joint inversions of seismic and geodynamic data for models of three dimensional mantle heterogeneity the seismic models of three dimensional 3 d mantle heterogeneity may be interpreted in terms of the density perturbations which drive mantle flow and thus provide important predictions of flow related observables such as the nonhydrostatic geoid the current models of global scale shear velocity heterogeneity provide reasonably good fits to the long wavelength nonhydrostatic geoid data 60 70 variance reductions but rather poor fits to the corresponding free air gravity anomalies 30 40 variance reductions this major difference is due to two factors 1 the very different amplitude spectrum of the gravity anomalies which is nearly flat for degrees l 3 the largest mismatch between the pattern of predicted and observed gravity anomalies is in the southern hemisphere this observation suggests that one reason for the poor overall match between the two fields may be that the global seismic data are not resolving sufficiently well the heterogeneity in the southern hemisphere portion of the deep mantle in contrast the gravity data provide accurate and geographically uniform constraints on the vertically integrated heterogeneity in the mantle we therefore perform a series of experiments in which we simultaneously invert a large set of seismic data which includes long period waveforms ss s and scs s differential travel times and normal mode structure coefficients and the long wavelength gravity anomaly data we thus determine whether it is possible to derive new 3 d heterogeneity models which satisfy both data sets the gravity anomaly data are interpreted in the context of spherically symmetric viscous flow models of the mantle in these inversion experiments we test several radial viscosity and ln ln profiles and thereby assess their plausibility the joint seismic geodynamic inversions reveal that it is indeed possible to greatly improve the fit to the free air gravity anomalies with variance reductions of 80 90 readily accessible while preserving the fit to the seismic data this improvement is achieved with some adjustment to the heterogeneity in the depth range 1500 2500 km where the seismic data constraints appear to be weakest the joint inversions also reveal new structures in the southern hemisphere portion of the lower mantle which apparently are not resolved by the seismic data alone

uppermost inner core seismic structure new insights from body waveform inversion abstract differential travel times and waveforms of pkikp and pkikp phases in the 129 141 distance range deconvolved for the effects of source time functions and average mantle attenuation operators are inverted for velocity and attenuation in the uppermost 80 km of the inner core and the velocity gradient and attenuation in the lowermost 200 km of the outer core f region results confirm degree one velocity structure in the inner core whose fast and slow regions appear to be separated by transitions with a velocity contrast of about 1 although attenuation in the inner core also exhibits degree one pattern a high attenuation region q p 1 0 002 0 0067 extends to the central pacific which has been previously considered a part of the western hemisphere characterized by slower velocity and lower attenuation the rest of the inner core exhibits a positive correlation between velocity and attenuation as observed previously an observed mantle like relationship between velocity and attenuation in the central pacific can be interpreted as originating from higher than average homologous temperature consistent with a model of inner core solidification driven by outer core convection coupled to core mantle boundary thermal heterogeneity alternative mechanisms including differences in grain size and impurity concentration and lateral differences in solidification rate might be required to explain the structure of the inner core the f region velocity and attenuation are best explained by the ak135 f velocity model and q p 1 0 0 001 respectively

applying deep learning for identifying bioturbation from core photos advances and availability of deep learning software have recently allowed the development testing and deployment of automated image classification schemes for sedimentary features from core images the development of these methods is especially relevant for extracting useful geological features from otherwise unused core photos this paper demonstrates and tests the use of a deep learning workflow for the automated extraction of bioturbation data from a core photo dataset the proposed workflow includes extracting image tiles from core photos along a grid and referencing each tile with collected sedimentary data each labeled image tile is then used as a training and testing input for a machine learning algorithm this method allows users to quickly generate thousands of labeled training images to demonstrate and test this workflow a dataset collected using pychno an open source software specifically designed to collect sedimentary data from core photos the resulting dataset comprising 13 545 tiles of 128x128 pixel resolution is used to train a deep learning algorithm to automatically predict if a core photo contains evidence of bioturbation the trained model was able to predict whether or not an image demonstrated evidence of bioturbation with up to 88 accuracy the workflow demonstrates one of many possible applications for automatically extracting biogenic or physical sedimentary structure data from core photos models built using this approach can be used to seed wells from a given area or interval which can therefore significantly increase the value of core photo datasets with relative ease

latest spin on the core during the 1990s evidence has emerged from seismic data that the earth s inner core may be rotating slightly faster than the mantle and crust estimates of the rate have been as high as 3 per year the conclusion of the latest study however is that there is no or very little differential rotation

axial and equatorial rotations of the earth s cores associated with the quaternary ice age abstract the differential axial and equatorial rotations of both cores associated with the quaternary glacial cycles were evaluated based on a realistic earth model in density and elastic structures the rheological model is composed of compressible maxwell viscoelastic mantle inviscid outer core and incompressible maxwell viscoelastic inner core the present study is however preliminary because i assume a rigid rotation for the fluid outer core in models with no frictional torques at the boundaries of the outer core the maximum magnitude of the predicted axial rotations of the outer and inner cores amounts to 2 year 1 and 1 year 1 respectively but that for the secular equatorial rotations of both cores is 0 0001 at most however oscillating parts with a period of 225 years are predicted in the equatorial rotations for both cores then i evaluated the differential rotations by adopting a time dependent electromagnetic em torque as a possible coupling mechanism at the core mantle boundary cmb and inner core boundary icb in a realistic radial magnetic field at the cmb estimated from surface magnetic field the axial and equatorial rotations couple through frictional torques at the cmb although these rotations decouple for dipole magnetic field model the differential rotations were evaluated for conductivity models with a conductance of 10 8 s of the lowermost mantle inferred from studies of nutation and precession of the earth and decadal variations of length of day lod the secular parts of equatorial rotations are less sensitive to these parameters but the magnitude for the axial rotations is much smaller than for frictionless model these models however produce oscillating parts in the equatorial rotations of both cores and also in the axial rotations of the whole earth and outer and inner cores these oscillations are sensitive to both the magnitude of radial magnetic field at the cmb and the conductivity structure no sharp isolated spectral peaks are predicted for models with a thin conductive layer 200 m at the bottom of the mantle in models with a conductive layer of 100 km thickness however sharp spectral peaks are predicted at periods of 225 and 25 years for equatorial and axial rotations respectively although these depend on the strength of radial magnetic field at the cmb while the present study is preliminary in modelling the fluid outer core and coupling mechanism at the cmb the predicted axial rotations of the whole earth may be important in explaining the observed lod through interaction between the equatorial and axial rotations

is the rotation real earth9s interior consists of a mantle liquid core and at the very center a solid inner core made of iron one of the inner core9s most peculiar properties is its anisotropy seismic waves travel slightly faster if they are parallel to earth9s rotation axis in her perspective souriau describes recent seismic studies that suggest the inner core rotates faster than earth9s mantle and comments on the current dilemma in interpreting the experimental findings

shoreline response to autogenic processes of sediment storage and release in the fluvial system 1 experimentally determined shoreline migration rates show high frequency autogenic variability superimposed on low frequency allogenic shoreline responses induced by eustatic base level change this variability persists even when the shoreline migration is averaged laterally indicating time variation in total sediment discharge reaching the shoreline the magnitude of autogenic variability in shoreline migration rate changes by roughly a factor of 3 depending on the shoreline migration direction it is strongest during transgression when the shoreline is on average migrating against the mean sediment flow and weakest during regression when the shoreline is migrating with the mean sediment flow we propose that this time variation is due to overall sediment storage and release in the fluvial system we use a one dimensional geometric model to model the autogenic signals observed in the experiment the model uses small periodic changes in the fluvial slope to represent the effects of storage and release of supplied sediment due to intrinsic variation in the transport efficiency of the fluvial system the periodic pulses of sediment discharge to the shoreline required in the model to explain the variations in shoreline migration can exceed by an order of magnitude the mean allogenic sediment discharge the slope variability required in the model to explain the autogenic shoreline signals is 1 4 of the mean slope this is well within the range of observed variability in depositional fluvial slopes we propose that at least part of this observed variability is real that is the long profile slope of a depositional river system may have an intrinsic elasticity of a few percent of its mean value even under steady forcing autogenic slope variation of this magnitude could readily produce parasequence scale deposits in the stratigraphic record

on the viscosity and creep mechanism of earth s inner core 1 the viscosity and creep mechanism of earth s inner core are evaluated based on microphysical models of the flow properties of iron under high pressure and temperature low stress and large grain size harper dorn creep a newtonian viscous dislocation mechanism is shown to be the likely deformation process and the viscosity is predicted to be 1011 pa s at the low end of previous estimates such a low viscosity implies that the inner core can adjust its shape to maintain alignment with the gravitational field imposed by the mantle on a timescale of approximately one minute it also implies that strain sufficient to produce significant lattice preferred orientation could develop in a few years to a few hundred years which suggests that seismic anisotropy of the inner core is the product of active deformation and has no memory of primary crystallization

inner core anisotropy and heterogeneity level an analysis of core phase travel times is performed in order to estimate the relative contributions of heterogeneities and anisotropy and their distribution inside the inner core a stochastic analysis performed on the equatorial paths which are poorly sensitive to anisotropy indicates that the inner core exhibits a heterogeneity level smaller than 0 3 at all depths on scale lengths larger than 200 km this result extended to all path orientations suggests a predominant effect of the anisotropy on travel times anomalies a simultaneous inversion of absolute and differential core phase travel times for any path orientation favours a simple inner core model in which a large homogeneous structure with 3 uniform anisotropy is asymmetrically surrounded by a homogeneous isotropic layer with a thickness of 100 200 km on the western hemisphere increasing to 400 km over a large part of the eastern hemisphere

