fertilizing potential of volcanic ash in ocean surface water the fertilization potential of newly erupted and well preserved ash from the 2000 hekla eruption in iceland was measured for the first time by flow through experiments as previously shown 1 the north atlantic ocean including the subarctic seas surrounding iceland is the largest net sink of the world s oceans for atmospheric co 2 owing to biological drawdown during summer 2 almost complete consumption of phosphate in chlorophyll rich areas of the north atlantic ocean might limit primary production and 3 in the southern pacific ocean and parts of the equatorial pacific ocean iron might limit primary production we found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate 1 7 mmol g 21 h 21 iron 37 0 mmol g 21 h 21 silica 49 5 mmol g 21 h 21 and manganese 1 7 mmol g 21 h 21 dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water macronutrients and bioactive trace metals are released fast enough to become available to support primary production

a new global pkp data set to study earth s core and deep mantle abstract we present an extension of the previously developed algorithm for simulated annealing waveform inversion of body waves sawib to resolve the interference between direct pkp seismic phases and their corresponding depth phases ppkp and spkp which occurs for shallow earthquakes this allows us to process shallow earthquakes previously discarded by the analysts and therefore improve spatial sampling of the deep earth by pkp phases the sawib algorithm is applied to available waveform data to determine pkp travel times and amplitudes the new data set of pkp travel times and amplitudes is significantly larger than previous ones pkp bc df differential travel time residuals display a hemispherical pattern in the inner core when plotted as a function of the angle between pkpdf propagation direction in the inner core and earth s rotation axis most anomalous differential travel times are along polar paths in the quasi western hemisphere 180 w 40 e corresponding to earthquakes in the south sandwich islands recorded at northern seismic stations pkp ab df differential travel times display a larger scatter which we attribute to heterogeneities at the base of the mantle relative amplitudes and t attenuation parameters are analyzed in terms of inner core attenuation the inner core attenuation decreases with increasing depth in the upper inner core in the depth range 150 220 km an hemispherical pattern appears with a quasi western hemisphere 40 e 180 e faster and more attenuating than the rest of the inner core when stacking pkp waveforms deconvolved by their source time function we do not find evidence of a global innermost inner core velocity discontinuity however we cannot rule out the existence of strong local heterogeneities or radial anisotropy variations from our data

a p wave velocity model of earth s core present earth core models derived from the retrieval of global earth structure are based on absolute travel times mostly from the international seismological centre isc and or free oscillation eigenfrequencies many core phase data are left out of these constructions e g pkp differential travel times amplitude ratios and waveforms this study is an attempt to utilize this additional information to construct a model of core p wave velocity which is consistent with the different types of core phase data available in conjunction with our waveform modeling we used 150 differential time measurements and 87 amplitude ratio measurements which were the highest quality observations chosen from a large population of global digital seismograph network gdsn records as a result of fitting these various data sets a one dimensional p wave velocity model of the core prem2 is proposed this model modified from the preliminary reference earth model prem dziewonski and anderson 1981 shows a better fit to the combined data set than any of the existing core models major features of the model include a sharp velocity discontinuity at the inner core boundary icb with a large jump 0 78 km s and a low velocity gradient at the base of the fluid core the velocity is nearly constant over the lower 100 km of the outer core the model features a depth dependent q structure in the inner core such that a constant t for the inner core fits the amplitude ratios and waveforms of short period waves moderately well this means the top of the inner core is more attenuating than the deeper part of the inner core in addition the p velocity in the lowermost mantle is reduced from that of prem as a baseline adjustment for the observed separations of the df and ab branches of pkp at large distances

a glassy lowermost outer core summary new theories for the viscosity of metallic melts at core pressures and temperatures together with observations of translational modes of oscillation of earth s solid inner core suggest a rapid increase in the dynamic viscosity near the bottom of the liquid outer core if the viscosity of the lowermost outer core f region is sufficiently high it may be in a glassy state characterized by a frequency dependent shear modulus and increased viscoselastic attenuation in testing this hypothesis the amplitudes of high frequency pkikp waves are found to be consistent with an upper bound to shear velocity in the lowermost outer core of 0 5 km s 1 at 1 hz the fit of a maxwell rheology to the frequency dependent shear modulus constrained by seismic observations at both low and high frequency favours a model of the f region as a 400 km thick chemical boundary layer this layer has both a higher density and higher viscosity than the bulk of the outer core with a peak viscosity on the order of 10 9 pa s or higher near the inner core boundary if lateral variations in the f region are confirmed to correlate with lateral variations observed in the structure of the uppermost inner core they may be used to map differences in the solidification process of the inner core and flow in the lowermost outer core

formation and growth of deep mantle plumes summary if whole mantle convection occurs in the earth s mantle then the core mantle boundary constitutes the lower boundary layer for mantle convection this boundary layer appears to be unstable on a small scale and thus may be a source of plumes of hot matter which penetrate the mantle and occasionally even the lithosphere producing hot spots a finite amplitude numerical code is used to study the formation of such plumes and their growth through the mantle the plumes are restricted to being two dimensional sheets rather than cylinders the initial conditions consist of a steadily convecting mantle and plumes are produced by introducing a perturbation in the form of either a pulse or a steady stream of heat into the bottom of the mantle two main results are obtained 1 a critical perturbation size has been found for a mantle with a rayleigh number of lo small perturbations produce plumes which fail to penetrate the mantle and instead are swept up by the pre existing convective pattern while large perturbations succeed in penetrating the mantle and reaching the lithosphere the critical perturbation size is shown empirically to be proportional to the effective bouyancy and to a factor related to the shape of the perturbation a perturbed region 150km wide and 60 km deep should produce a successful plume when the temperature perturbation is 200k or more 2 deep mantle plumes appear to require on the order of 50 100myr to penetrate the mantle episodic plumes on shorter time scales appear unlikely a similar time is required for plumes forming in an initially static uniform temperature mantle

coupled normal mode sensitivity to inner core shear velocity and attenuation summary we have studied the response of normal modes to perturbations in inner core shear velocity and attenuation using fully coupled mode synthetics our results indicate that i mode pairs n s l n 1 s l are strongly coupled by anelasticity ii this coupling causes shear velocity perturbations to strongly affect the q values of modes through exchange of inner core characteristics iii there is no evidence for a weakly attenuating inner core in shear and iv the discrepancy between attenuation models returned from normal modes and body waves is small these results suggest that inversions for inner core attenuation and shear velocity should be performed simultaneously and should take account of the strong cross coupling due to attenuation

lateral heterogeneity and azimuthal anisotropy in the north atlantic determined from ss s differential travel times to explore upper mantle heterogeneity beneath the north atlantic we have measured 70 ss s differential travel times using the waveform cross correlation method both the two way preliminary reference earth model prem and j b jeffreys bullen residuals exhibit a maximum variation of 17 s ranging from 10 to 7 and 9 to 8 s respectively the lack of correlation between ss s and s residuals along with the strong correlation between ss s and ss residuals suggests that ss s differential travel times eliminate source and receiver effects and sample the upper mantle anomalies near the ss bounce points without being strongly affected by lower mantle heterogeneities we find evidence for a strong local anomaly in the north atlantic residuals for bounce points immediately to the north of the azores gibraltar plate boundary average about 4 s faster than for the bounce points to the south of the boundary we infer that this velocity contrast exists in the lithosphere and continues below a depth of 200 km a series of linear multiple regression experiments demonstrate that variation in velocity with increasing age of the seafloor and azimuthal anisotropy are both significant contributors to the prem and j b residuals assuming that travel time delays are a linear function of the square root of the seafloor age we find the coefficient for age to be about 1 0 s m y this is smaller than but not significantly different from the corresponding slope for the s delays of intraplate earthquakes in the atlantic reported by j d duschenes and s c solomon 1977 and favors the presence of small amounts of water e g 0 1 in the upper mantle in modeling anisotropy we carry out an experiment using synthetic seismograms to examine the shear wave splitting phenomena in the anisotropic medium and investigate three possible forms for sh wave delay as a function of azimuth sinusoidal variations as a function of 2 4 and a combination of 4 predominant and 2 that mimics the delay expected in olivine crystals when the axis is aligned horizontally our regression models strongly prefer the predominance of a 4 to a 2 variation and the last type of anisotropy explains our data best from the preferred anisotropy model the olivine axis or the upper mantle shearing flow is inferred to be oriented n s the magnitude of the azimuthal variation suggests that anisotropy extends over a depth range of several hundred kilometers in the upper mantle

deep earth structure major developments in earth structure in the last four years have been concentrated in the description of the earth s lateral heterogeneity the regions that are heterogenous and the per cent variation of velocity and density in each region most studies find that lateral variation is concentrated in the upper 400 and lower 200 km of the mantle a radially symmetric earth model has been defined that represents the best average fit to seismic data in a broad frequency band sampling many regions p and s velocity is found to increase in zones of 50 km or less at 400 and 650 to 700 km depth the model is transversely anisotropic in the upper mantle it possesses a vertical axis of symmetry such that the elastic constants are different for vertical propagation than for horizontal and intermediate angles of propagation the real earth generally exhibits azimuthal anisotropy as well but the azimuthal anisotropy cannot be resolved by a global average of data the nature and magnitude of the anisotropy agrees with that found in ultramafic samples of the upper mantle in attenuation models of intrinsic attenuation have included the dispersive properties of intrinsic anelasticity and constructed relaxation models consistent with an observed frequency dependence of q in the body wave band there has been progress in mapping the scattering properties of the lithosphere attenuation due to scattering in the crust and lithosphere has been shown to have strong effects on the amplitudes of seismic waves at local and teleseismic distances

structure of the earth s inner core jacobs1 proposed that the earth s inner core is growing through the freezing of outer core material as the earth gradually cools2 recent studies have shown that compositional effects associated with this freezing process can release energy at a rate sufficient to power the geodynamo3 4 and may be crucial in determining the dynamic state of the outer core5 here we investigate the effects of composition on the freezing process itself drawing on metallurgical experience and speculate on the structure and state of the inner core we propose that the interface separating the inner and outer core is dendritic and argue that the region in which freezing takes place may extend throughout the entire inner core consequently the compositionally driven convective motions which stir the outer core and sustain the geodynamo also occur within the interdendritic spaces of the inner core the seismic evidence which corroborates this proposal is briefly reviewed

