variations of the effective elastic thickness reveal tectonic fragmentation of the antarctic lithosphere abstract to this day little is known about thermal and rheological properties of the antarctic lithosphere we derive the effective elastic thickness t e as a proxy for these parameters by using ice thickness bedrock topography and a combination of new satellite and high resolution terrestrial gravity data cross spectral analysis based on the fan wavelet technique was employed to calculate t e variations by means of admittance and coherence techniques our results confirm a clear tectonic division of antarctica with predominantly high values in east antarctica eant t e 60 80 km and low values in west antarctica want t e 5 20 km for the transantarctic mountains separating these provinces we found t e to be around 10 km along the whole chain which is comparable to want apart from this general division we found fragmentation of the lithosphere within these provinces especially eant doesn t represent a single lithospheric block but shows strong variations of t e the highest values are found around the aurora subglacial basin t e 90 km and in dronning maud land t e 80 km the minimum value of t e within eant 15 km is found in the lambert graben such a low value can be associated with active rifting in the permian triassic strong localized erosion or possibly the effect of a cenozoic mantle plume according to the coherence calculations the weak zone extends to the gamburtsev subglacial mountains gsm showing a distinct decrease of t e to 25 30 km thus this weak channel divides the previously mentioned strong blocks however the admittance analysis gives relatively high values t e 70 km for the gsm based on the analysis of the wavelength dependent admittance and coherence results and misfits for several principal locations we give some preference to the coherence based values

the role of lithospheric flexure in the landscape evolution of the wilkes subglacial basin and transantarctic mountains east antarctica reconstructions of the bedrock topography of antarctica since the eocene oligocene boundary ca 34 ma provide important constraints for modelling antarctic ice sheet evolution this is particularly important in regions where the bedrock lies below sea level since in these sectors the overlying ice sheet is thought to be most susceptible to past and future change here we use 3d flexural modelling to reconstruct the evolution of the topography of the wilkes subglacial basin wsb and transantarctic mountains tam in east antarctica we estimate the spatial distribution of glacial erosion beneath the east antarctic ice sheet and restore this material to the topography which is also adjusted for associated flexural isostatic responses we independently constrain our post 34 ma erosion estimates using offshore sediment stratigraphy interpretations our reconstructions provide a better defined topographic boundary condition for modelling early east antarctic ice sheet history we show that the majority of glacial erosion and landscape evolution occurred prior to 14 ma which we interpret to reflect more dynamic and erosive early ice sheet behaviour in addition we use closely spaced 2d flexural models to test previously proposed hypotheses for a flexural origin of the tam and wsb the pre 34 ma topography shows lateral variations along the length of the tam and wsb that cannot be explained by uniform flexure along the front of the tam we show that some of these variations may be explained by additional flexural uplift along the south western flank of the wsb and the rennick graben in northern victoria land

the impact of dynamic topography change on antarctic ice sheet stability during the mid pliocene warm period the evolution of the antarctic ice sheet during the mid pliocene warm period mpwp remains uncertain and has important implications for our understanding of ice sheet response to modern global warming the extent to which marine based sectors of the east antarctic ice sheet eais retreated during the mpwp is particularly contentious with geological observations and geochemical analyses being cited to argue for either a relatively minor or a significant ice sheet retreat in response to mid pliocene warming the stability of marine based ice sheets is intimately linked to bedrock elevation at their grounding lines and previous ice sheet modeling assumed that antarctic bedrock elevation during the mpwp was the same as today with the exception of a correction for the crustal response to ice loading however various processes may have perturbed bedrock elevation over the past 3 m y most notably vertical deflections of the crust driven by mantle convective flow or dynamic topography here we present simulations of mantle convective flow that are consistent with a wide range of present day observables and use them to predict changes in dynamic topography and reconstruct bedrock elevations during the mpwp we incorporate these elevations into a simulation of the antarctic ice sheet during the mpwp and find that the correction for dynamic topography change has a significant effect on the stability of the eais within the marine based wilkes basin with the ice margin in that sector retreating considerably further inland 200 560 km relative to simulations that do not include this correction for bedrock elevation

uplift and tilting of the shackleton range in east antarctica driven by glacial erosion and normal faulting unravelling the long term evolution of the subglacial landscape of antarctica is vital for understanding past ice sheet dynamics and stability particularly in marine based sectors of the ice sheet here we model the evolution of the bedrock topography beneath the recovery catchment a sector of the east antarctic ice sheet characterized by fast flowing ice streams that occupy overdeepened subglacial troughs we use 3d flexural models to quantify the effect of erosional unloading and mechanical unloading associated with motion on border faults in driving isostatic bedrock uplift of the shackleton range and theron mountains which are flanked by the recovery slessor and bailey ice streams inverse spectral free air admittance and forward modeling of topography and gravity anomaly data allow us to constrain the effective elastic thickness of the lithosphere te in the shackleton range region to 20 km our models indicate that glacial erosion and the associated isostatic rebound has driven 40 50 of total peak uplift in the shackleton range and theron mountains a further 40 50 can be attributed to motion on normal fault systems of inferred jurassic and cretaceous age our results indicate that the flexural effects of glacial erosion play a key role in mountain uplift along the east antarctic margin augmenting previous findings in the transantarctic mountains the results suggest that at 34 ma the mountains were lower and the bounding valley floors were close to sea level which implies that the early ice sheet in this region may have been relatively stable

erosion driven uplift in the gamburtsev subglacial mountains of east antarctica the relative roles of climate and tectonics in mountain building have been widely debated central to this debate is the process of flexural uplift in response to valley incision here we quantify this process in the gamburtsev subglacial mountains a paradoxical tectonic feature in cratonic east antarctica previous studies indicate that rifting and strike slip tectonics may have provided a key trigger for the initial uplift of the gamburtsevs but the contribution of more recent valley incision remains to be quantified inverse spectral free air admittance and bouguer coherence methods indicate that unusually for continents the coherence between free air gravity anomalies and bedrock topography is high 0 5 and that the elastic thickness of the lithosphere is anomalously low 15 km in contrast to previously reported values of up to 70 km the isostatic effects of two different styles of erosion are quantified dendritic fluvial incision overprinted by alpine style glacial erosion in the gamburtsevs and outlet glacier type selective linear erosion in the lambert rift part of the east antarctic rift system 3d flexural models indicate that valley incision has contributed ca 500 m of peak uplift in the gamburtsevs and up to 1 2 km in the lambert rift which is consistent with the present day elevation of oligocene miocene glaciomarine sediments overall we find that 17 25 of gamburtsev peak uplift can be explained by erosional unloading these relatively low values are typical of temperate mountain ranges suggesting that most of the valley incision in the gamburtsevs occurred prior to widespread glaciation at 34 ma the pre incision topography of the gamburtsevs lies at 2 2 5 km above sea level confirming that they were a key inception point for the development of the east antarctic ice sheet tectonic and or dynamic processes were therefore responsible for ca 80 of the elevation of the modern gamburtsev subglacial mountains

