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 sea level fingerprint of west antarctic collapse recent projections of sea level rise after a future collapse of thewest antarctic ice sheet for example the fourth intergovernmental panel on climate change assessment report assume that meltwater will spread uniformly that is eustatically across the oceans once marine based sectors of the west antarctic are filled a largely neglected 1977 study predicted that peak values would be 20 higher than the eustatic in the north pacific and 5 to 10 higher along the u s coastline we show with use of a state of the art theory that the sea level rise in excess of the eustatic value will be two to three times higher than previously predicted for u s coastal sites

testing the sensitivity of the east antarctic ice sheet to southern ocean dynamics past changes and future implications the stability of antarctic ice sheets and their potential contribution to sea level under projected future warming remains highly uncertain the last interglacial 135 000 116 000 years ago provides a potential analogue with global temperatures 2uc higher and rates of sea level rise 5 6m ka 1 leading to sea levels 6 6 9 4m higher than present the source s of this sea level rise remain fiercely debated here we report a series of independent model simulations exploring the effects of migrating southern hemisphere westerlies shws on southern ocean circulation and antarctic ice sheet dynamics we suggest that southerly shifts in winds may have significantly impacted the sub polar gyres inducing pervasive warming 0 2 0 8uc in the upper 1200m adjacent to sectors of the east antarctic ice sheet eais which due to their geometries and connectivity to the southern ocean are highly sensitive to ocean forcing we conclude that the eais potentially made a substantial hitherto unsuspected contribution to interglacial sea levels and given 21st century projections in the southern annular mode and associated shw migration we highlight how pervasive circum antarctic warming may threaten eais stability copyright 2013 john wiley sons ltd

variability in the mass flux of the ross ice streams west antarctica over the last millennium we synthesize previously published remote sensing observations radar data and model output to obtain a 1000 year ice flow history for the siple coast ice stream system in west antarctica to investigate the timing and magnitude of changes in mass flux the synthesized history shows significant short term variability in ice stream shear margin and grounding line position due to internal variability of the coupled system the chronology highlights the interplay between adjacent ice streams which implies that the behavior of any individual ice stream should not be examined in isolation furthermore individual events cannot be fully interpreted without an understanding of the broad scale long term variability in the ice sheet in the context of this millennium scale history we interpret the relatively recent stagnation of kamb ice stream kis as just one stage in the thermodynamic cycle of an ice stream in this region the changes in mass balance that result from the kis stagnation may thus be viewed as century scale noise relative to the longer term trend understanding and characterizing this noise is a necessary step before accurate model based predictions of ice sheet mass balance for the next century can be made

glacial meltwater identification in the amundsen sea abstractpine island ice shelf in the amundsen sea is losing mass because of warm ocean waters melting the ice from below tracing meltwater pathways from ice shelves is important for identifying the regions most affected by the increased input of this water type here optimum multiparameter analysis is used to deduce glacial meltwater fractions from water mass characteristics temperature salinity and dissolved oxygen concentrations collected during a ship based campaign in the eastern amundsen sea in february march 2014 using a one dimensional ocean model processes such as variability in the characteristics of the source water masses on shelf and biological productivity respiration are shown to affect the calculated apparent meltwater fractions these processes can result in a false meltwater signature creating misleading apparent glacial meltwater pathways an alternative glacial meltwater calculation is suggested using a pseudo circumpolar deep water endpoint and using an artificial increase

a sea level equation for seismic perturbations summary large earthquakes are a potentially important source of relative sea level variations since they can drive global deformation and simultaneously perturb the gravity field of the earth for the first time we formalize a gravitationally self consistent integral sea level equation suitable for earthquakes in which we account both for direct effects by the seismic dislocation and for the feedback from water loading associated with sea level changes our approach builds upon the well established theory first proposed in the realm of glacio isostatic adjustment modelling the seismic sea level equation is numerically implemented to model sea level signals following the 2004 sumatra andaman earthquake showing that surface loading from ocean water redistribution so far ignored in post seismic deformation modelling may account for a significant fraction of the total computed post seismic sea level variation

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

constraints on global mean sea level during pliocene warmth reconstructing the evolution of sea level during past warmer epochs such as the pliocene provides insight into the response of sea level and ice sheets to prolonged warming1 although estimates of the global mean sea level gmsl during this time do exist they vary by several tens of metres2 4 hindering the assessment of past and future ice sheet stability here we show that during the mid piacenzian warm period which was on average two to three degrees celsius warmer than the pre industrial period5 the gmsl was about 16 2 metres higher than today owing to global ice volume changes and around 17 4 metres when thermal expansion of the oceans is included during the even warmer pliocene climatic optimum about four degrees celsius warmer than pre industrial levels 6 our results show that the gmsl was 23 5 metres above the present level with an additional 1 6 metres from thermal expansion we provide six gmsl data points ranging from 4 39 to 3 27 million years ago that are based on phreatic overgrowths on speleothems from the western mediterranean mallorca spain this record is unique owing to its clear relationship to sea level its reliable u pb ages and its long timespan which allows us to quantify uncertainties on potential uplift our data indicate that ice sheets are very sensitive to warming and provide important calibration targets for future ice sheet models7 using phreatic overgrowths on speleothems sea level during the mid piacenzian warm period which was about two to three degrees celsius warmer than the pre industrial period is shown to have been about 16 metres higher than today

