zoning of platinum group mineral assemblages in the ug2 chromitite determined through in situ sem eds based image analysis in situ scanning electron microscopy energy dispersive x ray spectrometry analysis of platinum group minerals pgm and base metal sulfides in the ug2 chromitite shows that this ore body is zoned along at least 6 km of strike the uppermost part of the ug2 chromitite referred to as the leader seam is 16 cm thick and has a pgm assemblage that is dominated by pge arsenides sulpho arsenides and alloys 70 vol of all pgm which are typical secondary pgm assemblages in other segments of ug2 this is the first time such laterally persistent secondary assemblages have been identified in the ug2 chromitite as previously they were only known to occur adjacent to transgressive fluid bearing structures e g pipes faults the underlying main seam is thicker one to nine seams totaling 130 cm and has a pgm assemblage that consists mostly of pt sulfide pt pd sulfide pt rh cu sulfide laurite and fe pt alloys 85 vol of all pgm typically regarded as primary magmatic constituents of ug2 chromitite there are however some subtle vertical changes in the pgm assemblages of the main seam that include the occasional presence of secondary assemblages in the top and bottom parts the origin of these secondary pgm assemblages is related to alteration by hydrothermal fluids and or fluid rich melts that infiltrated during crystallization of the ug2 and may possibly have been derived from the ug2 chromitite itself

ventifacts at the pathfinder landing site about half of the rocks at the mars pathfinder ares vallis landing site appear to be ventifacts rocks abraded by windborne particles comparable resolution images taken by the imager for mars pathfinder imp camera and the viking landers show that ventifacts are more abundant at the pathfinder site the ventifacts occur in several forms including rocks with faceted edges finger like projections elongated pits flutes grooves and possible rills the trends of elongated pits flutes grooves and rills cluster at 280 330 clockwise from north and generally dip 10 30 away from their trend direction these orientations are indicative of southeast to northwest winds and differ from the trend of wind tails at the landing site the direction of local wind streaks and predictions of the global circulation model all of which indicate northeast to southwest winds the disparity between these data sets strongly suggests that local circulation patterns have changed since the abrasion of the ventifacted rocks the greater number of ventifacts at the pathfinder site compared to either of the viking sites is most easily explained as being due to a larger supply of abrading particles composed of either sand sized grains or indurated dust aggregates and higher surface roughness which should increase the momentum of saltating grains the pathfinder ventifacts may have formed shortly after the deposition of outflow channel sediments nearly 2 gry ago when a large local supply of abrading particles should have been abundant and atmospheric conditions may have been more conducive to rock abrasion from saltating grains based on how ventifacts form on earth the several ventifact forms seen at the pathfinder site and their presence on some rocks but not on others are probably due to local airflow conditions original rock shape exposure duration rock movement and to a lesser extent rock lithology the abundance of ventifacts at the pathfinder site together with other evidence of weathering indicates that unaltered rock surfaces are rare on mars

pressure observations by the curiosity rover initial results 1 rems p the pressure measurement subsystem of the mars science laboratory msl rover environmental measurement station rems is performing accurate observations of the martian atmospheric surface pressure it has demonstrated high data quality and good temporal coverage carrying out the first in situ pressure observations in the martian equatorial regions we describe the rems p initial results by msl mission sol 100 including the instrument performance and data quality and illustrate some initial interpretations of the observed features the observations show both expected and new phenomena at various spatial and temporal scales e g the gradually increasing pressure due to the advancing martian season signals from the diurnal tides as well as various local atmospheric phenomena and thermal vortices among the unexpected new phenomena discovered in the pressure data are a small regular pressure drop at every sol and pressure oscillations occurring in the early evening we look forward to continued high quality observations by rems p extending the data set to reveal characteristics of seasonal variations and improved insights into regional and local phenomena

possible dust devils vortices on mars this paper presents the results of a study of local vortices and dust devils on mars as observed by viking landers 1 and 2 it is found that these vortices are most common during martian spring and summer as occurs on earth seven of the vortices involve wind speeds that may raise dust from the martian surface there is no indication that these possible dust devils contribute to the planet wide spread of major dust storms however it appears that they may help in maintaining the atmospheric dust content the data indicate that there is no preference in rotation direction at least to core diameters of 300 m corresponding to a region of influence of about 3 km diameter

katabatic jumps in the martian northern polar regions abstract martian polar regions host active regional wind circulations such as the downslope katabatic winds which develop owing to near surface radiative cooling and sloped topography many observations stratigraphy from radar profiling frost streaks spectral analysis of ices concur to show that aeolian processes play a key role in glacial processes in martian polar regions a spectacular manifestation of this resides in elongated clouds that forms within the polar spiral troughs a series of geological depressions in mars polar caps here we report mesoscale atmospheric modeling in martian polar regions making use of five nested domains operating a model downscaling from horizontal resolutions of twenty kilometers to 200 m in a typical polar trough we show that strong katabatic jumps form at the bottom of polar troughs with an horizontal morphology and location similar to trough clouds large vertical velocity up to 3 m s and temperature perturbations up to 20 k propitious to cloud formation this strongly suggests that trough clouds on mars are caused by katabatic jumps forming within polar troughs this phenomena is analogous to the terrestrial loewe phenomena over antarctica s slopes and coastlines resulting in a distinctive wall of snow during katabatic events our mesoscale modeling results thereby suggest that trough clouds might be present manifestations of the ice migration processes that yielded the internal cap structure discovered by radar observations as part of a cyclic step process this has important implications for the stability and possible migration over geological timescales of water ice surface reservoirs and overall for the evolution of mars polar caps over geological timescales

numerical simulation of atmospheric bore waves on mars abstract the viking orbiters imaged early morning long linear wave clouds along the flanks of the tharsis volcanoes during late northern spring and early summer these clouds are believed to be a product of either an atmospheric bore wave or a hydraulic jump generated by nightly katabatic winds the mars regional atmospheric modeling system was used to study the interaction of the katabatic flows with the surrounding atmosphere to determine what mechanism is responsible for the clouds simulations at l s 90 100 142 180 270 and 358 were conducted focusing on the eastern flank of olympus mons model results compare well with viking observations and closely approximate theoretical treatments of atmospheric bores strong downslope flows are simulated during the night with a bore wave forming on and behind a well defined katabatic front the observed seasonality of the clouds was reproduced in the simulations the bore was deeper and faster during northern summer and weakest during the winter when the bore was strong it was undular in form and generated vertically propagating gravity waves in the atmosphere above during the winter the atmospheric structure was such that any gravity waves generated damped with height less atmospheric water vapor abundance during northern winter as compared to the summer is also a factor in the seasonality of the wave clouds this study concludes that bore waves are the most likely mechanism for the generation of the observed linear wave clouds