controlling factors and dynamical formation models of lacustrine organic matter accumulation for the jurassic da anzhai member in the central sichuan basin southwestern china abstract the lacustrine shale in the jurassic da anzhai member is considered as an excellent source rock in the central sichuan basin however geochemical studies of lacustrine organic matter om accumulation factors and mechanisms are scarce this study investigated the variations in total organic carbon toc major elements trace elements tes and 13c and 18o values to reconstruct the paleoenvironmental conditions biotic productivity terrestrial inputs and other factors to improve the understanding of the controlling factors and dynamical formation models for lacustrine om the target shale was deposited in a fluctuating and complicated terrestrial open lake that exhibited oxic suboxic oxygen levels weak to moderate hydrodynamic conditions a dry to humid climate moderate weathering and fresh to saline water conditions the lake experienced moderate high biotic productivity under a warm humid climate and featured abundant flora and fauna compared to the da13 shale the da1 shale featured higher salinity levels a hotter and drier climate greater weathering and more reduced conditions the da13 shale experienced stronger hydrodynamic forces and a more humid climate moreover the toc values of the da13 correlate better with the indicators of redox conditions and exhibit little or no correlation with indicators of climate weathering salinity and biotic productivity indicating that the lacustrine om was mainly controlled by the redox conditions additionally factors such as hydrodynamic conditions and terrestrial inputs exerted some degree of influence based on these factors and their relationships two dynamical formation models are proposed a high salinity low oxygen dynamical formation model model i and a deep water low oxygen dynamical formation model model ii model i stresses that the low oxygen levels were mainly caused by salinity whereas model ii stresses that the low oxygen levels were mainly caused by deep depth both models can be classified as preservation models

fluvial origin of the valley system in northern victoria land antarctica from quantitative geomorphic analysis a network of sinuous valleys with typical dendritic pattern characterizes northern victoria land nvl in antarctica subparallel to parallel and angular to rectangular patterns are also present quantitative geomorphic analysis of the valley network has been carried out utilizing gis spatial analysis while drainage densities and drainage frequencies show low values segments of the nvl valley network are substantially well organized as indicated by bifurcation ratio r b and direct bifurcation ratio r bd parameters all basins faithfully adhere to horton s laws of drainage network composition quantitative geomorphic analysis suggests that the valley system can be ascribed to fl uvial origin and that consequently a morphoclimatic system completely different from that of present day must have driven its carving the resulting data provide indications about the origin of the valley network and this invaluable information can be used for the reconstruction of earlier phases of glacial history and climatic and tectonic evolution of this signifi cant antarctic region fluvial erosion enhanced the denudation of the transantarctic mountains from at least 55 ma to at least the eocene oligocene boundary ca 34 ma fluvial basins adapted to the tectonic structure following the main regional fault systems a well developed alpine topography postdates the fl uvial morphology temperate glaciers were responsible for denudation until the late miocene parasitic glaciers presently mantle the previously sculpted topography present day glacial erosion is negligible and denudation has been exceedingly slow since 7 5 ma

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

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

freezing of ridges and water networks preserves the gamburtsev subglacial mountains for millions of years once an ice sheet grows beyond a critical thickness the basal thermal regime favors melting and development of subglacial water networks subglacial water is necessary for bedrock erosion but the exact mechanisms that lead to preservation of subglacial topography are unclear here we resolve the freezing mechanisms that lead to long term high altitude preservation across the gamburtsev subglacial mountains in east antarctica analyses of a comprehensive geophysical data set reveal a large scale water network along valley floors the ice sheet often drives subglacial water up steep topography where it freezes along high ridges beneath thinner ice statistical tests of hypsometry show the gamburtsevs resemble younger midlatitude mountains indicating exceptional preservation we conclude that the gamburtsevs have been shielded from erosion since the latest eocene 34 ma these freezing mechanisms likely account for the spatial and temporal patterns of erosion and preservation seen in other glaciated mountain ranges

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

antarctic bedrock topography uncertainty and ice sheet stability antarctic bedrock elevation estimates have uncertainties exceeding 1 km in certain regions bedrock elevation particularly where the bedrock is below sea level and bordering the ocean can have a large impact on ice sheet stability we investigate how present day bedrock elevation uncertainty affects ice sheet model simulations for a generic past warm period based on the mid pliocene although these uncertainties are also relevant to present day and future ice sheet stability we perform an ensemble of simulations with random topographic noise added with various length scales and with amplitudes tuned to the uncertainty of the bedmap2 data set total antarctic ice sheet retreat in these simulations varies between 12 6 and 17 9 m equivalent sea level rise after 3 kyrs of warm climate forcing this study highlights the sensitivity of ice sheet models to existing uncertainties in bedrock elevation and the ongoing need for new data acquisition

early pliocene marine sediments coastline and climate of east antarctica we record the first onshore late tertiary fossiliferous marine deposit from the 8000 km long coastline of east antarctica glaciomarine sediments containing abundant diatoms and molluscs were deposited in shallow waters off an open coast during the early pliocene 4 5 3 5 ma and are now exposed less than 15 m above sea level on marine plain in the vestfold hills lat 68 359s long 78 009e marine diatoms suggest early pliocene as the most probable age of the sediments fossil sand wedges show that the deposit was above sea level at least briefly before it was covered with water and subsequently capped with glaciomarine till the coastline at the time of deposition of the marine sediments is inferred to have been close to but farther inland than that of today the ice margin may have been 50 km farther inland considerably reducing the ice volume of antarctica climate at the time of deposition was interglacial and perhaps warmer than the present

pangea rifting shaped the east antarctic landscape east antarctica remains one of the few continental regions on earth where an understanding of the origin and causal processes responsible for topographic relief is largely missing low temperature thermochronology studies of exposed precambrian basement revealed discrete episodes of cooling and denudation during the paleozoic mesozoic however the significance of these thermal events and their relationship to topography across the continental interior remains unclear here we use zircon and apatite u th he thermochronology to resolve the low temperature thermal evolution of a poorly exposed section of east antarctic basement in the bunger hills region and gain insights into the chronology and style of landscape evolution across east antarctica thermal history modeling results indicate that precambrian basement in the bunger hills region experienced a distinct cooling episode during the late paleozoic triassic which we relate to 2 4 km of regional exhumation associated with intracontinental rifting followed by a second episode of localized cooling and 1 km exhumation during the late jurassic cretaceous separation of india from east gondwana these findings combined with existing thermochronological and tectonic evidence support a continent scale denudation event associated with uplift and exhumation of large sections of precambrian basement during late paleozoic triassic pangea wide intracontinental extension by contrast continental extension associated with the jurassic cretaceous breakup of east gondwana resulted in significant denudation only locally in regions west of the bunger hills we propose that the combined effects of these paleozoic mesozoic tectonic events had a profound impact on the topography across the east antarctic interior and influenced the long term landscape evolution of east antarctica

ice distal upper miocene marine strata from inland antarctica abstract glacimarine strata of the battye glacier formation 130 m thick pagodroma group exposed in the amery oasis of east antarctica provide a record of late miocene palaeoenvironmental conditions in an ice distal setting the formation overlies the amery erosion surface 300 m to 270 m above sea level that formed during an advance of the lambert glacier into prydz bay odp site 739 at least 750 km further north than today two lithological members a grey and muddier lower member and a brown sand rich upper member reflect variation in proximity to the terminus of the lambert glacier ice distal glacimarine diatom bearing mud up to 12 biogenic silica and in situ articulated molluscs occur in the lower member the battye glacier formation is significant because of its inland location which indicates that ice distal marine conditions existed 250 km inland from the current amery ice shelf edge similar neogene strata are known on land only from the pliocene sorsdal formation in the vestfold hills near the antarctic coast three stratigraphic intervals of diatom bearing mud are recognized from glacially reworked clasts and from in situ strata informally referred to as the mcleod beds and bed a the diatom bearing mud also contains sponge spicules and minor silicoflagellates and ebridians marine diatom biostratigraphy constrains the age of the beds to between 10 7 and 9 0 ma late miocene abundant benthic diatoms suggest deposition within shallow euphotic waters the high abundance of intercalary valves of eucampia antarctica from an interval of the mcleod beds suggests that there was less winter sea ice than in prydz bay today it is unlikely that sea ice was perennial because the presence of thalassionema spp and stellarima stellaris roper hasle et sims suggests that summer sea surface temperatures were too warm 0 c and 3 c respectively the palaeoclimate at the time of deposition appears to have been analogous to that in modern fjords of east greenland e g kangerdlugssuaq fjord which is consistent with the depositional model proposed previously for the pagodroma group the three diatom bearing mud intervals were deposited in the amery oasis 250 km inland of the current amery ice shelf edge when the east antarctic ice sheet was reduced in size relative to today