response of the global ocean to greenland and antarctic ice melting 1 we investigate the transient response of the global ocean circulation to enhanced freshwater forcing associated with melting of the greenland and antarctic ice sheets increased freshwater runoff from greenland results in a basin wide response of the north atlantic on timescales of a few years communicated via boundary waves equatorial kelvin waves and westward propagating rossby waves in addition modified air sea interaction plays a fundamental role in setting up the basin scale response of the atlantic circulation in its subpolar and subtropical gyres in particular the modified ocean dynamics and thermodynamics lead to a depression in the central north and south atlantic that would not be expected from linear wave dynamics moreover the heat content increases on basin and global scales in response to anomalous freshwater forcing from greenland suggesting that the ocean s response to enhanced freshwater forcing would be a coupled problem other parts of the world ocean experience a much slower adjustment in response to greenland freshwater forcing communicated via planetary waves but also involving advective diffusive processes especially in the southern ocean over the 50 years considered here most of the sea level increase associated with freshwater input from greenland remains in the atlantic ocean in contrast ice melting around antarctica has a much reduced effect on the global ocean in both cases none of the basins came to a stationary state during the 50 year experiment

west antarctic ice sheet elevations in the ohio range geologic constraints and ice sheet modeling prior to the last highstand abstract knowledge of the timing and extent of past west antarctic ice sheet wais elevation changes provides insight to the wais response to sea level and climate forcing as well as constraints for ice sheet models trimlines and erratics indicate that maximum ice elevation at the ohio range located near the wais divide was 125 m above the present ice surface and was reached at 10 ka however 3 he and 10 be exposure ages of most granitic erratics and supra glacial boulders in adjacent blue ice areas are older than the last highstand and provide constraints on earlier interior wais elevation changes although diffusive loss of 3 he occurs in quartz an excellent correlation between 3 he and 10 be concentrations in samples up to 400 ka is observed in the ohio range demonstrating the utility of 3 he measurements in antarctic quartz the correlation is used to calculate equivalent 10 be exposure ages from the larger 3 he data set the exposure ages occur in distinct clusters 10 20 ka 70 80 ka 130 140 ka and 180 190 ka that we relate to pulses in the emergence of englacial debris in localized blue ice ablation areas a combined ice sheet ice shelf model predicts that wais elevations near the ohio range have varied only 125 m over the last 200 kyr with highstands at 10 ka and 130 ka in good agreement with observations of trimlines and peaks in the exposure age distribution at the ohio range in the model interior wais elevations are controlled by the interaction of accumulation rates and ice dynamics related to ice sheet ocean interactions at the grounding line wais highstands occur early in interglacial periods during intervals of warmer temperatures and high accumulation rates prior to the arrival of a wave of thinning we hypothesize that the correspondence of rising regional wais elevation with debris pulses relates to increased ice debris flux and ablation in the local blue ice areas resulting from the warmer temperatures the occurrence of clasts with exposure ages up to 200 ka on the wais surface indicates elevation changes near the ohio range were limited in extent during stage 5e the geologic observations combined with model results place constraints on wais geometry during stage 5e and limit the wais contribution to the higher sea levels observed during the last interglacial to 3 m

sea level changes geoid and gravity anomalies due to pleistocene deglaciation by means of multilayered analytical earth models abstract a new class of analytical multilayered viscoelastic earth models based on prem with an incompressible linear viscoelastic maxwell rheology is applied to the modeling of global sea level changes due to pleistocene deglaciation until now analytical schemes based on normal mode theory have dealt with at most five layers an elastic lithosphere a three layered mantle including a transition zone and a core spada et al 1992 geophys j int 109 683 700 the novelty of our approach used for the first time in sea level studies stands on an analytical scheme that can reproduce continuous elastic and rheological stratification when a sufficient number of layers is taken into account we specifically assess the importance of our results for the gravity field and steady state ocean circulation explorer goce satellite mission goce will resolve the gravity field with a spatial resolution half wavelength of 75 km and amplitude of 1 5 mgal with a uniform coverage over the earth including presently unsurveyed remote areas our models lead to post glacial rebound induced free air gravity anomalies of a few mgals peak to peak in the harmonic degree range l 80 200 which will be discernible by goce this finding demonstrates that post glacial rebound has a high frequency component in the gravity field that can in principle be resolved by high resolution gravity satellite missions we show that post glacial rebound can contribute a substantial fraction to present day sea level variations and point out that for the mediterranean sea they are of the same order of magnitude as those induced by tectonic processes

a viscoelastic flowline model applied to tidal forcing of bindschadler ice stream west antarctica abstract the motion of bindschadler ice stream west antarctica is dominated by sliding over a nearly plastic bed according to analysis of kinematic gps data using a new viscoelastic flowline model inversions of time averaged velocity data with viscous ice flow models can be consistent with multiple sliding laws but propagation of velocity perturbations in a viscoelastic model can distinguish between sliding laws with different exponents we develop such a model and apply it to a time series of velocity for the tidally modulated flow of bindschadler ice stream formerly ice stream d observed velocity perturbations are found to be consistent with a flow law exponent m 8 which indicates basal motion with a relatively weak till bed lower exponents consistent with motion dominated by deformation within the ice over a hard or frozen bed are found to be unlikely this result suggests that bindschadler ice stream would respond rapidly and significantly to any future loss of buttressing from the ross ice shelf