comment on wave propagation effects and the earth s structure in the lower mantle in a recent contribution haddon and buchbinder introduced a new shear velocity model for the lower mantle which combined with effects of velocity inhomogeneity at the base of the mantle they concluded to be consistent with observed sh arrivals preceding the core reflected phase scsh at distances beyond 70 o using kirchhoff wave theory they computed synthetic waveforms for the radially symmetric version of their model which has a 1 4 discontinuous velocity decrease at 2300 km depth that seem to match some sh data even without allowing for lateral heterogeneity however synthetic waveforms for this model computed using generalized ray theory and reflectivity do not match the kirchhoff synthetics or the data casting doubt upon the conclusions drawn in their study earlier models by lay and helmberger involving a 2 75 discontinuous velocity increase at a depth of about 2600 km require only slight modification in order to match all of the sh wave observations

scattered pkkp further evidence for scattering at a rough core mantle boundary abstract pkkp signals from novaya zemlya recorded at lasa at distances around 60 show consistent anomalies in both slowness and azimuth the observed anomaly suggests that the signal is a bc branch arrival although the arrival time corresponds to the df branch the bc branch however does not extend back to this distance the azimuth of approach is in the range 229 245 instead of the expected 186 these anomalies are associated only with pkkp analysis of the core phases pkikp and p p bc from the same events show that they arrived at lasa with the appropriate slownesses and azimuths the pkkp signals can be interpreted as scattered pkkp the scattering occurs on underside reflection at the core mantle boundary and is probably caused by topographic irregularities on the boundary itself the calculated scattering region has a surface projection at about 60 s 134 e which is outside the diametral plane through source and receiver and about 21 from the expected pkkp reflection point at 76 s 95 e both the direct and scattered arms of the pkkp signal have a pk path close to that of the c end of the bc branch the unexpectedly large amplitude of the arrival suggests that there may be a focusing of energy at c which would indicate a change in velocity gradient just above the inner core boundary the observations nevertheless require on the scattering interpretation lateral variations in the topography of the core mantle boundary and a region of relatively large topography responsible for the anomalous pkkp observations

seismic velocity and attenuation structures in the top 400 km of the earth s inner core along equatorial paths 1 we study seismic velocity and attenuation structures in the top 400 km of the earth s inner core based on modeling of differential traveltimes amplitude ratios and waveforms of the pkikp pkikp phases observed at the epicentral distance range of 120 141 and the pkpbc pkikp phases observed at the distance range of 146 160 along equatorial paths our data are selected from the seismograms recorded in the global seismographic network from 1990 to 2001 and many regional seismic networks the observed pkikp pkikp and pkpbc pkikp phases exhibit distinctive east west hemispheric patterns 1 at the distance ranges of 131 141 and 146 151 pkikp phases arrive about 0 3 s earlier than the theoretical arrivals based on the preliminary reference earth model prem for the pkikp phases sampling the eastern hemisphere 40 e 180 e of the inner core and about 0 4 s later for those sampling the western hemisphere 180 w 40 e at the distance range of 151 160 pkikp phases arrive about 0 7 s earlier than the predicted arrivals based on prem for those sampling the eastern hemisphere and about 0 1 s later for those sampling the western hemisphere 2 amplitude ratios of the pkikp pkikp phases at the distance range of 131 141 and of the pkikp pkpbc phases at the distance range of 146 151 are in general smaller for the pkikp phases sampling the eastern hemisphere than for those sampling the western hemisphere at distances greater than 151 the pkikp pkpbc amplitude ratios become indistinguishable for the two hemispheres these observations can be best explained by two different types of seismic velocity and attenuation models along equatorial paths one for each hemisphere in the top 400 km of the inner core for the eastern hemisphere the velocity structure has a velocity increase of 0 748 km s across the inner core boundary icb a small velocity gradient of 0 0042 km s 100 km in the top 235 km followed by a steeper velocity gradient of 0 1 km s 100 km extending from 235 km to 375 km and a velocity gradient of 0 01 km s 100 km in the deeper portion of the inner core the attenuation structure has an average q value of 300 in the top 300 km and an average q value of 600 in the deeper portion of the inner core for the western hemisphere the velocity structure has a velocity increase of 0 645 km s across the icb and a velocity gradient of 0 049 km s 100 km in the top 375 km the attenuation structure has an average q value of 600 in the top 375 km of the inner core our results suggest that the inner core hemispheric variations in velocity extend deeper than 375 km below the icb and the top 235 km of the inner core in the eastern hemisphere is anomalous compared to the rest of the inner core in having a small velocity gradient high velocity and high attenuation

a search for lateral heterogeneity in the inner core from differential travel times near pkp d and pkp c a search is made for lateral heterogeneity in the earth s inner core by analyzing the differential travel times between pkp df pkp cd and pkp cdiff these are p waves that are respectively transmitted through reflected by and diffracted around the inner core from this data heterogeneity in and near the inner core is found to be small residuals from prem in the 134 to 157 range are bounded by 0 8 sec consistent with a 0 9 variation in p velocity in the upper 200 km of the inner core the regional pattern of velocity variation inferred from the differential times is consistent with those obtained from global inversions of absolute pkp df times

seismic modelling of lateral heterogeneity at the base of the mantle summary results from several recent studies suggest that there are lateral heterogeneities of up to a few per cent in the lowermost 150 200 km of the mantle bullen s d region inferred anomaly sizes span the range from less than 50 km to greater than 1000 km in this study differences in the velocity structure among regions at the base of the mantle were inferred from an analysis of amplitude ratios of pkpab and pkpdf for given earthquake station pairs at distances greater than 155 sacks snoke beach we distinguish two kinds of regions a anomalous regions in which the mean median and spread in ab df amplitude ratios are significantly higher 50 per cent than for a reference radial earth model and n normal regions in which the distribution of the amplitude ratios is as expected the ab branch has near grazing incidence to the core and therefore maximum sensitivity to velocity structure compared to the near normal incident df phases using an iterative forward modelling approach we have determined general characteristics of the velocity structure for regions at the base of the mantle which can produce amplitude ratio distributions similar to those for an a region agreement between model and data is obtained over the period range from 0 5 s to greater than 10 s using a laterally heterogeneous model for the d region the model consists of cells which are 200 km in lateral extent with velocity variations of up to 1 per cent this structure is modulated by a region wide 1000km perturbation which increases smoothly from zero at the edges of the region to a negative 1 per cent at the centre small cells 40 km cannot produce anomalously large amplitude long period ab arrivals and larger cells 1000km cannot match the observed scatter the 200 km scale anomalies could be small scale convection cells confined to the d region

laboratory measurement of electrification of wind blown sands and simulation of its effect on sand saltation movement 1 this article presents a measurement of electrification generated by wind blown sands in a field wind tunnel and a numerical methodology to simulate the effect of electrification on the sand saltation movement after the mutual couple interaction between the sand movement and the wind flow is taken into account the measured data of electric charge on the uniform sands in the wind tunnel tests show that the sign of electric charge either negative or positive is mainly dependent on the diameter size of sand particles i e negative charge is gained when the diameter is smaller than 250 m and positive charge is obtained if the diameter is larger than 500 m and that for both uniform and mixed sands the average charge to mass ratio decreases with increasing the wind velocity and increases with height from sand bed meanwhile the measurement of electric field in wind sand cloud related to the electric charge displays that the magnitude of electric field increases generally as the wind velocity and the height increase and the direction of the field is always upwardly vertical to the earth s surface which is opposite to that of the fair weather field in order to exhibit the effect of electrification on sand saltation movement a theoretical model by considering the mutual coupling interaction between wind flow and sand movement is proposed after the electric force exerted on the moving sands is considered through solving the nonlinear coupling dynamic equations by a proposed program the effect of electrification on sand saltation motion e g trajectory is discussed quantitatively after that its effect on wind sand transport flux sand ejecta flux and wind profile is also displayed the results show that the prediction for the bagnold s kink is good agreement with the measurement in literature

transport and reaction of iron and iron stable isotopes in glacial meltwaters on svalbard near kongsfjorden from rivers to estuary to ocean abstract glacial meltwater has been suggested as a significant source of potentially bioavailable iron to the oceans however the supply of dissolved iron dfe in glacial meltwaters is poorly constrained as few sites have been studied and because the chemical processing of fe during transport from glaciers to the adjacent coastal ocean is not well understood in order to better constrain glacial fluxes of dfe to the ocean iron concentrations iron stable isotopes 56fe and other supporting chemical and physical measurements were made along a 4 km long glacial meltwater river on svalbard and in estuarine waters that it flows into dissolved iron concentrations in the bayelva river decreased from a maximum of 734 nm near the glacier to an average value of 116 nm near the mouth of the river measurements in the kongsfjorden estuary suggest that 3 to 10 nm of dfe from the bayelva river is stabilized in glacial waters by the time it mixes into the ocean incubation of bayelva river waters over two weeks in both the light and dark show similar results with the majority of dfe being quickly precipitated and 4 to 7 nm fe stabilized in the dissolved phase evidence suggests that fe is most likely lost from the dissolved phase by aggregation and adsorption of nanoparticulate and colloidal fe to particles dissolved 56fe was between 0 11 and 0 09 for all river samples and did not vary systematically with dfe concentrations we infer that the fe is lost from the dissolved phase by a process that fractionates fe isotopes by less than 0 05 indicating that the fe bonding environment does not change during precipitation this is consistent with doc loss that is much faster than predicted photo oxidation rates suggesting that doc is also lost through adsorption and precipitation dissolved fe concentrations in the bayelva river 15 734 nm and fe concentrations which are stabilized in the dissolved phase 4 7 nm are much lower than some previous estimates of fe in glacial meltwaters with roughly 80 of dfe lost during transit in the bayelva river and roughly 90 of the remaining dfe lost in the estuary this may mean that glaciers are a less significant source of dissolved fe to the global oceans than has been previously hypothesized that cold base glaciers of the type studied here do not contribute significantly to the dissolved fe flux or that the flux of reactive particulate fe to the oceans is more important than the dissolved flux in arctic regions with similar proglacial environments bedrock composition weathering intensity and as precipitation of colloidal and nanoparticulate fe may all play an important role in regulating the glacial meltwater iron flux to the ocean