reconstructions of antarctic topography since the eocene oligocene boundary abstract accurate models of past antarctic ice sheet behaviour require more realistic reconstructions of the evolution of bedrock topography however other than a preliminary attempt to reconstruct antarctic topography at the eocene oligocene boundary the long term evolution of antarctica s subglacial topography throughout its glacial history has not previously been quantified here we derive new reconstructions of antarctic topography for four key time slices in antarctica s climate and glacial history the eocene oligocene boundary ca 34 ma the oligocene miocene boundary ca 23 ma the mid miocene climate transition ca 14 ma and the mid pliocene warm period ca 3 5 ma to reconstruct past topography we consider a series of processes including ice sheet loading volcanism thermal subsidence horizontal plate motion erosion sedimentation and flexural isostatic adjustment and validate our models where possible using onshore and offshore geological constraints our reconstructions show that the land area of antarctica situated above sea level was 25 larger at the eocene oligocene boundary than at the present day offshore sediment records and terrestrial constraints indicate that the incision of deep subglacial topographic troughs around the margin of east antarctica occurred predominantly in the oligocene and early miocene whereas in west antarctica erosion and sedimentation rates accelerated after the mid miocene changes to the topography after the mid pliocene were comparatively minor our new palaeotopography reconstructions provide a critical boundary condition for models seeking to understand past behaviour of the antarctic ice sheet and have implications for estimating changes in global ice volume temperature and sea level across major cenozoic climate transitions

early east antarctic ice sheet growth recorded in the landscape of the gamburtsev subglacial mountains the gamburtsev subglacial mountains are regarded as a key nucleation site for the antarctic ice sheet and they retain a unique long term record of pre glacial and early glacial landscape evolution here we use a range of morphometric analyses to constrain the nature of early glaciation and subsequent ice sheet evolution in the interior of east antarctica using a new digital elevation model of the gamburtsev subglacial mountains derived from an extensive airborne radar survey we find that an inherited fluvial landscape confirms the existence of the gamburtsev subglacial mountains prior to the onset of glaciation at the eocene oligocene climate boundary ca 34 ma features characteristic of glaciation at a range of scales are evident across the mountains high elevation alpine valley heads akin to cirques identified throughout the mountains are interpreted as evidence for early phases of glaciation in east antarctica the equilibrium line altitudes associated with these features combined with information from fossil plant assemblages suggest that they formed at or prior to 34 ma it cannot be ruled out that they may have been eroded by ephemeral ice between the late cretaceous and the eocene 100 34 ma hanging valleys overdeepenings truncated spurs and steep sided linear valley networks are indicative of a more widespread alpine glaciation in this region these features represent ice growth at or before 33 7 ma and provide a minimum estimate for the scale of the east antarctic ice sheet between ca 34 and 14 ma when dynamic fluctuations in ice extent are recorded at the coast of antarctica the implications are that the early east antarctic ice sheet grew rapidly and developed a cold based core that preserved the alpine landscape the patterns of landscape evolution identified provide the earliest evidence for the development of the east antarctic ice sheet and can be used to test coupled ice climate evolution models

potential seaways across west antarctica the west antarctic ice sheet wais has long been considered vulnerable to rapid retreat and today parts are rapidly losing ice projection of future change in wais is however hampered by our poor understanding of past changes especially during interglacial periods that could be analogs for the future but which undoubtedly provide an opportunity for testing predictive models we consider how ice loss would open seaways across wais these would likely alter southern ocean circulation and climate and would broadly define the de glacial state but they may also have left evidence of their existence in the coastal seas they once connected we show the most likely routes for such seaways and that a direct seaway between weddell and ross seas which did not pass through the amundsen sea sector is unlikely continued ice loss at present rates would open seaways between amundsen and weddell seas a w and amundsen and bellingshausen seas a b in around one thousand years this timescale indicates potential future vulnerability but also suggests seaways may have opened in recent interglacial periods we attempt to test this hypothesis using contemporary bryozoan species assemblages around antarctica concluding that anomalously high similarity in assemblages in the weddell and amundsen seas supports recent migration through a w other authors have suggested opening of seaways last occurred during marine isotope stage 7a 209 ka bp but we conclude that opening could have occurred in mis 5e 100 ka bp when antarctica was warmer than present and likely contributed to global sea levels higher than today

globsed updated total sediment thickness in the world s oceans we present globsed a new global 5 arc minute total sediment thickness grid for the world s oceans and marginal seas globsed covers a larger area than previously published global grids and incorporates updates for the ne atlantic arctic southern ocean and mediterranean regions which results in a 29 7 increase in estimated total oceanic sediment volume we use this new global grid and a revised global oceanic lithospheric age grid to assess the relationship between the total sediment thickness and age of the underlying oceanic lithosphere and its latitude an analytical approximation model is used to mathematically describe sedimentation trends in major oceanic basins and to allow paleobathymetric reconstructions at any given geological time this study provides a much needed update of the sediment thickness distribution of the world oceans and delivers a model for sedimentation rates on oceanic crust through time that agrees well with selected drill data used for comparison

topographic controls on post oligocene changes in ice sheet dynamics prydz bay region east antarctica within the general trend of post eocene cooling the largest and oldest outlet of the east antarctic ice sheet underwent a change from ice cliff to ice stream and or ice shelf dynamics with an associated switch from line source to fan sedimentation available geological data reveal little about the causes of these changes in ice dynamics during the miocene epoch or the subsequent effects on pliocene pleistocene ice sheet history icesheet numerical modeling reveals that bed morphology was probably responsible for driving changes in both ice sheet extent and dynamics in the lambert amery system at prydz bay the modeling shows how the topography and bathymetry of the lambert graben and prydz bay control ice sheet extent and flow the changes in bathymetric volume required for shelf edge glaciation correlate well with the prydz channel fan sedimentation history this suggests a negative feedback between erosion and glaciation whereby the current graben is overdeepened to such an extent that shelf edge glaciation is now not possible even if a last glacial maximum environment recurs we conclude that the erosional history of the lambert graben and prydz bay in combination with the uplift histories of the surrounding mountains are responsible for the evolution of this section of the east antarctic ice sheet once the necessary initial climatic conditions for glaciation were achieved at the start of the oligocene epoch

cenozoic landscape evolution of an east antarctic oasis radok lake area northern prince charles mountains and its implications for the glacial and climatic history of antarctica abstract ice free areas antarctica reveal a multi million year history of landscape evolution but most attention up to now has focused on the transantarctic mountains the amery oasis in the northern prince charles mountains borders the lambert glacier amery ice shelf system that drains 1 million km2 of the east antarctic ice sheet and therefore provides a record of fluctuations of both local and regional ice since the ice sheet first formed in early oligocene time this glacial record has been deciphered by i geomorphological mapping from aerial photographs and on the ground ii documenting the relationship between thick well dated uplifted glaciomarine strata and the underlying palaeolandscape iii examining surficial sediment facies and iv surface exposure dating using 10be and 26al the se amery oasis records at least 10 million years of landscape evolution beginning with a pre late miocene phase of glacial erosion followed by deposition of glaciomarine strata of the battye glacier formation pagodroma group in late miocene time a wet based ice sheet next expanded over the se amery oasis following which deposition of the glaciomarine pliocene bardin bluffs formation pagodroma group took place both formations were uplifted by at least 500 and 200 m respectively their tops are characterised by geomorphological surfaces upon which intensive periglacial activity took place higher level bedrock areas were subjected to deep weathering and tor formation early pleistocene time was characterised by expansion of a cold based ice sheet across the whole area but it left little more than patches of sandy gravel and erratic blocks late pleistocene expansion of local ice the battye glacier saw deposition of moraine mound complexes on low ground around radok lake and ice dammed lake phenomena subglacial drainage of the lake escaped to the east exhuming the sediment filled gorges holocene landscape modification has been relatively superficial overall the landscape of the amery oasis evolved primarily under the influence of wet based probably polythermal glaciers in miocene and pliocene times whereas the quaternary period was characterised mainly by cold based glaciers that had comparatively little impact on the landscape