first geomorphological record and glacial history of an inter ice stream ridge on the west antarctic continental shelf inter ice stream areas cover significant portions of antarctica s formerly glaciated shelves but have been largely neglected in past geological studies because of overprinting by iceberg scours here we present results of the first detailed survey of an inter ice stream ridge from the west antarctic continental shelf well preserved sub and proglacial bedforms on the seafloor of the ridge in the eastern amundsen sea embayment ase provide new insights into the flow dynamics of this sector of the west antarctic ice sheet wais during the last glacial cycle multibeam swath bathymetry and parasound acoustic sub bottom profiler data acquired across a mid shelf bank between the troughs of the pine island thwaites pitpis and cosgrove palaeo ice streams copis reveal large scale ribbed moraines hill hole pairs terminal moraines and crevasse squeeze ridges together these features form an assemblage of landforms that is entirely different from that in the adjacent ice stream troughs and appears to be unique in the context of previous studies of antarctic seafloor geomorphology from this assemblage the history of ice flow and retreat from the inter ice stream ridge is reconstructed the bedforms indicate that ice flow was significantly slower on the inter ice stream ridge than in the neighbouring troughs while terminal moraines record at least two re advances or stillstands of the ice sheet during deglaciation an extensive field of crevasse squeeze ridges indicates ice stagnation subsequent to re advancing ice which deposited the field of terminal moraines in the ne the presented data suggest that the ice flow behaviour on the inter ice stream ridge was substantially different from that in the adjacent troughs however newly obtained radiocarbon ages on two sediment cores recovered from the inter ice stream ridge suggest a similar timing in the deglaciation of both areas this information closes an important gap in the understanding of past wais behaviour in the eastern ase our newly documented bedforms will also serve as an important diagnostic tool in future studies for interpreting ice sheet histories in similar inter ice stream areas

a chronology of foreland deformation ultra violet laser 40ar 39ar dating of syn late orogenic intrusions from the variscides of southwest ireland abstract the upper palaeozoic sedimentary rocks of the munster and south munster basins southern ireland lie within the rhenohercynian zone of the european variscan orogeny this foreland region accommodated shortening during the asturian phase of variscan deformation at the end of the carboniferous by the development of kilometre scale and lower order folding high angle reverse faulting and regional fabric development at the southwestern extremity of the belt lies the black ball white ball heads area of the beara peninsula where high level igneous intrusions locally exhibit a close relationship with both the ductile and late brittle phases of variscan deformation 40 ar 39 ar ultra violet laser analysis of phlogopite crystals from these intrusions principally trachytic dykes has yielded ages that when combined with structural field relationships help to constrain the timing of variscan deformation in southern ireland these ages include 314 44 1 00 ma for a penetratively deformed lamprophric pipe on black ball head 301 98 1 47 298 08 0 61 ma for dyke material associated with later stage brittle deformation and a date of 296 88 0 60 ma for an undeformed post orogenic dyke on white ball head

the sedimentary legacy of a palaeo ice stream on the shelf of the southern bellingshausen sea clues to west antarctic glacial history during the late quaternary a major trough belgica trough eroded by a palaeo ice stream crosses the continental shelf of the southern bellingshausen sea west antarctica and is associated with a trough mouth fan belgica tmf on the adjacent continental slope previous marine geophysical and geological studies investigated the bathymetry and geomorphology of belgica trough and belgica tmf erosional and depositional processes associated with bedform formation and the temporal and spatial changes in clay mineral provenance of subglacial and glaciomarine sediments here we present multi proxy data from sediment cores recovered from the shelf and uppermost slope in the southern bellingshausen sea and reconstruct the ice sheet history since the last glacial maximum lgm in this poorly studied area of west antarctica we combined new data physical properties sedimentary structures geochemical and grain size data with published data shear strength clay mineral assemblages to refine a previous facies classification for the sediments the multi proxy approach allowed us to distinguish four main facies types and to assign them to the following depositional settings 1 subglacial 2 proximal grounding line 3 distal sub ice shelf sub sea ice and 4 seasonal open marine in the seasonal open marine fades we found evidence for episodic current induced winnowing of near seabed sediments on the middle to outer shelf and at the uppermost slope during the late holocene in addition we obtained data on excess pb 210 activity at three core sites and 44 ams c 14 dates from the acid insoluble fraction of organic matter aio and calcareous micro fossils respectively at 12 sites these chronological data enabled us to reconstruct for the first time the timing of the last advance and retreat of the west antarctic ice sheet wais and the antarctic peninsula ice sheet apis in the southern bellingshausen sea we used the down core variability in sediment provenance inferred from clay mineral changes to identify the most reliable aio c 14 ages for ice sheet retreat the palaeo ice stream advanced through belgica trough after similar to 36 0 corrected c 14 ka before present b p it retreated from the outer shelf at similar to 25 5 ka b p the middle shelf at similar to 19 8 ka b p the inner shelf in eltanin bay at similar to 12 3 ka b p and the inner shelf in ronne entrance at similar to 6 3 ka b p the retreat of the wais and apis occurred slowly and stepwise and may still be in progress this dynamical ice sheet behaviour has to be taken into account for the interpretation of recent and the prediction of future mass balance changes in the study area the glacial history of the southern bellingshausen sea is unique when compared to other regions in west antarctica but some open questions regarding its chronology need to be addressed by future work c 2010 elsevier ltd all rights reserved

