iceberg calving flux and mass balance of the austfonna ice cap on nordaustlandet svalbard 1 satellite radar interferometry 60 mhz airborne ice penetrating radar data and visible band satellite imagery were used to calculate the velocity structure ice thickness and the changing ice marginal extent of austfonna 8000 km2 and 2500 km3 the largest ice cap in the eurasian arctic ice cap motion is generally less than about 10 m a 1 except where faster flowing curvilinear features with velocities of several tens to over 200 m a 1 are present most drainage basins of austfonna have undergone ice marginal retreat over the past few decades at an average of a few tens of meters per year integrating margin change around the whole ice cap gives a total area loss of about 10 km2 a 1 iceberg flux from the marine margins of austfonna is about 2 5 0 5 km3 a 1 water equivalent about 45 of the total calving flux from the whole svalbard archipelago when mass loss by iceberg production is taken into account the total mass balance of austfonna is negative by between about 2 5 and 4 5 km3 a 1 this iceberg flux represents about 33 5 of total annual mass loss from austfonna with the remainder lost through surface ablation iceberg flux should be included in calculations of the total mass balance of the many large arctic ice caps including those located in the russian and canadian arctic that end in tidewater the neglect of this term has led to underestimates of mass loss from these ice caps and thus to underestimates of the contribution of arctic ice caps to global sea level rise

secular gravity variation at svalbard norway from ground observations and grace satellite data the svalbard archipelago norway is affected by both the present day ice melting pdim and glacial isostatic adjustment gia subsequent to the last pleistocene deglaciation the induced deformation of the earth is observed by using different techniques at the geodetic observatory in ny alesund precise positioning measurements have been collected since 1991 a superconducting gravimeter sg has been installed in 1999 and six campaigns of absolute gravity ag measurements were performed between 1998 and 2007 moreover the gravity recovery and climate experiment grace satellite mission provides the time variation of the earth gravity field since 2002 the goal of this paper is to estimate the present rate of ice melting by combining geodetic observations of the gravity variation and uplift rate with geophysical modelling of both the gia and earth s response to the pdim we estimate the secular gravity variation by superimposing the sg series with the six ag measurements we collect published estimates of the vertical velocity based on gps and vlbi data we analyse the grace solutions provided by three groups csr gfz grgs the crux of the problem lies in the separation of the contributions from the gia and pdim to the earth s deformation to account for the gia we compute the response of viscoelastic earth models having different radial structures of mantle viscosity to the deglaciation histories included in the models ice 3g or ice 5g to account for the effect of pdim we compute the deformation of an elastic earth model for six models of ice melting extension and rates errors in the gravity variation and vertical velocity are estimated by taking into account the measurement uncertainties and the variability of the grace solutions and gia and pdim models the ground observations agree with models that involve a current ice loss of 25 km3 water equivalent yr 1 over svalbard whereas the space observations give a value in the interval 5 18 km3 water equivalent yr 1 a better modelling of the pdim which would include the precise topography of the glaciers and altitude dependency of ice melting is necessary to decrease the discrepancy between the two estimates

complex anisotropy in d beneath the eastern pacific from sks skks splitting discrepancies article i nfo although observations of seismic anisotropy in the lowermost mantle are abundant the mechanism which generates anisotropy in the d layer is not well understood most observational constraints on d anisotropy come from the splitting of shear waves that propagate nearly horizontally through the lowermost mantle however anisotropy in the d layer can also give rise to discrepancies in shear wave splitting for sks and skks phases for the same event station pair as these phases sample different regions of the lowermost mantle here i report observations of strongly discrepant sks skks splitting observed at broadband stations in western mexico and california in particular strong skks splitting with fast polarization directions near 60 and delay times up to 3 s is observed for a group of raypaths that sample a region of the d layer beneath the eastern pacific ocean a comparison of skks splitting with sks splitting observed from the same events as well as with sks splitting observed at a variety of backazimuths at each station suggests that the anomalous anisotropic structure is in the lowermost mantle my preferred model for the unusual anisotropic geometry in this region is large shear deformation in d at the edge of a region where slab material impinges upon the core mantle boundary resulting in lattice preferred orientation of lower mantle minerals

evaluating post perovskite as a cause of d anisotropy in regions of palaeosubduction seismic anisotropy in the earth s lowermost mantle d is often attributed to the alignment of mgsio3 post perovskite ppv by the movement of dislocations in response to mantle flow however ppv s plastic yield surface is not known nor do we know if this is the main deformation mechanism we make use of a heterogeneous generally anisotropic model of elasticity in d derived from a 3 d model of mantle flow which is obtained by inversion of geophysical observables unlike previous approaches completely general 3 d flow and full anisotropy are permitted yielding more information to compare with observations than has been possible before we model observations of anisotropy in d by calculating the shear wave splitting predicted in scs waves for a series of models of ppv plasticity we find that observations in regions of the lowermost mantle beneath subduction zones are best fit by a model which accommodates slip on 010 our results show that within one standard deviation slip on 010 or a mechanism giving the same style of anisotropy explains d anisotropy beneath these regions

small scale lateral variations in azimuthally anisotropic d structure beneath the cocos plate abstract shear waves from intermediate and deep focus south american events recorded by california broadband seismometers reveal complex anisotropy in the lowermost mantle scs waves densely sample the d region beneath the cocos plate just west of central america 1 16 n 267 277 e our data show evidence for significant near source anisotropy which we constrain for each event by performing polarization analyses on an expanded dataset of s waveforms scs waveforms are corrected for upper mantle and near source anisotropy and estimates of d anisotropy are made using the covariance method we find splits between fast and slow components of scs ranging from 0 4 to 2 5 s with an average of 1 6 s fast polarization directions in the southern portion of our study area are approximately orthogonal to the raypaths north of 7 latitude there is a rapid change in fast polarization direction to nearly raypath parallel beyond 10 latitude fast directions are more highly scattered than in southern regions past work in the region has inferred strong lateral variations in shear wave velocity but fairly uniform transverse isotropy in contrast our results indicate that the lowermost mantle beneath the cocos plate has azimuthal anisotropy that varies laterally over scales of 100 200 km in addition our data suggest connections between previously imaged topography on the d discontinuity and the character of anisotropy

