barotropic tides on the north carolina shelf observations from 18 near bottom pressure sensors and 8 current meter moorings provide a characterization of the barotropic tides over the north carolina continental shelf between chesapeake bay and cape hatteras the largest tidal constituents in this region are the m2 sea level amplitude 47 cm n2 11 cm and s2 10 cm semidiurnal tides and the k1 p1 7 cm and o1 5 cm diurnal tides the barotropic tidal currents are small less than 3 cm s21 except for the m2 current which reaches 10 cm s21 at mid shelf cross shelf currents increase linearly from approximately zero near the coast to a maximum over the mid and outer shelf alongshelf currents are nonzero near the coast and increase to roughly twice the coastal value over the mid and outer shelf while bottom friction is weak over most of the shelf in water depths of less than 10 m bottom friction results in a rapid phase decrease toward the coast in the semidiurnal alongshelf velocities this phase difference is not observed in the k1 p1 alongshelf flow possibly because diurnal wind forcing causes an opposing phase increase toward the coast alongshelf variations in tidal amplitudes and phases near the coast are much larger than expected based on variations along the shelf break inferred from basin scale altimeter estimates the shelf width in this region increases from 25 to 100 km over an alongshelf distance of about 150 km results from an analytic flat bottom two dimensional model indicate that widening of the shelf toward the north causes the observed alongshelf increase in the semidiurnal amplitude and phase but does not explain alongshelf variations in the weaker diurnal constituents

a noachian source region for the black beauty meteorite and a source lithology for mars surface hydrated dust the martian surface is covered by a fine layer of oxidized dust responsible for its red color in the visible spectral range bibring et al 2006 morris et al 2006 in the near infrared the strongest spectral feature is located between 2 6 and 3 6 m and is ubiquitously observed on the planet jouglet et al 2007 milliken et al 2007 although this absorption has been studied for many decades its exact attribution and its geological and climatic implications remain debated we present new lines of evidence from laboratory experiments orbital and landed missions data and characterization of the unique martian meteorite nwa 7533 all converging toward the prominent role of hydroxylated ferric minerals martian breccias so called black beauty meteorite nwa7034 and its paired stones nwa7533 and nwa 7455 are unique pieces of the martian surface that display abundant evidence of aqueous alteration that occurred on their parent planet agee et al 2013 these dark stones are also unique in the fact that they arose from a near surface level in the noachian southern hemisphere humayun et al 2013 we used ir spectroscopy fe xanes and petrography to identify the mineral hosts of hydrogen in nwa 7533 and compare them with observations of the martian surface and results of laboratory experiments the spectrum of nwa 7533 does not show mafic mineral absorptions making its definite identification difficult through nir remote sensing mapping however its spectra are virtually consistent with a large fraction of the martian highlands abundant nwa 7034 7533 and paired samples lithologies might abound on mars and might play a role in the dust production mechanism

modeling the thermal and physical evolution of mount sharp s sedimentary rocks gale crater mars implications for diagenesis on the msl curiosity rover traverse gale crater the mars science laboratory msl landing site contains a central mound named aeolis mons informally mount sharp that preserves 5 km of sedimentary stratigraphy formation scenarios include 1 complete filling of gale crater followed by partial sediment removal or 2 building of a central deposit with morphology controlled by slope winds and only incomplete sedimentary fill here we model temperature time paths for both scenarios compare results with analyses provided by msl curiosity and provide scenario dependent predictions of temperatures of diagenesis along curiosity s future traverse the effects of variable sediment thermal conductivity and historical heat flows are also discussed modeled erosion and deposition rates are 5 37 m yr consistent with previously published estimates from other mars locations the occurrence and spatial patterns of diagenesis depend on sedimentation scenario and surface paleotemperature for 1 temperatures experienced by sediments decrease monotonically along the traverse and up mount sharp stratigraphy whereas for 2 temperatures increase along the traverse reaching maximum temperatures higher up in mount sharp s lower units if early mars surface temperatures were similar to modern mars mean 50 c only select locations under select scenarios permit diagenetic fluids in contrast if early mars surface temperatures averaged 0 c or brines had lowered freezing points diagenesis is predicted in most locations with temperatures 225 c comparing our predictions with future msl results on diagenetic textures secondary mineral assemblages and their spatial variability will constrain past heat flow mount sharp s formation processes the availability of liquid water on early mars and sediment organic preservation potential

mass flux and undertow in a surf zone abstract the mass of water carried shoreward by the breaking waves in a surf zone will in a two dimensional situation be compensated by a seaward return flow the undertow it is shown that the undertow is driven by the local difference between radiation stress and the set up pressure gradient which only balance each other in average over the depth turbulent shear stresses are required to maintain a steady situation comparison with measurements confirms the theoretical results

curiosity at gale crater mars characterization and analysis of the rocknest sand shadow the rocknest aeolian deposit is similar to aeolian features analyzed by the mars exploration rovers mers spirit and opportunity the fraction of sand 150 micrometers in size contains 55 crystalline material consistent with a basaltic heritage and 45 x ray amorphous material the amorphous component of rocknest is iron rich and silicon poor and is the host of the volatiles water oxygen sulfur dioxide carbon dioxide and chlorine detected by the sample analysis at mars instrument and of the fine grained nanophase oxide component first described from basaltic soils analyzed by mers the similarity between soils and aeolian materials analyzed at gusev crater meridiani planum and gale crater implies locally sourced globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations

discovery of jarosite within the mawrth vallis region of mars implications for the geologic history of the region abstract analysis of visible to near infrared reflectance data from the mro crism hyperspectral imager has revealed the presence of an ovoid shaped landform approximately 3 by 5 km in size within the layered terrains surrounding the mawrth vallis outflow channel this feature has spectral absorption features consistent with the presence of the ferric sulfate mineral jarosite specifically a k bearing jarosite kfe3 so4 2 oh 6 terrestrial jarosite is formed through the oxidation of iron sulfides in acidic environments or from basaltic precursor minerals with the addition of sulfur previously identified phyllosilicates in the mawrth vallis layered terrains include a basal sequence of layers containing fe mg smectites and an upper set of layers of hydrated silica and aluminous phyllosilicates in terms of its fine scale morphology revealed by mro hirise imagery the jarosite bearing unit has fracture patterns very similar to that observed in fe mg smectite bearing layers but unlike that observed in the al bearing phyllosilicate unit the ovoid shaped landform is situated in an east west bowl shaped depression superposed on a north sloping surface spectra of the ovoid shaped jarosite bearing landform also display an anomalously high 600 nm shoulder which may be consistent with the presence of goethite and a 1 92 m absorption which could indicate the presence of ferrihydrite goethite jarosite and ferrihydrite can be co precipitated and or form through transformation of schwertmannite both processes generally occurring under low ph conditions ph 2 4 to date this location appears to be unique in the mawrth vallis region and could represent precipitation of jarosite in acidic sulfur rich ponded water during the waning stages of drying

