sedimentological characteristics of small rivers with loessic headwaters in the chaco south america some sedimentological characteristics of uvial environments located in the northeastern region of the chaco pampa plain were analysed in order to determine the possible in uence of the loessic headwaters of local basins concentrations of suspended sediments as well as grain size of the river beds were compared unexpectedly it was found that the suspended load has an inverse relationship with the hydrometric levels with the exception of highly saline streams conductivity values between 4300 and 11 000 l sc m 1 the mean concentration of suspended sediments was 63 1 and 206 3 mg l 1 in ood and low water periods respectively the grain size of bed sediments was relatively homogeneous along the whole hydrological cycle sandy silty bottoms predominate in channels followed by silty sandy and clayey silty bottom types sediment transport mainly occurs in accelerating ow suspension overcoming the critical erosion velocity during ood periods some parameters exceeded by 70 the values recorded during the low water phase 2000 elsevier science ltd and inqua all rights reserved

characteristics of atmospheric divergence and convergence in the indian ocean inferred from scatterometer winds abstract large scale surface atmospheric convergence and divergence patterns in the indian ocean are mapped using high spatial resolution merged scatterometer wind vectors during 1991 2000 the convergence zone evolves to north of 15 s as a result of convection promoted by warm 28 c equatorial sea surface temperature sst and it exhibits strong intensity during boreal summer and winter a divergence zone evolves to the south of 15 s as a result of subdued convection caused by colder sst

clay mineral assemblages from late quaternary deposits on vancouver island southwestern british columbia canada resume dans le secteur de l ile de vancouver les formations de dashwood drift cowichan head quadra sand et vashon drift se sont deposees au cours des periodes glaciaires et non glaciaires du pleistocene terminal elles presentent des variations importantes du cortege argileux dont certaines sont relatives aux fluctuations climatiques les periodes glaciaires sont caracterisees par des chlorites riches en fer des illites toutes deux bien cristallisees et des smectites avec une morphologie rappelant celle de smectites developpees a partir de roches volcaniques la mineralogie des argiles des depots non glaciaires est plus complexe elle est marquee en outre par la presence de vermiculite kaolinite halloysite et de mineraux interstratifies irreguliers ces assemblages sont mediocrement preserves et montrent une degre d alteration pedologique plus eleve par rapport aux assemblages glaciaires les variations importantes enregistrees dans les depots nonglaciaires sont egalement dues a des facteurs secondaires tels la sedimentation differentielle les sources sedimentaires variantes et des possibles modification diagenetiques toutefois ces facteurs ne semblent pas obliterer de maniere significative les empreintes climatiques des mineraux argileux cette etude permet egalement de differencier des sediments remanies sous regime glaciaire de determiner les relations entre les unites lithologiques d une meme coupe et d etablir l origine des mineraux argileux rencontres

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

inner core freezing and melting constraints from seismic body waves abstract hypotheses for the mechanisms of growth of earth s inner core can be tested from observations of lateral variations of elastic and anelastic properties near the inner core boundary differential travel times of pkikp pkikp and the apparent travel time of p waves diffracted around the inner core are consistent with the existence of a stably stratified globally uniform region of reduced velocity gradient at the bottom of the outer core this layer may be a zone of iron enrichment relative to the bulk of the outer core representing a zone either of crystallization or melting of the inner core weak backscattered pkikp in the equatorial eastern hemisphere can be made consistent with either a hypothesis of freezing or melting in a melting hypothesis the eastern hemisphere is texturally older and smoother with larger crystals or smaller elastic contrasts across grain boundaries providing weaker backscatter to the coda of pkikp additional observations consistent with higher homologous temperature and melting in this region are the existence of a thin low velocity layer in the uppermost inner core inferred from multipathing of pkikp pkikp waves and a bright spot in the amplitude of pkiikp waves observed at antipodal distances alternatively a freezing hypothesis in the eastern hemisphere is an inner core that is growing radially outward with crystals stretched in the vertical direction this hypothesis can simultaneously explain weak backscattered pkikp coda and high attenuation of transmitted pkikp from the loss of backscattered energy at angles perpendicular to vertically oriented crystals strong backscattering observed in the coda of pkikp sampling the equatorial western hemisphere of the inner core agrees best with a heterogeneity having an isotropic distribution of scale lengths in the uppermost inner core

