effects of redetermination of source time functions on the 3 d velocity structure inferred by waveform inversion abstract as recent waveform inversion studies to determine 3 d earth structure are increasingly using data in shorter period ranges the sensitivity of the inversion results to source parameters the source time function stf in particular will increase in this study we redetermine the centroid and moment tensor cmt solutions for 41 deep and intermediate earthquakes beneath south america using only body wave data in the same period range used in localized waveform inversion we then redetermine the stfs of 35 of these events by stacking the displacement of p waves we use four slightly different methods to obtain four sets of redetermined source parameters we find that all four sets of redetermined source parameters generally agree with the gcmt solutions but the stf durations are systematically shorter than those for the gcmt solutions particularly for events with moment magnitudes larger than 6 5 we then apply the four sets of redetermined source parameters for the 35 events to localized waveform inversion for the 3 d seismic velocity structure of the d region beneath central america and the caribbean using prem as the 1 d initial model we improve the 3 d structure as shown by improved variance reduction particularly after redetermination of moment tensors and stfs the velocity patterns of the four new 3 d structure models for the d region inferred by inversions using the redetermined source parameters do not differ significantly from those inferred using the gcmt source parameters however the amplitude of the lateral heterogeneity decreases when synthetics for the redetermined stfs are used

re assessing the surface cycling of molybdenum and rhenium we re evaluate the cycling of molybdenum mo and rhenium re in the near surface environment world river average mo and re concentrations initially based on a handful of rivers are calculated using 38 rivers representing five continents and 11 of 19 large scale drainage regions our new river concentration estimates are 8 0 nmol kg 1 mo and 16 5 pmol kg 1 re natural anthropogenic the linear relationship of dissolved re and so 2 4 in global rivers r 2 0 76 indicates labile continental re is predominantly hosted within sulfide minerals and reduced sediments it also provides a means of correcting for the anthropogenic contribution of re to world rivers using independent estimates of anthropogenic sulfate approximately 30 of re in global rivers is anthropogenic yielding a pre anthropogenic world river average of 11 2 pmol re kg 1 the potential for anthropogenic contribution is also seen in the non negligible re concentrations in precipitation 0 03 5 9 pmol kg 1 and the nmol kg 1 level re concentrations of mine waters the linear mo so 2 4 relationship r 2 0 69 indicates that the predominant source of mo to rivers is the weathering of pyrite an anthropogenic mo correction was not done as anthropogenically influenced samples do not display the unambiguous metal enrichment observed for re metal concentrations in high temperature hydrothermal fluids from the manus basin indicate that calculated end member fluids i e mg free yield negative mo and re concentrations showing that mo and re can be removed more quickly than mg during recharge high temperature hydrothermal fluids are unimportant sinks relative to their river sources 0 4 mo and 0 1 pre anthropogenic re we calculate new seawater response times of 4 4 10 5 yr smo and 1 3 10 5 yr sre pre

abundance and mineralogical association of arsenic in the suwannee limestone florida implications for arsenic release during water rock interaction arsenic as is being released from the suwannee limestone upper floridan aquifer during aquifer storage and recovery asr cycle testing with concentrations of up to 130 g l in the recovered water to determine the abundance and mineralogical association of as in the suwannee limestone matrix we have conducted a detailed mineralogical and geochemical study of 306 core samples in addition to random sampling of core material we also collected targeted samples of core material that contained organic material hydrous ferric oxide pyrite phosphate minerals and clays bulk as concentrations were determined by acid digestion followed by hydride generation atomic fluorescence spectrometry hg afs specific mineral phases were analyzed using scanning electron microscopy sem and electron probe microanalyses epma the average as concentration for all 306 samples is 3 5 ppm but only 1 7 ppm after exclusion of the targeted samples the average for the targeted samples is 9 5 ppm the detailed lithologic mineralogical and geochemical study of as in the upper floridan aquifer suwannee limestone shows that 1 arsenic is present in the suwannee limestone in low concentrations but is concentrated in minor mineral phases particularly pseudo framboidal pyrite 2 pyrite is generally as rich and can contain concentrations between 100 and 11 200 ppm as average 2300 ppm n 25 3 compared to pyrite other trace minerals contain much less as 4 pyrite is ubiquitous throughout the suwannee limestone but is most abundant in high porosity zones 5 previously suggested hydrous ferric oxide clay minerals and apatite are not an important source of as this study also provided some insight into the question whether the interaction reaction of water with an aquifer matrix that contains only a few part per million as is capable of producing high as concentrations in groundwater our findings indicate that it can be relatively easy to generate a high as groundwater despite a low bulk as concentration in the aquifer matrix a change in physico chemical conditions that selectively affects the stability of as bearing minerals is sufficient to increase as concentrations by several orders of magnitude

the variation of morphological features and mineralogical components of biological soil crusts in the gurbantunggut desert of northwestern china increasingly complex life forms were found in older biological soil crusts in the gurbantaunggut desert in northwestern china these crusts may play a critical role in mineral erosion and desert soil formation by modifying the weathering environment and ultimately affecting mineralogical variance to test this hypothesis variations in the morphological features and mineralogical components of successional biological soil crusts at 1 cm were studied by optical microscopy sem and grain size analysis concentrations of erosion resistant minerals decreased with crust succession while minerals susceptible to weathering increased with crust development neogenetic minerals were found in late stage crusts but not in early stage crusts silt and clay concentrations were highest in early formation crusts and soil mean particle size decreased with crust succession cyanobacteria lichen and moss were shown to erode and etch rocks and secondary minerals produced by weathering were localized with the living organisms thus more developed crusts appeared to contribute to greater mineral weathering and may be a major cause of mineralogical variance seen in the gurbantunggut desert the greater activity and complexity of older crusts as well as their improved moisture condition may function to accelerate mineral weathering therefore protection and recovery of biological crusts is vital for desert soil formation

global adjoint tomography first generation model we present the first generation global tomographic model constructed based on adjoint tomography an iterative full waveform inversion technique synthetic seismograms were calculated using gpu accelerated spectral element simulations of global seismic wave propagation accommodating effects due to 3d anelastic crust mantle structure topography bathymetry the ocean load ellipticity rotation and self gravitation frechet derivatives were calculated in 3d anelastic models based on an adjoint state method the simulations were performed on the cray xk7 named titan a computer with 18 688 gpu accelerators housed at oak ridge national laboratory the transversely isotropic global model is the result of 15 tomographic iterations which systematically reduced differences between observed and simulated three component seismograms our starting model combined 3d mantle model s362ani kustowski et al 2008 with 3d crustal model crust2 0 bassin et al 2000 we simultaneously inverted for structure in the crust and mantle thereby eliminating the need for widely used crustal corrections we used data from 253 earthquakes in the magnitude range 5 8 mw 7 0 for the first 12 iterations we combined 30 s body wave data with 60 s surface wave data the shortest period of the surface waves was gradually decreased and in the last three iterations we combined 17 s body waves with 45 s surface waves we started using 180 min long seismograms after the 12th iteration and assimilated minor and major arc body and surface waves the 15th iteration model features enhancements of well known slabs an enhanced image of the samoa tahiti plume as well as various other plumes and hotspots such as caroline galapagos yellowstone and erebus furthermore we see clear improvements in slab resolution along the hellenic and japan arcs as well as subduction along the east of scotia plate which does not exist in the starting model point spread function tests demonstrate that we are approaching the resolution of continental scale studies in some areas for example underneath yellowstone this is a consequence of our multi scale smoothing strategy in which we define our smoothing operator as a function of the approximate hessian kernel thereby smoothing gradients less wherever we have good ray coverage such as underneath north america

finite frequency tomography of d shear velocity heterogeneity beneath the caribbean 1 the shear velocity structure in the lowermost 500 km of the mantle beneath the caribbean and surrounding areas is determined by seismic tomography applied to a suite of sd sks scs s scd sbc s and scs scd sbc differential times where scd sbc is a pair of overlapping triplication arrivals produced by shear wave interaction with an abrupt velocity increase at the top of the d region the inclusion of the triplication arrivals in the inversion a first for a deep mantle tomographic model is possible because of the widespread presence of a d velocity discontinuity in the region the improved ray path sampling provided by the triplication arrivals yields improved vertical resolution of velocity heterogeneity within and above the d region the reference velocity model taken from a prior study of waveforms in the region has a 2 9 shear velocity discontinuity 250 km above the core mantle boundary cmb effects of aspherical structure in the mantle at shallower depths than the inversion volume are suppressed by applying corrections for several different long wavelength shear velocity tomography models born frechet kernels are used to characterize how the finite frequency data sample the structure for all of the differential arrival time combinations inversions are performed with and without the kernels the use of three dimensional kernels stabilizes the tomographic inversion relative to a ray theory parameterization and a final model with 60 and 50 km correlation lengths in the lateral and radial dimensions respectively is retrieved the resolution of the model is higher than that of prior inversions with 3 4 velocity fluctuations being resolved within what is commonly described as a circum pacific ring of high velocities a broad zone of relatively high shear velocity material extends throughout the lower mantle volume beneath the gulf of mexico with several percent lower shear velocities being found beneath northern south america concentrated low velocity regions extend through the d layer under the caribbean colombia and ecuador suggestive of small scale plumes in the boundary layer and possible lateral variations of the d discontinuity one scenario consistent with the imaged features involves subducted farallon plate ponding at the base of the mantle and laterally displacing hot boundary layer material that piles up and destabilizes on its margins