chemistry and mineralogy of outcrops at meridiani planum analyses of outcrops created by the impact craters endurance fram and eagle reveal the broad lateral continuity of chemical sediments at the meridiani planum exploration site on mars approximately ten mineralogical components are implied in these salt rich silicic sediments from measurements by instruments on the opportunity rover compositional trends in an apparently intact vertical stratigraphic sequence at the karatepe west ingress point at endurance crater are consistent with non uniform deposition or with subsequent migration of mobile salt components dominated by sulfates of magnesium striking variations in cl and enrichments of br combined with diversity in sulfate species provide further evidence of episodes during which temperatures ph and water to rock ratios underwent significant change to first order the sedimentary sequence examined to date is consistent with a uniform reference composition modified by movement of major sulfates upward and of minor chlorides downward this reference composition has similarities to martian soils supplemented by sulfate anion and the alteration products of mafic igneous minerals lesser cementation in lower stratigraphic units is reflected in decreased energies for grinding with the rock abrasion tool survival of soluble salts in exposed outcrop is most easily explained by absence of episodes of liquid h2o in this region since the time of crater formation

stability and fate of ferrihydrite during episodes of water rock interactions on early mars an experimental approach the presence on the surface of mars of ferrihydrite a nanocrystalline iron oxide species has long been suspected from spectroscopic observations and is further suggested by recent results from the mer mars exploration rovers and msl mars science laboratory robotic missions however because ferrihydrite is a metastable species in terrestrial environments it is unclear what would have been its fate during episodes of water rock interactions that are known to have occurred at the landing sites of the above mentioned robotic missions accordingly the laboratory experiments presented in this paper investigate the recrystallization of ferrihydrite under various conditions applicable to early mars these included low temperature experiments one month at 40 c at ph ranging from circum neutral to strongly acidic and high temperature experiments 8 days at 150 c at circum neutral ph the effect of mixtures with other mineral phases namely amorphous silica and olivine was also tested results obtained at low temperature are at odds with some earlier studies and suggest that ferrihydrite behaves differently in rock dominated conditions compared to water dominated conditions the co existence of amorphous silica favored the formation of jarosite under low temperature acidic conditions whereas a sample of pure ferrihydrite produced only goethite under the same conditions at high temperature ferrihydrite converted into hematite in all samples but the ferrihydrite silica mixture led to hematite with much broader diffraction peaks than other experiments indicating an inhibiting effect of dissolved silica on the recrystallization process the implications of these results for the aqueous history of early mars are discussed

an asymptotic theory for the interaction of waves and currents in coastal waters a multi scale asymptotic theory is derived for the evolution and interaction of currents and surface gravity waves in water of finite depth under conditions typical of coastal shelf waters outside the surf zone the theory provides a practical and useful model with which wave current coupling may be explored without the necessity of resolving features of the flow on space and time scales of the primary gravity wave oscillations the essential nature of the dynamical interaction is currents modulating the slowly evolving phase of the wave field and waves providing both phase averaged forcing of long infra gravity waves and wave averaged vortex and bernoulli head forces and hydrostatic static set up for the low frequency current and sea level evolution equations analogous relations are derived for wave averaged material tracers and density stratification that include advection by horizontal stokes drift and by a vertical stokes pseudo velocity that is the incompressible companion to the horizontal stokes velocity illustrative solutions are analysed for the special case of depth independent currents and tracers associated with an incident surface wave field and a vortex with o 1 rossby number above continental shelf topography

calcium sulfate veins characterized by chemcam curiosity at gale crater mars the curiosity rover has analyzed abundant light toned fracture fill material within the yellowknife bay sedimentary deposits the chemcam instrument coupled with mastcam and chemcam remote micro imager images was able to demonstrate that these fracture fills consist of calcium sulfate veins many of which appear to be hydrated at a level expected for gypsum and bassanite anhydrite is locally present and is found in a location characterized by a nodular texture an intricate assemblage of veins crosses the sediments which were likely formed by precipitation from fluids circulating through fractures the presence of veins throughout the entire similar to 5 m thick yellowknife bay sediments suggests that this process occurred well after sedimentation and cementation lithification of those sediments the sulfur rich fluids may have originated in previously precipitated sulfate rich layers either before the deposition of the sheepbed mudstones or from unrelated units such as the sulfates at the base of mount sharp the occurrence of these veins after the episodes of deposition of fluvial sediments at the surface suggests persistent aqueous activity in relatively nonacidic conditions

ferrian saponite from the santa monica mountains california u s a earth characterization as an analog for clay minerals on mars with application to yellowknife bay in gale crater ferrian saponite from the eastern santa monica mountain near griffith park los angeles california was investigated as a mineralogical analog to smectites discovered on mars by the chemin x ray diffraction instrument onboard the mars science laboratory msl rover the martian clay minerals occur in sediment of basaltic composition and have 02 l diffraction bands peaking at 4 59 a consistent with tri octahedral smectites the griffith saponite occurs in basalts as pseudomorphs after olivine and mesostasis glass and as fillings of vesicles and cracks and has 02 l diffraction bands at that same position we obtained chemical compositions by electron microprobe x ray diffraction patterns with a lab version of the chemin instrument mossbauer spectra and visible and near ir reflectance vnir spectra on several samples from that locality the griffith saponite is magnesian mg mg fe 65 70 lacks tetrahedral fe 3 and octahedral al 3 and has fe 3 fe from 64 to 93 its chemical composition is consistent with a fully tri octahedral smectite but the abundance of fe 3 gives a nominal excess charge of 1 to 2 per formula unit the excess charge is likely compensated by substitution of o 2 for oh causing distortion of octahedral sites as inferred from mossbauer spectra we hypothesize that the griffith saponite was initially deposited with all its iron as fe 2 and was oxidized later x ray diffraction shows a sharp 001 peak at 15 a 00 l peaks and a 02 l diffraction band at the same position 4 59 a and shape as those of the martian samples indicating that the martian saponite is not fully oxidized vnir spectra of the griffith saponite show distinct absorptions at 1 40 1 90 2 30 2 32 and 2 40 m arising from h 2 o and hydroxyl groups in various settings the position of the 2 31 m spectral feature varies systematically with the redox state of the octahedrally coordinated fe this correlation may permit surface oxidation state to be inferred in some cases from vnir spectra of mars obtained from orbit and in any case ferrian saponite is a viable assignment for spectral detections in the range 2 30 2 32 m

momentum balances on the north carolina inner shelf four months of moored current pressure temperature conductivity wave and wind observations on the north carolina shelf indicate three dynamically distinct regions the surf zone the inner shelf between the surf zone and the 13 m isobath and the midshelf in the surf zone the along shelf momentum balance is between the cross shelf gradient of the wave radiation stress and the bottom stress the linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone on the inner shelf the along shelf momentum balance is also frictional the along shelf wind stress and pressure gradient are balanced by bottom stress in the cross shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the coriolis force geostrophy and wave setdown from shoaling unbroken surface gravity waves at midshelf the along shelf momentum balance is less frictional and hence flow accelerations are important the cross shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown the cross shelf density gradient is in thermal wind balance with the vertical shear in the along shelf flow in depths as shallow as 10 m the dominant along shelf momentum balances provide a simple estimate of the depth averaged along shelf current in terms of the measured forcing i e wind stress wave radiation stress divergence and along shelf pressure gradient that reproduces accurately the observed cross shelf variation of the depth averaged along shelf current between the surf zone and midshelf