benthic nutrient recycling in port phillip bay australia benthic chamber measurements of the reactants and products involved with biogenic matter remineralization oxygen ammonium nitrate nitrite phosphate silicate tco2and alkalinity were used to define solute exchange rates between the sediment and overlying water column of port phillip bay australia measurements at various sites throughout the bay conducted during the summers of 1994 and 1995 indicate that the variability in flux values within a site is comparable to year to year variability 50 four regions of the bay were distinguished by sediment properties and the northern region was identified as having 3 30 times greater nutrient regeneration rates than the other regions benthic recycling accounted for 63 and 72 of the annualized n and p input respectively to the entire bay as determined by summing benthic dissolved riverine atmospheric and dissolved effluent sources however bay wide sedimentary denitrification accounted for a loss of 63 of the potentially recyclable n this fraction is higher than many other coastal regions with comparable carbon loading denitrification efficiency is apparently not enhanced by benthic productivity nor by bio irrigation the rate of bio irrigation is negatively correlated with denitrification efficiency bio irrigation was studied using radon 222 and cscl spike injection chamber measurements radon fluxes from sediments in port phillip bay were enhanced over the diffusive flux by 3 16 times the modelled rate of loss of cs from chamber water was positively correlated with radon flux enhancement results both methods identify regions within port phillip bay that have particularly high rates of non diffusive pore water overlying water solute exchange

windy mars a dynamic planet as seen by the hirise camera 1 with a dynamic atmosphere and a large supply of particulate material the surface of mars is heavily influenced by wind driven or aeolian processes the high resolution imaging science experiment hirise camera on the mars reconnaissance orbiter mro provides a new view of martian geology with the ability to see decimeter size features current sand movement and evidence for recent bedform development is observed dunes and ripples generally exhibit complex surfaces down to the limits of resolution yardangs have diverse textures with some being massive at hirise scale others having horizontal and cross cutting layers of variable character and some exhibiting blocky and polygonal morphologies reticulate fine polygonal texture bedforms are ubiquitous in the thick mantle at the highest elevations

some observational constraints on the global scale wind systems of mars wind direction measurements from a variety of indicators taken over several mars years and covering the entire planet have been collected these include observations of lee wave clouds not previously studied the data exhibit a high degree of consistency and seasonal reproducibility making it possible to interpret most of the observations in terms of the zonally symmetric circulation of mars we examine these data in the context of the constraints the observed wind directions place upon the thermal and polar cap mass flux fields which force the flows within the limitations of the data set mid and high latitude winds appear to be controlled by the thermal field during mid and late summer and winter and in the northern hemisphere during early spring and early summer at other times the cap flows dominate at high latitudes the strongest yearly winds are probably generated by cap formation in the north and cap recession in the south the hemispheric asymmetry seems to result primarily from the effects of global dust storms on the north polar cap turning of the prograde wind from poleward to equatorward in midautumn is observed consistent with reduced poleward mass flux and increased meridional temperature gradient at that time the latitudinal extent of the equatorial hadley cell when observed is probably larger than that predicted by nearly inviscid models of low latitude circulation the cross equational hadley cell and high latitude poleward flows which occur in both hemispheres during the summer seasons may set additional constraints on the thermal forcing mechanisms at these times

downslope windstorms in the lee of ridges on mars abstract the semianalytical theory of downslope windstorms originally developed to understand large increases in surface winds in the lee of major mountain chains on earth such as the famous windstorms in boulder colorado is applied to martian conditions the focus of this work is to assess whether this theory can help us understand dark erosional wind streaks downstream of ridges on the martian surface these streaks provide a well documented example of dust raising on mars however the formation of the streaks remains a mystery because atmospheric circulation models indicate surface friction velocities far lower than those required for the initiation of eolian activity downslope windstorms result from the interaction of topographically launched finite amplitude gravity waves with a level of zero wind which vertically traps the waves when this zero wind level is at the proper height large increases in downstream surface winds up to a factor of 4 can be produced during the martian night downslope windstorms can occur in the lee of quite small ridges heights tens of meters when a level of zero wind is present in the lowest few kilometers of the atmosphere three independent models of the martian atmospheric circulation indeed show levels of zero wind in the form of wind reversals at the appropriate height and season and at the locations where the ridge related dark streaks are concentrated the strong upstream downstream difference in surface winds produced by the downslope windstorm mechanism when a suitable wind reversal is present rather than a particularly strong upstream wind is what controls the occurrence of the ridge related dark streaks downslope windstorms also appear to be potentially useful in understanding the build up of dust in the atmosphere preceding the martian global dust storms

evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 exomars landing ellipse in meridiani planum mars we present evidence for a complex multigenerational bed form pattern and a new type of wind streak the ripple streak in the landing site ellipse of the 2016 exomars entry descent and landing demonstrator module edm in meridiani planum mars we identified three main groups of bright toned bed forms population 3 represented by ne sw trending bed forms located inside craters was emplaced by winds coming from the nw or the se population 2 emplaced by strong easterlies formed by intracrater transverse aeolian ridges tars and n s trending megaripples plains ripples population 1 consists of a relict bed form pattern emplaced by winds coming from the north or south alternatively population 1 can represent a sand ribbon pattern that formed together with the plain ripples we also report the presence of a new type of wind streak the ripple streak which is formed by the population 2 bed forms clustered in the wake zone of impact craters based on the results of this work we now know the edm module is set to land in a complex aeolian environment data from the dust characterization risk assessment and environment analyser on the martian surface onboard the edm can help to better decipher the wind regime in meridiani planum

aeolian processes and dune morphology in gale crater abstract datasets at resolutions many times greater than previously available were used to study aeolian features within gale crater high resolution thermal inertia data allowed for detailed particle size estimation with the data sufficient to resolve dunefields a wide range of grain sizes have now been identified in the gale crater dunefields ranging from medium to very coarse sand high resolution imaging science experiment hirise and themis vis data allowed for detailed analysis of the dune morphology and slip faces which shows that the dunes have responded to topographic influences on prevailing wind directions under a present day wind regime this result was corroborated by a regional mesoscale model for the crater under dust storm conditions the central mound and smaller scale crater floor topography has altered the prevailing wind regime and dune patterns aeolian activity has thus played and continues to play an important role in shaping many of the present surface features of gale crater the arrival of a future lander mission such as the mars science laboratory would be able to sample these surface features directly and add a wealth of data to the understanding of gale crater