antarctic mass rates from grace 1 we estimate mass trends over antarctica using gravity variations observed by the gravity recovery and climate experiment grace satellite mission during its first 3 5 years april 2002 november 2005 an image of surface mass trends is constructed from 1 1 pixels over the entire continent and shows two prominent features a region of mass loss along the coast of west antarctica and one of accumulation in east antarctica after adjusting for bias due to smoothing and to grace s limited spatial resolution and removing post glacial rebound pgr effects the rate in west antarctica is 77 14 km3 year similar to a recent estimate of ice mass loss from satellite altimetry and remote sensing data the prominent east antarctic feature in the enderby land region has a rate of 80 16 km3 year published snow ice mass rates from remote sensing measurements indicate approximate ice mass balance in this region suggesting that this feature is either from unquantified snow accumulation in this region or more likely due to unmodeled pgr

post processing removal of correlated errors in grace data 1 gravity fields produced by the gravity recovery and climate experiment grace satellite mission require smoothing to reduce the effects of errors present in short wavelength components as the smoothing radius decreases these errors manifest themselves in maps of surface mass variability as long linear features generally oriented north to south i e stripes the presence of stripes implies correlations in the gravity field coefficients here we examine the spectral signature of these correlated errors and present a method to remove them finally we apply the filter to a model of surface mass variability to show that the filter has relatively little degradation of the underlying geophysical signals we seek to recover

origin of seismic anisotropy in the d layer inferred from shear deformation experiments on post perovskite phase abstract seismic anisotropy is one of the significant features in the d layer of the earth and is thought to be derived from the lattice preferred orientation lpo of constituent materials or shape preferred orientation spo of heterogeneous materials such as melt and inclusions recent experimental and theoretical studies strongly suggest that the d layer consists mainly of a mgsio3 post perovskite phase together with ferro periclase to understand the anisotropy in the d layer we have conducted a series of simple shear deformation experiments at high temperature and pressure on polycrystalline cairo3 as an analogue of mgsio3 and measured the lpo of the post perovskite phase crystallographic orientation analysis of the deformed post perovskite phase showed strong lpos with the dominant slip system being 100 010 calculation of the elastic wave velocities considering the effect of lpos of post perovskite and ferro periclase showed as azimuthal and polarization anisotropies in the horizontal shear plane where the velocity of horizontally polarized s wave is considerably faster than that of vertically polarized s wave thus the seismic anisotropy observed in the d layer can be reasonably explained by the lpo of the mixture of post perovskite and ferro periclase where the lpo may result from the horizontal shear flow generated by the mantle convection

deformation in the lowermost mantle from polycrystal plasticity to seismic anisotropy in the deep earth deformation occurs at many scales large scale convection produces subduction of slabs and upwelling of plumes in the mantle at the high temperature high pressure conditions strain is accommodated through crystal plasticity either by diffusion or the movement of dislocations slip causes crystal rotations and thus produces a characteristic pattern of crystal preferred orientation and corresponding anisotropy of physical properties at the macroscopic scale in this study we use polycrystal plasticity with experimentally derived deformation mechanisms for perovskite post perovskite and magnesiowuestite to predict texture development along streamlines in a 2d geodynamic convection model of the lowermost mantle strong preferred orientation develops during subduction and upwelling while during spreading along the core mantle boundary the orientation pattern is relatively stable from preferred crystal orientation and single crystal elastic properties bulk elastic properties can be calculated and compared with seismic observations post perovskite with predominant 001 slip and magnesiowuestite with 110 and 111 slip produce anisotropy patterns which are consistent with observed anisotropy i e fast s waves polarized parallel to the core mantle boundary and anti correlation between p and s wave anisotropies in contrast perovskite with dominant 001 slip and two post perovskite models with dominant slip on 010 and 100 produce anisotropy patterns which are inconsistent with seismic observations

lowermost mantle anisotropy and deformation along the boundary of the african llsvp shear wave splitting of sk k s phases is often used to examine upper mantle anisotropy in specific cases however splitting of these phases may reflect anisotropy in the lowermost mantle here we present sks and skks splitting measurements for 233 event station pairs at 34 seismic stations that sample d beneath africa of these 36 pairs show significantly different splitting between the two phases which likely reflects a contribution from lowermost mantle anisotropy the vast majority of discrepant pairs sample the boundary of the african large low shear velocity province llsvp which dominates the lower mantle structure beneath this region in general we observe little or no splitting of phases that have passed through the llsvp itself and significant splitting for phases that have sampled the boundary of the llsvp we infer that the d region just outside the llsvp boundary is strongly deformed while its interior remains undeformed or weakly deformed

recent glacier mass changes in the gulf of alaska region from grace mascon solutions the mass changes of the gulf of alaska goa glaciers are computed from the gravity recovery and climate experiment grace inter satellite range rate data for the period april 2003 september 2007 through the application of unique processing techniques and a surface mass concentration mascon parameterization the mass variations in the goa glacier regions have been estimated at high temporal 10 day and spatial 2 2 arc degrees resolution the mascon solutions are directly estimated from a reduction of the grace k band inter satellite range rate data and unlike previous grace solutions for the goa glaciers do not exhibit contamination by leakage from mass change occurring outside the region of interest the mascon solutions reveal considerable temporal and spatial variation within the goa glacier region with the largest negative mass balances observed in the st elias mountains including the yakutat and glacier bay regions the most rapid losses occurred during the 2004 melt season due to record temperatures in alaska during that year the total mass balance of the goa glacier region was 84 5 gt a 1 contributing 0 23 0 01 mm a 1 to global sea level rise from april 2003 through march 2007 highlighting the large seasonal and interannual variability of the goa glaciers the rate determined over the period april 2003 march 2006 is 102 5 gt a 1 which includes the anomalously high temperatures of 2004 and does not include the large 2007 winter balance year snowfall the mascon solutions agree well with regional patterns of glacier mass loss determined from aircraft altimetry and in situ measurements

analysis of seismic sv waves in the core s penumbra vertically polarized s waves sv attenuate rapidly as they diffract around the earth s core whereas horizontally polarized s waves sh propagate to large distances in the core shadow zone the amplitude decay of diffracted sv signals is so strong that few studies have been made of these phases despite their acute sensitivity to velocity structure just above the core mantle boundary we analyze sv signals in the penumbra of the core s shadow finding systematic waveform complexities indicative of local stratification and apparent anisotropy at the base of the mantle with implications for the dynamic processes in this internal boundary layer

