spectral mineralogical and geochemical variations across home plate gusev crater mars indicate high and low temperature alteration over the last 3 years in gusev crater mars the spirit rover observed coherent variations in color mineralogy and geochemistry across home plate an 80 m diameter outcrop of basaltic tephra observations of home plate from orbit and from the summit of husband hill reveal clear differences in visible near infrared vnir colors between its eastern and western regions that are consistent with mineralogical compositions indicated by mossbauer spectrometer mb and by miniature thermal emission spectrometer mini tes pyroxene and magnetite dominate the east side while olivine nanophase fe oxide npox and glass are more abundant on the western side alpha particle x ray spectrometer apxs observations reveal that eastern home plate has higher si mg al zn ni and k while cl and br are higher in the west we propose that these variations are the result of two distinct alteration regimes that may or may not be temporally related a localized higher temperature recrystallization and alteration of the east side of home plate and lower temperature alteration of the western side that produced npox

fluid and sediment dynamics of upper stage plane beds to understand more fully the fluid and sediment dynamics of upper stage plane beds laboratory experiments were conducted using mobile and fixed beds where turbulent motions of fluid and sediment were measured using laser anemometry bed elevation fluctuations on mobile upper stage plane beds reveal millimeter high bed waves vertical profiles of flow velocity mixing length and eddy viscosity diffusivity are represented well by the law of the wall for the mobile bed von karman s 0 33 and equivalent sand roughness to mean bed grain size varies from 9 to 17 because of the presence of bed load and low relief bed waves for fixed beds with no sediment transport 0 41 and equivalent sand roughness is equal to the mean bedgrain size the decrease in for mobile beds is related to the relative motion of grains and fluid mobile bed turbulence intensities are greater than those for sediment free fixed beds because of enhanced wake formation from the lee side of near bed grains and low relief bed waves sediment diffusivities es calculated in a similar way to fluid diffusivities e indicate that es e sediment diffusivities calculated using the equilibrium balance between upward diffusion and downward settling of sediment are similar to e in near bed regions y d 0 3 suggesting that larger more energetic turbulent eddies are responsible for sediment suspension higher in the flow

variable and conflicting shear stress estimates inside a boundary layer with sediment transport this paper presents a comparison between two methods for estimating shear stress in an atmospheric internal boundary layer over a beach surface under optimum conditions using wind velocities measured synchronously at 13 heights over a 1 7 m vertical array using ultrasonic anemometry the reynolds decomposition technique determines at a point shear stresses at each measurement height while the law of the wall yields a single boundary layer estimate based on fitting a logarithmic velocity profile through the array data analysis reveals significant inconsistencies between estimates derived from the two methods on both a whole event basis and as time series despite a near perfect fit of the law of the wall the point estimates of reynolds shear stress vary greatly between heights calling into question the assumed presence of a constant stress layer a comparison with simultaneously measured sediment transport finds no relationship between transport activity and the discrepancies in shear stress estimates results do show however that reynolds shear stress measured nearer the bed exhibits slightly better correlation with sand transport rate the findings serve as a major cautionary message to the interpretation and application of single height measurements of reynolds shear stress and their equivalence to law of the wall derived estimates and these concerns apply widely to boundary layer flows in general 2015 the authors earth surface processes and landforms published by john wiley sons ltd

contemporary research in aeolian geomorphology abstract the first international conference on aeolian geomorphology icar was held in 1986 and every four years since then aeolian geomorphologists from around the world have assembled to discuss their research and to showcase recent advancements in understanding and modeling of aeolian processes a content analysis of the bibliography of aeolian research stout j e warren a gill t e 2009 publication trends in aeolian research an analysis of the bibliography of aeolian research geomorphology 105 6 17 this volume shows that the number of publications on aeolian topics has increased exponentially from the mid 20th century with approximately 50 publications per year to about 500 publications per year when the first icar was held to almost 1000 publications per year currently areas of focus have shifted historically from initial concerns with aeolian erosion and dust events as isolated phenomenon of localized curiosity or only regional importance to comprehensive physically based investigations and modeling of the mechanics of aeolian transport recently more applied studies have been motivated by the recognition of the importance of aeolian processes to dust emissions into the atmosphere with relevance for human health and for meteorological conditions and climate change and within regional management contexts especially on coasts where impending sea level rise is of great concern and in arid and semi arid environments given the dependence of sediment surface stability and remobilization on meteorological and ecological conditions aeolian geomorphology is a rapidly growing sub discipline of geomorphology that offers rich opportunities for interdisciplinary collaborations with colleagues from the atmospheric sciences climatology sedimentology quaternary geology fluid mechanics physics mathematics computer science physical geography ecology and agricultural sciences as well as our counterparts in fluvial coastal and arid lands geomorphology who are similarly concerned with fluid sediment interactions and the consequent genesis of landforms