vegetation driven morphodynamic adjustments of a sand bed vegetation is ubiquitous in riverine and coastal environments but the physics governing morphodynamic interactions modulated by vegetation are still poorly understood here we use a simple experiment to study the impact of a vegetated patch on the morphodynamics of a sand bed we show that the vegetation patch reduces the sediment transport capacity of the flow and that the topography responds to this by an increase of the bed slope to accommodate the upstream sediment supply final bed slope and adjustment time scale depend on the ratio between the grain related shear stress and the total shear stress this demonstrates the mechanisms underlying a direct morphodynamic response to the presence of a vegetation patch

internal loading of an inhomogeneous compressible earth with phase boundaries summary we use an approach described by dehant wahr 1991 to estimate the geoid and boundary topography caused by mass loads inside the earth we show how the estimates are affected by compressibility and a radially varying density distribution and by the presence of phase boundaries with density discontinuities we compare results for earth models that have a chemical boundary at 670 km depth with those that have a phase boundary at that depth we find that the 670 km topographies predicted for models with a chemical boundary are several times larger than for models with a phase boundary depending principally on the value of the clapeyron slope in the phase case the geoid predicted in the chemical boundary case is about 30 40 per cent smaller than that predicted in the phase case the effects of compressibility and radially varying density are likely to be small we estimate the laterally varying structure inside the fluid core by computing the topography on constant potential surfaces within the core we conclude that this structure is not likely to be a complicating factor when using nutation and earth tide observations to estimate the flattening of the core mantle boundary finally we compute the inner core outer core icb topography for loading inside the mantle and for loading inside the inner core we show that in the first case the icb topography is small and dominated by long wavelengths in the second case we conclude that if the density heterogeneities inside the inner core are two orders of magnitude smaller than in the mantle the icb topography can be about 100 m peak to peak

significant effect of sediment cohesion on delta morphology delta morphology is thought to be controlled by factors such as river discharge tides and waves numerical modelling shows that sediment cohesion also strongly influences the development of a delta s characteristics the morphologies of the world s deltas are thought to be determined by river discharge tidal range and wave action 1 more recently sea level rise 2 3 and human engineering4 have been shown to shape delta evolution the effects of factors such as sediment type and the overall amount of sediment carried by rivers are considered secondary4 5 6 in particular the role of sediment cohesion which is controlled by sediment size and type of vegetation is unclear here we use a numerical flow and transport model7 8 9 10 to show that sediment cohesiveness also strongly influences the morphology of deltas we find that holding all other factors constant highly cohesive sediments form bird s foot deltas with rugose shorelines and highly complex floodplains whereas less cohesive sediments result in fan like deltas with smooth shorelines and flat floodplains in our simulations sediment cohesiveness also controls the number of channels that form within the deltas and the average angle of bifurcation of those channels as vegetation generally acts as a cohesive agent we suggest that deltas that formed before the expansion of land plants in the devonian period should show fan like characteristics a finding consistent with the limited data from the sedimentological record11

anomalously strong observations of pkikp pcp amplitude ratios on a global scale the inner core boundary marks the phase transition between the solid inner core and the fluid outer core as the site of inner core solidification the boundary provides insight into the processes generating the seismic structures of the inner core in particular it may hold the key to understanding the previously observed hemispherical asymmetry in inner core seismic velocity anisotropy and attenuation here we use a large pkikp pcp amplitude ratio and travel time residual data set to investigate velocity and density contrast properties near the inner core boundary although hemispherical structure at the boundary has been proposed by previous inner core studies we find no evidence for hemispheres in the amplitude ratios or travel time residuals in addition we find that the amplitude ratios are much larger than can be explained by variations in density contrast at the inner core boundary or core mantle boundary this indicates that pkikp is primarily observed when it is anomalously large due to focusing along its raypath using data in which pkikp is not detected above the noise level we calculate an upper estimate for the inner core boundary icb density contrast of 1 2 kg m 3 the travel time residuals display large regional variations which differ on long and short length scales these regions may be explained by large scale velocity variations in the f layer just above the inner core boundary and or small scale topography of varying magnitude on the icb which also causes the large amplitudes such differences could arise from localized freezing and melting of the inner core

sediment transport and shear stress partitioning in a vegetated flow vegetation is a common feature in natural coastal and riverine water ways interacting with both the water flow and sediment transport however the physical processes governing these interactions are still poorly understood which makes it difficult to predict sediment transport and morphodynamics in a vegetated environment we performed a simple experiment to study how sediment transport responds to the presence of flexible single blade vegetation and how this response is influenced by the vegetation density we found that the skin friction and sediment transport are reduced in a plant patch and that this effect is larger for denser vegetation we then evaluated several methods to calculate the skin friction in a vegetated flow which is the key to sediment transport prediction among these the inversion of bed load transport formulas and the einstein and banks 1950 methods appeared to produce the most reasonable values of the skin friction finally we suggest using the parameter which is the ratio of the skin friction computed by these methods to the total bed shear stress to make more realistic sediment transport predictions in morphodynamic models

coupled dynamics of earth s geomagnetic westward drift and inner core super rotation this phd work focuses on the rotational dynamics of the coupled inner core outercore mantle system the conservation of the angular momentum our coupled earth model indeed involves two direct electromagnetic torques at the fluid core boundaries and a remote gravitational torque between the inner core and the mantle the rotational dynamics is described by four typical shears and studied in convective numerical simulations of the geodynamo which are able to reproduce the main characteristics of the geomagnetic field and its secular variation this secular variation is mainly embodied by the westward drift of magnetic flux patches at the cmb concentrated on the equator of the atlantic hemisphere and is well documented for the last four centuries we provide constrains on the inner core differential rotation by expressing its link to the geomagnetic westward drift this is performed through the formulation and the validation of dynamical electromagnetic torque models which are then introduced in the conservation of the angular momentum of the system in the long term state the global shear in the fluid outer core is distributed between the westward drift and the differential rotation of the inner core in proportions controlled by the state of couplings as a present day estimate of this shear is close to the observed westward drift we conclude there is no differential rotation of the inner core on time average in the time dependent state we observed that the strength of gravitational coupling is the dominant parameter this places limit on the decadal fluctuations of the inner core differential rotation which should not exceed a few hundredths of degree per year

interaction between neighboring vegetation patches impact on flow and deposition flow and sedimentation around patches of vegetation are important to landscape evolution and a better understanding of these processes would facilitate more effective river restoration and wetlands engineering in wetlands and channels patches of vegetation are rarely isolated and neighboring patches influence one another during their development in this experimental study an adjacent pair of emergent vegetation patches were modeled by circular arrays of cylinders with their centers aligned in a direction that was perpendicular to the flow direction the flow and deposition patterns behind the pair of patches were measured for two stem densities and for different patch separations gap widths the wake pattern immediately behind each individual patch was similar to that observed behind an isolated patch with a velocity minimum directly behind each patch that produced a well defined region of enhanced deposition in line with the patch for all gap widths the velocity on the centerline between the patches uc was elevated to a peak velocity umax that persisted over a distance lj although umax was not a function of lj decreased with decreasing beyond lj the wakes merged and uc decayed to a local minimum the merging of wakes and associated velocity minimum produced a local maximum in deposition downstream from and on the centerline between the patches if this secondary region of enhanced deposition promotes new vegetation growth the increased drag on the centerline could slow velocity between the upstream patch pair leading to conditions favorable to their merger

earth s variable rotation recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the earth9s rotation theinterpretation of these fluctuations is inextricably linked with studies of the dynamics of the earth moon system and dynamical processes in the liquid metallic core of the earth where the geomagnetic field originates other parts of the earth9s interior and the hydrosphere and atmosphere fluctuations in the length of the day occurring on decadal time scales have implications for the topography of the core mantle boundary and the electrical magnetic and other properties of the core and lower mantle investigations of more rapid fluctuations bear on meteorological studies of interannual seasonal and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations

thermochemical flows couple the earth s inner core growth to mantle heterogeneity the uppermost 100 km of the earth s inner core is subject to an east west divide seismic waves travel more rapidly and are attenuated more severely in the eastern than in the western hemisphere and the west is more anisotropic that is seismic waves travel at different speeds in different directions than the eastern hemisphere the origin of this hemispherical dichotomy has remained enigmatic aubert et al now show that a model incorporating thermochemical convection and dynamo action can account for these effects by producing a large scale long term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle seismic waves sampling the top 100 km of the earth s inner core have revealed that the eastern hemisphere is seismically faster more isotropic and more attenuating than the western hemisphere it is now shown that a single model of thermo chemical convection and dynamo action can account for all these effects by producing a large scale long term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle seismic waves sampling the top 100 km of the earth s inner core reveal that the eastern hemisphere 40 e 180 e is seismically faster1 2 more isotropic2 3 and more attenuating4 than the western hemisphere the origin of this hemispherical dichotomy is a challenging problem for our understanding of the earth as a system of dynamically coupled layers previously laboratory experiments have established that thermal control from the lower mantle can drastically affect fluid flow in the outer core5 which in turn can induce textural heterogeneity on the inner core solidification front6 the resulting texture should be consistent with other expected manifestations of thermal mantle control on the geodynamo specifically magnetic flux concentrations7 8 in the time average palaeomagnetic field9 10 over the past 5 myr and preferred eddy locations11 in flows imaged below the core mantle boundary by the analysis of historical geomagnetic secular variation12 here we show that a single model of thermochemical convection and dynamo action can account for all these effects by producing a large scale long term outer core flow that couples the heterogeneity of the inner core with that of the lower mantle the main feature of this thermochemical wind is a cyclonic circulation below asia which concentrates magnetic field on the core mantle boundary at the observed location and locally agrees with core flow images this wind also causes anomalously high rates of light element release in the eastern hemisphere of the inner core boundary suggesting that lateral seismic anomalies at the top of the inner core result from mantle induced variations in its freezing rate