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

effects of three dimensional earth structure on cmt earthquake parameters abstract we investigate errors in centroid earthquake parameters due to unmodeled structural heterogeneity we generate a simulated dataset consisting of synthetic seismograms for 50 earthquakes and 150 stations distributed globally to generate the synthetic seismograms we use a spectral element wave propagation package specfem3d globe that accounts for the earth s three dimensional structure an established centroid moment tensor inversion algorithm from the global cmt project is used to invert the synthetic dataset with and without added noise for earthquake source parameters this algorithm uses a one dimensional earth structure together with approximate corrections for three dimensional structure to model the seismograms we interpret the differences between the estimated source parameters and the parameters used to compute the synthetic dataset as errors due to unmodeled structural heterogeneity and the presence of noise we expect that the errors obtained in this study are representative of the errors in the global cmt catalogue we find that the errors in scalar moment moment tensor elements and location are small on average the depth and centroid time are however biased by a small amount we find that the error in depth can be reduced significantly by applying corrections for the difference in the velocity structure at the source and receiver locations from the earth s average structure in the cmt inversions this modification has a minimal effect on the errors in centroid time we do not find large errors in scalar moments even where the crustal thickness at the source is very different from the earth s average crustal thickness

biological soil crust effects must be included to accurately model infiltration and erosion in drylands an example from tabernas badlands in dryland ecosystems runoff is mainly generated in bare areas which are also more susceptible to water erosion than vegetated areas these bare areas are often covered and protected by biological soil crusts bscs which modify numerous physicochemical surface properties involved in runoff and erosion processes bscs are considered as one of the most important stabilizing factors in the soil surface but most previous research has concentrated only on patch or hillslope scale effects of bscs and their effect at coarser scales has rarely been studied in this article we present a new approach based on previous surface cover quantification for including the effects of bscs in physically based runoff and erosion modeling the limburg soil erosion model lisem was used to parameterize and simulate the effects of bscs on runoff and erosion in a small semiarid catchment characterized by fine textured soils and predominantly covered by bscs paired model simulations under two scenarios with and without including the effects of bscs were run under different rainfall intensities to evaluate the effect of bscs on runoff and erosion under different rainfall conditions runoff and erosion rates recorded in the field at the catchment outlet were predicted much more accurately when bscs were included because there was less overestimation of runoff rate maximum runoff peaks and erosion rates in the areas dominated by bscs the proposed approach enables bscs to be included in spatially distributed runoff and erosion models improving their predictions and may be used for evaluating how the effect of human activity on bscs affects catchment scale water erosion

groundwater dynamics and arsenic contamination in bangladesh although arsenic contaminated groundwater in bangladesh is a serious health issue little is known about the complex transient patterns of groundwater flow that flush solutes from aquifers and carry solutes into the subsurface hydrologic modeling results for our field site in the munshiganj district indicate that groundwater flow is vigorous flushing the aquifer over time scales of decades to a century and also transporting solute loads into the aquifer with recharge from ponds rivers and rice fields the combined hydrologic and biogeochemical results from our field site imply that the biogeochemistry of the aquifer system may not be in steady state and that the net effect of competing processes could either increase or decrease arsenic concentrations over the next decades modeling results suggest that irrigation has greatly changed the location timing and chemical content of recharge to the aquifer flushing water through the system more quickly and also cycling large fluxes of water through rice fields during the dry season that could mobilize arsenic from oxides in near surface sediments furthermore the hydrologic model reveals that ponds many of which have been excavated over the last 50 years now provide much of the groundwater recharge these ponds receive most of the waste from the villages and thus provide another potential source of organic carbon to the groundwater system

the mineralogy of arsenic in uranium mine tailings at the rabbit lake in pit facility northern saskatchewan canada a detailed investigation of the mineralogy of as in the tailings of the rabbit lake uranium ore processing facility was conducted the milling ore extraction process was sampled at three different locations to obtain information about when where and under what condition secondary as phases form these samples were compared with four samples of varying as content from the rabbit lake in pit tailings management facility tmf up to 20 as in the tailings are present in primary minerals that reach the tailings directly because they are not dissolved during the uranium extraction the remaining 80 constitute as that was dissolved during ore extraction and then re precipitated before being discharged into the tailings pond it was not possible to conclusively identify any individual re precipitated secondary as minerals in the rabbit lake tmf indirect evidence from sequential extraction analyses suggests the presence of an amorphous ca as phase and a possible but unlikely minor amount of an amorphous fe as phase however the close association between hydrous ferric oxide hfo and as could be clearly demonstrated hfo was identified to be 2 line ferrihydrite and its xrd pattern geometry indicates a substantial amount of adsorbed as this is in good agreement with sem tem and sequential extraction analyses that all showed the close association of hfo and as

seismicity and geometry of a 110 km long blind thrust fault 1 the 1985 kettleman hills california earthquake the august 4 1985 kettleman hills earthquake was the third in a sequence of moderate shocks to occur beneath the northern half of a 110 km long fold chain bounding the eastern california coast ranges the 1982 mw 5 4 new idria 1983 mw 6 5 coalinga and 1985 mw 6 1 kettleman hills events define a southward progression of seismic activity beneath the fold we use teleseismic waveforms geodetic modeling hypocenters relocated in a three dimensional velocity model and subsurface structural data to investigate the kettleman hills earthquake the main shock results from motion on a shallowly dipping thrust fault buried at 10 km depth aftershocks and coseismic fault slip extend 20 km along the fold axis nearly the full extent of the kettleman hills north dome anticline aftershocks occur primarily several kilometers in front of the fault tip and in the core of the anticline the main shock and several foreshocks occurred at a 2 km right step in the quaternary fold axis which also corresponds to the southern end of the 1983 coalinga and northern end of the 1985 kettleman hills aftershock zones from this we infer that the step in the fold is caused by an offset or tear in the underlying fault the scalar seismic moment is 1 6 1018 n m consistent with the geodetic deformation and the duration of rupture is 16 s 3 4 times greater than for the average earthquake with this scalar moment the slow rate of moment release provides an explanation for the low level of ground shaking and low local magnitude reported for the event the peak of the geodetic uplift is located 5 km perpendicular to the quaternary fold axis we argue that the fault is propagating northeast into the undeformed san joaquin valley sediments and that the overlying fold is growing at about 0 5 mm yr

δ34s isotope values of dissolved sulfate so42 as a tracer for battery acid h2so4 contamination in groundwater the application of sulfur isotope 34s values of sulfate in groundwater provided the information necessary to evaluate the source transport and fate of battery acid and associated contaminants at the gulf coast recycling gcr facility the chemical and isotopic composition of groundwater beneath the gcr property a battery recycling facility in east tampa florida varies more than expected for an area of comparable size sulfate so42 values for example range from 1 2 to 11 500 mg l and oxygen and hydrogen isotopes do not attenuate towards the weighted annual mean those samples that are high in sulfate generally have a low ph which immediately indicates battery acid h2so4 contamination as a potential source for the sulfate the low ph and high reactivity of the sulfuric acid groundwater cause the formation of hydrogeological microenvironments due to preferential dissolution of carbonate minerals which in turn causes enhanced recharge and groundwater flow in certain areas thus the extreme scatter in the data set because of the difficult hydrogeology it is not straightforward to delineate the point sources of contamination and up to five potential scenarios have to be evaluated 1 seawater intrusion 2 upwelling of high sulfate groundwater 3 local dissolution of gypsum 4 an up gradient contaminant source to the northeast of the gcr property and 5 battery acid contamination

global models of surface wave attenuation 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive global models of surface wave attenuation 1 q the data set consists of measurements of rayleigh wave amplitude anomalies in the period range 50 250 s for 347 earthquakes observed at 179 seismic stations the amplitude anomalies are considered to depend on four factors intrinsic attenuation along the ray path elastic focusing effects along the ray path a source factor accounting for uncertainties in the strength of excitation and a receiver factor accounting for uncertainties in the response at the station the amplitude data are inverted simultaneously for global maps of attenuation expanded in spherical harmonics up to degree 12 global maps of phase velocity expanded to degree 20 and source and receiver correction factors all four variable types are shown to be important in explaining the amplitude anomalies a data set of phase delay measurements provides additional constraints on velocity structure the maps of attenuation obtained by simultaneous inversion for elastic and anelastic models contain important features that are not robustly imaged when the effect of focusing on wave amplitude is ignored these include high attenuation along western north america and along the east pacific rise and other ridge systems and low attenuation associated with stable continental interiors the global attenuation maps exhibit a strong correlation with phase velocity maps corrected for the effect of the crust particularly for periods 200 s the correlation suggests that the variability in both q and velocity in the shallow upper mantle is primarily thermal in origin