mars atmospheric winds indicated by motion of the viking landers during parachute descent winds in the martian atmosphere at altitudes from 1 5 to 3 5 km have been determined from parachute descent trajectories of the two viking landers viking 2 reached equilibrium with nearly steady winds of 8 m s to the southeast below 3 3 km at 1000 lt viking 1 winds at 1615 lt rotated clockwise with decreasing altitude but were generally to the northwest at 20 m s at 1 5 km the viking 1 wind direction was close to that measured by the landed anemometer at the same local time while at the viking 2 site wind direction at 1 5 km was nearly opposite that near the surface this is consistent with the fact that viking 1 descended within a vigorously convective boundary layer while viking 2 at 1 5 km was above the boundary layer turbulent velocities in the viking 1 boundary layer were 3 m s mean upflow velocity was 1 m s the viking 2 atmosphere was relatively quiescent with orderly wind directional variation possibly suggesting the presence of waves comparison of the measured winds with a recent global circulation model showed little or no correspondence probably an indication that the winds were locally controlled the boundary layer slope wind model of haberle et al 1993 with ground slope adjusted to give best fit to these and landed meteorology data gave roughly the wind direction and the observed magnitude within a factor of 2 but with opposite rotation of the wind vector with altitude the ground slopes deduced are consistent with terrain observed in approach to the viking 1 landing and do not conflict with the less definitive terrain data at the viking 2 site the high sensitivity of winds at altitudes up to several kilometers to terrain slopes as small as a few meters per kilometer would suggest that slope winds may be widely found in the lowest few kilometers of mars atmosphere

observation of mountain lee waves with modis nir column water vapor mountain lee waves have been previously observed in data from the moderate resolution imaging spectroradiometer modis water vapor 6 7 m channel which has a typical peak sensitivity at 550 hpa in the free troposphere this paper reports the first observation of mountain waves generated by the appalachian mountains in the modis total column water vapor cwv product derived from near infrared nir 0 94 m measurements which indicate perturbations very close to the surface the cwv waves are usually observed during spring and late fall or some summer days with low to moderate cwv below 2 cm the observed lee waves display wavelengths from 3 4 to 15 km with an amplitude of variation often comparable to 50 70 of the total cwv since the bulk of atmospheric water vapor is confined to the boundary layer this indicates that the impact of these waves extends deep into the boundary layer and these may be the lowest level signatures of mountain lee waves presently detected by remote sensing over the land

diel variation of benthic respiration in a coral reef sediment reunion island indian ocean oxygen and total dissolved inorganic carbon dic fluxes at the water sediment interface were measured using benthic chambers to assess the short term variations of community respiration cr in the back reef sediments of reunion island indian ocean benthic cr had a daily cycle of minimal 6 00 am and maximal values 6 00 pm showing increases of oxygen and dic fluxes of 2 8 and 3 8 fold respectively average cr values were observed at midday and midnight the evolution of fluxes was positively related to oxygen concentration in ambient water but not to temperature changes in the study area high daytime primary production augments the amount of energy available for community metabolism and increases benthic respiration the benthic communities are therefore subjected to short term variable environmental conditions with oxygen supersaturation during the day and moderately hypoxic conditions at the end of the night

the spatial and seasonal distribution of martian clouds and some meteorological implications the spatial and seasonal distributions of martian atmospheric clouds organized according to simple morphologic criteria exhibit distinct patterns when interpreted self consistently using analogies to terrestrial cloud forms and martian temperature wind direction and water vapor measurements patterns of cloud occurrence provide some loose constraints on global scale near surface wind speed static stability and humidity we have examined all mariner 9 and viking orbiter images for this study we concentrate primarily on the larger viking data set whenever observations are possible relatively high near surface winds appear to follow the seasonal cap edges during early fall late winter and spring moderate to high winds are also inferred in mid latitudes for mid southern winter and in low latitudes mainly in the steeply sloping areas of tharsis near the solstices at other times lower winds are suspected hemispheric asymmetries are traced to differences in atmospheric hydration state and to global dust storm related effects on the atmospheric temperature structure and the north polar cap recession schedule cloud occurrence data suggest that the near surface daytime static stability is low in the northern hemisphere during summer and at low latitudes during mid northern spring relatively high static stability is deduced near the winter poles and globally during the dust storm season in spite of low atmospheric temperatures the correspondingly low absolute humidity apparently precludes the formation of thick water ice clouds at high latitudes in mid to late autumn and winter in both hemispheres and in southern mid latitudes during early winter during northern spring and summer saturation conditions seem to be easily achieved at mid latitudes and condensate clouds are abundant the situation is complicated by atmospheric dust in southern spring and summer low latitudes generally appear to be farther from saturation than mid latitudes and clouds generally form more easily in the northern hemisphere than in the south during corresponding seasons

litho and chemostratigraphy of the flatreef pge deposit northern bushveld complex the flatreef is a world class platinum group element pge deposit recently discovered down dip from existing mining and exploration operations on the northern limb of the bushveld complex current indicated resources stand at 42 moz pge 346 mt with 3 8 g t pt pd rh au 0 32 ni and 0 16 cu which in the case of pt is equivalent to 10 years global annual production making it one of the largest pge deposits on earth the grade and thickness of the flatreef mineralised interval is highly unusual with some drill core intersections containing up to 4 5 g t pt pd rh au over 90 m in drill core here we document the down dip and along strike litho and chemostratigraphy of the flatreef and its footwall and hanging wall rocks based on a diamond drill core database totalling 720 km at the base of the sequence intersected in the drill cores are up to 700 m thick sills of ultramafic rocks dunite harzburgite pyroxenite emplaced into pelitic dolomitic and locally quartzitic and evaporitic rocks belonging to the duitschland formation of the transvaal supergroup next is an approximately 100 200 m sequence of low grade sulphide mineralised layered mafic ultramafic rocks containing abundant sedimentary xenoliths and in places several chromite seams or stringers this is overlain by a 100 m thick sequence of well mineralised mafic ultramafic rocks the flatreef sensu strictu overlain by a laterally persistent mottled anorthosite layer at the base of 1 km of homogenous main zone gabbronorite based on stratigraphic lithological and compositional analogies to the layered rocks in the eastern and western bushveld complex we correlate the flatreef and its chromite bearing footwall rocks with the upper critical zone notably the interval between the ug2 chromitite and the bastard reef as found elsewhere in the bushveld complex this includes recognition of a merensky reef correlative the ultramafic rocks below the main chromitite seam ug2 correlative in the flatreef footwall are correlated with the lower critical and lower zones however compared to the western and eastern bushveld limbs the studied sequence is strongly enriched in sulphide and pge many of the rocks show elevated cao k2o rb and zr contents and lateral continuity of layers between drill cores is less pronounced than elsewhere in the bushveld whereas ultramafic units are locally considerably thickened these compositional and lithological traits are interpreted to result from a range of processes which include contamination with calcsilicate and hornfels intrusion of granitic magmas and the influence of multiple structural events such as pre to syn emplacement regional scale open folding and growth faults evidence for the existence of potholes also exists in the shallow up dip portions of the project area the entire magmatic sequence below the main zone becomes increasingly contaminated to the extent that individual units are somewhat more difficult to correlate between drill cores this package represents the platreef as exposed in outcrop and shallow bore holes across much of the northern limb of the bushveld complex the new data presented here thus indicate that the platreef is a relatively more contaminated up dip extension of parts of the critical and lower zones