ocean basin evolution and global scale plate reorganization events since pangea breakup we present a revised global plate motion model with continuously closing plate boundaries ranging from the triassic at 230 ma to the present day assess differences among alternative absolute plate motion models and review global tectonic events relatively high mean absolute plate motion rates of approximately 9 10 cm yr 1 between 140 and 120 ma may be related to transient plate motion accelerations driven by the successive emplacement of a sequence of large igneous provinces during that time an event at 100 ma is most clearly expressed in the indian ocean and may reflect the initiation of andean style subduction along southern continental eurasia whereas an acceleration at 80 ma of mean rates from 6 to 8 cm yr 1 reflects the initial northward acceleration of india and simultaneous speedups of plates in the pacific an event at 50 ma expressed in relative and some absolute plate motion changes around the globe and in a reduction of global mean plate speeds from about 6 to 4 5 cm yr 1 indicates that an increase in collisional forces such as the india eurasia collision and ridge subduction events in the pacific such as the izanagi pacific ridge play a significant role in modulating plate velocities

detection of overpressure zones and a statistical model for pore pressure estimation from well logs in the krishna godavari basin india abnormally high pressures measured by repeat formation tester rft and detected by well log data from 10 wells in the krishna godavari k g basin occur in the vadaparru shale of miocene and raghavapuram shale of early cretaceous age overpressures generated by disequilibrium compaction and pore pressures have been estimated using the conventional eaton sonic equation with an exponent of 3 0 the observed abnormal pore pressure gradient ranges from 11 85 to 13 10 mpa km whereas fracture pressure gradient varies from 17 40 to 19 78 mpa km the magnitude of vertical stress sv has a gradient from 21 00 to 23 10 mpa km the minimum horizontal principal stress sh magnitude is found to vary from 64 to 77 of the sv in normally pressured to overpressured sediments a multiple linear regression model with a squared multiple correlation coefficient r2 of 0 94 is proposed for pore pressure prediction from gamma ray density and sonic logs to focus on efficient drilling operations and to prevent borehole instability the statistical model has been calibrated with the rft data from five wells covering about 3400 sq km area of the onshore k g basin the model predicted pore pressure values are in close agreement with the actual rft data for another four wells including a well in the offshore k g basin hence the proposed regression model may be useful for predicting pore pressure from other well logs in the k g basin

extremely low long term erosion rates around the gamburtsev mountains in interior east antarctica the high elevation and rugged relief 3 km of the gamburtsev subglacial mountains gsm have long been considered enigmatic orogenesis normally occurs near plate boundaries not cratonic interiors and large scale tectonic activity last occurred in east antarctica during the pan african 480 600 ma we sampled detrital apatite from eocene sands in prydz bay at the terminus of the lambert graben which drained a large pre glacial basin including the northern gamburtsev mountains apatite fission track and u th he cooling ages constrain bedrock erosion rates throughout the catchment we double dated apatites to resolve individual cooling histories erosion was very slow averaging 0 01 0 02 km myr for 250 myr supporting the preservation of high elevation in interior east antarctica since at least the cessation of permian rifting long term topographic preservation lends credence to postulated high elevation mountain ice caps in east antarctica since at least the cretaceous and to the idea that cold based glaciation can preserve tectonically inactive topography

dynamic behaviour of the east antarctic ice sheet during pliocene warmth warm intervals within the pliocene epoch 5 33 2 58 million years ago were characterized by global temperatures comparable to those predicted for the end of this century1 and atmospheric co2 concentrations similar to today2 3 4 estimates for global sea level highstands during these times5 imply possible retreat of the east antarctic ice sheet but ice proximal evidence from the antarctic margin is scarce here we present new data from pliocene marine sediments recovered offshore of adelie land east antarctica that reveal dynamic behaviour of the east antarctic ice sheet in the vicinity of the low lying wilkes subglacial basin during times of past climatic warmth sedimentary sequences deposited between 5 3 and 3 3 million years ago indicate increases in southern ocean surface water productivity associated with elevated circum antarctic temperatures the geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the wilkes subglacial basin an area today buried beneath the east antarctic ice sheet we interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the east antarctic ice sheet was sensitive to climatic warmth during the pliocene

minimal pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains a key parameter in ice sheet reconstructions we propose that there has been little or no pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains on the basis of isotopic dating and mapping of in situ cinder cone deposits on the walls of taylor valley twenty seven 40ar 39ar incremental heating analyses on whole rock samples from subaerially erupted olivine basanite volcanic outcrops of known elevations define 14 eruptions ranging in age from 3 89 to 1 50 ma because taylor valley opens directly onto the ross sea these results show that any surface uplift during the past 2 57 m y was 300 m our conclusion of minimal uplift contradicts previous models of dramatic uplift up to 3000 m since 3 ma and associated hypotheses that uplift caused climatic cooling and growth of a polar east antarctic ice sheet

preglacial to glacial sediment thickness grids for the southern pacific margin of west antarctica circum antarctic sediment thickness grids provide constraints for basin evolution and paleotopographic reconstructions which are important for paleo ice sheet formation histories by compiling old and new seismic data we identify sequences representing pre glacial transitional and full glacial deposition processes along the pacific margin of west antarctica the pre glacial sediment grid depicts 1 3 to 4 0 km thick depocenters relatively evenly distributed along the margin the depocenters change markedly in the transitional phase at or after the eocene oligocene boundary when the first major ice sheets reached the shelf full glacial sequences starting in the middle miocene indicate new depocenter formation north of the amundsen sea embayment and localized eastward shifts in the bellingshausen sea and antarctic peninsula basins using present day drainage paths and source areas on the continent our calculations indicate an estimated observed total sedimentary volume of 10 x 106 km3 was eroded from west antarctica since the separation of new zealand in the late cretaceous of this 4 9 x 106 km3 predates the onset of glaciation and need to be considered for a paleotopography reconstruction of 34 ma whereas 5 1 x 106 km3 postdate the onset of glaciation of which 2 5 x 106 km3 were deposited in post mid miocene full glacial conditions this article is protected by copyright all rights reserved

west antarctic paleotopography estimated at the eocene oligocene climate transition 1 one generally recognized limitation of models for rapid growth of antarctic ice near the eocene oligocene transition is that they are based on present topography corrected only for removal of modern ice for west antarctica this results in large areas below sea level that would not readily host ice in the recently active west antarctic rift system other factors may have contributed to significant vertical motions since the eocene additional corrections for thermal contraction resulting from tectonic extension and for erosion and sedimentation since 34 ma restore most of west antarctica to above sea level increasing total antarctic land area by 10 20 because ice sheets have convex slopes the potential increase in ice volume is larger than the increase in land area accounting for large changes in west antarctic topography may resolve conflicts between ice models and data by demonstrating the possibility of an early large west antarctic ice sheet