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

pleistocene collapse of the west antarctic ice sheet some glacial sediment samples recovered from beneath the west antarctic ice sheet at ice stream b contain quaternary diatoms and up to 108 atoms of beryllium 10 per gram other samples contain no quaternary diatoms and only background levels of beryllium 10 less than 10 6 atoms per gram the occurrence of young diatoms and high concentrations of beryllium 10 beneath grounded ice indicates that the ross embayment was an open marine environment after a late pleistocene collapse of the marine ice sheet

a near field sea level record of east antarctic ice sheet instability from 32 to 27 myr 1 fossil facies and isotope analyses of an early high paleolatitude 55 s section suggests a highly unstable east antarctic ice sheet from 32 to 27 myr the waxing and waning of this ice sheet from 140 to 40 of its present volume caused sea level changes of 25 m ranging from 30 to 50 m related to periodic glacial 100 000 to 200 000 years and shorter interglacial events the near field gippsland sea level gsl curve shares many similarities to the far field new jersey sea level njsl estimates however there are possible resolution errors due to biochronology taphonomy and paleodepth estimates and the relative lack of lowstand deposits in njsl that prevent detailed correlations with gsl nevertheless the lateral variations in sea level between the gsl section and njsl record that suggest ocean siphoning and antisiphoning may have propagated synchronous yet variable sea levels

evidence for iceberg armadas from east antarctica in the southern ocean during the late miocene and early pliocene abstract sediments from ocean drilling program site 1165 in the indian ocean sector of the southern ocean off prydz bay contain a series of layers that are rich in ice rafted debris ird here we present evidence that ird rich layers at site 1165 at 7 4 8 and 3 5 ma record short lived massive discharges of icebergs from wilkes land and adelie land more than 1500 kilometers to the east of the depositional site this distant source of icebergs is clearly defined by the presence of ird hornblende grains with 40ar 39ar ages of 1200 1100 ma and 1550 1500 ma ages that are not found on the east antarctic continent in locations closer to site 1165 this observation requires enormous amounts of detritus carrying drifting icebergs most likely in the form of large icebergs these events probably reflect destabilization surge and break up of ice streams on the wilkes land and adelie land margins of the east antarctic ice sheet in the vicinity of the low lying aurora and wilkes basins they occurred under warming conditions but each coast seems to have produced ice rafting events independently at different times the data presented here constitute the first evidence of far traveled icebergs from specific source areas around the east antarctic perimeter launch of these icebergs may have happened during quite dramatic events perhaps analogous to heinrich events in the north atlantic

ocean temperature thresholds for last interglacial west antarctic ice sheet collapse the west antarctic ice sheet wais is considered the major contributor to global sea level rise in the last interglacial lig and potentially in the future exposed fossil reef terraces suggest sea levels in excess of 7 meters in the last warm era of which probably not much more than 2 meters are considered to originate from melting of the greenland ice sheet we simulate the evolution of the antarctic ice sheet during the lig with a 3d thermomechanical ice sheet model forced by an atmosphere ocean general circulation model aogcm our results show that high lig sea levels cannot be reproduced with the atmosphere ocean forcing delivered by current aogcms however when taking reconstructed southern ocean temperature anomalies of several degrees sensitivity studies indicate a southern ocean temperature anomaly threshold for total wais collapse of 2 3 c accounting for a sea level rise of 3 4 meters during the lig potential future antarctic ice sheet dynamics range from a moderate retreat to a complete collapse depending on rate and amplitude of warming

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

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

constraining past accumulation in the central pine island glacier basin west antarctica using radio echo sounding the potential for future dynamical instability of pine island glacier west antarctica has been addressed in a number of studies but information on its past remains limited in this study we use airborne radio echo sounding res data acquired over pine island glacier to investigate past variations in accumulation pattern in the dataset a distinctive pattern of layers was identified in the central part of the glacier basin we use these layers as chronological identifiers in order to construct elevation maps of the internal stratigraphy the observed internal layer stratigraphy is then compared to calculated stratigraphy from a three dimensional ice flow model that has been forced with different accumulation scenarios the model results indicate that the accumulation pattern is likely to have changed at least twice since the deposition of the deepest identified layer additional res data linked to the byrd ice core provide an approximate timescale this timescale suggests that the layers were deposited at the beginning of or during the holocene period thus the widespread changes occurring in the coastal extent of thewest antarctic ice sheet at the end of the last glacial period could have been accompanied by changes in accumulation pattern

