antarctic snow accumulation mapped using polarization of 4 3 cm wavelength microwave emission different parts of antarctica receive different amounts of snowfall each year in this paper we map the variations of the mean annual snow accumulation across the ice sheet we also quantify the uncertainty in our estimates more objectively than has been possible for earlier maps the new map is produced using observations from satellites and ground based measurements after a logarithmic transformation these are combined using the geostatistical method of continuous part universal kriging to give an estimate of the snow accumulation within each cell of a rectangular grid covering antarctica we also derive spatial averages over the major drainage systems of the ice sheet along with their confidence intervals we obtain a value of 143 4 kg m 2 a 1 for the average rate of snow accumulation upon the grounded ice sheet of antarctica

airborne gravity reveals interior of antarctic volcano abstract understanding antarctic volcanoes is important as they provide a window on magmatic and tectonic processes of the antarctic plate and contain datable records of ice sheet changes we present the results from the first detailed airborne radar and gravity surveys across james ross island northern antarctic peninsula which is dominated by mt haddington an ice covered miocene recent alkaline stratovolcano the surveys provide new insights into the subsurface structure of the volcano and hence its development which are unavailable from the surface geology alone we show that mt haddington is associated with a significant negative bouguer gravity anomaly 26 mgal which suggests that there has not been significant pooling and solidification of a dense shallow level mafic magma chamber during the growth of the volcano over at least the past 6 m y which is consistent with independent geochemical evidence simple flexural isostatic models cannot explain the localised negative bouguer anomaly 3d modelling techniques show that the negative anomaly is best explained by a shallow low density intra crustal body with its top close to or at the surface although comparable gravity anomalies are commonly associated with large 20 km ash filled calderas as seen at yellowstone or toba there is no geological evidence on james ross island for a similar structure we therefore propose that the james ross island volcanic edifice subsided into the thick underlying pile of relatively soft jurassic and cretaceous sediments which were displaced by low density hyaloclastite breccia the type of deformation envisaged is similar to that associated with concepciou or iwaki volcanoes in south america although mt haddington is much larger

pine island glacier antarctica a study of the catchment using interferometric synthetic aperture radar measurements and radar altimetry we have mapped the catchment region of pine island glacier antarctica using ers 1 and ers 2 radar altimetry and synthetic aperture radar sar interferometry the radar altimeter data were converted to a digital elevation model dem using an algorithm we developed that corrects for slopes and grids the surface elevation estimates in a single step we used the dem and precise postprocessed orbital ephemerides to generate terrain corrected and geolocated complex radar imagery interferometric pairs on both ascending and descending orbits corrected by means of the dem yielded components of ice surface motion in the radar look direction where possible we combined velocity components from ascending and descending tracks to produce vector velocities elsewhere the velocity was calculated by assuming the direction of motion is down the surface slope the velocity map reveals a system of tributaries that channel ice from the basin like catchment area into the fast flowing downstream trunk of pine island glacier none of the tributaries shows a clear onset region instead the ice speed gradually increases along with a gradual decrease in driving stress along each tributary we combined the velocity data with sparse information on ice thicknesses and snow accumulation rates to calculate an approximate mass balance we find that the region is in balance within an uncertainty of 30 of the total mass throughput

cryosphere fire and ice ice sheet stability is affected by a complex interplay between meltwater and the geological characteristics of the bedrock under the ice the identification of a recently active subglacial volcano in antarctica adds uncertainty to this system

warm ocean is eroding west antarctic ice sheet 1 satellite radar measurements show that ice shelves in pine island bay have thinned by up to 5 5 m yr 1 over the past decade the pattern of shelf thinning mirrors that of their grounded tributaries the pine island thwaites and smith glaciers and ocean currents on average 0 5 c warmer than freezing appear to be the source the synchronised imbalance of the inland glaciers is the result of reduced lateral and basal tractions at their termini and the drawdown of grounded ice shows that antarctica is more sensitive to changing climates than was previously considered

ice dynamical constraints on the existence and impact of subglacial volcanism on west antarctic ice sheet stability 1 subglacial volcanism in west antarctica may play a crucial role in the dynamics and stability of the west antarctic ice sheet wais evidence supporting the existence of an individual subglacial volcanic center mt casertz in the upper catchments of whillans and kamb ice stream wis and kis comes from a comparison of ice sheet modeling results with measured ice velocities lubrication of an area which otherwise should be frozen to its bed is best explained by basal melt water generated in the vicinity of mt casertz the estimated melt water production of mt casertz corresponds to 8 of the total melt water production in the two catchments this would be sufficient to offset basal freezing in the dormant kis relubricating its bed and potentially causing a restart near future volcanic activity changes are speculative but would have far reaching implications on the dynamics and stability of the wais requiring further investigation

changes in static stress on southern california faults after the 1992 landers earthquake the magnitude 7 5 landers earthquake of 28 june 1992 was the largest earthquake to strike california in 40 years the slip that occurs in such an earthquake would be expected to induce large changes in the static stress on neighbouring faults these changes in stress should in turn affect the likelihood of future earthquakes stress changes that load faults towards failure have been cited as the cause of small1 5 moderate6 and large7 earthquakes conversely those that relax neighbouring faults have been related to a decrease in seismicity5 here we use an elastic half space model8 to estimate the stress changes produced by the landers earthquake on selected southern california faults including the san andreas we find that the estimated stress changes are consistent with the triggering of four out of the five aftershocks with magnitude greater than 4 5 and that the largest changes 1 10 bar occurring on part of the san bernardino segment of the san andreas fault may have decreased the time to the next magnitude 8 earthquake by about 14 years