age provinces in the antarctic craton evidence from detrital zircons in permian strata from the beardmore glacier region antarctica abstract the antarctic gondwana sequence crops out along the transantarctic mountains permian strata at mt bowers and mt weeks in the central part of the range were mainly derived from the ice covered east antarctic craton for which the geology is inferred from coastal outcrops and the miller range in the transantarctic mountains analysis of detrital zircons from permian sandstones at those two localities demonstrate a slowly changing zircon age probability distribution for four samples from the lower part of the sequence with an abrupt change for the upper buckley formation sandstone the stratigraphically lowest sample from a unit informally designated the mt bowers sandstone is dominated by zircons in the age range 610 540 ma with minor components at 1 0 ga and 2 7 ga upward the pagoda formation sandstone is likewise dominated by zircons of 600 550 ma age together with a significant grenville age cluster 1 3 1 0 ga and a minor 1 5 1 4 ga cluster the fairchild formation sandstone has a preponderance of grains in the range 600 530 ma with a scatter of older ages zircon grains in the lower buckley formation sandstone are principally in the range 575 520 ma with another cluster at 470 450 ma and a scattering of older ages most zircons in the upper buckley formation sandstone are permian in age but with a very small component in the range 650 475 ma and a trace of older ages archean to early mesoproterozoic zircon grains are few in number and may have been recycled from distal outcrops the 1 5 1 4 ga grains suggest an unexposed mesoproterozoic source within the east antarctic craton which could have been linked to laurentian north america the grenville age source is considered to be similarly a sub glacial belt in the interior of east antarctica zircons with a late neoproterozoic to ordovician signature 600 460 ma were derived from a ross orogen foreland sequence and or an early and inland extension of the orogen itself permian zircons in the upper buckley sandstone reflect the development of a magmatic arc on the gondwana pacific margin

erosion at extended continental margins insights from new aerogeophysical data in eastern dronning maud land abstract modelling rock cooling sedimentation and exposure based interpretations of the mechanisms by which topography evolves at extended continental margins vary widely observations from the margin of dronning maud land antarctica have until now not strongly contributed to these interpretations here we present new airborne gravity and radar data describing the eastern part of this margin inland of a tall 2 5 km great escarpment a plateau topped by a branching network of valleys suggests preservation of a fluvial landscape with sw directed drainage beneath a cold based ice sheet the valley floor slopes show that this landscape was modified during a period of alpine style glaciation prior to the onset of the current cold based phase around 34 ma the volume of sediments in basins offshore in the riiser larsen sea balances with the volume of rock estimated to have been eroded and transported by north directed drainage from between the escarpment and the continental shelf break the stratigraphy of these basins shows that most of the erosion occurred during the 40 myr following late jurassic continental breakup this erosion is unlikely to have been dominated by backwearing because the required rate of escarpment retreat to its present location is faster than numerical models of landscape evolution suggest to be possible we suggest an additional component of erosion by downwearing seawards of a pre existing inland drainage divide the eastern termination of the great escarpment and inland plateau is at the west ragnhild trough a 300 km long 15 20 km wide and up to 1 6 km deep subglacial valley hosting the west ragnhild glacier numerous overdeepened by 300 m segments of the valley floor testify to its experience of significant glacial erosion thick late jurassic and early cretaceous sediments fanning out from the trough s mouth into the eastern riiser larsen sea betray an earlier history as a river valley the lack of late jurassic relief forming processes in this river s catchment in the interior of east antarctica suggests this erosion was related to regional climatic change

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

bedrock erosion surfaces record former east antarctic ice sheet extent east antarctica hosts large subglacial basins into which the east antarctic ice sheet eais likely retreated during past warmer climates however the extent of retreat remains poorly constrained making quantifying past and predicted future contributions to global sea level rise from these marine basins challenging geomorphological analysis and flexural modeling within the wilkes subglacial basin is used to reconstruct the ice margin during warm intervals of the oligocene miocene flat lying bedrock plateaus are indicative of an ice sheet margin positioned 400 500 km inland of the modern grounding zone for extended periods of the oligocene miocene equivalent to a 2 meter rise in global sea level our findings imply that if major eais retreat occurs in the future isostatic rebound will enable the plateau surfaces to act as seeding points for extensive ice rises thus limiting extensive ice margin retreat of the scale seen during the early eais

global cenozoic paleobathymetry with a focus on the northern hemisphere oceanic gateways abstract the evolution of the northern hemisphere oceanic gateways has facilitated ocean circulation changes and may have influenced climatic variations in the cenozoic time 66 ma 0 ma however the timing of these oceanic gateway events is poorly constrained and is often neglected in global paleobathymetric reconstructions we have therefore re evaluated the evolution of the northern hemisphere oceanic gateways i e the fram strait greenland scotland ridge the central american seaway and the tethys seaway and embedded their tectonic histories in a new global paleobathymetry and topography model for the cenozoic time our new paleobathymetry model incorporates northeast atlantic paleobathymetric variations due to iceland mantle plume activity updated regional plate kinematics and models for the oceanic lithospheric age sediment thickness and reconstructed oceanic plateaus and microcontinents we also provide a global paleotopography model based on new and previously published regional models in particular the new model documents important bathymetric changes in the northeast atlantic and in the tethys seaway at eocene oligocene transition 34 ma the time of the first glaciations of antarctica believed to be triggered by the opening of the southern ocean gateways i e the drake passage and the tasman gateway and subsequent antarctic circumpolar current initiation our new model can be used to test whether the northern hemisphere gateways could have also played an important role modulating ocean circulation and climate at that time in addition we provide a set of realistic global bathymetric and topographic reconstructions for the cenozoic time at one million year interval for further use in paleo ocean circulation and climate models

late oligocene early miocene glacial record of the ross sea antarctica evidence from dsdp site 270 foraminifera from deep sea drilling project site 270 ross sea antarctica are used to trace an early phase of glaciation during the late oligocene early miocene the central ross sea underwent significant bathymetric and oceanographic evolution with the inception of glaciomarine sedimentation resulting in the sequential development of four contrasting foraminiferal populations assemblage zones gradual climatic change in the ross sector during latest paleogene early neogene time culminated in major ice build up by the late early miocene conclusions derived from our microfaunal studies reaffirm climatic and oceanographic trends interpreted from oxygen isotope data for sub antarctic deep sea sites north of the ross sea intensification of glaciation within the ross sea area may be responsible for the increase in production of antarctic bottom water and associated development of widespread early neogene deep sea hiatuses reported from lower latitude regions

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

the berkner island antarctica ice core drilling project we describe a project to retrieve a 948 m deep ice core from berkner island antarctica using relatively lightweight logistics and a small team the drilling operation over three austral summer seasons used electromechanical drilling technology described in detail from a covered shallow pit and a fluid filled borehole a basal temperature well below pressure melting point meant that no drilling problems were encountered when approaching the bed and the borehole penetrated through to the base of the ice sheet and sediment was retrieved from beneath the ice

exploration of high resistivity basement using electrical and magnetic fields of quasi static point sources determination of thickness of sediments usually of high conductivity overlying a high resistivity basement is one of the basic problems of electrical exploration methods this paper proposes to determine horizontal electrical conductance on the basis of impedance calculated from electrical and magnetic fields of distant quasi static low frequency point sources using the proposed method horizontal conductance of the sediments can be determined also from artificial quasi static noise impulses coming from sources of unknown position and intensity the results of analogue modeling and field examples prove the potential of the proposed technique