ocean mixing beneath pine island glacier ice shelf west antarctica ice shelves around antarctica are vulnerable to an increase in ocean driven melting with the melt rate depending on ocean temperature and the strength of flow inside the ice shelf cavities we present measurements of velocity temperature salinity turbulent kinetic energy dissipation rate and thermal variance dissipation rate beneath pine island glacier ice shelf west antarctica these measurements were obtained by ctd adcp and turbulence sensors mounted on an autonomous underwater vehicle auv the highest turbulent kinetic energy dissipation rate is found near the grounding line the thermal variance dissipation rate increases closer to the ice shelf base with a maximum value found 0 5 m away from the ice the measurements of turbulent kinetic energy dissipation rate near the ice are used to estimate basal melting of the ice shelf the dissipation rate based melt rate estimates is sensitive to the stability correction parameter in the linear approximation of universal function of the monin obukhov similarity theory for stratified boundary layers we argue that our estimates of basal melting from dissipation rates are within a range of previous estimates of basal melting

new boundary conditions for the west antarctic ice sheet subglacial topography beneath pine island glacier 1 predictions about future changes in the amundsen sea sector of the west antarctic ice sheet wais have been hampered by poorly known subglacial topography extensive airborne survey has allowed us to derive improved subglacial topography for the pine island glacier basin the trunk of this glacier lies in a narrow 250 km long 500 m deep sub glacial trough suggesting a long lived and constrained ice stream two tributaries lie in similar troughs others lie in less defined shallower troughs the lower basin of the glacier is surrounded by bedrock which after deglaciation and isostatic rebound could rise above sea level this feature would impede ice sheet collapse initiated near the grounding line of this glacier and prevent its progress into the deepest portions of wais the inland slope of the bed beneath the trunk of the glacier however confirms potential instability of the lower basin containing sufficient ice to raise global sea by 24 cm

controls on interior west antarctic ice sheet elevations inferences from geologic constraints and ice sheet modeling abstract knowledge of the west antarctic ice sheet wais response to past sea level and climate forcing is necessary to predict its response to warmer temperatures in the future the timing and extent of past interior wais elevation changes provides insight to wais behavior and constraints for ice sheet models constraints prior to the last glacial maximum lgm however are rare surface exposure ages of glacial erratics near the wais divide at mt waesche in marie byrd land and at the ohio range in the transantarctic mountains range from 10 ka to 500 ka without a dependence on elevation the probability distribution functions pdf of the exposure ages at both locations are remarkably similar during the last glaciation maximum interior ice elevations as recorded by moraines and erratics were reached between 10 ka and 12 ka however most exposure ages are older than the lgm and cluster around 40 ka and 80 ka the peak in the exposure age distributions at 40 ka includes ages of alpine moraine boulders at mercer ridge in the ohio range comparison of the pdf of exposures ages from the ohio range and mt waesche with the temperature record from the fuji dome ice core indicates that the youngest peak in the exposure age distributions corresponds to the abrupt warming during the last glacial termination a prominent peak in the ohio range pdf corresponds to the penultimate termination stage 5e during the intervening glacial period there is not a consistent relationship between the peaks in the pdf at each location and temperature a combined ice sheet ice shelf model with forcing scaled to marine 18 o predicts that interior wais elevations near the ice divide have varied 300 m over the last glacial cycle peaks in the pdf correspond to model highstands over the last 200 ka in the simulated elevation history maximum ice elevations at ohio range 100 m and mt waesche 60 m occur at 10 ka in agreement with observations from these sites during collapse of the marine portion of the wais ice elevations at ohio range and mt waesche are drawn down at least 200 m below the present ice elevation the good correspondence between the model results and observations at both the ohio range and mt waesche supports the conclusion that interior wais highstands do not occur during glacial maximums rather the highstands are controlled primarily by increased accumulation during temperature maximums that occur early in the interglacials interior down draw events follow highstands resulting from the arrival of a wave of thinning triggered by retreat of the wais grounding line coupled with decreasing accumulation rates

on postglacial geoid subsidence over the equatorial oceans we develop two new spectral formalisms for the gravitationally self consistent solution of the sea level equation which governs the redistribution of glacial meltwater on a visco elastic earth the first is a purely spectral technique based on an extension of theory outlined by dahlen 1976 for determining the equilibrium oceanic tide on an elastic planet using this technique with a feasible spherical harmonic truncation level l 30 we can obtain convergence in the computed sea level variations within the degree range l 10 we also develop a second pseudospectral technique however which permits the construction of gravitationally self consistent solutions to much higher degree and order l 100 the pseudospectral formalism is employed here to develop a comprehensive physical explanation for the global pattern of present day sea level variations due to ongoing glacial isostatic adjustment in particular we focus upon a mechanism which we term equatorial ocean syphoning that acts to draw water toward the oceanic portion of the collapsing peripheral bulge that encircles previously glaciated regions the collapse of the forebulge induces a flow of water which is required to maintain hydrostatic equilibrium the syphoning mechanism dominates the relative sea level rsl variation in oceans in the far field of the ice sheets that is beyond the peripheral bulge during periods such as the interglacial of the past 4000 years during which the volume of the ice sheets has not apparently changed appreciably while at the same time isostatic adjustment persists the rsl change in the near field is in contrast dominated by the local vertical displacement of the solid surface finally comparison of gravitationally self consistent predictions of rsl change in the far field with the observational data at small pacific island sites has provided an upper bound of 1 to 2 m for the eustatic sea level rise produced by any recent last 3000 years melting of the antarctic ice sheet

