weathering of mars antarctic analog studies abstract terrestrial analog studies of potential martian weathering processes are reported four major weathering environments are identified i hydrothermal alteration of impact melt sheets and impact breccias ii solid gas and related reactions iii subpermafrost intrusion of lavas involving liquid water and iv subaerial extrusion of lavas in the absence of liquid water weathering in environments i iii has been discussed by other authors this report discusses weathering in environment iv an analog of which is antarctica we conclude that weathering is geologically slow in the absence of liquid water and that zeolites predominate over clays as secondary minerals on volumetric grounds it appears that hydrothermal alteration of impact melt sheets should be the most important time averaged weathering mechanism provided that h2o was present as liquid or permafrost such hydrothermal alteration should operate predominately on ancient crustal material gas solid reactions and photochemical weathering should also operate primarily on ancient crustal material on a time averaged basis weathering products of younger subpermafrost or subaerially erupted basalts should be subordinate to hydrothermal alteration and gas solid reactions it appears that the present martian regolith as analyzed by the viking landers contains a major contribution from ancient crust as typified today by the southern cratered highlands with a lesser contribution from the younger hemispherically restricted basaltic lavas

the effect of salt crust on the thermal conductivity of one sample of fluvial particulate materials under martian atmospheric pressures 1 a line heat source apparatus was used to measure thermal conductivities of a lightly cemented fluvial sediment salinity 1 1 g kg 1 and the same sample with the cement bonds almost completely disrupted under low pressure carbon dioxide atmospheres the thermal conductivities of the cemented sample were approximately 3 higher over the range of atmospheric pressures tested than the thermal conductivities of the same sample after the cement bonds were broken a thermal conductivity derived particle size was determined for each sample by comparing these thermal conductivity measurements to previous data that demonstrated the dependence of thermal conductivity on particle size actual particle size distributions were determined via physical separation through brass sieves when uncemented 87 of the particles were less than 125 m in diameter with 60 of the sample being less than 63 m in diameter as much as 35 of the cemented sample was composed of conglomerate particles with diameters greater than 500 m the thermal conductivities of the cemented sample were most similar to those of 500 m glass beads whereas the thermal conductivities of the uncemented sample were most similar to those of 75 m glass beads this study demonstrates that even a small amount of salt cement can significantly increase the thermal conductivity of particulate materials as predicted by thermal modeling estimates by previous investigators

a lagrangian model for boundary layer growth and bed shear stress in the swash zone abstract a new model for the boundary layer development and associated skin friction coefficients and shear stress within the swash zone is presented the model is developed within a lagrangian reference frame following fluid trajectories and can be applied to both laminar flow and smooth turbulent flow the model is based on the momentum integral approach for steady flat plate boundary layers with appropriate modifications to account for the unsteady flow regime and flow history the model results are consistent with previous measurements of bed shear stress and skin friction coefficients within the swash zone these indicate strong temporal and spatial variation throughout the swash cycle and a clear distinction between the uprush and backwash phase this variation has been previously attributed the unsteady flow regime and flow history effects both of which are accounted for in the new model fluid particle trajectories and velocity are computed using the non linear shallow water wave equations and the boundary layer growth across the entire swash zone is estimated predictions of the bed shear stress and skin friction coefficients agree reasonably well with direct bed shear stress measurements reported by barnes et al barnes m p o donaghue t alsina j m baldock t e 2009 direct bed shear stress measurements in bore driven swash coastal engineering 56 8 853 867 and for a given flow velocity give stresses which are consistent with the bias toward uprush sediment transport which has consistently been observed in measurements the data and modelling suggest that the backwash boundary layer is initially laminar which results in the late development of significant bed shear during the backwash with a transition to a turbulent boundary layer later in the backwash a new conceptual model for the boundary layer structure at the leading edge of the swash is proposed which accounts for both the no slip condition at the bed and the moving wet dry interface however further development of the lagrangian boundary layer model is required in order to include bore generated turbulence and to account for variable roughness and mobile beds

hydrothermally altered impact melt rock and breccia contributions to the soil of mars samples of melt rock and breccia from 12 terrestrial impact craters were examined to identify alteration minerals and their conditions of formation the dominant assemblage in most cases is clay silica k feldspar zeolite indicating hydrothermal alteration at low pressures and temperatures of 100 300 c the clays are predominantly fe chlorites and smectites in most cases depleted in al and enriched in fe and mg relative to their source rocks alteration of impact glass is often complete while alteration of crystalling melt rock is limited to a few percent of the rock volume impact breccia is altered to only a small extent compared to the alteration of glass impact induced hydrothermal alteration is to be expected at martian impact sites if significant quantities of ground ice and or water are present the alteration products are likely to resemble the clays found at terrestrial craters al fe fractionation similar to that observed on earth is strongly suggested by the viking soil analyses the quantitative contribution of hydrothermal clays to the soil of mars is estimated based on a model which predicts the generation of the equivalent of a 61 m thick blanket of impact melt planet wide the inefficiency of melt production in small craters and the inefficiency of alteration in large craters limit the expected production of clay to a few percent of this figure clays produced by impact induced hydrothermal alteration may be expected to contribute to the fines on mars but this contribution is probably not dominant relative to other suggested sources

hydrothermal jarosite and hematite in a pyroxene hosted melt inclusion in martian meteorite miller range mil 03346 implications for magmatic hydrothermal fluids on mars low temperature aqueous processes have been implicated in the generation of jarosite and hematite on the martian surface but little is known regarding the role that high temperature magmatic fluids may have played in producing similar assemblages on mars we have identified jarosite and hematite in a clinopyroxene hosted melt inclusion in martian meteorite mil 03346 that shows evidence of having been hydrothermally precipitated in addition to jarosite and hematite the melt inclusion contains titanomagnetite pyrrhotite potassic chlorohastingsite an iron rich silicate glass and possibly goethite these phases were identified and characterized using scanning electron microscopy sem con focal raman spectroscopy and electron probe microanalysis epma based on observed textural relationships and the compositions of the hosted phases we report that the jarosite bearing melt inclusion in mil 03346 has recorded a fluid rich history that began in the magmatic stage and continued to low temperatures this history begins at entrapment of a volatile rich silicate melt that likely reached fluid saturation after only minor crystallization within the melt inclusion this fluid rich in chlorine reacted with surrounding silicate material to produce the potassicchlorohastingsite as cooling proceeded the liquid phase eventually became more oxidized and reacted with the pyrrhotite sulfide oxidation resulted in so4 2 formation and concomitant acid production setting the stage for jarosite formation once the fluid cooled beyond the upper thermal stability of jarosite 200 c as the fluid cooled below 200 c jarosite continued to precipitate with hematite and or goethite until equilibrium was established or reactions became kinetically unfavorable this work suggests an additional jarosite hematite formation pathway on mars one that may be important wherever magmatic hydrothermal fluids come into contact with primary sulfide grains at the martian surface or subsurface moreover hydrothermal fluids rich in chlorine sulfur and iron are important for ore forming processes on earth and their indirect identification on mars may have important implications for ore formation on mars

simulation and prediction of swash oscillations on a steep beach this paper presents numerical simulations and analytical predictions of key aspects of swash oscillations on a steep beach simulations of the shoreline displacement based on bore run up theory are found to give excellent agreement with recent experimental data for regular waves wave groups and random waves the theory is used to derive parameters that predict the onset of swash saturation and the spectral characteristics of the saturated shoreline motion these parameters are again in good agreement with the measured laboratory data and are also consistent with previous experimental data simulation of irregular wave run up using a series of overlapping monochromatic swash events is found to reproduce typical features of swash oscillations and can accurately describe both the low and high frequency spectral characteristics of the swash zone in particular the low frequency components of the run up can be modelled directly using a sequence of incident short wave bores with no direct long wave input to the numerical simulations this suggests that wave groupiness must be accounted for when modelling shoreline oscillations