three dimensional seismic velocity structure of the earth s mantle using body wave travel times from intra plate and deep focus earthquakes this paper combines the recent measurements of p and s wave travel times from intra plate earthquakes with travel times from deep focus earthquakes reported earlier to infer the velocity structure of the mantle it is reasonable that the source bias for intra plate earthquakes is less pronounced than that for other shallow focus earthquakes such as those occurring in island arcs the inclusion of intra plate earthquakes compensates for the lack of uniform areal distribution exhibited by the deep focus earthquake data and augments the number of high quality travel time observations the features observed in the variation of teleseismic travel times from intra plate earthquakes are consistent with the travel time variation determined from deep focus earthquakes especially the p wave travel time variation the combined intra plate and deep focus earthquake travel time data were converted to determine an average spherically symmetric compressional and shear velocity model and subsequently a three dimensional compressional velocity model for the earth s mantle lateral variation in the mantle accounted for most of the scatter in the observed p wave travel times the average compressional velocity model suggests two rapid velocity increases at 500 and 670 km depths and a small velocity gradient in the depth interval of 100 450 km the 3 d model determined from the augmented travel time data set corroborated the earlier findings 1 that the lateral heterogeneities are more pronounced near the upper mantle and near the core mantle boundary and 2 that the surface tectonic features are correlated with compressional velocity anomalies near the upper mantle but not with velocity anomalies below the upper mantle

strong responses of southern ocean phytoplankton communities to volcanic ash volcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms however little direct evidence of stimulatory responses has been obtained in the field here we present the results of twenty one 1 2 day bottle enrichment experiments from cruises in the south atlantic and southern ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash furthermore experiments in the southern ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone at these sites dissolved manganese concentrations were among the lowest ever measured in seawater and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese co limitation our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms potentially capable of significant impacts on regional carbon cycling

short period body wave constraints on properties of the earth s inner core boundary in this study we model short period waveform data in an attempt to constrain the p and s velocity structure at the earth s inner core boundary icb the data set consists of recordings from 10 events in the south pacific and the data selection criteria as well as methods of analysis were designed to avoid problems with receiver response often associated with short period waveform data these data are modeled using a calculation technique that facilitates the consideration of a wide variety of models for the icb results suggest that q in the inner core has the frequency dependence proposed by doornbos 1983 the data determine the p velocities above and below the icb to within a trade off that is well constrained by the data for example with a p velocity structure above the icb given by prem the p velocity below the icb is 11 03 0 03 km s similarly for the data analyzed here the estimate of the s velocity at the top of the inner core trades off with the estimate of q but we use the q model of doornbos 1983 to estimate the jump in s velocity to be 3 1 km s

depth dependent attenuation in the uppermost inner core from the taiwan short period seismic array pkp data inner core attenuation properties from two spots were examined in detail using pkikp and pkp bc phases with a distance range of between 147 and 154 as recorded by both the short period regional seismic array in taiwan and the broadband stations of the german regional seismic network the ray paths from the six south american events to taiwan sampled the inner core region beneath the eastern part of the northern pacific ocean while those from fiji to europe reflected the inner core boundary under the western part of the northern pacific ocean results of this study show the depth dependent attenuation of qp beneath the eastern part of the northern pacific ocean from 241 21 8 at depths 270 km with a weighted mean of 305 25 4 within the frequency band 0 5 2 0hz the average qp under the western part of the northern pacific ocean is 160 33 5 0 5 1 5hz which is consistent with that previously reported it is found that qp under the western part of the northern pacific is clearly lower than that under the eastern part this discrepancy might be related to regional variations in the uppermost inner core

the structure of the inner core inferred from short period and broadband gdsn data summary broadband displacement and velocity records of pkp phases are formed by the simultaneous deconvolution of the instrument responses of waveforms recorded by the short and long period channels of the global digital seismograph network revisions of standard earth models are inferred from the comparison of synthetic and observed waveforms the synthetics incorporate a q model designed for the bandwidth of the data and a source model that accounts for the variations of waveform about the focal sphere due to the effects of finiteness and complexity of the rupture process the interpretation of the data waveforms allows the position of the d cusp to be fixed at 121 f 1 and the c cusp at 154 f 2 for a surface source the cusp positions are consistent with a p velocity of 10 82 f 0 02 km s on the underside of an inner core boundary at 1216 km and a p velocity of 10 30 f 0 05 kms on its upper side resulting in a p velocity jump of aa 0 52 k 0 07 km s based on the agreement of synthetic and observed waveforms that have been diffracted beyond the ccusp there is no zone of small or negative p velocity gradient or of strong anelasticity at the bottom of the outer core second order features in the observed waveforms near the d cusp suggest that the s velocity may be nearly zero at the top of the inner core q must increase with depth in the inner core in order to satisfy the pulse width of the pkp df phase at distances greater than 150 in order to satisfy average properties of the inner core inferred from travel times and normal modes these combined results require strong gradients in p velocity s velocity and anelasticity in the upper 200 300 km of the inner core

assessment of leachable elements in volcanic ashfall a review and evaluation of a standardized protocol for ash hazard characterization abstract volcanic ash presents a widespread and common hazard during and after eruptions complex interactions between solid ash surfaces and volcanic gases lead to the formation of soluble salts that may be mobilized in aqueous environments a variety of stakeholders may be concerned about the effects of ash on human and animal health drinking water supplies crops soils and surface runoff as part of the immediate emergency response rapid dissemination of information regarding potentially hazardous concentrations of soluble species is critical however substantial variability in the methods used to characterize leachable elements makes it challenging to compare datasets and eruption impacts to address these challenges the international volcanic health hazard network www ivhhn org organized a two day workshop to define appropriate methods for hazard assessment the outcome of this workshop was a consensus protocol for analysis of volcanic ash samples for rapid assessment of hazards from leachable elements which was subsequently ratified by leading volcanological organizations the purpose of this protocol is to recommend clear standard and reliable methods applicable to a range of purposes during eruption response such as assessing impacts on drinking water supplies and ingestion hazards to livestock and also applicable to research purposes where possible it is intended that the methods make use of commonly available equipment and require little training to evaluate method transferability an interlaboratory comparison exercise was organized among six laboratories worldwide each laboratory received a split of pristine ash and independently analyzed it according to the protocol for a wide range of elements collated results indicate good repeatability and reproducibility for most elements thus indicating that the development of this protocol is a useful step towards providing standardized and reliable methods for ash hazard characterization in this article we review recent ash leachate studies report the outcomes of the comparison exercise and present a revised and updated protocol based on the experiences and recommendations of the exercise participants the adoption of standardized methods will improve and facilitate the comparability of results among studies and enable the ongoing development of a global database of leachate information relevant for informing volcanic health hazards assessment

palaeocontinental configurations and geoid anomalies reconstructions of past continental configurations help our understanding of the evolution of planetary surface morphology and impose valuable constraints on the models for planetary dynamics the problem is that although well established palaeogeographical maps now exist for mesozoic and later times1 2 thanks to excellent agreement between palaeomagnetic and marine magnetic deductions this is not true for earlier times mainly due to the lack of independent palaeogeophysical control over otherwise longitudinally ambiguous palaeomagnetic data the prospect of relating palaeocontinental configurations to geoid anomalies recently raised by anderson3 has thus given a fresh perspective to this problem here his continental insulation model is shown to be an inadequate explanation of the undulations of subduction compensated geoid instead the geoid highs and lows are shown to correlate well with the overall divergent and convergent plate tectonism since the middle palaeozoic and are thus ascribed respectively to the ascending and descending patterns of lower mantle convection

the harmonious character in equilibrium aeolian transport on mixed sand bed wind tunnel experiments were carried out to measure the spatial distribution in equilibrium transport of four types of mixed sand the flux profiles of each grain size group were calculated it is found that the vertical distribution of mean grain size has a close relation with the grain size distribution in the sand bed in a log linear plot the flux profiles of main grain size groups are all straight lines and their slopes are nearly equal it is also found that the ratio of transport rate of each size group to the whole transport rate is directly proportional to the mass ratio of each size group in the sand bed and the proportion value is only dependent on the grain size this harmonious law is applicable to all four types of mixed sand used in the experiment

reference data set of volcanic ash physicochemical and optical properties uncertainty in the physicochemical and optical properties of volcanic ash particles creates errors in the detection and modeling of volcanic ash clouds and in quantification of their potential impacts in this study we provide a dataset that describes the physicochemical and optical properties of a representative selection of volcanic ash samples from nine different volcanic eruptions covering a wide range of silica contents 50 80 wt sio2 we measured and calculated parameters describing the physical size distribution complex shape and dense rock equivalent mass density chemical bulk and surface composition and optical complex refractive index from ultra violet to near infrared wavelengths properties of the volcanic ash and classified the samples according to their sio2 and total alkali contents into the common igneous rock types basalt to rhyolite we found that the mass density ranges between 2 49 and 2 98 g cm3 for rhyolitic to basaltic ash types and that the particle shape varies with changing particle size d 100 m the complex refractive indices in the wavelength range between 300 nm and 1500 nm depends systematically on the composition of the samples the real part values vary from n 1 38 to 1 66 depending on ash type and wavelength and the imaginary part values from k 0 00027 to 0 00268 we place our results into the context of existing data and thus provide a comprehensive dataset that can be used for future and historic eruptions when only basic information about the magma type producing the ash is known