mossbauer mineralogy of rock soil and dust at gusev crater mars spirit s journey through weakly altered olivine basalt on the plains and pervasively altered basalt in the columbia hills 1 the mossbauer spectrometer on spirit measured the oxidation state of fe identified fe bearing phases and measured relative abundances of fe among those phases for surface materials on the plains and in the columbia hills of gusev crater eight fe bearing phases were identified olivine pyroxene ilmenite magnetite nanophase ferric oxide npox hematite goethite and a fe3 sulfate adirondack basaltic rocks on the plains are nearly unaltered fe3 fet px and minor npox and magnetite columbia hills basaltic rocks are nearly unaltered peace and backstay moderately altered woolypatch wishstone and keystone and pervasively altered e g clovis uchben watchtower keel and paros with fe3 fet 0 6 0 9 fe from pyroxene is greater than fe from olivine ol sometimes absent and fe2 from ol px is 40 49 and 9 24 for moderately and pervasively altered materials respectively ilmenite fe from ilm 3 6 is present in backstay wishstone keystone and related rocks along with magnetite fe from mt 10 15 remaining fe is present as npox hematite and goethite in variable proportions clovis has the highest goethite content fe from gt 40 goethite feooh is mineralogical evidence for aqueous processes because it has structural hydroxide and is formed under aqueous conditions relatively unaltered basaltic soils fe3 fet 0 3 occur throughout gusev crater 60 80 fe from ol px 10 30 from npox and 10 from mt pasorobles soil in the columbia hills has a unique occurrence of high concentrations of fe3 sulfate 65 of fe magnetite is identified as a strongly magnetic phase in martian soil and dust

iron mineralogy and aqueous alteration from husband hill through home plate at gusev crater mars results from the mossbauer instrument on the spirit mars exploration rover 1 spirit s mossbauer mb instrument determined the fe mineralogy and oxidation state of 71 rocks and 43 soils during its exploration of the gusev plains and the columbia hills west spur husband hill haskin ridge northern inner basin and home plate on mars the plains are predominantly float rocks and soil derived from olivine basalts outcrops at west spur and on husband hill have experienced pervasive aqueous alteration as indicated by the presence of goethite olivine rich outcrops in a possible mafic ultramafic horizon are present on haskin ridge relatively unaltered basalt and olivine basalt float rocks occur at isolated locations throughout the columbia hills basalt and olivine basalt outcrops are found at and near home plate a putative hydrovolcanic structure at least three pyroxene compositions are indicated by mb data mb spectra of outcrops barnhill and torquas resemble palagonitic material and thus possible supergene aqueous alteration deposits of fe3 sulfate soil located at paso robles arad and tyrone are likely products of acid sulfate fumarolic and or hydrothermal activity possibly in connection with home plate volcanism hematite rich outcrops between home plate and tyrone e g montalva may also be products of this aqueous activity low water to rock ratios isochemical alteration are implied during palagonite goethite and hematite formation because bulk chemical compositions are basaltic so3 free basis high water to rock ratios leaching under acid sulfate conditions are implied for the high sio2 rock and soil in eastern valley and the float rock fuzzysmith which has possible pyrite marcasite as a hydrothermal alteration product

subinertial currents on the southern califoinia shelf abstract subinertial currents on the southern california shelf are investigated using observations from a current meter array deployed near san diego during the summer fall and winter of 1978 79 this region is characterized by weak winds order 1 2 m s 1 and thus other driving mechanisms for the subinertial currents may be important a simplified depth averaged longshore momentum equation consisting of a balance between current accelerations the adjusted sea level asl gradient and the wind and bottom stress is examined the asl gradient is estimated using sea level and atmospheric pressure observations separated by 350 km a linear parameterization of the bottom stress is used with a drag coefficient of 5 10 4 m s 1 during fall and winter the first order balance of terms in the longshore momentum equation over the inner shelf 15 m depth is between the wind and bottom stress over the outer shelf 60 m the primary balance is between the asl gradient and the bottom stress at midshelf 30 m bo

dynamics of a high energy dissipative surf zone vright l d guza r t and short a d 1982 dynamics of a high energy dissipative surf zone mar geol 45 41 62 pressure and horizontal current u v time series were measured at different positions across the inner 150 m of a wide 500 m surf zone of a microtidal high wave energy beach incident waves had average heights of 3 4 m with maxima of 5 m and periods of 12 to 15 sec bores of broken waves diminished in height at a nearly constant rate as they progressed across the surf zone the ratio of bore height h to local water depth h was everywhere less than 1 for even the highest bores and was on the order of 0 40 for the significant bores at incident wave frequencies rip circulation was weak or absent but a moderate longshore current was present shore normal flows were vertically segregated with strong net onshore flows prevailing just below the surface accompanied by weaker net seaward flows near the bed spectra of water surface oscillations as determined from pressure u and v reveal that most of the energy in the inner surf zone was at infragravity frequencies periods greater than 30 sec shoreward decay of wave energy at incident wave frequencies was accompanied by shoreward growth of infragravity energy near the beach the infragravity oscillations had heights on the order of 1 m cross spectra show that the infragravity oscillations were standing in the shore normal direction from the relative magnitudes of infragravity versus incident wave currents it is inferred that the surf beat may be an order of magnitude more important than incident waves to the transport of sediment in the inner surf zone

goethite and hematite in a climosequence in southern brazil and their application in classification of kaolinitic soils abstract the goethite hematite goethite ratio of 11 profiles of oxisols ultisols and inceptisols along a 600 km e w transect in s brazil varied systematically with climatic and soil factors the ratio increased with decreasing mean annual air temperature increasing excess moisture rainfall minus evapotranspiration increasing soil organic carbon and decreasing ph this is explained in light of the current concept of goethite and hematite formation in soils higher temperatures favor hematite whereas higher excess moisture higher organic carbon and lower ph favor goethite a basis is suggested for using goethite and hematite in the mineralogical classes at the family level of soil taxonomy