the mesozoic victoria basin vanished link between antarctica and australia the transantarctic mountains tam are the largest non compressional mountain belt in the world their origin is traditionally related to crustal thickening during the jurassic ferrar magmatic event that was followed by episodic uplift in the early and late cretaceous and since the paleocene this concept of a long lived morphological high constitutes a base of virtually all gondwana reconstructions and global climate models here we demonstrate that crossover age relationships between thermochronological apatite fission track data and stratigraphic information contradict this established interpretation instead these data together with a wealth of independent thermal indicators and geological evidence require the existence of a vast intra gondwana basin between at least late triassic and late cretaceous times including during the ferrar magmatic event referred to here as the mesozoic victoria basin mvb this basin formed during crustal extension across the paleo pacific margin of antarctica and australia uplift of the tam with associated basin inversion commenced only with the development of the west antarctic rift system in paleogene times the recognition of the long lived mvb has primary consequences for the general understanding of the landscape of gondwana and the breakup between antarctica and australia west antarctic rifting and uplift of the tam and global long term climate evolution and faunal radiation

proterozoic crustal evolution of central east antarctica age and isotopic evidence from glacial igneous clasts and links with australia and laurentia abstract rock clasts entrained in glacial deposits sourced from the continental interior of antarctica provide an innovative means to determine the age and composition of ice covered crust zircon u pb ages from a suite of granitoid clasts collected in glacial catchments draining central east antarctica through the transantarctic mountains show that crust in this region was formed by a series of magmatic events at 2 01 1 88 1 85 1 79 1 57 1 50 1 41 and 1 20 1 06 ga the dominant granitoid populations are ca 1 85 1 45 and 1 20 1 06 ga none of these igneous ages are known from limited outcrop in the region in addition to defining a previously unrecognized geologic history zircon o and hf isotopic compositions from this suite have 1 mantle like 18o signatures 4 0 4 5 and near chondritic hf isotope compositions ehf 1 5 for granitoids of 2 0 ga age 2 mostly crustal 18o 6 0 8 5 and variable hf isotope compositions ehf 6 to 5 in rocks with ages of 1 88 1 85 1 79 and 1 57 ga in which the 1 88 1 79 ga granitoids require involvement of older crust 3 mostly juvenile isotopic signatures with low mantle like 18o 4 5 and radiogenic hf isotope signatures ehf 6 to 10 in rocks of 1 50 1 41 ga age with some showing crustal sources or evidence of alteration and 4 mixed crustal and mantle 18o signatures 6 0 7 5 and radiogenic hf isotopes ehf 3 to 4 in rocks of 1 2 ga age together these age and isotopic data indicate the presence in cratonic east antarctica of a large composite igneous province that formed through a punctuated sequence of relatively juvenile proterozoic magmatic events further they provide direct support for geological correlation of crust in east antarctica with both the gawler craton of present day australia and proterozoic provinces in western laurentia prominent clast ages of 2 0 1 85 1 57 and 1 45 ga together with sediment source linkages provide evidence for the temporal and spatial association of these cratonic elements in the columbia supercontinent abundant 1 2 1 1 ga igneous and metamorphic clasts may sample crust underlying the gamburtsev subglacial mountains indicating the presence of a mesoproterozoic orogenic belt in the interior of east antarctica that formed during final assembly of rodinia

chronostratigraphic framework for the iodp expedition 318 cores from the wilkes land margin constraints for paleoceanographic reconstruction the integrated ocean drilling program expedition 318 to the wilkes land margin of antarctica recovered a sedimentary succession ranging in age from lower eocene to the holocene excellent stratigraphic control is key to understanding the timing of paleoceanographic events through critical climate intervals drill sites recovered the lower and middle eocene nearly the entire oligocene the miocene from about 17 ma the entire pliocene and much of the pleistocene the paleomagnetic properties are generally suitable for magnetostratigraphic interpretation with well behaved demagnetization diagrams uniform distribution of declinations and a clear separation into two inclination modes although the sequences were discontinuously recovered with many gaps due to coring and there are hiatuses from sedimentary and tectonic processes the magnetostratigraphic patterns are in general readily interpretable our interpretations are integrated with the diatom radiolarian calcareous nannofossils and dinoflagellate cyst dinocyst biostratigraphy the magnetostratigraphy significantly improves the resolution of the chronostratigraphy particularly in intervals with poor biostratigraphic control however southern ocean records with reliable magnetostratigraphies are notably scarce and the data reported here provide an opportunity for improved calibration of the biostratigraphic records in particular we provide a rare magnetostratigraphic calibration for dinocyst biostratigraphy in the paleogene and a substantially improved diatom calibration for the pliocene this paper presents the stratigraphic framework for future paleoceanographic proxy records which are being developed for the wilkes land margin cores it further provides tight constraints on the duration of regional hiatuses inferred from seismic surveys of the region

an extensive subglacial lake and canyon system in princess elizabeth land east antarctica the subglacial landscape of princess elizabeth land pel in east antarctica is poorly known due to a paucity of ice thickness measurements this is problematic given its importance for understanding ice sheet dynamics and landscape and climate evolution to address this issue we describe the topography beneath the ice sheet by assuming that ice surface expressions in satellite imagery relate to large scale subglacial features we find evidence that a large previously undiscovered subglacial drainage network is hidden beneath the ice sheet in pel we interpret a discrete feature that is 140 20 km in plan form and multiple narrow sinuous features that extend over a distance of 1100 km we hypothesize that these are tectonically controlled and relate to a large subglacial basin containing a deep water lake in the interior of pel linked to a series of long deep canyons the presence of 1 km deep canyons is confirmed at a few localities by radio echo sounding data and drainage analysis suggests that these canyons will direct subglacial meltwater to the coast between the vestfold hills and the west ice shelf

quaternary erosion induced isostatic rebound in the western alps the high elevation and deep incision of the alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates normal faulting and horizontal extension however dominate current tectonic activity and isostatic compensation of thinning crust should lead not to increased but to decreased mean elevations here we test the idea that enhanced quaternary erosion of the alps and isostatic compensation of the mass removed can account for the distribution of present day geodetically measured rates of vertical movement in the western alps using geophysical relief and kuhlemann s estimated average erosion rate for the alps we quantify the spatial distribution of erosion and the volume of eroded rock respectively from these we obtain a map of rock eroded within a given time span the calculated isostatic response of the alpine lithosphere to erosional unloading for a variety of values of the flexural rigidity of the alpine lithosphere reaches a maximum of 500 m since 1 ma in the inner swiss alps and vertical movement extends across the entire belt including peri alpine basins assuming a steady erosion rate since 1 ma this rebound accounts for half of the measured vertical motion of 1 1 mm yr in the southern valais thus a significant fraction 50 of the present day vertical movement results from the isostatic response to enhanced erosion during plio quaternary time

a new volcanic province an inventory of subglacial volcanoes in west antarctica abstract the west antarctic ice sheet overlies the west antarctic rift system about which due to the comprehensive ice cover we have only limited and sporadic knowledge of volcanic activity and its extent improving our understanding of subglacial volcanic activity across the province is important both for helping to constrain how volcanism and rifting may have influenced ice sheet growth and decay over previous glacial cycles and in light of concerns over whether enhanced geothermal heat fluxes and subglacial melting may contribute to instability of the west antarctic ice sheet here we use ice sheet bed elevation data to locate individual conical edifices protruding upwards into the ice across west antarctica and we propose that these edifices represent subglacial volcanoes we used aeromagnetic aerogravity satellite imagery and databases of confirmed volcanoes to support this interpretation the overall result presented here constitutes a first inventory of west antarctica9s subglacial volcanism we identified 138 volcanoes 91 of which have not previously been identified and which are widely distributed throughout the deep basins of west antarctica but are especially concentrated and orientated along the 3000 km central axis of the west antarctic rift system