improved estimation of the mass balance of glaciers draining into the amundsen sea sector of west antarctica from the cecs nasa 2002 campaign in november december 2002 a joint airborne experiment by centro de estudios cientificos and nasa flew over the antarctic ice sheet to collect laser altimetry and radio echo sounding data over glaciers flowing into the amundsen sea a p 3 aircraft on loan from the chilean navy made four flights over pine island thwaites pope smith and kohler glaciers with each flight yielding 1 5 2 hours of data the thickness measurements reveal that these glaciers flow into deep troughs which extend far inland implying a high potential for rapid retreat interferometric synthetic aperture radar data insar and satellite altimetry data from the european remote sensing satellites ers 1 2 show rapid grounding line retreat and ice thinning of these glaciers using the new thickness data we have re evaluated glacier fluxes and the present state of mass balance which was previously estimated using ice thicknesses deduced largely from inversion of elevation data assuming hydrostatic equilibrium the revised total ice discharge of 241 5 km 3 a 1 exceeds snow accumulation by 81 17 km 3 a 1 of ice equivalent to a sea level rise of 0 21 0 04 mm a 1 this magnitude of ice loss is too large to be caused by atmospheric forcing and implies dynamic thinning of the glaciers this is confirmed by ice flow acceleration observed with insar we attribute the flow acceleration and ice thinning to enhanced bottom melting of the ice shelves by a warmer ocean which reduces buttressing of the glaciers and in turn accelerates them out of balance

ice volcano interaction of the 1996 gjalp subglacial eruption vatnajokull iceland volcanic eruptions under glaciers can cause dangerous floods and lahars1 2 3 and create hyaloclastite fragmented glassy rock mountains4 5 6 7 8 but processes such as the rate of heat transfer between ice and magma edifice formation and the response of the surrounding glacier are poorly understood because of the lack of data here we present observations from the fissure eruption at vatnajokull ice cap iceland in october 1996 in the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6 7 km long and 200 300 m high under 500 750 m of ice meltwater of temperatures of 15 20 c flowed along a narrow channel at the glacier bed into the grimsvotn subglacial lake for five weeks before draining in a sudden flood or jokulhlaup subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path whereas elsewhere the glacier surface remained intact suggesting that subglacial eruptions do not trigger widespread basal sliding in warm based glaciers

morphometry of bedrock meltwater channels on antarctic inner continental shelves implications for channel development and subglacial hydrology abstract expanding multibeam bathymetric data coverage over the last two decades has revealed extensive networks of submarine channels incised into bedrock on the antarctic inner continental shelf the large dimensions and prevalence of the channels implies the presence of an active subglacial hydrological system beneath the past antarctic ice sheet which we can use to learn more about inaccessible subglacial processes here we map and analyse over 2700 bedrock channels situated across 100 000 km2 of continental shelf in the western antarctic peninsula and amundsen sea to produce the first inventory of submarine channels on the antarctic inner continental shelf morphometric analysis reveals highly similar distributions of channel widths depths cross sectional areas and geometric properties with subtle differences between channels in the western antarctic peninsula compared to those in the amundsen sea at 75 3400 m wide 3 280 m deep 160 290 000 m2 in cross sectional area and typically 8 times as wide as they are deep the channels have similar morphologies to tunnel valleys and meltwater channel systems observed from other formerly glaciated landscapes despite differences in substrate geology and glaciological regime we propose that the antarctic bedrock channels formed over multiple glacial cycles through the episodic drainage of at least 59 former subglacial lakes identified on the inner continental shelf

the configuration sensitivity and rapid retreat of the late weichselian icelandic ice sheet abstract the fragmentary glacial geological record across the icelandic continental shelf has hampered reconstruction of the volume extent and chronology of the late weichselian ice sheet particularly in key offshore zones marine geophysical data collected over the last two decades reveal that the ice sheet likely attained a continental shelf break position in all sectors during the last glacial maximum though its precise timing and configuration remains largely unknown within this context we review the available empirical evidence and use a well constrained three dimensional thermomechanical model to investigate the drivers of an extensive late weichselian icelandic ice sheet its sensitivity to environmental forcing and phases of deglaciation our reconstruction attains the continental shelf break across all sectors with a total ice volume of 5 96 105 km3 with high precipitation rates being critical to forcing extensive ice sheet flow offshore due to its location astride an active mantle plume a relatively fast and dynamic ice sheet with a low aspect ratio is maintained our results reveal that once initial ice sheet retreat was triggered through climate warming at 21 8 ka bp marine deglaciation was rapid and accomplished in all sectors within c 5 ka at a mean rate of 71 gt of mass loss per year this rate of ice wastage is comparable to contemporary rates observed for the west antarctic ice sheet the ice sheet subsequently stabilised on shallow pinning points across the near shelf for two millennia but abrupt atmospheric warming during the bolling interstadial forced a second dramatic collapse of the ice sheet onshore with a net wastage of 221 gt a 1 over 750 years analogous to contemporary greenland rates of mass loss geothermal conditions impart a significant control on the ice sheet s transient response particularly during phases of rapid retreat insights from this study suggests that large sectors of contemporary ice sheets overlying geothermally active regions such as siple coast antarctica and ne greenland have the potential to experience rapid phases of mass loss and deglaciation once initial retreat is initiated