a systematic study of source time functions and moment tensors of intermediate and deep earthquakes 1 we developed an inversion algorithm to determine the source time function and moment tensor of intermediate and deep earthquakes from a set of teleseismic body wave records the method proceeds in two stages first a nonlinear inversion by simulated annealing is performed to simultaneously a align the waveforms in time b determine a common source time function and c measure a collection of observed station amplitudes the station amplitudes are then used in a second stage as secondary observables to invert for the moment tensors we perform three different inversions to estimate the complete moment tensor solution the pure deviatoric solution and the double couple solution all the calculations are extremely simple and in particular it is not necessary to compute synthetic seismograms the method requires well isolated phases at different stations which restricts its application to intermediate and deep events the algorithm is applied to the fdsn broadband records corresponding to the period 1990 2005 of worldwide intermediate and deep seismicity depth100 km of magnitude greater than 6 5 the source time functions are compared to those obtained from other studies of intermediate and deep events the moment tensors are also systematically compared to the harvard cmt and usgs solutions both show a very good agreement with previous studies

deep earthquake rupture histories determined by global stacking of broadband p waveforms 1 we conduct a systematic investigation of time histories of moment release in deep earthquakes whose physical mechanism remains unknown we have constructed source time functions stfs of 111 large deep earthquakes depth 100 km and mw 6 4 by stacking p waveforms from broadband seismograms recorded by the global seismographic network aligning and stacking waveforms cancels noise and allows us to identify the rupture initiation and termination times accurately each stf is scaled to a reference moment of 1019 n m using the duration moment relation m01 3 in order to investigate depth dependence of the stfs we bin them into three depth ranges 100 350 km 350 550 km and deeper than 550 km based on physical properties of the mantle and the distribution of the data we infer a change in character near 550 km earthquakes deeper than about 550 km are shorter have simpler time functions and are more uniform in their characteristics further we find longer than expected scaled durations and greater complexity in the 350 550 km depth range the scaled durations of the 350 550 km earthquakes do not decrease with depth as 1 vs instead possessing a slightly longer average scaled duration than those 100 350 km deep we further categorize the earthquakes by subduction zone and find a similar depth dependence within individual zones finally the events that have achieved highest moment rate in the first 1 2 s after initiation tend to be deeper and or larger events the latter suggesting that dynamic rupture propagation affects the final size of the earthquake the depth dependence of duration and complexity suggests more complicated rupture histories between 350 and 550 km and a possible change in the physical mechanism of rupture at about 550 km

insignificant isotropic component in the moment tensor of deep earthquakes the mechanism responsible for deep focus earthquakes which occur at depths of 300 700 km in subducting slabs has been a long standing problem in geophysics unlike shallow earthquakes deep earthquakes cannot be attributed to frictional instabilities across a fault plane because of high frictional resistance to sliding at depth a volumetric change associated with a phase transition expected to occur at depth1 3 is often invoked as the physical mechanism if so the resulting source mechanism should contain a major isotropic component although many researchers have attempted to observe such an isotropic component4 10 no one has yet convincingly proved or disproved its presence there exists a portion of the seismogram which is well suited to resolve the isotropic component of deep earthquakes but which has not been analysed by previous workers here i use this component in a systematic analysis of 19 large deep earthquakes and show that no significant isotropic component 10 of the seismic moment exists a sudden implosive phase change can thus be ruled out as the primary physical mechanism for deep earthquakes

q tomography of the upper mantle using three component long period waveforms summary we present a degree 8 3 d q model qrlw8 of the upper mantle derived from three component surface waveform data in the period range 60 400 s the inversion procedure involves two steps in the first step 3 d whole mantle velocity models are derived separately for elastic sh transverse component and sv vertical and longitudinal component velocity models using both surface and body waveforms and the non linear asymptotic coupling theory nact approach in the second step the surface waveforms thus aligned in phase are inverted to obtain a 3 d q model in the depth range 80 670 km various stability tests are performed to assess the quality of the resulting q model and in particular to assess possible contamination from focusing effects we find that the 3 d patterns obtained are stable but the amplitude of the lateral variations in q is not well constrained because large damping is necessary to extract the weak q signal from data the model obtained agrees with previous results in that a strong correlation of q with tectonics is observed in the first 250 km of the upper mantle with high attenuation under oceanic regions and low attenuation under continental shields it is gradually replaced by a simpler pattern at larger depth at the depths below 400 km the q distribution is generally dominated by two strong minima one under the southern pacific and one under africa yielding a strong degree 2 pattern most hotspots are located above regions of low q at this depth ridges are shallow features in both velocity and q models

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

earthquake source parameters and stress distribution in the adak island region of the central aleutian islands alaska source parameters have been systematically determined for all earthquakes with mw 5 that occurred between 172 w and 179 w longitude in the adak island region of the central aleutian islands during 1977 march 1987 we relocate the events using a plate velocity model developed for the region and use two alternative methods of depth determination the first method uses arrival times of direct and prominent reflected phases primarily pwp the second method uses broadband p wave displacement seismograms in an inversion for source depth the analysis of these events provides a well constrained data set for the study of stress release along an active subduction zone three earthquakes which occurred seaward of the trench axis are located just below the crust mantle interface and show extension nearly perpendicular to the trench axis seven events occurred in the wadati benioff zone sixty four events are located in the main thrust zone and except for five unusual events are characterized by thrust mechanisms with one nodal plane dipping north at a shallow angle in cross section the thrust zone appears as a thin 10 15 km thickness interplate region which extends from 15 to 50 km depth a 10 15 average discrepancy between observed slip vector azimuths and the predicted relative motion direction between the pacific and north american plates exists for these events the observed slip vectors are oriented more normal to the trench than is predicted by plate motions five earthquakes which occurred as aftershocks to the may 7 1986 earthquake mw 8 0 in the crust of the overriding plate have strike slip mechanisms consistent with right lateral motion on arc parallel fault planes observations of slip vectors along the whole aleutian arc show a similar trend to that observed in the adak island region the largest differences 30 between observed and predicted slip azimuths occur around 175 e we propose a model of plate interaction in which a portion of the along arc motion occurs along a weak strike slip shear zone in the upper plate near the volcanic line the slip azimuths in the main thrust zone fit this model well if the amount of transcurrent slip occurring in the upper plate is 60 of the arc parallel relative plate motion a consequence of the model is along arc extension of the overriding plate between the accretionary wedge and the volcanic line especially in the western part of the aleutian arc calculations based on a tectonic model by geist et al 1988 for the formation of arc summit basins through block rotation and translation suggest that along arc extension has been significant since late miocene or early pliocene

short period surface wave phase velocities across the conterminous united states abstract surface wave phase velocity maps for the full footprint of the usarray transportable array ta across the conterminous united states are developed and tested three component long period continuous seismograms recorded on more than 1800 seismometers most of which were deployed for 18 months or longer are processed using a noise cross correlation technique to derive inter station love and rayleigh dispersion curves at periods between 5 and 40 s the phase velocity measurements are quality controlled using an automated algorithm and then used in inversions for love and rayleigh phase velocity models at discrete periods on a 0 25 by 0 25 pixel grid the robustness of the results is examined using comparisons of maps derived from subsets of the data a winter summer division of the cross correlation data results in small model differences indicating relatively minor sensitivity of the results to seasonal variations in the distribution of noise sources division of the dispersion data based on inter station azimuth does not result in geographically coherent model differences suggesting that azimuthal anisotropy at the regional scale is weak compared with variations in isotropic velocities and does not substantially influence the results for isotropic velocities the phase velocity maps and dispersion measurements are documented and made available as data products of the 10 year long usarray ta deployment

distribution speciation and bioavailability of arsenic in a shallow water submarine hydrothermal system tutum bay ambitle island png shallow water hydrothermal vent systems can introduce large amounts of potentially toxic elements such as arsenic as into coastal marine environments the first step in understanding and describing the potential impact of these elements throughout hydrothermally influenced coastal ecosystems is to determine the element s distribution and speciation which in turn influences the availability of the toxin for biological uptake shallow submarine hot springs near ambitle island papua new guinea are discharging as much as 1 5 kg per day of arsenic directly into a coral reef ecosystem we have investigated the bioavailability of the as throughout tutum bay by studying vent fluid seawater pore water precipitates and sediments in addition to measuring as abundance as speciation as iii as v and the methylated species dma and mma was determined in various waters the as concentration for discrete mineral phases in vent precipitates and sediments was determined by sequentially extracting arsenic from the easily extractable carbonate fe oxyhydroxide or hydrous ferric oxide hfo and residual fractions each of which have a different bioavailability diffuse venting seems to play a critical role on the distribution of as throughout tutum bay surface sediments which have a mean as concentration of 527 ppm while excluding the vent precipitates range 1483 to 52 ppm up to 54 ppm as were extracted from the easily extractable fraction of surface sediments mean 19 7 ppm using a k2hpo4 kh2po4 buffer at ph 7 2 arsenic from this fraction is considered to be the most available for biological processes and therefore the most dangerous for biota however sequential extraction shows that 98 6 of the as in vent precipitates and a mean of 93 3 in surface sediments range 88 2 to 96 3 is coprecipitated with the hydrous ferric oxide hfo fraction thus the bulk of the as being discharged into tutum bay is scavenged by the hfo and should remain stable unless the physicochemical conditions surrounding the oxides change in surface seawaters of tutum bay we found as much as four times the average seawater concentration of as 8 4 ag l compared to 2 ag l the abundance of as in seawater just above the sediment water interface is near normal although as iii in both surface and bottom seawater throughout tutum bay is substantially enriched compared to average seawater hydrothermal venting therefore provides bioavailable as by two major pathways throughout tutum bay 1 easily exchangeable as from hydrothermally influenced sediments to as far away as 200 m from focused venting and 2 in surface seawaters which may allow for biological uptake by phytoplankton and transfer up the food web d 2005 elsevier b v all rights reserved

reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments abstract sporadic direct observations over a 50 yr period inadequately characterize the history of seasonal hypoxia and anoxia in chesapeake bay a large estuary threatened by eutrophication here we undertake a reconstruction of 20th century oxygen depletion in this estuary using mo concentrations in 210pb dated sediments cu concentrations are used to control for anthropogenic influences cores from the central channel display mild mo enrichments above crustal backgrounds up to 5 g g and strong cu enrichments up to 35 g g temporally cu enrichment mostly anthropogenic began earlier and stabilized in the last two thirds of the 20th century in contrast mo enrichment has grown during the last two thirds of the century molybdenum enrichment is mostly hydrogenic except in a section of the channel that receives additional mo from erosion of early miocene shore deposits two geochemical mechanisms promote mo enrichment manganese refluxing concentrates dissolved moo42 at the sediment water interface and sulfide substitution into moo42 produces thiomolybdates which can be fixed by particles the mo enrichment mechanisms operate primarily during periods when bottom waters are anoxic and thiomolybdate formation can occur near the sediment water interface this implies a temporal coupling between water column anoxia and mo fixation even though fixation occurs only within sediments the mo enrichment profiles suggest that chesapeake bay has experienced growing o2 depletion since the first half of the 20th century but especially after 1960

controls on high sulfate concentrations in the upper floridan aquifer in southwest florida chemical profiles of groundwater in the upper floridan aquifer in southwest florida vary between an inland and a coastal site at the inland site sulfate concentrations increase with depth and chloride concentrations remain low at the coastal site sulfate concentrations are high and constant but chloride concentrations increase with depth the sulfate source at the inland site is gypsum dissolution whereas at the coastal site the sulfate source is predominantly gypsum dissolution overprinted by saltwater mixing mass transfer modeling in conjunction with isotopic data was used to evaluate hypothetical flow paths within the aquifer dedolomitization reactions gypsum and dolomite dissolution with calcite precipitation dominate along flow paths where sulfate concentrations increase the distribution of gypsum in the aquifer indicates that a deeply circulating flow path controls the chemical evolution of groundwater between the two sites fresh groundwater moves into deep zones in the aquifer where gypsum is found farther along the flow path in the discharge area this groundwater moves upward to shallower depths prior to the saltwater mixing zone saltwater mixing becomes more pronounced with both proximity to the coast and with increasing depth these results underscore the importance of evaluating vertical as well as lateral flow paths when quantifying geochemical reactions in a chemically stratified aquifer

time functions of deep earthquakes from broadband and short period stacks to constrain dynamic source properties of deep earthquakes we have systematically constructed broadband time functions of deep earthquakes by stacking and scaling teleseismic p waves from u s national seismic network terrascope and berkeley digital seismic network broadband stations we examined 42 earthquakes with depths from 100 to 660 km that occurred between july 1 1992 and july 31 1995 to directly compare time functions or to group them by size depth or region it is essential to scale them to remove the effect of moment which varies by more than 3 orders of magnitude for these events for each event we also computed short period stacks of p waves recorded by west coast regional arrays the comparison of broadband with short period stacks yields a considerable advantage enabling more reliable measurement of event duration a more accurate estimate of the duration better constrains the scaling procedure to remove the effect of moment producing scaled time functions with both correct timing and amplitude we find only subtle differences in the broadband time function shape with moment indicating successful scaling and minimal effects of attenuation at the periods considered here the average shape of the envelopes of the short period stacks is very similar to the average broadband time function the main variations seen with depth are 1 a mild decrease in duration with increasing depth 2 greater asymmetry in the time functions of intermediate events compared to deep ones and 3 unexpected complexity and late moment release for events between 350 and 550 km with seven of the eight events in that depth interval displaying markedly more complicated time functions with more moment release late in the rupture than most events above or below the first two results are broadly consistent with our previous studies while the third is reported here for the first time the greater complexity between 350 and 550 km suggests greater heterogeneity in the failure process in that depth range

distribution and mobility of geogenic molybdenum and arsenic in a limestone aquifer matrix abstract to investigate the potential of mo and as as possible geogenic contaminants three sediment cores were examined to evaluate their mineralogical association distribution and mobility the cores were described and analyzed for total organic carbon toc ca mg si al p sr as mo fe and s content except in the uppermost segment limestone was the main lithology with the occasional presence of dolomite and clay that change in lithology was also observed in the bulk chemical composition where ca mg and sr concentrations increased with depth while si al and p concentrations decreased with depth minor minerals included pyrite fes 2 powellite camoo 4 and ferrihydrite the minimum maximum median and standard deviations for all analyzed elements including as and mo were comparable for all three cores molybdenum and as however varied significantly with depth and median as and mo values were above their respective crustal averages of approximately 1 1 mg kg and 1 5 mg kg the median values for as were 1 9 mg kg in core dep 1 3 3 mg kg in dep 2 and 1 mg kg in dep 5 the median values for mo were 2 3 mg kg in core dep 1 2 5 mg kg in dep 2 and 2 5 mg kg in dep 5 maximum concentrations for as were 101 9 mg kg 47 5 mg kg and 56 2 mg kg in cores dep 1 dep 2 and dep 5 respectively maximum concentrations for mo were 880 mg kg 123 mg kg and 225 mg kg in cores dep 1 dep 2 and dep 5 respectively electron microprobe analyses of individual minerals revealed variable concentrations of as ranging from approximately 300 to 9000 mg kg in pyrite and up to 17 600 mg kg in powellite camoo 4 the mo concentration in pyrite was consistently below the detection limit of approximately 100 mg kg in powellite the mo concentration was up to 42 wt a subset of 10 samples from different stratigraphic sections and with different as and mo concentrations was further investigated to assess as and mo mobility under changing physicochemical conditions leaching the aquifer matrix with a 1 m naoac solution at a ph of 8 1 removed more than 70 mo in 8 of the 10 samples the maximum value was 97 in contrast to mo as was mobilized to a lesser degree in 8 of the samples less than 30 were removed and the maximum was only 50 molybdenum which seemed to be loosely bound to mineral and organic matter surfaces thus could easily be removed from the aquifer matrix while as on the other hand should be much less mobile because it occurred either tightly adsorbed by hydrous ferric oxide or as an impurity in pyrite thus it is advisable to include mo in the analytical program whenever elevated as concentrations are encountered in groundwater

geogenic as and mo groundwater contamination caused by an abundance of domestic supply wells abstract lacking a connection to a municipal water supply each household in the municipality of lithia approximately 30 km southeast of tampa florida usa is responsible for its own supply of drinking water causing a high density of private domestic supply wells dsw in this area there a multilayered aquifer system exists which can be subdivided into three distinct hydro stratigraphic units which are from the top down the surficial aquifer system sas the intermediate aquifer system ias and the upper floridan aquifer system ufa despite the relatively small area the geochemical and hydrogeological setting in lithia is complex consisting of i extensive cyclical pumping in a municipal well field to the west ii large seasonal changes in hydraulic head ii multiple aquifers with different hydraulic heads and iv a large density of domestic supply wells dsw within the zone of highest as concentrations there are approximately 100 wells in an area of 2 5 km 1 5 km most of these wells have large open screened intervals often open to all three aquifers allowing the downward flow of oxygenated and upward flow of anoxic groundwater a survey of groundwater quality found that as and mo concentrations in the dsw were up to 371 g l and 4740 g l respectively to obtain information about the individual aquifers 5 well clusters with 4 monitoring intervals approximately 50 m 65 m 80 m and 95 m below surface and 8 push core wells approximately 9 m below surface were installed and sampled in those wells as and mo were only elevated in a permeable layer within the ias at a depth of 50 m values were up to 195 g l for as and up to 5050 g l for mo using the tritium helium 3h 3he method the ages of those samples high in as and mo were determined to be 40 30 and 30 years respectively while all other samples had ages older than 50 years this indicated that mixing between young and old groundwater could be responsible for the high as and mo concentrations a good negative correlation for the whole data set was also observed between the concentration 3h and 18o values which together with hydrogeological modeling confirmed that the increased permeability created by the high density of dsw resulted in flow paths that permitted the perpetual mixing of shallow and deep groundwater the release of the as and mo appeared to be a consequence of changes to the physicochemical conditions in the aquifer either via the introduction of oxygen rich fluids into the ias or the mixing of different fluids in the ias or the introduction of oxygen depleted fluids into the ias while the mobilization of geogenic trace metals is often associated with pumping induced hydraulic gradient changes we found that a certain density of multi aquifer wells can be sufficient to alter hydrologic flow paths and induce the mobilization of geogenic trace metals even in the absence of significant pumping in lithia the dsw effectively increased the local scale permeability of the aquifer causing the mixing of oxygen rich surface and deeper anoxic groundwater across a confining unit because the alteration to the hydrologic flow paths was a consequence of changes to the physical structure of the aquifer system rather than due to pumping the alteration is not easily reversible thus significantly complicating site remediation our results provide a cautionary warning of the risks of undue private dsw development in rapidly growing communities