normal mode sensitivity to earth s d layer and topography on the core mantle boundary what we can and cannot see the core mantle boundary cmb is earth s most profound internal boundary separating the liquid iron outer core and the solid silicate mantle the detailed structure near the cmb has a major influence on mantle convection and the evolution of the core seismic observations such as topography on the cmb thin ultra low velocity zones ulvzs seismic anisotropy and the anticorrelation between shear wave and bulk sound velocity heterogeneities have mainly been made using body waves and are still poorly constrained we investigate the sensitivity of earth s free oscillations to these features and specifically show how large individual anomalies must be for them to be observable in addition we discuss the possible trade offs between these different lowermost mantle structures although modes have strong sensitivity to all the structures inserted the results illustrate the limits of what normal modes can resolve our tests show that i even small scale features such as ulvzs with a thickness larger than 19 km can be observed as long as their distribution contains a long wavelength component ii the peak to peak amplitude of cmb topography has a larger influence than its pattern and has to be smaller than 5 km to fit the data iii the effect of scaling between shear wave velocity and density anomalies is less constrained but a laterally varying pattern is implied by a simple test suggesting the presence of chemical variations iv a strong trade off exists between anisotropy in compressional wave velocity and incidence angle whereas shear wave anisotropy is less observable these findings provide valuable information for future normal mode studies on structures in earth s lowermost mantle and their trade offs

deformation and texture development in cairo3 post perovskite phase up to 6 gpa and 1300 k at near ambient conditions cairo3 is isostructural with the high pressure polymorph mgsio3 post perovskite ppv mgsio3 ppv is thought to be a major phase in the earth s lowermost mantle cairo3 can thus serve as an analog for studying deformation of the ppv phase under conditions achievable with a multi anvil deformation apparatus here we study the rheologic behavior of cairo3 ppv at a variety of pressure and temperature conditions from 2 gpa to 6 gpa and 300 k to 1300 k and various strain rates sintered polycrystalline cairo3 ppv cylindrical in shape was deformed in the d dia multi anvil press in several shortening cycles up to 20 axial strain at each temperature and pressure shortening cycles were followed by lengthening back to 0 strain quantitative texture information was obtained using in situ synchrotron x ray diffraction and the rietveld method to analyze images in all cases we find that 010 lattice planes align perpendicular to the compression direction upon shortening and that there is little change in texture with temperature or pressure this texture pattern is consistent with slip on 010 100 the texture observed here is different from that produced in room temperature diamond anvil cell dac experiments on mggeo3 and mgsio3 ppv which both display textures of 100 and 110 lattice planes at high angles to the compression direction this implies that cairo3 ppv may not be a good analog for the plastic behavior of mgsio3 ppv 2008 elsevier b v all rights reserved

the development of shape and crystallographic preferred orientation in capto3 post perovskite deformed in pure shear knowledge of the deformation mechanism of post perovskite is important for interpreting observed seismic anisotropy in terms of mantle flow experiments on post perovskite mgsio3 and the low pressure analog material cairo3 yield different textures leaving the interpretation of the observed seismic signatures unclear here we present results of deformation experiments on capto3 post perovskite that may be a better analog to mgsio3 post perovskite capto3 deforms by glide of 100 dislocations on the 010 plane consistent with previous experimental results on cairo3 in addition samples containing a weak minority phase also display shape preferred orientation with grains elongated in the crystallographic a direction forming a planar fabric perpendicular to the compression direction this shape preferred orientation strengthens the observed crystallographic preferred orientation and results in a rapid development of texture during deformation this observation supports the recent suggestion that the d reflector might be due to a rapid generation of texture in post perovskite furthermore the role of shape preferred orientation in generating seismic anisotropy in multi phase assemblages should be considered for the d assemblage

fabric transitions in quartz via viscoplastic self consistent modeling part i axial compression and simple shear under constant strain quartz is a common crustal mineral that deforms plastically in a wide range of temperatures and pressures leading to the development of different types of crystallographic preferred orientation cpo patterns in this contribution we present the results of an extensive modeling of quartz fabric transitions via a viscoplastic self consistent vpsc approach for that we have performed systematic simulations using different sets of relative critical resolved shear stress of the main quartz slip systems we have performed these simulations in axial compression and simple shear regimes under constant von mises equivalent strain of 100 1 73 assuming that the aggregates deformed exclusively by dislocation glide some of the predicted cpos patterns are similar to those observed in naturally and experimentally deformed quartz nevertheless some classical cpo patterns usually interpreted as result from dislocation glide e g y maxima due to prism slip are clearly not developed in the simulated conditions in addition we reported new potential preferred orientation patterns that might happen in high temperature conditions both in axial compression and simple shear we have demonstrated that cpos generated under axial compression are usually stronger that those predicted under simple shear due to the continuous rotation observed in the later simulations the fabric strength depends essentially on the dominant active slip system and normally the stronger cpos result from dominant basal slip in followed by rhomb and prism c slip whereas prism slip does not produce strong fabrics the opening angle of quartz 0001 fabric used as a proxy of temperature seems to be reliable for deformation temperatures of 400 c when the main slip systems have similar behaviors

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

a three dimensional radially anisotropic model of shear velocity in the whole mantle summary we present a 3 d radially anisotropic s velocity model of the whole mantle saw642an obtained using a large three component surface and body waveform data set and an iterative inversion for structure and source parameters based on non linear asymptotic coupling theory nact the model is parametrized in level 4 spherical splines which have a spacing of 8 the model shows a link between mantle flow and anisotropy in a variety of depth ranges in the uppermost mantle we confirm observations of regions with vsh vsv starting at 80 km under oceanic regions and 200 km under stable continental lithosphere suggesting horizontal flow beneath the lithosphere we also observe a vsv vsh signature at 150 300 km depth beneath major ridge systems with amplitude correlated with spreading rate for fast spreading segments in the transition zone 400 700 km depth regions of subducted slab material are associated with vsv vsh while the ridge signal decreases whilethemid mantlehasloweramplitudeanisotropy vsv in the lowermost 300 km which appears to be a robust conclusion despite an error in our previous paper which has been corrected here the 3 d deviations from this signature are associated with the large scale low velocity superplumes underthecentralpacificandafrica suggestingthatvsh vsv isgeneratedinthepredominant horizontal flow of a mechanical boundary layer with a change in signature related to transition to upwelling at the superplumes

