a major seeding center of the paleo west antarctic ice sheet and its margins represent the pinning point at which future retreat of the marine based west antarctic ice sheet would be arrested

formation of patterned ground and sublimation till over miocene glacier ice in beacon valley southern victoria land antarctica a thin glacial diamicton informally termed granite drift occupies the floor of central beacon valley in southern victoria land antarctica this drift is 40 ar 39 ar analyses of presumed in situ ash fall deposits that occur within granite drift at odds with the great age of this ice are high centered polygons that cut granite drift if polygon development has reworked and retransported ash fall deposits then they are untenable as chronostratigraphic markers and cannot be used to place a minimum age on the underlying glacier ice our results show that the surface of granite drift is stable at polygon centers and that enclosed ash fall deposits can be used to define the age of underlying glacier ice in our model for patterned ground development active regions lie only above polygon troughs where enhanced sublimation of underlying ice outlines high centered polygons the rate of sublimation is influenced by the development of porous gravel and cobble lag deposits that form above thermal contraction cracks in the underlying ice a negative feedback associated with the development of secondary ice lenses at the base of polygon troughs prevents runaway ice loss secondary ice lenses contrast markedly with glacial ice by lying on a d versus 18 o slope of 5 rather than a precipitation slope of 8 and by possessing a strongly negative deuterium excess the latter indicates that secondary ice lenses likely formed by melting downward percolation and subsequent refreezing of snow trapped preferentially in deep polygon troughs the internal stratigraphy of granite drift is related to the formation of surface polygons and surrounding troughs the drift is composed of two facies a nonweathered matrix supported diamicton that contains 25 striated clasts in the 16 mm fraction and a weathered clast supported diamicton with varnished and wind faceted gravels and cobbles the weathered facies is a coarse grained lag of granite drift that occurs at the base of polygon troughs and in lenses within the nonweathered facies the concentration of cosmogenic 3 he in dolerite cobbles from two profiles through the nonweathered drift facies exhibits steadily decreasing values and shows the drift to have formed by sublimation of underlying ice these profile patterns and the 3 he surface exposure ages of 1 18 0 08 ma and 0 18 0 01 ma atop these profiles indicate that churning of clasts by cryoturbation has not occurred at these sites in at least the past 10 5 and 10 6 yr although granite drift is stable at polygon centers low frequency slump events occur at the margin of active polygons slumping together with weathering of surface clasts creates the large range of cosmogenic nuclide surface exposure ages observed for granite drift maximum rates of sublimation near active thermal contraction cracks calculated by using the two 3 he depth profiles range from 5 m m y to 90 m m y sublimation rates are likely highest immediately following major slump events and decrease thereafter to values well below our maximum estimates nevertheless these rates are orders of magnitude lower than those computed on theoretical grounds during eruptions of the nearby mcmurdo group volcanic centers ash fall debris collects at the surface of granite drift either in open thermal contraction cracks or in deep troughs that lie above contraction cracks these deposits subsequently lower passively as the underlying glacier ice sublimes the fact that some regions of granite drift have escaped modification by patterned ground for at least 8 1 ma indicates long term geomorphic stability of individual polygons once established polygon toughs likely persist for as long as 10 5 10 6 yr our model of patterned ground formation which applies to the hyperarid cold desert polar climate of antarctica may also apply to similar sized polygons on mars that occur over buried ice in utopia planitia

the evolution of the subglacial landscape of antarctica the aim is to investigate the evolution of the subglacial landscape of antarctica using an ice sheet and erosion model we identify different stages of continental glaciation and model the erosion processes associated with each stage the model links erosion to the basal thermal regime and indicates that much of the antarctic interior may have been subject to less than 200 m of erosion the depth of erosion reflects the presence or absence of warm based ice and the consistency of ice flow direction this information linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography is used to generate a map of the subglacial antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the laurentian and scandinavian shields near the continental margins selective linear erosion has overdeepened pre existing river valleys by as much as 2 8 km high elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold based ice high erosion rates result from steep thermal gradients in basal ice mountain regions such as the gamburtsev mountains uplands in dronning maud land and massifs in west antarctica are likely to bear features of local alpine glaciation such landscapes may have been protected under cold based ice for the last 34 myrs or possibly longer