climatology of the itcz derived from era interim reanalyses 1 the intertropical convergence zone itcz is usually analyzed in terms of the precipitation field this study presents a new climatology of the itcz based on winds from era interim reanalyses for the period 1990 2009 the central latitude of the itcz is defined as the zero crossing of the meridional wind averaged over 10 model levels below 900 hpa results of the zonal averaging of the meridional wind and wind convergence are compared with the zonally averaged precipitation from the era interim and trmm data sets collocation properties of precipitation maxima and the central latitude of the itcz are discussed for different land and ocean regions it is found that the location of the itcz in wind and precipitation fields coincides over the atlantic and east pacific over other regions and especially over the tropical continents the fields on average do not coincide

relationship between surface atmospheric convergence over indian ocean and indian rainfall atmospheric convergence regions over the tropical indian ocean have been mapped for the first time using 31 years of vector wind data the convergence fields reveal that the energetic summer monsoon winds enhance convergence in the central arabian sea and in the eastern bay of bengal when compared with weak winter monsoon winds the summer monsoon is also effective in spatial migration of convergence regions in both basins area integrated convergence time series reveals an annual cycle with high amplitude during summer monsoon which occurs in phase with indian rainfall the study explores the prospects of using the convergence as one of the predictors of indian rainfall

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

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

seasonal and interannual variability of atmospheric convergence zones in the tropical pacific observed with ers 1 scatterometer monthly images of atmospheric convergence zones in the tropical pacific were produced with 1992 1994 ers 1 scatterometer wind vectors from the images the position width and intensity of the convergence zones can be determined latitude time sections of ocean surface wind divergence show that the summer position of the itcz in the eastern pacific during the observed period exceeded the normal position northward by 3 6 latitude and the annual cycle in the western pacific for 1994 was quite weak implying a persistently unusual case

double intertropical convergence zones a new look using scatterometer 1 the high resolution wind vectors observed by the space based scatterometer quikscat from 1999 to 2002 show that the double intertropical convergence zones itcz exist in the atlantic and the eastern pacific oceans for most of the annual cycle and are far more extensive than previously recognized for most of the time the southern itcz is weaker than the northern one the stronger itcz occurs when the northerly trade winds meet the southerly trade winds over warm water resulting in deep convection the weaker itcz over cooler water is caused by the deceleration of the surface winds as they approach the cold upwelling water near the equator decreases in vertical mixing and increases in vertical wind shear in the atmospheric boundary layer are suggested to be the causes of the deceleration of the trade winds as they move from warmer to colder water

detrital clay grain coats in estuarine clastic deposits origin and spatial distribution within a modern sedimentary system the gironde estuary south west france

evolutionary structure of the eastern pacific double itcz based on satellite moisture profile retrievals abstract for about a month near the boreal vernal equinox the eastern pacific intertropical convergence zone itcz is observed to form two troughs quasi symmetrically situated about the equator near 5 7 latitude during years when an equatorial sea surface cold tongue is present e g la nina years the three dimensional structure and temporal evolution of the eastern pacific double itcz is documented using weekly cloud liquid and ice water fields and relative humidity profiles retrieved from special sensor microwave temperature 2 measurements the depth of convection in the southern branch of the double itcz as determined by the coincident presence of cloud liquid and ice as well as by upward motion inferred from the relative humidity field is observed to be sensitive to both the underlying sst and subsidence from the northern branch the equatorial sea surface cold tongue appears to be the determining factor regulating the formation of a double itcz in the eastern pacific areas of deep convectio

facies associations detrital clay grain coats and mineralogical characterization of the gironde estuary tidal bars a modern analogue for deeply buried estuarine sandstone reservoirs abstract estuarine tidal bar sandstones are complex reservoir geobodies commonly exploited by the oil and gas industry in order to better predict the reservoir potential of these geobodies this study provides a modern day reservoir analogue describing tidal bars in the inner and outer gironde estuary from the microscopic to the macroscopic scale the originality of this work lies in the multi scale study of modern estuarine tidal bars based on numerous piston cores extracted in a high energy environment this work demonstrates that these tidal bars are composite sedimentary bodies made up of individual reservoir sand units separated by thick muddy layers their vertical facies associations and internal architectures are controlled by local hydrodynamic variations and seasonal river influxes detrital clay grain coats are notably characterized using a portable and handheld mineral spectrometer from the base to the top of the tidal bars x ray diffraction and electron microscopes reveal that these coats are mainly composed of di octahedral smectite illite chlorite and kaolinite associated with other components such as diatoms or pyrite the best reservoir geobodies are those with the minimum clay permeability barriers at the macro and mesoscale an optimum coated grain content and clay fraction volume is also needed for generating authigenic clay coatings and inhibiting quartz overgrowth these conditions are met within the tidal sand bars of the outer estuary funnel that are expected to be the best reservoir geobodies in deeply buried sandstones