the limits of ray theory when measuring shear wave splitting in the lowermost mantle with scs waves observations of shear wave splitting provide unambiguous evidence of the presence of anisotropy in the earth s lowermost mantle a region known as d much recent work has attempted to use these observations to place constraints on strain above the core mantle boundary cmb as this may help map flow throughout the mantle previously this interpretation has relied on the assumption that waves can be modelled as infinite frequency rays or that the earth is radially symmetric due to computational constraints it has not been possible to test these approximations until now we use fully three dimensional generally anisotropic simulations of scs waves at the frequencies of the observations to show that ray methods are sometimes inadequate to interpret the signals seen we test simple uniform models and for a d layer as thin as 50 km significant splitting may be produced and we find that recovered fast orientations usually reflect the imposed fast orientation above the cmb ray theory in these cases provides useful results though there are occasional notable differences between forward methods isotropic models do not generate apparent splitting we also test more complex models including ones based on our current understanding of mineral plasticity and elasticity in d the results show that variations of anisotropy over even several hundred kilometres cause the ray theoretical and finite frequency calculations to differ greatly importantly models with extreme mineral alignment in d yield splitting times not dissimilar to observations t 3 s suggesting that anisotropy in the lowermost mantle is probably much stronger than previously thought potentially 10 shear wave anisotropy or more we show that if the base of the mantle is as complicated as we believe future studies of lowermost mantle anisotropy will have to incorporate finite frequency effects to fully interpret observations of shear wave splitting

in situ measurement of texture development rate in cairo3 post perovskite the rate of crystallographic preferred orientation cpo development during deformation of post perovskite is crucial in interpreting seismic anisotropy in the lowermost mantle but the stability field of mgsio3 post perovskite prevents high strain deformation experiments being performed on it therefore to constrain the rate of cpo development in post perovskite we deformed cairo3 a low pressure analogue of mgsio3 post perovskite in simple shear at 3 2 gpa and 400 c to a shear strain of 0 81 from x ray diffraction patterns acquired during deformation we invert for cpo as a function of strain by comparing the cpo that develops with visco plastic self consistent vpsc models we constrain the critical resolved shear stresses crss of the non primary slip systems in cairo3 to be of order 6 times stronger than the primary 100 010 slip system this value is significantly less than has been assumed by previous studies and if applicable to mgsio3 implies that seismic anisotropy in the d layer develops slower than has previously been assumed

lowermost mantle anisotropy beneath the north pacific from differential s scs splitting summary seismic anisotropy is an important tool for studying the nature origin and dynamics of the lowermost mantle d we introduce differential s scs splitting as a tool for removing the effect of near source and near receiver anisotropy to estimate splitting accrued in the d region this is applicable to events recorded at epicentral distances between 60 and 85 near source anisotropy has often been ignored in previous studies of lowermost mantle anisotropy we apply differential s scs splitting to records from canadian national seismic network stations of western pacific earthquakes these sample the lowermost mantle beneath the north pacific the residual splitting in scs which we attribute to d shows lag times between 1 0 and 3 9 s given the near horizontal ray path of scs in d we interpret the recovered fast directions as the orientation of the fast shear wave in the plane defined by the vertical and transverse directions and observe a clearly non vti transverse isotropy with a vertical axis of symmetry style of anisotropy the largest population of results shows an approximately southeasterly dipping symmetry axis which we speculate might be explained by descending palaeoslab material being swept horizontally across the core mantle boundary towards an upwelling region beneath the central pacific non vti symmetry and the many possible contributions to d anisotropy from lower mantle minerals melt and subducted materials suggest that our understanding of the lowermost mantle could be greatly improved by trying to resolve a more general style of anisotropy

elastic anisotropy of d predicted from global models of mantle flow in order to test the hypothesis that seismic anisotropy in the lowermost mantle is caused by the development of a post perovskite lattice preferred orientation and that anisotropy can thus be used as a probe of the dynamics of the mantle s lower boundary layer an integrated model of texture generation in d is developed this is used to predict the elastic anisotropy of the lowermost mantle as probed by global anisotropic tomographic inversions the model combines the current 3d mantle flow field with simulations of the deformation of post perovskite polycrystalline aggregates different descriptions of single crystal plasticity can lead to model results which are anti correlated to each other in models where post perovskite deformation is accommodated by dislocations moving on 010 or 100 patterns of anisotropy are approximately correlated with the results of tomographic inversions on the other hand in models where dislocations move on 001 patterns of anisotropy are nearly anti correlated with tomographic inversions if all the seismic anisotropy in d extracted from global anisotropic inversions is due to the presence of a lattice preferred orientation in post perovskite in the lowermost mantle and if the results of the tomographic inversions are not strongly biased by the sampling geometries these results suggest that in contrast to ideas based on the 1d anisotropic signal deformation of post perovskite in the lowermost mantle may be accommodated by dislocations moving on 010 or 100 alternatively a significant portion of the anisotropic signal may be caused by mechanisms other than the alignment of post perovskite crystals

satellite gravity measurements confirm accelerated melting of greenland ice sheet using time variable gravity measurements from the gravity recovery and climate experiment grace satellite mission we estimate ice mass changes over greenland during the period april 2002 to november 2005 after correcting for the effects of spatial filtering and limited resolution of grace data the estimated total ice melting rate over greenland is 239 23 cubic kilometers per year mostly from east greenland this estimate agrees remarkably well with a recent assessment of 224 41 cubic kilometers per year based on satellite radar interferometry data grace estimates in southeast greenland suggest accelerated melting since the summer of 2004 consistent with the latest remote sensing measurements

alaskan mountain glacial melting observed by satellite gravimetry abstract we use satellite gravity measurements from the gravity recovery and climate experiment grace as an indication of mass change to study potential long term mountain glacial melting in southern alaska and west canada the first 3 5 yr of grace monthly gravity data spanning april 2002 november 2005 show a prominent glacial melting trend in the mountain regions around the gulf of alaska goa grace observed surface mass changes correlate remarkably well with available mass balance data at gulkana and wolverine two benchmark glaciers of the u s geological survey usgs although the grace signals are smaller in magnitude in addition terrestrial water storage tws changes estimated from an advanced land surface model show significant mass loss in this region during the same period after correcting for the leakage errors and removing tws contributions using model estimates we conclude that grace observed glacial melting in the goa mountain region is equivalent to 101 22 km 3 yr which agrees quite well with the assessment of 96 35 km 3 yr based on airborne laser altimetry data and is consistent with an earlier estimate based on the first 2 yr of grace data this study demonstrates the significant potentials of satellite gravity measurements for monitoring mountain glacial melting and regional climate change