early cretaceous uplift in the ellsworth mountains of west antarctica apatite fission track analysis of samples covering a 4 2 kilometer vertical section from the western flank of vinson massif antarctica s highest mountain indicates that the ellsworth mountains were uplifted by 4 kilometers or more during the early cretaceous following the initial separation of east and west gondwana and accompanying the opening of the weddell sea relief of at least 1 8 kilometers has persisted in the ellsworth mountains since the early cretaceous and a maximum of 3 kilometers of uplift has occurred since that time

major ice sheet change in the weddell sea sector of west antarctica over the last 5 000 years until recently little was known about the weddell sea sector of the west antarctic ice sheet in the last 10 years a variety of expeditions and numerical modelling experiments have improved knowledge of its glaciology glacial geology and tectonic setting two of the sector s largest ice streams rest on a steep reverse sloping bed yet despite being vulnerable to change satellite observations show contemporary stability there is clear evidence for major ice sheet reconfiguration in the last few thousand years however knowing precisely how the ice sheet has changed in the past and when would allow us to better understand whether it is now at risk two competing hypotheses have been established for this glacial history in one the ice sheet retreated and thinned progressively from its last glacial maximum position retreat stopped at or very near the present position in the late holocene alternatively in the late holocene the ice sheet retreated significantly upstream of the present grounding line and then advanced to the present location due to glacial isostatic adjustment and ice shelf and ice rise buttressing both hypotheses point to data and theory in their support yet neither has been unequivocally tested or falsified here we review geophysical evidence to determine how each hypothesis has been formed where there are inconsistencies in the respective glacial histories how they may be tested or reconciled and what new evidence is required to reach a common model for the late holocene ice sheet history of the weddell sea sector of west antarctica

cenozoic landscape evolution of the convoy range to mackay glacier area transantarctic mountains onshore to offshore synthesis on the basis of geomorphic mapping we reconstruct the landscape evolution of the convoy range to mackay glacier area of the rifted margin of the transantarctic mountains and compare the land record with that obtained from offshore marine sedimentary rocks in the ross sea three landform assemblages reflect 1 fluvial planation and dissection 2 local glaciation under temperate conditions and 3 overriding by the east antarctic ice sheet overall landscape evolution is typical of a passive continental margin contrasts in morphology between the convoy range and the adjacent dry valleys and royal society mountains reflect the varying location of the initial drainage divide in relationship to the rifted coast in a wider synthesis we draw the following conclusions for the 260 km long mcmurdo sector of the transantarctic mountains denudation since rifting at ca 55 ma has removed a wedge 4 7 km thick at the coast declining inland to 1 km most denudation occurred in the eocene from planation and incision of river valleys near the coast a subsequent pulse of denudation most rapid at 34 31 ma and declining until ca 17 ma coincided with further crustal extension and a change from cool temperate to polar climate during the same interval there was a progressive decrease in landscape modification by warm based glaciers and or rivers between 14 8 and 13 6 ma the maximum overriding antarctic ice sheet flowed northeastward across the mountains leaving meltwater features crossing high altitude saddles and areally scoured bedrock near the coast since 13 6 ma the landscape has seen little change under a hyperarid polar climate either by local glaciers or subaerially fragile middle miocene surficial deposits still survive there has been tectonic stability since the middle miocene

detrital thermochronology records changing source areas and steady exhumation in the western european alps a dramatic increase in sediment flux since ca 5 ma has been inferred for the european alps and worldwide and is interpreted to reflect a climatically driven increase in erosion rates however detrital thermochronology data from the alpine forelands suggest steady miocene pliocene exhumation contradicting the sediment budget data we present new detrital apatite fission track aft data from the foreland of the western alps to better resolve miocene to present day exhumation rates and to determine sediment provenance a shift in aft lag time from