estimating swash zone friction coefficients on a sandy beach abstract video based swash motions from three studies on two separate beaches were analyzed with respect to theoretical swash trajectories assuming plane beach ballistic motions under quadratic friction friction coefficient values for both the uprush and backwash were estimated by comparing measured swash space time trajectories to these theoretical expectations given an initial velocity and beach slope observations were made spanning high tides and in one case during a light rain analysis of over 4500 individual swash events showed that the uprush friction coefficient was nearly constant during all three studies with a mean value of roughly 0 007 and showed no trends over a tidal cycle in contrast backwash friction coefficient values varied over the tidal cycles ranging between 0 01 and 0 07 with minimum values corresponding to the highest tides although these values are close to the theoretical estimates based on a law of the wall formulation and values commonly referenced in the literature these observations show a consistent tendency for backwash friction estimates to greatly exceed uprush friction estimates the disparity between uprush and backwash friction coefficients can be partially attributed to the exclusion of a pressure gradient term in the ballistic model however results indicate that backwash friction coefficients adjusted to account for this effect may be three times larger than the uprush friction values during lower tides this tidal dependence for backwash friction coefficients is attributed to a complex interaction between swash infiltration and entrained sediment loads these findings imply that friction estimates necessary for sediment transport calculations and hydrodynamic predictions based solely on grain roughness may not be correct for backwash flows

hydrodynamics and sediment transport in the swash zone a review and perspectives the dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are reviewed combined with a discussion of future measurement and modelling requirements the importance of swash zone processes in the overall behaviour of the nearshore littoral zone are identified with the paper subsequently focusing on aspects that directly relate to sediment transport on beaches the review considers analytical and numerical modelling work and both field and laboratory data the hydrodynamics of the swash zone are first discussed with reference to the surf zone boundary swash characteristics forcing mechanisms and shoreline oscillations subsequent sections consider more micro scale processes such as the internal flow kinematics turbulence the bed boundary layer and infiltration exfiltration through permeable beds the second part of the paper outlines the fundamental mechanics of sediment transport in the swash zone followed by a more detailed discussion of sediment transport modes induced by the dominant hydrodynamic conditions modelling concepts are reviewed and the strengths and weaknesses of different approaches identified a final summary and future modelling perspectives conclude the paper

recent advances in modeling swash zone dynamics influence of surf swash interaction on nearshore hydrodynamics and morphodynamics the role of the swash zone in influencing the whole nearshore dynamics is reviewed with a focus on the interaction between surf and swash zone processes local and global hydromorphodynamic phenomena are discussed in detail and a description of the overall swash zone operation is given the effects of swash zone boundary conditions are highlighted together with the importance of surf zone boundary conditions major emphasis is placed on illustrating the interactions of various hydrodynamic modes which in turn control the swash and surf zone morphology finally methods to account for swash zone processes in coastal models with different temporal and spatial resolutions are proposed

a geological map of the scotia sea area constrained by bathymetry geological data geophysical data and seismic tomography models from the deep mantle abstract the scotia sea is one of the tectonically most complex and least understood back arc basins on earth which partly results from its remote location making the acquisition of data challenging here we provide a review of current publicly available geophysical and geological data in the scotia sea realm including magnetic bouguer gravity anomaly high resolution bathymetric heat flow and reflection seismic data and rock type data from cored and dredged samples with this inter disciplinary data set we performed an offshore geological mapping exercise that allowed us to identify lithologies in the predominantly submerged scotia sea domain cross sections combining crustal structure and mantle tomography enabled us to address some of the still persisting geological challenges in this tectonically complex area the data review revealed that basalt is the dominant lithology in the scotia sea area occupying most of the west and east scotia sea wss and ess andesitic and more felsic lithologies are identified in the central scotia sea css and the northern east scotia sea ess mesozoic palaeozoic metamorphic sedimentary lithologies are reported from the highs along the north and south scotia ridges nsr and ssr these highs originate from a land bridge that until the late mesozoic connected the south american and antarctic continents scarcely available and contradicting data prevent the age determination of several structural units surrounding and located on the scotia plate but our mapping exercise allowed us to confirm the presence of the early oligocene late miocene ancestral south sandwich arc assa in the east of the css setting the minimum age of the older segment of the css crust to eocene earliest oligocene three cross sections cross cutting the scotia sea reveal two high velocity zones indicating cold mantle material one is situated below the structural highs along the ssr which we interpreted as remnant slab material of the assa and another below south georgia and the css which we interpreted as the front of the slab that currently subducts at the south sandwich trench ssat the neutral velocity discontinuity below the wss implies mantle conditions of a recently extinct spreading centre the upper mantle low velocity anomaly below the css is interpreted as warmer toroidal flows around the slab edges of the subducting plate at the ssat we have demonstrated that the geological and geophysical data publicly available today allows us to create offshore geological maps in remote inaccessible offshore domains this is a less time consuming economically advantageous exercise which re uses existing geological and geophysical data for a new purpose it is the most data inclusive study there is today of the scotia sea region and serves as a guideline for future expeditions targeting the css and the structural features along the nsr to identify their age and origin a georeferenced version of the map is provided in the supplementary material

forearc tectonic evolution of the south shetland margin antarctic peninsula the main provinces of the south shetland margin antarctic peninsula characterized on the basis of multichannel seismic long range side scan sonar and swath bathymetry data include from northwest to southeast 1 the oceanic crust of the former phoenix plate flexed down toward the margin and affected by normal faulting in the upper crust 2 a narrow trench with a horizontally layered sediment fill which onlaps the thin sedimentary cover on the oceanic crust and shows incipient deformation near its landward edge 3 an accretionary prism with a complex internal structure the toe of which is overthrust above the youngest trench deposits 4 a midslope forearc basin with an asymmetric synformal structure and 5 the continental shelf which includes two distinct tectonic provinces calculations of the late cenozoic convergence history at the trench indicate a rapid decrease in convergence rate after 6 7 ma from about 60 mm yr resulting from the slowing and eventual cessation of spreading on the antarctic phoenix ridge once spreading had completely ceased 3 5 2 4 ma the convergence rate at the trench equalled the rate of extension in bransfield strait which was probably less than 10 mm yr at first but may have increased since 1 3 ma and this in turn would imply a corresponding increase in convergence rate above the basal detachment the toe of the accretionary prism is composed of a stack of thrust fault bounded wedges laterally and vertically segmented by normal faults most of the trench fill sediments are overthrust by the toe of the accretionary prism and subducted beneath it for as far as they can be traced on the seismic profiles this suggests that there may be tectonic erosion of the forearc since a large part of the trench sediment appears to be derived from erosion on the forearc slope the forearc basin records a long history of subsidence during which the depocenter migrated landward paralleling retrogradational erosion of the distal margin of the basin subduction of the hero fracture zone at approximately the same location since 10 ma may have enhanced tectonic erosion of the accretionary prism in the forearc basin a synform is coincident with a bathymetric reentrant but its axis is oblique to the trends of both the basin and the fracture zone the origin of this synform and the final phase of uplift of the blueschist facies terrane on which smith island stands are probably related to their position above the subducting fracture zone ridge the present elevation of smith island is thought to result from uplift which followed a ridge crest trench collision directly southwest of the hero fracture zone at 5 5 ma the northwestern edge of the mesozoic to early cenozoic arc batholith trending northeast southwest on the shelf is proposed to have acted as a backstop to the accretionary prism during cenozoic subduction

crustal model of the bransfield rift west antarctica from detailed obs refraction experiments summary the first detailed deep seismic refraction study in the bransfield strait west antarctica using sensitive obss ocean bottom seismographs was carried out successfully during the antarctic summer of 1990 1991 the experiment focused on the deep crustal structure beneath the axis of the bransfield rift seismic profile dss 20 was located exactly in the bransfield trough which is suspected to be a young rift system along the profile five obss were deployed at spacings of 50 70 km 51 shots were fired along the 310 km profile this paper gives the first presentation of the results a detailed model of the crustal structure was obtained by modelling the observed traveltimes and amplitudes using a 2 d ray tracing technique the uppermost sedimentary cover with velocities of 2 0 5 5 km s 1 reaches a depth of up to 8 km below this a complex with velocities of 6 4 6 8 km s 1 is observed the presence of a high velocity body with vp 7 3 7 7 km s 1 was detected in the 14 32 km depth range in the central part of the profile these inhomogeneities can be interpreted as a stage of back arc spreading and stretching of the continental crust coinciding with the deception bridgeman volcanic line velocities of 8 1 km s 1 characteristic of the moho are observed along the profile at a depth of 30 32 km