a petrogenetic model for the origin and compositional variation of the martian basaltic meteorites the major element trace element and isotopic compositional ranges of the martian basaltic meteorite source regions have been modeled assuming that planetary differentiation resulted from crystallization of a magma ocean the models are based on low to high pressure phase relationships estimated from experimental runs and estimates of the composition of silicate mars from the literature these models attempt to constrain the mechanisms by which the martian meteorites obtained their superchondritic cao al2o3 ratios and their source regions obtained their parent daughter 87 rb 86 sr 147 sm 144 nd and 176 lu 177 hf ratios calculated from the initial sr nd and hf isotopic compositions of the meteorites high pressure experiments suggest that majoritic garnet is the liquidus phase for mars relevant compositions at or above 12 gpa early crystallization of this phase from a martian magma ocean yields a liquid characterized by an elevated cao al2o3 ratio and a high mg olivine pyroxene garnet dominated cumulates that crystallize subsequently will also be characterized by superchondritic cao al2o3 ratios melting of these cumulates yields liquids with major element compositions that are similar to calculated parental melts of the martian meteorites furthermore crystallization models demonstrate that some of these cumulates have parent daughter ratios that are similar to those calculated for the most incompatible element depleted source region i e that of the meteorite queen alexandra que 94201 the incompatible element abundances of the most depleted que 94201 like source region have also been calculated and provide an estimate of the composition of depleted martian mantle the incompatible element pattern of depleted martian mantle calculated here is very similar to the pattern estimated for depleted earth s mantle melting the depleted martian mantle composition reproduces the abundances of many incompatible elements in the parental melt of que 94201 e g ba th k p hf zr and heavy rare earth elements fairly well but does not reproduce the abundances of rb u ta and light rare earth elements the source regions for meteorites such as shergotty are successfully modeled as mixtures of depleted martian mantle and a late stage liquid trapped in the magma ocean cumulate pile melting of this hybrid source yields liquids with major element abundances and incompatible element patterns that are very similar to the shergotty bulk rock

refined data of alpha proton x ray spectrometer analyses of soils and rocks at the mars pathfinder site implications for surface chemistry 1 an extensive recalibration of the alpha proton x ray spectrometer apxs was performed to improve the data evaluation of the mars pathfinder mpf rock and soil in situ measurements many samples and geostandards were measured with an mpf identical spare apxs under simulated martian atmospheric pressure and low night temperature conditions precise calibration curves for major and minor elements were obtained using an improved spectral evaluation method for the original mpf spectra refined and new elemental compositions of the mpf rocks and soils were derived however all initial conclusions about soils and rocks remained valid the mpf soil composition revealed the mafic nature of the surface as inferred from the results of viking 1 and 2 data however the mpf rocks reflect a felsic composition for all samples linear correlations of sulphur with all other elements were noticed reflecting the fact that the rocks were covered with varying degrees of soil which compared to the rocks is rich in sulphur extrapolating to low sulphur abundance 0 3 the composition of a soil free rock was calculated the mpf rock composition is high in si and k and low in mg and fe compared to the soil using elemental data from mpf and martian meteorites a global estimation of the martian crust composition was derived the crust is of basaltic nature with a high abundance of incompatible elements k rb nd u th and volatile elements s cl while carbonates are lower or absent

comparing dune migration measured from remote sensing with sand flux prediction based on weather data and model a test case in qatar this study explores validating and calibrating the wind regime predicted by global circulation models gcm on earth and other planets using optical remote sensing of dune dynamics we use spot 5 images to track the migration of 64 barchan dunes in qatar using the cosi corr technique we estimate the volume of the dunes using a scaling law calibrated from one particular dune which was surveyed in the field using volume and migration rate we determine the sand flux from a single dune q dunes and scale this estimate to the whole dune field we compare the measured sand flux with those derived from wind velocity measurements at a local meteorological station as well as with those predicted from era interim a global circulation model the comparison revealed that the wind velocity predicted by era interim is inappropriate to calculate the sand flux this is due to the 6 h sampling rate and to systematic bias revealed by a comparison with the local wind data we describe a simple procedure to correct for these effects with the proposed correction similar sand flux are predicted using the local and era interim data independently of the value of the value of the shear velocity threshold u t the predicted sand flux is about 65 of q dunes the agreement is best assuming the value u t 0 244 m s which is only slightly larger than the value of u t 0 2612 m s estimated based in the sand granulometry measured from field samples the influence of the dune topography on the wind velocity field could explain the underestimation in any case the study demonstrates the possibility of validating gcm model and calibrating aeolian sand transport laws using remote sensing measurements of dune dynamics and highlights the caveats associated to such an approach

aerodynamic parameters over an eroding bare surface reconciliation of the law of the wall and eddy covariance determinations assessing accurately the surface friction velocity is a key issue for predicting and quantifying aeolian soil erosion this is usually done either indirectly from the law of the wall low of the mean wind velocity profile or directly from eddy covariance ec of the streamwise and vertical wind velocity fluctuations however several recent experiments have reported inconsistency between friction velocities deduced from both methods here we reinvestigate the determination of aerodynamic parameters friction velocity and surface roughness length over an eroding bare surface and look at the possible reasons for observing differences on these parameters following the method for that purpose a novel field experiment was performed in south tunisia under the research program wind o v wind erosion in presence of sparse vegetation we find no significant difference between friction velocities obtained from both law of the wall and ec approaches when the friction velocity deduced from the ec method was extrapolated to the surface surface roughness lengths show a clear increase with wind erosion with more scattered values when deduced from the ec friction velocity our measurements further suggest an average value of the von karman constant of 0 407 0 002 although individual wind events lead to different average values due probably to the definition of the ground level or to the stability correction importantly the von karman constant was found independent of the wind intensity and thus of the wind soil erosion intensity finally our results lead to several recommendations for estimating the aerodynamic parameters over bare surface in order to evaluate saltation and dust fluxes