a satellite derived climatology of the itcz abstract this paper presents fundamental climatological characteristics of the intertropical convergence zone itcz in a simple concise manner using the highly reflective cloud hrc dataset this satellite derived dataset uses both visible and infrared observations to measure the frequency of occurrence of large scale convective systems over the global tropics at a 1 spatial resolution these dataset characteristics make the hrc particularly well suited for climatological analysis of the itcz because the dataset is based on estimates of organized deep convective cloud systems rather than observations of clouds as a whole and it provides the spatial resolution needed to identify thew large wale convective structures furthermore the dataset covers a time period extending nearly two decades which provides for a fairly robust climatology and the opportunity to examine seasonal and interannual variability of both the convection and the latitude of the itcz

a laboratory model for convection in earth s core driven by a thermally heterogeneous mantle thermal convection experiments in a rapidly rotating hemispherical shell suggest a model in which the convection in earth s liquid outer core is controlled by a thermally heterogeneous mantle experiments show that heterogeneous boundary heating induces an eastward flow in the core which at a sufficiently large magnitude develops into a large scale spiral with a sharp front the front separates the warm and cold regions in the core and includes a narrow jet flowing from the core mantle boundary to the inner core boundary the existence of this front in the core may explain the pacific quiet zone in the secular variation of the geomagnetic field and the longitudinally heterogeneous structure of the solid inner core

a laboratory examination of floc characteristics with regard to turbulent shearing abstract turbulent shear generated within the water column is recognised as having a controlling influence over both the flocculation of fine grained cohesive sediments within estuarine waters and their respective aggregate break up this study examines the inter relationships between floc characteristics over increasing turbidity 80 200 mg l 1 and turbulent shear 0 0 6 n m 2 environments by the use of a laboratory flume within which a suspension can be sheared at a controlled rate and with an unintrusive macro lens miniature video camera mounted in a viewing port on the flume channel wall the camera enables the direct simultaneous measurement of both floc size and settling velocity from which accurate estimates of floc effective density and porosity can be made measurements were made 120 s after the induced turbulence has ceased the instrument has an upper viewing turbidity limit of 210 mg l 1 and a lower resolution of 20 m the sediment was collected from the inter tidal mudflats at weir quay on the tamar estuary in devon southwest england the results indicated that increasing turbidity at low shear levels encouraged floc growth but the effect of the increasing turbulent shear 0 35 n m 2 together with increasing concentration in suspension causes disruption rather than enhancing the flocculation process at shears up to 0 35 n m 2 the largest size and settling velocity flocs were produced at high concentrations whereas above 0 35 n m 2 disruption caused smaller flocs at higher concentrations the use of algorithms which were based either on a single floc characteristic i e size or settling velocity or a mean fractal dimension were seen not to accurately approximate the experimental data a multiple regression analysis of the experimental data produced the following formula based on mean values of the 20 largest flocs sampled under each of the imposed environmental conditions referred to as max20size mean values settling velocity 0 301 0 00337 rms of the gradient in turbulent velocity fluctuations 0 000606 spm 0 00335 floc size which proved to be the most accurate representation with an r 2 value of 0 95 a similar formula was determined for the average value of the four fastest settling flocs within each sample group max4w s this highlights the importance of modelling algorithms that are developed from data that take into account effective density variations i e simultaneous size and settling velocity measurement

estimates of heat flow in the deep mantle based on the power requirements for the geodynamo 1 regeneration of the magnetic field by convection in the core places demands on heat flow into the base of the mantle if the heat flow is too low thermal convection is shut off and the rate of generation of compositional buoyancy by the solidification of the core becomes too low to sustain the geodynamo conversely a large heat flow causes rapid growth of the inner core so that convection prior to the appearance of the inner core must be sustained by thermal buoyancy alone the attendant requirements on primordial heat become more severe as the age of the inner core decreases we show that estimates of the present day heat flow satisfy the power requirements for the geodynamo however the resulting thermal history is incompatible with estimates of mantle temperatures prior to 3 ga this discrepancy can be resolved by accumulating radioactive isotopes in d or adding heat sources to the core