seismic anisotropy of the earth s inner core resulting from flow induced by maxwell stresses seismological observations indicate that the inner core of the earth is elastically anisotropic1 anisotropic structures are likely to be formed by dynamic processes and therefore such observations have the potential to provide constraints on flow in the inner core and on the geodynamo itself but in addition to the difficulties in estimating the relevant physical properties of iron under inner core conditions2 3 4 even the macroscopic processes responsible for generating seismic anisotropy in this region have yet to be determined5 6 7 8 9 as a result the geodynamic significance of seismic anisotropy in the inner core has remained unknown here i propose based on geodynamic and mineral physics considerations that flow induced by the stress due to the magnetic field the maxwell stress near the inner core boundary produces an axisymmetric fabric responsible for the observed seismic anisotropy the resultant seismic anisotropy reflects the geometry of the magnetic field near the inner core boundary and therefore seismological observations might provide constraints on the geodynamo this flow also causes non uniform release of energy at the inner core boundary associated with solidification and melting which may affect the pattern of convection in the outer core

currents and sediment transport in mangrove forests abstract a field study of the tidal currents cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at middle creek cairns australia the interaction of tidal currents and the vegetation generated jets eddies and zones of stagnant waters which were numerically modelled a high value of the manning friction coefficient n 0 1 was derived by the dense vegetation about 80 of the suspended sediment brought in from coastal waters at spring flood tide was trapped in the mangroves corresponding to about 10 12 kg of sediment m 1creek length spring tide resulting in a rise of the substrate by about 0 1 cm year 1 the selective trapping of clay was caused by flocculation of the finer particles in the mangroves there was an indication of a slight inwelling of organic carbon creek water was readily differentiated from mangrove water by large differences in the molecular weight distribution of the dissolved organic carbon

geodynamic estimates of the viscosity of the earth s inner core recent seismological studies1 2 have suggested that the inner core is rotating relative to the bulk of the earth a situation which according to numerical simulations3 may be sustained by convective flow in the liquid outer core on the other hand large gravitational forces due to the heterogeneous distribution of mass in the earth s mantle should be sufficient to keep the inner core aligned with the mantle4 here i show that the differential rotation of the inner core can be reconciled with these strong gravitational forces by allowing the shape of the inner core to adjust as it rotates so permitting an estimate of the effective viscosity of this innermost region of the earth the inferred rotation rate constrains the viscosity of the inner core to be less than 1016 pa s or greater than 1020 pa s as two different dynamical regimes are possible the viscosity estimates for these two regimes have very different implications for the origin of seismic anisotropy in the inner core

using earthquake doublets to study inner core rotation and seismicity catalog precision 1 we report our search for doublets in the south sandwich islands ssi region among 906 earthquakes from january 1982 to december 1998 event pairs with source separation less than 40 km which was calculated using pde locations were checked using vertical component short period and broadband digital records cross correlation coefficients of p or pkp waveforms were computed for similarity comparison whole waveforms of those event pairs with correlation coefficients larger than 0 8 were checked by eye by this process 17 doublets were found some of which form multiplets however only one doublet event pair 14 august 1995 and 28 march 1987 has clear pkp df phases on both records at college alaska col the pkp df travel time change measured by cross correlation is a decrease by 0 15 s with standard deviation 0 02 s over a time period of about 8 years this result strongly supports differential rotation of the earth s inner core relative to the mantle and the crust the estimated rotation rate ranges from 0 4 to 1 per year eastward the special case of a locked inner core can then be ruled out we also checked the precision of pde and isc locations using the 17 doublets results show that both catalogs have relatively high location precision standard deviations in latitude longitude and depth are less than 4 km 6 km and 10 km respectively supporting prior claims of detection of inner core rotation song and richards 1996

a 6 year westward rotary motion in the earth detection and possible micg coupling mechanism abstract seeking geophysical explanations for the periodic six year oscillation syo previously found in the earth s length of day variation lod we analyze the global gps displacement and geomagnetic data using the array processing technique of ose optimal sequence estimation and find clear evidences of the 6 yr signals which manifest as a westward rotary propagating wave of the sectoral spherical harmonic pattern of degree 2 order 2 y 22 based on the period the spatial pattern and the amplitudes and the estimated phases that exhibit consistent synchronicity among the three datasets we propose the following scenario the mantle inner core gravitational micg coupling gives rise to a 6 yr axial torsional libration of the inner core controlled by the sectoral y 22 density anomalies or the equatorial ellipticities in the inner core and the lower mantle the angular momentum exchange between which manifests as the syo in lod it forces into action a pressure wave 2 cyclic in 6 yr through the fluid outer core which in turn produces the corresponding gps and geomagnetic variations our findings provide insight into the dynamics of the deep earth and corroborate a positive density anomaly for the lower mantle large low shear velocity provinces

seismological evidence for differential rotation of the earth s inner core the travel times of seismic waves that traverse the earth s inner core show a small but systematic variation over the past three decades this variation is best explained by a rotation of the inner core that moves the symmetry axis of its known seismic anisotropy the inferred rotation rate is on the order of 1 per year faster than the daily rotation of the mantle and crust

low viscosity of the bottom of the earth s mantle inferred from the analysis of chandler wobble and tidal deformation abstract viscosity of the d layer of the earth s mantle the lowermost layer in the earth s mantle controls a number of geodynamic processes but a robust estimate of its viscosity has been hampered by the lack of relevant observations a commonly used analysis of geophysical signals in terms of heterogeneity in seismic wave velocities suffers from major uncertainties in the velocity to density conversion factor and the glacial rebound observations have little sensitivity to the d layer viscosity we show that the decay of chandler wobble and semi diurnal to 18 6 years tidal deformation combined with the constraints from the postglacial isostatic adjustment observations suggest that the effective viscosity in the bottom 300 km layer is 1019 1020 pa s and also the effective viscosity of the bottom part of the d layer 100 km thickness is less than 1018 pa s such a viscosity structure of the d layer would be a natural consequence of a steep temperature gradient in the d layer and will facilitate small scale convection and melt segregation in the d layer

estimate of inner core rotation rate from united kingdom regional seismic network data and consequences for inner core dynamical behaviour abstract we analyse over 12 500 records of southwest pacific earthquakes recorded by the uk network for pkpbc and pkpdf phases to seek constraints on the inner core s rotation rate careful analysis and strict rejection criteria yield 655 pkpbc pkpdf differential travel time residuals computed with respect to the ak135 reference model densely sampling a small region of the inner core over a time period of 15 years the data images both lateral and radial velocity heterogeneity in the inner core located geographically beneath the north pacific between radii of 870 and 1080 km the dominant feature is a longitudinal wave speed gradient centred at about 180 longitude in combination with different earthquake catalogues and inner core anisotropy models we explore different techniques to use this gradient to constrain the rotation rate our estimates range from 0 45 0 25 to 0 74 0 29 yr relative to the mantle with two of four estimates including zero rotation at the 95 2 confidence level indicating that rotation is marginally detectable as an alternative to monotonic rotation we find weak evidence for rotational oscillation of the inner core on time scales of about 280 days in consequence these observations suggest that 1 viscous coupling between the outer and inner core simulated using viscous hyperdiffusivity is not appropriate for modelling inner core rotation 2 temperature gradients between the interior and exterior of the tangent cylinder in the core are also small 3 gravitational torques coupling the inner core to the mantle are large on the order of 2 1021 nm and 4 the inner core s viscosity is high 3 9 1019 pas

depth dependence of anisotropy of earth s inner core both body wave pkp travel times creager 1992 song and helmberger 1993a mcsweeney and creager 1993 shearer 1994 and fits to the splitting of core modes tromp 1993 show general agreement that the top 300 km of inner core is very anisotropic the anisotropy displays axial symmetry around the earth s spin axis with the polar direction 3 faster than the equatorial direction one key problem now is the depth dependence of the inner core anisotropy here we extend our polar path studies to include both long period and short period modeling for the pkp phases at ranges 120 to 173 arrivals from the top of the inner core pkikp and reflections from the inner core boundary pkikp can be observed distinctly in short period records at ranges 130 to 140 and as waveform distortions in the long period records at ranges 130 to 146 these waveforms provide a new set of data for examining the topmost 150 km of the inner core which is not well sampled by the previous body wave travel times record sections of waves traversing the inner core nearly parallel to the earth s spin axis polar paths from three events two beneath the south sandwich islands and one along the macquarie ridge recorded at world wide standardized seismograph network canadian network and long range seismic measurements stations are analyzed our results suggest that the top 150 km of the inner core is only weakly anisotropic less than 1 with strong evidence indicating that the top 60 km is not anisotropic at all