hydrochemical effects of saltwater intrusion in a limestone and dolomitic limestone aquifer in lebanon this study demonstrates groundwater quality differences between a limestone and a dolomitic limestone sub oxic coastal aquifer in the eastern mediterranean lebanon with and without ongoing moderate salinization since the last decades for this purpose 8 major and 50 trace elements tes were analyzed in 80 water and 65 rock samples and interpreted with a quad fold approach utilizing 1 nonparametric statistical tests 2 concentration deviations from ideal conservative freshwater seawater mixing lines 3 a new parameter called mixing enrichment factor to assess the mobility of chemical constituents under salinizing conditions and 4 1 d dual porosity flow path modeling with phreeqc dissolution precipitation of caxmgysrzco3 and cation exchange were the main disclosed hydrogeochemical processes besides minor signs of organic matter oxidation in the dolomitic limestone aquifer less carbonate dissolved as compared to the limestone aquifer partly because of lower pco2 in addition to seawater inflow triggering mg calcite precipitation by cation exchange saltwater intrusion led to mobilization of as ba cu ni rb sr and u in both aquifers sometimes likely by cation exchange e g ba and sr some of these tes notably cu and ni recorded higher concentrations in the dolomitic limestone regardless of salinization other elements like al be ce cr nb pb v y and zr revealed no or a low mobilization tendency the concentration of all tes in groundwater remained below drinking water limits notwithstanding moderate salinization this classifies carbonate rocks as a weak geogenic source of tes whereas encroaching seawater appears to be a more important source

calcite cementation in the upper floridan aquifer a modern example for confined aquifer cementation models detailed petrographic study of the oligocene suwannee limestone a principal unit of the upper floridan aquifer system indicates that all the calcite cements in the suwannee limestone are precompaction in origin most are clearly associated with either early mineralogical stabilization or oligocene subaerial exposure features none of the cements are in isotopic 18 o and 13 c or trace element fe mn and sr equilibrium with the extant aquifer waters the cements therefore formed prior to the onset of regionally confined freshwater aquifer conditions these rocks have been basically inert with respect to calcite cementation during the past 5 to 10 m y while they have been part of the regional confined aquifer using this modern aquifer as an example it is likely that confined paleoaquifer cementation has been overestimated as an explanation for regional cementation patterns in ancient limestones

ongoing oversanding induces biological soil crust layering a new approach for biological soil crust structure elucidation determined from high resolution penetration resistance data abstract the aim of this study was to determine the in situ strength and microscopic characteristics of bio physical micro horizons in the top 40 mm of oversanded sand soils detected by depth dependent penetration resistance pr these micro horizons result from the burial of biological soils crust bsc surfaces and contribute to soil stability they are also important as the biotic source for seeding new surficial crusts ex situ polarised optical micrograph was employed to determine the bio physical structures associated with the fossil bsc horizons an automated electronic micro penetrometer emp determining in situ depth dependent soil pr was used for the quantitative detection of surface and buried micro horizons pr data was modelled using a multi component soil and micro horizon multilayer plastic shear stress model this enabled determination of soil and sediment structure the contribution of buried fossil bscs to soil strength and structural mapping we also employed proxy synthetic layered soil systems to determine the effect of emp shaft and probe tip shape upon the pr profile this methodology represents a significant improvement over penetrometer methods that only use single value surface breaking point information we find that buried bsc structures can contribute over 80 of the soil strength even at ca 20 mm depth and that the strength of a buried crust at least in the medium term can exceed that of developing surficial ones typical soil strengths of bscs in the negev desert israel lie between 1 5 and 3 6 mpa finally we discuss the effects and potential importance that buried bsc horizons may have upon heat and the percolation and diffusion of moisture and gas through structured bio physical bsc capped sand soil systems

effects of microbiotic crusts under cropland in temperate environments on soil erodibility during concentrated flow several studies illustrate the wind and water erosion reducing potential of semi permanent microbiotic soil crusts in arid and semi arid desert environments in contrast little is hitherto known on these biological crusts on cropland soils in temperate environments where they are annually destroyed by tillage and quickly regenerate thereafter this study attempts to fill the research gap through a a field survey assessing the occurrence of biological soil crusts on loess derived soils in central belgium in space and time and b laboratory flume 2 m long experiments simulating concentrated runoff on undisturbed topsoil samples 0 4 0 1 m2 quantifying the microbiotic crust effect on soil erosion rates three stages of microbiotic crust development on cropland soils are distinguished 1 development of a non biological surface seal by raindrop impact 2 colonization of the soil by algae and gradual development of a continuous algal mat and 3 establishment of a well developed microbiotic crust with moss plants as the dominant life form as the silt loam soils in the study area seal quickly after tillage microbiotic soil crusts are more or less present during a large part of the year under maize sugar beet and wheat representing the main cropland area on average the early successional algae dominated crusts of stage 2 reduce soil detachment rates by 37 whereas the well developed moss mat of stage 3 causes an average reduction of 79 relative soil detachment rates of soil surfaces with microbiotic crusts compared with bare sealed soil surfaces are shown to decrease exponentially with increasing microbiotic cover b 0 024 for moss dominated and b 0 006 for algae dominated crusts in addition to ground surface cover by vegetation and crop residues microbiotic crust occurrence can therefore not be neglected when modelling small scale spatial and temporal variations in soil loss by concentrated flow erosion on cropland soils in temperate environments copyright 2007 john wiley sons ltd

processes influencing extreme as enrichment in shallow sea hydrothermal fluids of milos island greece abstract arsenic as is naturally enriched in most terrestrial and marine hydrothermal systems its discharge from shallow sea hydrothermal vents into coastal marine environments can dramatically affect the surrounding ecosystems shallow sea hydrothermal venting of acidic ph 5 hot 40 116 c and highly sulfidic up to 3 1 mm h2s fluids occurs at palaeochori and spathi bays off the southeast coast of milos island greece two distinct types of fluids both extremely as enriched were collected from the submarine vents often within a few meters of each other 1 a high cl fluid enriched in cl by up to 47 relative to seawater depleted in mg and so4 and enriched in major na ca k b sr and br and minor trace elements si li rb ce as fe mn and ba and 2 a low cl fluid depleted in cl by up to 66 relative to seawater also depleted in na mg so4 and br the maximum concentration of as reached 39 m in the high cl fluids and up to 78 m in the low cl fluids this is approximately 3000 times the concentration of as in seawater and far exceeds the concentrations typically found in mid ocean ridge mor and back arc basin bab fluids which are typically we used a combination of elemental analyses and stable and radiogenic isotope data oxygen deuterium and strontium to understand the primary controls on as enrichment those parameters all indicated that the fluids were a mixture of seawater and a hydrothermal fluid originally derived from seawater but altered by water rock interaction subcritical phase separation boiling and vapor brine segregation since as was extremely enriched in both the high cl and the low cl thermal fluids we conclude that this element readily partitions into the vapor phase in the milos hydrothermal system the original source of as is most likely the leaching of the greenschist facies metamorphic basement rocks transpierced by an abundance of secondary quartz and calcite veins rich in pyrite it is possible that these veins were deposited from as rich magmatic fluids similar to some epithermal au deposits a poorly crystalline orpiment precipitates as hydrothermal fluids mix with overlying seawater and removes much of the dissolved as prior to discharge

a wind tunnel study of the resilience of three fungal crusts to particle abrasion during aeolian sediment transport abstract this study is a comparison of the strength stability and resistance to abrasion of monospecific sand crusts formed by three species of free living fungi aureobasidium pullulans trichoderma harzianum and absidia corymbifera compared to three photoautotrophs examined in a previous study the fungal crusts were thicker and stronger in flexure by a factor of two or more in addition to the morphological properties of these fungi the organic substrate required for growth contributes to the total crust strength wind tunnel tests in which the crusts were subjected to particle impact from an upwind sediment source nominally 0 014 kg m 1 s 1 and varied levels of freestream velocity u showed that crusts comprised of trichoderma and absidia were stable at wind velocities under 10 m s 1 crusts of aureobasidium generally ruptured at velocities well below this level and to a much greater extent the distinctive morphologies and metabolic rates of the three fungi appear to explain these differences as compared to the wind tunnel experiments independent tests of crust strength in flexure which were intended to simulate crust flaking were found to be less sensitive indicators of relative crust stability in aeolian settings analysis of the time rate of expansion of the perimeter of crust loss indicates that this relation is approximately exponential with the exception of low wind velocities near the threshold for grain ejection where the momentum of the saltators at impact appears to be of prime importance

assessment of physical and hydrological properties of biological soil crusts using x ray microtomography and modeling biological soil crusts bscs are formed by aggregates of soil particles and communities of microbial organisms and are common in all drylands the role of bscs on infiltration remains uncertain due to the lack of data on their role in affecting soil physical properties such as porosity and structure quantitative assessment of these properties is primarily hindered by the fragile nature of the crusts here we show how the use of a combination of non destructive imaging x ray microtomography xmt and lattice boltzmann method lbm enables quantification of key soil physical parameters and the modeling of water flow through bscs samples from kalahari sands botswana we quantify porosity and flow changes as a result of mechanical disturbance of such a fragile cyanobacteria dominated crust results show significant variations in porosity between different types of crusts and how they affect the flow and that disturbance of a cyanobacteria dominated crust results in the breakdown of larger pore spaces and reduces flow rates through the surface layer we conclude that the xmt lbm approach is well suited for study of fragile surface crust samples where physical and hydraulic properties cannot be easily quantified using conventional methods