production rate of cosmogenic 21ne in quartz estimated from 10be 26al and 21ne concentrations in slowly eroding antarctic bedrock surfaces abstract we estimated the production rate of 21ne in quartz using a set of samples from slowly eroding sandstone surfaces in the antarctic dry valleys geologic evidence as well as cosmogenic 10be and 26al concentrations indicate that i these sites have experienced millions of years of surface exposure at low erosion rates and ii steady erosion has been sustained long enough that surface 10be and 26al concentrations have reached equilibrium with the erosion rate under these conditions surface cosmogenic 21ne concentrations should be a function only of the erosion rate and the 21ne production rate as the erosion rate can be determined from 10be and 26al concentrations this allows an estimate of the 21ne production rate estimating the reference 21ne production rate on this basis with the assumption that all 21ne production is by neutron spallation yields a poor fit to measured 21ne concentrations and a systematic residual that is correlated with the erosion rate of the sample site the same steady erosion assumption with a production model that includes production by deeply penetrating muons yields a good fit both to our measurements and to similar independent measurements from an antarctic bedrock core both data sets together yield a total reference 21ne production rate of 18 3 0 4 atoms g 1 a 1 of which 0 66 0 10 atoms g 1 a 1 is due to muon interactions

the honeymoon well nickel sulfide deposits western australia the honeymoon well ni fe sulfide deposits occur in a thick assemblage of altered intrusive dunires and extrusive komatiites in an archean greenstone belt near wiluna in the eastern yilgarn block western australia the sulfides host rocks and surrounding intermediate to basic volcanics have undergone greenschist facies metamorphism in a low strain environment ultramafic rocks have been totally serpentinized and or carbonated but igneous textures are commonly well preserved the coarse grained dunitic rocks are interpreted as slowly cooled igneous cumulates on the basis of textural features and mineralogical and cryptic layering spinilex textures within the ultramafic assemblage and rare interbedded black shale suggest an extrusive origin for some of the rocks and the dunite bodies are possibly consanguineous subvolcanic sills disseminated ni fe sulfide mineralization occurs in two zones up to 100 m wide near the western and eastern contacts of the ultramarie assemblage pentlandite is the dominant sulfide in lizardite serpentinites and occurs in an intercumulus position moulded around former olivine grains in talc carbonate rocks locally developed adjacent to the ultramarie contacts pyrrhotite is also common exploration to date has outlined two major zones of ni fe sulfide mineralization with mean grades ranging from 0 5 to 1 percent ni honeymoon well sulfide mineralogy is ni rich in comparison with most other intrusive dunite associated deposits in the region and regular differences in s ni fe ni and ni cu ratios appear to correlate with the metamorphic setting and host rock mineralogy

observations of the quasi 2 day wave from the high resolution doppler imager on uars a strong westward traveling oscillation with a period of 2 days and zonal wave number 3 is observed in the mesospheric and lower thermospheric winds from the high resolution doppler imager on the upper atmosphere research satellite the important events happen in january july and september october of which the occurrence in january is the strongest with an amplitude over 60ms 1 detailed analyses for the periods of january 1992 and january 1993 reveal a cause and effect relationship in the wave developing process at 95km the global structures of the wave amplitude and phase are also presented

