precise analysis of icesat altimetry data and assessment of the hydrostatic equilibrium for subglacial lake vostok east antarctica summary based on the ice cloud and land elevation satellite icesat laser altimetry data the hydrostatic equilibrium he condition for the subglacial lake vostok east antarctica is evaluated a digital elevation model dem of the ice surface is derived by a regional crossover adjustment the analysis of the dem and its comparison with gps derived ice surface elevations and an ice surface dem based on radar altimetry data reveal an overall accuracy of better than 0 7 m for the lake area the dem is combined with an ice thickness model and a regional geoid model to determine the deviation of the local ice surface height from he for large parts of the lake the ice sheet fulfils the he our results reveal a strong positive deviation of about 10 m along the lake shoreline in addition positive deviations are found in the northern part of the lake which coincide with ice rumples detected by radio echo sounding in the southern part of the lake we find a linear negative deviation 4 0 m which coincides with the convoy route from vostok station to mirny base in addition to the dem relative biases for the icesat laser operational periods are determined in the regional crossover adjustment

new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

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

geodetic versus geophysical perspectives of the gravity anomaly summary a gravity anomaly is essentially the difference between the gravitational acceleration caused by the earth s masses and that generated by some reference mass distribution however there are numerous subtleties to the definition and moreover to the practical realization of a gravity anomaly an attempt is made here to clarify the definition of a gravity anomaly from the geodetic and geophysical perspectives point out some of the key differences in terminology and philosophy and to identify some of the problems remaining in its practical realization from a variety of observation types it is argued that if the gravity anomaly is defined and realized in a rigorous and consistent manner this may lead to the improvement of its use in both geodesy and geophysics

the subglacial geology of wilkes land east antarctica wilkes land is a key region for studying the configuration of gondwana and for appreciating the role of tectonic boundary conditions on east antarctic ice sheet eais behavior despite this importance it remains one of the largest regions on earth where we lack a basic knowledge of geology new magnetic gravity and subglacial topography data allow the region s first comprehensive geological interpretation we map lithospheric domains and their bounding faults including the suture between indo antarctica and australo antarctica furthermore we image subglacial sedimentary basins including the aurora and knox subglacial basins and the previously unknown sabrina subglacial basin commonality of structure in magnetic gravity and topography data suggest that pre eais tectonic features are a primary control on subglacial topography the preservation of this relationship after glaciation suggests that these tectonic features provide topographic and basal boundary conditions that have strongly influenced the structure and evolution of the eais

new aerogeophysical view of the antarctic peninsula more pieces less puzzle new airborne geophysical data reveal subglacial imprints of crustal growth of the antarctic peninsula by mesozoic arc magmatism and terrane accretion along the paleo pacific margin of gondwana potential field signatures indicate that the antarctic peninsula batholith is a composite magmatic arc terrane comprising two distinct arcs separated by a 1500 km long suture zone similar to the peninsular ranges batholith in southern and baja california aeromagnetic aerogravity and geological data suggest that a mafic early cretaceous western arc was juxtaposed against a more felsic eastern arc which in mid cretaceous times was intruded by highly magnetic tonalitic granodioritic plutons of island arc affinity suturing of the two arcs against the gondwana margin caused the mid cretaceous palmer land orogenic event convergence and suturing may have been driven by two subduction zones or alternatively by a decrease in slab dip leading to an inboard migration of the arc as in california

widespread persistent thickening of the east antarctic ice sheet by freezing from the base an international polar year aerogeophysical investigation of the high interior of east antarctica reveals widespread freeze on that drives substantial mass redistribution at the bottom of the ice sheet although the surface accumulation of snow remains the primary mechanism for ice sheet growth beneath dome a 24 of the base by area is frozen on ice in some places up to half of the ice thickness has been added from below these ice packages result from the conductive cooling of water ponded near the gamburtsev subglacial mountain ridges and the supercooling of water forced up steep valley walls persistent freeze on thickens the ice column alters basal ice rheology and fabric and upwarps the overlying ice sheet including the oldest atmospheric climate archive and drives flow behavior not captured in present models

new antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in antarctica gravity surveying is challenging in antarctica because of its hostile environment and inaccessibility nevertheless many ground based airborne and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s we present the first modern antarctic wide gravity data compilation derived from 13 million data points covering an area of 10 million km2 which corresponds to 73 coverage of the continent the remove compute restore technique was applied for gridding which facilitated levelling of the different gravity datasets with respect to an earth gravity model derived from satellite data alone the resulting free air and bouguer gravity anomaly grids of 10 km resolution are publicly available these grids will enable new high resolution combined earth gravity models to be derived and represent a major step forward towards solving the geodetic polar data gap problem they provide a new tool to investigate continental scale lithospheric structure and geological evolution of antarctica

the new esa satellite only gravity field model via the direct approach 1 reprocessed gravity field and steady state ocean circulation explorer goce gravity gradient data were combined with data from laser geodynamics satellite lageos 1 2 and gravity recovery and climate experiment grace to generate a satellite only gravity field model to degree 260 using the direct approach named dir r4 when compared to earth gravitational model 2008 egm2008 it is more accurate at low to medium resolution thanks to goce and grace data when compared to earlier releases of esa goce models it is more accurate at high degrees owing to the larger amount of data ingested it is also slightly more accurate than esa s fourth release of the time wise model tim r4 as demonstrated by gps leveling orbit determination tests and an oceanographic evaluation according to the formal probably too optimistic by a factor of 2 2 5 cumulated geoid 1 3 cm and gravity anomaly 0 4 mgal errors at 100 km resolution the goce mission objectives have been reached

the initial gondwana break up a synthesis based on new potential field data of the africa antarctica corridor abstract the initial opening of the africa antarctica corridor in the heart of gondwana is still enigmatic due to missing information on the origin of major crustal features and the exact timing of the onset of the first oceanic crust in the jurassic therefore in 2014 new ship borne magnetic data were systematically acquired in the northern mozambique basin and across beira high which we merged with all accessible magnetic data in the mozambique basin herein distinct magnetic lineations are observed which allow a refined identification of a whole set of jurassic magnetic spreading anomalies constraining the timing of the onset of oceanization beginning at m38n 2n 164 1 ma in combination with high resolution potential field data from the conjugate antarctic margin well expressed fracture zones can be traced throughout the africa antarctica corridor and allow the precise rotation of antarctica back to africa the initial fit depicts striking continuations of onshore tectonic features across the plate boundaries taking onshore aeromagnetic data of both margins into account within a tight gondwana fit the beira high can be restored along the major sinistral namama orvin shear zone of the east african antarctic orogen the beira high represents a continental block which was detached from antarctica by 157 ma at the latest simultaneously the antarctic plate cleared the area of the mcp however the crustal nature of the southern mcp remains ambiguous the northern natal valley and the mozambique ridge consist of thick oceanic crust being emplaced between m26r m18n 157 1 144 ma and m18n m6n 144 131 7 ma respectively about the half of this crust was won from the antarctic plate by a series of southwards directed ridge jumps to the northern boundary of the explora wedge a refined kinematic break up model constrained by the most extensive magnetic dataset is presented describing consistently the initial opening of the africa antarctica corridor and the somali basin

δd and δ18o variations of the magmatic system beneath deception island volcano antarctica implications for magma ascent and eruption forecasting abstract geochemistry of volatiles in active volcanoes provides insights into the magmatic processes and evolution at depth such as magma evolution and degassing which can be implemented into volcanic hazards assessment deception island is one of the most active volcanoes in antarctica with more than twenty explosive eruptions documented over the past two centuries hydrogen and oxygen isotopic variations in the volatiles trapped in the deception island rocks glass and melt inclusions in phenocrysts provide essential information on the mechanisms controlling the eruptive history in this volcanic suite thus understanding the petrological and related isotopic variations in the island has the potential to foresee the possible occurrence and its main eruptive features of a future eruption the new isotopic results of this study combined with exhaustive petrologic knowledge reveal in deception island i fast ascent and quenching of most magmas preserving pre eruptive magmatic signal of water contents and isotopic ratios with local modification by rehydration due to glass exposition to seawater and by meteoric and fumarolic waters ii a plumbing system s variable with time and currently dominated by closed system degassing leading to explosive eruptions iii control on the interactions of ascending magmas with the surface waters producing hydrovolcanic activity throughout the two main fault systems in deception island and at different magma stagnation depths these results can be considered in further studies of volcanic monitoring to improve the capability to interpret geophysical data and signals recorded during volcanic unrest episodes and hence forecast volcanic eruptions and related hazards