factors controlling as and u in shallow ground water southern carson desert nevada abstract unusually high as and u concentrations 100 g l are widespread in shallow ground water beneath the southern carson desert the high concentrations which locally exceed 1000 g l are of concern from a human health standpoint because the shallow ground water is used for domestic supply possible affects on wildlife are also of concern because the ground water flows into shallow lakes and marshes within wildlife refuges arsenic and u concentrations in ground water of the southern carson desert appear to be affected by evaporative concentration redox reactions and adsorption the relation of these elements with cl suggest that most of the high concentrations can be attributed to evaporative concentration of carson river water the primary source of recharge some ground water contains higher as and u concentrations that cannot be explained by evaporative concentration alone oxidation reduction reactions involving metal oxides and sedimentary organic matter appear to contribute as u inorganic c fe and mn to the ground water arsenic in fe oxide was confirmed by chemical extraction and is consistent with laboratory adsorption studies uranium in both sedimentary organic c and fe oxide coatings has been confirmed by fission tracks and petrographic examination arsenic concentrations in the ground water and chemical extracts of aquifer sediments are broadly consistent with adsorption as a control on some dissolved as concentrations an apparent loss of as from some ground water as evaporative concentration proceeds is consistent with adsorption as a control on as however evidence for adsorption should be viewed with caution because the adsorption model used values for the adsorbent that have not been shown to be valid for the aquifer sediments throughout the southern carson desert hydrologic and geochemical conditions in the carson desert are similar to other areas with high as and u concentrations in ground water including the salton sea basin and southern san joaquin valley of california hydrologic and geochemical conditions that produced some sandstone type u ore deposits including those in the non marine closed basin sediments of the morrison formation near grants new mexico suggest that the carson desert may be a modern analog for those systems

biological soil crust development and its topsoil properties in the process of dune stabilization inner mongolia china this study was undertaken at horqin sand land inner mongolia northern china field samples of biological soil crusts bscs and underlying topsoil 0 5 cm under bsc were taken in areas of different dune stabilization stages and their physicochemical properties were analyzed including particle size distribution bulk density organic matter nitrogen phosphorus electrical conductivity ec ph and caco3 content the results revealed that semi mobile dunes semi fixed dunes and fixed dunes had developed a physical crust algae crust and moss crust respectively the thickness hardness water content fine fraction and nutrient contents of bscs were gradually increasing along the dune stabilization gradient meanwhile bsc establishment and development enhanced the bulk density silt and clay content and nutrients of the topsoil under it in an increasing tend from semi mobile dune to fixed dune organic matter concentrations and other nutrients in the 0 5 cm topsoil layer under bscs were significantly higher compared to unconsolidated soil control moreover there were strong significant positive correlations between topsoil and bscs organic matter total nitrogen available nitrogen available phosphorus caco3 and 0 05 mm particle content suggesting that bscs have an influence on some of the properties of the underlying topsoil

lithospheric expression of geological units in central and eastern north america from full waveform tomography abstract the earthscope ta deployment has provided dense array coverage throughout the continental us and with it the opportunity for high resolution 3d seismic velocity imaging of both lithosphere and asthenosphere in the continent building upon our previous long period waveform tomographic modeling in north america we present a higher resolution 3d isotropic and radially anisotropic shear wave velocity model of the north american lithospheric mantle constructed tomographically using the spectral element method for wavefield computations and waveform data down to 40 s period the new model exhibits pronounced spatial correlation between lateral variations in seismic velocity and anisotropy and major tectonic units as defined from surface geology in the center of the continent the north american craton exhibits uniformly thick lithosphere down to 200 250 km while major tectonic sutures of proterozoic age visible in the surface geology extend down to 100 150 km as relatively narrow zones of distinct radial anisotropy with vsv vsh notably the upper mantle low velocity zone is present everywhere under the craton between 200 and 300 km depth east of the continental rift margin the lithosphere is broken up into a series of large somewhat thinner 150 km high velocity blocks which extend laterally 200 300 km offshore into the atlantic ocean between the craton and these deep rooted blocks we find a prominent narrow band of low velocities that roughly follows the southern and eastern laurentia rift margin and extends into new england we suggest that the lithosphere along this band of low velocities may be thinned due to the combined effects of repeated rifting processes and northward extension of the hotspot related bermuda low velocity channel across the new england region we propose that the deep rooted high velocity blocks east of the laurentia margin represent the proterozoic gondwanian terranes of pan african affinity which were captured during the rodinia formation but left behind after the opening of the atlantic ocean our results suggest that recurring episodes of tectonic events that are well exposed at the surface also leave persistent scars in the continental lithosphere mantle marked by isotropic and radially anisotropic velocity anomalies that reach as deep as 100 150 km

paleoceanographic model of neogene phosphorite deposition u s atlantic continental margin the neogene stratigraphic section of the southeastern u s continental shelf coastal plain system is characterized by i a series of major regional phosphogenic episodes ii a strong spatial relationship between the structural or topographic framework and phosphate deposition and iii distinct cyclical and regional patterns of deposition of the terrigenous carbonate and phosphate lithofacies the complex depositional patterns are explained by a paleoceanographic model based upon the interaction of glacial eustatic sea level fluctuations associated changes in climate and the dynamics of the gulf stream in response to the bathymetric configurations of the continental margin during the past 20 million years

molybdenum mo stable isotopic variations as indicators of mo attenuation in mine waste rock drainage abstract measurements of molybdenum mo stable isotopes 98mo were applied along with conventional geochemical analyses of water and rock samples at a mo mine in the usa to assess controls on mo mobility in two unsaturated waste rock storage facilities wrsfs that are differentiated by acidic and alkaline drainages unweathered waste rock mo ore and mine tailings from the site were also analyzed to constrain the isotopic composition of the source of mo entering mine drainage via weathering processes the surfaces of weathered waste rock samples were sequentially leached using a two step chemical extraction to determine the distribution and isotopic composition of mo among primary and secondary mineral assemblages the observed variation in 98mo among all samples exceeded 5 the 98mo of mo rich 340 g l mine process water and pit wall runoff ranged from 0 6 to 0 7 which was equal within error to the average 98mo of waste rock tailings and ore samples and indicated negligible isotopic fractionation during molybdenite oxidative dissolution in contrast drainage from the base of both waste rock storage facilities was isotopically heavier ranging from 1 6 to 1 9 coupled 98mo and mo so42 ratios in mine drainage and sequential chemical extractions of weathered waste rock surfaces indicated that mo adsorption onto mineral surfaces was most likely driving the increase in 98mo in drainage from both wrsfs molybdenum stable isotope data provided a powerful tracer of processes controlling mo mobility when used in conjunction with conventional geochemical analyses

the microstructure of microbiotic crust and its influence on wind erosion for a sandy soil surface in the gurbantunggut desert of northwestern china abstract microscopic examination of microbiotic soil crust shows that the profiles of soil with a dense cyanobacterial cover had two different layers a surface thin layer composed of aeolian born materials and an organic layer formed by filamentous cyanobacteria associated with sand particles the results indicate that microbiotic cover is an important determinant of sand fixation in the gurbantunggut desert northern part of xinjiang northwestern china microscopic examination of microbiotic crusts in this study revealed an intricate network of filamentous cyanobacteria and exopolysaccharides which binds and entraps sand grains and conglutinate fine particles with each other resistance to wind erosion paralleled the different disturbance levels on microbiotic soil crust sandy soil surface disturbances resulted in greatly decreased soil resistance to wind erosion maximum wind tunnel velocity in this test 25 m s 1 did not lead to any wind erosion on the surface of undisturbed microbiotic soil crust i e 100 covered by microbiotic soil crust as for different disturbance levels the highest threshold friction velocity was seen in the sand surface with 10 disturbance of microbiotic crust the surface microbiotic soil crusts have great effects on wind erosion rates wind erosion rates for sandy soil with 0 crust cover was about 46 21 17 times the soil with 90 crust cover at wind velocities of 18 22 25 m s 1 respectively this study confirms that the planners and managers of nature reserves in this area should understand the important ecological roles of microbiotic crust in desert ecosystems the reduction of trampling on the soil will eventually result in the re establishment of biological crusts and their associated organisms and ultimately lead to lower levels of wind erosion additionally strategies should be developed to manage livestock and oil exploration in order to avoid concentrated zones of impact

global and along strike variations of source duration and scaling for intermediate depth and deep focus earthquakes the systematic behavior of earthquake rupture as a function of earthquake magnitude and or tectonic setting is a key in our understanding of the physical mechanisms involved during earthquake rupture geophysical evidence suggests that although deep earthquakes including intermediate depth and deep are similar to shallow ones the mechanism involved during deep earthquakes is different from that of shallow ones in particular the magnitude and depth dependence of scaled duration a measure of earthquake rupture duration has led to controversy of what controls deep earthquake behavior here we estimate scaled source durations for 600 intermediate depth and deep focus earthquakes recorded at teleseismic distances and show deviation from self similar scaling no depth dependence is observed which we interpret as due to little differences between intermediate depth and deep focus earthquake mechanisms the data show no correlation between durations and plate age or thermal parameters suggesting that the thermal properties of the plate have little effect on source durations we nevertheless report differences in average source duration and scaling between subduction zones and along strike variations of source durations that more closely resemble the geometry of subduction flat or steep subduction rather than plate age