antarctic ice sheet mass loss estimates using modified antarctic mapping mission surface flow observations 1 the long residence time of ice and the relatively gentle slopes of the antarctica ice sheet make basal sliding a unique positive feedback mechanism in enhancing ice discharge along preferred routes the highly organized ice stream channels extending to the interior from the lower reach of the outlets are a manifestation of the role of basal granular material in enhancing the ice flow in this study constraining the model simulated year 2000 ice flow fields with surface velocities obtained from insar measurements permits retrieval of the basal sliding parameters forward integrations of the ice model driven by atmospheric and oceanic parameters from coupled general circulation models under different emission scenarios provide a range of estimates of total ice mass loss during the 21st century the total mass loss rate has a small intermodel and interscenario spread rising from approximately 160 km3 yr at present to approximately 220 km3 yr by 2100 the accelerated mass loss rate of the antarctica ice sheet in a warming climate is due primarily to a dynamic response in the form of an increase in ice flow speed ice shelves contribute to this feedback through a reduced buttressing effect due to more frequent systematic tabular calving events for example by 2100 the ross ice shelf is projected to shed 40 km3 during each systematic tabular calving after the frontal section s attrition the remaining shelf will rebound consequently the submerged cross sectional area will reduce as will the buttressing stress longitudinal differential warming of ocean temperature contributes to tabular calving because of the prevalence of fringe ice shelves oceanic effects likely will play a very important role in the future mass balance of the antarctica ice sheet under a possible future warming climate

ocean access to a cavity beneath totten glacier in east antarctica totten glacier has the largest thinning rate in east antarctica a derivation of the sea floor bathymetry reveals entrances to the ice cavity beneath the glacier that could allow deep warm water to enter and enhance basal melting

a comparative study of changes in the lambert glacier amery ice shelf system east antarctica during 2004 2008 using gravity and surface elevation observations we present results of a regional comparative study of surface mass changes from 2004 to 2008 based on gravity recovery and climate experiment grace the ice cloud and land elevation satellite icesat and chinare observations over the lambert glacier amery ice shelf system las estimation of the icesat mass change rates benefitted from the density measurements along the chinare traverse and a spatial density adjustment method for reducing the effect of spatial density variations in the high elevation inland region a positive trend was estimated from both icesat and grace data which is in line with the chinare accumulation measurements in the coastal region there were areas with high level accumulations in both icesat and grace trend maps in many high flow speed glacier areas negative mass change rates may be caused by dynamic ice flow discharges that have surpassed the snow accumulation overall the mass change rate estimate in the las of 2004 2008 from the grace icesat and chinare data is 5 41 4 59 gt a 1 indicating a balanced to slightly positive mass trend along with other published results this suggests that a longer term positive mass trend in the las may have slowed in recent years

suppression of marine ice sheet instability a long standing open question in glaciology concerns the propensity for ice sheets that lie predominantly submerged in the ocean marine ice sheets to destabilise under buoyancy this paper addresses the processes by which a buoyancy driven mechanism for the retreat and ultimate collapse of such ice sheets the marine ice sheet instability is suppressed by lateral stresses acting on its floating component the ice shelf the key results are to demonstrate the transition between a mode of stable easily reversible retreat along a stable steady state branch created by ice shelf buttressing to tipped almost irreversible retreat across a critical parametric threshold the conditions for triggering tipped retreat can be controlled by the calving position and other properties of the ice shelf profile and can be largely independent of basal stress in contrast to principles established from studies of unbuttressed grounding line dynamics the stability and recovery conditions introduced by lateral stresses are analysed by developing a method of constructing grounding line stability bifurcation diagrams which provide a rapid assessment of the steady state positions their natures and the conditions for secondary grounding giving clear visualisations of global stabilisation conditions a further result is to reveal the possibility of a third structural component of a marine ice sheet that lies intermediate to the fully grounded and floating components the region forms an extended grounding area in which the ice sheet lies very close to flotation and there is no clearly distinguished grounding line the formation of this region generates an upsurge in buttressing that provides the most feasible mechanism for reversal of a tipped grounding line the results of this paper provide conceptual insight into the phenomena controlling the stability of the west antarctic ice sheet the collapse of which has the potential to dominate future contributions to global sea level rise

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

postglacial sea level change on a rotating earth summary we present a complete derivation of the equation governing long term sea level variations on a spherically symmetric self gravitating maxwell viscoelastic planet this new sea level equation extends earlier work by incorporating in a gravitationally self consistent manner both a time dependent ocean continent geometry and the in uence of contemporaneous perturbations to the rotation vector of the planet we also outline an e cient pseudo spectral numerical methodology for the solution of this equation and present a variety of predictions based on a suite of earth models of relative sea level rsl variations due to glacial isostatic adjustment gia these results show that the contribution to the predicted rsl signal from gia induced perturbations to the rotation vector can reach 7 8 m over the postglacial period in geographic regions where the rotationally induced signal is a maximum this result is sensitive to variations in the adopted lower mantle viscosity and is relatively insensitive to variations in the adopted lithospheric thickness we also show that the rotationally induced component of rsl change is su cient to in uence previous estimates of late holocene melting events and ongoing sea level change due to giawhich were based on a rsl theory for a non rotating earth in particular estimates of antarctic melting over the last 5 kyr based on the amplitude of sea level highstands from the australian region may require an adjustment downwards of the order of 0 5 m of equivalent sea level rise furthermore present day rates of sea level change are perturbed by as much as 0 2 mm yr 1 by the rotational component of sea level change and this has implications for gia corrections of the global tide gauge record over the period from the last glacial maximum to the present we predict a distinctly non monotonic variation in the rotation induced component of rsl this is in agreement with our previous preliminary study milne mitrovica 1996 but contrasts signi cantly with predictions presented by han wahr 1989 and bills james 1996 we demonstrate that the disagreement arises as a consequence of approximations adopted in the latter studies we furthermore refute an assertion by bills james 1996 that previously published constraints on mantle viscosity and ice sheet histories which did not incorporate a rotation induced rsl component are largely invalidated by this omission