esa s satellite only gravity field model via the direct approach based on all goce data gravity field and steady state ocean circulation explorer goce gravity gradient data of the entire science mission and data from lageos 1 2 and gravity recovery and climate experiment grace were combined in the construction of a satellite only gravity field model to maximum degree 300 when compared to earth gravitational model 2008 it is more accurate at low to medium resolution thanks to goce and grace data when compared to earlier releases of european space agency goce models it is more accurate at high degrees owing to the larger amount of data ingested which was moreover taken at lower altitude the impact of orbiting at lower altitude in the last year of the mission is large a model based on data of the last 14 months is significantly more accurate than the release 4 model constructed with the first 28 months the calibrated cumulated geoid error estimate at 100 km resolution is 1 7 cm the optimal resolution of the goce model for oceanographic application is between 100 and 125 km

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

holocene changes in the position and intensity of the southern westerly wind belt the position and intensity of the southern westerly wind belt varies seasonally as a consequence of changes in sea surface temperature during the austral winter the belt expands northward and the wind intensity in the core decreases conversely during the summer the belt contracts and the intensity within the core is strengthened reconstructions of the westerly winds since the last glacial maximum however have suggested that changes at a single site reflected shifts throughout the entire southern wind belt 1 4 here we use sedimentological and pollen records to reconstruct precipitation patterns over the past 12 500 yr from sites along the windward side of the andes precipitation at the sites located in the present core and northern margin of the westerlies is driven almost entirely by the wind belt 5 and can be used to reconstruct its intensity rather than varying coherently throughout the holocene epoch we find a distinct anti phasing of wind strength between the core and northern margin over multi millennial timescales during the early holocene the core westerlies were strong whereas the northern margin westerlies were weak we observe the opposite pattern in the late holocene as this variation resembles modern seasonal variability we suggest that our observed changes in westerly wind strength can best be explained by variations in sea surface temperature in the eastern south pacific ocean chile is ideally located to reconstruct past variability of the southern westerly wind belt sww as the sww almost entirely controls precipitation on the western side of the andes in southern south america with an extreme northsouth

decompensative gravity anomalies reveal the structure of the upper crust of antarctica as antarctica is almost entirely covered by thick ice shields impeding in situ measurements information about upper crustal structures and sedimentary basins is still sparse and the analysis of the gravity anomalies offers new insights isostatic gravity anomalies are often used to investigate upper crust structures however compensating masses significantly reduce the gravity effect of unknown sedimentary and upper crustal structures to separate these effects we apply so called decompensative corrections to the isostatic anomalies for the antarctic continent which reach values of up to 70 mgal the obtained decompensative anomalies well correspond to the known sedimentary basins such as in the areas of the filchner ronne ice shelf and lambert graben and also suggest the existence of other large sedimentary deposits both in west and east antarctica which are not or only sparsely mapped by existing seismic surveys e g in coastal dronning maud land and enderby land a dipole like structure exists at the transantarctic mountains and the wilkes subglacial basin suggesting the presence of isostatic disturbances linked to the dynamic uplift of the transantarctic mountains and thick sedimentary accumulations in the east extended positive anomalies in east antarctica are likely related to the old and dense cratonic crust as well as to isostatic disturbances caused by the transition from local to regional compensation around the lambert graben

combined satellite gravity field model goco01s derived from goce and grace 1 the satellite only gravity field model goco01s is a combination solution based on 61 days of goce gravity gradient data and 7 years of grace gps and k band range rate data resolved up to degree order 224 of a harmonic series expansion the combination was performed consistently by addition of full normal equations and stochastic modeling of goce and grace observations the model has been validated against external global gravity models and regional gps leveling observations while low to medium degrees are mainly determined by grace significant contributions by the new measurement type of goce gradients can already be observed at degree 100 beyond degree 150 goce becomes the dominant contributor correspondingly with goco01s a global gravity field model with high performance for the complete spectral range up to degree order 224 is now available this new gravity model will be beneficial for many applications in geophysics oceanography and geodesy