subglacial bathymetry and sediment distribution beneath pine island glacier ice shelf modeled using aerogravity and in situ geophysical data new results pine island glacier pig in the amundsen sea sector of the west antarctic ice sheet wais is losing mass and contributing to global sea level rise at an accelerating rate although recent observations and modeling have identified the incursion of relatively warm circumpolar deep water cdw beneath the pig ice shelf pigis as the main driver of this ice mass loss the lack of precise bathymetry limits furthering our understanding of the ice ocean interactions and improving the accuracy of modeling here we present updated bathymetry and sediment distribution beneath the pigis modeled by the inversion of aerogravity data with constraints from active source seismic data observations from an autonomous underwater vehicle and the regional gravity anomaly field derived from satellite gravity observations modeled bathymetry shows a submarine ridge beneath the middle of pigis that rises 350 to 400 m above the surrounding sea floor with a minimum water column thickness of 200 m above it this submarine ridge continues across the whole width of the 45 km wide ice shelf with no deep troughs crossing it confirming the general features of the previously predicted sub ice shelf ocean circulation however the relatively low resolution of the aerogravity data and limitations in our inversion method leave a possibility that there is an undetected few kilometers wide or narrower trough that may alter the predicted sub ice shelf ocean circulation modeled sediment distribution indicates a sedimentary basin of up to 800 m thick near the current grounding zone of the main pig trunk and extending farther inland and a region seaward of the submarine ridge where sediments are thin or absent with exposed crystalline basement that extends seaward into pine island bay therefore the submarine ridge marks the transition from a thick sedimentary basin providing a smooth interface over which ice could flow easily by sliding or sediment deformation to a region with no to little sediments and instead a rough interface over which ice flows mainly by deformation we hypothesize that the post last glacial maximum retreat of pig stabilized at this location because of the spatial transition in basal conditions this in turn supports the hypothesis that the recent retreat of pig was strongly forced probably by changes in ocean circulation rather than occurring because of ongoing response to the end of the ice age or other changes inland of or beneath pig

displacement field and slip distribution of the 2005 kashmir earthquake from sar imagery 1 the 8th october 2005 kashmir earthquake mw 7 6 involved primarily thrust motion on a ne dipping fault sub pixel correlation of envisat sar images gives the location of the 80 km long fault trace within 300 800 m and a 3d surface displacement field with a sub metric accuracy covering the whole epicentral area the slip distribution inverted using elastic dislocation models indicates that slip occurs mainly in the upper 10 km between the cities of muzaffarabad and balakot the rupture reached the surface in several places in the hanging wall horizontal motions show rotation from pure thrust to oblique right lateral motion that are not observed in the footwall a segmentation of the fault near muzaffarabad is also suggested north of the city of balakot slip decreases dramatically but a diffuse zone of mainly vertical surface displacements which could be post seismic exists further north where most of the aftershocks occur aligned along the nw se indus kohistan seismic zone

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

the aeromagnetic method as a tool to identify cenozoic magmatism in the west antarctic rift system beneath the west antarctic ice sheet a review thiel subglacial volcano as possible source of the ash layer in the waiscore abstract the west antarctic ice sheet wais flows through the volcanically active west antarctic rift system wars the aeromagnetic method has been the most useful geophysical tool for identification of subglacial volcanic rocks since 1959 64 surveys particularly combined with 1978 radar ice sounding the unique 1991 97 central west antarctica cwa aerogeophysical survey covering 354 000 km 2 over the wais 5 km line spaced orthogonal lines of aeromagnetic radar ice sounding and aerogravity measurements still provides invaluable information on subglacial volcanic rocks particularly combined with the older aeromagnetic profiles these data indicate numerous 100 1000 nt 5 50 km width shallow source magnetic anomalies over an area greater than 1 2 10 6 km 2 mostly from subglacial volcanic sources i interpreted the cwa anomalies as defining about 1000 volcanic centers requiring high remanent normal magnetizations in the present field direction about 400 anomaly sources correlate with bed topography at least 80 of these sources have less than 200 m relief at the wais bed they appear modified by moving ice requiring a younger age than the wais about 25 ma exposed volcanoes in the wars are the present rapid changes resulting from global warming could be accelerated by subglacial volcanism

static stress change from the 8 october 2005 m 7 6 kashmir earthquake 1 we calculated static stress changes from the devastating m 7 6 earthquake that shook kashmir on 8 october 2005 we mapped coulomb stress change on target fault planes oriented by assuming a regional compressional stress regime with greatest principal stress directed orthogonally to the mainshock strike we tested calculation sensitivity by varying assumed stress orientations target fault friction and depth our results showed no impact on the active salt range thrust southwest of the rupture active faults north of the main boundary thrust near peshawar fall in a calculated stress decreased zone as does the raikot fault zone to the northeast we calculated increased stress near the rupture where most aftershocks occurred the greatest increase to seismic hazard is in the indus kohistan seismic zone near the indus river northwest of the rupture termination and southeast of the rupture termination near the kashmir basin