variability of particulate flux over the mid atlantic ridge abstract the magnitude and composition of the sinking particle flux were studied over the northern mid atlantic ridge mar from june 2007 to july 2010 four moorings equipped with dual sediment traps 100 m and 1000 m above the sea floor sampled regions north and south of the charlie gibbs fracture zone between 49 n and 54 n and east and west of the mar biogenic data were coupled with satellite estimates of primary production and modelled particle source to assess the variability in export flux large variations were found in the seasonality chemical composition magnitude and source of sinking particulate material between mooring sites the northern moorings recorded both greater mean primary production and greater particle mass flux than the southern moorings although the large inter annual variability within the sites exceeded inter site differences while estimates of primary production and organic carbon fluxes are comparable to other investigations of this type they are notably lower than previous estimates for the abyssal plain of the north atlantic the deeper traps consistently recorded a higher mass flux compared to the shallower traps however we suggest that the overall flux recorded by the shallower traps was reduced by trapping inefficiency which in the light of the low current velocities may largely be due to the physical nature of the sinking material although deep trap flux estimates may be more susceptible to errors due to re suspended and advected material from nearby topography mass flux and current velocity are not linked in addition the relatively low aluminium concentration of the deep trap material indicates that this contribution is relatively small the organic carbon flux to the ne nw se and sw station was 0 8 1 2 1 1 and 1 1 g m 2 y 1 respectively corresponding to an export flux of 0 6 over this region of the mar

constraints on d structure using pkp ab df pkp bc df and pcp p traveltime data from broad band records summary the effects of complex structure in the deep mantle and d on pkp differential traveltimes should be estimated accurately in order to reach reliable conclusions concerning the physical and chemical properties of the earth s inner and outer core in particular it is important to assess how much of the data can be explained by mantle structure alone for this purpose we have assembled global data sets of high quality pkp ab df pkp bc df and pcp p differential traveltimes measured on mostly broad band records the pkp ab df data were inverted alone or jointly with pcp p data to retrieve p velocity maps of the lowermost 300 km of the mantle corrections for mantle structure above d were performed prior to inversion using recent tomographic models and the fit to the pkp bc df data set was used to constrain damping in the inversions we compare models obtained with and without polar pkp paths and find that their inclusion or exclusion does not significantly affect the resulting d model except under north america where coverage is poor without polar paths our preferred model obtained using pkp ab df and pcp p data combined explains over 80 per cent of the variance in pkp ab df almost 60 per cent of the variance in pcp p and 27 per cent of the variance in pkp bc df a significant portion considering that the pkp bc df data set was not used in the inversion our models are characterized by prominent fast features under mid america and east asia a fast belt across the pacific a slow region under the southwestern pacific and southern africa as well as sharp transitions from fast to slow for instance under alaska and the south atlantic the anomalous south sandwich to alaska data cannot fully be explained by d structure alone unless very short wavelength lateral vari

unusual subpolar north atlantic phytoplankton bloom in 2010 volcanic fertilization or north atlantic oscillation in summer and autumn 2010 a highly anomalous phytoplankton bloom with chlorophyll concentration more than double that of previous years was observed in the irminger basin southwest of iceland two unusual events occurred during 2010 which had the potential to promote the unusual bloom first in spring 2010 the eyjafjallajokull volcano in iceland erupted depositing large quantities of tephra into the subpolar north atlantic second during the winter of 2009 2010 the north atlantic oscillation nao became extremely negative developing into the second strongest negative nao on record hydrographic conditions were highly anomalous in the region with an influx of freshwater spreading through the basin and unusual nutrient and mixed layer depth conditions here we use a combination of satellite modeled and in situ data to investigate whether the input of iron from the volcanic eruption or change in hydrographic conditions due to the extreme negative nao were responsible for the anomalous phytoplankton bloom we conclude that changes in physical forcing driven by the nao and not the volcanic eruption stimulated the unusual bloom

volcanic controls on ash iron solubility new insights from high temperature gas ash interaction modeling abstract recent studies strongly suggest that volcanic ash can fertilize the surface ocean by releasing soluble iron however the volcanic and atmospheric processes that solubilize ash iron during its transport from the volcano to the ocean are poorly understood using thermodynamic equilibrium calculations we investigate the influence of gas ash interaction within the hot core t 600 c of the volcanic plume and the consequences of this for ash iron solubility simulations are performed by considering the plume hot core as a box model in which 1000 c magmatic gas ash and 25 c ambient air are mixed together we show that mixing and the resulting cooling of the gas ash air mixture affect the mineralogy and oxidation state of iron in the ash surface rim iron mineralogy in the ash surface layer after high temperature plume processing is primarily governed by the ratio of the h2 and h2s content of the magmatic gas to the amount of entrained o2 into the hot plume xmix the model results indicate that most of the iron in the ash surface layer is oxidized to ferric iron fe iii when log xmix drops below 3 5 in the hot core such conditions may be encountered at convergent plate volcanoes which release h2o rich magmatic gases in contrast high temperature gas ash interaction at divergent plate and hot spot volcanoes which tend to be associated with co2 rich and so2 rich magmatic gases respectively may produce ash surfaces where iron mostly occurs as ferrous fe ii these volcanoes seem to be more favorable for iron fertilization because log xmix does not fall below 3 5 and 80 of the iron in the ash surface remains ferrous fe ii which is more soluble in water than fe iii

high frequency pkkp bc around 2 5 hz recorded globally anomalous high frequency pkkpbc signals displaying a large amount of energy around 2 5 hz recorded globally for deep and intermediate depth earthquakes are compared to pkkpab signals the attenuation difference t text ab t text bc is evaluated from spectral amplitudes in the range 96 111 being approximately twice the results provided by full wave theory and prem with no low q zone in the lowermost mantle and a nearly infinite qk in the outer core most ray paths for such recordings are piercing the d region in the proximity of regions where ultra low velocity zones ulvz have been previously reported beneath the north atlantic ocean the southwest pacific and the southwestern part of south america if bc amplitudes around 2 5 hz and at low frequencies 0 5 1 5 hz are comparable the observed attenuation difference in the frequency range 0 2 2 5 hz is small around 0 25 s and close to the prem value the particle motion of the high frequency pkkpbc at 2 5 hz is quite similar to that of the raw recording suggesting a deep source an explanation for this might be scattering of the bc branch in some very restricted areas of the lowermost mantle alternately the presence of a thin layer with high attenuation in the d region would most likely be associated with either the ultra low velocity zone ulvz or light sediments on the underside of the core mantle boundary cmb correlated to other methods to investigate the lowermost mantle the high frequency pkkpbc can be used to map lateral variations of attenuation above the cmb possibly associated with the boundary of the superplumes especially when pkkpab is observed

soluble iron inputs to the southern ocean through recent andesitic to rhyolitic volcanic ash eruptions from the patagonian andes patagonia due to its geographic position and the dominance of westerly winds is a key area that contributes to the supply of nutrients to the southern ocean both through mineral dust and through the periodic deposits of volcanic ash here we evaluate the characteristics of fe dissolved into soluble and colloidal species from volcanic ash for three recent southern andes volcanic eruptions having contrasting features and chemical compositions contact between cloud waters wet deposition and end members of andesitic hudson volcano and rhyolitic chaiten volcano materials was simulated results indicate higher fe release and faster liberation rates in the andesitic material fe release during particle seawater interaction dry deposition has higher rates in rhyolitic type ashes rhyolitic ashes under acidic conditions release fe in higher amounts and at a slower rate while in those samples containing mostly glass shards fe release was lower and faster the 2011 puyehue eruption was observed by a dust monitoring station puyehue type eruptions can contribute soluble fe to the ocean via dry or wet deposition nearly reaching the limit required for phytoplankton growth in contrast the input of fe after processing by an acidic eruption plume could raise the amount of dissolved fe in surface ocean waters several times above the threshold required to initiate phytoplankton blooms a single eruption like the puyehue one represents more than half of the yearly fe flux contributed by dust

the effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the skafta river iceland abstract this study describes the chemical composition of dissolved degased and suspended fluxes of the 2002 skafta glacial flood which emerged from one of the skafta subglacial lake due to geothermal activity beneath the icelandic vatnajokull glacier the dissolved and suspended fluxes during the flood are compared with those normally observed in the skafta river to determine the effect of such floods on the annual fluxes of material delivered to the coastal waters concentrations of most dissolved elements during the flood were significantly higher than those normally observed in the skafta river in addition dissolved concentrations of nutrients such as sio 2 fe and v increased more than an order of magnitude during the flood these will affect biological processes on a local scale the 34 s composition in the flood water suggests that the dissolved so 4 was derived from the oxidation of h 2 s and the geothermal fluid the total suspended particulate load measured in the skafta river during the 8 day 2002 flood was approximately half of the non flood total annual skafta suspended load as particles carry the bulk of limiting nutrients to the oceans this demonstrates the importance of glacial floods for primary production of coastal waters the composition of the flood water and the skafta subglacial lake together with reaction path modelling suggest that substantial degasing of co 2 and h 2 s occurred at the glacial outlet during the flood this degasing may have released as much as 262 000 and 7 980 tonnes of co 2 and h 2 s respectively to the atmosphere having a considerable impact on the local carbon and sulphur cycles during the flood event

amplitudes of core waves near the pkp caustic from nuclear explosions in the south pacific recorded at the laboratoire de detection et geophysique network in france the purpose of this paper is 2 fold it is first a continuation of the study of massot and rocard 1982 on the amplitude variations of the core waves near the pkp caustic for french nuclear explosions in the south pacific recorded on the ldg network in france taking advantage of a larger available data set and using current methods to compute synthetic seismograms such as the wkbj method we reinvestigate the core waves amplitude versus distance variation pattern derived by massot and rocard 1982 the second purpose is to give precise constraints on the pkp caustic phenomenon using waveform and amplitude comparisons between data and synthetics wkbj synthetics are computed for several global spherical earth models recent models with a d discontinuity or a low velocity gradient at the top and the bottom of the liquid core are also tested our computations do not support the highly variable amplitude versus distance profile of massot and rocard which displays a major peak at 145 6 and many secondary interference fringes between 142 and 147 the theoretical amplitude variations we have calculated are dominated by the large pkp caustic peak and only modulated by the simultaneous arrival of the pkikp wave near 145 using a data set of 17 nuclear explosions we have measured relative amplitudes as a function of distance in the 142 to 147 distance range and analyzed the waveform variations our observations amplitudes and waveforms are well modeled by the 1066b model of gilbert and dziewonski 1975 the agreement on amplitude variations is still good for models prem dziewonski and anderson 1981 and iasp91 kennett and engdahl 1991 accurate quantitative constraints are derived on the pkp caustic among which the position of the b caustic point 144 5 0 5 for the mean 296 mururoa ldg network azimuth this location depends as a whole on the depth of the core mantle boundary and on the velocity gradients in the mantle and in outermost core although the depth of the core mantle boundary and the existence of a discontinuity at the top of d can slightly affect the position of the b caustic point the focusing effect at the pkp caustic is rather a global derivation of the models