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

inland extent of the weddell sea rift imaged by new aerogeophysical data the weddell sea rift was a major focus for jurassic extension and magmatism during the early stages of gondwana break up and underlies the weddell sea embayment which separates east antarctica from a collage of crustal blocks in west antarctica newly collected aerogeophysical data over the catchments of institute and moller ice streams reveal the inland extent of the weddell sea rift against the ellsworth whitmore block and a hitherto unknown major left lateral strike slip boundary between east and west antarctica aeromagnetic and gravity anomalies define the regional subglacial extent of proterozoic basement middle cambrian rift related volcanic rocks jurassic intrusions and sedimentary rocks of inferred post jurassic age 2d and 3d magnetic depth to source estimates were used to help constrain joint magnetic and gravity models for the region the models reveal that proterozoic crust similar to that exposed at haag nunataks extends southeast of the ellsworth mountains to the margin of the coastal basins thick granitic jurassic intrusions are modelled at the transition between the ellsworth whitmore block and the thinner crust of the weddell sea rift and within the pagano shear zone the crust beneath the inland extension of the weddell sea rift is modelled as being either 4 km thinner compared to the adjacent ellsworth whitmore block or as underlain by an up to 8 km thick mafic underplate

air and shipborne magnetic surveys of the antarctic into the 21st century the antarctic geomagnetics community remains very active in crustal anomaly mapping more than 1 5 million line km of new air and shipborne data have been acquired over the past decade by the international community in antarctica these new data together with surveys that previously were not in the public domain significantly upgrade the admap compilation aeromagnetic flights over east antarctica have been concentrated in the transantarctic mountains the prince charles mountains lambert glacier area and western dronning maud land dml coats land additionally surveys were conducted over lake vostok and the western part of marie byrd land by the us support office for aerogeophysical research projects and over the amundsen sea embayment during the austral summer of 2004 2005 by a collaborative us uk aerogeophysical campaign new aeromagnetic data over the gamburtsev subglacial mountains 120 000 line km acquired within the ipy antarctica s gamburtsev province project reveal fundamental geologic features beneath the east antarctic ice sheet critical to understanding precambrian continental growth processes roughly 100 000 line km of magnetic data obtained within the international collaboration for exploration of the cryosphere through aerogeophysical profiling promises to shed light on subglacial lithology and identify crustal boundaries for the central antarctic plate since the 1996 97 season the alfred wegener institute has collected 90 000 km of aeromagnetic data along a 1200 km long segment of the east antarctic coast over western dml recent cruises by australian german japanese russian british and american researchers have contributed to long standing studies of the antarctic continental margin along the continental margin of east antarctica west of maud rise to the george v coast of victoria land the russian polar marine geological research expedition and geoscience australia obtained 80 000 and 20 000 line km respectively of integrated seismic gravity and magnetic data additionally us expeditions collected 128 000 line km of shipborne magnetic data in the ross sea sector

egm_tim_rl05 an independent geoid with centimeter accuracy purely based on the goce mission after more than 4 5 years in orbit the gravity field and steady state ocean circulation explorer goce mission ended with the reentry of the satellite on 11 november 2013 this publication serves as a reference for the fifth gravity field model based on the time wise approach egm tim rl05 a global model only determined from goce observations due to its independence of any other gravity data a consistent and homogeneous set of spherical harmonic coefficients up to degree and order 280 corresponding to spatial resolution of 71 5 km on ground is provided including a full covariance matrix characterizing the uncertainties of the model the associated covariance matrix realistically describes the model quality it is the first model which is purely based on goce including all observations collected during the entire mission the achieved mean global accuracy is 2 4 cm in terms of geoid heights and 0 7 mgal for gravity anomalies at a spatial resolution of 100 km