terrestrial analogues of the surface rocks of mars the pathways of chemical weathering processes on earth and the virtual absence of them on the moon are well characterized because we have direct access to samples of primary igneous rocks their upper mantle sources and derivative sedimentary rocks and soil forming the regolith tracing chemical changes on the surface of mars however is more difficult because of limited access to samples from mars terrestrial rocks and minerals are continually being sought which might serve as analogues for martian materials evidence presented here suggests that hisingerite iddingsite and several ferric sulphate minerals derived from deuteric alteration of iron rich basalts may provide clues to the evolutionary history of the surface of mars

jarosite formation by an amd sulphide oxidizing environmental enrichment implications for biomarkers on mars abstract the formation of jarosite in acid mine drainage amd accompanies microbial oxidation of reduced sulphidic minerals such as pyrite fes 2 and pyrrhotite fe 1 x s found in mining waste materials the discovery of jarosite at meridiani planum mars has been used to interpret past hydrologic conditions as episodically wet acidic and evaporative based on evidence from jarosite formed abiotically or through microbial iron oxidation to date no study has specifically assessed jarosite formation via microbial sulphide oxidation the most likely pathway in amd or the mineral stability of any jarosite formed via this pathway here using both aerobic and anaerobic conditions to control iron and sulphide oxidation metabolisms we demonstrate that oxidation of pyrrhotite a putative mars mineral by a sulphur oxidizing environmental amd enrichment produces crystalline jarosite at a higher ph than previously described we further show that jarosite produced via microbial sulphide oxidation is stable under the drying heating and wet aging conditions shown to impact abiotic and microbial iron oxidation derived jarosite our results indicate that preservation of microbially produced jarosite via pyrrhotite associated sulphide oxidation does not require the evaporitic conditions that have been proposed to date if water is established to have persisted on mars then this new evidence signals that the occurrence of stable crystalline jarosite at meridiani planum may itself be a clear biomarker indicating that not only water occurred at some time s on mars but also life

experimental study of bore run up bore propagation near the shoreline the transition from bore to wave run up and the ensuing run up motion on a uniformly sloping beach are investigated experimentally as a bore approaches the shoreline the propagation speed first decelerates by compressing its wave form and then suddenly accelerates at the shoreline although this behaviour is qualitatively in agreement with the inviscid shallow water wave prediction the acceleration is caused by the momentum exchange process

backarc basin evolution and cordilleran orogenesis insights from new ocean bottom seismograph refraction profiling in bransfield strait antarctica bransfield strait a backarc basin off the northwestern antarctic peninsula is a modern analog for cretaceous basins inverted in the compressional tectonic regime that initiated the andean cordillera eight new refraction ocean bottom seismograph profiles in the strait demonstrate that crustal thickness in the deep central basin increases from northeast to southwest from 10 km to 14 16 km this confirms multichannel seismic interpretation of upper crustal structures suggesting that the bransfield basin is opening by northeast to southwest rift propagation within arc crust of the antarctic peninsula a process also recorded in the obducted cretaceous rocas verdes basin of the southernmost andes thinning is most prominent along the axis of the strait where the crust is 9 11 km thick in contrast thicknesses beneath the antarctic peninsula margin and the inactive south shetland islands pedestal are 18 km and 24 km respectively seismic velocities and thicknesses suggest that new oceanic crust is not yet being generated extension is focused along the northwest margin imparting the physiographic asymmetry to the strait comparing the bransfield basin with the inverted rocas verdes basin and intraoceanic counterparts in the western pacific suggests that rift propagation and trench side focusing of extension may be fundamental features of young backarc basins resultant asymmetry may facilitate observed obduction of backarc basin floor and arc rocks onto continental margins during compressional orogenesis

swash overtopping and sediment overwash on a truncated beach new experimental laboratory data are presented on swash overtopping and sediment overwash on a truncated beach approximating the conditions at the crest of a beach berm or inter tidal ridge runnel the experiments provide a measure of the uprush sediment transport rate in the swash zone that is unaffected by the difficulties inherent in deploying instrumentation or sediment trapping techniques at laboratory scale overtopping flow volumes are compared with an analytical solution for swash flows as well as a simple numerical model both of which are restricted to individual swash events the analytical solution underestimates the overtopping volume by an order of magnitude while the model provides good overall agreement with the data and the reason for this difference is discussed modelled flow velocities are input to simple sediment transport formulae appropriate to the swash zone in order to predict the overwash sediment transport rates calculations performed with traditional expressions for the wave friction factor tend to underestimate the measured transport additional sediment transport calculations using standard total load equations are used to derive an optimum constant wave friction factor of f w 0 024 this is in good agreement with a broad range of published field and laboratory data however the influence of long waves and irregular wave run up on the overtopping and overwash remains to be assessed the good agreement between modelled and measured sediment transport rates suggests that the model provides accurate predictions of the uprush sediment transport rates in the swash zone which has application in predicting the growth and height of beach berms c 2005 elsevier b v all rights reserved

observations of wave run up and groundwater seepage line motions on a reflective to intermediate meso tidal beach abstract swash sw and ground water seepage line gwsl motions have been recorded at an exposed meso tidal reflective to intermediate beach using a coastal video monitoring system during a 15 month period the monitoring period allowed the collection of imagery under a wide variety of wave and beach morphological conditions and sw and gwsl velocities were extracted on a wave by wave basis the continuous double bounded kumaraswamy kw probability distribution is proposed to parameterize the sw and gwsl height distributions and since the distribution shape of the latter was shown to be influenced by the tidal elevation generic tidal elevation dependent kw pdfs are proposed the beach face slope more than any other factor tested was found to apply certain control to the mean uprush backwash and gwsl velocities the results also indicate that in reflective to intermediate beaches the gwsl lies between the mean and 2 exceedance swash elevation with the occurrence of swash running above a saturated beach face being controlled by the tidal gradient and the significant wave height

the predictability of cross shore bed evolution of sandy beaches at the time scale of storms and seasons using process based profile models deterministic and probabilistic profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons the large scale laboratory experiment is a pure 2d case and offers and ideal test case for cross shore profile models as disturbing alongshore non uniformities are absent the field experiments are performed at the egmond site the netherlands during the eu coast3d project and represent storm time scale oct nov 1998 as well as seasonal time scale conditions may 1998 sep 1999 the objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities coastal process based profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons profile models can quite accurately errors smaller than 10 represent the cross shore significant wave height distribution in the surf zone if the wave breaking model is properly calibrated the wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results profile models can reasonably represent the cross shore and longshore currents undertow in a pure 2d case and in 3d field conditions profile models including cross shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross shore current velocities profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale profile models can reasonably simulate the post storm onshore bar migration provided that the near bed orbital velocities and wave asymmetry related sand transport are represented in a sufficiently accurate way using non linear wave theories profile models cannot simulate the beach recovery processes on the post storm time scale because these essentially 3d processes are not sufficiently known to be included in the models profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles the simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning

cosmogenic and nucleogenic isotopic changes in mars their rates and implications to the evolutionary history of martian surface abstract we present calculations of rates of production of several nuclides in the martian atmosphere and in the regolith due to nuclear interactions of cosmic ray and radiogenic particles and consider their implications to the evolutionary history of mars nuclides selected are those which considering their chemical properties may be useful as tracers for delineating the past histories of the martian atmosphere and regolith calculations are presented for different assumed atmospheric pressures the regolith production rates for the present thin martian atmosphere 20 g cm 2 are expected to be fairly robust because they are based primarily on observed cosmogenic effects in the moon for which semiempirical estimates of nuclide production rates have been provided earlier by reedy 1981 uncertainties which arise in the calculations of nuclide production rates for an earlier hypothetical martian atmosphere of 300 500 g cm 2 thickness are discussed compared to cosmic ray production rates the nucleogenic production rates are smaller by several orders of magnitude however the nucleogenic production extends to much deeper levels whereas the cosmogenic production is essentially confined to the top 750 1000 g cm 2 depth important examples of nucleogenic production are discussed isotopes of neon and argon appear to be very promising for delineating relative magnitudes of a number of planetary processes related to the temporal changes in the thickness of the atmosphere as well as their release from the regolith however quantification of the processes would require higher precision isotopic data for the atmosphere and also direct measurements of isotopic ratios in the martian regolith along with supplementary information on changes in the isotopic compositions of hydrogen carbon and nitrogen which are affected by a variety of mechanisms of escape of gases from the atmosphere cosmogenic effects are minimal in these cases we show that although we can at present draw but limited inferences the planet mars presents a unique opportunity to use cosmogenic nuclides as tools to delineate the evolutionary history of the planet as a whole as well as its regolith and the atmosphere this arises because of two factors minimal degassing of the planet and a fairly intense chemical weathering history of the upper surface consequently an appreciable fraction of some of the isotopes of volatile elements is contributed by nuclear reactions