accumulation of fine grained material in a danish tidal area abstract the exchange of fine grained material m between the north sea and the tidal area of gradyb in the danish wadden sea has been determined by means of the 210 pb dating method the amount of fine grained material accumulating in the area 169 km 2 has been calculated to be 142 10 3 t yr 1 of this approximately 85 is derived from the north sea 5 6 from rivers 4 from internal coastal erosion and another 5 6 from the combined effect of waste atmospheric deposition and net primary production these results have been verified through a budget for excess 210 pb it is demonstrated that fine sediments from the north sea are sorted before accumulating in the wadden sea with the result that the deposited material contains more coarse silt and less clay than is found in the source material from the north sea the relation between accumulated fine grained material and the volume of exchanged water is found to be in the same order of magnitude in gradyb as in jadebusen and dollard this relation is suggested to be a characterising parameter of the sedimentation in tidal areas

extremes of the indian summer monsoon rainfall enso and equatorial indian ocean oscillation it is well known that anomalies of the indian summer monsoon rainfall ismr are linked to el nino and southern oscillation enso we show that large anomalies of the ismr are also linked to the equatorial indian ocean oscillation equinoo between states with enhancement suppression of atmospheric convection over the western part of the equatorial indian ocean with suppression enhancement over the eastern part and associated changes in the anomaly of the zonal wind along the equator equinoo is the atmospheric component of the coupled indian ocean dipole mode there is a strong relation between the large anomalies of ismr and a composite index which is a linear combination of the indices for enso and equinoo with all seasons with large deficits excess characterized by small large values of the index however the variation of ismr within one standard deviation is more complex and does not appear to be related to the composite index

clay mineral and heavy metal distributions in the northeastern north sea abstract clay mineralogy and heavy metal distribution of surface sediments of the northeastern north sea have been analysed in order to show the origin and transport pathways of fine grained sediments the distribution patterns of clay minerals largely reflect regional current patterns fine material enriched in smectite derived mostly from the german bight sector in the south is transported by the jutland current parallel to the west coast of denmark into the skagerrak where a decreasing proportion of smectite indicates the increasing influence of the central and northern north sea currents illite and chlorite have identical distribution patterns in the northeastern north sea which suggests a common origin for both clay minerals this origin is located in pleistocene relict sediments of the northern north sea rather than in a contribution from the north atlantic zinc cadmium copper and lead in surface sediments of the north sea when compared to background values are significantly enriched sediments of the inner german bight are in comparison with other north sea sediments highly polluted a zone of high heavy metal contents zn cd and cu is found along the german and danish coasts comparable to the smectite distribution indicating the transport of fine grained polluted sediments to the north further to the north these sediments are diluted by less polluted sediments finally in the skagerrak and the norwegian trench a relatively low stage of pollution is reached

the possibility of lateral structure inside the core and its implications for nutation and earth tide observations summary we show that there can be lateral structure inside the fluid core caused by gravitational forcing from the mantle from the inner core or from topography on the core mantle or inner core outer core boundaries we describe a method for calculating the internal structure given knowledge of the forcing we discuss the possible effects of this structure on results for the core mantle boundary topography inferred from observations of the earth s forced nutations and diurnal earth tides we consider the possible implications of a thin low density fluid layer at the top of the core

thermochemical structure and dynamics of the african superplume 1 we present a new three dimensional 3 d model of the thermochemical structure of the african superplume region obtained from simultaneous inversion of global seismic and convection related data convection related observations include the global free air gravity field tectonic plate motions dynamic surface topography and the excess ellipticity of the core mantle boundary a 3 d image of the chemically induced density perturbations provides direct evidence that intrinsically dense material is entrained within the superplume and concentrated into a rounded structure 1000 km above the core mantle boundary the thermally induced density perturbations are greater in magnitude than the chemically induced implying overall positive buoyancy throughout the superplume the observed morphology and density signatures are consistent with a thermochemical plume that has risen from a compositionally distinct pile at the base of the mantle and may be currently deforming under the influence of its intrinsic negative chemical buoyancy citation simmons n a a m forte and s p grand 2007 thermochemical structure and dynamics of the african superplume geophys res lett 34 l02301 doi 10 1029 2006gl028009