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

radar attenuation and temperature within the greenland ice sheet 2015 american geophysical union all rights reserved the flow of ice is temperature dependent but direct measurements of englacial temperature are sparse the dielectric attenuation of radio waves through ice is also temperature dependent and radar sounding of ice sheets is sensitive to this attenuation here we estimate depth averaged radar attenuation rates within the greenland ice sheet from airborne radar sounding data and its associated radiostratigraphy using existing empirical relationships between temperature chemistry and radar attenuation we then infer the depth averaged englacial temperature the dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry where radar transects intersect boreholes radar inferred temperature is consistently higher than that measured directly we attribute this discrepancy to the poorly recognized frequency dependence of the radar attenuation rate and correct for this effect empirically resulting in a robust relationship between radar inferred and borehole measured depth averaged temperature radar inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice sheet model particularly in southern greenland this pattern suggests that past changes in surface boundary conditions temperature and accumulation rate affect the ice sheet s present temperature structure over a much larger area than previously recognized this radar inferred temperature structure provides a new constraint for thermomechanical models of the greenland ice sheet

timing of recent accelerations of pine island glacier antarctica 1 we have used interferometric synthetic aperture radar insar data and sequential landsat imagery to identify and temporally constrain two acceleration events on pine island glacier pig these two events are separated by a period of at least seven years 1987 1994 the change in discharge between two flux gates indicates that the majority of the increase in discharge associated with the second acceleration originates well inland 80 km from the grounding line an analysis indicates that changes in driving stress consistent with observed thinning rates are sufficient in magnitude to explain much of the acceleration

modeling of kashmir aftershock decay based on static coulomb stress changes and laboratory derived rate and state dependent friction law we model the spatial and temporal evolution of october 8 2005 kashmir earthquake s aftershock activity using the rate and state dependent friction model incorporating uncertainties in computed coseismic stress perturbations we estimated the best possible value for frictional resistance a n background seismicity rate r and coefficient of stress variation cv using maximum log likelihood method for the whole kashmir earthquake sequence we measure a frictional resistance a n 0 0185 mpa r 20 m3 7 events year and cv 0 94 0 01 the spatial and temporal forecasted seismicity rate of modeled aftershocks fits well with the spatial and temporal distribution of observed aftershocks that occurred in the regions with positive static stress changes as well as in the apparent stress shadow region to quantify the effect of secondary aftershock triggering we have re run the estimations for 100 stochastically declustered catalogs showing that the effect of aftershock induced secondary stress changes is obviously minor compared to the overall uncertainties and that the stress variability related to uncertain slip model inversions and receiver mechanisms remains the major factor to provide a reasonable data fit

aftershock modeling based on uncertain stress calculations 1 we discuss the impact of uncertainties in computed coseismic stress perturbations on the seismicity rate changes forecasted through a rate and state dependent frictional model we aim to understand how the variability of coulomb stress changes affects the correlation between predicted and observed changes in the rate of earthquake production we use the aftershock activity following the 1992 m7 3 landers california earthquake as a case study to accomplish these tasks we first analyze the variability of stress changes resulting from the use of different published slip distributions we find that the standard deviation of the uncertainty is of the same size as the absolute stress change and that their ratio the coefficient of variation cv is approximately constant in space this uncertainty has a strong impact on the forecasted aftershock activity if a rate and state frictional model is considered we use the early aftershocks to invert for friction parameters and the coefficient of variation by means of the maximum likelihood method we show that when the uncertainties are properly taken into account the inversion yields stable results which fit the spatiotemporal aftershock sequence the analysis of the 1992 landers sequence demonstrates that accounting for realistic uncertainties in stress changes strongly improves the correlation between modeled and observed seismicity rate changes for this sequence we measure a friction parameter asn 0 017 mpa and a coefficient of stress variation cv 0 95

subglacial melt channels and fracture in the floating part of pine island glacier antarctica 1 a dense grid of ice penetrating radar sections acquired over pine island glacier west antarctica has revealed a network of sinuous subglacial channels typically 500 m to 3 km wide and up to 200 m high in the ice shelf base these subglacial channels develop while the ice is floating and result from melting at the base of the ice shelf above the apex of most channels the radar shows isolated reflections from within the ice shelf comparison of the radar data with acoustic data obtained using an autonomous submersible confirms that these echoes arise from open basal crevasses 50 100 m wide aligned with the subglacial channels and penetrating up to 1 3 of the ice thickness analogous sets of surface crevasses appear on the ridges between the basal channels we suggest that both sets of crevasses were formed during the melting of the subglacial channels as a response to vertical flexing of the ice shelf toward the hydrostatic condition finite element modeling of stresses produced after the formation of idealized basal channels indicates that the stresses generated have the correct pattern and if the channels were formed sufficiently rapidly would have sufficient magnitude to explain the formation of the observed basal and surface crevasse sets we conclude that ice shelf basal melting plays a role in determining patterns of surface and basal crevassing increased delivery of warm ocean water into the sub ice shelf cavity may therefore cause not only thinning but also structural weakening of the ice shelf perhaps as a prelude to eventual collapse