tsunami run up and draw down on a plane beach tsunami run up and draw down motions on a uniformly sloping beach are evaluated based on fully nonlinear shallow water wave theory the nonlinear equations of mass conservation and linear momentum are first transformed to a single linear hyperbolic equation to solve the problem with arbitrary initial conditions we apply the fourier bessel transform and inversion of the transform leads to the green function representation the solutions in the physical time and space domains are then obtained by numerical integration with this semi analytic solution technique several examples of tsunami run up and draw down motions are presented in particular detailed shoreline motion velocity field and inundation depth on the shore are closely examined it was found that the maximum flow velocity occurs at the moving shoreline and the maximum momentum flux occurs in the vicinity of the extreme draw down location the direction of both the maximum flow velocity and the maximum momentum flux depend on the initial waveform it is in the inshore direction when the initial waveform is predominantly depression and in the offshore direction when the initial waves have a dominant elevation characteristic

eulerian flow velocities in the swash zone field data and model predictions measurements of eulerian flow velocity obtained within the swash zone on a relatively steep beach face gradient 1 23 are compared with an extended ballistic swash model the model only requires a friction factor beach slope and terminal bore velocity as input the following model predictions matched well with observations 1 the maximum eulerian flow velocity is the shoreline velocity when it arrives at the fixed point of interest on the beach face 2 at any location the time of flow reversal occurs prior to the shoreline reaching its maximum landward excursion 3 the maximum flow velocity in the backwash is the velocity recorded as the shoreline recedes past the fixed point of interest and this is less than the maximum uprush velocity and 4 the duration of the uprush flow is shorter than the duration of the backwash flow previous studies have already confirmed that the ballistic swash model including friction can accurately predict shoreline motion and maximum run up on steep beaches this study shows that it is similarly successful in predicting eulerian flow velocities during individual swash events the model does not presently account for interacting swash however and so may be less appropriate on gently sloping beaches

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

separation of incident and reflected waves over sloping bathymetry abstract an existing 2d method for separating incident and reflected waves over a horizontal bed frigaard p brorsen m 1995 a time domain method for separating incident and reflected irregular waves coastal eng 24 205 215 is modified to account for normally incident linear waves propagating over a bed with arbitrary 2d bathymetry linear shoaling is used to determine the amplitude and phase change between two measurement positions thereafter the existing technique can be applied comparisons between the existing and modified methods are made using numerically simulated data errors in the reflection coefficient are found to be small for large reflection coefficients but may become large if reflection is low however if an accurate assessment of the amplitude of the incident and reflected wave trains is required the bathymetry must be accounted for in order to avoid significant errors up to 90 for cases considered

wave transformation across the inner surf zone sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches a steep concave up beach a gently sloped approximately planar beach and a beach with an approximately flat terrace adjacent to a steep foreshore were depth limited i e approximately independent of the offshore wave height consistent with previous observations the wave evolution is well predicted by a numerical model based on the one dimensional nonlinear shallow water equations with bore dissipation the model is initialized with the time series of sea surface elevation and cross shore current observed at the most offshore sensors located about 50 to 120 m from the mean shoreline in mean water depths 0 80 to 2 10 m the model accurately predicts the cross shore variation of energy at both infragravity nominally 0 004 f 0 05 hz and sea swell here 0 05 f 0 18 hz frequencies in models of surf zone hydrodynamics wave energy dissipation is frequently parameterized in terms of s the ratio of the sea swell significant wave height to the local mean water depth the observed and predicted values of s increase with increasing beach slope and decreasing normalized by a characteristic wavenumber k water depth kh and are well correlated with kh a measure of the fractional change in water depth over a wavelength errors in the predicted individual values of s are typically less than 20 it has been suggested that infragravity motions affect waves in the sea swell band and hence s but this speculation is difficult to test with field observations numerical simulations suggest that for the range of conditions considered here s is insensitive to infragravity energy levels

mineral chemistry of the shergottites nakhlites chassigny brachina pallasites and urelites the mineral chemistry is compared for selected achondrites olivine in the alha 77005 and eeta79001 shergottites olivine rich chassigny and brachina and the nakhlites contains ni indicative of oxidizing conditions whereas pallasitic and ureilitic olivines contain much lower ni due to reducing conditions the brachina olivine and pyroxene have distinctively higher fe mn than the shergottites and chassigny further indicating that brachina is unique the chassigny and 77005 olivines contain lower cr2o3 0 03 wt than the brachina and 79001 olivines values of fe mn for cumulus augites in nakhlites are higher than for the shergottites whereas those for ferropigeonites are not the 77005 shergottite contains troilite fes in contrast to 79001 shergotty zagami and chassigny which contain pyrrhotite further analyses are needed but the present survey indicates that at least brachina is not chemically cogenetic with the other oxidized achondrites and that the fe mn ratio of the cumulus augites in nakhlites is a problem for the assignment of the nakhlites shergottites and chassigny to a single genetic group

the influence of seaward boundary conditions on swash zone hydrodynamics abstract the influence of the seaward boundary condition on the internal swash hydrodynamics is investigated new numerical solutions of the characteristics form of the nonlinear shallow water equations are presented and applied to describe the swash hydrodynamics forced by breaking wave run up on a plane beach the solutions depend on the specification of characteristic variables on the seaward boundary of the swash zone equivalent to prescribing the flow depth or the flow velocity it is shown that the analytical solution of shen and meyer shen m c meyer r e 1963 climb of a bore on a beach part 3 runup j fluid mech 16 113 125 is a special case of the many possible solutions that can describe the swash flow but one that does not appear appropriate for practical application for real waves the physical significance of the boundary conditions is shown by writing the volume and momentum fluxes in terms of the characteristic variables results are presented that illustrate the dependence of internal flow depth and velocity on the boundary condition this implies that the internal swash hydrodynamics depend on the shape and wavelength of the incident bore which differs from the hydrodynamic similarity inherent in the analytical solution a solution appropriate for long bores is compared to laboratory data to illustrate the difference from the analytical solution the results are important in terms of determining overwash flows flow forces and sediment dynamics in the run up zone

chemical composition of martian fines of the 21 samples acquired for the viking x ray fluorescence spectrometer 17 were analyzed to high precision compared to typical terrestrial continental soils and lunar mare fines the martian fines are lower in al higher in fe and much higher in s and cl concentrations protected fines at the two lander sites are almost indistinguishable but concentration of the element s is somewhat higher at utopia duricrust fragments successfully acquired only at the chryse site invariably contained about 50 higher s than fines no elements correlate positively with s except cl and possibly mg a sympathetic variation is found among the triad si al ca positive correlation occurs between ti and fe sample variabilities are as great within a few meters as between lander locations 4500 km apart implying the existence of a universal martian regolith component of constant average composition the nature of the source materials for the regolith fines must be mafic to ultramafic

jarosite in a pleistocene east african saline alkaline paleolacustrine deposit implications for mars aqueous geochemistry 1 jarosite occurs within altered tephra from the saline alkaline paleolake deposits of pliocene pleistocene olduvai gorge tanzania zeolites mainly phillipsite authigenic k feldspar and mg fe smectites dominate the mineral assemblage indicating saline alkaline diagenetic conditions ph 9 as jarosite is ordinarily an indicator of acidic conditions on earth and mars its association with such undisputed high ph indicators is unexpected of 55 altered tephra samples collected from the paleolake basin and margin deposits eleven contained jarosite detectable by x ray diffraction xrd 0 15 mossbauer spectroscopy fourier transform infrared reflectance ftir electron probe microanalysis epma x ray fluorescence xrf and scanning electron microscopy sem analyses confirm the presence and nature of the jarosite this paper documents this occurrence and presents mechanisms that could produce this unusual and contradictory mineral assemblage we favor a mechanism by which jarosite formed recently perhaps as modern ground and meteoric water interacted with and oxidized paleolacustrine pyrite providing local and temporary acidic conditions however local groundwater at modern springs has a ph 9 in recent studies of mars the presence of jarosite or other fe or mg sulfates is often used to indicate dominantly acidic conditions regardless the current study shows that jarosite can form in sediments dominated by alkaline minerals and solutions its coexistence with mg fe smectites in particular makes it relevant to recent observations of martian paleolakes