tectonic oceanographic and climatic controls on the cretaceous cenozoic sedimentary record of the australian antarctic basin understanding the patterns and characteristics of sedimentary deposits on the conjugate australian antarctic margins is critical to reveal the cretaceous cenozoic tectonic oceanographic and climatic conditions in the basin however unraveling its evolution has remained difficult due to the different seismic stratigraphic interpretations on each margin and sparse drill sites here for the first time we collate all available seismic reflection profiles on both margins and use newly available offshore drilling data to develop a consistent seismic stratigraphic framework across the australian antarctic basins we find sedimentation patterns similar in structure and thickness prior to the onset of antarctic glaciation enabling the basinwide correlation of four major sedimentary units and their depositional history we interpret that during the warm and humid late cretaceous 83 65 ma large onshore river systems on both australia and antarctica resulted in deltaic sediment deposition offshore we interpret that the onset of clockwise bottom currents during the early paleogene 58 48 ma formed prominent sediment drift deposits along both continental rises we suggest that these currents strengthened and progressed farther east through the eocene coevally global cooling 48 ma and progressive aridification led to a large scale decrease in sediment input from both continents two major eocene hiatuses recovered by the integrated ocean discovery program site u1356a at the antarctic continental slope likely formed during this preglacial phase of low sedimentation and strong bottom currents our results can be used to constrain future paleo oceanographic modeling of this region and aid the understanding of the oceanographic changes accompanying the transition from a greenhouse to icehouse world

inland thinning of west antarctic ice sheet steered along subglacial rifts current ice loss from the west antarctic ice sheet wais accounts for about ten per cent of observed global sea level rise1 losses are dominated by dynamic thinning in which forcings by oceanic or atmospheric perturbations to the ice margin lead to an accelerated thinning of ice along the coastline2 3 4 5 although central to improving projections of future ice sheet contributions to global sea level rise the incorporation of dynamic thinning into models has been restricted by lack of knowledge of basal topography and subglacial geology so that the rate and ultimate extent of potential wais retreat remains difficult to quantify here we report the discovery of a subglacial basin under ferrigno ice stream up to 1 5 kilometres deep that connects the ice sheet interior to the bellingshausen sea margin and whose existence profoundly affects ice loss we use a suite of ice penetrating radar magnetic and gravity measurements to propose a rift origin for the basin in association with the wider development of the west antarctic rift system the ferrigno rift overdeepened by glacial erosion is a conduit which fed a major palaeo ice stream on the adjacent continental shelf during glacial maxima6 the palaeo ice stream in turn eroded the belgica trough which today routes warm open ocean water back to the ice front7 to reinforce dynamic thinning we show that dynamic thinning from both the bellingshausen and amundsen sea region is being steered back to the ice sheet interior along rift basins we conclude that rift basins that cut across the wais margin can rapidly transmit coastally perturbed change inland thereby promoting ice sheet instability

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

evidence against a young volcanic origin of the gamburtsev subglacial mountains antarctica 1 the gamburtsev subglacial mountains of east antarctica are among earth s most enigmatic mountain ranges they are situated in the middle of antarctica buried under hundreds of meters of ice and reach an elevation of more than 3000 m these characteristics have given rise to speculation about their origin and composition in particular whether they are a hotspot or remnants of ancient orogenic events we studied fluvio deltaic sands from odp site 1166 in prydz bay which were deposited prior to the onset of east antarctic glaciation to address the question of their origin results for u pb dating of detrital zircons reveal an important age population of 530 ma which is accompanied by a dominant 40ar 39ar age population of 519 ma for detrital hornblendes the data show no sign of young volcanic contributions suggesting an old continental origin of the mountains leaving as enigmatic the cause of their great height and size

dynamic antarctic ice sheet during the early to mid miocene geological data indicate that there were major variations in antarctic ice sheet volume and extent during the early to mid miocene simulating such large scale changes is problematic because of a strong hysteresis effect which results in stability once the ice sheets have reached continental size a relatively narrow range of atmospheric co2 concentrations indicated by proxy records exacerbates this problem here we are able to simulate large scale variability of the early to mid miocene antarctic ice sheet because of three developments in our modeling approach i we use a climate ice sheet coupling method utilizing a high resolution atmospheric component to account for ice sheet climate feedbacks ii the ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice cliff failure and ice shelf hydrofracture iii we account for changes in the oxygen isotopic composition of the ice sheet by using isotope enabled climate and ice sheet models we compare our modeling results with ice proximal records emerging from a sedimentological drill core from the ross sea andrill 2a that is presented in a companion article the variability in antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0 52 0 66 or a sea level equivalent change of 30 36 m for a range of atmospheric co2 between 280 and 500 ppm and a changing astronomical configuration this result represents a substantial advance in resolving the long standing model data conflict of miocene antarctic ice sheet and sea level variability

seaward growth of antarctic continental shelves since establishment of a continent wide ice sheet patterns and mechanisms abstract the location and setting of the continental shelf break along the antarctic continental shelves influences the paleoceanographic circulation patterns as well as sedimentation and ice sheet dynamics by evaluating the available multichannel seismic reflection data and drill core information we mapped the base of progradational features associated with the first advances of grounded ice sheet to the outer shelf the distance between the modern shelf edge and the pre glacial shelf edge varies from 200 km e g ross sea to

bedrock platforms within the ross embayment west antarctica hypotheses for ice sheet history wave erosion cenozoic extension and thermal subsidence ice penetrating radar mostly airborne and marine seismic surveys have revealed plateaus and terraces about 100 350 m below sea level beneath parts of the ross embayment including the west antarctic ice sheet the ross ice shelf and the eastern ross sea these surfaces cover many thousands of square kilometers and are separated by bedrock troughs occupied by the west antarctic ice streams prominent plateaus are under edward vii peninsula siple dome and roosevelt island marine seismic data and gravity data over the buried plateaus support an interpretation that they were caused by erosion into basement the flat and level nature of the surfaces that were formed by erosion are near the same depth over large distances and fringe the buried rugged bedrock topography of marie byrd land supports an interpretation of marine rather than glacial erosion marine seismic reflection profiles over one of the plateau remnants show it as an angular unconformity cut into gently dipping sediments of late oligocene age draped with thin flat lying sediments implying that the plateau is early miocene or younger the younger limit for plateau erosion follows from the interpretation of the mechanism erosion must predate permanent ice along the coast associated with the growth of the west antarctic ice sheet probably prior to 10 ma and possibly prior to 14 ma the plateaus along the siple coast with depths around 350 meters do not rebound to close to sea level and wave base for models of removing past and present ice load this discrepancy can be explained if ross embayment lithosphere has been cooling and subsiding since significant extension in eocene to oligocene time our interpretation requires crustal subsidence in the ross sea which in turn implies higher bedrock elevations in the past within this region higher standing topography presented an opportunity for the accumulation of local ice sheets and caused sea level fluctuation prior to late cenozoic time

major neogene fluctuations of the east antarctic ice sheet stratigraphic evidence from the lambert glacier region stratigraphic and sedimentological data are presented from a region likely to directly record the evolution of the east antarctic ice sheet along the western margin of the lambert graben which now drains 1 106 km2 or one eighth of the total area of the east antarctic ice sheet extensive remnants of cenozoic glaciomarine fjordal sediment known as the pagodroma group are preserved as far as several hundred kilometers inland from the open coast the sediments resemble those produced by tidewater glaciers in the arctic rather than those of modern antarctica four separate formations of the pagodroma group spanning the interval from early miocene or older to pliocene or early pleistocene are preserved the oldest and highest crop out at nearly 1500 m above sea level each formation was deposited in close proximity to an ice margin grounded on the fjord bottom during major recessional phases of the lambert glacier underlying each formation is a glacially cut erosion surface each surface records a separate stage of fjord excavation when ice expanded onto the continental shelf in prydz bay evidence from offshore drilling in prydz bay and these data indicate fluctuations of the lambert glacier terminus in excess of 500 km in neogene time thereby reflecting large changes in the volume of the ice sheet depositional episodes were succeeded by phases of uplift totalling more than 1500 m