modeling dislocations and plasticity of deep earth materials it is widely recognized that earth sciences were revolutionized when continental drift proposed by wegener in 1912 took the more comprehensive form of plate tectonics following the early suggestion of holmes hess proposed in the early sixties what missed to wegener s model a mechanism and a driving force i e the presence of large flows within the convecting mantle to evacuate the internal heat the earth appears now as a dynamic system dominated by flows and deformation processes almost everywhere convective flow in the liquid core which is the source of the earth magnetic field slow deformation of the hot viscous solid mantle and rigid brittle deformations of the cold crust understanding and modeling the deformation mechanisms of earth materials is thus one of the most important challenges of geophysics among the three large topics listed above we will focus on mantle convection only two scientific fields which developed approximately at the same time i e just before and just after the second world war meet here geophysics and materials science which aims at explaining how solids can deform see below mantle convection raises however some questions that are specific to this field although some very significant advances have been achieved recently on the experimental side see for instance karato and weidner 2008 most of these questions remain largely unsolved and at the limits of our capabilities it appears thus necessary to complement the usual experimentally based approach by a numerical multi scale modeling approach in order to increase the significance of our models this multi scale modeling must be based on the physics at the relevant scales see fig 1 and will

whole earth tomography from delay times of p pcp and pkp phases lateral heterogeneities in the outer core or radial anisotropy in the mantle we perform tomographic inversions of compressional wave travel time measurements in order to image the laterally varying radial anisotropy of p wave velocity in the entire mantle in order to achieve an adequate sensitivity to both horizontal and vertical p velocity throughout the mantle we include in our data set travel time measurements corresponding to ray paths of very different geometries specifically we use data associated with the phases p pcp core reflected and pkpbc pkp df core refracted all extracted from the bulletins of the international seismological centre 1964 1993 pcp pkpbc and pkpdf data are also sensitive to the topography of the core mantle boundary cmb and pkp only to the velocity structure of the earth s core these circumstances require that we also allow for cmb topographic anomalies as free parameters in our inversions and investigate the possibility of the existence of lateral heterogeneities in the outer core e g ritzwoller et al 1986 stevenson 1987 wahr and de vries 1989 vasco and johnson 1998 the solution models that we propose include alternatively a laterally heterogeneous outer core a radially anisotropic mantle or both so that trade offs between those features can also be evaluated we conclude that only minor and very localized radially anisotropic anomalies are present in the middle and lower mantle the most prominent being located in the deepest 400 km under the western pacific we find a discrepancy particularly evident by a comparison between different models of the cmb topography between the travel time measurements that are sensitive to the earth s core and those that are not we show that it is not possible to explain this discrepancy only in terms of radial anisotropy of the mantle and or lateral heterogeneity of the outer core

acceleration of greenland ice mass loss in spring 2004 in 2001 the intergovernmental panel on climate change projected the contribution to sea level rise from the greenland ice sheet to be between 0 02 and 0 09 m from 1990 to 2100 ref 1 however recent work has suggested that the ice sheet responds more quickly to climate perturbations than previously thought particularly near the coast here we use a satellite gravity survey by the gravity recovery and climate experiment grace conducted from april 2002 to april 2006 to provide an independent estimate of the contribution of greenland ice mass loss to sea level change we detect an ice mass loss of 248 36 km3 yr 1 equivalent to a global sea level rise of 0 5 0 1 mm yr 1 the rate of ice loss increased by 250 per cent between the periods april 2002 to april 2004 and may 2004 to april 2006 almost entirely due to accelerated rates of ice loss in southern greenland the rate of mass loss in north greenland was almost constant continued monitoring will be needed to identify any future changes in the rate of ice loss in greenland

patagonia icefield melting observed by gravity recovery and climate experiment grace 1 using recently released reprocessed gravity solutions from the gravity recovery and climate experiment grace we estimate the ice loss rate for the patagonia icefield pif of south america for the period april 2002 through december 2006 after postglacial rebound and hydrological effects are corrected the estimated rate is 27 9 11 km 3 year equivalent to an average loss of 1 6 m year ice thickness change if evenly distributed over the entire pif area the estimated contribution to global sea level rise is 0 078 0 031 mm year this is an independent confirmation of relatively large melting rate estimates from earlier studies employing topographic and cartographic data

constraints from seismic anisotropy on the nature of the lowermost mantle the d layer lies at the bottom of the earth s rocky mantle and separates it from the liquid metal alloy core this region extending from the core mantle boundary to a few hundred kilometres above fig 1 is geodynamically analogous to the more easily studied lithosphere at the top of the mantle the structure of d may reflect the style of lower mantle convection the nature of core mantle interaction and perhaps even the fate of subducting lithosphere1 observations of lithospheric seismic anisotropy have provided valuable insight into the nature of the upper mantle boundary layer but discussion of lower mantle seismic anisotropy has been somewhat contentious2 5 here we present evidence from seismic waves that have traversed the lowermost mantle beneath the caribbean region for a zone of seismic anisotropy below the d discontinuity which in this region lies 250 km above the core mantle boundary the anisotropy is most probably due to horizontal layering or aligned inclusions of a material with differing shear wave velocity if d is a graveyard for subducted lithosphere a plausible explanation of the anisotropy may be the contrast between cold lithospheric mantle and material that formerly constituted the oceanic crust which may have lower shear wave velocity owing to the presence of melt

spatial distribution of earthquake potential along the himalayan arc abstract to determine the spatial distribution of earthquake potential along the active himalayan arc we utilize gps measurements and earthquake data we derive horizontal velocity field and 2 d strain rates from a new set of 41 regional gps stations along with 446 published velocities we convert these strain rate tensors to geodetic moment rate build up within 24 contiguous segments and compare to the seismic moment rate release derived from a reassessed earthquake catalog of 900 years the geodetic to seismic moment rate ratio an indicator of stored strain energy varies from below unity to more than 50 in different segments the estimated geodetic moment rate ranges from 1 7 1018 nm yr to 10 2 1018 nm yr whereas the seismic moment rate ranges from 3 7 1016 nm yr to 5 1 1019 nm yr this variation between the geodetic and seismic moment rate corresponds to a moment deficit rate of 1 15 1017 nm yr to 7 97 1018 nm yr along various segments of the study region the above moment deficit rate provides an equivalent earthquake potential of magnitude 5 7 8 2 in different segments specifically the higher earthquake potential mw 8 0 corresponds to the segments in the central seismic gap and the northeast part of himalaya whereas the lower earthquake potential mw