tomographic inversions for mantle p wave velocity structure based on the minimization of l 2 and l 1 norms of international seismological centre travel time residuals we use international seismological centre isc p arrival data 1964 1987 and iterative algorithms which minimize the l1 and l2 residual norms to solve simultaneously for three dimensional p velocity variations in earth s mantle source mislocations and station corrections we find that the maximum velocity perturbations produced by the l1 minimization approximately 4 in our final model are relatively insensitive to smoothing and damping constraints therefore using an l1 norm criterion allows us to keep the bias introduced to the inversion to a minimum among the well resolved features contained in both the l1 and the l2 velocity models are a fast anomaly in the lower mantle beneath the tonga new hebrides subduction zone to a depth of 1670 km and another fast anomaly beneath the japanese island arc and eastern asia continuity between these anomalies and shallower fast anomalies is not clear a fast anomaly extending from 670 km to 2070 km depth appears beneath eastern north america the caribbean and north central south america a broad fast anomaly appears beneath eastern asia just above the core mantle boundary as well as several slow anomalies under the pacific basin of comparable size both models contain a circum pacific ring of 2 lower velocities in the depth range 0 200 km associated with back arc basins high velocities over 2 associated with the continental shields tend to disappear below 400 km though a significant region of high velocity remains beneath the siberian platform in the 400 to 670 km depth interval

impact of iron release by volcanic ash alteration on carbon cycling in sediments of the northern hikurangi margin abstract we present geochemical data collected from volcanic ash bearing sediments on the upper slope of the northern hikurangi margin during the rv sonne so247 expedition in 2016 gravity coring and seafloor drilling with the marum mebo200 allowed for collection of sediments down to 105 meters below seafloor mbsf release of dissolved sr2 with isotopic composition enriched in 86sr 87sr 86sr minimum 0 708461 at 83 5 mbsf is indicative of ash alteration this reaction releases other cations in the 30 70 mbsf depth interval as reflected by maxima in pore water ca2 and ba2 concentrations in addition we posit that fe iii in volcanogenic glass serves as an electron acceptor for methane oxidation a reaction that releases fe2 measured in the pore fluids to a maximum concentration of 184 m several lines of evidence support our proposed coupling of ash alteration with fe mediated anaerobic oxidation of methane fe aom beneath the sulfate methane transition smt which lies at 7 mbsf at this site in the 30 70 mbsf interval we observe a concurrent increase in fe2 and a depletion of ch4 with a well defined decrease in 13 c ch4 values indicative of microbial fractionation of carbon the negative excursions in 13 c values of both dic and ch4 are similar to that observed by sulfate driven aom at low so 4 2 concentrations and can only be explained by the microbially mediated carbon isotope equilibration between ch4 and dic mass balance considerations reveal that the iron cycled through the coupled ash alteration and aom reactions is consumed as authigenic fe bearing minerals this iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals as estimated from sequential extraction analyses using a numerical modeling approach we estimate the rate of fe aom to be on the order of 0 4 mol cm 2 yr 1 which accounts for 12 of total ch4 removal in the sediments although not without uncertainties the results presented reveal that fe aom in ash bearing sediments is significantly lower than the sulfate driven ch4 consumption which at this site is 3 0 mol cm 2 yr 1 we highlight that fe iii in ash can potentially serve as an electron acceptor for methane oxidation in sulfate depleted settings this is relevant to our understanding of c fe cycling in the methanic zone that typically underlies the smt and could be important in supporting the deep biosphere

aerosol iron and aluminum solubility in the northwest pacific ocean results from the 2002 ioc cruise dust aerosol samples were collected across the western north pacific ocean during may june 2002 samples were analyzed for soluble aerosol fe ii fe ii fe iii and al as well as major cations and anions the aerosol samples were leached using a 10 second exposure to either filtered surface seawater or ultrapure deionized water yielding a measure of the instantaneous soluble fraction a variety of analytical methods were employed including 57fe isotope dilution high resolution icp ms energy dispersive x ray fluorescence graphite furnace aas ion chromatography and the felume chemiluminescent technique fe was found to be more soluble in ultrapure deionized water leaches especially during periods of higher dust concentrations fe solubility averaged 9 8 in ultrapure water leaches and 6 5 in seawater leaches significant correlations were found between both soluble aerosol fet and soluble fe ii concentrations and aerosol acidity however the percentages of soluble aerosol fet and fe ii did not correlate with aerosol acidity we also did not observe significant correlations between total and soluble aerosol fe concentrations and the concentrations of either particulate fe or dissolved fe in surface waters

exploring the ocean for hydrothermal venting new techniques new discoveries new insights abstract enumerating active hydrothermal fields on the seafloor has been a challenge since their discovery almost 40 years ago high temperature hydrothermal fields are readily discoverable primarily by detecting mineral laden plumes but low temperature particle poor vent fields resist discovery decades of exploration for vent fields have covered though often cursorily about one third of the global lengths of both oceanic spreading ridges osrs and volcanic arcs identifying some 630 active vent fields about 80 of these fields are on osrs and the spatial frequency of those fields is currently estimated as 0 5 5 100 km generally increasing with spreading rate over the last decade however a few detailed surveys have added sensors capable of detecting ephemeral chemical tracers oxidation reduction potential in addition to standard sensors that detect quasi conservative optical tracers such as light backscattering this approach has revealed a new view of the distribution of venting fields along fast spreading 55 mm yr osrs studies of four such ridge sections totaling 1470 km length suggest that the present inventory of vent fields may underestimate the true global population of vent fields on fast spreading osrs by a factor of 3 6 this increase implies that ridge axes are unexpectedly leaky reservoirs from which hydrothermal fluids escape at far more sites than presently assumed that the supply of dissolved hydrothermal iron which may be fertilizing the primary production of the southern ocean is higher than now calculated and that present estimates of recoverable sulfide tonnage from ridge axes may be too low along slow spreading ridges which account for 60 of the global osr length and 86 of known sulfide tonnage expansive axial valleys present special exploration challenges that will not be easily overcome

q in the inner core short period vertical seismograms from ten earthquakes and one nuclear explosion in the distance range of 140 170 degrees are examined for a study of the anelastic properties of the inner core the depth of the earthquake foci varies between 116 and 625 km the phases of interest are pkp bc branch and pkikp with bottoming depths in the upper few hundred kilometers of the inner core the data consist of high quality digital data at sampling rates 20 40 samples per second selected after an extensive search of the 1985 1986 gdsn event tapes for short period p waves with a high signal to noise ratio the results are based primarily upon observations between distances of 147 and 154

fertilization potential of volcanic dust in the low nutrient low chlorophyll western north pacific subtropical gyre satellite evidence and laboratory study volcanic particles and a phytoplankton bloom flh was found to be 9 17 10 3 mw cm 2 mm 1 sr 1 in the patch and 3 5 1 0 3 mw cm 2 mm 1 sr 1 in the ambient water indicating that a 2 5 fold increase in biological activity occurred during the week following the eruption satellite altimetry indicated that the bloom took place in the presence of downwelling and was not a result of upwelled nutrients in this oligotrophic ocean analysis of satellite ocean color spectra of the bloom region found similar spectra as the reference trichodesmium spectra laboratory experiments further substantiate the satellite observations which show elevated concentrations of limiting nutrients provided by the anatahan samples and the averaged soluble nitrate phosphate and fe were 42 3 1 and 2 0 nm respectively though it was not possible to obtain in situ observations of the ocean biogeochemical responses that followed the anatahan eruption this study provided evidence based on remote sensing data and laboratory experiment that fertilization of volcanic aerosols occurred following this eruption in one of the most oligotrophic low nutrient low chlorophyll ocean deserts on earth

neodymium isotopic composition and concentration in the western north atlantic ocean results from the geotraces ga02 section the neodymium nd isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation the modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete here we present new observational data for nd isotopes and concentrations from twelve seawater depth profiles which follow the flow path of north atlantic deep water nadw from its formation region in the north atlantic to the northern equatorial atlantic samples were collected during two cruises constituting the northern part of the dutch geotraces transect ga02 in 2010 the results show that the different water masses in the subpolar north atlantic ocean which ultimately constitute nadw have the following nd isotope characteristics upper labrador sea water ulsw end 14 2 0 3 labrador sea water lsw end 13 7 0 9 northeast atlantic deep water neadw end 12 5 0 6 northwest atlantic bottom water nwabw end 11 8 1 4 in the subtropics where these source water masses have mixed to form nadw which is exported to the global ocean upper nadw is characterised by end values of 13 2 1 0 2sd and lower nadw exhibits values of end 12 4 0 4 2sd while both signatures overlap within error the signature for lower nadw is significantly more radiogenic than the traditionally used value for nadw end 13 5 due to the dominance of source waters from the nordic seas nwabw and neadw comparison between the concentration profiles and the corresponding nd isotope profiles with other water mass properties such as salinity silicate concentrations neutral densities and chlorofluorocarbon cfc concentration provides novel insights into the geochemical cycle of nd and reveals that different processes are necessary to account for the observed nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column while our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension the results for open ocean seawater demonstrate at an unprecedented level the suitability of nd isotopes to trace modern water masses in the strongly advecting western atlantic ocean

glacial isostatic adjustment and the free air gravity anomaly as a constraint on deep mantle viscosity summary a gravitationally self consistent theory for relative sea level variations forced by pleistocene deglaciation events is employed to explore the extent to which rsl and free air gravity observations together constrain the viscosity of the mantle beneath the seismic discontinuity at 670 km depth a trade off is revealed between errors in the assumed deglaciation history and errors in the inferred value of the viscosity of the lower mantle taking full account of such uncertainty plausible values of the viscosity beneath the transition region are bounded above by 1023 poise cgs units the preferred value is at least a factor of 2 lower than this and is strongly constrained by the observed free air gravity anomaly over hudson bay the calculations described in detail here show for the first time that the relatively large gravity anomalies observed over sites of wurm wisconsin deglaciation do not require any pronounced increase of mantle viscosity with depth in order to explain them