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

emergence of the shackleton range from beneath the antarctic ice sheet due to glacial erosion abstract this paper explores the long term evolution of a subglacial fjord landscape in the shackleton range antarctica we propose that prolonged ice sheet erosion across a passive continental margin caused troughs to deepen and lower the surrounding ice sheet surface leaving adjacent mountains exposed geomorphological evidence suggests a change in the direction of regional ice flow accompanied emergence simple calculations suggest that isostatic compensation caused by the deepening of bounding ice stream troughs lowered the ice sheet surface relative to the mountains by 800 m use of multiple cosmogenic isotopes on bedrock and erratics 26al 10be 21ne provides evidence that overriding of the massif and the deepening of the adjacent troughs occurred earlier than the quaternary perhaps this occurred in the mid miocene as elsewhere in east antarctica in the mcmurdo dry valleys and the lambert basin the implication is that glacial erosion instigates feedback that can change ice sheet thickness extent and direction of flow indeed as the subglacial troughs evolve over millions of years they increase topographic relief and this changes the dynamics of the ice sheet

reconstruction of changes in the weddell sea sector of the antarctic ice sheet since the last glacial maximum the weddell sea sector is one of the main formation sites for antarctic bottom water and an outlet for about one fifth of antarctica s continental ice volume over the last few decades studies on glacial geological records in this sector have provided conflicting reconstructions of changes in ice sheet extent and ice sheet thickness since the last glacial maximum lgm at ca 23 19 calibrated kiloyears before present cal ka bp terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the weddell sea ice sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding line advance at the lgm other marine geological and geophysical studies concluded that subglacial bedforms mapped on the weddell sea continental shelf subglacial deposits and sediments over compacted by overriding ice recovered in cores and the few available radiocarbon ages from marine sediments are consistent with major ice sheet advance at the lgm reflecting the geological interpretations different ice sheet models have reconstructed conflicting lgm ice sheet configurations for the weddell sea sector consequently the estimated contributions of ice sheet build up in the weddell sea sector to the lgm sea level low stand of 130 m vary considerably in this paper we summarise and review the geological records of past ice sheet margins and past ice sheet elevations in the weddell sea sector we compile marine and terrestrial chronological data constraining former ice sheet size thereby highlighting different levels of certainty and present two alternative scenarios of the lgm ice sheet configuration including time slice reconstructions for post lgm grounding line retreat moreover we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research the aim of our study is to provide two alternative interpretations of glacial geological datasets on antarctic ice sheet history for the weddell sea sector which can be utilised to test and improve numerical ice sheet models

glaciology and geological signature of the last glacial maximum antarctic ice sheet dynamical changes in contemporary ice sheets account for significant proportions of their current rates of mass loss but assessing whether or not these processes are a natural part of ice sheet evolution requires inference from palaeo glaciological records however a robust mechanism for translating sparse geological data into meaningful interpretations of past glacier dynamics at the continental scale is lacking since geological archives can be ambiguous and often their chronology is only poorly constrained to address this we combine the interpretation of high resolution antarctic ice sheet model results with continent wide geological evidence pertinent to the dynamical configuration of the ice sheet during the last and possibly preceding glacial maxima we first focus on the thermal regime of the ice sheet its pattern and velocity of flow variability in likely subglacial erosion and sediment transport and how these characteristics evolve during glacial transitions we show that rapid basal sliding was restricted to discrete outlets that eroded and advected sediment toward and across the continental shelf primarily during the early stages of advance and retreat of the ice sheet highlighting the need to consider time transgressive behaviour in the interpretation of geological archives secondly we present new modelling that attempts to improve the fit of our numerical model to geologically based reconstructions in the ross sea by accounting for locally enhanced ablation in mcmurdo sound our new simulation achieves a much closer fit to empirically derived flow patterns than previously growth of the modelled last glacial maximum ice sheet takes place primarily by marine ice accretion in the major embayments as a consequence of cooler ocean temperatures and reduced sub ice shelf melting and at its maximal extent represents a grounded ice volume excess above present of approximately 8 3 m sea level equivalent this figure thus provides an upper bound on the possible antarctic contribution to deglacial meltwater pulses