the origin and implications of clay minerals from yellowknife bay gale crater mars the mars science laboratory msl rover curiosity has documented a section of fluvio lacustrine strata at yellowknife bay ykb an embayment on the floor of gale crater approximately 500 m east of the bradbury landing site x ray diffraction xrd data and evolved gas analysis ega data from the chemin and sam instruments show that two powdered mudstone samples named john klein and cumberland drilled from the sheepbed member of this succession contain up to 20 wt clay minerals a trioctahedral smectite likely a ferrian saponite is the only clay mineral phase detected in these samples smectites of the two samples exhibit different 001 spacing under the low partial pressures of h2o inside the chemin instrument relative humidity 1 smectite interlayers in john klein collapsed sometime between clay mineral formation and the time of analysis to a basal spacing of 10 a but largely remain open in the cumberland sample with a basal spacing of 13 2 a partial intercalation of cumberland smectites by metal hydroxyl groups a common process in certain pedogenic and lacustrine settings on earth is our favored explanation for these differences the relatively low abundances of olivine and enriched levels of magnetite in the sheepbed mudstone when compared with regional basalt compositions derived from orbital data suggest that clay minerals formed with magnetite in situ via aqueous alteration of olivine mass balance calculations are permissive of such a reaction moreover the sheepbed mudstone mineral assemblage is consistent with minimal inputs of detrital clay minerals from the crater walls and rim early diagenetic fabrics suggest clay mineral formation prior to lithification thermodynamic modeling indicates that the production of authigenic magnetite and saponite at surficial temperatures requires a moderate supply of oxidants allowing circum neutral ph the kinetics of olivine alteration suggest the presence of fluids for thousands to hundreds of thousands of years mineralogical evidence of the persistence of benign aqueous conditions at ykb for extended periods indicates a potentially habitable environment where life could establish itself mediated oxidation of fe 2 in olivine to fe 3 in mag

observation of undertow and turbulence in a laboratory surf zone abstract undertow and turbulence in the surf zone have been studied in a wave flume for a spilling breaker and a plunging breaker fluid velocities across a 1 on 35 sloped false bottom were measured using a fiber optic laser doppler anemometer and wave decay and set up were measured using a capacitance wave gage the characteristics of mean flow and turbulence in spilling versus plunging breakers were studied the mean flow is the organized wave induced flow defined as the phase average of the instantaneous velocity while the turbulence is taken as the deviations from the phase average it was found that under the plunging breaker turbulence levels are much higher and vertical variations of undertow and turbulence intensity are much smaller in comparison with the spilling breaker it was also found that turbulent kinetic energy is transported seaward under the spilling breaker and landward under the plunging breaker by the mean flow the study indicates that there are fundamental differences in the dynamics of turbulence between spilling and plunging breakers which can be related to the processes of wave breaking and turbulence production it is suggested that the types of beach profile produced by storm and swell waves may be the results of different relationships between mean flow and turbulence in these waves

opaline silica in young deposits on mars high spatial and spectral resolution reflectance data acquired by the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism instrument reveal the presence of h 2o and sioh bearing phases on the martian surface the spectra are most consistent with opaline silica and glass altered to various degrees confirming predictions based on geochernicall experiments and models that amorphous silica should be a common weathering product of the basaltic martian crust these materials are associated with hydrated fe sulfates including h 3o bearing jarosite and are found in finely stratified deposits exposed on the floor of and on the plains surrounding the valles marineris canyon system stratigraphic relationships place the formation age of these deposits in the late hesperian or possibly the amazonian implying that aqueous alteration continued to be an important and regionally extensive process on mars during that time

nature and origin of matrix in the unique type 3 chondrite kakangari the mineralogy and textural characteristics of fine grained matrix 1 m in the unique type 3 chondrite kakangari have been investigated by high resolution and analytical electron microscopy the matrix contains a diverse primary mineralogy dominated by enstatite and olivine with lesser amounts of albite anorthite cr spinel troilite and fe ni metal texturally the matrix is characterized by irregular clusters or aggregates of crystals which constitute distinct structural units within the matrix 2 8 m in diameter and frequently have distinct mineralogies enstatite in these clusters is an intergrowth of monoclinic and orthorhombic polymorphs with a microstructure indicative of an origin by high temperature inversion from protopyroxene during rapid cooling corroded inclusions of olivine frequently occur within enstatite suggesting that enstatite formed by reaction of olivine with a silica polymorph at high temperature the matrix mineralogy of kakangari formed by high temperature annealing and reaction of fine grained dust which probably consisted of amorphous or partially crystalline presolar or solar nebula condensates the constituents of kakangari matrix cannot therefore be considered as pristine unprocessed solar system material annealing probably occurred in a thermal event similar to that which formed the chondrules but the microstructures and textures of the matrix components suggest that melting did not occur chondrules in kakangari were probably formed from identical precursors to the matrix but reached temperatures sufficiently high to produce melting despite this high temperature processing the mineralogical clusters in the matrix preserve mineralogical and hence chemical heterogeneities in the precursor materials similar to those observed in interplanetary dust particles

undertow over a barred beach the spatial distribution of the mean cross shore flow undertow over a barred beach is examined with field data obtained on three energetic wave days during the duck94 experiment the vertical structure of the undertow is modeled using a turbulent eddy viscosity closure and includes the important effects of wave breaking described using the roller concept and convective acceleration of the current other than a more realistic description of observed turbulence variations a depth dependent eddy viscosity compared with a constant does not improve the agreement between predicted and observed undertow profiles the effect of using different boundary conditions is investigated by extending the formulations of stive and wind 1986 and svendsen et al 1987 to include random waves by ensemble averaging over the wave height distribution the contribution of breaking wave rollers to the surface mass flux can be of the same order or greater than the contribution associated with the organized wave motion the largest discrepancies between model predictions and observations occur over the sandbar where the mass transport of the breaking waves appears to be underestimated

mineralogy provenance and diagenesis of a potassic basaltic sandstone on mars chemin x ray diffraction of the windjana sample kimberley area gale crater the windjana drill sample a sandstone of the dillinger member kimberley formation gale crater mars was analyzed by chemin x ray diffraction xrd in the msl curiosity rover from rietveld refinements of its xrd pattern windjana contains the following sanidine 21 weight or95 augite 20 magnetite 12 pigeonite olivine plagioclase amorphous and smectitic material 25 and percent levels of others including ilmenite fluorapatite and bassanite from mass balance on the alpha proton x ray spectrometer apxs chemical analysis the amorphous material is fe rich with nearly no other cations like ferrihydrite the windjana sample shows little alteration and was likely cemented by its magnetite and ferrihydrite from chemcam laser induced breakdown spectrometer libs chemical analyses windjana is representative of the dillinger and mount remarkable members of the kimberley formation libs data suggest that the kimberley sediments include at least three chemical components the most k rich targets have 5 6 k2o 1 8 times that of windjana implying a sediment component with 40 sanidine e g a trachyte a second component is rich in mafic minerals with little feldspar like a shergottite a third component is richer in plagioclase and in na2o and is likely to be basaltic the k rich sediment component is consistent with apxs and chemcam observations of k rich rocks elsewhere in gale crater the source of this sediment component was likely volcanic the presence of sediment from many igneous sources in concert with curiosity s identifications of other igneous materials e g mugearite implies that the northern rim of gale crater exposes a diverse igneous complex at least as diverse as that found in similar age terranes on earth