sonic anemometers in aeolian sediment transport research abstract fast response wind and turbulence instruments including sonic anemometers are used more and more in aeolian sediment transport research these instruments give information on mean wind but also on fluctuations and turbulent statistics such as the uw covariance which is a direct measure of reynolds stress rs and friction velocity this paper discusses the interpretation of sonic anemometer data the transformations needed to get proper results and turbulence spectra and how they are influenced by instrument size sampling frequency and measurement height turbulence spectra characterize how much the different frequencies in the turbulent signals contribute to the variance of wind speed or to the covariance of horizontal and vertical wind speed they are important in determining the measurement strategy when working with fast response instruments such as sonic anemometers and are useful for interpreting the measurement results choices on the type of sonic anemometer observation height sampling period sampling frequency and filtering can be made on the basis of expected high and low frequency losses in turbulent signals which are affected by those variables as well as wind speed and atmospheric stability friction velocity and rs important variables in aeolian sediment transport research are very sensitive to tilt or slope errors during a field experiment the slope sensitivity of the rs was established as 9 per degree of slope which is 1 5 times the value reported in literature on the basis of theoretical considerations an important reason for the difference probably is the large influence of streamline curvature on turbulence statistics and thereby on the slope sensitivity of the rs an error of 9 per degree of slope in the rs will translate into an error of approximately 4 per degree of slope in the calculated friction velocity space time correlation of the horizontal wind speed is much larger than that of the vertical wind speed and the instantaneous rs this largely explains why in previous studies a poor correlation was found between instantaneous rs measured at 3 m height and saltation flux near the surface whereas the correlation between wind speed at some height and saltation flux was much better therefore the poor correlation between rs away from the surface and saltation flux does not contradict that saltation flux is caused by rs

weathering rinds and rock coatings from an arctic alpine environment northern scandinavia coarse rock debris exposed in the subaerial environment of northern sweden displays the development of a wide variety of surface coatings these include weathering rinds as well as a great diversity of geochemical coatings including those dominated by ca fe si and al each of these types of rock coatings displays a high degree of geochemical complexity the weathering rinds exhibit both geochemical and morphologic changes to the parent rock cores including extensive dissolution oxidation and hydration as well as disaggregation fracturing and cementation by secondary geochemical coatings chemical breakdown of the rock to form weathering rinds includes loss of k si mg and ca and buildup of fe weathering rinds are fundamentally the result of dissolution as no clay minerals were identified in the rinds rock coatings are distinguished from rinds by their clear accretionary nature despite the distinction made between weathering rinds and rock coatings it is important to note that often the two are intimately related the presence of rock coatings as well as weathering rinds on rock surfaces amplifies the important role played by geochemical processes in the arctic alpine climate of northern sweden in particular as well as its significance in landscape evolution in such environments in general

alpha particle x ray spectrometer apxs results from gusev crater and calibration report 1 the chemical composition of rocks and soils on mars analyzed during the mars exploration rover spirit mission was determined by x ray analyses with the alpha particle x ray spectrometer apxs details of the data analysis method and the instrument calibration are presented measurements performed on mars to address geometry effects and background contributions are shown cross calibration measurements among several instrument sensors and sources are discussed an unintentional swap of the two flight instruments is evaluated new concentration data acquired during the first 470 sols of rover spirit in gusev crater are presented there are two geological regions the gusev plains and the columbia hills the plains contain soils that are very similar to previous landing sites on mars a meteoritic component in the soil is identified rocks in the plains revealed thin weathering rinds the underlying abraded rock was classified as primitive basalt one of these rocks contained significant br that is probably associated with vein filling material of different composition one of the trenches showed large subsurface enrichments of mg s and br disturbed soils and rocks in the columbia hills revealed different elemental compositions these rocks are significantly weathered and enriched in mobile elements such as p s cl or br even abraded rock surfaces have high br concentrations thus in contrast to the rocks and soils in the gusev plains the columbia hills material shows more significant evidence of ancient aqueous alteration

understanding wind blown sand six vexations abstract the study of aeolian geomorphological systems over the last half century has advanced along several important fronts supported by developments in technologies and analytic methods and the evolution of modeling approaches remote sensing has led to a wealth of knowledge concerning the distribution and dynamics of dunes on earth and elsewhere and wind tunnels have elucidated the roles of aeolian processes in reshaping surfaces improvements in laboratory and field instrumentation allow measurement of aeolian sand transport systems at levels of detail unimaginable when the binghamton geomorphology symposium began we have seen for example the advent of large sophisticated field campaigns and advanced modeling approaches using cellular automata and computational fluid dynamics methods select avenues of development especially concerned with depositional environments are briefly summarized advances in many fields have not been matched with proportional advances in our ability to predict rates of sand transport in natural environments one of the most fundamental challenges at least eight commonly cited sand transport rate models do not agree with each other and do not replicate field observations even under near ideal conditions this review focuses on select reasons why that might be so and categorizes those reasons into six principal theoretical and empirical vexations that have made sand transport an intractable problem predicting rates of transport characterizing grain size characterizing fluid and sand densities estimating shear velocity predicting the threshold of motion including the effects of sand moisture content and understanding granular electrification the examination of potential sources of error in the rate of transport and threshold of motion models leads to a point by point consideration of our current assumptions and protocols or lack thereof the objective is to help us identify the hard targets and the soft targets for future research

a fully predictive model for aeolian sand transport abstract this paper presents the development calibration and verification of a fully predictive model for wind blown dry sand the model is based on the modification of the well known bagnold equation by including the threshold shear velocity which is also slightly modified to ensure a smoother transition from the non transport regime to the transport regime the sand transport rate is related to the static and dynamic grain roughness by using a semi empirical roughness predictor which is calibrated based on sand transport data from wind tunnel experiments with a flat mobile sand surface the model input for dry sand is the wind velocity at one height above the surface and the sand characteristics d50 d90 the effects of moisture vegetation and shells on the sand transport process are included by fairly simple expressions which are acting on the shear velocity the threshold value and the transport rate in all 105 high quality data sets have been used for verification of the proposed predictive model about 72 of the predicted values are within a factor of 2 of measured values of the transport rate