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

inssev an instrument to measure the size and settling velocity of flocs in situ abstract an instrument has been developed to observe the settling of individual flocs in turbid water in order to measure size and settling velocity spectra of estuarine cohesive suspended sediments inssev in situ settling velocity instrument is bed mounted and comprises a computer controlled decelerator chamber that collects a sample of water from which some of the suspended matter is allowed to enter the top of a settling column the settling flocs are viewed using a miniature video system subsequent analysis of video tapes can provide direct measurements of size and settling velocity of individual flocs down to 20 m from this information floc density can be estimated the main feature of the instrument is its ability to video flocs in situ irrespective of the concentration in the estuary with as little disturbance to their hydrodynamic environment as possible preliminary field testing in the tamar estuary has given useful results in flow velocities up to 0 4 m s 1 and in concentrations up to 200 mg 1 1 the video recordings show large numbers of low density flocs with multiple structures linked by fine organic fibres

the age of the inner core abstract the energy conservation law when applied to the earth s core and integrated between the onset of the crystallization of the inner core and the present time gives an equation for the age of the inner core in this equation all the terms can be expressed theoretically and given values and uncertainties of all relevant physical parameters the age of the inner core can be obtained as a function of the heat flux at the core mantle boundary and the concentrations in radioactive elements it is found that in absence of radioactive elements in the core the age of the inner core cannot exceed 2 5 ga and is most likely around 1 ga in addition to have an inner core as old as the earth concentrations in radioactive elements needed in the core are too high to be acceptable on geochemical grounds

estuarine flocs their size settling velocity and density the size and settling velocity of flocs of suspended sediments from the chesapeake bay were measured in laboratory experiments and in the field the curves between floc diameter and settling velocity showed a non stoke s relationship that was best described by the following settling velocity cm s 1 73 floc diameter cm 0 78 furthermore the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size in addition to changing density a cylinder shape was found to be the best shape factor

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

tectonic history of the earth s inner core preserved in its seismic structure seismic data show that the earth s inner core is structurally complex numerical simulations suggest that whereas the deeper structure may be inherited from past episodes of inner core growth the origin of the shallow structure is due to ongoing deformation

settling speeds of floes in fresh water and seawater the settling speeds of floes of fine grained natural sediments approximately 10 200 m in diameter have been measured in both fresh water and seawater these floes were formed at fluid shears of 100 200 and 400 s 1 and at sediment concentrations of 10 100 and 400 mg l values typical of conditions in the near shore areas of lakes and oceans especially during storm conditions it is demonstrated that the settling speed of a floe is a strong function of fluid shear and sediment concentration as well as of the diameter of the floe but it is a weak function of salinity for the same diameter and salinity floes produced at the lower fluid shears and sediment concentrations have lower settling speeds than do floes produced at higher fluid shears and sediment concentrations if the conditions of fluid shear and sediment concentration under which the floes were produced are unknown or ignored it is shown that the settling speed of a floe is a weak function of diameter and salinity

coagulation rates of clay minerals and natural sediments abstract coagulation experiments conducted using illite kaolinite montmorillonite and four natural sediment samples in blade and couette reactors with solutions of various salinities yielded collision efficiency factors significantly higher than those in the previous literature indicating that coagulation begins at lower salinities 1 2 1 the natural sediments do not generally behave as might be predicted for a mixture of the standards of the minerals of which the natural sediment samples were comprised the half times for coagulation of the particles indicate that in nature the coagulation process would probably be completed in the first few parts per thousand salinity