assessing elastic coulomb stress transfer models using seismicity rates in southern california and southwestern japan 1 we investigated whether observed changes in seismicity rate following the 1992 landers and 1995 kobe earthquakes correspond with predictions from coulomb stress transfer models to quantify the relationship between coulomb stress change and seismicity rate change we compared spatial changes in observed seismicity rates to the modeled changes in coulomb failure stress cfs for the two subject earthquakes we begin with the simplest and most common cfs model which assumes that regional stress orientations are uniform and the stress change is resolved on optimally oriented strike slip planes we then extended the cfs models to include the more geophysically realistic assumptions of spatially varying regional stress orientations and optimally oriented planes in three dimensions for all the tested cfs models we found that virtually everywhere seismicity rate changes could be resolved the rate increased regardless of whether the cfs theoretically promoted or inhibited failure and that we were not able to reliably resolve seismicity rate decreases an improvement in the correlation between the sign of the cfs and where rate increases occur when estimating the cfs on optimally oriented planes in three dimensions rather than two dimensions is a consequence of using optimally oriented planes and the ability to primarily observe rate increases the region of positive cfs increases by allowing more degrees of freedom so the correlation with positive rate change appears to increase the areas of highest seismicity rate following the main shock did not correlate with the sign or the magnitude of the cfs rather the areas most active after the main shock were also the most active before the main shock

analysis of deep penetrating radar surveys of west antarctica us itase 2001 1 we collected 1850 km of ground based radio echo sounding res data in west antarctica along the 2001 us leg of the international trans antarctic scientific expedition traverse us itase these data represent the first high resolution measurements of ice thickness and internal stratigraphy for portions of this area that bear on questions about the stability of the west antarctic ice sheet wais internal layers depicting isochrones have been traced continuously for much of the profile length and a date from the byrd deep core is ascribed to one of these isochrones from which we estimate vertical velocities across the traverse route comparison of our ice thickness measurements with bedmap show good agreement in regions where the database is well constrained by data coverage where the bedmap dataset was forced to interpolate differences are as high as 45 of the ice thickness

basement control on past ice sheet dynamics in the amundsen sea embayment west antarctica abstract the development of landscapes and morphologies follows initially the tectonic displacement structures of the basement and sediments such fault zones or lineaments are often exploited by surface erosional processes and play therefore an important role in reconstructing past ice sheet dynamics observations of bathymetric features of the continental shelf of the amundsen sea embayment and identification of tectonic lineaments from geophysical mapping indicate that the erosional processes of paleo ice stream flows across the continental shelf followed primarily such lineaments inherited from the tectonic history since the cretaceous break up between new zealand and west antarctica three major ice flow trends correspond to different tectonic phases in east west northwest southeast and north south directions east west oriented basement trends correlate with coastline trends and overlay tectonic lineaments caused by former rift activities directional trends with northwest southeast orientation are observed for the glacial troughs of the western embayment outer shelf the western pine island bay coastal zones and the inner pine island glacial trough and are associated with a distributed southern plate boundary zone of the former bellingshausen plate the north south trend of the main pine island glacial trough and the north northeast trend of the abbot ice shelf trough on the outer shelf follow the predicted lineation trend of an eastern branch of the west antarctic rift system extending from the thwaites drainage basin northward into pine island bay an understanding of this context helps better constrain the geometries and sea bed substrate conditions for regional paleo ice sheet models

antarctic cenozoic climate history from sedimentary records andrill and beyond mounting evidence from models and geological data implies that the antarctic ice sheet may behave in an unstable manner and retreat rapidly in response to a warming climate which is a key factor motivating efforts to improve estimates of antarctic ice volume contributions to future sea level rise here we review antarctic cooling history since peak temperatures of the middle eocene climatic optimum approx 50 ma to provide a framework for future initiatives to recover sediment cores from subglacial lakes and sedimentary basins in antarctica9s continental interior while the existing inventory of cores has yielded important insights into the biotic and climatic evolution of antarctica strata have numerous and often lengthy time breaks providing a framework of snapshots through time further cores and more work on existing cores are needed to reconcile antarctic records with the more continuous far field records documenting the evolution of global ice volume and deep sea temperature to achieve this we argue for an integrated portfolio of drilling and coring missions that encompasses existing methodologies using ship and sea ice ice shelf based drilling platforms as well as recently developed seafloor based drilling and subglacial access systems we conclude by reviewing key technological issues that will need to be overcome