new boundary conditions for the west antarctic ice sheet subglacial topography of the thwaites and smith glacier catchments airborne radar sounding over the thwaites glacier tg catchment and its surroundings provides the first comprehensive view of subglacial topography in this dynamic part of the west antarctic ice sheet wais and reveals that tg is underlain by a single broad basin fed by a dendritic pattern of valleys while smith glacier lies within an extremely deep narrow trench subglacial topography in the tg catchment slopes inland from a broad low relief coastal sill to the thickest ice of the wais and makes deep connections to both pine island glacier and the ross sea embayment enabling dynamic interactions across the wais during deglaciation simple isostatic rebound modeling shows that most of this landscape would be submarine after deglaciation aside from an island chain near the present day ross amundsen ice divide the lack of topographic confinement along tg s eastern margin implies that it may continue to widen in response to grounding line retreat

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

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

ice marginal dynamics of the last british irish ice sheet in the southern north sea ice limits timing and the influence of the dogger bank the southern north sea is a particularly important area for understanding the behaviour of the british irish ice sheet biis during the last glacial cycle it preserves a record of the maximum extent of the eastern sector of the biis as well as evidence for multiple different ice flow phases and the dynamic re organisation of the biis however to date the known ice sheet history and geochronology of this region is predominantly derived from onshore geological evidence and the offshore imprint and dynamic history of the last ice sheet remain largely unknown using new data collected by the britice chrono project this paper explores the origin and age of the dogger bank re assesses the extent and age of the glaciogenic deposits across the shallow areas of the north sea between the dogger bank and the north norfolk coast and re examines the dynamic behaviour of the biis in the southern north sea between 31 6 and 21 5 ka this paper shows the core of the dogger bank to be composed glaciolacustrine sediment deposited between 31 6 and 25 8 ka following its formation the western end of the dogger lake was overridden with ice reaching 54 n where the ice margin is co incident with the southerly extent of subglacial tills previously mapped as bolders bank fm this initial ice override and retreat northwards back across the dogger lake was complete by 23 1 ka but resulted in widespread compressive glaciotectonism of the lake sediments and the formation of thrust moraine complexes along the northern edge of the bank moraines are on lapped by later phase glaciolacustrine and marine sediments but do not show evidence of subsequent ice override the shallow seafloor to the west and southwest of the dogger bank records several later phases of ice advance and retreat as the north sea lobe flowed between the dogger bank and the yorkshire lincolnshire coasts and reached north norfolk new optically stimulated luminescence osl ages from garrett hill on outwash limit the arrival of the biis on the norfolk coast to 22 8 21 5 ka multiple till sheets and chains of moraines on the seafloor north of norfolk mark dynamic oscillation of the north sea lobe margin as it retreated northwards this pattern of behaviour is broadly synchronous with the terrestrial record of deposition of subglacial glaciofluvial and glaciolacustrine sediments along the yorkshire coast which relate to post dimlington stadial ice marginal oscillations after 21 5 ka with respect to forcing mechanisms it is likely that during the early phases of the last glacial maximum 30 23ka the interaction between the southern margin of the biis and the dogger lake was critical in influencing flow instability and rapid ice advance and retreat however during the latter part of the last glacial maximum 22 21 ka late phase ice advance in the southern north sea became restricted to the western side of the dogger bank which was a substantial topographic feature by this time this topographic confinement in addition to decoupling of the biis and the fennoscandian ice sheet fis further north enabled ice to reach the north norfolk coast overprinting the seabed with late phase tills of the bolders bank fm

durations and propagation patterns of ice sheet instability events continued atmospheric and ocean warming places parts of the west antarctic ice sheet at risk for collapse through accelerated ice flow and grounding line retreat over reversed bed slopes however

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

co seismic displacements folding and shortening structures along the chelungpu surface rupture zone occurred during the 1999 chi chi taiwan earthquake abstract a nearly 100 km long surface rupture zone called chelungpu surface rupture zone occurred mostly along the pre existing chelungpu fault on the northwestern side of taiwan accompanying the 1999 chi chi ms 7 6 earthquake the chelungpu surface rupture zone can be divided into four segments based on the characteristics of co seismic displacements geometry of the surface ruptures and geological structures these segments generally show a right step en echelon form and strike ne sw to n s and dip to the east with angles ranging from 50 to 85 the co seismic flexural slip folding structures commonly occurred in or near the surface rupture zone from a few meters to a few hundreds of meters in width which have an orientation in fold axes parallel or oblique to the surface rupture zone the displacements measured in the southern three segments are approximately 1 0 3 0 m horizontally and 2 0 4 0 m vertically the largest displacements were measured in the northern segment 11 1 m horizontally and 7 5 m vertically respectively the amount of co seismic horizontal shortening caused by flexural slip folding and reverse faulting in the surface rupture zone is generally less than 3 m it is evident that the co seismic displacements of the surface rupture zone are a quantitative surface indicator of the faulting process in the earthquake source fault the relations between the geometry and geomorphology of the surface rupture zone dips of the co seismic faulting planes and the striations on the main fault planes generated during the co seismic displacement show that the chelungpu surface rupture zone is a reverse fault zone with a large left lateral component