satellite observations of the southeast pacific intertropical convergence zone during 1993 1998 an intertropical convergence zone in the southeast pacific ocean is described from monthly mean 1 1 ocean vector wind rainfall sea surface temperature and integrated water vapor measurements recorded from satellites time interval of the investigation was january 1993 to december 1998 when ocean and atmosphere conditions during 1993 1996 were normal compared to the 1997 1998 el nino the southeast pacific intertropical convergence zone sitcz occurred in march april at 8 s 2 s 130 w 90 w during 1993 1996 the average march april values of sitcz surface wind convergence rain rate sea surface temperature and integrated water vapor were 3 3 10 6 s 1 3 3 mm d 1 27 3 c and 45 3 mm respectively a statistical model of the monthly mean observations predicted rainfall greater than the 2 mm d 1 threshold when surface wind convergence was greater than the 1 5 10 6 s 1 threshold and sea surface temperature was above 27 c during non el nino conditions sitcz sea surface temperature was greater than sea surface temperature in the 2 s 2 n equatorial band with maximum difference in march april which would create a surface wind convergence larger in march april compared to other months the intertropical convergence zone itcz which occurred north of the equator throughout the year and the sitcz were separated by divergent wind low 2 mm d 1 rainfall and cold 27 c surface water except during the intense 1998 el nino the rain rate of the itcz was minimum in march april during 1993 1996 and comparable to the sitcz rain rate

effect of flow depth ions and salinity on suspended sediment concentration abstracteffects of flow depth ions and salinity on the evolution of suspended sediment concentration ssc are presented experiments are conducted in an annular flume using three different sediments rhine mud alumina and silica in ionic and saline water observations show that at a constant bed shear stress in ionic water the ssc of all sediments decreases because of an increase in the flow depth h at a constant h the ssc increased with an increase in when h and remained constant alumina and silica particles quickly flocculated and attained a lower equilibrium concentration ceq in ionic water than in saline water similarly the flocculation process of rhine mud is faster in ionic water but the ceq in ionic water is higher than that of saline water for all the sediments tested the time to reach ceq is greater in saline water than in ionic water in saline water the evolution of ssc of rhine mud is in between that of alumina and silica

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

hemispherical variations in seismic velocity at the top of the earth s inner core knowledge of the seismic velocity structure at the top of the earth s inner core is important for deciphering the physical processes responsible for inner core growth1 2 3 previous global seismic studies4 5 6 7 8 9 have focused on structures found 100 km or deeper within the inner core with results for the uppermost 100 km available for only isolated regions10 11 12 here we present constraints on seismic velocity variations just beneath the inner core boundary determined from the difference in travel time between waves reflected at the inner core boundary and those transmitted through the inner core we found that these travel time residuals observed on both global seismograph stations and several regional seismic networks are systematically larger by about 0 8 s for waves that sample the eastern hemisphere of the inner core 40 e to 180 e compared to those that sample the western hemisphere 180 w to 40 e these residuals show no correlation with the angle at which the waves traverse the inner core this indicates that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0 8 higher than that of the western hemisphere

ocean atmosphere interaction over agulhas extension meanders abstract many years of high resolution measurements by a number of space based sensors and from lagrangian drifters became available recently and are used to examine the persistent atmospheric imprints of the semipermanent meanders of the agulhas extension current aec where strong surface current and temperature gradients are found the sea surface temperature sst measured by the advanced microwave scanning radiometer earth observing system amsr e and the chlorophyll concentration measured by the sea viewing wide field of view sensor seawifs support the identification of the meanders and related ocean circulation by the drifters the collocation of high and low magnitudes of equivalent neutral wind enw measured by quick scatterometer quikscat which is uniquely related to surface stress by definition illustrates not only the stability dependence of turbulent mixing but also the unique stress measuring capability of the scatterometer the observed rotation of enw in opposition to the rotation

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

heterogeneity and anisotropy of earth s inner core seismic observations provide strong evidence that earth s inner core is anisotropic with larger velocity in the polar than in the equatorial direction the top 60 80 km of the inner core is isotropic evidence for an innermost inner core is less compelling the anisotropy is most likely due to alignment of hcp hexagonal close packed iron crystals aligned either during solidification or by deformation afterward the existence of hemispherical variations used to be controversial but there is now strong evidence from both seismic body wave and normal mode observations showing stronger anisotropy less attenuation and a lower isotropic velocity in the western hemisphere two mechanisms have been proposed to explain the hemispherical pattern either a inner core translation wherein one hemisphere is melting and the other is solidifying or b thermochemical convection in the outer core leading to different solidification conditions at the inner core boundary neither is yet able to explain all se

the shuffling rotation of the earth s inner core revealed by earthquake doublets earth s inner core rotates at a different rate than the mantle and discrepancies exist between rotation rates derived from geophysical observations and geodynamical simulations an inverse analysis of seismic data from repeating earthquakes over the past 50 years suggests that the rotation rate of the inner core fluctuates on decadal timescales