influence of sea squirt halocynthia roretzi aquaculture on benthic pelagic coupling in coastal waters a study of the south sea in korea abstract the influence of sea squirt aquaculture on benthic pelagic coupling was evaluated in semi enclosed korean coastal waters with an in situ benthic chamber and results show for the first time that suspended sea squirt cultures play an important role in benthic pelagic coupling in the coastal zone measurements of primary production vertical particulate fluxes and benthic fluxes were made at two stations a sea squirt halocynthia roretzi farm ssf and an area of organic matter enriched sediment in jinhae bay the vertical material fluxes of organic carbon nitrogen and biogenic silicate bsi were significantly higher at ssf than in jinhae bay indicating massive biodeposits in the surface sediments at ssf the organic carbon oxidation rates c ox were estimated after correction for caco 3 dissolution the average c ox at ssf 204 mmol c m 2 d 1 was significantly higher than that in the organic enriched jinhae bay sediment 77 mmol c m 2 d 1 the organic carbon burial fluxes were determined using vertical profiles of organic carbon of up to 30 cm and the sedimentation rate calculated from the excess 210 pb distribution at both stations 95 of the settled organic carbon was oxidized and only 5 was buried in the deep sediment layer the benthic fluxes of dissolved inorganic nitrogen and phosphate at ssf were 2 12 times higher than in jinhae bay corresponding to 85 and 270 respectively of the requirements for primary production

platinum group element distribution in base metal sulfides of the ug2 chromitite bushveld complex south africa a reconnaissance study two drill cores of the ug2 chromitite from the eastern and western bushveld complex were studied by whole rock analysis ore microscopy sem mineral liberation analysis mla and laser ablation inductively coupled plasma mass spectrometry la icp ms analysis the top and base of the ug2 main seam have the highest bulk rock pd and pt concentrations sulfides mostly occur as aggregates of pentlandite chalcopyrite and rare pyrrhotite and pyrite or as individual grains associated mostly with chromite grains in situ la icp ms analyses reveal that pentlandite carries distinctly elevated platinum group element pge contents in contrast pyrrhotite and chalcopyrite contain very low pge concentrations pentlandite shows average maximum values of 350 1 000 ppm pd 200 ppm rh 130 175 ppm ru 20 ppm os and 150 ppm ir and is the principal host of pd and rh in the studied ores of the ug2 mass balance calculations were conducted for samples representing the ug2 main seam of the drill core dt46 eastern bushveld pentlandite consistently hosts elevated contents of the whole rock pd up to 55 and rh up to 46 and erratic contents of os up to 50 ir 2 to 17 and ru 1 39 platinum group mineral pgm investigations support these mass balance results most of the pgm are pt dominant such as braggite cooperite and pt fe alloys or laurite carrying elevated concentrations of os and ir palladium and rh bearing pgm are rare both pge concentrations and their distribution in base metal sulfides bms in the ug2 largely resemble that of the merensky reef as most of the pd and rh are incorporated in pentlandite whereas pyrrhotite chalcopyrite and pyrite are almost devoid of pge

a comparative study of daytime thermally induced upslope flow on mars and earth abstract several characteristics of thermally induced mesoscale upslope flow on mars and its comparison with that on earth were investigated using both analytical and numerical model approaches the conclusions obtained from the analytical and the numerical evaluations for mars are generally in agreement the main conclusions are i the intensity of the martian summer daytime upslope flow with a moderate slope reaches nearly 10 m s 1 and its depth is about 5 km ii the longwave radiation flux divergence heating within the lower boundary layer of mars has a nonnegligible contribution to the intensity of the upslope flows and iii on mars the values of upslope wind speed are typically about 2 5 times larger than on earth under similar conditions the depth of the daytime upslope flow and the air temperature increase near the surface are 3 to 4 times larger the vertical eddy exchange coefficient for heat and momentum is about 10 times larger on mars

new mossbauer measurements of fe3 σfe ratios in chromites from the early proterozoic bushveld complex south africa abstract new mossbauer measurements of fe 3 fe ratios from chromites in the upper critical zone of the rustenberg layered suite of the bushveld complex south africa vary between 0 139 and 0 232 mean 0 185 0 025 1 a more oxidised group have fe 3 fe ratios in the range 0 766 0 738 textural studies indicate that these more oxidised samples experienced post magmatic oxidation during brecciation the chromitites have a narrow range of cr 0 618 0 671 and are fe rich there is some variability in cr with stratigraphic height implying variation in the composition of the parental magmas variation within the less oxidised group of chromitites is attributed to variations in the oxidation state of the parent magma which in turn is thought to reflect different degrees of mixing between magmatic sources with differing oxidation states comparison with geologically recent chromitites of similar composition suggests that upper mantle redox conditions have remained unchanged since 2 06 ga

influence of sediment permeability and mineral composition on organic matter degradation in three sediments from the gulf of aqaba red sea abstract in order to investigate the influence of sediment physical and chemical characteristics on the degradation of deposited organic matter decomposition in three sediments from the gulf of aqaba red sea that differ in permeability and mineral composition were compared freeze dried spirulina was added to coarse carbonate and silicate sands from a shallow nearshore region and silt clay sediment from the deeper center region of the gulf incubated in laboratory chambers the stirring in the chambers caused higher solute exchange in the coarse permeable sands relative to the fine less permeable silt due to the generation of advective fluid exchange between the sediment and overlying water this enhanced exchange increased the decomposition rates of organic matter in the incubated sands the decomposition rates of total organic carbon in the permeable carbonate 3 0 mg c m 2 d 1 and silicate sands 2 0 mg c m 2 d 1 exceeded that in the fine grained sediment 1 4 mg c m 2 d 1 oxygen consumption in the coarse sands was 3 fold higher than in the silt clay sediment with highest rates in the carbonate sand in carbonate and silicate sands of the same grain size the carbonate sediment was more permeable than the silicate resulting in 1 4 fold higher fluid exchange rates and 1 4 fold larger sedimentary organic matter mineralization rates an in situ experiment comparing trapping efficiencies in carbonate and silicate sands showed that the higher fluid exchange rate in the carbonate sand results in larger filtration rates and a faster accumulation of particulate organic matter from the boundary layer these experiments demonstrate that with respect to sedimentary mineralization rates higher transport rates in permeable coarse sediments can outweigh the effect of a higher specific surface area in fine grained silt sediments in permeable sands however the higher specific surface area and fluid exchange in biogenic carbonate sands result in higher mineralization rates than in silicate sands of the same grain size

long cloud observations on mars and implications for boundary layer characteristics over slopes viking orbiter images of mars show several instances of long continuous cloud formations on the slopes of arsia and pavonis mons we have searched all the images of the planet for occurrences of such formations only in the tharsis region were long clouds unambiguously identified we have measured the times and locations of occurrence the wavelengths and when possible the apparent velocity of motion of these clouds we have also tabulated the wavelengths of patches of ripple clouds that are often found with the long formations the long clouds are observed only in the early morning hours suggesting that they are associated with drainage winds due to a cold planetary boundary layer we develop simple mathematical models to examine various aspects of such boundary layer winds these allow us to construct a complete and self consistent explanation of all the observed features of the cloud formations we use the results to characterize some physical properties of the mars boundary layer there is strong downslope flow in the boundary layer on the high slopes of both volcanos in the saddle region between the peaks the flow slows and undergoes a hydraulic jump producing the long clouds downstream of the jump standing internal gravity waves can exist and are excited by flow over surface irregularities small variations in their observed wavelengths behind the jump may be attributed to variation in the flow speed and depth finally we can account for the location of the jumps by the variation of relative strength of the boundary layer flows on the two volcanos