an isochron method for cosmogenic nuclide dating of buried soils and sediments we describe an improved method for dating buried paleosols using measurements of the cosmic ray produced radionuclides 10be and 26al in quartz grains and apply it to a sequence of intercalated tills and paleosols in central missouri usa that record plio pleistocene advances of the laurentide ice sheet a buried paleosol implies a period of surface exposure and nuclide accumulation followed by burial and a halt to nuclide production if the paleosol is formed in a sedimentary unit such as till this unit may also have been emplaced with unknown 26al and 10be concentrations inherited from past surface exposure if the inherited nuclide concentrations are the same at all depths in the soil as is true for well mixed sediments such as till then the 26al and 10be concentrations at different depths in the paleosol will show a linear relationship the slope of this line depends on the duration of burial of the paleosol but not on the inherited nuclide concentrations or on the sample depths thus one can date strata overlying buried paleosols by measuring 26al and 10be at multiple depths in the paleosol and calculating the burial age of the paleosol from the resulting isochron we focus on applying this approach to till paleosol sequences but the basic idea of forming an 26al 10be burial isochron with a set of samples that share the same burial age but differ in other aspects of their exposure history applies to other stratigraphic settings as well the method yields ages for four tills in missouri that are stratigraphically consistent agree with paleomagnetic age constraints and show that ice advanced into missouri near 1 25 ma near 0 8 ma and twice between ca 0 4 and 0 2 ma

ice cap erosion patterns from bedrock 10be and 26al southeastern tibetan plateau quantifying glacial erosion contributes to our understanding of landscape evolution and topographic relief production in high altitude and high latitude areas combining in situ be 10 and al 26 ana

west antarctica in gondwanaland crustal blocks reconstruction and breakup processes abstract a combined bas usarp west antarctic tectonic project has provided new constraints on the crustal structure and geological evolution of west antarctica and its relationship to the rest of gondwanaland rb sr age dating has confirmed the presence of 1200 1000 m y old precambrian gneisses within west antarctica and aeromagnetic data have defined the extent of this precambrian crustal block paleomagnetic data have constrained the position of four of the five geologically distinctive west antarctic crustal blocks within gondwanaland they can be restored to their original position prior to breakup by 15 25 counter clockwise rotation with little or no relative displacement between the blocks a major period of within plate middle jurassic magmatism associated with an important crustal melting event that is clearly related to the breakup of the supercontinent has also been identified based on new isotopic and geochemical data

airborne radar evidence for tributary flow switching in institute ice stream west antarctica implications for ice sheet configuration and dynamics despite the importance of ice streaming to the evaluation of west antarctic ice sheet wais stability we know little about mid to long term dynamic changes within the institute ice stream iis catchment here we use airborne radio echo sounding to investigate the subglacial topography internal stratigraphy and holocene flow regime of the upper iis catchment near the ellsworth mountains internal layer buckling within three discrete topographically confined tributaries through ellsworth independence and horseshoe valley troughs provides evidence for former enhanced ice sheet flow we suggest that enhanced ice flow through independence and ellsworth troughs during the mid to late holocene was the source of ice streaming over the region now occupied by the slow flowing bungenstock ice rise although buckled layers also exist within the slow flowing ice of horseshoe valley trough a thicker sequence of surface conformable layers in the upper ice column suggests slowdown more than 4000 years ago so we do not attribute enhanced flow switch off here to the late holocene ice flow reorganization intensely buckled englacial layers within horseshoe valley and independence troughs cannot be accounted for under present day flow speeds the dynamic nature of ice flow in iis and its tributaries suggests that recent ice stream switching and mass changes in the siple coast and amundsen sea sectors are not unique to these sectors and that they may have been regular during the holocene and may characterize the decline of the wais