evaluating the role of sulfide weathering in the formation of sulfates or carbonates on mars orbital and landed missions to mars have revealed complex sulfate and fe oxide bearing mineralogical assemblages which have been interpreted as the result of a late planet wide acidic period due to large so2 emissions however this global scenario does not explain the recent discovery of hesperian and noachian aged carbonates in several regions because they should have been dissolved by the acidic conditions nor the restriction of sulfate occurrences in preferential regions here we present the results of a 4 year long experimental study designed to test the impact of fe sulfides pyrrhotite fe0 9s on the weathering of basaltic silicates olivine clino and orthopyroxene under an early martian like co2 rich atmosphere our weathered silicate sulfide mixtures showed complex parageneses containing elemental sulfur hydrated sulfates gypsum hexahydrite jarosite and fe oxy hydroxides olivine only samples produced nesquehonite an mg carbonate precursor of hydromagnesite and magnesite these secondary phases are similar to those observed in the martian sulfate and carbonate bearing deposits therefore we propose a geochemical model in which on the one hand martian sulfates mainly formed from weathering of sulfide enriched basalts producing locally acidic environments and on the other hand carbonates were preserved and could even have formed in regions initially devoid of sulfides thereby resolving the apparent paradox arising from the possible coeval formation of the two types of minerals these results raise doubts on the need for a global acidic event to produce the sulfate bearing assemblages suggest that regional sequestration of sulfate deposits is due to regional differences in sulfide content of the bedrock and pave the way for reevaluating the likelihood that early sediments preserved biosignatures from the earliest times

magnitude and cross shore distribution of bed return flow measured on natural beaches abstract field measurements of cross shore currents 0 25 m from the bed were made on two natural beaches under a range of incident wave conditions the results indicated the presence of a relatively strong offshore directed mean current both within and seaward of the surf zone typical velocities within the surf zone were of the order of 0 2 0 3 m s this bed return flow or undertow represents a mass conservation response returning water seaward that was initially transported onshore in the upper water column primarily above the trough of the incident waves the measurements demonstrated that the bed return flow velocity increases with the incident wave height in addition the crossshore distribution of the bed return flow is characterised by a mid surf zone maximum which exhibits a strong decrease in velocity towards the shoreline and a more gradual decay in the offshore direction several bed return flow models based on mass continuity were formulated to predict the cross shore distribution of the bed return flow under an irregular wave field and were compared with the field data best agreement was obtained using shallow water linear wave theory after including the mass transport associated with unbroken waves the contribution of the unbroken waves enables net offshore directed bottom currents to persist outside the region of breaking waves providing a mechanism other than rip currents to transport sediment offshore beyond the surf zone

mineralogy of the light toned outcrop at meridiani planum as seen by the miniature thermal emission spectrometer and implications for its formation 1 analysis of miniature thermal emission spectrometer mini tes data has led to the recovery of a pure end member spectral shape related to the light toned outcrop observed at meridiani planum data from the mer mossbauer spectrometer apxs and previous mini tes measurements were used to constrain a spectral library used to determine the mineralogy of the outcrop from this spectral shape linear deconvolution of the outcrop spectral shape suggests that it is composed primarily of al rich opaline silica mg ca and fe bearing sulfates plagioclase feldspar nontronite and hematite conversion of modeled mineralogy to chemistry shows good agreement with the chemical composition of the outcrops determined by apxs details of the analysis procedure and implications for the formation of the outcrop are discussed along with terrestrial analogs of the ancient environment at meridiani

athena mars rover science investigation 1 each mars exploration rover carries an integrated suite of scientific instruments and tools called the athena science payload the primary objective of the athena science investigation is to explore two sites on the martian surface where water may once have been present and to assess past environmental conditions at those sites and their suitability for life the remote sensing portion of the payload uses a mast called the pancam mast assembly pma that provides pointing for two instruments the panoramic camera pancam and the miniature thermal emission spectrometer mini tes pancam provides high resolution color stereo imaging while mini tes provides spectral cubes at mid infrared wavelengths for in situ study a five degree of freedom arm called the instrument deployment device idd carries four more tools a microscopic imager mi for close up imaging an alpha particle x ray spectrometer apxs for elemental chemistry a mossbauer spectrometer mb for the mineralogy of fe bearing materials and a rock abrasion tool rat for removing dusty and weathered surfaces and exposing fresh rock underneath the payload also includes magnets that allow the instruments to study the composition of magnetic martian materials all of the athena instruments have undergone extensive calibration both individually and using a set of geologic reference materials that are being measured with all the instruments using a mer like rover and payload in a number of field settings we have devised operations processes that will enable us to use the mer rovers to formulate and test scientific hypotheses concerning past environmental conditions and habitability at the landing sites

vertical flow structure during sandy duck observations and modeling abstract observations of the vertical distribution of time averaged cross shore and alongshore flows during the sandy duck field experiment are compared with model predictions to assess the parameters governing the flow behaviour the measurements were obtained with a vertical stack of eight two component current meters with the lowest and highest sensor at respectively o 0 1 and o 2 7 m above the bed observations under breaking wave conditions within the surfzone show that the maximum return flow velocities occur in the lower part of the water column consistent with laboratory observations under non breaking conditions outside the surfzone the maximum return flow velocities are observed closer to the water surface again in line with laboratory results analogous to previous observations the measured longshore current velocity profiles are logarithmic under non breaking conditions and become more depth uniform under breaking conditions the model description of the vertical structure of the flow includes the presence of wind stresses wave stresses pressure gradients turbulent eddy viscosity and a wave boundary layer the model utilizes parabolic shape functions to describe the vertical distribution of the turbulent eddy viscosity in the middle layer and within the bottom boundary layer eddy viscosity is enhanced in regions where turbulence is produced i e near the surface in the case of breaking waves and within the bottom boundary layer estimates of the wave breaking induced turbulent eddy viscosity and bottom friction are obtained by minimizing the model measurement discrepancies predictions utilizing calibrated expressions for both the turbulent eddy viscosity and bottom friction are in general agreement with the observations provided the wave transformation and associated mass flux are modeled correctly and a parabolic eddy viscosity distribution is used using a piecewise constant eddy viscosity distribution generally results in a degrading of the agreement between measurements and model results

observations and a model of undertow over the inner continental shelf abstract onshore volume transport stokes drift due to surface gravity waves propagating toward the beach can result in a compensating eulerian offshore flow in the surf zone referred to as undertow observed offshore flows indicate that wave driven undertow extends well offshore of the surf zone over the inner shelves of martha s vineyard massachusetts and north carolina theoretical estimates of the wave driven offshore transport from linear wave theory and observed wave characteristics account for 50 or more of the observed offshore transport variance in water depths between 5 and 12 m and reproduce the observed dependence on wave height and water depth during weak winds wave driven cross shelf velocity profiles over the inner shelf have maximum offshore flow 1 6 cm s 1 and vertical shear near the surface and weak flow and shear in the lower half of the water column the observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the su

acid sulfate weathering of synthetic martian basalt the acid fog model revisited the acid fog model has received considerable attention as a model of soil formation on mars previous evaluations of this model have focused on experimental weathering of terrestrial basalt samples however these samples differ significantly from what now is thought to be typical of martian basalt the acid fog model is tested here using synthetic basaltic analogs derived from mars pathfinder soil and rock compositions reaction of synthetic basalt with various acidic solutions and subsequent evaporation has led to the formation of several putative secondary mineral phases many of these phases were not produced in prior experimental studies aimed at aqueous interactions on mars of these alteration phases mg fe ca and al sulfates were identified in addition secondary ferric oxide phases formed via rapid fe oxidation under relatively high ph levels buffered by basalt dissolution amorphous silica is a ubiquitous product in these experiments and has formed by precipitation from solution and by the dissolution of minerals and glasses leaving behind leached surface layers composed of residual silica the secondary products formed in these experiments demonstrate the importance of primary mineralogy when testing models of aqueous interactions on mars new constraints are placed on both the reactivity of primary basalt and the secondary mineralogy present at the martian surface copyright 2004 by the american geophysical union