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

meteorological predictions for 2003 mars exploration rover high priority landing sites 1 the mars regional atmospheric modeling system is used to predict meteorological conditions that are likely to be encountered by the mars exploration rovers at several proposed landing sites during entry descent and landing seven areas five of which contain specific high priority landing ellipses are investigated hematite two sites isidis planitia elysium planitia two sites valles marineris and gusev crater the last two locations are in regions of extreme topography and the local and regional thermal circulations that result are equally extreme horizontal wind speeds near the floor of valles marineris exceed 50 ms 1 vertical velocities near the walls exceed 40 ms 1 and penetrate 10 km in altitude above the rim of the canyon thermal convection is suppressed within valles marineris by subsidence that forms in response to the upslope flows along the canyon walls wind magnitudes at gusev crater are approximately one third of those at the canyon but horizontal wind shear is greater deep convective thermals are noted at the relatively flat hematite site where 10 ms 1 updrafts rising to heights of 5 km are not uncommon during the midafternoon linearly organized convective updrafts superimposed on upslope circulations dominate over most of isidis planitia hexagonal and linearly organized convection predominates at elysium planitia afternoon circulations at all sites pose some risk significant risk in some cases to entry descent and landing most of the atmospheric hazards are not evident in current observational data and general circulation model simulations and can only be ascertained through mesoscale modeling of the region

wind streaks on mars meteorological control of occurence and mode of formation abstract why do some craters on mars produce depositional wind streaks while others produce erosional ones there is no evidence to suggest that crater morphology or topography plays the determining role some craters can form either type of streak at different times of the martian year suggesting that the controlling factor is meteorological we propose that atmospheric stability is the determining factor a stable atmosphere should lead to blocking of the wind flow by crater rims producing wind shadows over distances comparable to those of observed bright streaks such conditions should prevail in a belt about the equator at the time of major dust storms as the atmosphere becomes more transparent following the end of the dust storms the rate of surface heating increases and the stability of the atmosphere is reduced under such conditions blocking is not expected flow over obstacles results in increased surface stress downwind conditions which encourage the formation of erosional dark streaks these ideas are shown to be consistent with the seasons at which erosional and depositional streaks are formed as well as with their distribution on the planet specifically the scheme explains why craters which have both erosional and depositional streaks occur only within a very restricted latitude belt

the significance of magmatic erosion for bifurcation of ug1 chromitite layers in the bushveld complex abstract one of the most puzzling features of the ug1 chromitite layers in the famous exposures at dwars river eastern bushveld complex is the bifurcation i e convergence and divergence of layers along strike that isolate lenses of anorthosite the bifurcations have been variously interpreted as resulting from 1 the intermittent accumulation of plagioclase on the chamber floor as lenses terminated by crystallization of continuous chromitite layers the depositional model 2 late stage injections of chromite mush or chromite saturated melt along anastomosing fractures that dismembered semi consolidated plagioclase cumulates the intrusive model 3 post depositional deformation of alternating plagioclase and chromite cumulates resulting in local amalgamation of chromitite layers and anorthosite lenses that wedge out laterally the deformational model none of these hypotheses account satisfactorily for the following field observations a wavy and scalloped contacts between anorthosite and chromitite layers b abrupt lateral terminations of thin anorthosite layers within chromitite c in situ anorthosite inclusions with highly irregular contacts and delicate wispy tails within chromitite many of these inclusions are contiguous with footwall and hanging wall cumulates d transported anorthosite fragments enclosed by chromitite e disrupted anorthosite and chromitite layers overlain by planar chromitite f protrusions of chromitite into underlying anorthosite g merging of chromitite layers around anorthosite domes we propose a novel hypothesis that envisages basal flows of new dense and superheated magma that resulted in intense thermo chemical erosion of the temporary floor of the chamber the melting and dissolution of anorthosite was patchy and commonly inhibited by chromitite layers resulting in lens like remnants of anorthosite resting on continuous layers of chromitite on cooling the magma crystallized chromite on the irregular chamber floor draping the remnants of anorthosite and merging with pre existing chromitite layers excavated by erosion with further cooling the magma crystallized chromite bearing anorthosite emplacement of multiple pulses of magma led to repetition of this sequence of events resulting in a complex package of anorthosite lenses and bifurcating chromitite layers this hypothesis is the most satisfactory explanation for most of the features of this enigmatic igneous layering in the bushveld complex

the formation of pt ir alloys and cu pd rich sulfide melts by partial desulfurization of fe ni cu sulfides results of experiments and implications for natural systems abstract we propose a model of high temperature formation of platinum group element pge alloys from base metal sulfides subjected to decreasing sulfur fugacity f s 2 for this purpose we experimentally investigated the effect of partial desulfurization of monosulfide solid solution mss with variable ni and cu contents on the distribution behaviour of pt ir and pd at 1000 c we partially removed sulfur from the pge bearing mss using the tube in tube technique and pyrrhotite as an f s 2 buffer we found that mss undergoing s loss can produce 1 pt and ir exsolution from the mss matrix in the form of pge bearing alloys 2 partial melting of the cu ni bearing mss to form fe rich mss cu ni pd rich sulfide liquid and fe ir pt alloy both of these processes are geologically important the partial melting of the s depleted sulfides could explain the presence of two types of sulfides found in the mantle mss dominated sulfides and s poor sulfides consisting mainly of pentlandite and chalcopyrite we also suggest that the cu ni pd rich liquid formed by partial melting of the sulfides could migrate away from the mss and fe ir pt alloys thus spatially decoupling ir pt and cu pd as observed in reefs and mantle nodules in addition the formation of pge alloys in response to the desulfurization processes potentially could occur 1 after pressure falls during transport of the basalt magma with entrained sulfide droplets 2 after sulfur removal by s undersaturated melts or fluids from pge enriched sulfide proto ore 3 after degassing of the sulfide droplets occurring in a sub volcanic chamber and 4 as a result of sulfide interaction with chromite