vegetation modulated landscape evolution effects of vegetation on landscape processes drainage density and topography 1 topography acts as a template for numerous landscape processes that include hydrologic ecologic and biologic phenomena these processes not only interact with each other but also contribute to shaping the landscape as they influence geomorphic processes we have investigated the effects of vegetation on thresholds for channel initiation and landform evolution using both analytical and numerical approaches vegetation is assumed to form a uniform ground cover runoff erosion is modeled based on a power function of excess shear stress in which shear stress efficiency is inversely proportional to vegetation cover this approach is validated using data plant effect on slope stability is represented by additional cohesion provided by plant roots vegetation cover is assumed to reduce sediment transport rates due to physical creep processes rainsplash dry ravel and expansion and contraction of sediments according to a negative exponential relationship vegetation grows as a function of both available cover and unoccupied space by plants and is killed by geomorphic disturbances runoff erosion and landsliding and wildfires analytical results suggest that in an equilibrium basin with a fixed vegetation cover plants may cause a transition in the dominant erosion process at the channel head a runoff erosion dominated landscape under none or poor vegetation cover may become landslide dominated under a denser vegetation cover the sign of the predicted relationship between drainage density and vegetation cover depends on the relative influence of vegetation on different erosion phenomena with model parameter values representative of the oregon coast range ocr numerical experiments conducted using the channel hillslope integrated landscape development child model confirm the findings based on the analytical theory a highly dissected fluvial landscape emerges when surface is assumed bare when vegetation cover is modeled landscape relief increases resulting in hollow erosion dominated by landsliding interestingly our simulations underscore the importance of vegetation disturbances by geomorphic events and wildfires on the landscape structure simulated landscapes resemble real world catchments in the ocr when such disturbances are considered

contrasting morphodynamics in alluvial fans and fan deltas effect of the downstream boundary alluvial fans and fan deltas can in principle have exactly the same upstream conditions but fan deltas by definition have ponding water at their downstream boundary this ponding creates effects on the autogenic behaviour of fan deltas such as backwater adaptation mouth bars and backward sedimentation whereas alluvial fans may lack these effects hence the present authors hypothesize that morphodynamics on alluvial fans are determined primarily by upstream boundary conditions whereas morphodynamics on fan deltas are determined by both the upstream and the downstream boundary condition and changes therein to isolate the effects of the upstream and downstream boundaries five new alluvial fan experiments are compared with the details of three fan deltas published earlier that were formed under very similar and simple conditions similar to the fan deltas the alluvial fans build up by sheet flow whilst quasi regular periods of incision cause temporary channelized flow incision is followed by channel backfilling after which the fan returns to sheet flow the channelization and backfilling in alluvial fans is markedly less pronounced and more prone to autogenic disturbance than in fan deltas the difference is caused by morphodynamics at the downstream boundary in a fan delta the flow expansion of the channel causes deposition of all the sediment which forms a mouth bar and causes strong backfilling in an alluvial fan on the other hand the slope break at the fan perimeter causes some deposition but transport is not reduced to zero consequently the backfilling in alluvial fans is less pronounced than in fan deltas other published experiments support this trend removal of the mouth bar by a river leads to permanent channelization whilst pronounced mouth bar formation in highly channelized deltas promotes backward sedimentation the experimental results for this study predict that when alluvial fans prograde into lakes or deep rivers they transition to fan deltas with increasingly deeper channels and thicker backfill deposits

interdiffusion of earth s core materials to 65 gpa and 2200 k abstract diffusion of iron and nickel in an fe 64 ni 36 alloy was measured via the use of focused ion beam fib milling and energy dispersive x ray spectroscopy edx to 65 gpa and 2200 k the experiments were performed using a combination of micro fabricated samples in the laser heated diamond anvil cell dac increasing the pressure range for experimentally determined interdiffusion coefficients in feni alloys by 40 gpa diffusivity in the iron nickel system follows a homologous temperature relationship d d 0 exp 19 3 2 7 t m t where d 0 is 4 6 7 10 4 m 2 s 1 with zero pressure activation energy 301 40 kj mol 1 consistent with measurements at lower pressures at inner core conditions this predicts an inner core solid state diffusivity of 1 10 14 m 2 s 1 t m t 0 95 with an inner core viscosity of 10 20 10 22 pa s assuming power law creep n 3 with a deviatoric stress of 10 3 10 4 pa

swiftness of biomorphodynamics in lilliput to giant sized rivers and deltas physical experiments of self formed river channels and floodplains with live vegetation are pathways for understanding that complement numerical modelling recent experiments succeeded in creating braided rivers and dynamic meandering systems with clastic and vegetated floodplains however application of the insights gained from such experiments to natural systems depends on understanding potential scale effects temporal and spatial here we combine review analysis and experiments to identify fundamental problems of biomorphological river pattern formation that are open for further research in experiments we first show by review and analysis that physics based linear bar theory predicts negligible spatial scale effects in bar and bend wavelength relative to channel width time scaling on the other hand remains problematic because it integrates multiple processes of sediment transport floodplain formation and bank failure affected by bank stratigraphy and riparian vegetation as a tentative solution we secondly present experimental methods to assess bank strength effects that can be used in the design of river pattern experiments the third issue is that riparian vegetation has often been represented in experiments by uniformly seeded sprouts of a single plant species whilst spectacularly different patterns are obtained with contrasting seeding protocols showing the need for other experimental procedures and alternative riparian species the main challenge for future experiments is better understanding of temporal scaling of biomorphodynamics

functional relationships between vegetation channel morphology and flow efficiency in an alluvial anabranching river 1 water and sediment flux interactions are examined in magela creek an alluvial anabranching sand bed river in the northern australian tropics dense riparian vegetation stabilizes the channels and floodplains thereby preventing erosional instability at flow depths up to 6 2 times bankfull and discharges up to 15 times bankfull narrow anabranching channels characterize 92 of the alluvial reach and transport bed load more efficiently than short reaches of wide single channels yet overall 29 12 of the bed load is sequestered and the average vertical accretion rate is 0 41 0 17 mm yr 1 along the 12 km study reach the most effective discharge for transporting sediment 40 45 m3 s 1 is consistent at all 5 stations 10 channels examined and is equivalent to the channel forming discharge it has an average recurrence interval of 1 01 years occurs for an exceptionally long portion 13 15 of the annual flow duration and averages a remarkable 2 1 times bankfull the high flow efficiency i e bed load transport rate to stream power ratio of the anabranches is facilitated by low width depth channels with banks reinforced by vegetation colonnades of bank top trees confine high velocity flows overbed i e over the channel bed at stages well above bankfull at even larger overbank flows momentum exchange between the channels and forested floodplains restrains overbed velocities in some cases causing them to decline thereby limiting erosion magela creek exhibits a complicated set of planform cross sectional and vegetative adjustments that boost overbed velocities and enhance bed load yield in multiple channels while restraining velocities and erosion at the largest discharges

detection of a gravitational oscillation in length of day abstract a high resolution length of day data set spanning approximately the last 42 years is found to contain an oscillation with a period of 5 8 0 8 years this oscillation is interpreted to represent a normal mode of the earth that arises due to gravitational coupling between the mantle and inner core in order to match the observed period of the oscillation the strength of the gravitational coupling between the mantle and inner core must be 3 0 1020 n m this coupling constant depends on the heterogeneous density distribution of the mantle including flow induced deformation of the core mantle boundary the existence of this normal mode requires that the relaxation time of the inner core be sufficiently long on the order of a few years or more that a perturbation from equilibrium results predominantly in solid body rotation not viscous deformation of the inner core the inferred lower bound for the viscosity of the inner core is of the order of 1017 pa s

balancing aggradation and progradation on a vegetated delta the importance of fluctuating discharge in depositional systems vegetation is an important component of constructional landscapes as plants enhance deposition and provide organic sediment that can increase aggradation rates to combat land loss we conducted two sets of laboratory experiments using alfalfa medicago sativa to determine the effects of plants on channel organization and large scale delta dynamics in the first set we found that rapid vegetation colonization enhanced deposition but inhibited channelization via increased form drag that reduced the shear stress available for sediment entrainment and transport a second set of experiments used discharge fluctuations between flood and base flow or interflood interfloods were critical for reworking the topset via channel incision and lateral migration to create channel relief and prevent rapid plant colonization these low flow periods also greatly reduced the topset slope in the absence of vegetation by removing topset sediment and delivering it to the shoreline floods decreased relief by filling channels with sediment resulting in periods of rapid progradation and enhanced aggradation over the topset surface which was amplified by vegetation the combination of discharge fluctuations and vegetation thus provided a balance of vertical aggradation and lateral progradation we conclude that plants can inhibit channelization in depositional systems and that discharge fluctuations encourage channel network organization to naturally balance against aggradation thus variations in discharge are an important aspect of understanding the ecomorphodynamics of aggrading surfaces and modeling vegetated deltaic systems and the combined influences of plants and discharge variations can act to balance vertical and lateral delta growth