influence of ultramafic rocks and hot springs with travertine depositions on geochemical composition and baseline of soils application to eastern central greece abstract ultramafic rocks and hot springs which occur on almost every continent of our planet lead to enriching concentration to several elements including some potentially toxic ones to the soil groundwater fauna and flora and subsequently are posing potential risks to human health a geochemical and mineralogical soil survey was undertaken in eastern central greece an area characterised by the presence of ultramafic rocks of ophiolite complexes and hot springs with thermogenic travertine depositions the research aimed to investigate their influence on soil mineralogy and geochemistry and to establish the soil geochemical baseline values one hundred four soil samples were collected from 74 sites at depths of 0 25 cm and 25 50 cm they were found to be enriched in ca 5 17 fe 3 72 mg 2 08 co 28 mg kg cr 252 mg kg cu 32 mg kg and ni 267 mg kg relative to the median values of both greek and european soil and upper continental crust factor analysis revealed three main factors controlling the soil chemical composition reflecting the influence of ultramafic rocks ni co cr and fe pedogenesis processes ba al and k and thermogenic travertine deposits ca and sr all the factors showed a significant spatial correlation with the geological features within the study area geochemical baselines were estimated for three sub areas based on the three controlling factors revealed by the multivariance statistical analysis and spatial data calculating only one baseline value based on the total dataset would lead to incorrect baseline values for several elements the outcome of the present research could be used in future studies at regions with similar geological features i e serpentine soils and hot springs depositions providing a comparative example concerning the concentrations of several elements including some potentially toxic ones to the soil their host mineral phases and a scientific approach for setting pragmatic geochemical baseline values for pollution assessment

alteration assemblages in the miller range and elephant moraine regions of antarctica comparisons between terrestrial igneous rocks and martian meteorites the weathering products present in igneous terrestrial antarctic samples were analyzed and compared with those found in the four miller range nakhlite martian meteorites the aim of these comparisons was to determine which of the alteration phases in the miller range nakhlites are produced by terrestrial weathering and what effect rock composition has on these phases antarctic terrestrial samples mil 05031 and eet 96400 along with the miller range nakhlites mil 03346 and 090032 were found to contain secondary alteration assemblages at their externally exposed surfaces despite the difference in primary mineralogy the assemblages of these rocks consist mostly of sulfates jarosite in mil 05031 jarosite and gypsum in eet 96400 and iddingsite like fe clay as neither of the terrestrial samples contains sulfur bearing primary minerals and these minerals are rare in the miller range nakhlites it appears that so42 possibly along with some of the na k and ca in these phases was sourced from wind blown sea spray and biogenic emissions from the southern ocean cl enrichment in the terrestrially derived iddingsite of mil 05031 and mil 03346 and the presence of halite at the exterior edge of mil 090032 can also be explained by this process however jarosite within and around the olivine bound melt inclusions of mil 090136 is present in the interior of the meteorite and therefore is probably the product of preterrestrial weathering on mars

mossbauer parameters of iron in sulfate minerals although fe sulfate minerals occur only rarely on earth as alteration products of sulfidic basalts or in hydrothermal systems multiple lines of evidence point to the importance of fe and other sulfate minerals on the surface of mars one such martian data set comes from the mimos ii mossbauer spectrometers on the mars exploration rovers which acquired hundreds of spectra from the martian surface at two locations interpretation of those spectra has been limited by the lack of a comprehensive set of laboratory analog spectra of the broad range of naturally occurring sulfate minerals accordingly this study reports mossbauer data of 98 samples representing 47 different sulfate mineral species all containing six or higher coordinated fe the resultant mossbauer parameters are related to the local polyhedral environment around the fe cation in each mineral to explain variations in spectral characteristics results show that the size of the coordination polyhedron is the best predictor of quadrupole splitting which increases with both octahedral volume and mean bond length species within groups of structurally similar minerals are shown to have comparable spectral peaks that generally fall within small ranges although coordination polyhedron geometry is not necessarily unique to any particular mineral species or group mossbauer data can be used to help constrain mineral identifications from martian spectra the number of mineral species is large but the range of crystal structures and hyperfine parameters may be small so that in many cases individual minerals cannot be uniquely fingerprinted examples would include quenstedtite coquimbite kornelite and lausenite which have indistinguishable spectra as do apjohnite bilinite dietrichite and romerite overlap of mossbauer parameters is a particular complication for identification of fe 3 rich phases because the range of mossbauer parameters for fe 3 in any coordination number is so small previous analyses of martian mossbauer spectra reported the presence of jarosite klingelhofer et al 2004 morris et al 2004 and an unspecific ferric sulfate morris et al 2008 new data presented here indicate that botryogen metasideronatrite and slavikite exhibit mossbauer spectra similar to those attributed to jarosite at meridiani planum fibroferrite and rhomboclase have parameters similar to those observed at arad samra and copiapite and parabutlerite could be present at tyrone mount darwin and berkner island unique mineral identifications are generally not possible from mossbauer data alone particularly for paramagnetic phases although combining mossbauer results with other data sets enables a greater level of confidence in constraining mineralogy this study provides a new expansive data set for future interpretation of iron sulfates on mars

interpretation of reconnaissance gravity and aeromagnetic surveys of the antarctic peninsula two dimensional models are presented for the crustal structure of the antarctic peninsula a mesozoic cenozoic magmatic arc on the southeast pacific margin the models are constrained by measured rock properties the west coast magnetic anomaly wcma is caused by a zone of mafic plutons which is 70 150 km wide and over 1500 km long in modelling of bouguer anomalies isostatic compensation is maintained by crustal thickness variations the model moho is deepest 35 km beneath the mid cretaceous axis of the arc and shallowest 20 km beneath a late cenozoic marginal basin positive isostatic residual gravity anomalies are associated with the wcma and a mafic terrane in the mesozoic accretionary complex three broad areas of consistent crustal structure are identified the junctions of these areas are sinistral fault zones which displace the curvilinear magnetic physiographic and gravity patterns by several tens of kilometers

near infrared spectral reflectance of mineral mixtures systematic combinations of pyroxenes olivine and iron oxides near infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals mixtures were chosen for application to the study of the dark materials on mars but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 m the addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics using only spectral data in the 1 m region it is difficult to differentiate orthopyroxene and limonite goethite in a mixture additional spectral coverage or other evidence may be required for a unique interpretation all composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end member absorptions and have bandwidths greater than or equal to those for the end members in general spectral properties in an intimate mixture combine in a complex nonadditive manner with features demonstrating a regular but usually nonlinear variation as a function of end member phase proportions

surf zone dynamics simulated by a boussinesq type model part ii surf beat and swash oscillations for wave groups and irregular waves abstract this is the second of three papers on the modelling of various types of surf zone phenomena in the first paper the general model was described and it was applied to study cross shore motion of regular waves in the surf zone in this paper part ii we consider the cross shore motion of wave groups and irregular waves with emphasis on shoaling breaking and runup as well as the generation of surf beats these phenomena are investigated numerically by using a time domain boussinesq type model which resolves the primary wave motion as well as the long waves as compared with the classical boussinesq equations the equations adopted here allow for improved linear dispersion characteristics and wave breaking is modelled by using a roller concept for spilling breakers the swash zone is included by incorporating a moving shoreline boundary condition and radiation of short and long period waves from the offshore boundary is allowed by the use of absorbing sponge layers mutual interaction between short waves and long waves is inherent in the model this allows for example for a general exchange of energy between triads rather than a simple one way forcing of bound waves and for a substantial modification of bore celerities in the swash zone due to the presence of long waves the model study is based mainly on incident bichromatic wave groups considering a range of mean frequencies group frequencies modulation rates sea bed slopes and surf similarity parameters additionally two cases of incident irregular waves are studied the model results presented include transformation of surface elevations during shoaling breaking and runup and the resulting shoreline oscillations the low frequency motion induced by the primary wave groups is determined at the shoreline and outside the surf zone by low pass filtering and subsequent division into incident bound and free components and reflected free components the model results are compared with laboratory experiments from the literature and the agreement is generally found to be very good finally the paper includes special details from the breaker model time and space trajectories of surface rollers revealing the breakpoint oscillation and the speed of bores envelopes of low pass filtered radiation stress and surface elevation sensitivity of surf beat to group frequency modulation rate and bottom slope is investigated part iii of this work sorensen et al 1998 presents nearshore circulations induced by the breaking of unidirectional and multi directional waves