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

the structure of the base of the outer core inferred from seismic waves diffracted around the inner core 1 we systematically searched for seismograms of waves diffracted around the inner core pkpcdiff from all the temporary seismic arrays with data currently available at the iris dmc as well as some permanent regional seismic arrays including f net in japan and grf in germany to assemble the largest high quality pkpcdiff database ever created pkpcdiff waves preferentially sample the base of the outer core and so contain important clues about earth structure in this region we measured pkpdf pkpcdiff differential traveltimes and pkpcdiff pkpdf amplitude ratios in the distance range of 154 160 and modeled the observations using grid searches and full wave theory synthetic seismograms the optimum model found by fitting the differential traveltimes has relatively low velocity at the base of the outer core as in ak135 which is consistent with many previous traveltime studies however the optimum model found by fitting the amplitude ratios pkpcdiff pkpdf does not exhibit this feature and instead is closer to prem the discrepancy may be explained by two likely causes one is that small scale topography or roughness on the icb tends to scatter energy away from pkpcdiff waves by generating trailing coda waves the other is that there exists a thin layer with relatively low q at the base of the outer core this might be expected if there are suspended solid particles at the base of the outer core as proposed decades ago both mechanisms could generate smaller pkpcdiff amplitudes without significantly affecting pkpcdiff traveltimes

evaluation of the electrical properties of dust storms by multi parameter observations and theoretical calculations abstract dusty phenomena such as wind blown sand dust devils and dust storms play key roles in earth s climate and geological processes dust electrification considerably affects the lifting and transport of dust particles however the electrical properties of dust storms remain poorly understood here we conducted multi parameter measurements and theoretical calculations to investigate the electrical properties of dust storms and their application to dust storm prediction the results show that the vertical electric field e field decreases first then increases and finally decreases with the height above the ground reversing its direction at two heights 8 12 and 24 m this suggests that the charge polarity of dust particles changes from negative to positive and back to negative again as the height increases by carefully analyzing the e field and dust concentration data we further found that there is a significant positive linear relationship between the measured e field intensity and dust concentration at the given ambient conditions in addition measurements and calculations demonstrate that a substantial enhancement in the vertical e field can be observed several hours before the arrival of the external source dust storms indicating that the e field can be used to provide an early warning of external source dust storms

evidence for a shear velocity discontinuity in the lower mantle beneath india and the indian ocean abstract sh and ssh seismograms are modeled to determine the shear velocity structure in the d region beneath india and the indian ocean the signals show waveform complexities similar to those observed in data sampling the d region beneath alaska the caribbean and eurasia lay and helmberger which have been attributed to a 2 7 shear velocity discontinuity 280 km above the core mantle boundary the new data set consists of long period tangential component recordings at wwssn stations in africa the middle east and europe for 11 intermediate and deep focus indonesian earthquakes in the distance range 70 82 the waveforms show an arrival between sh and scsh with systematic moveout from 89 to 94 there is a strong distortion of the sh waveforms indicating the arrival of several phases closely spaced in time the relative time shifts of similar complexity in the corresponding ssh phases requires a deep mantle origin the depth dependence and moveout of the interference effects are well predicted for both sh and ssh phases by a model with a lower mantle discontinuity alternative explanations of the interference as resulting from receiver reverberations sks contamination multiple source complexity or near source multipathing are ruled out by systematic tests while it is apparent that lateral variations in the lower mantle velocity structure prevent any single model from fitting all of the data synthetic waveform modeling using generalized ray theory and reflectivity shows that the data can be well fit by a model with a discontinuity similar in size and depth to that proposed for the previously investigated regions lay and helmberger but with a negative velocity gradient within the d layer

frequency dependent seismic attenuation in the inner core 1 a viscoelastic interpretation 1 using reference source time functions broadband velocity waveforms of pkikp in the distance range 150 180 are inverted for a viscoelastic model of inner core attenuation a mean q at 1 hz of 307 90 is determined from 345 available pkikp ray paths both global and regional results find a depth dependent attenuation in the deep inner core with anisotropic attenuation resolved in regional results attenuation is much stronger in the upper 300 km of the inner core the preferred model of viscoelastic attenuation is frequency dependent with very weak velocity dispersion our data do not resolve any hemispherical differences of attenuation in the deep inner core

measurements of electric charge distribution in volcanic plumes at sakurajima volcano japan measurements of perturbations in the atmospheric potential gradient around volcanic plumes at multiple from two to five sites and measurements of the charge mass ratio of ash particles falling from volcanic plumes were carried out at sakurajima volcano japan results from 28 and 29 october 1995 show that the nature of the perturbations depends on the intensity of plume activity although plume activity was vigorous on 28 october negative perturbations were predominant as plume activity peaked the magnitude of negative perturbations decreased just below the plume and increased at an off axis site during the peak period positively charged ash particles fell out from the plume this suggests that the active plume dominantly contained negatively charged materials and that positively and negatively charged materials were added to the lower and upper parts of the plume respectively during the peak period on the other hand as plume activity became less vigorous on 29 october the perturbations were characterized by a positive anomaly followed by a negative anomaly because wind velocity increased with altitude that day we infer that positive and negative charges were distributed in the upper and lower parts of the plume respectively the differences in perturbations observed on 28 and 29 october suggest that volcanic plumes are generally composed of three parts an upper part with positively charged gas and aerosol a middle part with negatively charged fine ash particles and a lower part with positively charged coarse ash particles the compilation of present and previous results from sakurajima and other volcanoes indicates that the effect of the negative charge in the middle part was predominant in most cases although positive perturbations caused by the upper part were observed around some weak plumes the effect of positively charged particles in the lower part was observable only when plume activity was sufficiently strong because positively charged coarse particles tended to fall out near the vent

volcanic ash as an oceanic iron source and sink volcanic ash deposition to the ocean forms a natural source of iron fe to surface water microbial communities inputs of lithogenic material may also facilitate fe removal through scavenging combining dissolved fe dfe and thorium 234 observations alongside modeling we investigate scavenging of fe in the north atlantic following the eyjafjallajokull volcanic eruption under typical conditions biogenic particles dominate scavenging whereas ash particles dominate during the eruption the size of particles is important as smaller scavenging particles can become saturated with surface associated ions model simulations indicate that ash deposition associated with eyjafjallajokull likely led to net fe removal our model suggests a threefold greater stimulation of biological activity if ash deposition had occurred later in the growing season when the region was fe limited the implications of ash particle scavenging eruption timing and particle saturation need to be considered when assessing the impact of ash deposition on the ocean fe cycle and productivity

a seismic model of a partially molten inner core fearn et al 1981 recently proposed a mechanism whereby the inner core contains a significant fraction of liquid we construct a model of a partially molten inner core compatible with seismic observation specifically we develop an improved model of bulk anelasticity including the effect of thermal and material diffusion and show that it is quantitatively capable of explaining the observed anelasticity also studies of the reflection of seismic waves from the inner core boundary are used to estimate the mass fraction of liquid in the inner core

core structure re examined using new teleseismic data recorded in antarctica evidence for at most weak cylindrical seismic anisotropy in the inner core we present a significant addition to the data set of traveltimes of seismic pkp waves that sample the earth s lowermost mantle and core along the earth s rotation axis recorded at permanent global seismic network gsn and temporary sscua deployment broad band seismographic stations in antarctica the new data improve the previously poor and biased coverage that underlies the seismic constraints on recent models of inner core structure and anisotropy on the one hand new differential pkp traveltime measurements improve the sampling of predominantly the eastern inner core hemisphere pkpab df and pkpbc df differential traveltime residuals with respect to the spherically symmetric model ak135 are consistently smaller than two seconds along the north south paths sampled axially symmetric models of inner core seismic anisotropy with fast axis parallel to the earth s rotation axis require a weak anisotropy of 0 7 0 1 per cent to be consistent with our pkpbc df observations pkpbc df residuals from the quasi eastern hemisphere indicate 0 4 0 1 per cent anisotropy if only pkpbc df observations from the top 200 km of this hemisphere are considered this is reduced to 0 1 0 2 per cent consistent with an isotropic layer on the other hand new absolute pkp traveltime measurements add to the sampling of both hemispheres of the inner core but it is difficult to use them with more confidence to assess structure of the core since they are affected by crustal and mantle structure and source uncertainties the newly collected data set also increases constraints on d structure beneath the south pole in contrast to previous inferences based on data from northern stations we find no evidence of a velocity heterogeneity in the outer core near the inner core boundary associated with the cylinder tangent to the inner core in the southern hemisphere

natural iron fertilization by the eyjafjallajokull volcanic eruption aerosol deposition from the 2010 eruption of the icelandic volcano eyjafjallajokull resulted in significant dissolved iron dfe inputs to the iceland basin of the north atlantic unique ship board measurements indicated strongly enhanced dfe concentrations up to 10 nm immediately under the ash plume bioassay experiments performed with ash collected at sea under the plume also demonstrated the potential for associated fe release to stimulate phytoplankton growth and nutrient drawdown combining fe dissolution measurements with modeled ash deposition suggested that the eruption had the potential to increase dfe by 0 2 nm over an area of up to 570 000 km2 although satellite ocean color data only indicated minor increases in phytoplankton abundance over a relatively constrained area comparison of in situ nitrate concentrations with historical records suggested that ash deposition may have resulted in enhanced major nutrient drawdown our observations thus suggest that the 2010 eyjafjallajokull eruption resulted in a significant perturbation to the biogeochemistry of the iceland basin