measurements of time variable gravity show mass loss in antarctica using measurements of time variable gravity from the gravity recovery and climate experiment satellites we determined mass variations of the antarctic ice sheet during 2002 2005 we found that the mass of the ice sheet decreased significantly at a rate of 152 80 cubic kilometers of ice per year which is equivalent to 0 4 0 2 millimeters of global sea level rise per year most of this mass loss came from the west antarctic ice sheet

evaluating contributions to sk k s splitting from lower mantle anisotropy a case study from station dbic cote d ivoire measurements of seismic anisotropy constitute a very important tool for examining patterns of flow and mineral properties in the earth s mantle a popular strategy for gaining insight into upper mantle processes is to examine the splitting of sk k s phases and interpret them in terms of upper mantle anisotropy and deforma tion in such studies any contribution to splitting from anisotropy in the lower mantle is usually ignored here we present measurements of sks and skks splitting at global seismograph network station dbic in the cote d ivoire which exhibits a very unusual pattern of shear wave splitting the splitting pattern is dominated by null measurements over a wide range of back azimuths with non null measurements found over a very limited back azimuthal range we also identified examples of dis crepant sks skks splitting for the same event station pair splitting at dbic has previously been interpreted in terms of upper mantle anisotropy but we argue that this splitting pattern can best be explained by an apparently isotropic upper mantle with a contribution from anisotropy in the lower mantle likely in the d layer using station dbic as a case study we discuss the potential pitfalls in interpreting sks splitting measurements and suggest a set of best practices to decrease the like lihood of misinterpreting shear wave splitting results at a seismic station online material summary of events used in the study with their associated splitting parameters

svalbard glacier elevation changes and contribution to sea level rise 1 we compare satellite altimetry from the ice cloud and land elevation satellite icesat 2003 2007 to older topographic maps and digital elevation models 1965 1990 to calculate long term elevation changes of glaciers on the svalbard archipelago results indicate significant thinning at most glacier fronts with either slight thinning or thickening in the accumulation areas except for glaciers that surged which show thickening in the ablation area and thinning in the accumulation areas the most negative geodetic balances occur in the south and on glaciers that have surged while the least negative balances occur in the northeast and on glaciers in the quiescent phase of a surge cycle geodetic balances are related to latitude and to the dynamical behavior of the glacier the average volume change rate over the past 40 years for svalbard excluding austfonna and kvitoya is estimated to be 9 71 0 55 km3 yr 1 or 0 36 0 02 m yr 1 w equivalent for an annual contribution to global sea level rise of 0 026 mm yr 1 sea level equivalent

some comments on the effects of lower mantle anisotropy on sks and skks phases anisotropy in the lowermost few 100 km of mantle or d region is indicative of deformation induced alignment of crystals and or inclusions of material and as such offers insights into the dynamic nature of this region observations of shear wave splitting in phases that transit this region provide constraints on such anisotropy we investigate the effects of lower mantle seismic anisotropy on sks and skks phases through linked effective medium modelling and ray based waveform modelling a mantle with vertical transverse isotropy vti will not produce any splitting in such core phases instead we consider the effects of azimuthal anisotropy due to aligned disk shaped and tubular inclusions and aligned perovskite periclase and columbite models are constructed subject to constraints imposed by observed anisotropy 3 and plausible variations in aggregate isotropic velocities 2 5 melt filled inclusions are much more effective in generating anisotropy than solid filled inclusions and disk shaped inclusions produce more anisotropy than tubular inclusions in general the degree of splitting produced by most of the models is small similar to that produced by the crust 0 5 s the exceptions are melt filled vertically aligned disk shaped inclusions and horizontally aligned periclase the former most likely in low velocity regions the latter in high velocity regions both models produce splitting significant enough to mask the effects of upper mantle anisotropy strong azimuthal variations in splitting and discrepancies in sks and skks splitting are diagnostic of these anisotropic models 2004 published by elsevier b v

the anisotropic signal of topotaxy during phase transitions in d abstract while observations and modelling of seismic anisotropy in the lowermost mantle offers the possibility of imaging mantle flow close to the core mantle boundary current models do not explain all observations here we seek to explain a long wavelength pattern of shear wave anisotropy observed in anisotropic tomography where vertically polarised shear waves travel faster than horizontally polarised shear waves in the central pacific and under africa but this pattern is reversed elsewhere in particular we test an explanation derived from experiments on analogues which suggest that texture may be inherited during phase transitions between bridgmanite perovskite structured mgsio3 and post perovskite and that such texture inheritance may yield the long wavelength pattern of anisotropy we find that models that include this effect correlate better with tomographic models than those that assume deformation due to a single phase in the lowermost mantle supporting the idea that texture inheritance is an important factor in understanding lowermost mantle anisotropy it is possible that anisotropy could be used to map the post perovskite stability field in the lowermost mantle and thus place constraints on the temperature structure above the core mantle boundary

grace observes small scale mass loss in greenland using satellite gravity data between february 2003 and january 2008 we examine changes in greenland s mass distribution on a regional scale during this period greenland lost mass at a mean rate of 179 25 gt yr equivalent to a global mean sea level change of 0 5 0 1 mm yr rates increase over time suggesting an acceleration of the mass loss driven by mass loss during summer the largest mass losses occurred along the southeastern and northwestern coast in the summers of 2005 and 2007 when the ice sheet lost 279 gt and 328 gt of ice respectively within 2 months in 2007 a strong mass loss is observed during summer at elevations above 2000 m for the first time since the start of the observations

seismic anisotropy in the d layer we present observations of diffracted sv svd for a path between the fiji tonga islands and the eastern coast of north america at distances greater than 110 observed features of s diffracted suggest that coupling between svd and shd can be ruled out as a first order effect for this path arrivals of shd are late relative to iasp91 travel times by about 10 s and those of svd are late relative to shd by 3 s for most records the slope of the log svd shd spectral ratio is around 3hz 1 in the range 0 06 0 15 hz a transversely isotropic low velocity layer in the lowermost mantle with a thickness of 200 300 km may account for most of the observed properties of svd

outer core density heterogeneity and the discrepancy between pkp and pcp travel time observations 1 we derive 3 d tomographic maps of the earth s mantle cmb and outer core from seismic p pcp pkpbc pkpdf travel time data based on the bulletins of the international seismological centre 1964 1995 after source relocation by antolik et al 2001 and phase re identification by engdahl et al 1998 maps of the cmb derived independently from core reflected pcp or core refracted pkp phases are not well correlated we attempt to explain this discrepancy and study the radial coherence of whole earth tomographic images to identify possible trade offs between cmb undulations and velocity anomalies in the mantle or outer core imaged velocity anomalies in the lowermost mantle are anticorrelated with the topography of the cmb likewise imaged lateral heterogeneities in the outer core are correlated with the topography of the cmb this together with the study of piersanti et al 2001 suggests that the core anomalies might not be entirely fictitious