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

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

matrix mineralogy of the orgueil ci carbonaceous chondrite a petrographic and transmission electron microscopic study of the orgueil ci carbonaceous chondrite shows that the matrix consists mainly of fe bearing mg rich serpentine and smectite saponite as well as a poorly crystallized fe rich material that contains minor variable s and ni the fe rich material is probably ferrihydrite a ferric hydroxide the ferrihydrite occurs in small particles 80 a in diameter and the s and ni are probably adsorbed on its surfaces the serpentine and saponite occur in poorly crystallized fine crystallites fine phyllosilicates that are intimately associated with the ferrihydrite coarsely crystallized phyllosilicates coarse phyllosilicates occur in clusters relatively free of ferrihydrite the ferrihydrite is a major matrix constitutent and probably accounts for most of the fe3 as well as the superparamagnetic fraction in the orgueil matrix the textures suggest that the fine phyllosilicates resulted from alteration of the coarse phyllosilicates the alteration probably involved a substantial amount of water and coincided with the period of sulfate vein formation during the aqueous alteration magnetite grains disaggregated from framboids and fe ni sulfides were replaced by ferrihydrite simultaneously aqueous solutions reacted with the coarse phyllosilicates and precipitated ferrihydrite producing intimate pervasive mixtures with the fine phyllosilicates the matrix mineralogy of the orgueil chondrite suggests that orgueil experienced considerably different alteration conditions from the cm chondrites the mineralogical and petrological differences between ci and cm chondrites can not simply be explained as the result of different degrees of aqueous alteration

analyses of high iron sedimentary bedrock and diagenetic features observed with chemcam at vera rubin ridge gale crater mars calibration and characterization curiosity investigated a topographic rise named vera rubin ridge vrr in gale crater for which a distinct hematite like signature was observed from orbit however the chemcam and apxs instruments on board the rover did not record any significant iron enrichment in the bulk of the ridge compared to previous terrains for this study we have re verified chemcam iron calibration at moderate abundances and developed more accurate calibrations at high iron abundances using iron oxide mixtures in a basaltic matrix in order to complete the chemcam calibration database the high iron calibration was first applied to the analysis of dark toned diagenetic features encountered at several locations on vrr which showed that their chemical compositions are close to pure anhydrous iron oxides then we tracked iron abundances in the vrr bedrock and demonstrated that although there is no overall iron enrichment in the bulk of the ridge 21 2 1 8 wt feo t compared to underlying terrains the iron content is more variable in its upper section with areas of enhanced iron abundances in the bedrock up to 26 6 0 85 wt feo t since the observed variability in iron abundances does not conform to the stratigraphy the involvement of diagenetic fluid circulation was likely an in depth chemical study of these fe rich rocks reveals that spatial gradients in redox potential eh may have driven iron mobility and reactions that precipitated and accumulated iron oxides we hypothesize that slightly reducing fluids were probably involved in transporting ferrous iron mobile fe could have precipitated as iron oxides in more oxidizing conditions

the inner shelf response to wind driven upwelling and downwelling abstract a two dimensional numerical model is used to study the response to upwelling and downwelling favorable winds on a shelf with a strong pycnocline during upwelling or downwelling the pycnocline intersects the surface or bottom forming a front that moves offshore the characteristics of the front and of the inner shelf inshore of the front are quite different for upwelling and downwelling for a constant wind stress the upwelling front moves offshore at roughly a constant rate while the offshore displacement of the downwelling front scales as t because the thickness of the bottom layer increases as the front moves offshore the geostrophic alongshelf transport in the front is larger during downwelling than upwelling for the same wind stress magnitude because the geostrophic shear is near the bottom in downwelling as opposed to near the surface in upwelling during upwelling weak stratification is maintained over the inner shelf by the onshore flux of denser near bottom water this weak stratif

constraints on abundance composition and nature of x ray amorphous components of soils and rocks at gale crater mars x ray diffraction patterns of the three samples analyzed by curiosity s chemistry and mineralogy chemin instrument during the first year of the mars science laboratory mission the rocknest sand and the john klein and cumberland drill fines both extracted from the sheepbed mudstone show evidence for a significant amorphous component of unclear origin we developed a mass balance calculation program that determines the range of possible chemical compositions of the crystalline and amorphous components of these samples within the uncertainties of mineral abundances derived from chemin data in turn the chemistry constrains the minimum abundance of amorphous component required to have realistic compositions all oxides 0 wt 21 22 wt for rocknest and 15 20 wt for cumberland in good agreement with estimates derived from the diffraction patterns 27 and 31 wt respectively despite obvious differences between the rocknest sand and the sheepbed mudstone the amorphous components of the two sites are chemically very similar having comparable concentrations of sio2 tio2 al2o3 cr2o3 feot cao na2o k2o and p2o5 mgo tends to be lower in rocknest although it may also be comparable between the two samples depending on the exact composition of the smectite in sheepbed the only unambiguous difference is the so3 content which is always higher in rocknest the observed similarity suggests that the two amorphous components share a common origin or formation process the individual phases possibly present within the amorphous components include volcanic or impact glass hisingerite or silica ferrihydrite amorphous sulfates or adsorbed so42 and nanophase ferric oxides

comparative planetary mineralogy implications of martian and terrestrial jarosite a crystal chemical perspective abstract the importance of the discovery of jarosite at the meridiani planum region of mars is discussed terrestrial studies demonstrate that jarosite requires a unique environment for its formation crystallizing from highly acidic ph 2 that reacted with aqueous solutions in shallow aquifers or on the martian surface this interaction forms both h 2 so 4 and h 2 s a martian oxidant must be identified to both oxidize h 2 s to produce the required acidity of the fluid and to oxidize fe 2 to fe 3 we suggest that reactions involving both sulfur and the reduction of co 2 to co may provide part of the answer the jarosite crystal structure is truly remarkable in terms of its tolerance for the substitution of a large number of different cations with different ionic radii and charges the structure accommodates hydrogen oxygen and sulfur the stable isotope systematics of which are strong recorders of low temperature fluid rock atmosphere interactions jarosite has been proven to be a robust chronometer for ar ar and k ar dating techniques and there is every reason to believe that u pb rb sr and nd sm techniques for older jarosite from mars will also be robust although the discovery of jarosite on mars alone with no other analytical measurements on the phase has given us insights to martian surficial processes the true power of jarosite can not be exploited until jarosite is sampled and returned from mars mars sample return is a long way off but until then we should be vigilant about examining martian meteorites for alteration assemblages that contain jarosite a suite of jarosite samples representing a significant time span on mars may hold the key to reading the record of martian atmospheric evolution