punctuated sand transport in the lowermost mississippi river 1 measurements of sand flux and water flow in the mississippi river are presented for a portion of the system 35 50 km upstream from the head of its subaerial delta these data are used to provide insight into how nonuniform flow conditions present in the lower reaches of large alluvial rivers affect the timing and magnitude of sand transport near the river outlet field surveys during both low and high water discharge include 1 sequential digital bathymetric maps defining mobile river bottom topography which were used to estimate bed material flux 2 multiple water velocity profiles and 3 multiple suspended sediment profiles collected using a point integrated sampler these data show that total sand transport increases by two orders of magnitude over the measured range in water discharge 11 300 to 38 400 m3 s 1 during low water discharge no sand is measured in suspension and sand discharge via bed form migration is minimal during high water discharge 54 of the sand discharge is measured in suspension while 46 of the sand discharge is part of bed form migration the component of boundary shear stress associated with moving this sediment is estimated using a set of established sediment transport algorithms and values for the total boundary shear stress are predicted by fitting logarithmic velocity functions to the measured profiles the estimates of boundary shear stress using measurements of suspended sand transport bed form transport and downstream oriented velocity profiles are internally consistent moreover the analyses show that boundary shear stress increases by nearly 10 fold over the measured water discharge range we show how this increase in shear stress is consistent with backwater flow arising where the river approaches its outlet the hydrodynamic properties of backwater flow affect the timing and magnitude of sand flux and produce punctuated sand transport through the lowermost mississippi river our field data are used to evaluate the influence of this sand transport style on development of the mixed bedrock alluvial channel for the lowermost mississippi river

detection of inner core solidification from observations of antipodal pkiikp pkiikp waves reflected from the underside of the inner core boundary are very sensitive to the s velocity in the uppermost 80 km of the inner core at antipodal distances undergoing a phase change and a factor of 4 amplification as the distance approaches 180 modeled pkiikp waveforms are consistent with a near zero shear modulus in the uppermost inner core in a 20 40 km thick patch beneath the eastern equatorial hemisphere this bright spot of pkiikp reflection correlates with a thin zone of low p velocity inferred from the complexity of pkikp waveforms sampling this patch estimates of grain sizes from seismic attenuation the absence of backscattered pkikp coda in this region and a prediction for enhanced heat flow through this patch suggest that it is a region of solidification rather than melting

inner core rotation rate from small scale heterogeneity and time varying travel times the time it takes seismic waves to propagate from south atlantic earthquakes through the inner core to station col in alaska has decreased systematically over the past 30 years travel times from three earthquakes in 1991 to an array of 37 seismometers in alaska suggest that lateral gradients in seismic wavespeeds are steep in this part of the inner core this combination of observations can be explained by postulating that the inner core is rotating 0 2 to 0 3 per year faster than the mantle

sediment patterns near a model patch of reedy emergent vegetation this laboratory study describes the sediment patterns formed in a sand bed around circular patches of rigid vertical cylinders representing a patch of reedy emergent vegetation the patch diameter was much smaller than the channel width two patch densities solid volume fraction 3 and 10 and two patch diameters 22 and 10 cm were considered for flows above the threshold of sediment motion patterns of sediment erosion and deposition were observed around and within the patch scouring within the patch was positively correlated with turbulent kinetic energy in the patch for sparse patches sediment scoured from within the patch was mostly deposited within one patch diameter downstream of the patch for dense patches which experience greater flow diversion sediment scoured from the patch was carried farther downstream before deposition along the patch centerline differences between the sparse and dense patch patterns of deposition are explained in the context of flow diversion and wake structure which are related to a nondimensional flow blockage parameter while sediment was redistributed near the patch observations suggest that net deposition was not recorded at the reach scale

planet within a planet rotation of the inner core of earth the time dependence of the orientation of earth9s inner core relative to the mantle was determined using a recently discovered 10 degree tilt in the axis of symmetry of the inner core9s seismic velocity anisotropy two methods of analyzing travel time variations for rays traversing the inner core on the basis of 29 years of data from the international seismological centre 1964 1992 reveal that the inner core appears to rotate about 3 degrees per year faster than the mantle an anomalous variation in inner core orientation from 1969 to 1973 coincides in time with a sudden change jerk in the geomagnetic field

structure and dynamics of earth s inner core abstract the seismological exploration of the earth s inner core has revealed unexpected and puzzling structural complexities its elastic anisotropy is now well established and has been shown to vary spatially there is a well defined hemispherical dichotomy in anisotropy and attenuation and significant variations in the radial direction with weaker anisotropy in the uppermost regions and possibly different properties in an innermost inner core of radius 300 600 km perhaps even more puzzling is the observation of a stably stratified layer at the base of the outer core which has recently been proposed to result from melting of inner core material if confirmed the presence of this layer has major implications for our understanding of convection in the outer core inner core differential rotation with respect to the mantle remains controversial we will review here recent progress in understanding the dynamics of the inner core a number of different models have been proposed for the development of the inner core s structure and formation of the stable layer at the base of the outer core and particular care will be taken to clarify under which conditions the proposed mechanisms can be active

attenuation and excitation of the 6 year oscillation in the length of day variation abstract we carefully reanalyze the 6 yr oscillation syo which has been previously found in the earth s length of day variation lod and has been considered important for understanding the core mantle interactions and core dynamics based on the morlet wavelet and ar z spectra of a long period yearly lod record 1760 2018 we identify eight long period signals 149 yr 68 yr 33 yr 22 3 yr 18 6 yr 13 5 yr 11 yr and 8 5 yr signals except the 18 6 yr signal the other signals are clearly identified for the first time although the physical mechanisms need to be understood some of them may relative to the torsional waves or magnetic archimede coriolis waves after removing the atmospheric oceanic angular momentum effects the seasonal tidal signals and the eight low frequency signals from the 1962 2016 lod time series from eopc04 a much cleaner sequence for the syo is obtained and we confirm that there is no clear decay trend for the syo in the residual sequence after using a deconvolution method to this syo time series we first validate that the quality factor q of the syo cannot be less than 200 assuming the attenuation of syo is mainly caused by the electromagnetic coupling at cmb and taking the mantle conductance g m 10 8 s the radial magnetic field strength b m at the cmb should be larger than 0 31 mt in addition for the first time we calculate the excitation function of the syo from the deconvolution of lod and the results demonstrate that the syo seems to be continuously excited by comparing the geomagnetic jerks with the excitation function of the syo no clear correlation has been found between them while we also cannot rule out the possibility of the geomagnetic jerks as one kind of the excitation sources of the syo our findings are necessary for building a systematic physical mechanism of the syo and useful for constraining the magnetic field b of the earth s core

sharpness of the hemispherical boundary in the inner core beneath the northern pacific abstract the hemispherical nature of heterogeneities of the isotropic velocity and attenuation of the inner core has been extensively studied by seismic observations but consensus on the character of the boundary between two hemispheres has not yet been achieved to investigate the hemispherical boundary in detail we analyze core phase data whose ray paths propagate beneath the northern pacific we employ a waveform inversion approach based on simulated annealing to measure the differential traveltime and the attenuation parameter of the core phases measured differential traveltimes for data from european stations for events in the fiji tonga region show positive anomalies consistent with the eastern hemisphere model while those from usarray for events in indonesia show relatively small values ray theory based forward modeling of the differential traveltimes is conducted by varying the shape and the transition width of the boundary an arc like shape boundary that connects points 0 n 159 w on the equator and 79 n 110 e in far north with a transition width of 600 km best explains the observed differential traveltimes rather than a sharp boundary this model also accounts for the observed variation of attenuation parameters

mantle control of the geodynamo consequences of top down regulation the mantle global circulation including deep subduction and lower mantle superplumes exerts first order controls on the evolution of the core the history of the geodynamo and the structure of the geomagnetic field mantle global circulation models that include realistic plate motions deep subduction and compositional heterogeneity similar to the observed large low seismic velocity provinces in the lower mantle predict that the present day global average heat flux at the core mantle boundary cmb exceeds 85 mw m 2 this is sufficient to drive the present day geodynamo by thermochemical convection and implies a very young inner core with inner core nucleation between 400 and 1100 ma the mantle global circulation also generates spatially heterogeneous heat flux at the cmb with peak to peak lateral variations exceeding 100 mw m 2 such extreme lateral variability in cmb heat flux in conjunction with the high thermal conductivity of the core implies that the liquid outer core is thermally unstable beneath the high seismic velocity regions in the lower mantle but thermally stable beneath the large low seismic velocity provinces numerical dynamo simulations show how this pattern of heterogeneous boundary heat flux affects flow in the outer core producing localized circulation patterns beneath the cmb tied to the mantle heterogeneity and long lived deviations from axial symmetry in the geomagnetic field

bed morphological changes around a finite patch of vegetation for the appropriate management and restoration of rivers isolated vegetation is often a practical means for improving stream habitat and ecology the effect of a finite vegetation patch on flow and bed morphology in an open channel was investigated using laboratory experiments the patch containing emergent and submerged vegetation was modeled using circular cylinders and located mid channel along a side wall several configurations of the patch and submergence ratio i e water depth to the height of vegetation and two flow conditions i e below and above the sediment motion threshold were considered for flows below the sediment motion threshold erosion occurred primarily on the opposite side of the patch and near the leading edge of the patch the degree of scouring depth observed in both these regions was affected by the submergence ratio and it increased with the non dimensional flow blockage i e the product of the patch density and width in contrast for flows above the sediment motion threshold sediment accumulated within and around the patch due to a reduction in bed shear stress which was strongly influenced by the flow blockage and the obstruction ratio i e the ratio of patch width to channel width the eroded area observed within the patch was consistent with the interior adjustment region where the deceleration and diversion of flow occurred through the patch as the flow blockage increased or as the obstruction ratio decreased the deposition rate within and behind the patch decreased furthermore the deposition rate increased with an increase in the ratio of flow rate through the patch to total flow rate regardless of the submergence ratio copyright 2014 john wiley sons ltd