mossbauer mineralogy of rock soil and dust at meridiani planum mars opportunity s journey across sulfate rich outcrop basaltic sand and dust and hematite lag deposits additonal co authors p gutlich e kankeleit t mccoy dw mittlefehldt f renz me schmidt b zubkov sw squyres re arvidson

a note on wave energy dissipation over steep beaches abstract this paper revisits the derivation of the parametric surf zone model proposed by baldock et al baldock t e holmes p bunker s van weert p 1998 cross shore hydrodynamics within an unsaturated surf zone coast eng 34 173 196 we show that a consistent use of the proposed rayleigh distribution for surf zone wave heights results in modification of the expressions for the bulk dissipation rate and enhanced dissipation levels on steep beaches and over saturated surf zone conditions as a consequence the modification proposed herein renders the model robust even on steep beaches where it could otherwise develop a shoreline singularity

flow velocities sediment transport and morphological change in the swash zone of two contrasting beaches abstract as part of a large uk research project focussing on the role of swash on shoreline change two field experiments were conducted on contrasting sandy beaches a flatter dissipative beach and a steeper intermediate beach this paper describes almost 300 h of nearshore velocity data collected during this project supplemented by suspended sediment transport sediment tracer and beach profile data during both field experiments the upper part of the beach experienced progressive accretion indicating that onshore sediment transport prevailed in the swash and inner surf zones suspended sediment transport and tracer dispersal were also onshore the associated cross shore flow field was however dominated by offshore directed mean flows especially on the steeper beach velocity skewness defined as u 3 u 2 1 5 where u is the cross shore velocity and kurtosis defined as u 3 u u 2 2 were mainly directed offshore implying that energetics based sediment transport models are unable to predict the direction of sediment transport in the swash zone possible explanations for the observed accretion include enhanced bed shear stress on the uprush due to in exfiltration effects flow acceleration and or bore turbulence and advection of bore entrained sediment into the swash zone

seismic studies of the crustal structure in west antarctica 1979 1980 preliminary results abstract the polish geophysical expedition to west antarctica in the summer of 1979 1980 was organized by the institute of geophysics of the polish academy of sciences the purpose of the expedition was to carry out studies of deep structures of the earth s crust by reflection refraction and deep seismic sounding methods special attention was paid to tectonically active zones and to the contact zones between the blocks of the earth s crust and the lithospheric plates geophysical measurements were carried out in the area extending between 61 and 65 s and between 56 and 66 w the measurements covered the southern shetlands the antarctic peninsula the bransfield strait the drake passage the palmer archipelago the gerlache strait and the bismarck strait towards the southern pacific deep seismic soundings were made along profiles with a total length of about 2000 km seismic reflection measurements were made along profiles about 1100 km long a detailed analysis of the seismic wave field shows that the structure of the earth s crust in this part of west antarctica is very complex numerous deep fractures divide the earth s crust into blocks of different physical properties the thickness of the earth s crust changes from 32 km in the region of the south shetland islands to 40 45 km in the region of the antarctic peninsula a preliminary geodynamical model of this part of west antarctica is presented

active margin processes along the antarctic peninsula abstract the antarctic peninsula has a remarkable record of active margin processes which include subduction with progressive ridge trench collisions margin segmentation by major fracture zones rifting in a hybrid back arc and sheared plate margin context fore arc basin development and glacial marine controlled trench fill processes several facets of these active margin processes both of internal crustal dynamic and external origin climate controlled have been documented by a geophysical survey during the antarktis vi 2 cruise of r v polarstem october december 1987 reflection seismic profiles have been shot over the rift basin of bransfield strait over an elongated sediment filled trough interpreted as a fore arc basin over accretional and progradational slopes over recent and ancient trench environments and over the facing oceanic domain in this oceanic domain different fracture zones have highly contrasting morphological and geophysical expressions the subduction of a fracture zone like hero f z characterized by a significant relief possibly related to the presence of buoyant serpentinite ridges may have been a factor of subduction termination for the last segment of the aluk drake plate it may also have played a role in the separation of a blueschist bearing fragment smith island from the base of the accretionary plate margin and in its lift to the surface the magnetic anomaly pattern of the oceanic slabs facing the northwestern peninsula margin shows evidence of an intriguing spreading acceleration which apparently preceded ridge trench collision the same anomaly pattern provides a clue to the stratigraphie interpretation of the oceanic sediment cover and of the frontal part of the prograding now passive margin south of the south shetland island arc an apparently broken and tilted oceanic plate fragment squeezed between the south shetland trench and shackleton fracture zone may argue for the role of transpression associated with the oblique convergence of the antarctic and scotia plates

p wave velocity structure beneath the northern antarctic peninsula evidence of a steeply subducting slab and a deep rooted low velocity anomaly beneath the central bransfield basin summary upper mantle structure between 100 and 300 km depth below the northern antarctic peninsula is imaged by modelling p wave traveltime residuals from teleseismic events recorded on the king sejong station ksj the argentinean italian stations juba and espz an iris gsn station pmsa and the seismic experiment in patagonia and antarctica sepa broad band stations for measuring traveltime residuals we applied a multichannel cross correlation method and inverted for upper mantle structure using vandecar s method the new 3 d velocity model reveals a subducted slab with a 70 dip angle at 100 300 km depth and a strong low velocity anomaly confined below the se flank of the central bransfield basin the low velocity is attributed to a thermal anomaly in the mantle that could be as large as 350 560 k and which is associated with high heat flow and volcanism in the central bransfield basin the low velocity zone imaged below the se flank of the central bransfield basin does not extend under the northern bransfield basin suggesting that the rifting process in that area likely involves different geodynamic processes

on the transport of suspended sediment by a swash event on a plane beach we develop solutions for the transport of suspended sediment by a single swash event following the collapse of a bore on a plane beach and we investigate the morphodynamical role that such transport may play although the intrinsic asymmetry between uprush and backwash velocities tends to encourage the export of sediment we find that swash events may be effective in distributing across the swash zone much or all of the sediment mobilised by bore collapse additionally settling lag effects may promote a weak onshore movement of sediment we quantify both effects in terms of the properties of the sediment and of the swash event and comment on the relationship between our findings and recent field studies of swash zone sediment transport

the runup of solitary waves this is a study of the runup of solitary waves on plane beaches an approximate theory is presented for non breaking waves and an asymptotic result is derived for the maximum runup of solitary waves a series of laboratory experiments is described to support the theory it is shown that the linear theory predicts the maximum runup satisfactorily and that the nonlinear theory describes the climb of solitary waves equally well different runup regimes are found to exist for the runup of breaking and non breaking waves a breaking criterion is derived for determining whether a solitary wave will break as it climbs up a sloping beach and a different criterion is shown to apply for determining whether a wave will break during rundown these results are used to explain some of the existing empirical runup relationships

water abundance of dunes in gale crater mars from active neutron experiments and implications for amorphous phases we report the water abundance of bagnold dune sand in gale crater mars by analyzing active neutron experiments using the dynamic albedo of neutrons instrument we report a bulk water equivalent hydrogen abundance of 0 68 0 15 wt which is similar to measurements several kilometers away and from those taken of the dune surface thus the dune is likely dehydrated throughout furthermore we use geochemical constraints including bulk water content to develop compositional models of the amorphous fraction for which little information is known we find the amorphous fraction contains 26 to 64 wt basaltic glass and up to 24 wt rhyolitic glass suggesting at least one volcanic source for the dune material we also find a range of hydrated phases may be present in appreciable abundances either from the incorporation of eroded aqueously altered sediments or the direct alteration of the dune sand