a comment on the distribution and mobility of geogenic molybdenum and arsenic in a limestone aquifer matrix by thomas pichler and ali mozaffari

the source and transport of arsenic in a bedrock aquifer new hampshire usa the geographic distribution of elevated groundwater as concentrations in a fractured silicate bedrock aquifer in central new hampshire correlates with the presence of pegmatites which border late devonian granites and intrude metasedimentary rocks as concentrations in the pegmatites averaged 9 6 mg kg which is much higher than the associated granites 0 24 mg kg and metasedimentary rocks 0 8 mg kg as was concentrated in these pegmatites by partial melting of calcareous metapelites and subsequent recrystallization as granites with low as concentrations and pegmatites with high as concentrations arsenic behaves similarly to b which was also concentrated into these late stage fluids arsenopyrite feass with an oxidation reaction rim of scorodite feaso4 2h2o was observed in aquifer materials elevated as concentrations have been observed to occur in other new england locations in pelitic metasediments intruded by anatectic plutons it is proposed that pegmatite formation from partial melting of pelitic metasediments may be an important mechanism for concentrating as in crystalline aquifer materials which can then cause local as enrichment of groundwaters groundwater as concentrations ranged from 26 nmol l to 5300 nmol l with a median value 210 nmol l that is more than 30 times higher than the median for groundwaters from all of new hampshire 6 5 nmol l high chloride concentrations 1 mmol l resulting from road salt contamination of recharge waters suggest that groundwaters are most likely young 670 nmol l or 50 g l have very low fe concentrations 7 samples with low as 7 fe oxyhydroxides form rapidly and have a neutral or negative net surface charge that does not readily adsorb as at ph 7 fe oxyhydroxide formation is slow and depends on dissolved o2 availability however the resultant fe oxyhydroxides have a positive net surface charge and appear to adsorb as readily

role of a cyanobacterial cover on structural stability of sandy soils in the sahelian part of western niger microbiotic soil crusts mostly formed by cyanobacteria are widespread on the surface of fallow land in western niger they lie adjacent to completely bare soils we have investigated the structural stability of these soils by testing aggregate breakdown under fast wetting slow wetting and mechanical breakdown the tests were effected on aggregates ranging from 3 to 5 mm in size these experiments were completed by micromorphological examinations under light and scanning electron microscope for all tests the fragment size distribution and the mean weight diameter mwd revealed the great stability of aggregates from soils with a cyanobacterial cover mwd 1 82 to 3 10 mm compared to those from soils devoid of cyanobacterial cover mwd 0 25 to 1 26 mm fast and slow wetting of microbiotic soil crust material induced a lesser disaggregation of aggregates compared to mechanical breakdown on the contrary fast wetting and mechanical breakdown of aggregates from soils devoid of cyanobacterial cover induced a greater disaggregation than slow wetting microscopic examination of microbiotic crusts revealed an intricate network of filamentous cyanobacteria and extracellular polymer secretions which binds and entraps mineral particles on the soil surface organo mineral aggregates ranging from 0 10 to 0 12 mm were observed below the superficial crusts filaments and residual organic matter bind tightly soil particles thus giving a compact structure the great stability of aggregates of soil with cyanobacterial cover is likely related to the binding and gluing effect of cyanobacteria and derived organic matter this is consistent with the positive correlation between mwd values and organic carbon content the present results thereby confirm the resistance to erosion of soil with microbial cover as indicated by field measurements

molybdenum geochemistry in a seasonally dysoxic mo limited lacustrine ecosystem lakes are important for storage of the essential micronutrient molybdenum mo during its transfer from the continents to the oceans but little is known about the major sources and sinks for mo in lacustrine ecosystems we studied mo cycling in castle lake a small subalpine lake in the klamath siskiyou mountains of northern california underlain primarily by mafic and ultramafic rocks where primary productivity is limited by mo bioavailability the deeper water of the lake becomes dysoxic 9 90 m dissolved oxygen during the summer this study was undertaken to identify the sources of mo to castle lake and establish a mo budget we measured mo concentrations in a suite of bulk solids lake sediments soils and bedrock and aqueous samples sediment porewaters soil runoff spring waters snow and ice from castle lake and its watershed lake sediments have elevated mo 7 36 ppm compared to soils and bedrock 0 2 2 ppm and mo al values were nearly two orders of magnitude higher than the crustal abundance sediment porewaters had higher mo 4 15 nm than lake water 2 4 nm soil runoff 0 1 6 2 nm snowmelt 0 1 nm lake ice 0 3 2 2 nm and local spring waters 0 03 2 72 nm bulk lake sediments had negative 98 95 mo values ranging from 0 5 to 1 0 0 1 we used the numerical model profile to estimate the net reaction rate of mo in the porewater model calculations ruled out diagenesis as a source of mo to lake sediments diagenetic mo always represented 5 of the total mo content in sediment we also ruled out dissolved mo inputs from groundwater and watershed inflow as important sources of mo two whole lake experimental mo additions in the 1960 s could have contributed a sizeable amount of mo to the lake sediments but only over a short period atmospheric deposition of anthropogenic mo from extensive copper smelting that occurred south of castle lake from 1896 to 1919 and from major californian urban centers today were negligible mo sources mo flux from the sediments 0 4 0 5 nmol cm 2 yr 1 was roughly equal to mo fluxes from surface inflow and outflow whereas mo burial fluxes were significantly higher 11 5 nmol cm 2 yr 1 because dissolved mo fluxes were minimal and atmospheric mo deposition was estimated to be a minor source of mo 1 nmol cm 2 yr 1 the largest source of mo is non detrital particulate matter 12 nmol cm 2 yr 1 likely a mixture of organic matter and fe mn oxyhydroxides as supported by mo isotopic data

spectral element moment tensor inversions for earthquakes in southern california we have developed and implemented an automated moment tensor inversion procedure to determine source parameters for southern california earthquakes the method is based upon spectral element simulations of regional seismic wave propagation in an integrated 3d southern california velocity model sensitivity to source parameters is determined by numerically calculating the frechet derivatives required for the moment tensor inversion we minimize a waveform misfit function and allow limited time shifts between data and corresponding synthetics to accommodate additional 3d heterogeneity not included in our model the technique is applied to three recent southern california earthquakes the 9 september 2001 m l 4 2 hollywood event the 22 february 2003 m l 5 4 big bear event and the 14 december 2001 m l 4 0 diamond bar event using about half of the available three component data at periods of 6 sec and longer we obtain focal mechanisms depths and moment magnitudes that are generally in good agreement with estimates based upon traditional body wave and surface wave inversions

a methodology for inversion of broadband seismic waveforms for elastic and anelastic structure and its application to the mantle transition zone beneath the northwestern pacific abstract we develop a quantitative and objective methodology for inversion of body wave waveform data for elastic and anelastic structure and apply it to the upper mantle and mantle transition zone mtz beneath the northwestern pacific using prem as the starting model we use the singular value decomposition svd as the basis for our inversion and use akaike s information criterion aic to evaluate the statistical significance of the models although the resulting models are preliminary we obtain an average positive s wave velocity anomaly in the mtz beneath the philippine sea plate and the japan sea we also find a negative s wave velocity anomaly in the depth range 300 400 km beneath the subduction zone to the east of northern japan and its southern extension beneath the izu bonin marianas arc our inversions obtained a lower q as compared to prem for all of the subregions

full waveform tomography of the upper mantle in the south atlantic region imaging a westward fluxing shallow asthenosphere abstract a prominent feature of the south atlantic region is its strongly asymmetric residual bathymetry across the ocean basin it has been suggested that the residual bathymetry is dynamic in nature arising from the large slow velocity seismic anomaly located in the lower mantle beneath the african plate unfortunately the pattern of mantle heterogeneity particularly in the upper mantle is not well known owing to the sparsity of seismic stations and the existence of large aseismic regions on the african and south american plates here we present a new seismic tomographic study of the south atlantic upper mantle our model is based on a full seismic waveform inversion of 4000 high quality seismograms for isotropic 3 d seismic structure using a powerful adjoint methodology capable of extracting maximum information from each seismogram the theory requires simulation of seismic wave propagation in 3 d heterogeneous earth models computed with a spectral element method where the differences between observed and synthetic seismograms are quantified using phase misfits obtained through a time frequency transform the model images a continuous channel of pronounced slow seismic velocity in the shallow sublithospheric mantle between 150 and 300 km depth that branches in between the cratonic roots under the african and south american continents at greater depth below 300 350 km the slow anomalies are less pronounced and a change in the convective planform is indicated by isolated round shaped patches in an overall faster mantle it is possible that the depthwise change of the convective planform from vertical to horizontal advection of hot buoyant material in a low viscosity asthenosphere can reconcile the anomalous residual bathymetry in the region and we present a simple fluid dynamic model of pressure driven flow to assess the feasibility of this scenario