lowermost mantle anisotropy beneath the northwestern pacific evidence from pcs scs sks and skks phases 1 in this study we utilize data from broadband seismic stations of the japanese f net network to investigate anisotropic structure in the lowermost mantle beneath the northwestern pacific the comparison of shear wave splitting from phases that have similar paths in the upper mantle but different paths in the lowermost mantle such as pcs scs or sks skks can yield constraints on anisotropy in the d region we measured splitting for sks skks pcs and scs phases at f net stations and compared the measured splitting parameters to previously published estimates of upper mantle anisotropy beneath the region we observed many examples of discrepant sks skks splitting and splitting of scs pcs sks and skks phases that does not agree well with the known upper mantle anisotropy beneath individual stations the most likely explanation for these discrepancies is a contribution to splitting from anisotropy in the lowermost mantle in particular for sks skks phases that sample the lowermost mantle just to the south and east of the kamchatka peninsula we observed generally n s fast directions with delay times between 0 5 and 1 5 s these data suggest the presence of a fairly large coherent region of deformation in the lowermost mantle beneath the northwestern pacific our preferred model for these observations is that solid state flow at the base of the mantle induces a lattice preferred orientation of lowermost mantle minerals generating a seismically anisotropic fabric

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

present rate of uplift in fennoscandia from grace and absolute gravimetry abstract fennoscandia is a key region for studying effects of glacial isostatic adjustment the associated mass variations can be detected by the gravity recovery and climate experiment grace satellite mission which observes the earth s gravity field since april 2002 as well as by absolute gravimetry field campaigns since 2003 annual absolute gravity ag measurements have been performed in fennoscandia by the institut fur erdmessung ife institute of geodesy of the leibniz universitat hannover germany within a multi national cooperation this offers a unique opportunity for validation and evaluation of the grace results in this preliminary study the grace results are compared to secular gravity changes based on the surveys from 2004 to 2007 with the fg5 220 gravimeter of the ife the results from grace monthly solutions provided by different analysis centres show temporal gravity variations in fennoscandia the included secular variations are in good agreement with former studies the uplift centre is located west of the bothnian bay the whole uplift area comprises northern europe nevertheless the differences between the grace solutions are larger than expected and the different centre specific processing techniques have a very strong effect on possible interpretations of grace results the comparison of grace to the ag measurements reveals that the determined trends fit well with results from grace at selected stations especially for the solution provided by the gfz variations of land hydrology clearly influence results from grace and the ag measurements

predictions of vertical uplift caused by changing polar ice volumes on a viscoelastic earth measurements of crustal uplift from bedrock around the edges of antarctica or greenland could help constrain the mass balance of those ice caps present day changes in ice could cause vertical displacement rates of several mm yr around antarctica and up to 10 15 mm yr around greenland horizontal displacement rates are likely to be about 1 3 the vertical rates the viscoelastic response of the earth to past changes in ice could cause uplift rates that are several times larger by measuring both gravity and vertical displacements it is possible to remove the viscoelastic effects so that the observations can be used to constrain present day thickness changes

synthetic seismic anisotropy models within a slab impinging on the core mantle boundary the lowermost few hundreds of kilometres of the earth s mantle are elastically anisotropic seismic velocities vary with direction of propagation and polarization observations of strong seismic anisotropy correlate with regions where subducted slab material is expected in this study we evaluate the hypothesis that crystal preferred orientation cpo in a slab as it impinges on the core mantle boundary is the cause of the observed anisotropy next we determine if fast polarization directions seen by shear waves can be mapped to directions of geodynamic flow this approach is similar to our previous study performed for a 2 d geodynamic model in this study we employ a 3 d geodynamic model with temperature dependent viscosity and kinematic velocity boundary conditions defined at the surface of the earth to create a broad downwelling slab tracers track the deformation that we assume to be accommodated by dislocation creep we evaluate the models for the presence of perovskite or post perovskite and for different main slip systems along which dislocation creep may occur in post perovskite 100 010 and 001 resulting in four different mineralogical models of cpo combining the crystal pole orientations with single crystal elastic constants results in seismically distinguishable models of seismic anisotropy the models are evaluated against published seismic observations by analysing different anisotropic components the radial anisotropy the splitting for sub vertical phases i e azimuthal anisotropy and the splitting for subhorizontal phases the patterns in radial anisotropy confirm our earlier results in 2 d observations of radial anisotropy and splitting in subhorizontal phases are mostly consistent with our models of post perovskite with 010 slip and 001 slip our model of 001 slip predicts stronger splitting than for 010 slip for horizontally propagating phases in all directions the strongest seismic anisotropy in this model occurs where the slab impinges on the core mantle boundary the azimuthal anisotropy pattern for 001 slip shows fast axis directions at the edges of the slab sub parallel to flow directions suggesting horizontal flows may be mapped out in the lowermost mantle using seismic observations

on the increase in thermal diffusivity caused by the perovskite to post perovskite phase transition and its implications for mantle dynamics the thermal diffusivity of perovskite and post perovskite cairo3 has been measured at elevated pressure and temperatures up to 600 c using the x radiographic angstrom method at high temperatures we find that the thermal diffusivity of post perovskite is slightly below twice that of isochemical perovskite over the temperature range investigated assuming a similar effect occurs in mgsio3 post perovskite the effect of the contrasting thermal transport properties between perovskite and post perovskite on mantle dynamics has been investigated using simple two dimensional convection models these show a reduction in extent and increase in depth of post perovskite lenses as well as increased core mantle boundary heat flux broader upwellings and more vigorous downwellings when compared to the reference constant a case

inferences on flow at the base of earth s mantle based on seismic anisotropy we applied global waveform tomography to model radial anisotropy in the whole mantle we found that in the last few hundred kilometers near the core mantle boundary horizontally polarized s wave velocities vsh are on average faster by 1 than vertically polarized s wave velocities vsv suggesting a large scale predominance of horizontal shear this confirms that the d region at the base of the mantle is also a mechanical boundary layer for mantle convection a notable exception to this average signature can be found at the base of the two broad low velocity regions under the pacific ocean and under africa often referred to as superplumes where the anisotropic pattern indicates the onset of vertical flow