large eddy simulation of dam break driven swash on a rough planar beach turbulence characteristics in the swash zone are investigated using a 3d large eddy simulation model the numerical model is implemented based on openfoam which solves the filtered navier stokes equations for two immiscible fluids with a standard smagorinsky sub grid scale closure the numerical model is validated with laboratory data for swash flow driven by a dam break apparatus the model results demonstrate that the main characteristics of turbulence in the swash zone are different from those in the surf zone which are mainly induced by surface wave breaking during uprush phase bore generated turbulence has 2d turbulence characteristics because of limited water depth near bed generated turbulence is mainly observed during backwash turbulence production and turbulent dissipation rate estimated from the model results indicate an imbalance possibly due to advection at swash front and large roughness used touching down of turbulent coherent structure tcs is observed during uprush which drives intense bed shear stress during the backwash interaction between tcs and bed is less clear however finger like patterns in the spatial extent of bed shear stress and vertical components of vorticity are predicted during the backwash the location of the strongest finger patterns in the vertical direction is collocated with that of maximum turbulence production these finger patterns are likely caused by boundary layer instabilities injected vertically from the bed this article is protected by copyright all rights reserved

overview of the opportunity mars exploration rover mission to meridiani planum eagle crater to purgatory ripple the mars exploration rover opportunity touched down at meridiani planum in january 2004 and since then has been conducting observations with the athena science payload the rover has traversed more than 5 km carrying out the first outcrop scale investigation of sedimentary rocks on mars the rocks of meridiani planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine grained siliciclastics and sulfates the siliciclastic fraction was produced by chemical alteration of a precursor basalt the sulfates are dominantly mg sulfates and also include ca sulfates and jarosite the stratigraphic section observed to date is dominated by eolian bedforms with subaqueous current ripples exposed near the top of the section after deposition interaction with groundwater produced a range of diagenetic features notably the hematite rich concretions known as blueberries the bedrock at meridiani is highly friable and has undergone substantial erosion by wind transported basaltic sand this sand along with concretions and concretion fragments eroded from the rock makes up a soil cover that thinly and discontinuously buries the bedrock the soil surface exhibits both ancient and active wind ripples that record past and present wind directions loose rocks on the soil surface are rare and include both impact ejecta and meteorites while opportunity s results show that liquid water was once present at meridiani planum below and occasionally at the surface the environmental conditions recorded were dominantly arid acidic and oxidizing and would have posed some significant challenges to the origin of life copyright 2006 by the american geophysical union

the nanophase iron mineral s in mars soil a series of surface modified clays containing nanophase np iron oxide oxyhydroxides of extremely small particle sizes with total iron contents as high as found in mars soil were prepared by iron deposition on the clay surface from ferrous chloride solution comprehensive studies of the iron mineralogy in these mars soil analogs were conducted using chemical extractions solubility analyses ph and redox x ray and electron diffractometry electron microscopic imaging specific surface area and particle size determinations differential thermal analyses magnetic properties characterization spectral reflectance and viking biology simulation experiments the clay matrix and the procedure used for synthesis produced nanophase iron oxides containing a certain proportion of divalent iron which slowly converts to more stable fully oxidized iron minerals the clay acted as an effective matrix both chemically and sterically preventing the major part of the synthesized iron oxides from ripening i e growing and developing larger crystals the precipitated iron oxides appear as isodiametric or slightly elongated particles in the size range 1 10 nm having large specific surface area the noncrystalline nature of the iron compounds precipitated on the surface of the clay was verified by their complete extractability in oxalate lepidocrocite gamma feooh was detected by selected area electron diffraction it is formed from a double iron fe ii fe iii hydroxy mineral such as green rust or ferrosic hydroxide magnetic measurements suggested that lepidocrocite converted to the more stable maghemite gamma fe2o3 by mild heat treatment and then to nanophase hematite alpha fe2o3 by extensive heat treatment after mild heating the iron enriched clay became slightly magnetic to the extent that it adheres to a hand held magnet as was observed with mars soil the chemical reactivity of the iron enriched clays strongly resembles and offers a plausible mechanism for the somewhat puzzling observations of the viking biology experiments their unique chemical reactivities are attributed to the combined catalytic effects of the iron oxide oxyhydroxides and silicate phase surfaces the reflectance spectrum of the clay iron preparations in the visible range is generally similar to the reflectance curves of bright regions on mars this strengthens the evidence for the predominance of nanophase iron oxides oxyhydroxides in mars soil the mode of formation of these nanophase iron oxides on mars is still unknown it is puzzling that despite the long period of time since aqueous weathering took place on mars they have not developed from their transitory stage to well crystallized end members the possibility is suggested that these phases represent a continuously on going extremely slow weathering process

an astrobiological perspective on meridiani planum sedimentary rocks exposed in the meridiani planum region of mars record aqueous and eolian deposition in ancient dune and interdune playa like environments that were arid acidic and oxidizing on earth microbial populations have repeatedly adapted to low ph and both episodic and chronic water limitation suggesting that to a first approximation the meridiani plain may have been habitable during at least part of the interval when deposition and early diagenesis took place on the other hand the environmental conditions inferred for meridiani deposition would have posed a challenge for prebiotic chemical reactions thought to have played a role in the origin of life on earth orbital observations suggest that the combination of sulfate minerals and hematite found in meridiani rocks may be unusual on the martian surface however there is reason to believe that acidity aridity and oxidizing conditions were broadly distributed on ancient mars when these conditions were established and how much environmental heterogeneity existed on early mars remain to be determined because sulfates and iron oxides can preserve detailed geochemical records of environmental history as well as chemical textural and microfossil signatures of biological activity meridiani planum is an attractive candidate for mars sample return

inclusion of additional energy dissipation due to plunging breakers in parametric type wave models one of the most critical issues in coastal engineering problems is to accurately predict the wave height profile across the surfzone parametric wave models are broadly used in modelling the wave energy dissipation in this regard three parametric wave models based on the bore energy dissipation model were evaluated against new field measurements under various conditions from mild to stormy the results indicate that a discrepancy between models and data occurred near the break point for cases where the wave breaking was of the plunging type but after the breakpoint the wave height decay rates compared well in order to improve this model shortcoming comprehensive new laboratory tests were conducted to quantify the additional energy dissipation due to plunging breakers based on the data new empirical equations were derived and incorporated into the most recent bore dissipation parametric wave model the inclusion of the extra energy dissipation due to plunging breakers results in significant improvement in the prediction of the wave height profile

mineralogy composition and alteration of mars pathfinder rocks and soils evidence from multispectral elemental and magnetic data on terrestrial analogue snc meteorite and pathfinder samples major element multispectral and magnetic properties data were obtained at ares vallis during the mars pathfinder mission to understand the compositional mineralogical and process implications of these data we obtained major element mineralogical and magnetic data for well crystalline and nanophase ferric minerals terrestrial analogue samples with known geologic context and snc meteorites analogue samples include unaltered palagonitic and sulfatetic tephra from mauna kea volcano hydrolytic and acid sulfate alteration steam vent material from kilauea volcano hydrolytic alteration and impactites from meteor crater relithification salient results for mars pathfinder include 1 band depths bd530b and bd600 and the reflectivity ratio r800 r750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of h2o and occurring in composite particles along with subordinate amounts of other ferric minerals hematite and hematite plus nanophase goethite are most consistent with the data but maghemite akaganeite schwertmannite and nanophase lepidocrocite are also possible interpretations ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well crystalline goethite and lepidocrocite 2 the strength of the ferric adsorption edge r750 r445 implies the fe3 fe2 values for pathfinder rock and soil are within the ranges 0 7 3 and 3 20 respectively 3 ferrous silicates are indicated for subsets of pathfinder rocks and soils one subset has a band minimum near 930 nm that can attributed to low ca pyroxene alternatively the band could be a second manifestation of certain ferric oxides including nanophase goethite maghemite akaganeite and schwertmannite another subset has a negative spectral slope from 800 to 1005 nm which could result from the high energy wing of a high ca pyroxene and or olivine band a mixture of bright and dark materials and for rocks thin coatings of bright dust on dark rocks 4 chemical data on pathfinder rocks and soils are consistent with two component mixtures between an andesitic rock with low mgo and so3 concentrations soil free rock and a global basaltic soil with high mgo and so3 concentrations rock free soil pathfinder rock free soil can be modeled as a chemical mixture of snc meteorites and the pathfinder soil free rock 5 pathfinder soil cannot be obtained by chemical alteration of pathfinder rocks by any of the hydrolytic and acid sulfate alteration processes we studied presumably global mixing has obscured and possibly erased the elemental signatures of chemical alteration 6 the strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite fe ti spinels the saturation magnetization of the tephra samples 0 5 2 0 am2 kg is at or below the low end of the range inferred for martian dust 4 2 am2 kg implying that lithogenic fe ti spinels are a possible candidate for the martian strongly magnetic phase 7 the predominantly palagonitic spectral signature and magnetic nature of martian soil and dust are consistent with glassy precursors with imbedded fe ti spinel particles comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on mars by volcanic and impact processes is sufficient to account for these observations