the topographic signature of vegetation development along a braided river results of a combined analysis of airborne lidar color air photographs and ground measurements 1 this paper combines archived remotely sensed data airborne lidar and digital color air photographs with nonsynchronous ground observations including observations of topographic form and vegetation cover and growth to test the hypothesis that colonization of exposed river sediments by riparian trees has an impact on channel form and to quantify any impact that is identified this is achieved along a 21 km reach of the braided gravel bed tagliamento river in northeast italy where the width of the braided corridor typically exceeds 800 m lidar data are analyzed to extract a 2 m resolution digital evolution model dem and determine riparian vegetation extent height and structure within the active corridor aerial photographs are used to map the topography of the submerged parts of the corridor these data are divided into 1 km length subreaches which possess strong contrasts in vegetation height and extent joint analysis of vegetation and morphological properties of these subreaches reveals significant associations between vegetation properties and reach morphology residuals from a gamma function fitted to the topographic data for each subreach show a good fit with poorly vegetated reaches but a weakening fit with increasing vegetation cover largely as a result of the appearance of secondary peaks in the elevation frequency distribution associated with the heavily vegetated areas furthermore the overall skewness and kurtosis of the elevation frequency distribution within each of the subreaches are both significantly correlated with vegetation extent height median elevation and growth rate indicating a clear topographic signature of vegetation development along this braided river that reflects sediment accumulation within and around the vegetated patches

formation of a solid inner core during the accretion of earth the formation of an inner core during the accretion of earth is investigated using self gravitating and compressible earth models formed by accreting a total of 25 or 50 moon to mars size planetary embryos the impact of an embryo heats the proto earth s interior differentially more below the impact site than elsewhere the rotating core dynamically overturns and stratifies shortly after each impact creating a spherically symmetric and radially increasing temperature distribution relative to an adiabatic profile merging of an embryo to the proto earth increases the lithostatic pressure that results in compressional temperature increase while further enhances the melting temperature of the core causing solidification a total of 36 thermal evolution models of the growing proto earth s core are calculated to investigate effects of major physical parameters no solidification is considered in the first 21 models where modified two body escape velocities are used as the impact velocities of the embryos at the end of accretion temperatures in the upper part of the core are significantly different among these models whereas temperatures in the deeper parts are similar the core solidification considered in the remaining 15 models where impact velocities higher than the modified two body escape velocities are adopted drastically changes the temperature distribution in the deeper parts of the core all of the models produce partially solidified stiff inner cores 1000 2100 km in radius at the end of accretion where the solid fraction is larger than 50 the innermost of the stiff inner cores are completely solidified to radii 250 1500 km

gravitationally driven inner core differential rotation abstract a heterogeneous heat flux at the core mantle boundary can maintain time averaged convective structures in the fluid core this includes a steady pattern of heterogeneous heat flux at the inner core boundary which leads to aspherical inner core growth if this growth pattern is longitudinally misaligned with the mantle induced geoid the latter would impart a gravitational torque on the newly created topography of the inner core allowing for continuous melting solidification and viscous deformation of the inner core a steady gravitationally driven differential rotation of the inner core with respect to the mantle can be sustained in this work we present calculations of inner core rotation driven by such a mechanism using recently published models of the heat flux at the inner core boundary and of the geoid at the base of the mantle we show that for a fast mean inner core growth rate of 1 mm yr and a bulk viscous relaxation time longer than 100 yr the inner core differential rotation can be as high as 100 deg myr in the westward direction although this is much too slow and in the wrong direction to explain the seismically inferred inner core rotation eastward of the order of 0 2 deg yr this mechanism by itself would rotate the inner core by one full rotation in only a few million years this gravitational torque would then partly offset the viscomagnetic torque from the steady eastward zonal flow near the inner core boundary the driving mechanism typically invoked to explain a steady inner core super rotation under the combined action of these two torques the overall steady differential rotation of the inner core may then be small this would allow the development of an inner core texture with a distinct longitudinal pattern connected to its aspherical freezing rate as has been suggested to explain seismic observations

spatial distribution of deposition within a patch of vegetation 1 this laboratory study describes the spatial pattern of deposition observed in a patch of vegetation located at the wall of a channel there are two sources of sediment flux to the patch the advection of particles across the upstream leading edge and the lateral dispersion of particles from the adjacent open channel the relative contribution of these two supplies determines the spatial pattern of net deposition in the patch we define the advection length scale within the patch as the longitudinal distance over which advection contributes a significant sediment source at distances from the leading edge that are within the advection length scale net deposition in the patch is laterally uniform reflecting the laterally uniform mean flow delivering the particles at distances farther than the advection length scale from the leading edge the net deposition is highest near the flow parallel edge and decreases into the patch which is the signature of dispersive transport from the patch edge two processes contribute to the lateral dispersion both of which are associated with the shear layer vortices formed at the flow parallel interface between the patch and the channel the vortices generate turbulence and enhance the turbulent diffusion of sediment across the interface in addition the vortices induce a wave oscillation in the flow field within the patch that appears to enhance the lateral transport inside the patch

earth s core and the geodynamo earth s magnetic field is generated by fluid motion in the liquid iron core details of how this occurs are now emerging from numerical simulations that achieve a self sustaining magnetic field early results predict a dominant dipole field outside the core and some models even reproduce magnetic reversals the simulations also show how different patterns of flow can produce similar external fields efforts to distinguish between the various possibilities appeal to observations of the time dependent behavior of the field important constraints will come from geological records of the magnetic field in the past

coherent interannual and decadal variations in the atmosphere ocean system 1 we investigate the source of poleward propagating atmospheric zonal wind anomalies originating at the equator and penetrating to high latitudes in both hemispheres in conjunction with enso dickey et al 1992 and report the discovery of similar variability on decadal and longer timescales since atmospheric dissipation times are generally on the order of a month or less we examine the ocean as a memory source for these globally coherent anomalies this hypothesis is substantiated by the observation of complementary oscillation in the sea surface temperature sst field further we detect a robust decadal variability 10 12 yrs in both the sst and contemporaneous atmospheric angular momentum aam series analyzing gisst sst data beginning in 1902 we confirm this decadal mode and find signatures of longer multidecadal sst variability centered in the equatorial and north pacific

effects of vegetation on braided stream pattern and dynamics 1 investigations using a 16 m by 2 m recirculating experimental flume model of an ephemeral braided river indicate that the presence of large and erosion resistant plants within the channel e g trees or shrubs can have a significant impact on channel pattern and planform dynamics simulations show that these plants have two effects first they act as obstructions in some cases forcing the flow to divide this flow separation can allow the deposition of a small island immediately in the lee of the plant splitting the channel the net result is a substantial increase in the number of channels and correspondingly the braid index this is in direct contrast to previous studies where increased levels of vegetation in perennial streams have decreased the braid index second the plants stabilize braid bars and can form relatively stable islands in their lee significantly reducing the longitudinal migration of islands typically associated with braided rivers

inner core anisotropy in three dimensions the purpose of this paper is the investigation of cylindrical anisotropy in the inner core based on the travel time anomalies of the pkikp phase we use the arrival times reported in the international seismological centre bulletins for years 1964 1990 we select only earthquakes which have a good azimuthal coverage and a sufficiently large number of reporting stations the earthquakes are relocated using corrections for lateral heterogeneity computed for our most recent three dimensional mantle model we use a total of 313 422 observations of the df branch of pkp travel time anomalies within the epicentral distance ranges of 120 140 and 150 180 reported by 2335 stations for 26 377 earthquakes we process the data using an averaging procedure which we call cylindrical anisotropy stacking that enhances the effects of anisotropy but is expected to suppress those due to lateral heterogeneity and random errors the processed residuals show a remarkably consistent pattern this confirms the dominance of the cylindrical elastic anisotropy in the inner core with approximately a constant axis of symmetry this axis of symmetry is found to be tilted 10 5 1 from the earth s rotation axis in the direction 160 e 5 in the northern hemisphere in this new coordinate system we determine a four layer axisymmetric model of transverse anisotropy with each layer approximately 300 km thick the model shows that the anisotropy is strongest 3 within the innermost part of the core the travel time anomalies show significant 1 5 s longitudinal variations even when the tilt of the axis of symmetry is considered there is a substantial increase in the amplitude of the longitudinal variations which are dominated by the second and fourth harmonics for rays with bottoming depths exceeding 400 km below the inner core boundary the measurable tilt of the axis of symmetry and the presence of significant nonaxisymmetric signal may provide important clues with respect to the possible causes of anisotropy the increase in the anisotropy in the innermost part of the core departs from earlier inferences that anisotropy may be limited to the outermost 200 300 km of the earth s inner core