high frequency waves following pkp cdiff at distances greater than 155 using a seismic network in hokkaido tohoku region japan the author observes pkp waves in the distance range 152 to 157 degree from a deep earthquake in argentina the seismic network consists of 26 stations and provides a data set of dense distance sampling the examination of amplitude variation of pkp bc and pkp c sub diff with distance locates the c cusp at about 155 5 degree for a surface source for the path from argentina to japan this c cusp position suggests a p velocity of 10 27 km s at the bottom of the outer core the bandpass filtering of the data shows that high frequency waves are observed following pkp c sub diff at distances beyond the c cusp the waves are characterized by a dominant frequency of about 29 to 3 hz a long duration of oscillation until the arrival of pkp ab and an apparent onset slowness of about 4 s deg which is approximately equal to that of pkp ab in the distance range the onset time of the high frequency waves seems to be consistent with the least time of the scattering of pkp bc on the receiver side near the bottom of the upper mantle

attenuation tomography of the upper inner core the solidification of the earth s inner core shapes its texture and rheology affecting the attenuation and scattering of seismic body waves transmitted through it applying attenuation tomography in a bayesian framework to 398 high quality pkikp waveforms we invert for the apparent qp for the uppermost 400 km below the inner core boundary at latitudes 45 s to 45 n we use damping and smoothing for regularization of the inversion and it seems that the smoothing regularization combined with the discrepancy principle works better for this particular problem of attenuation tomography the results are consistent with a regional variation in inner core attenuation more complex than hemispherical suggesting coupling between inner core solidification and the thermal structure of the lowermost mantle

summary of seismological constraints on the structure of the earth s core we review the current state of the seismological constraints on core structure the evidence supports a simple two layer model of the core the fluid outer core seems to have properties which are consistent with those of a vigorously convecting region the inner core has a sharp boundary characterised by a 0 5 0 6 g cc density jump a 0 6 0 7 km s jump in p velocity and a jump in shear velocity to 2 5 km s or greater there is weak evidence for an anomalously steep shear velocity gradient at the top of the inner core finally the attenuation of both body waves and free oscillations indicate that the inner core is strongly attenuating near its surface though the data suggest that the attenuation is frequency dependent

heterogeneity and anisotropy of seismic attenuation in the inner core 1 we evaluate seismic attenuation in the inner core from the spectral ratio between the seismic phase pkp df and either pkp ab or pkp bc at the epicentral distances from 150 to 170 the global data set is divided into two groups according to the position of the turning point of pkp df either in the eastern from 50 e to 120 w or the western hemisphere in the eastern hemisphere the parameter t shows strong dependence on the epicentral distance and no dependence on the angle between the earth s spin axis and pkp df ray at the turning point in the western hemisphere t is weakly dependent on the distance and varies between approximately 0 7 s and 0 1 s for the angles between 0 and 90 respectively our results allow us to reconcile seemingly incompatible results of many previous studies the anisotropy of attenuation is correlated with the anisotropy of p velocity

intrusion triggering of the 2010 eyjafjallajokull explosive eruption the ash cloud that brought chaos to european air traffic in april this year was the result of emissions from an icelandic volcano that had been intermittently active for about 18 years a combination of detailed space based geodetic measurements and seismic monitoring of the eyjafjallajkull volcano in the run up to the ash producing explosive summit eruption reveals an unusual deformation pattern that may be attributed to its off rift setting with relatively cool subsurface structure and limited magma at shallow depth as to the predictability of such a dramatic reawakening the immediate precursors to the initial eruption of the volcano in 2010 were subtle and difficult to detect but the clear signs of volcanic unrest during the weeks months and years preceding it may provide better clues to the catastrophic explosion

electrification of saltating particles in wind blown sand experiment and theory 1 the electrification of sand particles is a common phenomenon in wind blown sand movement the charge to mass ratio of particles is an important parameter to characterize the property of charged particles however understanding of the charge to mass ratio remains open and significant discrepancies exist between previous contact electrification models and measurements this work focuses on the charge to mass ratio of saltating particles in wind blown sand experiments were carried out in a wind tunnel using sand particles with the mean diameter d 160 m the motions of the saltating particles in the air flow were analyzed by particle image velocimetry and the charge to mass ratios were determined by measuring both the charge and mass of saltating sand particles collected in a faraday cup the measured results show that the charge to mass ratio increases exponentially with the height above the surface and the vertical profiles of the charge to mass ratios can be reproduced well by considering the multiple collisions process between saltating particles and sand bed in addition the results suggest that the charge to mass ratio is determined by the number of collisions impacting velocity and sand grain diameter combined

p wave travel time and amplitude in western north america a study of teleseismic short period 1 s p wave travel time and amplitude variations in western north america reported here reveals a high level of correlation early arrivals relate to low amplitudes and late arrivals to higher amplitudes this trend is opposite to observations noted for the usa and southern canada as a whole1 with some exceptions seismic stations east of the rocky mountain front generally record faster travel times2 8 and higher amplitudes9 15 than those to the west these differences have been attributed to higher attenuation and lower velocities in the upper mantle beneath the tectonically active western region11 16 the correlation in the west between p wave travel time residuals and relative amplitudes is consistent with elastic focusing and defocusing effects and is found for both world wide standardized seismograph network wwssn and long range seismic measurement lrsm stations these results are relevant to the estimation of yields of nuclear explosions because by reciprocity similar elastic focusing and defocusing effects can alter the amplitudes and travel times of p waves from explosions

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

organic matter accumulation of the wufeng longmaxi shales in southern sichuan basin evidence and insight from volcanism abstract the wufeng longmaxi formations wf lm fms in the sichuan basin are sets of graptolite bearing shale strata containing high frequency bentonite layers in order to investigate the influence of volcanism on the organic matter om accumulation in shales detailed observations of several typical profiles and wells were performed also analyses including total organic carbon toc contents and mineral compositions were conducted on 126 shale and 5 bentonite core samples major and trace element analyses were conducted on the selected 25 shale and 5 bentonite samples in the wf lm fms of well lu a results show that wf and lm1 4 members are the bentonites concentrated sections while lm5 6 are the bentonites relatively concentrated sections and no bentonite is found in lm7 9 members the high potassium k content of bentonites have the typical characteristics of intermediate acid calcium alkaline volcanic rocks such as andesite and dacite which probably originated from intraplate collision or volcanic arc structural backgrounds related to the collision belt of the cathaysia block to the yangtze block productivity indicators p content excess si p al cu al and ni al in the wf and lm1 3 members are all significantly higher than those in the lingxiang lx and lm4 5 members the higher biological productivity during the ordovician silurian o s transition was attributed to the massive and intensive volcanism the fertilization by volcanic ash brought abundant biologically relevant nutrient elements n p si fe and al into the ocean thus triggering the phytoplankton bloom and enhancing primary biological productivity all the redox condition indexes moef uef nief vef mo toc corg p and u th positively correlate with toc content during the o s transition the intensive and massive volcanic eruptions triggered global cooling sea level changes late ordovician mass extinction and primary productivity increases thus promoting anoxic and possibly intermittently euxinic bottom conditions in addition the deposited bentonite layers had a strong capacity for oxygen isolation volcanism should be considered when modeling the om accumulation of the wf lm shales

pkp bc versus pkp df differential travel times and aspherical structure in the earth s inner core pkp bc versus pkp df differential travel times show coherent patterns of residuals indicating aspherical structure within the earth s inner core using a waveform correlation method we measure 318 differential pkp bc versus pkp df travel times from 5 years of global digital seismograph network gdsn short period data at ranges between 145 and 155 in addition we obtain 19 470 probable bc versus df travel times at these ranges by searching through 23 years of the international seismological centre isc catalog plots of residuals versus turning point location and residuals versus ray direction show clear patterns which indicate that the differential travel times are highly correlated along similar ray paths this pattern is robust with respect to range and source depth these anomalies are almost certainly due to aspherical inner core structure since pkp bc and pkp df have nearly coincident ray paths in the mantle and outer core the gdsn and isc residual patterns are in general agreement but the isc residuals underpredict the gdsn residuals by about a factor of 2 the isc data have better spatial coverage particularly for n s ray paths within the inner core these n s ray paths show positive residuals of about 0 5 s indicating faster inner core p velocities in this direction a result consistent with previous studies of absolute pkp df travel times but derived from an independent data set due to the sparse ray coverage of our data either heterogeneity or anisotropy within the inner core with about 1 velocity variations could explain these residual patterns however inversions of the isc data for heterogeneity require many more free parameters to achieve the same variance reduction as a simple two parameter anisotropy model

short period pkp phases and the anelastic mechanism of the inner core abstract short period seismograms are synthesized for pkp phases in anelastic earth models the synthetics were constructed using a synthetic technique valid at grazing incidence a source time function appropriate for deep focus earthquakes and an instrument response for either a short period wwssn or sro seismograph the agreement between predicted and observed amplitudes and spectral ratios requires neither a low q zone at 0 2 2 hz nor a low or negative p velocity gradient at the bottom of the outer core thin low q zones beneath the inner core boundary fit spectral ratio data that sample the upper 200 km of the inner core but fail to fit data that sample the lower inner core only a model having q 1 0 003 0 004 at 0 2 2 hz nearly constant with depth in the inner core satisfies all of the spectral ratio and amplitude data the assumption of a bulk viscosity of 10 10 3 pa s for the liquid phase of a partially molten inner core combined with the observation of low shear attenuation in the inner core at frequencies less than 0 005 hz limit the physical parameters associated with two possible attenuation mechanisms 1 fluid flow and viscous relaxation due to ellipsoidally shaped inclusions of melt and 2 the solid liquid phase transformation induced by the stress change during the passage of a seismic wave both mechanisms require an order of 0 1 partial melt to reproduce the observed q 1 in the outer core the time constant of the mechanism of phase transformation is predicted to be 10 4 10 6 s confirmation of small shear attenuation in the inner core in the frequency band of seismic body waves would favor the mechanism of phase transformation