authigenic molybdenum formation in marine sediments a link to pore water sulfide in the santa barbara basin pore water and sediment mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the santa barbara basin to examine the connection between authigenic mo formation and pore water sulfide concentration only at the deepest site 580 m where pore water sulfide concentrations rise to 0 1 mm right below the sediment water interface was there active authigenic mo formation at shallower sites 550 430 and 340 m where pore water sulfide concentrations were consistently 0 05 mm mo precipitation was not occurring at the time of sampling a sulfide concentration of 0 1 mm appears to be a threshold for the onset of mo fe s co precipitation a second threshold sulfide concentration of 100 mm is required for mo precipitation without fe possibly as mo s or as particle bound mo mass budgets for mo were constructed by combining pore water and sediment results for mo with analyses of sediment trap material from santa barbara basin as well as sediment accumulation rates derived from 210 pb the calculations show that most of the authigenic mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters there is however a non lithogenic particulate mo associated with sinking particles that contributes 15 to the total authigenic mo accumulation analysis of sediment trap samples and supernant brine solutions indicates the presence of non lithogenic particulate mo a large fraction of which is easily remobilized and perhaps associated with mn oxides our observations show that even with the very high flux of organic carbon reaching the sediment of santa barbara basin active formation of sedimentary authigenic mo requires a bottom water oxygen concentration below 3 mm however small but measurable rates of authigenic mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 mm indicating that the formation of authigenic mo occurred in the recent past but not at the time of sampling copyright 2000 elsevier science ltd

enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales there have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition among them molybdenum mo is frequently cited as an effective proxy for sediments and sedimentary rocks recently helz et al helz g r miller c v charnock j m mosselmans j l w pattrick r a d garner c d vaughan d j 1996 mechanisms of molybdenum removal from the sea and its concentration in black shales exafs evidences geochim cosmochim acta 60 3631 3642 and adelson et al adelson j m helz g r miller c v 2001 reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments geochim cosmochim acta 65 237 252 suggested that mo does not behave conservatively in the water column when h2s reaches a threshold concentration above this concentration a switch operates and mo is scavenged by forming bonds with metal rich notably iron particles sulfur rich organic molecules and pyrite in this paper mo trapping by sulfur rich organic matter om in ancient marine deposits is emphasized the following mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized om the akkuyu formation turkey the calcaires d orbagnoux france and kimmeridge clay uk and its timeequivalent in boulonnais france the kashpir oil shales russia and the la luna formation venezuela the sulfur rich om is identified by either measured organic s abundance or kerogen microscope observation our results show that mo is systematically more enriched relative to the other redox sensitive sulfide forming elements studied u v ni cu zn cr and mo enrichment is positively correlated with the amount of sulfurized om but not with pyrite abundance these results illuminate the role played by sulfurized om in geologic scale mo capture and retention but they also underline the role played by reactive iron significant om sulfurization is only possible when reactive iron is limited nevertheless pyrite formation though limited could act as an initial mo trap prior to mo uptake by om that is sulfurized after the pyritization step in future paleoenvironmental reconstructions attention must be paid to this enhanced mo enrichment in the presence of sulfurized organic matter in such cases the use of mo could lead to overestimation of the reducing conditions of the depositional environment

microbiotic crusts as biomarkers for surface stability and wetness duration in the negev desert microbiotic crusts play an important role in arid and semi arid regions yet very little information exists regarding the factors that impact their development in an attempt to assess the main factors that may determine their growth measurements of the amount of fines silt and clay rain moisture content wetness duration and wind erosion and deposition were carried out along a 12 station transect within a partially crusted dune field in the western negev desert and compared to the crust cover and chlorophyll content surface stability was the only variable that exhibited significant relationship with crust cover while daylight wetness duration exhibited strong positive relationship r2 0 92 0 99 with the crust s chlorophyll content the data point out that microbiotic crusts may serve as a useful biomarker for surface stability while wetness duration and wind will control crust cover and the crust chlorophyll content in semi stable habitats with absolute annual change in sand level of 2 3 mm stable habitats absolute change 1 mm will be controlled primarily by moisture while habitats with low surface stability absolute change of tens and hundreds of millimeters will be primarily controlled by wind furthermore owing to the strong positive relationship between daylight wetness duration and the crust s chlorophyll content the crust may serve as a useful biomarker for the quantification of surface wetness duration copyright 2009 john wiley sons ltd

quantifying the surface covering binding and bonding effects of biological soil crusts on soil detachment by overland flow biological soil crusts bscs have impacts on soil detachment process through surface covering and binding and bonding b b mechanisms which might vary with successional stages of bscs this study was conducted to quantify the effects of surface covering binding and bonding of bscs on soil detachment capacity by overland flow in a 4 m long hydraulic flume with fixed bed two dominant bsc types developed well in the loess plateau the early successional cyanobacteria and the later successional moss were tested using natural undisturbed soil samples collected from the abandoned farmlands two treatments of undisturbed crusts and one treatment of removing the above ground tissue of bscs were designed for each bsc type for comparison bare loess soil was used as the baseline the collected soil samples were subjected to flow scouring under six different shear stresses ranging from 6 7 to 21 2 pa the results showed that soil detachment capacity dc and rill erodibility kr decrease with bsc succession and the presence of bscs obviously increased the critical shear stress especially for the later successional moss crust for the early successional cyanobacteria crust dc was reduced by 69 2 compared to the bare loess soil where 37 7 and 31 5 are attributed to the surface covering and b b respectively for the later successional moss crust dc decreased by 89 8 compared to the bare loess soil where 68 9 and 20 9 contributed to the surface covering and b b respectively these results are helpful in understanding the influencing mechanism of bscs on soil erosion and in developing the process based erosion models for grassland and forestland copyright 2017 john wiley sons ltd

the global attenuation structure of the upper mantle 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive a new global three dimensional model of shear wave attenuation in the upper mantle the amplitude observations span a range of periods between 50 and 250 s and are derived from earthquakes with mw 6 0 that occurred between 1993 and 2005 four separate factors may influence an amplitude anomaly intrinsic attenuation along the raypath elastic focusing effects along the raypath uncertainties in the strength of excitation and uncertainties in the response at the station in an earlier paper dalton and ekstrom 2006a dependence of the retrieved attenuation structure on these terms was shown to be significant and an approach was developed to invert the amplitudes simultaneously for each term the new three dimensional attenuation model qrfsi12 which is the subject of this paper is derived using this method the model contains large lateral variations in upper mantle attenuation 60 to 100 and exhibits strong agreement with surface tectonic features at depths shallower than 200 km at greater depth qrfsi12 is dominated by high attenuation in the southeastern pacific and eastern africa and low attenuation along many subduction zones in the western pacific resolution tests confirm that the change in pattern of attenuation above and below 200 km depth can be determined with confidence using the fundamental mode data set the new model is highly correlated with global models of shear wave velocity particularly in the uppermost mantle suggesting that the same factors may control both seismic attenuation and velocity in this depth range however forcing the lateral perturbations in attenuation to match those found in global velocity models decreases the data variance reduction which suggests that subtle differences between patterns of attenuation and velocity are robust

occurrence of molybdenum in british surface water and groundwater distributions controls and implications for water supply data for mo in british surface water and groundwater collated from a number of databases show that concentrations are in most cases low of the order of 2 g l or less however variability is large and sporadic high values are found in both streamwaters and groundwaters data for some 11 600 british streamwater samples indicate a 10 90th percentile range of 0 08 2 44 g l with a median of 0 57 g l and maximum observation of 230 g l high values tend to be from streams on clay rich formations and sulphide mineralised bedrock and streams affected by localised urban and industrial contamination monitored lowland river waters also typically have median concentrations 1 g l although higher values are present in a number of urban industrialised english rivers highest observed concentrations median 20 g l occur under low flow conditions in a river system from an urban industrial area of ne england and are likely the products of industrial contamination and mine drainage concentrations in 96 upland lakewater samples from nw england are universally 0 1 g l or less data for 1735 groundwater samples from across britain have a 10 90th percentile range for mo of 0 035 1 80 g l with a median of 0 20 g l and maximum observation of 89 g l relatively high values derive from some lower cretaceous greensand carboniferous limestone and mudstone coal measures aquifers particularly under anaerobic conditions release from fe oxides and possibly mn oxides by reductive dissolution is a likely mechanism for the concentrations under more rarely observed sulphate reducing conditions in british aquifers concentrations of mo diminish likely due to sequestration by precipitating sulphide minerals the observed ranges in aqueous samples indicate that most water sources in britain have mo concentrations more than an order of magnitude below the who health based value for mo in drinking water 70 g l such sources are unlikely to pose a risk to drinking water from the current who guidance provided those impacted locally by mining or other industrial contamination are avoided

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member

influence of cryptogamic crust disturbance to wind erosion on sand and loam rangeland soils a portable field wind tunnel was used to assess the sediment flux rates of loam and sand textured soils in the mallee region of southeastern australia three levels of crust disturbance nil moderate and severe simulating stock trampling were investigated the results demonstrated the importance of cryptogamic crusts in binding the soil surface and providing roughness after the soil was moderately disturbed on the loamy soil the crust helped maintain sediment flux rates below the erosion control target to 5 g m 1 s 1 for a 65 km h 1 wind measured at 10 m height once the crust was severely disturbed sediment fluxes increased to 1 6 times the erosion target on the sandy soil even with no crust disturbance the sediment flux was 1 6 times the erosion control target disturbing the crust increased sediment fluxes to a maximum of 6 7 times the erosion control target removal of the crust also decreased the threshold wind velocity that resulted in an increase to the ris k of erosion from 5 per cent to 20 per cent 1998 john wiley sons ltd