bounce rock a shergottite like basalt encountered at meridiani planum mars additional co authors thanasis economou steven p gorevan brian c hahn gostar klingelhofer timothy j mccoy harry y mcsween jr douglas w ming richard v morris daniel s rodionov steven w squyres heinrich wanke shawn p wright michael b wyatt albert s yen

constraints on the structure of the martian interior determined from the chemical and isotopic systematics of snc meteorites the crystallization ages of martian snc meteorites give evidence that martian volcanism has continued until recent times perhaps until the present these meteorites also indicate that the mantle source regions of this volcanism are modestly to extremely depleted by terrestrial standards these 2 observations produce a conundrum how is it that such depleted source regions have produced basaltic magma for such a long time this contribution attempts to quantify the radiogenic heat production in 2 distinct martian mantle source regions those of the shergottites and nakhlites compared to the depleted upper mantle of the earth morb the nakhlite source region is depleted by about a factor of 2 and the shergottite source region is depleted by a factor of 6 according to current geophysical models the nakhlite source contains the minimum amount of radioactive heat production to sustain whole mantle convection and basalt generation over geologic time a corollary of this conclusion is that the shergottite source contains much too little radioactivity to produce recent 200 ma basalts a model martian interior with a deep nakhlite mantle that is insulated by a shallow shergottite mantle may allow basalt production from both source regions if the divide between the nakhlite shergottite mantles acts as a thermal boundary layer similarities between lunar and martian isotopic reservoirs indicate that the moon and mars may have experienced similar styles of differentiation

timescale dependence of aeolian sand flux observations under atmospheric turbulence 1 the transport of sand in saltation is driven by the persistently unsteady stresses exerted by turbulent winds based on coupled high frequency observations of wind velocity and sand flux on a desert dune during intermittent saltation we show here how observations of saltation by natural winds depend significantly on the timescale and method used for determining shear stress and sand flux the correlation between sand flux and excess shear stress stress above a threshold value systematically improves for longer averaging timescale t and is better for stress determined by the law of the wall versus the reynolds stress method fitting parameters for the stress flux relationship do not converge with increasing t which may be explained by the nonstationary nature of wind velocity statistics we show how it may be possible based on the scale dependent statistics of stress fluctuations to rescale saltation flux predictions for wind observations made at different timescales however our observations indicate hysteresis and time lags in thresholds for initiation and cessation of saltation which complicate threshold based approaches to predicting sediment transport at different timescales

aeolian sand transport a wind tunnel model wind sand transport is an important geological process on earth and some other planets formulating the wind sand transport model has been of continuing significance majority of the existing models relate sand transport rate to the wind shear velocity based on dynamic analysis however the wind shear velocity readapted to blown sand is difficult to determine from the measured wind profiles when sand movement occurs especially at high wind velocity moreover the effect of grain size on sand transport is open to argument detailed wind tunnel tests were carried out with respect to the threshold velocity threshold shear velocity and transport rate of differently sized loose dry sand at different wind velocities to reformulate the transport model the results suggest that the relationship between threshold shear velocity and grain size basically follow the bagnold type equation for the grain size d 0 1 mm however the threshold coefficient a in the equation is not constant as suggested by bagnold but decreases with the particle reynolds number the threshold velocity at the centerline height of the wind tunnel proved to be directly proportional to the square root of grain diameter attempts have been made to relate sand transport rate to both the wind velocity and shear velocity readapted to the blown sand movement the reformulated transport model for loose dry sand follows the modified o brien rindlaub type equation q f1 d 1 ru 2 g v3 or the modified bagnold type equation q f2 d 1 rt 0 25 g u 3 where q is the sand transport rate the sand flux per unit time and per unit width in kg m 1 s 1 is the air density 1 25 kg m 3 g is the acceleration due to gravity 9 81 m s 2 ru vt v rt u t u v is the wind velocity at the centerline of the wind tunnel in m s 1 vt is the threshold velocity measured at the same height as v in m s 1 u is the shear velocity with saltating flux in m s 1 u t is threshold shear velocity in m s 1 f1 d 1 475 24 93 62d d f2 d 1 41 4 98exp 0 5 ln d 1 55d 0 57 2 d is the grain diameter in mm and d is the reference grain diameter equals 0 25 mm the bagnold s equation that asserts for a given wind drag the rate of movement of a fine sand is less than that of a coarse sand is not supported by the reformulated models

the origin and evolution of the peace vallis fan system that drains to the curiosity landing area gale crater mars the landing site for the curiosity rover is located at the distal end of the peace vallis fan in gale crater peace vallis fan covers 80 km2 and is fed by a 730 km2 catchment which drains an upland plains area through a 15 km wide gap in the crater rim valley incision into accumulated debris delivered sediment through a relatively low density valley network to a main stem channel to the fan an estimated total fan volume of 0 9 km3 matches the calculated volume of removal due to valley incision 0 8 km3 and indicates a mean thickness of 9 m the fan profile is weakly concave up with a mean slope of 1 5 for the lower portion numerous inverted channels outcrop on the western surface of the fan but on the eastern portion such channels are rare suggesting a change in process from distributary channel domination on the west to sheet flow on the eastern portion of the fan runoff discharge watershed area to produce the fan is estimated to be more than 600 m perhaps as much as 6000 m indicating a hydrologic cycle that likely lasted at least thousands of years atmospheric precipitation possibly snow not seepage produced the runoff based on topographic data peace vallis fan likely onlapped bradbury rise and spilled into a topographic low to the east of the rise this argues that the light toned fractured terrain within this topographic low corresponds to the distal deposits of peace vallis fan and in such a setting lacustrine deposits are expected