benthic photosynthesis and oxygen consumption in permeable carbonate sediments at heron island great barrier reef australia abstract in order to investigate benthic photosynthesis and oxygen demand in permeable carbonate sands and the impact of benthic boundary layer flow on sedimentary oxygen consumption in situ and laboratory chamber experiments were carried out at heron island great barrier reef australia total photosynthesis net primary production and respiration were estimated to be 162 9 43 4 98 0 40 7 and 64 9 15 0 mmol c m 2 d 1 respectively din and dip fluxes for these sands reached 0 34 and 0 06 mmol m 2 d 1 respectively advective pore water exchange had a strong impact on oxygen consumption in the permeable sands consumption rates in the chamber with larger pressure gradient 20 rpm 1 2 pa between centre and rim simulating a friction velocity of 0 6 cm s 1 were approximately two fold higher than in the chambers with slow stirring 10 rpm 0 2 pa between centre and rim friction velocity of 0 3 cm s 1 in the laboratory chamber experiments with stagnant water column oxygen consumption was eight times lower than in the chamber with fast stirring laboratory chamber experiments with br tracer revealed solute exchange rates of 2 6 2 2 0 7 ml cm 2 d 1 at stirring rates of 20 10 and 0 rpm respectively in a laboratory experiment investigating the effect of sediment permeability on oxygen and dic fluxes a three fold higher permeability resulted in two to three fold higher oxygen consumption and dic release rates these experiments demonstrate the importance of boundary flow induced flushing of the upper layer of permeable carbonate sediment on oxygen uptake in the coral sands the high filtration and oxidation rates in the sub tropical permeable carbonate sediments and the subsequent release of nutrients and dic reveal the importance of these sands for the recycling of matter in this oligotrophic environment

arctic shelves as platforms for biogeochemical activity nitrogen and carbon transformations in the chukchi sea alaska abstract continental shelves comprise 50 of marine denitrification the hanna shoal region part of the continental shelf system in the northeast chukchi sea alaska is recognized for its high biodiversity and productivity we investigated the role of sediments in organic matter decomposition and nutrient cycling at five stations on the shallow hanna shoal in particular we asked 1 how much sediment organic matter is remineralized in the chukchi sea and what factors drive this degradation 2 do sediments function as a net source for fixed nitrogen thus fueling primary production in the overlying water or as a net sink for fixed nitrogen thereby removing it from the system and 3 what is the balance between sediment nh4 uptake and regeneration and what factors drive nh4 cycling we conducted dark sediment core incubations to measure sediment o2 consumption net n2 and nutrient nh4 no3 no2 po43 fluxes and rates of sediment nh4 cycling including uptake and regeneration rates of sediment o2 consumption and nh4 and po43 efflux suggest that high organic matter remineralization rates occurred in these cold 2 c sediments we estimated that total organic carbon remineralization accounted for 20 57 of summer export production measured on the chukchi shelf net n2 release was the dominant nitrogen flux indicating that sediments acted as a net sink for bioavailable nitrogen via denitrification organic carbon remineralization via denitrification accounted for 6 12 of summer export production which made up 25 of the total organic carbon oxidized in hanna shoal sediments these shallow productive arctic shelves are hotspots for organic matter remineralization

the geology and structure of the rustenburg layered suite in the potgietersrus mokopane area of the bushveld complex south africa a new geological map of the rustenburg layered suite south of the ysterberg planknek fault of the northern potgietersrus limb of the bushveld complex is presented displaying features that were not available for publication in the past and are considered contributing to the complexity of this region the northern limb is known for the platreef atypical mafic lithologies in sections of the layered sequence and the unusual development of the ultramafic lower zone as satellite bodies or offshoots at the base of the intrusion the outcrop and suboutcrop pattern of lower zone grasvally body and its relation to the surrounding geology of main zone critical zone and floor rocks is described the extent of the base metal sulfide bms and platinum group element pge mineralized cyclic unit 11 of the drummonlea harzburgite chromitite sub zone is shown only that which is considered to be the equivalents of the mafic upper critical zone has thus far been traced south of potgietersrus mokopane the platreef is traced from the farm townlands and further northwards the presence of platreef proper south of potgietersrus mokopane appears to be speculative however merensky reef ug 2 and equivalent layers outcrop or were intersected to the south of the town the kleinmeid syncline comprising main zone critical zone layers and its structure is discussed the lateral lithological transfomation of the merensky reef ug 2 and equivalent layers south of the ysterberg planknek fault to platreef north of this fault is recorded attenuation of both the main zone and upper zone is observed from the northwest towards the town and resulted in only the lower units being developed the lateral change of main zone and upper zone lithologies from the northwest towards the town is described the pge and bms economic potential south of the town are briefly tabulated

the geologic setting of the platiniferous ug 2 chromitite layer on the farm maandagshoek eastern bushveld complex the platiniferous ug 2 chromitite layer forms part of the upper chromitite group of the critical zone on the farm maandagshoek 254kt in the eastern bushveld complex the upper chromitite group is made up of four cyclic units namely ug 1 ug 2 ug 3 and ug 3a each of which consists of a basal chromitite layer with or without olivine overlain successively by melanorite and norite and terminated with anorthosite the ug 2 chromitite layer and its associated basal pegmatoid is found close to the base of the ug 2 cyclic unit the cyclic units are separated by sharp contacts and have a remarkable persistence along strike and downdip whole rock cu total ni pt and pd show an upward enrichment from the base of the ug 2 unit reaching a maximum in the main chromitite layer they are depleted in the hanging wall sequence of melanorite bulk analyses of the ug 2 chromitite and its enclosing lithologies for pt pd ru rh ir au s sulfide ni cu and co show that the platinum group elements and base metals are concentrated 1 close to the top and base of the main chromitite layer 2 in the leader layer and 3 in minor chromitite lenses and layers both in the footwall pegmatoid and the hanging wall melanorite the pt pt pd and cu ni ratios are low in the footwall pegmatoid and base of the main chromitite layer values of these ratios however increase upward with pt pt pd decreasing at the upper contact of the ug 2 layer the calculated concentration of platinum group metals in the sulfide phase in the ug 2 chromitite layer ranges from 3 000 to just under 12 000 ppm the above determination is primarily controlled by the concentration of s in the layer with the average precious metal distribution remaining relatively constant the calculated d super sulfide liquid sub silicate liquid with the parental liquid values in parentheses are pt 52 575 40 ppb pd 132 940 16 ppb rh 22 080 8 ppb ir 730 000 0 4 ppb and au 2 190 21 ppb evidence of an influx of magma into the eastern lobe of the bushveld complex at a level between the upper and middle chromitite groups is indicated by discontinuous and disturbed layers in borehole drilling on maandagshoek it is suggested that this magma batch was slightly more enriched in the platinum group elements in order to produce the increased value of these elements in the ug 2 chromitite layer it is proposed that preexisting sulfides in the ug 2 chromitite layer collected platinum group elements from upward migrating highly fractionated intercumulus fluids under highly reducing conditions during the early stages of formation of the layer the relatively large volume of sulfide initially present in the layer was later reduced by volatiles enriched in o 2 passing through the layer resorbing the sulfides and blowing off so 2 the partial resorption of the sulfides accounts for the presence of minor pt fe alloys and the abnormally high partition coefficients of the platinum group elements in the sulfide liquid of the ug 2 chromitite layer