reconstructing the last glacial maximum ice sheet in the weddell sea embayment antarctica using numerical modelling constrained by field evidence abstract the weddell sea embayment wse sector of the antarctic ice sheet has been suggested as a potential source for a period of rapid sea level rise meltwater pulse 1a a 20 m rise in 500 years previous modelling attempts have predicted an extensive grounding line advance in the wse to the continental shelf break leading to a large equivalent sea level contribution for the sector a range of recent field evidence suggests that the ice sheet elevation change in the wse at the last glacial maximum lgm is less than previously thought this paper describes and discusses an ice flow modelling derived reconstruction of the lgm ice sheet in the wse constrained by the recent field evidence the ice flow model reconstructions suggest that an ice sheet consistent with the field evidence does not support grounding line advance to the continental shelf break a range of modelled ice sheet surfaces are instead produced with different grounding line locations derived from a novel grounding line advance scheme the ice sheet reconstructions which best fit the field constraints lead to a range of equivalent eustatic sea level estimates between approximately 1 4 and 3 m for this sector this paper describes the modelling procedure in detail considers the assumptions and limitations associated with the modelling approach and how the uncertainty may impact on the eustatic sea level equivalent results for the wse

elevation change and ice flow at horseshoe valley patriot hills west antarctica patriot hills is located at 80 18 s 81 22 w at the southernmost end of the heritage range ellsworth mountains west antarctica a comparison of glacier elevation data and ice velocities obtained by the differential global positioning system in the period 1996 97 is presented ablation accumulation rates measured at a network of stakes in horseshoe valley show average accumulation of 70 kg m 2 a 1 in the central part of the valley and a maximum ablation of 170 kg m 2 a 1 at the edge of the blue ice area close to patriot hills changes in the surface elevation of the glacier measured at 81 stakes in the period 1995 97 show a mean thickening of 0 43 0 42 m a 1 which considering the uncertainties indicates that the ice sheet around patriot hills is in near steady state surface velocities in combination with ice thicknesses obtained by ground based radio echo sounding are used to compute the ice flux across the horseshoe valley transect a total outflow of 0 44 0 08 km 3 a 1 is obtained considering a catchment area for horseshoe valley of 1087 km 2 upstream from the flow transect and a net accumulation rate of 100 kg m 2 a 1 a total input of 0 11 0 04 km 3 a 1 by snow accumulation is obtained accepting a near equilibrium condition for the ice sheet the flux difference i e 0 33 km 3 a 1 must be supplied by flow from the inland ice sheet through ice cliffs located in mountain gaps in the heritage range if horseshoe valley is not in steady state but is thickening the positive mass balance could be due to increased snow accumulation or enhanced ice flow from the interior of the ice sheet new data are needed to elucidate this

super dual auroral radar network observations of meteor echoes radar echoes from ranges less than 500 km are routinely observed by the super dual auroral radar network superdarn on most days many of these echoes have properties which are markedly different from what one would expect from e or f region irregularities we show that these unusual short range hf echoes are due to scattering off meteor trails this explains why among other things the doppler shift from the short range echoes taken from the superdarn saskatoon antenna are consistent with the mesospheric winds observed by the saskatoon mf radar this means that the superdarn radars can be used to study neutral winds at meteor heights a result which is especially interesting since it opens up the capability for a global coverage of mesospheric winds using the worldwide distribution of superdarn radars

the million year evolution of the glacial trimline in the southernmost ellsworth mountains antarctica an elevated erosional trimline in the heart of west antarctica in the ellsworth mountains tells of thicker ice in the past and represents an important yet ambiguous stage in the evolution of the antarctic ice sheet here we analyse the geomorphology of massifs in the southernmost heritage range where the surfaces associated with the trimline are overlain by surficial deposits that have the potential to be dated through cosmogenic nuclide analysis analysis of 100 rock samples reveals that some clasts have been exposed on glacially moulded surfaces for 1 4 ma and perhaps more than 3 5 ma while others reflect fluctuations in thickness during quaternary glacial cycles modelling the age of the glacially moulded bedrock surface based on cosmogenic 10be 26al and 21ne concentrations from a depth profile indicates a minimum exposure age of 2 1 2 6 ma we conclude that the glacially eroded surfaces adjacent to the trimline predate the last glacial maximum and indeed the quaternary since erosion was by warm based ice near an ice sheet upper margin we suggest it first occurred during the early glaciations of antarctica before the stepped cooling of the mid miocene at 14 ma this was a time when the interior antarctic continent had summers warm enough for tundra vegetation to grow and for mountain glaciers to consist of ice at the pressure melting point during these milder conditions and subsequently erosion of glacial troughs is likely to have lowered the ice sheet surface in relation to the mountains this means that the range of orbitally induced cyclic fluctuations in ice thickness have progressively been confined to lower elevations