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

accelerated sea level rise from west antarctica recent aircraft and satellite laser altimeter surveys of the amundsen sea sector of west antarctica show that local glaciers are discharging about 250 cubic kilometers of ice per year to the ocean almost 60 more than is accumulated within their catchment basins this discharge is sufficient to raise sea level by more than 0 2 millimeters per year glacier thinning rates near the coast during 2002 2003 are much larger than those observed during the 1990s most of these glaciers flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates providing exit routes for ice from further inland if ice sheet collapse is under way

radiostratigraphy and age structure of the greenland ice sheet 2015 the authors several decades of ice penetrating radar surveys of the greenland and antarctic ice sheets have observed numerous widespread internal reflections analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections here we present a comprehensive deep radiostratigraphy of the greenland ice sheet from airborne deep ice penetrating radar data collected over greenland by the university of kansas between 1993 and 2013 to map this radiostratigraphy efficiently we developed new techniques for predicting reflection slope from the phase recorded by coherent radars when integrated along track these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing core intersecting reflections were dated using synchronized depth age relationships for six deep ice cores additional reflections were dated by matching reflections between transects and by extending reflection inferred depth age relationships using the local effective vertical strain rate the oldest reflections dating to the eemian period are found mostly in the northern part of the ice sheet within the onset regions of several fast flowing outlet glaciers and ice streams reflections typically do not conform to the bed topography disrupted radiostratigraphy is also observed in a region north of the northeast greenland ice stream that is not presently flowing rapidly dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly this radiostratigraphy provides a new constraint on the dynamics and history of the greenland ice sheet

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

subglacial to emergent basaltic volcanism at hloðufell south west iceland a history of ice confinement abstract hlo ufell is a familiar 1186 m high landmark located about 80 km northeast of reykjavik and 9 km south of the langkjokull ice cap in south west iceland this is the first detailed study of this well exposed and easily accessible subglacial to emergent basaltic volcano eight coherent and eleven volcaniclastic lithofacies are described and interpreted and its evolution subdivided into four growth stages i iv on the basis of facies architecture vents for stages i ii and iv lie along the same fissure zone which trends parallel to the dominant nne ssw volcano tectonic axis of the western volcanic zone in this part of iceland but the stage iii vent lies to the north and is probably responsible for the present n s elongation of the volcano the basal stage i is dominated by subglacially erupted lava mounds and ridges which are of 240 m maximum thickness were fed from short fissures and locally display lava tubes some of the stage i lavas preserve laterally extensive flat to bulbous steep glassy surfaces that are interpreted to have formed by direct contact with surrounding ice and are termed ice contact lava confinement surfaces these surfaces preserve several distinctive structures such as lava shelves pillows that have one flat surface and mini pillow

atmosphere ocean ice interactions in the amundsen sea embayment west antarctica over recent decades outlet glaciers of the amundsen sea embayment ase west antarctica have accelerated thinned and retreated and are now contributing approximately 10 to global sea level rise all the ase glaciers flow into ice shelves and it is the thinning of these since the 1970s and their ungrounding from pinning points that is widely held to be responsible for triggering the glaciers decline these changes have been linked to the inflow of warm circumpolar deep water cdw onto the ase s continental shelf cdw delivery is highly variable and is closely related to the regional atmospheric circulation the ase is south of the amundsen sea low asl which has a large variability and which has deepened in recent decades the asl is influenced by the phase of the southern annular mode along with tropical climate variability it is not currently possible to simulate such complex atmosphere ocean ice interactions in models hampering prediction of future change the current retreat could mark the beginning of an unstable phase of the ase glaciers that if continued will result in collapse of the west antarctic ice sheet but numerical ice sheet models currently lack the predictive power to answer this question it is equally possible that the recent retreat will be short lived and that the ase will find a new stable state progress is hindered by incomplete knowledge of bed topography in the vicinity of the grounding line furthermore a number of key processes are still missing or poorly represented in models of ice flow

a recent volcanic eruption beneath the west antarctic ice sheet a strong radar reflection in the west antarctic ice sheet is related to the eruption of the newly identified hudson mountains subglacial volcano dated to 207 bc this eruption probably caused short term changes in regional glacial and meltwater flow indirect evidence suggests that volcanic activity occurring beneath the west antarctic ice sheet influences ice flow and sheet stability1 2 3 however only volcanoes that protrude through the ice sheet4 and those inferred from geophysical techniques1 2 have been mapped so far here we analyse radar data from the hudson mountains west antarctica5 that contain reflections from within the ice that had previously been interpreted erroneously as the ice sheet bed we show that the reflections are present within an elliptical area of about 23 000 km2 that contains tephra from an explosive volcanic eruption the tephra layer is thickest at a subglacial topographic high which we term the hudson mountains subglacial volcano the layer depth dates the eruption at 207 bc 240 years which matches exceptionally strong but previously unattributed conductivity signals in nearby ice cores the layer contains 0 019 0 31 km3 of tephra which implies a volcanic explosive index of 3 4 production and episodic release of water from the volcano probably affected ice flow at the time of the eruption ongoing volcanic heat production may have implications for contemporary ice dynamics in this glacial system