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

variability of the apparent von karman parameter during aeolian saltation 1 the variability of the apparent von karman parameter a during aeolian saltation was evaluated in a field experiment at jericoacoara brazil to test this variability velocity profiles reynolds stress and sand transport data were gathered and analyzed we used 15 data sets with sand laden airflow and 2 runs with clear airflow results indicated an inverse linear relationship between a and bulk gravimetric sand concentration r2 0 746 and sand transport rate r2 0 577 we found values of a as low as 0 26 this means that using the von karman constant 0 40 rather than the variable a to estimate shear velocity based on the slope of the velocity profile will lead to over estimation of shear velocity averaging about 20 in this study this in turn produces an over estimation of wind blown sand transport rates based on models that have terms with shear velocity cubed

aerodynamic roughness lengths over movable beds comparison of wind tunnel and field data 1 we evaluate the increase in apparent roughness length during aeolian saltation using a data set comprising 291 wind profiles measured in wind tunnels or in the field we tested the charnock 1955 modified charnock sherman 1992 and raupach 1991 relationships for the entire data set and for segregated wind tunnel and field data sets we assessed the abilities of the models to predict enhanced roughness and investigated scaling differences between wind tunnels and field environments for the entire data set the charnock relationship worked best with an r2 of 0 25 for the segregated data sets the charnock relationship also worked best with an average r2 of 0 675 as opposed to 0 66 for the modified charnock and 0 61 for the raupach model for conditions with shear velocity 1 0 ms 1 the comparable average values of r2 are 0 54 0 625 and 0 645 respectively there was an order of magnitude difference in the roughness length responses for wind tunnel and field data for each model evaluated convincing evidence of a fundamental scaling constraint in the wind tunnel data the scaling differences are attributed to conceptual and bias errors that include the use of the law of the wall versus the wake defect law or differences in turbulence characteristics especially regarding the role of large coherent structures raupach s 1991 a was found to be an extremely volatile constant making the modified charnock relationship most suitable for predicting aerodynamic roughness lengths over movable sand beds

hesperian age for western medusae fossae formation mars the medusae fossae formation mff on mars is an intensely eroded deposit north of the cratered highlands it is widely thought that mff materials were emplaced through ignimbrite eruptions recent geologic mapping of western mff identified outliers of mff materials well beyond the previously mapped western extent for the deposit including outliers close to gale crater we report counts of impact craters on the mff units that have implications for our understanding of the general history of mff and the uppermost layered materials on the gale crater mound

on the rate of aeolian sand transport a simple explicit formula for the transport rate of windblown sand is derived based on physical reasoning the curve relating the dimensionless transport rate to the dimensionless friction speed exhibits the empirically well established peak in fact the theory developed in the paper can explain the peaked shape of this curve three empirically determined coefficients in the formula can be given a physical interpretation the formula is shown to fit transport rates measured in wind tunnel experiments well except for very coarse sand formulae for the wind profile in the saltation layer and for the grain dislodgement rate in dependence on the friction speed are obtained as part of the theory

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

streamline correction for the analysis of boundary layer turbulence abstract improvements in the design and affordability of ultrasonic anemometers have provided significant contributions to aeolian research by facilitating high frequency monitoring of three dimensional wind velocities from these data it is possible to calculate quasi instantaneous reynolds stresses to evaluate boundary layer turbulence moving beyond time averaged measures such as shear velocity u as ultrasonic anemometry is used more frequently in aeolian geomorphology it is important to question accepted conventions concerning data processing and analysis this paper examines data processing questions associated with the application of ultrasonic anemometry to field studies in aeolian geomorphology through an investigation of three streamline correction routines the two step three step and planar fit methods on data recorded on a gently sloping beach at magilligan strand northern ireland in may 2010 the planar fit technique has not previously been used in aeolian geomorphology results are compared with data that have been corrected only for wind direction yaw the effects that these different methods have on quadrant analysis and reynolds stress calculation are discussed streamline correction is applied as a time variable procedure using a characteristic timescale of 8 s following analysis of the resultant wind speed energy spectrum it is found that reynolds shear stress is dependent on streamline correction method with run mean estimates of resultant horizontal shear stress ranging from 0 05 to 0 11 n m 2 depending on the technique the two step method consistently maximises the shear stress and when the resultant horizontal shear is calculated it produces the most robust estimate for application to aeolian research in contrast the different methods have little effect on the identification or sequencing of turbulent structures using quadrant analysis streamline correction is an essential processing step when using reynolds decomposition however the method used has an effect on data quality as each correction re distributes stress across the whole tensor altering both normal and shear stresses the total stress tensor magnitude itself is a conserved value and may provide a suitable parameter to quantify boundary layer turbulence

unique meteorite from early amazonian mars water rich basaltic breccia northwest africa 7034 we report data on the martian meteorite northwest africa nwa 7034 which shares some petrologic and geochemical characteristics with known martian meteorites of the snc i e shergottite nakhlite and chassignite group but also has some unique characteristics that would exclude it from that group nwa 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent rover and orbiter missions it formed 2 089 0 081 billion years ago during the early amazonian epoch in mars9 geologic history nwa 7034 has an order of magnitude more indigenous water than most snc meteorites with up to 6000 parts per million extraterrestrial h2o released during stepped heating it also has bulk oxygen isotope values of 17o 0 58 0 05 per mil and a heat released water oxygen isotope average value of 17o 0 330 0 011 per mil suggesting the existence of multiple oxygen reservoirs on mars