deglacial history of the west antarctic ice sheet in the weddell sea embayment constraints on past ice volume change the retreat history of the west antarctic ice sheet wais since the last glacial maximum is important for understanding the process of rapid deglaciation constraining models that seek to predict the future trajectory of the ice sheet and for estimating rates of sea level change here we report new glacial geologic data from the southwestern weddell sea embayment that demonstrate that this part of the wais was thinner than previously suggested and that there was progressive thinning of the ice sheet by 230 480 m since ca 15 ka we use geomorphological data and a numerical ice sheet model to reconstruct the ice sheet in the weddell sea at the last glacial maximum the volume of this ice would have added between 1 4 and 2 0 m to postglacial sea level rise and would not have been sufficient to contribute significantly to meltwater pulse 1a a rapid rise in sea level 14 200 yr ago

fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model the evolution of ice sheet configuration and flow pattern in fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model i e a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets the model uses mapped flow traces and deglacial melt water landforms as well as relative chronologies derived from cross cutting striae and till lineations as input data flow trace systems were classified into four types i time transgressive wet bed deglacial fans ii time transgressive frozen bed deglacial fans iii surge fans and iv synchronous non deglacial event fans using relative chronologies and aggregation of fans into glaciologically plausible patterns a series of ice sheet configurations at different time slices was erected a chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume geological evidence exists for several discrete ice sheet configurations centred over the scandinavian mountain range during the early weichselian the build up of the main weichselian fennoscandian ice sheet started at approximately 70 ka and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern norway this configuration had a flow pattern which is poorly reproduced by current numerical models of the fennoscandian ice sheet at the last glacial maximum the main ice divide was located overthe gulf of bothnia a major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the scandinavian mountain chain widespread areas of preserved pre late weichselian landscapes indicate that the ice sheet had a frozen bed core area which was only partly diminished in size by inward transgressive wet bed zones during the decay phase

relation of ongoing deformation rates to the subduction zone process in southern alaska the rate and orientation of ongoing strain associated with subduction of the pacific plate and the accretion of the yakutat terrane to southern alaska has been estimated at 13 sites from global positioning system measurements made in june 1993 and 1995 along the gulf of alaska coast near cape yakataga the average rate of deformation relative to fairbanks was 38 mm yr at n32 w further inland above the region where the dip of the downgoing pacific plate changes from about 10 to 30 the deformation rate was 12mm yr at n26 w in the sourdough paxson area the deformation rate drops to 2 5 mm yr and suggests a low short term deformation rate across the denali fault elastic straining of the overriding plate due to back slip on a main thrust zone with an average dip of about 10 can account for the overall rate and distribution of short term compressional strain across south central alaska above the transitional region between unstable and stable sliding we suggest that strain associated with 15 mm yr of right lateral strike slip occurs also if the strain accumulated since the two 1899 earthquakes both mw 8 1 from the offshore pamplona fault zone to south of the border ranges fault down dip width 100 km was seismically released on a single fault it would correspond to a m 8 1 earthquake

deglacial history of the west antarctic ice sheet in the weddell sea embayment constraints on past ice volume change comment boundaries along valley or mountain slopes separating fresh largely unweathered glacial deposits or bedrock below from more highly weathered deposits or bedrock above weathering zones have long been used to constrain vertical ice limits in scandinavia dahl 1966 1 and the canadian arctic