quantitative estimation of bioturbation based on digital image analysis quantitative determination of modification of primary sediment features by the activity of organisms i e bioturbation is essential in geosciences some methods proposed since the 1960s are mainly based on visual or subjective determinations the first semiquantitative evaluations of the bioturbation index ichnofabric index or the amount of bioturbation were attempted in the best cases using a series of flashcards designed in different situations recently more effective methods involve the use of analytical and computational methods such as x rays magnetic resonance imaging or computed tomography these methods are complex and often expensive this paper presents a compilation of different methods using adobe photoshop software cs6 for digital estimation that are a part of the idiap ichnological digital analysis images package which is an inexpensive alternative to recently proposed methods easy to use and especially recommended for core samples the different methods similar pixel selection method spsm magic wand method mwm and the color range selection method crsm entail advantages and disadvantages depending on the sediment e g composition color texture porosity etc and ichnological features size of traces infilling material burrow wall etc the idiap provides an estimation of the amount of trace fossils produced by a particular ichnotaxon by a whole ichnocoenosis or even for a complete ichnofabric we recommend the application of the complete idiap to a given case study followed by selection of the most appropriate method the idiap was applied to core material recovered from the iodp expedition 339 enabling us for the first time to arrive at a quantitative estimation of the discrete trace fossil assemblage in core samples

delta progradation driven by an advancing sediment source coupled theory and experiment describing the evolution of elongated deltas 1 most of the models of alluvial fan and delta morphodynamics to date have used one of two assumptions concerning the upstream boundary condition 1 a fixed sediment feed point at the vertex or 2 a feed point corresponding to a bedrock alluvial transition that e g migrates upstream under conditions of constant base level here however we present both experimental and numerical results pertaining to a new configuration i e one in which the sediment feed point migrates downstream the research is motivated by the operation of the tailings pond of a mine in which a delta forms the mine operators must frequently move the outfalls of their slurry pipelines downstream to avoid their burial under sediment as the delta aggrades this downstream migration results in a characteristic delta configuration under the right conditions as the tailings delta progrades downstream it does not have time to fill all the available space in the lateral direction thus leaving unfilled open water on either side the result is the formation of an elongated delta here we use both experiments and numerical modeling to characterize the control of the feed point migration rate on the lateral extent of the prograding deltas we use these results to obtain a partial explanation of natural elongated deltas in the case of such deltas the downstream progradation of natural levees provides an analog to the downstream migration of the outfall of a slurry pipeline

autocyclic behaviour of fan deltas an analogue experimental study fan deltas are excellent recorders of fan building processes because of their high sedimentation rate particularly in tectonically active settings although previous research focuses mainly on allogenic controls there is clear evidence for autogenically produced storage and release of sediment by flume and numerical modelling that demands further definition of characteristics and significance of autogenically forced facies and stratigraphy analogue experiments were performed on fan deltas with constant extrinsic variables discharge sediment supply sea level and basin relief to demonstrate that fan delta evolution consists of prominent cyclic alternations of channellized flow and sheet flow the channellized flow is initiated by slope induced scouring and subsequent headward erosion to form a channel that connected with the valley while the removed sediment is deposited in a rapidly prograding delta lobe the resulting decrease in channel gradient causes a reduction in flow strength mouth bar formation flow bifurcation and progressive backfilling of the channel in the final stage of channel filling sheet flow coexists for a while with channellized flow semi confined flow although in cycle 1 this phase of semi confined flow was absent subsequent autocyclic incisions are very similar in morphology and gradient however they erode deeper into the delta plain and as a result take more time to backfill the duration of the semi confined flow increases with each subsequent cycle during the period of sheet flow the delta plain aggrades up to the critical gradient required for the initiation of autocyclic incision this critical gradient is dependent on the sediment transport capacity defined by the input conditions these autogenic cycles of erosion and aggradation confirm earlier findings that storage and release of sediment and associated slope variation play an important role in fan delta evolution the erosional surfaces produced by the autocyclic incisions are well preserved by the backfilling process in the deposits of the fan deltas these erosional surfaces can easily be misinterpreted as climate sea level or tectonically produced bounding surfaces

flow and deposition in and around a finite patch of vegetation this laboratory study describes the flow and deposition observed in and around a finite patch of vegetation located at the wall of a channel two patch densities are considered with 2 and 10 solid volume fraction the velocity field measured in and around the patch by acoustic doppler velocimetry revealed three distinct zones first there is a diverging flow region at the leading edge of the patch where the flow in line with the patch decelerates and the bulk of the flow is diverted toward the open channel second there is a fully developed region within the vegetation where the velocity is uniform across the patch width and along the length of the patch third a shear layer forms at the interface between the patch and adjacent open channel the pattern of deposition in and around the vegetation was characterized by releasing 12 micron spherical glass particles and recording net deposition on a set of glass slides in the diverging region net deposition increases in the stream wise direction as the local velocity decreases in the fully developed region of the patch deposition decreases with longitudinal position as the concentration in the water column is depleted the deposition pattern is nearly uniform across the patch width consistent with the velocity field and suggesting that turbulent diffusive flux across the lateral edge of the patch is not a significant source of particles to the patch under the conditions studied here

hydrodynamic and geomorphic controls on mouth bar evolution 1 while river deltas are one of the major repositories for sediments and carbon on earth there exists a paucity of field data on the formation of distributary mouth bars one of their key features here we present results from an experiment that tested a model of mouth bar development using hydroacoustic optical sedimentary and geochemical tools on a mouth bar in a crevasse splay near the mouth of the mississippi river our results validate an existing model for mouth bar development which we extend to explain mouth bar stratigraphy we propose that changes across a hydrological cycle are important for mouth bar development resulting in a stratigraphy that has alternating fine and coarse grain sediments results also indicate that sand is carried up to 6 km from the main stem of the mississippi river despite repeated channel bifurcations which has important implications for our interpretation of the rock record understanding of coastal sedimentary systems and the restoration of large deltas

a comparison of geodetic and seismic estimates of inner core rotation seismological observations suggest the inner core has been rotating faster than the mantle during the past 30 50 years differential rotation can produce large gravitational torques on the mantle which if not balanced by other torques would be detectable as changes in the rotation rate of the mantle length of day or lod we compare seismological estimates of inner core rotation with estimates derived by inverting lod observations using models of gravitational coupling model predictions depend on several parameters but for the expected range of parameter values the seismological estimates of relative rotation are at least an order of magnitude larger than those predicted by the lod data furthermore the lod data predict oscillation in the angular alignment of the inner core and mantle during the past 30 50 years while the seismological data seem to require a component of steady rotation we show that steady rotation of the inner core implies a steady torque on the mantle this torque is not accelerating the rotation rate of the mantle so it must be opposed by another torque the required torque is consistent with a frictional electromagnetic stress on the base of the mantle due to a westward flow at the top of the core

inner core differential motion confirmed by earthquake waveform doublets we analyzed 18 high quality waveform doublets with time separations of up to 35 years in the south sandwich islands region for which the seismic signals have traversed the inner core as pkp df the doublets show a consistent temporal change of travel times at up to 58 stations in and near alaska and they show a dissimilarity of pkp df coda using waveform doublets avoids artifacts of earthquake mislocations and contamination from small scale heterogeneities our results confirm that earth s inner core is rotating faster than the mantle and crust at about 0 3 degrees to 0 5 degrees per year

inner core rotation a test at the worldwide scale abstract in order to determine the angular velocity of a possible inner core differential rotation with respect to the mantle we analyse travel times of waves sampling the inner core at the worldwide scale over a period of about 30 years for situations in which the inner core heterogeneities are dominant with respect to the mantle heterogeneities travel times of summary rays i e bunches of seismic rays with the same geometry must have smaller mean standard deviations when computed in the inner core reference frame than when computed in the mantle reference frame thus we build summary rays by applying a backward rotation of the inner core at angular velocity in order to sum residuals which sample the same inner core region at different times the mean standard deviation of the summary ray residuals computed for different values of should exhibit a minimum for the effective value this method has been applied to absolute pkp df residuals in considering only polar paths for which inner core heterogeneities are dominant with respect to mantle heterogeneities the data used come from a high quality file derived by engdahl et al engdahl e r van der hilst r buland r 1998 global teleseismic earthquake relocation with improved travel times and procedures for depth determination bull seismol soc am 88 722 743 from the catalogs of the international seismological centre isc for the period 1964 1995 the minimum standard deviation is obtained for the null rotation rate a similar analysis on the absolute pkp bc residuals which correspond to paths that do not sample the inner core shows that mantle heterogeneities are not at the origin of the observed minimum the same method has also been applied to a set of more than 1200 worldwide distributed pkp bc pkp df differential travel time residuals hand picked by ourselves or gathered by different authors for specific core studies here again the minimum standard deviation is obtained for the null rotation implying a synchronous rotation of the inner core with the mantle however the limited number of very old data and the geographic distribution of the paths prevent us from obtaining a resolution better than 1 year in particular a small super rotation with 1 year cannot be ruled out with the presently available data the problem of the level of the inner core heterogeneities compared to that of the mantle which is another possible limitation of the method is also discussed

convection and anisotropy of the inner core estimation of the rayleigh number of the inner core suggests that this region is convecting the flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed phase of iron such that compressional wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent this result is in agreement with seismological evidence that the inner core is elastically anisotropic