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

cryospheric science vulnerable ice in the weddell sea of the west antarctic ice shelves those in the amundsen sea sector have given the most cause for concern ocean modelling of the weddell sea region together with a detailed survey of the ice bed morphology indicates that this region too may change soon

impact of ocean forcing on the aurora basin in the 21st and 22nd centuries the grounded ice in the totten and dalton glaciers is an essential component of the buttressing for the marine based aurora basin and hence their stability is important to the future rate of mass loss from east antarctica totten and vanderford glaciers are joined by a deep east west running subglacial trench between the continental ice sheet and law dome while a shallower trench links the totten and dalton glaciers all three glaciers flow into the ocean close to the antarctic circle and experience ocean driven ice shelf melt rates comparable with the amundsen sea embayment we investigate this combination of trenches and ice shelves with the bisicles adaptive mesh ice sheet model and ocean forcing melt rates derived from two global climate models we find that ice shelf ablation at a rate comparable with the present day is sufficient to cause widespread grounding line retreat in an east west direction across totten and dalton glaciers with projected future warming causing faster retreat meanwhile southward retreat is limited by the shallower ocean facing slopes between the coast and the bulk of the aurora sub glacial trench however the two climate models produce completely different future ice shelf basal melt rates in this region hadcm3 drives increasing sub ice shelf melting to 2150 while echam5 shows little or no increase in sub ice shelf melting under the two greenhouse gas forcing scenarios

evidence of a full west antarctic ice sheet back to the early oligocene insight from double dating of detrital apatites in ross sea sediments the west antarctic ice sheet is the most unstable component of the antarctic cryosphere its fluctuations are well documented since the pliocene but its behaviour over the last 35 ma is more controversial particularly during periods of past high global pco2 values similar to those predicted in future global climate scenarios here we present new u pb dating of detrital apatite grains previously dated by the fission track method from cape roberts project oligocene to pliocene marine sediments in the ross sea two past ice flow patterns were identified one formed by outlet glaciers sourcing short travelled apatites and one northerly directed bringing far travelled apatite grains the latter provides the first robust physical evidence for the presence and repeated expansion of an oligocene west antarctic ice sheet

an object based sar image iceberg detection algorithm applied to the amundsen sea abstract an object based method for automatic iceberg detection from advanced synthetic aperture radar asar images has been developed and applied in the amundsen sea antarctica the automatic identification is based on brightness and spatial parameters of the asar images at five scale levels and was verified with manual classification in four areas chosen to represent varying environmental conditions the presented algorithm works comparatively well with images of the ocean in freezing temperatures and strong wind conditions common in the amundsen sea the detection rate was 96 2 which corresponds to 93 2 of the icebergs area for all seasons the algorithm generated 3 8 errors in the form of misses and 7 0 of false alarms mainly caused by the presence of ice floes the method was applied on 432 radar images acquired in 2011 under different meteorological oceanographic and sea ice conditions as an output a map showing the probability of finding icebergs has been created it shows that high probability coincides with depth contours and indicates a westward drift of the bergs throughout the whole region

reassessment of the potential sea level rise from a collapse of the west antarctic ice sheet theory has suggested that the west antarctic ice sheet may be inherently unstable recent observations lend weight to this hypothesis we reassess the potential contribution to eustatic and regional sea level from a rapid collapse of the ice sheet and find that previous assessments have substantially overestimated its likely primary contribution we obtain a value for the global eustatic sea level rise contribution of about 3 3 meters with important regional variations the maximum increase is concentrated along the pacific and atlantic seaboard of the united states where the value is about 25 greater than the global mean even for the case of a partial collapse

grounding line retreat of totten glacier east antarctica 1996 to 2013 2015 american geophysical union all rights reserved totten glacier east antarctica a glacier that holds a 3 9 m sea level change equivalent has thinned and lost mass for decades we map its grounding line positions in 1996 and 2013 using differential radar interferometry insar data and develop precise high resolution topographies of its ice surface and ice draft using nasa operation icebridge data insar data and a mass conservation method we detect a 1 to 3 km retreat of the grounding line in 17 years the retreat is asymmetrical along a two lobe pattern where ice is only grounded a few 10 m above sea level or ice plain which may unground further with only modest amounts of ice thinning the pattern of retreat indicates ice thinning of 12 m in 17 years or 0 7 0 1 m yr at the grounding line on average sustained thinning will cause further grounding line retreat but may not be conducive to a marine instability key points grounding line of totten glacier is retreating not as fast as west antarctica retreat pattern explained by the newly inferred bed geometry if ice thinning maintains bed geometry conducive to further retreat