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

inventory of h2o in the ancient martian regolith from northwest africa 7034 the important role of fe oxides water rich martian regolith breccia northwest africa nwa 7034 was analyzed by fourier transform infrared spectroscopy and transmission electron microscopy to determine the inventory and phase distribution of h2o used herein to refer to both molecular h2o and oh structural components in hydrous minerals hydrous fe oxide phases hydromaghemite and an unidentified nanocrystalline fe bearing oxide phase observed with hydromaghemite and phyllosilicates saponite were identified as the primary mineralogic hosts for h2o with a minor contribution from cl rich apatite based on mass balance calculations and modal abundances of minerals constrained by powder x ray diffraction and petrography we can account for the entire 6000 ppm h2o measured in bulk rock analyses of nwa 7034 this h2o is distributed evenly between hydrous fe rich oxides and phyllosilicates indicating that fe oxides could be as important as phyllosilicates for h2o storage in martian surface material

role of biological soil crust cover in bioweathering and protection of sandstones in a semi arid landscape torrollones de gabarda huesca spain sandstone structural landscapes in the semi arid torrollones de gabarda area province of huesca ne spain are often covered by a well developed biological soil crust of lichens mosses and cyanobacteria and black coatings on vertical surfaces by using scanning electron microscopy with backscattered detector imaging the biological soil crust studied evidenced high activity in the sandstone crust interface processes such as physical disintegration etching and dwelling as well as biomineralization by calcium oxalate and xation of mineral particles by extracellular polymeric substances were observed on the horizontal sandstone surfaces these processes may cause the occurrence of gnammas and the development of a protective coating that favours intense aking when the crust is disturbed on the sandstone cliffs columnar and tafoni weathering development is clearly guided by the protective action of the biological soil crust these qualitative observations are important to develop methodologies to address their quantitative importance in geomorphological processes in semi arid landscapes copyright 2004 john wiley sons ltd

the reflectance spectra of opal a 0 5 25 μm from the taupo volcanic zone spectra that may identify hydrothermal systems on planetary surfaces 1 opal a the main component of siliceous sinters in many terrestrial hydrothermal systems is a hydrated silicate that commonly incorporates silicified microorganisms the detection of opal a on the surface of mars therefore may carry important implications in the search for extraterrestrial life sinters from the discharge apron of ohaaki pool north island new zealand yielded reflectance spectra wavelengths between 0 5 25 m that indicate the presence of absorbed water trapped water and silanol in opal a two classes 1 and 2 of reflectance spectra were detected between the wavelengths of 6 13 m the class 1 spectrum is similar to existing opal spectra and was collected from well consolidated samples that had low porosity the class 2 spectrum is unique when compared to the spectra of other silica polymorphs and was collected from poorly consolidated samples that had high porosity

mineralogy at meridiani planum from the mini tes experiment on the opportunity rover the miniature thermal emission spectrometer mini tes on opportunity investigated the mineral abundances and compositions of outcrops rocks and soils at meridiani planum coarse crystalline hematite and olivine rich basaltic sands were observed as predicted from orbital tes spectroscopy outcrops of aqueous origin are composed of 15 to 35 by volume magnesium and calcium sulfates a high silica component modeled as a combination of glass feldspar and sheet silicates 20 to 30 and hematite only minor jarosite is identified in mini tes spectra mini tes spectra show only a hematite signature in the millimeter sized spherules basaltic materials have more plagioclase than pyroxene contain olivine and are similar in inferred mineral composition to basalt mapped from orbit bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites bright wind streak material matches global dust waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering

elemental geochemistry of sedimentary rocks at yellowknife bay gale crater mars sedimentary rocks examined by the curiosity rover at yellowknife bay mars were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts no evidence of chemical weathering is preserved indicating arid possibly cold paleoclimates and rapid erosion and deposition the absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low temperature circumneutral ph rock dominated aqueous conditions analyses of diagenetic features including concretions raised ridges and fractures at high spatial resolution indicate that they are composed of iron and halogen rich components magnesium iron chlorine rich components and hydrated calcium sulfates respectively composition of a cross cutting dike like feature is consistent with sedimentary intrusion the geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of mars

silicic volcanism on mars evidenced by tridymite in high sio2 sedimentary rock at gale crater tridymite a low pressure high temperature 870 c sio2 polymorph was detected in a drill sample of laminated mudstone buckskin at marias pass in gale crater mars by the chemistry and mineralogy x ray diffraction instrument onboard the mars science laboratory rover curiosity the tridymitic mudstone has 40 wt crystalline and 60 wt x ray amorphous material and a bulk composition with 74 wt sio2 alpha particle x ray spectrometer analysis plagioclase 17 wt of bulk sample tridymite 14 wt sanidine 3 wt cation deficient magnetite 3 wt cristobalite 2 wt and anhydrite 1 wt are the mudstone crystalline minerals amorphous material is silica rich 39 wt opal a and or high sio2 glass and opal ct volatile bearing 16 wt mixed cation sulfates phosphates and chlorides perchlorates chlorates and has minor tio2 and fe2o3t oxides 5 wt rietveld refinement yielded a monoclinic structural model for a well crystalline tridymite consistent with high formation temperatures terrestrial tridymite is commonly associated with silicic volcanism and detritus from such volcanism in a lake gale catchment environment can account for buckskin s tridymite cristobalite feldspar and any residual high sio2 glass these cogenetic detrital phases are possibly sourced from the gale crater wall rim central peak opaline silica could form during diagenesis from high sio2 glass as amorphous precipitated silica or as a residue of acidic leaching in the sediment source region or at marias pass the amorphous mixed cation salts and oxides and possibly the crystalline magnetite otherwise detrital are primary precipitates and or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions temperatures and acidities anhydrite is post lithification fracture vein fill

chemical alteration of fine grained sedimentary rocks at gale crater abstract from sol 750 to 1550 the curiosity rover documented 100 m thick stack of fine grained sedimentary rocks making up part of the murray formation at the base of mt sharp gale crater here we use data collected by the chemcam instrument to estimate the level of chemical weathering in these sedimentary rocks both the chemical index of alteration cia and the weathering index scale wis indicate a progressive increase in alteration up section reaching values of cia of 63 and wis of 25 the increase in cia and wis values is coupled with a decrease in calcium abundance suggesting partial dissolution of ca bearing minerals clinopyroxene and plagioclase mineralogy from the chemin x ray diffraction instrument indicates a decrease in mafic minerals compared with previously analyzed strata and a significant proportion of phyllosilicates consistent with this interpretation these observations suggest that the sediments were predominantly altered in an open system before or during their emplacement contrasting with the rock dominated conditions inferred in sedimentary deposits analyzed at yellowknife bay