progressive cenozoic cooling and the demise of antarctica s last refugium the antarctic peninsula is considered to be the last region of antarctica to have been fully glaciated as a result of cenozoic climatic cooling as such it was likely the last refugium for plants and animals that had inhabited the continent since it separated from the gondwana supercontinent drill cores and seismic data acquired during two cruises shaldril i and ii in the northernmost peninsula region yield a record that when combined with existing data indicates progressive cooling and associated changes in terrestrial vegetation over the course of the past 37 million years mountain glaciation began in the latest eocene approximately 37 34 ma contemporaneous with glaciation elsewhere on the continent and a reduction in atmospheric co2 concentrations this climate cooling was accompanied by a decrease in diversity of the angiosperm dominated vegetation that inhabited the northern peninsula during the eocene a mosaic of southern beech and conifer dominated woodlands and tundra continued to occupy the region during the oligocene approximately 34 23 ma by the middle miocene approximately 16 11 6 ma localized pockets of limited tundra still existed at least until 12 8 ma the transition from temperate alpine glaciation to a dynamic polythermal ice sheet took place during the middle miocene the northernmost peninsula was overridden by an ice sheet in the early pliocene approximately 5 3 3 6 ma the long cooling history of the peninsula is consistent with the extended timescales of tectonic evolution of the antarctic margin involving the opening of ocean passageways and associated establishment of circumpolar circulation

landscape evolution of the dry valleys transantarctic mountains tectonic implications there are different views about the amount and timing of surface uplift in the transantarctic mountains and the geophysical mechanisms involved our new interpretation of the landscape evolution and tectonic history of the dry valleys area of the transantarctic mountains is based on geomorphic mapping of an area of 10 000 km2 the landforms are dated mainly by their association with volcanic ashes and glaciomarine deposits and this permits a reconstruction of the stages and timing of landscape evolution following a lowering of base level about 55 m y ago there was a phase of rapid denudation associated with planation and escarpment retreat probably under semiarid conditions eventually downcutting by rivers aided in places by glaciers graded valleys to near present sea level the main valleys were flooded by the sea in the miocene during a phase of subsidence before experiencing a final stage of modest upwarping near the coast there has been remarkably little landform change under the stable cold polar conditions of the last 15 m y it is difficult to explain the sirius group deposits which occur at high elevations in the area if they are pliocene in age overall denudation may have removed a wedge of rock with a thickness of over 4 km at the coast declining to 1 km at a point 75 km inland which is in good agreement with the results of existing apatite fission track analyses it is suggested that denudation reflects the differences in base level caused by high elevation at the time of extension due to underplating and the subsequent role of thermal uplift and flexural isostasy most crustal uplift 2 4 km is inferred to have occurred in the early cenozoic with 400 m of subsidence in the miocene followed by 300 m of uplift in the pliocene

simultaneous observations of the july 1996 2 day wave event using the super dual auroral radar network and the high resolution doppler imager simultaneous observations of a 2 day wave using the super dual auroral radar network superdarn and the upper atmospheric research satellite based uars high resolution doppler imager hrdi are presented recent comparisons of superdarn data with data from the saskatoon mf radar hall et al 1997 demonstrate that superdarn data at ranges close to the radar is most likely due to scatter from meteor trails and can be used to trace neutral winds in the meteor region this study exploits this near range scatter to observe the winds during july 1996 during the study period a clear 2 day wave event was observed in both the radar data and in the hrdi data comparisons between the two data sets show similarities and distinct differences both instruments observed a wave of similar amplitude in the same time interval both instruments indicated a westward propagating wave with zonal wave number 3 hrdi observed the wave to form and diminish at earlier times than superdarn observed in addition there were distinct differences between the winds observed by hrdi at the radar longitudes and the winds observed by the radars many of the differences may be explained by the latitude difference between the radars and the northern most latitude observed by hrdi