characteristics of the numerous and widespread recurring slope lineae rsl in valles marineris mars abstract recurring slope lineae rsl are narrow 0 5 5 m dark features on mars that incrementally lengthen down steep slopes fade in colder seasons and recur annually these traits suggest that liquid water is flowing in the shallow subsurface of mars today here we describe high resolution imaging science experiment hirise observations of rsl within valles marineris vm we have identified 239 candidate and confirmed rsl sites within all the major canyons of vm with the exception of echus chasma about half of all the globally known rsl locations occur within vm and the areal density of rsl on coprates montes appears to be the greatest on the planet vm rsl are heterogeneously distributed as they are primarily clustered in certain areas while being conspicuously absent in other locations that appear otherwise favorable rsl have been found on many of the interior layered deposits ilds within vm such ild rsl appear to traverse bedrock instead of regolith like all other rsl forty six of the vm rsl sites show incremental lengthening and exhibit similar behavior in most of the canyons of vm but the rsl duration at one site in juventae chasma is significantly reduced furthermore the lengthening seasonality depends solely on slope orientation with typical vm rsl on a given slope lengthening for 42 74 of a mars year there are always rsl lengthening within vm regardless of the season if rsl are caused by water such a long active season at hundreds of vm rsl sites suggests that an appreciable source of water must be recharging these rsl thermophysical modeling indicates that a melting temperature range of 246 264 k is needed to reproduce the seasonal phenomenology of the vm rsl suggesting the involvement of a brine consisting of tens of wt salt the mechanism s by which rsl are recharged annually remain uncertain overall gaining a better understanding of how rsl form and recur can benefit the search for extant life on mars and could provide details about an in situ water resource

plagioclase content of cyclic units in the bushveld complex south africa the upper critical zone of the bushveld complex south africa has been divided into so called cyclic units ideally they should consist of from the base upward layers of chromitite pyroxenite norite and anorthosite some hypotheses for their origin suggest that they result from the addition and mixing of a magnesian magma having orthopyroxene or olivine as liquidus mineral these models predict that the bulk cumulate composition in a cyclic unit formed from such magma ought to contain excess orthopyroxene to plagioclase relative to their cotectic proportions an hypothesis tested here all rocks investigated here from the upper critical zone at impala platinum mine are mixtures of cumulus plagioclase and orthopyroxene except for the chromitites with very minor intercumulus minerals mainly clinopyroxene hence the proportion of plagioclase can be determined by measurement of the density of a sample the density of every piece of continuous bore core from the upper group 2 ug2 and merensky cyclic units has been determined and the proportion of plagioclase calculated for the bastard cyclic unit estimates of the proportion of plagioclase have been made based on published modal and chemical analyses vertical summation of the proportion of plagioclase indicates that these three cyclic units ug2 merensky and bastard respectively contain 64 74 and over 80 plagioclase by weight for the merensky and bastard cyclic units such proportions exceed that of the plagioclase orthopyroxene cotectic and could not have been produced by processes involving magnesian magma

connectivity between the western and eastern limbs of the bushveld complex abstract the mafic layered rocks of the bushveld complex are 6 8 km thick and crop out over an area of 65 000 km 2 previous interpretations of the bouguer gravity anomalies suggested that the intrusion consisted of two totally separate bodies however the mafic sequences in these arcuate western and eastern limbs are remarkably similar with at least six petrologically distinctive layers and sequences being recognisable in both limbs such similarity of sequences in two totally discrete bodies 200 300 km apart is petrologically implausible and it is suggested that they formed within a single lopolithic intrusion all previous bouguer gravity models failed to consider the isostatic response of the crust to emplacement of this huge mass of mafic magma isostatic adjustment as a result of this intrusion would have caused the base of the crust to be depressed by as much as 6 km with this revised whole crustal model it becomes possible to construct a gravity model consistent with observed data which includes a 6 km thick sequence of mafic rocks connecting the western and eastern limbs of the bushveld complex the exact depth at which the mafic rocks of the bushveld complex lie in the centre of the structure cannot be constrained by the gravity data such a first order model is an approximation because there have been subsequent deformation and structural readjustments in the crust some of them probably related to the emplacement of the bushveld complex specifically the observed geometry of the rocks around the crocodile river dennilton marble hall and malope domes suggests that major upwarping of the crust occurred on a variety of scales triggered by emplacement of the bushveld complex

dust streaks on mars global mapping and photometry of selected areas on mars are used to investigate the nature of bright and dark wind streaks that extend from topographic obstacles occurrence of both bright and dark streaks is strongly latitude dependent and is only weakly correlated with surface properties such as albedo and thermal inertia data on the colors albedos and phase behavior of streaks are consistent with models of bright streaks as mosaics of plains material and brighter redder dust less than 20 of the ground need be covered by the optically thick dust in the brightest parts of the streaks the amount of dust in optically thick layers could be as little as 10 3 g cm2 dark streaks can be interpreted as erosional windows in a patchy dust cover our model of dust deposition in optically thick patches is sedimentologically different from scenarios involving the deposition of ubiquitous optically thin layers it has the advantage that large amounts of dust can be deposited without affecting regional albedos

mars atmospheric dynamics as simulated by the nasa ames general circulation model 2 transient baroclinic eddies a large set of experiments performed with the nasa ames mars general circulation model gcm have been analyzed to determine the properties structure and dynamics of the simulated transient baroclinic eddies the mars gcm simulations span a wide range of seasonal dates and dust loadings and include a number of special sensitivity experiments e g with flat topography there is strong transient baroclinic eddy activity in the extratropics of the northern hemisphere during the northern autumn winter and spring seasons the eddy activity remains strong for very large dust loadings though it shifts northward the eastward propagating eddies are characterized by zonal wavenumbers of 1 4 and periods of 2 10 days in several simulations the eddy variance is dominated by a single zonal wavenumber and a narrow range of periods the longer wavenumbers 1 and 2 transient eddies have a very deep vertical structure exhibiting a maximum kinetic energy density at the model top 45 50 km in many of the simulations in a simulation for early northern spring the eddies are quite shallow however the transient eddies generate the bulk of their energy baroclincally via large meridional and vertical heat fluxes at both lower and upper levels this is despite the fact that their vertical structure is typically close to equivalent barotropic above the lowest 10 km the eddies also appear to generate a substantial amount of energy barotropically via large meridional momentum fluxes at both lower and upper levels in the tropics and northern subtropics at upper levels 25 50 km there are strong transient eddy motions with structures resembling those characteristic of inertially unstable modes this eddy activity appears to be a response to the forcing of a region of marginal inertial stability by the extratropical transient baroclinic eddies as the wavenumbers and periods are the same as those in the extratropics a major surprise is the presence of very weak transient eddy activity in a number of the southern winter simulations it appears that this is partly a consequence of the stabilizing effects of the zonally symmetric topography in the gcm but it also must be associated with certain aspects of the zonal mean circulation in southern winter this is indicated by the presence of relatively large amplitude eddies in simulations for early southern autumn and spring and in a southern winter solstice simulation incorporating a different topography derived from the mars digital terrain model this topography differs from that used in most of the gcm simulations in not being characterized by steep symmetric slopes which are stabilizing to baroclinic instability in southern high latitudes it is hypothesized that the very large extent of the southern seasonal polar cap and high elevations in the south both might contribute to weakening the transient eddy activity large zonally symmetric topography in the northern hemisphere of the mars gcm also appears to have a strong impact on the transient eddies acting to increase the dominant zonal wavenumbers and phase speeds the properties of the gcm baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from viking lander meteorology observations the gcm eddies are found to be very similar to those observed in most respects a notable exception is that the eddy amplitudes in the highly dusty gcm simulations are much larger than those observed by viking during the 1977 winter solstice dust storm this is almost certainly at least partly due to the relatively small latitudinal expansion of the hadley circulation in the highly dusty gcm experiments