a model for sedimentary compaction of a viscous medium and its application to inner core growth summary a detailed study of the physics of a 1 d sedimentary compaction of a viscous medium was carried out both numerically and analytically for columnar and self gravitating spherical cases in view of applying it to the inner core growth process of the earth the effects of sedimentation rate and surface porosity upon the porosity profile were investigated it was found that the porosity profile differs depending on whether or not the sedimentation rate is larger than the darcy velocity velocity of the solid matrix when the fluid flows by buoyancy alone when the sedimentation rate is larger than the darcy velocity a thick constant porosity layer develops at the surface and below it the porosity decreases gradually towards the bottom when the sedimentation rate is smaller than the darcy velocity the porosity profile is characterized by a mushy layer at the top where the fluid is expelled by the deformation of the solid underlain by a thick layer of constant porosity termed the residual porosity such a porosity profile can be understood as the propagation of a half sided solitary wave the study was extended further for the self gravitating spherical case formation of an unstable porosity structure and the appearance of solitary waves were discovered for the case of monotonically decreasing sedimentation rate given the size of the sphere formed by sedimentary compaction according to the magnitude of the ratio of sedimentation rate to darcy velocity three types of porosity structure which differ in force balance and the typical length scale required for porosity decrease were discovered one such structure is where a low porosity layer forms at the top accompanied by solitary waves beneath it indicating that a crust like region can develop at the surface of the inner core

the existence of an inner core super rotation questioned by teleseismic doublets abstract the first evidence for a differential rotation of the earth s inner core with respect to the mantle comes from the detection of a variation over 30 years of the differential travel time anomalies of seismic core phases song x richards p g 1996 seismological evidence for differential rotation of the earth s inner core nature 382 221 224 the comparison of teleseismic doublets provides a powerful means to measure such differential travel times and to test their temporal variation contrary to direct measurements of differential travel times this technique does not require to have an accurate location of the seismic events this method is first checked on examples of doublets for which no differential travel time is expected these tests allow us to point out the difficulties such as polarity reversals which may be encountered in the use of the doublet method it is then applied to deep tonga events recorded in france and to the south sandwich islands events recorded at station college col alaska which led song and richards to propose an inner core rotation for the first path we find no time variation in agreement with previous studies for the path from south sandwich island to col the doublet analysis shows that no significant temporal change in pkp travel time can be detected within the resolution of the method which is about 0 05 s the variation of the residuals observed by song and richards about 0 3 s over 30 years is in a large extent ascribable to hypocenter mislocations consequently present seismological observations do not detect the inner core differential rotation because if it exists it is smaller than about 0 2 year the present detection capacity of seismology

alluvial fans formed by channelized fluvial and sheet flow i theory alluvial fans and fan deltas are of three basic types those built up primarily by the action of constantly avulsing river and stream channels those constructed by sheet flows and those resulting from the successive deposition of debris flows the present analysis is directed toward the first two types a mechanistic formulation of flow and sediment transport through river channels is combined with a simple quantification of the overall effect of frequent avulsion to derive relations describing the temporal and spatial evolution of mean i e averaged over many avulsions bed slope and elevation in an axially symmetric fan an example of a fan formed predominantly by the deposition of sand is compared to a similar one formed predominantly by the deposition of gravel in each example the case of channelized flow is compared to the case of sheet flow the model is applied to the tailings basin of a mine in the companion paper

palaeoflow reconstruction from fan delta morphology on mars abstract alluvial fans and deltas on mars record past hydrological conditions until now these conditions have been inferred from the morphology of the feeder channels and the deposits from images and digital terrain models dtms and from calculations of the bulk fluxes of water and sediment based on the dimensions of upstream channels neither method can distinguish between dilute river like flows and dense sediment laden flows however while the formation time scales for these two sediment transport modes differ by orders of magnitude the objective of this paper is to compare dtm data quantitatively with a morphological model to infer sediment transport mode and formative duration we present a quantitative morphological model for fan and delta formation that assumes as little as possible the model calculates the growth of a sedimentary body in a crater lake represented by a low gradient subaerial cone on top of a high gradient subaqueous cone the volume of the cone is constrained by the influx of sediment while the elevation of the break in slope that is the shoreline is constrained by the influx of water the water and sediment fluxes were calculated with physics based predictors based on the feeder channel small scale morphology such as crater wall irregularities concavity of the fan surface and channel avulsion is ignored the model produces alluvial fans stair stepped fan deltas and gilbert fan deltas as well as hitherto unidentified crater wall drapes the parameters that determine which morphology emerges are the supply of sediment and water to the basin the size of the basin and the duration of the flow a direct comparison between the cone model and hrsc dtm data for five deltas and an alluvial fan demonstrates that single event dilute flows of short duration days to years have created all of the deposits two gilbert fan deltas were formed in overspilling crater lakes from long low gradient upstream channels one alluvial fan was formed in a similar manner except that the damaged crater did not lead to ponding three stair stepped deltas were formed from short high gradient upstream channels that only partially filled the crater lakes

introducing fiji and icy image processing techniques in ichnological research as a tool for sedimentary basin analysis abstract in recent years image treatment has been appraised as a very powerful tool to facilitate ichnological analysis especially in marine cores of modern sediments supporting the determination of certain ichnological features however it is still a new approach and detailed research is necessary to encounter a faster and more efficient method the present study focuses on two image processing techniques fiji and icy and their comparison with a refined version of the well established high resolution image treatment strengths and weaknesses of the methodologies for the determination of three main features were explored i visibility of trace fossils ii quantification of the percentage of bioturbated surface and iii penetration depth estimation refined high resolution image treatment gives the best results for enhanced visibility of trace fossils whereas fiji is found to be a sound and rapid option one disadvantage shared by fiji and icy is the binary character of the produced images which may impede later ichnotaxonomical differentiation both fiji and icy fiji are rapid alternatives for quantifying the bulk amount of bioturbated surface the magic wand method refineedge based on high resolution image treatment provides good results regardless of the contrast of the images and it additionally allows for a more detailed quantification the semi automatic character of icy favors quick estimation of penetration depth and facilitates differentiation between distinct tracemaker communities based on a rapid quantification of pixel values thus fiji and icy methods offer good results and are much less time consuming than high resolution image treatment they are proposed as faster alternatives for the estimation of ichnological features especially useful at the beginning stages of research when a large number of samples must be analyzed

the pulse of calm fan deltas abstract at the heart of interpreting the history of earth surface evolution preserved in the rock record is distinguishing environmental allogenic forcing from internally generated autogenic noise allogenic deposits classically have been recognized by their cyclic nature which apparently results from periodic changes in base level sediment supply or tectonics autogenic deposits which are quite variable in their origin and scale are caused by the nonlinearity of sediment transport and might be expected to have a random or scale free fractal signature here we describe a robust mechanism that generates cyclic deposits by an autogenic process in experimental fan deltas sheet flow over the fan surface induces deposition and an increase in fluvial slope and curvature to a point where the surface geometry is susceptible to a channelization instability similar to channel initiation on hillslopes channelized flow results in incision and degrading of the fan surface to a lower slope releasing a

the strength of gravitational core mantle coupling gravitational coupling between earth s core and mantle has been proposed as an explanation for a 6 year variation in the length of day lod signal and plays a key role in the possible superrotation of the inner core explaining the observations requires that the strength of the coupling falls within fairly restrictive bounds however the value of is highly uncertain because it depends on the distribution of mass anomalies in the mantle we estimate from a broad range of viscous mantle flow models with density anomalies inferred from seismic tomography requiring models to give a correlation larger than 70 to the surface geoid and match the dynamic core mantle boundary ellipticity inferred from earth s nutations we find that 3 10 19 2 10 20 n m too small to explain the 6 year lod signal this new constraint on has important implications for core mantle angular momentum transfer and on the preferred mode of inner core convection

dynamic single thread channels maintained by the interaction of flow and vegetation most rivers on earth today flow as a single channel in some cases with occasional islands and follow a more or less sinuous course however single thread channels have proven difficult to reproduce and study experimentally experimental self formed channels tend to widen and subdivide leading to a braided pattern cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single thread channel we show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single thread our experimental strategy a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth leads to the evolution of a dynamic self maintaining single thread channel with well defined banks and floodplain by eliminating weak flow paths the vegetation corrals the water into a single dominant channel until the reduction in total wetted width leads to a new self organized state in which the flow removes vegetated area as fast as it is produced the new channel is deeper and has a broader distribution of depths than the braided one with channel size adjusted to carry almost all the flood flow the resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field specifically erosion at the outside of bends bend growth and bar development our methodology provides a basis for experimental development of self sustaining high amplitude meanders and has applications for river management and basic research purposes

a time varying 3 d displacement model of the 5 9 year westward motion and its applications for the global navigation satellite system positions and velocities

using pre critical pkikp pcp phases to constrain the regional structures of the inner core boundary beneath east asia abstract we collected 177 pre critical pkikp pcp records assembling a wealth of traveltime and amplitude data these observations sample the inner core boundary icb beneath east asia with good spatial coverage combined with previous studies our results demonstrate a 100 km wide anomaly with positive pkikp pcp traveltime residuals surrounded by negatives beneath the yellow sea area 123 e 33 n yellow sea anomaly after correcting the elliptic effects and mantle vp heterogeneities based on the tomography models the residuals of the yellow sea anomaly remain at least 0 6 s faster than those of the surrounding areas suggesting a thickening of 2 3 km between the icb and core mantle boundary cmb due to the negative cmb topography along the western pacific rim we attribute this anomaly mainly to negative icb topography across the northern border of the yellow sea anomaly pkikp pcp amplitude ratios increase by approximately 50 from north to south which can be explained by an approximately 0 6 g cm3 raise in icb density contrast these traveltime and amplitude features suggest a mosaic structure at the icb beneath the yellow sea areas