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

seismic profiling the continental lithosphere deep seismic reflection profiling is successfully being used worldwide to study the structure of the continental crust1 7 the moist8 profile recorded by birps british institutions reflection profiling syndicate was the first to show that the structure of the upper mantle could also be imaged given a powerful source and long recording times birps has recently acquired an ultra deep seismic reflection line drum deep reflections from the upper mantle the drum line was designed specifically to investigate the reflectivity of the lower continental lithosphere and was therefore recorded to a two way time twt of 30 s giving a depth of penetration into the lithosphere of 110 km this profile has now revealed strong reflections which are unequivocally from the lower lithosphere well below the base of the crust and which are as far as we are aware the deepest and most continuous structures imaged in the upper mantle by multi channel seismic reflection profiling

martian mantle mineralogy investigated by the 176lu 176hf and 147sm 143nd systematics of shergottites abstract chemical heterogeneities in the martian mantle are believed to result from the crystallization of a magma ocean in the first 100 million years of its history shergottite meteorites from mars are thought to retain a compositional record of such early differentiation and the resulting mineralogy at different depths the coupled 176 lu 176 hf and 147 sm 143 nd isotope systematics in 9 shergottites are used here to investigate these issues three compositional groups in the shergottites display distinct isotope systematics one group commonly termed as depleted is characterized by positive 176 hf i from 46 2 to 50 4 and 143 nd i from 36 2 to 39 1 another termed as enriched has negative 176 hf i 16 5 to 13 2 and 143 nd i 7 0 to 6 5 the third group is intermediate between the depleted and enriched groups with positive 176 hf i 30 0 to 33 4 and 143 nd i 16 9 together they describe mixing curves between 176 hf 177 hf 143 nd 144 nd lu hf and sm nd implying that they sample two distinct sources in the martian mantle all shergottites are characterized by sm nd source sample but lu hf source lu hf sample this decoupling can be explained by two successive partial melting episodes in the depleted shergottite source and localized in the martian upper mantle the genesis of shergottites can be modeled using non modal equilibrium partial melting in a source initially composed of 60 olivine 21 clinopyroxene 9 orthopyroxene and 10 garnet with degrees of partial melting of 8 8 and 3 9 respectively for the two successive events the enriched end member of the shergottite mixing curve is best modeled by late stage quenched residual melt resulting from the crystallization of a magma ocean the depleted shergottite source may be modeled as a mixture of cumulates and residual melt as convection in the martian magma ocean is expected to reduce the incompatible trace element heterogeneity in the final solidified layers consequently equilibrium crystallization is preferred to model the crystallization of the martian magma ocean the models that best explain the shergottite data are those where the magma ocean is at a depth of at least 1350 km in mars

in situ and experimental evidence for acidic weathering of rocks and soils on mars experimental data for alteration of synthetic martian basalts at ph 0 1 indicate that chemical fractionations at low ph are vastly different from those observed during terrestrial weathering rock surface analyses from gusev crater are well described by the relationships apparent from low ph experimental alteration data a model for rock surface alteration is developed which indicates that a leached alteration zone is present on rock surfaces at gusev this zone is not chemically fractionated to a large degree from the underlying rock interior indicating that the rock surface alteration process has occurred at low water to rock ratio the geochemistry of natural rock surfaces analyzed by apxs is consistent with a mixture between adhering soil dust and the leached alteration zone the chemistry of rock surfaces analyzed after brushing with the rat is largely representative of the leached alteration zone the chemistry of rock surfaces analyzed after grinding with the rat is largely representative of the interior of the rock relatively unaffected by the alteration process occurring at the rock surface elemental measurements from the spirit opportunity pathfinder and viking 1 landing sites indicate that soil chemistry from widely separated locations is consistent with the low ph low water to rock ratio alteration relationships developed for gusev rocks soils are affected principally by mobility of fe and mg consistent with alteration of olivine bearing basalt and subsequent precipitation of fe and mg bearing secondary minerals as the primary control on soil geochemistry copyright 2006 by the american geophysical union