strong inheritance of texture between perovskite and post perovskite in the d layer flow in the deep mantle is thought to create textures in the high pressure mineral post perovskite laboratory simulations of the transformation between lower pressure perovskite and post perovskite show that post perovskite can also inherit textures from the perovskite phase and vice versa

weakening of calcium iridate during its transformation from perovskite to post perovskite magnesium silicate perovskite the dominant mineral in the lower mantle is thought to transform into a post perovskite phase in the mantle s lowermost region laboratory experiments suggest substantial weakening could occur during the transformation from perovskite to post perovskite which could explain the anomalous physical properties of the lowermost mantle

efficacy of the post perovskite phase as an explanation for lowermost mantle seismic properties constraining the chemical rheological and electromagnetic properties of the lowermost mantle d is important to understand the formation and dynamics of the earth s mantle and core to explain the origin of the variety of characteristics of this layer observed with seismology a number of theories have been proposed including core mantle interaction the presence of remnants of subducted material and that d is the site of a mineral phase transformation this final possibility has been rejuvenated by recent evidence for a phase change in mgsio3 perovskite thought to be the most prevalent phase in the lower mantle at near core mantle boundary temperature and pressure conditions here we explore the efficacy of this post perovskite phase to explain the seismic properties of the lowermost mantle through coupled ab initio and seismic modelling of perovskite and post perovskite polymorphs of mgsio3 performed at lowermost mantle temperatures and pressures we show that a post perovskite model can explain the topography and location of the d discontinuity apparent differences in compressional and shear wave models and the observation of a deeper weaker discontinuity furthermore our calculations show that the regional variations in lower mantle shear wave anisotropy are consistent with the proposed phase change in mgsio3 perovskite

lowermost mantle flow at the eastern edge of the african large low shear velocity province abstract observations of seismic anisotropy in the lowermost mantle are plentiful but their interpretation in terms of mantle flow remains challenging here we interrogate the anisotropic structure of the lowermost mantle beneath the afar region just outside the edge of the african large low shear velocity province using a combination of shear wave splitting techniques applied to phases propagating at five distinct raypath orientations we then model the resulting data set by testing various candidate mechanisms for anisotropy the observations are best fit by a model that invokes the lattice preferred orientation lpo of post perovskite with the 100 crystallographic axis oriented either nearly vertically or highly obliquely to the horizontal plane plausible corresponding mantle flow scenarios involve a significant vertical flow component which suggests that the african large low shear velocity province edge may deflect ambient mantle flow upwards or may be associated with a sheet like upwelling

acceleration in thinning rate on western svalbard glaciers 1 geodetic measurements indicate that a number of glaciers in western svalbard ranging in size from 5 1000 km2 are losing mass at an accelerating rate the average thinning rate for midtre lovenbreen the glacier with the best data coverage has increased steadily since 1936 thinning rates for 2003 2005 are more than 4 times the average for the first measurement period 1936 1962 and are significantly greater than presented previously on slakbreen thinning rates for the latest measurement period 1990 2003 are more than 4 times that of the period 1961 1977 thinning of several glaciers along a previously measured airborne lidar profile in wedel jarls land has also increased doubling between the period 1990 1996 and 1996 2002 our results imply an increased sea level contribution from svalbard in addition the mass loss is an important influence on measured rates of rebound on western svalbard and should be factored into analysis of grace results

transformation textures in post perovskite understanding mantle flow in the d layer of the earth 1 deformation and texture formation in mg fe sio3 post perovskite ppv is a potential explanation for the strong seismic anisotropy that is found in the d layer of the earth however different experimental approaches have resulted in different lattice preferred orientations lpo in deformed ppv that have led to ambiguity in the interpretation of deformation in the lowermost mantle here we show that deformation of the analogue substance cairo3 during a phase transformation from perovskite to ppv leads to a transformation texture that differs from the cairo3 ppv deformation texture but resembles the results from ppv deformation experiments in diamond anvil cells assuming material spreading parallel to the core mantle boundary our results predict a widespread shear wave splitting with fast horizontal s waves which is compatible with seismic studies downwelling material that undergoes a phase transformation may develop a transformation texture that would locally result in vertically polarized fast s waves

constraining hydrological and cryospheric mass flux in southeastern alaska using space based gravity measurements 1 watersheds draining into the gulf of alaska goa experience large seasonal and inter annual variations of water in the form of rain snow and ice but accurate constraints on these variations have been difficult to obtain over larger geographic regions water variations can be inferred directly from the gravity recovery and climate experiment grace data however because goa variations occur over such a small region the inferred average value of water flux increases as the applied smoothing of the grace data decreases we use this observed scaling together with scaling results obtained from forward models to infer a seasonal amplitude of 115 20 km3 of water and an average contribution to sea level rise over the two years of data of 0 31 0 09 mm yr these results suggest that accelerated melting that began in the late 1990s as inferred from altimetry continues unabated

new developments in deformation experiments at high pressure although the importance of rheological properties in controlling the dynamics and evolution of the whole mantle of earth is well recognized experimental studies of rheological properties and deformation induced microstructures have mostly been limited to low pressure conditions this is mainly a result of technical limitations in conducting quantitative rheological experiments under high pressure conditions a combination of factors is changing this situation increased resolution of composition and configuration of earth s interior has created a greater demand for well resolved laboratory measurement of the effects of pressure on the behavior of materials higher strength materials have become readily available for containing high pressure research devices and new analytical capabilities in particular very bright synchrotron x ray sources are now readily available to high pressure researchers one of the biggest issues in global geodynamics is the style of mantle convection and the nature of chemical differentiation associated with convectional mass transport although evidence for deep mantle circulation has recently been found through seismic tomography e g van der hilst et al 1997 complications in convection style have also been noted they include 1 significant modifications of flow geometry across the mantle transition zone as seen from high resolution tomographic studies fukao et al 1992 masters et al 2000 van der hilst et al 1991 and 2 complicated patterns of flow in the deep lower mantle 1500 2500 km perhaps caused by chemical heterogeneity kellogg et al 1999 van der hilst and karason 1999 these studies indicate that while large scale circulation involving the whole mantle no doubt occurs significant deviations from simple flow geometry are also present two mineral properties have strong influence on convection 1 density and 2 viscosity rheology contrasts in the past the effects of density contrast have been emphasized honda et al 1993 kellogg et al 1999 tackley et al 1993 and the influence of