a 12 000 year record of explosive volcanism in the siple dome ice core west antarctica 1 air mass trajectories in the southern hemisphere provide a mechanism for transport to and deposition of volcanic products on the antarctic ice sheet from local volcanoes and from tropical and subtropical volcanic centers this study extends the detailed record of antarctic south american and equatorial volcanism over the last 12 000 years using continuous glaciochemical series developed from the siple dome a sdma ice core west antarctica the largest volcanic sulfate spike 280 g l occurs at 5881 b c e other large signals with unknown sources are observed around 325 b c e 270 g l and 2818 b c e 191 g l ages of several large equatorial or southern hemisphere volcanic eruptions are synchronous with many sulfate peaks detected in the sdma volcanic ice chemistry record the microprobe fingerprinting of glass shards in the sdma core points to the following antarctic volcanic centers as sources of tephra found in the sdma core balenny island pleiades mount berlin mount takahe and mount melbourne as well as mount hudson and possibly mount burney volcanoes of south america identified volcanic sources provide an insight into the poorly resolved transport history of volcanic products from source volcanoes to the west antarctic ice sheet

impact of the receiver fault distribution on aftershock activity 1 aftershock models are usually based either on purely empirical relations ignoring the physical mechanism or on deterministic calculations of stress changes on a predefined receiver fault orientation here we investigate the effect of considering more realistic fault systems in models based on static coulomb stress changes for that purpose we perform earthquake simulations with elastic half space stress interactions rate and state dependent frictional earthquake nucleation and extended ruptures with heterogeneous fractal slip distributions we find that the consideration of earthquake nucleation on multiple receiver fault orientations does not influence the shape of the temporal omori type aftershock decay but changes significantly the predicted spatial patterns and the total number of triggered events so called stress shadows with decreased activity almost vanish and activation decays continuously with increasing distance from the main shock rupture the total aftershock productivity which is shown to be almost independent of the assumed background rate increases significantly if multiple receiver fault planes exist the application to the 1992 m7 3 landers california aftershock sequence indicates a good agreement with the locations and the total productivity of the observed directly triggered aftershocks

inland thinning of the amundsen sea sector west antarctica 1 together with the pine island glacier pig the thwaites tg and smith sg glaciers are the principal drainage systems of the amundsen sea as sector of western antarctica here we use satellite radar altimetry and interferometry to show that a rapid thinning of ice has occurred within the fastest flowing sections of all as outlet glaciers the pattern of thinning extends to distances greater than 150 km inland between 1991 and 2001 the tg and sg thinned by more than 25 and 45 m at their grounding lines and a total of 154 16 km 3 of ice or 0 43 mm of eustatic sea level rise was lost from the as sector glaciers to the ocean we show that the thickness changes may have caused the pig tg and sg to retreat inland by over 8 4 and 7 km respectively in line with independent estimates of grounding line migration

a 70 ka record of explosive eruptions from the taldice ice core talos dome east antarctic plateau the new antarctic taldice ice core 72 49 s 159 11 e 1620 m depth containing abundant primary tephras provides the opportunity to elucidate the late quaternary volcanic history of the south polar region as well as to broaden the east antarctic tephrostratigraphic framework here grain size and glass compositional data for representative tephra layers from the last 70 ka core section are used for source identification results point to origin of layers from centres of the melbourne volcanic province mcmurdo volcanic group located 250 km from the coring site occurrence of tephra layers within the ice core record suggests that explosive activity in the identified source was not constant over the considered period with a minimum of activity between 20 and 35 ka and increased activity back to 65 ka in addition to palaeovolcanic implications the taldice tephra layers offer prospects for firm correlations between diverse widely separated palaeoarchives and for accurate dating of the antarctic climatic record

volcanology mobile magma under antarctic ice volcanoes have been active under the west antarctic ice sheet for millions of years and there is evidence for recent activity now swarms of tiny earthquakes detected in 2010 and 2011 hint at current magma movement in the crust beneath the ice

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

the sediment infill of subglacial meltwater channels on the west antarctic continental shelf subglacial meltwater plays a significant yet poorly understood role in the dynamics of the antarctic ice sheets here we present new swath bathymetry from the western amundsen sea embayment west antarctica showing meltwater channels eroded into acoustic basement their morphological characteristics and size are consistent with incision by subglacial meltwater to understand how and when these channels formed we have investigated the infill of three channels diamictons deposited beneath or proximal to an expanded grounded west antarctic ice sheet are present in two of the channels and these are overlain by glaciomarine sediments deposited after deglaciation the sediment core from the third channel recovered a turbidite sequence also deposited after the last deglaciation the presence of deformation till at one core site and the absence of typical meltwater deposits e g sorted sands and gravels in all three cores suggest that channel incision pre dates overriding by fast flowing grounded ice during the last glacial period given the overall scale of the channels and their incision into bedrock it is likely that the channels formed over multiple glaciations possibly since the miocene and have been reoccupied on several occasions this also implies that the channels have survived numerous advances and retreats of grounded ice