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

structure of the earth mantle and core the deep interior structure of the earth has been extensively analyzed using a wide variety of seismic phases and techniques during the last four years most studies have emphasized quantitative three dimensional mapping of the lateral velocity heterogeneity of the mantle and core these aspherical velocity variations are believed to be direct manifestations of thermal and compositional heterogeneity associated with convective processes a first generation of global models for the lateral velocity variations in the deep earth has been produced providing tantalizing images of large scale structures suggestive of a non steady state thermal convection system the upper 400 km of the mantle has the strongest lateral velocity variations of up to 10 for shear velocity surface wave analyses that do not require a priori regionalizations have demonstrated that there is a strong association between surface tectonic provinces and the uppermost mantle velocity variations thus the thermal and convective state of the upper 200 km of the mantle can be reliably interpreted in the context of plate tectonics the upper mantle models support the contention that continents have deep roots with differences in velocity structure from oceanic and active tectonic regions extending as deep as 400 km very long wavelength lateral velocity variations of a few percent have been detected in the transition zone at depths from 400 to 670 km as well as throughout the lower mantle these deep seated variations have little correspondence to surface tectonics and efforts to interpret their nature are just beginning the lowermost 200 km of the mantle d region has lateral velocity fluctuations comparable to those in the upper mantle and evidence has been presented for the presence of a sizable velocity discontinuity at the top of the d layer a combined thermal and compositional boundary layer roughly mirroring the lithosphere is a likely explanation for this anomalous zone the core mantle boundary appears to have significant 10 km long wavelength topography presumably sustained by dynamic stresses from deep mantle convection the inner core may have strong lateral heterogeneity or axially symmetric anisotropy suggesting a complex thermal and compositional state significant progress has been made in characterizing the frequency dependence of anelastic attenuation in the mantle in the short period body wave band models for teleseismic p wave attenuation operators have converged with t values of 0 7 1 0 s appropriate at 1 hz and t values of 0 4 0 6 s appropriate at 4 hz regional variations of attenuation are slowly being mapped out as well

seismic structures in the earth s inner core below southeastern asia documenting seismic heterogeneities in the earth s inner core ic is important in terms of getting an insight into its history and dynamics a valuable means for studying properties and spatial structure of such heterogeneities is provided by measurements of body waves refracted in the vicinity of the inner core boundary icb here we investigate eastern hemisphere of the solid core by means of pkpbc pkpdf differential travel times that sample depths from 140 to 360 km below its boundary we study 292 polar and 133 equatorial residuals measured over the traces that probe roughly the same volume of the ic in both planes equatorial residuals show slight spatial variations in the sampled ic volume mostly below the level of 0 5 whereas polar residuals are up to three times as big direction dependent and can exhibit higher local variations the measurements reveal fast changes in seismic velocity within a restricted volume of the ic we interpret the observations in terms of anisotropy and check against several anisotropy models few of which have been found capable of fitting the residuals scatter we particularly quantify the model where a dipping discontinuity separates fully isotropic roof of the ic from its anisotropic body whereas the depth of isotropy anisotropy transition increases in southeast direction from 190 km below southeastern asia off the coast of china to 350 km beneath australia another acceptable model cast in terms of localized anisotropic heterogeneities is valid if 33 largest polar measurements over the rays sampling a small volume below southeastern asia and the rest of polar data are treated separately this model envisages almost isotropic eastern hemisphere of the ic at least down to the depth of 360 km below the icb and constrains the anisotropic volume only to the ranges of north latitudes from 18 to 23 east longitudes from 125 to 135 and depths exceeding 170 km the anisotropy strength in either model is about 2 further effective pursuit of the models presents challenges in terms of resolution and coverage and basically requires a significant dataset extension

constraints on upper inner core structure from waveform inversion of core phases summary the determination of the inner core boundary structure is key to understanding the mechanisms of inner core growth iron solidification and anisotropy formation in the inner core a waveform inversion of a worldwide data set of pkikp and pkikp core phases is performed to investigate the velocity and the attenuation structure of this region the data set is chosen to sample the top 50 km of the inner core two inversion methods combining time and frequency domain observations are presented synthetic tests are performed in order to evaluate the resolution and the confidence intervals of the model parameters the attenuation of p waves in the uppermost inner core is poorly resolved but appears to be high q 100 the uppermost inner core interface is divided into two regions a region extending from 180 w to 60 e and characterized by negative p wave velocity perturbations dv v 0 per cent and a region extending from 60 e to 180 e and characterized by positive p wave velocity perturbations dv v 1 per cent the results of the inversion do not favour the presence of transverse isotropy aligned along the spin axis of the earth in the uppermost inner core for these two regions however these regions are correlated with those where large scale variations of the inner core anisotropy have been determined previously in the deeper inner core 100 km beneath the inner core boundary

localized velocity anomalies in the lower mantle summary two localized regions of velocity heterogeneity in the lower mantle with scale lengths of 1000 2000 km and 2 per cent velocity contrasts are detected and isolated through comparison of s scs p and pcp travel times and amplitudes from deep earthquakes in peru bolivia argentina and the sea of okhotsk comparison of the relative patterns of scs s differential travel times and s travel time residuals across north american wwssn and csn stations for the different source regions provides baselines for interpreting which phases have anomalous times a region of low s and p velocities is located beneath northern brazil and venezuela at depths of 1700 2700 km this region produces s wave delays of up to 4 s for signals from deep argentine events recorded at eastern north american stations the localized nature of the anomaly is indicated by the narrow bounds in azimuth 15 and take off angle 13 of the arrivals affected by it the long period s waves encountering this anomaly generally show 30 100 per cent amplitude enhancement while the short period amplitudes show no obvious effect the second anomaly is a high velocity region beneath the caribbean originally detected by jordan and lynn who used travel times from deep peruvian events the data from argentine and bolivian events presented here constrain the location of the anomaly quite well and indicate a possible short and long period s wave amplitude diminution associated with it when the travel time data are corrected for the estimated effects of these two anomalies a systematic regional variation in scs s station residuals is apparent between stations east of and west of the rocky mountains one possible explanation of this is a long wavelength lateral variation in the shear velocity structure of the lower mantle at depths greater than 2000 km beneath north america

structure of the inner core inferred from observations of its spheroidal shear modes spheroidal modes of elastic gravitational oscillation that have an energy partition dominated by shear energy in the inner core are called core modes recordings from the ida gravimeter network of an earthquake in the tonga region on june 22 1977 have provided the first unambiguous observations of core modes they conclusively show that at low frequencies the inner core has a very high q about 3500 they also tightly constrain the ratio of the inner core radius to the mean shear velocity to be 345s with an uncertainty of 0 5

controls on iron mobilisation from volcanic ash at low ph insights from dissolution experiments and mossbauer spectroscopy the deposition of volcanic ash from explosive eruptions to the surface ocean is a source of iron fe for marine phytoplankton however the factors that determine the soluble and thus potentially bioavailable fraction of fe in ash from magma source to ocean sink remain poorly understood we investigate for the first time the release of both fe ii and fe iii from six natural ash samples in ph 1 h2so4 representative of exposure to aqueous low ph conditions during airborne transport mossbauer spectroscopy analysis of the ash suggests that the overall 168 h trends in fetot and fe ii fetot release by individual samples are governed by dissolution of fe bearing aluminosilicates or oxides of the ash bulk in contrast the initial 6 h trends in fe release may reflect chemical properties of the ash surface imparted by the ash s eruptive history supported in part by x ray photoelectron spectroscopy analysis preferential release of fe iii relative to fe ii immediately on ash input to acid is attributed to oxidation of ash surfaces within the eruption plume additionally prior exposure of ash to a hf or hcl rich plume may enhance fe release by respectively reducing aluminosilicate resistance to acid dissolution or lowering the ph of the liquid film on airborne ash altogether our findings highlight that differing fe speciation in the ash bulk and surface reflecting its magmatic and eruptive history exerts a strong influence on the fe release behaviour of ash even from the same volcano the relative importance of bulk versus surface controls on fe mobilisation from ash during atmospheric transport will ultimately depend on the duration of contact with acids before deposition to the ocean

investigation of the inner outer core boundary structure from the seismograms of a deep earthquake recorded by a regional seismic array pep cdiff the pkp diffraction waves after pkp c cut off was identified in the pkikp or pkp df wave coda of teleseismic seismograms from a deep earthquake in western brazil an array stacking technique was applied to the short period waveforms from a regional seismic network in taiwan to retrieve the weak pkp cdiff waves between 159 and 162 the differential travel times and slowness of pkp cdiff and pkp df were used to constrain the p velocity structure near the inner outer core boundary icb the results of this study demonstrate that in some cases the icb structure can be constrained by data from a single event using presently available short period regional seismic data and applying suitable array techniques with a correction for axi symmetric anisotropy applied to the inner core the results of this study agree with the pkp properties of model vmoi a regional icb model revised from prem covering the icb sampled area of this study and model ak135 a new proposed earth model the c cusp position was reported at 151 4 from this event theoretical predictions for another new proposed earth model sp6 is in significant disagreement with the observed differential travel times between pkp cdiff and pkp df at a distance of 159 the residuals observation prediction included the observation errors 0 2 sec are approximately 0 17 sec 0 31 sec and 0 69 sec for vmoi ak135 and sp6 respectively neither model predicts a significant differential slowness residual this misfit along this path may be the result of the lateral heterogeneity of the sampled region near the icb relative to both spherically symmetric models or the complications imposed by the non axi symmetric anisotropy of the inner core

modeling saltation intermittency 1 in order to investigate the intermittency of the aeolian saltation a saltation model forced with instantaneous velocity fields has been introduced in a large eddy simulation airflow model the coupled model is evaluated on a flat erodible surface under various wind conditions and soil particle size distribution it is first shown that the model is able to simulate a well developed saltation layer in equilibrium with the turbulent flow the main characteristics of the saltation layer and their sensitivity to wind conditions are in good agreement with previous data set then the saltation intermittency is visualized through the presence of blowing sand structures near the surface known as aeolian streamers this is the first time that such structures are reproduced numerically from a correlation analysis we confirm previous thoughts that these sand structures are a visual footprint of past turbulent eddies propagating in the surface boundary layer the streamers appear to be embedded in larger saltation structures with increasing wind conditions the spatial scales of these streamers change with wind conditions and soil particle size distribution this is explained by two mechanisms 1 the modification of eddy structures with the main characteristics of the saltation layer and 2 the reduction of saltating particle sensitivity to the near surface eddies with increasing wind condition and soil median particle diameter as the eddy lifetime decreases within the saltation layer and the particle response time increases respectively the standard deviation of the saltation flux associated to these saltation patterns represents about 10 to 20 of the mean saltation flux