cross shore hydrodynamics within an unsaturated surf zone abstract this paper concerns the hydrodynamics induced by random waves incident on a steep beach new experimental results are presented on surface elevation and kinematic probability density functions cross shore variation in wave heights the fraction of broken waves and velocity moments the surf zone is found to be unsaturated at incident wave frequencies with a significant proportion of the incident wave energy remaining at the shoreline in the form of bores wave heights in both the outer and inner surf zones are best described by a full rayleigh distribution thornton e b guza r t 1983 transformation of wave height distribution j geophys res 88 5925 5938 rather than a truncated rayleigh distribution as used by battjes and janssen 1978 battjes j a janssen j p 1978 energy loss and setup due to breaking of random waves proc 16th int conf coastal eng asce new york pp 569 588 a new parametric wave transformation model is outlined which provides explicit expressions for the fraction of broken waves and the energy dissipation rate within the surf zone on steep beaches the model appears to offer improved predictive capabilities over the original battjes and janssen model cross shore variations in the velocity variance and velocity moments are best described using linear gaussian wave theory with less than 20 of the velocity variance in the inner surf zone due to low frequency energy

shear stress and sediment transport calculations for swash zone modelling it is shown that the observed difference in sediment transporting efficiency by the swash uprush compared with the downrush could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush the bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead phi tau of the bed shear stress compared with the free stream velocity at the peak frequency with this approach the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula without the need for different uprush and downrush coefficients while the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre suspended sediment in the uprush nevertheless the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre suspended sediment to the onshore sediment transport in swash zones c 2002 published by elsevier science b v

an experimental study of wave run up at a steep beach this paper presents experiments on run up of strongly nonlinear waves on a beach of 10 54 inclination velocity fields are obtained by the piv particle image velocimetry technique acceleration measurements are also attempted but it is difficult to obtain useful results in every case in addition free surface profiles are extracted from digital images and wave resistance probes the investigation focuses on the dynamics of the early stages of the run up when steep fronts evolve in the vicinity of the equilibrium shoreline but maximum run up heights are also reported measurements on moderately nonlinear waves are compared to results from long wave theories including a numerical boussinesq model and analytic shallow water results from the literature in particular the applicability of the long wave theories is addressed however most attention is given to run up of high incident solitary waves that are on the brink of breaking at the shoreline in one case a temporarily slightly overturning wave front is found that neither develops into a plunger or displays appreciable spilling this feature is discussed in view of measured velocity and acceleration patterns and with reference to the dam break problem effects of scaling as well as viscous damping are also briefly discussed

wave transformation and swash oscillation on gentle and steep slopes the numerical model developed previously for coastal structures is slightly modified and applied to predict the wave transformation in the surf and swash zones on gentle slopes as well as the wave reflection and swash oscillation on relatively steep beaches the numerical model is one dimensional in the cross shore direction and is based on the finite amplitude shallow water equations including the effect of bottom friction which are solved in the time domain for the incident wave train specified as input at the seaward boundary of the computation located outside the breakpoint the slight modification is related to the effect of the time averaged current on the seaward boundary condition and improves the agreement between the computed and measured mean water levels on gentle slopes the modified numerical model is compared with available small scale test data for monochromatic waves spilling on gentle slopes as well as for monochromatic waves plunging and surging on a relatively steep slope additional comparisons are made with small scale tests conducted using transient monochromatic and grouped waves on a 1 8 smooth slope with and without an idealized nearshore bar at the toe of the 1 8 slope as a whole the numerical model is shown to be capable of predicting both time varying and time averaged hydrodynamic quantities in the surf and swash zones on gentle as well as steep slopes

kinematics of breaking tsunami wavefronts a data set from large scale laboratory experiments abstract this paper provides an overview of a new large scale laboratory data set on the kinematics of breaking tsunami wavefronts the aim of the experiments was to provide an open access data set for model testing calibration and verification with particular emphasis on fluid kinematics in the wave breaking and run up swash zones the experiments were performed over a composite slope in the tsunami wave basin at the o h hinsdale wave research laboratory at oregon state university data for ten different wave conditions were collected including non breaking and breaking waves and both shore breaks and fully developed long bores surface elevation and fluid kinematics were measured with a closely spaced array of surface piercing wave gauges non contact ultrasonic wave gauges and four 3 d side looking acoustic doppler velocimeters the array was traversed from the nearshore depth 0 2 m to the middle and upper run up zone providing kinematic data at 30 cross shore locations video was also recorded from 4 cameras covering the propagation breaking and run up zones surface elevation flow velocities and the wave maker displacement were also recorded to provide offshore boundary conditions the experiments include conditions with wave heights up to 0 55 m notional wave periods up to 20 s and run up lengths of up to 15 2 m on a 1 30 slope in terms of the slope in the shoaling and breaker zones the data correspond to iribarren numbers in the range of 0 26 5 6 raw calibrated and processed data are stored with open access within the osu tsunami wave basin experiment notebook which provides full access to all the wave maker control signals data instrument coordinates and processing and plotting software this paper serves as an introduction to the data set demonstrates data quality and provides an initial analysis of some key parameters that govern the impact of tsunami events including run up versus offshore wave conditions and nearshore bore height the maximum inundation depths at the original shoreline position and the time to maximum inundation depth and flow reversal examples of temporal and convective accelerations and turbulent flow components are also presented to illustrate further details of the kinematics

swash overtopping a truncated plane beach swash on a plane beach is modelled by using a solution of the shallow water equations due to shen meyer 1963 the equations are used in a form appropriate for a plane at a finite angle to the horizontal the beach is cut off at a level below that of the maximum run up and the water is taken to fall freely over the end of the beach an explicit solution is found which permits evaluation of the overtopping flow and total volume for one swash event

an integral swash zone model with friction an experimental and numerical investigation abstract experimental and numerical analyses have been used to assess the validity and potentialities of the integral swash zone model by brocchini and peregrine proc coastal dynamics 95 asce 1 1996 221 which is extended to include seabed friction effects previously neglected applications of the model to experimental data show it represents a simple and useful tool for modelling swash zone flows the model allows for computation of integral swash zone properties and shoreline motion from local variables defined at the seaward limit of the swash for most properties correlation between local and integral properties is very good correlation coefficient about 0 80 a suitable parametric form of frictional forces in the swash zone is defined on the basis of both experimental data and analytical investigation numerical tests showed that the proposed parameterization models well integral frictional forces within the swash zone the parametric friction force improves capabilities of the integral swash zone model of representing real swash motions this is particularly evident when considering the momentum equation the correlation coefficient between the rate of change of the onshore momentum in the swash zone and its forcings increases from about 0 85 to about 0 95 due to the inclusion of the seabed friction

nature of serpentinization of ultramafic rocks from hero fracture zone antarctic constraints from stable isotopes abstract serpentinites from the hero fracture zone drake passage antarctica contain serpentine amphibole talc chlorite and magnetite as well as relict olivine pyroxene and spinel from a spinel peridotite precursor two episodes of serpentinization are recognized the first event produced lizardite and antigorite whereas the second produced only lizardite the initial and subsequent serpentinization events occurred at about 178 283 c and 170 298 c respectively calculated water rock ratios of the serpentinization events are less than 5 for the initial event and greater than 5 for the subsequent event a model involving deep seawater infiltration in the fracture zone followed by serpentinization of mantle peridotite and buoyancy driven uplift controlled by relatively small scale faults and not by a large scale detachment fault is invoked to explain the emplacement of serpentinite on the surface