the age of dar al gani 476 and the differentiation history of the martian meteorites inferred from their radiogenic isotopic systematics samarium neodymium isotopic analysis of the martian meteorite dar al gani 476 yields a crystallization age of 474 11 ma and an initial end143 value of 36 6 0 8 although the rb sr isotopic system has been disturbed by terrestrial weathering and therefore yields no age information an initial 87sr 86sr ratio of 0 701249 33 has been estimated using the rb sr isotopic composition of the maskelynite mineral fraction and the sm nd age the sr and nd isotopic systematics of dar al gani 476 like those of the basaltic shergottite que94201 are consistent with derivation from a source region that was strongly depleted in incompatible elements early in the history of the solar system nevertheless dar al gani 476 is derived from a source region that has a slightly greater incompatible enrichment than the que94201 source region this is not consistent with the fact that the parental magma of dar al gani 476 is significantly more mafic than the parental magma of que94201 and underscores a decoupling between the major element and trace element isotopic systematics observed in the martian meteorite suite combining the end142 end143 isotopic systematics of the martian meteorites yields a model age for planetary differentiation of 4 513 0 033 0 027 ga using this age the parent daughter ratios of martian mantle sources are calculated assuming a two stage evolutionary history the calculated sources have very large ranges of parent daughter ratios 87rb 86sr 0 037 0 374 147sm 144nd 0 182 0 285 176lu 177hf 0 028 0 048 these ranges exceed the ranges estimated for terrestrial basalt source regions but are very similar to those estimated for the sources of lunar mare basalts in fact the range of parent daughter ratios calculated for the martian meteorite sources can be produced by mixing between end members with compositions similar to lunar mare basalt sources two of the sources have compositions that are similar to olivine and pyroxene rich mafic cumulates with variable proportions of a rb enriched phase such as amphibole whereas the third source has the composition of liquid trapped in the cumulate pile i e similar to kreep after 99 crystallization correlation between the proportion of trapped liquid in the meteorite source regions and estimates of fo2 suggest that the kreep like component may be hydrous the success of these models in reproducing the martian meteorite source compositions suggests that the variations in trace element and isotopic compositions observed in the martian meteorites primarily reflect melting of the crystallization products of an ancient magma ocean and that assimilation of evolved crust by mantle derived magmas is not required furthermore the decoupling of major element and trace element isotopic systematics in the martian meteorite suite may reflect the fact that trace element and isotopic systematics are inherited from the magma source regions whereas the major element abundances are limited by eutectic melting processes at the time of magma formation differences in major element abundances of parental magma therefore result primarily from fractional crystallization after leaving their source regions

the evolution of a heterogeneous martian mantle clues from k p ti cr and ni variations in gusev basalts and shergottite meteorites abstract martian basalts represent samples of the interior of the planet and their composition reflects their source at the time of extraction as well as later igneous processes that affected them to better understand the composition and evolution of mars we compare whole rock compositions of basaltic shergottitic meteorites and basaltic lavas examined by the spirit mars exploration rover in gusev crater concentrations range from k poor as low as 0 02 wt k 2 o in the shergottites to k rich up to 1 2 wt k 2 o in basalts from the columbia hills ch of gusev crater the adirondack basalts from the gusev plains have more intermediate concentrations of k 2 o 0 16 wt to below detection limit the compositional dataset for the gusev basalts is more limited than for the shergottites but it includes the minor elements k p ti cr and ni whose behavior during mantle melting varies from very incompatible prefers melt to very compatible remains in the residuum the range in partitioning behavior of these elements provides leverage on interpreting igneous processes models are presented that demonstrate how concentrations of these elements in gusev basaltic magmas would change by simple igneous processes fractional crystallization crustal contamination and mantle partial melting the gusev basalts may be related by two stage batch melting of a primitive k rich mantle source to first generate the k rich columbia hills basalts and second the lower k adirondack basalts leaving behind a k poor residuum the mantle source for the gusev basalts is separate from the more depleted k poorer source region of the shergottites this indicates that primitive k rich mantle persisted until the early hesperian during formation of the columbia hills basalts we suggest that separate mantle reservoirs developed by inhomogeneous partial melting at melt fractions greater than 0 05 to form the martian crust in the first 1 ga of the planet s history

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

geochemical diversity in first rocks examined by the curiosity rover in gale crater evidence for and significance of an alkali and volatile rich igneous source the first four rocks examined by the mars science laboratory alpha particle x ray spectrometer indicate that curiosity landed in a lithologically diverse region of mars these rocks collectively dubbed the bradbury assemblage were studied along an eastward traverse sols 46 102 compositions range from na and al rich mugearite jake matijevic to fe mg and zn rich alkali rich basalt hawaiite bathurst inlet and span nearly the entire range in feo and mno of the data sets from previous martian missions and martian meteorites the bradbury assemblage is also enriched in k and moderately volatile metals zn and ge these elements do not correlate with cl or s suggesting that they are associated with the rocks themselves and not with salt rich coatings three out of the four bradbury rocks plot along a line in elemental variation diagrams suggesting mixing between al rich and fe rich components chemcam analyses give insight to their degree of chemical heterogeneity and grain size variations in trace elements detected by chemcam suggest chemical weathering li and concentration in mineral phases e g rb and sr in feldspars we interpret the bradbury assemblage to be broadly volcanic and or volcaniclastic derived either from near the gale crater rim and transported by the peace vallis fan network or from a local volcanic source within gale crater high fe and fe mn in et then likely reflect secondary precipitation of fe 3 oxides as a cement or rind the k rich signature of the bradbury assemblage if igneous in origin may have formed by small degrees of partial melting of metasomatized mantle

dynamics of sediment storage and release on aeolian dune slip faces a field study in jericoacoara brazil sediment transport on the lee sides of aeolian dunes involves a combination of grain fall deposition on the upper portion of the slip face until a critical angle is exceeded transport of a portion of those sediments down the slip face by grain flows and finally deposition at an angle of repose we measured the mean critical and repose angles and the rate of slip face avalanching using terrestrial laser scanning tls on two barchans of different size in jericoacoara brazil wind speeds and sand fluxes were measured simultaneously at the dune crests we found that the mean critical and repose angles decrease with increasing wind speed we attribute this to turbulent shear stresses the magnitude of which are predicted using 3d large eddy simulation les modeling that episodically act down the slip face i e in the direction of gravity to trigger grain flows at lower angles than with gravity stresses alone the rate of avalanching is a maximum in the morning at our study site and coincides with the maximum rate of increase in wind speed and not with the maximum rate of sediment supply to the slip face we developed and tested a new predictive model for the rate of avalanching that includes both sediment flux delivered to the slip face and the derivative of the critical angle with time our data also suggest that the mean critical angle varies inversely with slip face height these results have important implications for aeolian dune evolution interpretations of aeolian stratigraphy and granular mechanics