continuous simulations over the last 40 million years with a coupled antarctic ice sheet sediment model abstract much of the knowledge of antarctic ice sheet variations since its inception 34 ma derives from marine sediments on the continental shelf deposited in glacimarine or sub ice environments by advancing and retreating grounded ice and observed today by seismic profiling and coring here we apply a 3 d coupled ice sheet and sediment model from 40 ma to the present with the goal of directly linking ice sheet variations with the sediment record the ice sheet model uses vertically averaged ice dynamics and parameterized grounding line flux the sediment model includes quarrying of bedrock sub ice transport and marine deposition atmospheric and oceanic forcing are determined by uniform shifts to modern climatology in proportion to records of atmospheric co2 deep sea core 18o and orbital insolation variations the model is run continuously over the last 40 myr at coarse resolution 80 or 160 km modeling post eocene ice landscape evolution and off shore sediment packages in a single self consistent simulation strata and unconformities are tracked by recording times of deposition within the model sediment stacks which can be compared directly with observed seismic profiles the initial bedrock topography is initialized to 34 ma geologic reconstructions or an iterative procedure is used that yields independent estimates of paleo bedrock topography preliminary results are compared with recognized cenozoic ice sheet variations modern sediment distributions and seismic profiles and modern and paleo bedrock topographies

the enigma of oligocene climate and global surface temperature evolution falling atmospheric co2 levels led to cooling through the eocene and the expansion of antarctic ice sheets close to their modern size near the beginning of the oligocene a period of poorly documented climate here we present a record of climate evolution across the entire oligocene 33 9 to 23 0 ma based on tex86 sea surface temperature sst estimates from southwestern atlantic deep sea drilling project site 516 paleolatitude 36 s and western equatorial atlantic ocean drilling project site 929 paleolatitude 0 combined with a compilation of existing sst records and climate modeling in this relatively low co2 oligocene world 300 to 700 ppm warm climates similar to those of the late eocene continued with only brief interruptions while the antarctic ice sheet waxed and waned ssts are spatially heterogenous but generally support late oligocene warming coincident with declining atmospheric co2 this oligocene warmth especially at high latitudes belies a simple relationship between climate and atmospheric co2 and or ocean gateways and is only partially explained by current climate models although the dominant climate drivers of this enigmatic oligocene world remain unclear our results help fill a gap in understanding past cenozoic climates and the way long term climate sensitivity responded to varying background climate states

initiation of the west antarctic ice sheet and estimates of total antarctic ice volume in the earliest oligocene 1 reconstructions of antarctic paleotopography for the late eocene suggest that glacial erosion and thermal subsidence have lowered west antarctic elevations considerably since then with antarctic land area having decreased 20 a new climate ice sheet model based on these reconstructions shows that the west antarctic ice sheet first formed at the eocene oligocene transition 33 8 33 5ma e o in concert with the continental scale expansion of the east antarctica ice sheet and that the total volume of east and west antarctic ice 33 4 35 9 10 6 km 3 w as 1 4 times greater than previously assumed this larger modeled ice volume is consistent with a modest cooling of 1 2 c in the deep ocean during the e o transition lower than other estimates of 3 c cooling and suggests the possibility of substantial ice in the antarctic interior before the eocene oligocene boundary citation wilson d s d pollard r m deconto s s r jamieson and b p luyendyk 2013 initiation of the west antarctic ice sheet and estimates of total antarctic ice volume in the earliest oligocene geophys res lett 40 doi 10 1002 grl 50797

anomalous bathymetry and palaeobathymetric models of the mozambique basin and riiser larsen sea abstract in this study we introduce a palaeobathymetric model for the conjugate mozambique basin and riiser larsen sea built by employing backstripping techniques compensating for dynamic topography and plate motions the model is presented at 0 2 0 2 grid resolution making it suitable for future oceanographic and climate simulation model experiments aimed at a better understanding of the climatic and oceanographic relevance of oceanic gateways in the southern ocean at the present day the seafloor next to the mozambican continental margin is around 300 m shallower and that in the central mozambique channel is almost 1300 m shallower than their conjugate areas or the predictions of oceanic thermal subsidence models the cause of this anomalous depth is difficult to determine confidently because of sparse data in particular concerning sediment thickness and because of the wide range of amplitudes in modelled present day dynamic topography the distribution of shallow seafloor suggests that it might be attributed to the presence of thicker than usual oceanic crust which in turn can be attributed to the paleogene passage of the quathlamba plume beneath the basin we portray these effects in our palaeobathymetric models in contrast the riiser larsen sea has experienced fairly stable subsidence since its formation in jurassic times with only slight observable changes attributable to the onset of antarctic glaciation and during the middle miocene climate transition both basins display flexure over half wavelengths of 60 80 km with amplitudes of 1500 m towards their continental margins this plays an important role in models of palaeobathymetry for times older than 100 ma near the margins isolated areas of transitional or debatable crustal composition including beira high and gunnerus ridge are depicted to subside in a similar fashion to oceanic crust further into the indian ocean oceanic lithosphere younger than 100 ma on both plates has subsided to depths that are typical of thermal subsidence models finally the new palaeobathymetry had distinct consequences for the current systems in the young southern ocean during the time periods the onset of coast parallel bottom currents and associated contourite deposition in the mozambique channel at palaeo water depths of 3500 4000 m may be a consequence of either an opening of a deep water passage into the south atlantic between southwest indian ridge and agulhas plateau or into the tethys ocean in the late cretaceous

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

stability of the west antarctic ice sheet in a warming world equivalent to 0 28 to 0 56 mm yr 1 sea level rise with the rate growing over at least the past two decades 1 4 these observations intensify concerns about the ice sheet s stability that were first raised more than four decades ago 5

antarctic topography at the eocene oligocene boundary we present a reconstruction of the antarctic topography at the eocene oligocene ca 34 ma climate transition this provides a realistic key boundary condition for modeling the first big antarctic ice sheets at this time instead of using the present day bedrock topography which has changed significantly from millions of years of tectonism and erosion we reconstruct topography using a set of tools including ice sheet erosion models models of thermal subsidence and plate movement erosion estimates are constrained with offshore sediment volumes estimated from seismic stratigraphy maximum and minimum topographic reconstructions are presented as indicators of the range of uncertainty our results point to a significant upland area in the ross sea marie byrd land and weddell sea sectors in addition east antarctic coastal troughs are much shallower than today due to the restoration of material that has been selectively eroded by the evolving ice sheets parts of east antarctica have not changed since the e o boundary because they were protected under non erosive cold based ice the reconstructions provide a better defined boundary condition for modeling that seeks to understand interaction between the antarctic ice sheet and climate along with more robust estimates of past ice volumes under a range of orbital settings and greenhouse gas concentrations

contribution of antarctica to past and future sea level rise polar temperatures over the last several million years have at times been slightly warmer than today yet global mean sea level has been 6 9 metres higher as recently as the last interglacial 130 000 to 115 000 years ago and possibly higher during the pliocene epoch about three million years ago in both cases the antarctic ice sheet has been implicated as the primary contributor hinting at its future vulnerability here we use a model coupling ice sheet and climate dynamics including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine terminating ice cliffs that is calibrated against pliocene and last interglacial sea level estimates and applied to future greenhouse gas emission scenarios antarctica has the potential to contribute more than a metre of sea level rise by 2100 and more than 15 metres by 2500 if emissions continue unabated in this case atmospheric warming will soon become the dominant driver of ice loss but prolonged ocean warming will delay its recovery for thousands of years