a case of no wind plinian fallout at pululagua caldera ecuador implications for models of clast dispersal the caldera of pululagua is an eruptive centre of the northern volcanic zone of the south american volcanic arc located about 15 km north of quito ecuador activity leading to formation of the caldera occurred about 2450 b p as a series of volcanic episodes during which an estimated 5 6 km3 dre of hornblende bearing dacitic magma was erupted a basal pumice fall deposit covers more than 2 2x104 km2 with a volume of about 1 1 km3 and represents the principal and best preserved plinian layer circular patterns of isopachs and pumice lithic and md isopleths of the basal fallout bf around the caldera indicate emplacement in wind free conditions absence of wind is confirmed by an ubiquitous normally graded thin ash bed at the top of the lapilli layer which originated from slow settling of fines after cessation of the plinian column co plinian ash the unusual atmospheric conditions during deposition make the bf deposit particularly suitable for the application and evaluation of pyroclast dispersal models application of the carey and sparks 1986 model shows that whereas the 3 2 1 6 and 0 8 cm lithic isopleths predict a model column height of about 36 km the 6 4 cm isopleth yields and estimate of only 21 km the 4 9 and 6 4 cm isopleths yield a column height of 28 km using the model of wilson and walker 1987 the two models give the same mass discharge rate of 2x108 kg s 1 a simple exponential decrease of thickness with distance as proposed by pyle 1989 for plinian falls fits well with the bf exponential decrease of size with distance is followed by clasts less than about 3 cm suggesting in agreement with wilson and walker 1987 that only a small proportion of large clasts reach the top of the column variations with distance in clast distribution patterns imply that in order to obtain column heights by clast dispersal models the distribution should be known from both proximal and distal zones knowledge of only a few isopleths irrespective of their distance from the vent is not sufficient as seemed justified by the method of pyle 1989

the internal layering of pine island glacier west antarctica from airborne radar sounding data this paper presents an overview of internal layering across pine island glacier west antarctica as measured from airborne radar data acquired during a survey conducted by the british antarctic survey and the university of texas in the 2004 05 season internal layering is classified according to type continuous discontinuous missing and the results compared with insar velocities several areas exhibit disruption of internal layers that is most likely caused by large basal shear stresses signs of changes in flow were identified in a few inter tributary areas but overall the layering classification and distribution of layers indicate that only minor changes in ice flow regime have taken place this is supported by bed topography data that show the main trunk of the glacier as well as some of the tributaries are topographically controlled and located in deep basins

effects of ice number concentration on dynamics of a shallow mixed phase stratiform cloud 1 previous modeling studies have shown high sensitivity of mixed phase clouds to ice number concentration ni with simulated clouds often transitioning from mixed phase to ice only regime within a narrow range of ni to better understand the mechanisms behind this transition we analyze several simulations of a mixed phase stratiform arctic cloud observed on 26 april 2008 during the indirect and semi direct aerosol campaign isdac in the base run ni is constrained to match the measured value and a persistent mixed phase cloud is formed with properties similar to those observed when ni is quadrupled hi ice the liquid water path is reduced by half within two hours the changes in liquid water are accompanied by diminishing radiative cooling and slowing vertical mixing exposing complex interactions among microphysics radiation and dynamics deviations of base and hi ice from a simulation without ice are used to explore the linearity of the model response to variation in ni it is shown that early changes in cloud condensate amount and radiative cooling rate are proportional to ni while changes in the vertical buoyancy flux and dynamics are qualitatively different in hi ice compared to base the nonlinear with respect to ni reduction in buoyancy flux drives the initial response of the mixed layer dynamics to the appearance of ice and subsequently determines the sustainability of liquid water in the cloud in this case two additional sensitivity experiments link the decreased buoyancy production to the latent heat release from the depositional ice growth while confirming the importance of the cloud radiation feedback

seismic detection of an active subglacial magmatic complex in marie byrd land antarctica numerous volcanoes exist in marie byrd land a highland region of west antarctica high heat flow through the crust in this region may influence the stability of the west antarctic ice sheet 1 4 volcanic activity progressed from north to south in the executive committee mountain range between the miocene and holocene epochs but there has been no evidence for recent magmatic activity 5 7 here we use a recently deployed seismic network to show that in 2010 and 2011 two swarms of seismic activity occurred at 25 40 km depth beneath subglacial topographic and magnetic highs located 55 km south of the youngest subaerial volcano in the executive committee range we interpret the swarm events as deep long period earthquakes based on their unusual frequency content such earthquakes occur beneath active volcanoes are caused by deep magmatic activity and in some cases precede eruptions 8 11 we also use radar profiles to identify a prominent ash layer in the ice overlying the seismic swarm located at 1 400 m depth the ash layer is about 8 000 years old and was probably sourced from the nearby mount waesche volcano together these observations provide strong evidence for ongoing magmatic activity and demonstrate that volcanism continues to migrate southwards along the executive committee range eruptions at this site are unlikely to penetrate the 1 2 to 2 km thick overlying ice but would generate large volumes of melt water that could significantly affect ice stream flow

aeromagnetic evidence for a volcanic caldera complex beneath the divide of the west antarctic ice sheet a 1995 96 aeromagnetic survey over part of the sinuous ridge sr beneath the west antarctic ice sheet wais divide shows a 70 km diameter circular pattern of 400 1200 nt anomalies suggesting one of the largest volcanic caldera complexes on earth radar ice sounding ris shows the northern part of this pattern overlies the sr and extends south over the bentley subglacial trench bst modeled sources of all but one the caldera anomalies are at the base of 1 2 km thick ice and their volcanic edifices have been glacially removed the exception is a 700 m high 15 km wide volcano producing an 800 nt anomaly over the bst intrusion of this volcano beneath 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice the background area 300 to 500 nt surrounding the caldera is possibly caused by a shallow curie isotherm we suggest uplift of the sr forced the advance of the wais