response of south carolina continental shelf waters to wind and gulf stream forcing during winter of 1986 the south carolina shelf water response to strong winter atmospheric forcing and gulf stream variations over the slope is discussed with the aid of a comprehensive set of atmospheric and oceanic observations made during project gale genesis of atlantic lows experiment a mixed response is observed to wind and gulf stream forcing subtidal variability of inner and middle shelf waters is primarily a barotropic forced response to coherent synoptic scale alongshore winds this response is not trapped over the shelf as has been found for other wide non equatorial shelves but is also significant at the shelf edge possibly because of the comparable widths of the shelf and slope the outer shelf also shows a significant gulf stream influence the gulf stream appears to have two preferred position modes either onshore with the stream flowing over the charleston bump and along the shelf break or offshore when the stream can be located up to 100 km east of the shelf break transition between the two states is rapid subtidal variability in the outer shelf is dominated by weekly period frontal eddies and meanders when the stream is in an onshore mode and by persistent southward flow when the stream is offshore this southward flow is produced by enlarged cyclonic eddies with upwelled centers located over the slope between the offshore stream and the shelf edge sometimes referred to as the charleston gyre positive mean alongshore sea level slopes at the shelf edge due to the persistence of the cyclonic gyres are geostrophically balanced by mean onshore flow which transports upwelled waters onto the shelf enhancing the biological productivity of the area relative to other regions of the south atlantic bight

most mars minerals in a nutshell various alteration phases formed in a single environment in noctis labyrinthus 1 a closed depression in the noctis labyrinthus region of mars at 10 4 s 98 6 w believed to have formed in the late hesperian holds an inner pit partially filled with several hundred meters of stratified material compact reconnaissance imaging spectrometer for mars crism visible near infrared reflectance data reveal signatures of numerous hydrated minerals including halloysite kaolinite fe smectite si oh bearing phases and fe sulfates polyhydrated monohydrated and hydroxylated types including jarosite we use crism data high resolution imagery hirise and hrsc high resolution stereo camera derived elevation to analyze the morphology composition and stratigraphy of these materials we propose an alteration sequence including formation of acid sulfate solutions from groundwater and magmatic sulfur which then locally altered the basaltic bedrock and layered sediments mainly deposited from volcanic tephra forming fe smectite and fe sulfates the mineral variability can mostly be explained by local variations in the ph of the altering fluids with original acidity being buffered by dissolution of primary minerals and by variable fluid input and evaporation and or freezing rates resulting in various water rock ratios this site shows local formation of almost all classes of minerals identified thus far on mars without invoking global conditions processes related to local volcanic activity and associated hydrothermalism were able to produce during an era in which the climate is believed to have been cold a large variety of hydrated minerals this study highlights the importance of the geological setting of hydrated minerals in the understanding of mars geologic and climatic evolution

mineralogy of a mudstone at yellowknife bay gale crater mars sedimentary rocks at yellowknife bay gale crater on mars include mudstone sampled by the curiosity rover the samples john klein and cumberland contain detrital basaltic minerals calcium sulfates iron oxide or hydroxides iron sulfides amorphous material and trioctahedral smectites the john klein smectite has basal spacing of similar to 10 angstroms indicating little interlayer hydration the cumberland smectite has basal spacing at both similar to 13 2 and similar to 10 angstroms the larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating h2o retention basaltic minerals in the mudstone are similar to those in nearby eolian deposits however the mudstone has far less fe forsterite possibly lost with formation of smectite plus magnetite late noachian early hesperian or younger age indicates that clay mineral formation on mars extended beyond noachian time

spectral and stratigraphic mapping of hydrated minerals associated with interior layered deposits near the southern wall of melas chasma mars abstract orbital remote sensing data acquired from the compact reconnaissance imaging spectrometer for mars crism onboard mars reconnaissance orbiter mro in conjunction with other datasets are used to perform detailed spectral and stratigraphic analyses over a portion of south melas chasma mars the discrete ordinate radiative transfer disort model is used to retrieve atmospherically corrected single scattering albedos from crism i f data for mineral identification a sequence of interbedded poly and monohydrated sulfates associated with interior layered deposits ilds is identified and mapped analyses from laboratory experiments and spectral unmixing of crism hyperspectral data support the hypothesis of precipitation and dehydration of multiple inputs of complex mg ca fe so 4 cl brines in this scenario the early precipitated mg sulfates could dehydrate into monohydrated sulfate due to catalytic effects and the later precipitated mg sulfates from the late stage clean brine could terminate their dehydration at mid degree of hydration to form a polyhydrated sulfate layer due to depletion of the catalytic species e g ca fe and cl distinct jarosite bearing units are identified stratigraphically above the hydrated sulfate deposits these are hypothesized to have formed either by oxidation of a fluid containing fe ii and so 4 or by leaching of soluble phases from precursor intermixed jarosite mg sulfate units that may have formed during the later stages of deposition of the hydrated sulfate sequence results from stratigraphic analysis of the ilds show that the layers have a consistent northward dip towards the interior of the melas chasma basin a mean dip angle of 6 and neighboring strata that are approximately parallel these strata are interpreted as initially sub horizontal layers of a subaqueous sedimentary evaporite deposits that underwent post depositional tilting from slumping into the melas chasma basin the interbedded hydrated sulfate units and jarosite bearing units which have distinct stratigraphic relationships are indicative of a complex sedimentary and aqueous history in south melas chasma

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

video imaged surf zone wave and roller structures and flow fields 1 the measurement of mean water levels roller geometries and phase ensemble averaged velocity and turbulence intensity fields under spilling and plunging waves breaking in a two dimensional laboratory surf zone is presented the velocities were measured using digital correlation image velocimetry while water levels and roller geometries were determined through gray scale filtering of video images the phase ensemble averaged horizontal and vertical components of velocity and turbulence intensities are measured throughout the entire flow domain including the wave roller area by utilizing the aerated areas as part of the flow structure the time averaged horizontal velocities undertow turbulence intensities and turbulent kinetic energies are determined by averaging across the wave phase turbulence magnitudes are found to compare favorably with existing laser doppler anemometry measurements below the wave trough level where such measurements have generally been confined because of aeration contamination effects the significantly higher velocity and turbulence intensity magnitudes measured above the trough level in the present experiments highlight the novel nature of the present investigation for describing flow regimes in the surf zone

vertical structure of the undertow outside the surf zone the vertical structure of the undertow in the shoaling region outside the surf zone is quite different from that inside the surf zone inside the surf zone the undertow typically has a large seaward directed velocity near the bottom and either a shoreward directed or a small seaward directed velocity at trough level measurements show that outside the surf zone the undertow has a small seaward directed velocity near the bed and a large seaward directed velocity at trough level in this paper we develop theoretical expressions for the undertow outside the surf zone and show that the steady streaming from the bottom boundary layer which was earlier found to have a negligible effect in the surf zone svendsen et al 1987 does have a significant influence on the vertical structure of the undertow in that region