petrogenesis of high phosphorous wishstone class rocks in gusev crater mars 1 the spirit rover has analyzed a wide variety of alkaline volcanic rocks in gusev crater among them are wishstone class tephrites with unusually high p2o5 5 wt abundances to obtain the chemical compositions of rock interiors we extrapolated a trend defined by brushed and abraded surface compositions the extrapolation analysis suggests the high p2o5 tephrite signature is not attributable to secondary aqueous alteration but represents an igneous rock composition assessment of the compositional trend also suggests that merrillite is the phosphate mineral in wishstone class modified cipw norm calculations using merrillite instead of apatite show that wishstone class rocks are silica saturated hypersthene olivine normative and alkaline the high p2o5 whole rock compositions plot above solubility curves of merrillite in a diagram of p2o5 versus aluminosity suggesting that mechanical admixture of merrillite is required a source supplying merrillite cannot be a common silicate magma instead it could be a carbonatitic melt or a highly fractionated residual melt jotunite after anorthosite crystallization comparison with earth analogs suggests that the wishstone class is akin to alkaline basalts in the eastern snake river plain with regard to its chemistry texture and geologic context these alkaline basalts are interpreted to originate from mantle metasomatized by co2 fluids and highly alkaline melts in the wake of the yellowstone hot spot thus we propose that the wishstone class represents a silica saturated alkaline suite that has mechanically mixed xenocrystic merrillites probably during explosive volcanic eruption the merrillites crystallized from carbonate rich magma produced by melting of a co2 bearing martian mantle

geochemical properties of rocks and soils in gusev crater mars results of the alpha particle x ray spectrometer from cumberland ridge to home plate 1 geochemical diversity of rocks and soils has been discovered by the alpha particle x ray spectrometer apxs during spirit s journey over husband hill and down into the inner basin from sol 470 to 1368 the apxs continues to operate nominally with no changes in calibration or spectral degradation over the course of the mission germanium has been added to the spirit apxs data set with the confirmation that it occurs at elevated levels in many rocks and soils around home plate twelve new rock classes and two new soil classes have been identified at the spirit landing site since sol 470 on the basis of the diversity in apxs geochemistry the new rock classes are irvine alkaline basalt independence low fe outcrop descartes outcrop similar to independence with higher fe and mn algonquin mafic ultramafic igneous sequence barnhill volcaniclastic sediments enriched in zn cl and ge fuzzy smith high si and ti rock elizabeth mahon high si ni and zn outcrop and rock halley hematite rich outcrop and rock montalva high k hematite rich rock everett high mg magnetite rich rock good question high si low mn rock and torquas high k zn and ni magnetite rich rock new soil classes are gertrude weise very high si soil and eileen dean high mg magnetite rich soil aqueous processes have played a major role in the formation and alteration of rocks and soils on husband hill and in the inner basin

wind blown sand on beaches an evaluation of models five models for predicting rates of aeolian sand transport were evaluated using empirical data obtained from field experiments conducted in april 1994 at a beach on inch spit co kerry republic of ireland measurements were made of vertical wind profiles to derive shear velocity estimates beach slope and rates of sand transport sediment samples were taken to assess characteristics of grain size and surface moisture content estimates of threshold shear velocity were derived using grain size data after parsing the field data on the basis of the quality of shear velocity estimation and the occurrence of blowing sand 51 data sets describing rates of sand transport and environmental conditions were retained mean grain diameter was 0 17 mm surface slopes ranged from 0 02 on the foreshore to about 0 11 near the dune toe mean shear velocities ranged from 0 23 m s 1 just above the observed transport threshold to 0 65 m s 1 rates of transport ranged from 0 02 kg m 1 h 1 to more than 80 kg m 1 h 1 these data were used as input to the models of bagnold bagnold r a 1936 the movement of desert sand proc r soc london a157 594 620 kawamura kawamura r 1951 study of sand movement by wind translated 1965 as university of california hydraulics engineering laboratory report hel 2 8 berkeley zingg zingg a w 1953 wind tunnel studies of the movement of sedimentary material proc 5th hydraulics conf bull 34 iowa city inst of hydraulics pp 111 135 kadib kadib a a 1965 a function for sand movement by wind university of california hydraulics engineering laboratory report hel 2 8 berkeley and lettau and lettau lettau k and lettau h 1977 experimental and micrometeorological field studies of dune migration in k lettau and h lettau eds exploring the world s driest climate university of wisconsin madison ies report 101 pp 110 147 correction factors to adjust predictions of the rate of transport to account for the effects of slope and moisture content were calculated using the models of bagnold bagnold r a 1973 the nature of saltation and bed load transport in water proc r soc london ser a 332 473 504 and belly belly p y 1964 sand movement by wind u s army corps eng cerc tech mem 1 washington d c 38 pp respectively none of the models was able to produce a strong correspondence between measured and predicted rates of transport best results were obtained using the bagnold and zingg models and the kadib model was the least viable of this group the influence of sediment moisture content appeared to be the critical factor in degrading model viability overall none of the models is adequate for general applications to coastal aeolian environments where moisture content complications tend to override the predictive competence of the simple transport formulations c 1998 elsevier science b v

early martian mantle overturn inferred from isotopic composition of nakhlite meteorites following the crystallization of a magma ocean the martian mantle probably underwent an overturning event but its initiation timing and geochemical consequences are poorly constrained isotopic data for martian meteorites and numerical simulations provide strong evidence for early overturning in the martian mantle