the meteorology of gale crater as determined from rover environmental monitoring station observations and numerical modeling part ii interpretation abstract numerical modeling results from the mars regional atmospheric modeling system are used to interpret the landed meteorological data from the rover environmental monitoring station onboard the mars science laboratory rover curiosity in order to characterize seasonal changes throughout the martian year simulations are conducted at ls 0 90 180 and 270 two additional simulations at ls 225 and 315 are explored to better understand the unique meteorological setting centered on ls 270 the synergistic combination of model and observations reveals a complex meteorological environment within the crater seasonal planetary circulations the thermal tide slope flows along the topographic dichotomy mesoscale waves slope flows along the crater slopes and mt sharp and turbulent motions all interact in nonlinear ways to produce the observed weather ls 270 is shown to be an anomalous season when air within and outside the crater is well mixed by strong flushing northerly flow and large amplitude breaking mountain waves at other seasons the air in the crater is more isolated from the surrounding environment the potential impact of the partially isolated crater air mass on the dust water noncondensable and methane cycles is also considered in contrast to previous studies the large amplitude diurnal pressure signal is attributed primarily to necessary hydrostatic adjustments associated with topography of different elevations with contributions of less than 25 to the diurnal amplitude from the crater circulation itself the crater circulation is shown to induce a suppressed boundary layer

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

chemistry morphology and origin of magmatic reaction chromite stringers associated with anorthosite in the upper critical zone at winnaarshoek eastern limb of the bushveld complex

the martian slope winds and the nocturnal pbl jet abstract the summertime martian pbl diurnal wind variation slope winds and the nocturnal low level jets were studied using prandtl s theory a mesoscale numerical model and viking lander observations during moderate prevailing large scale flow nocturnal jets were simulated that were rather similar to those on earth they were mainly caused by inertial oscillation after sunset with some contribution from the slope wind effects over sloping regions which are very common in mars during weak large scale flow shallow nocturnal drainage flows with strong vertical shear developed over the cold martian slopes at middle and high latitudes these katabatic winds tended to turn to flow along the slope by dawn due to the coriolis force for sufficiently steep slopes near surface drainage winds could reach considerable speeds in contrast the typical afternoon upslope winds were vertically homogeneous up to 2 3 km and weak only 1 3 m s 1 in magnitude even over relatively steep large scale slopes

the first occurrence of platinum group minerals pgm in a chromite deposit in the eastern desert egypt the platinum group mineralogy pgm of the chromitite from gebel lawi in the southeastern desert has been investigated the most abundant base metal sulfides bms associated with the lawi chromite are pentlandite millerite and heazlewoodite the major platinum group minerals identified were as follows laurite irosru s2 osmian iridium osir hollingworthite rhass tellurian arsenopalladinite pdtesbas polarite pdhg besides cuprian palladian gold cupdau a pd sb hg and hgte phases laurite and osmian iridium occur preferentially in chromite os ir commonly forms composite pgm with laurite hollingworthite and tellurian arsenopalladinite are included within serpentine and close to the base metal sulfides the cuprian palladian gold shares boundaries with chromite polarite together with the pd sb hg and hgte phases are embedded in serpentine palladium is the most abundant pge in the gebel lawi chromite

daily and seasonal viking observations of martian bore wave systems a martian atmospheric phenomenon called a bore wave has been observed by the viking imaging system during late spring and early summer of two martian years in the tharsis ridge region of the planet the observational data are presented and a tentative explanation is offered for the occurrence of this feature formed by airflow and which behaves like a thermally induced diurnal katabatic breeze

martian intracrater splotches occurrence morphology and colors abstract martian intracrater splotches and related streaks are studied with global data on their occurrence and regional data on color and morphology the fraction of craters with splotches is greatest at high latitudes splotch occurrence is not strongly correlated with surface properties such as albedo and thermal inertia except where these correlate with substantial sediment cover large numbers of splotches are or include dunes especially at high southern latitudes color data show that the dune and nondune materials in splotches are part of one related group of materials that may be of similar composition but varying particle sizes the color data also show that some streaks are simply material deflated from splotches and mixed with local plains material while other streaks are more complex and may involve erosion of thin surface layers by material blown from the splotches splotches appear to be trapped eolian sand but probably have been formed by a great variety of mechanisms a large percentage of craters with splotches show evidence of complex histories of sediment deposition and erosion many splotches may be lag deposits from erosion of regional sediment cover present sediment budgets in splotches are not known but there is some evidence for loss of material and no evidence for resupply from outside the craters

thermal structure of the atmospheric boundary layer on mars based on mini tes observations this paper presents and discusses the vertical profiles of the potential temperature in the martian boundary layer the profiles were remotely sensed from on board the spirit mars exploration rover during the first 702 sols of its operation in 2004 2005 the rover carried the miniature thermal emission spectrometer mini tes which allowed it to retrieve temperature profiles up to a level 2 km above the ground surface the data analyzed here permit a reconstruction of the diurnal and seasonal structure of the lower part of the martian convective boundary layer an evaluation of the boundary layer depth and a computation of the temperature heat flux

the mars regional atmospheric modeling system model description and selected simulations the mars regional atmospheric modeling system mrams is introduced and selected model results are presented and compared with landed meteorological data when possible mrams is descended from a nonhydrostatic earth mesoscale and cloud scale model that is widely used for forecasting weather and simulating atmospheric systems over complex terrain mesoscale models such as mrams are ideal tools for making use of the high resolution data sets arriving from mars global surveyor experiments simulation of the mars pathfinder mpf landing site at lsd 142 using 1 2 degree mars orbiter laser altimeter mola derived topography and thermal emission spectrometer thermal inertia is shown to be in good agreement with observed near surface temperature pressure and wind direction simulations of topographically induced thermal circulations and mountain induced gravity waves are shown to be consistent with theory and earlier studies that tie large amplitude mountain waves to strong winds capable of producing dust streaks and local dust lifting events a large eddy simulation of the convective boundary layer provides estimates of vertical profiles of heat flux momentum flux turbulent kinetic energy and vertical velocity variance the model results suggest that the martian atmosphere is roughly two to three times more turbulent than the terrestrial atmosphere during the afternoon but fluxes are roughly an order of magnitude smaller due to the lower density dust devillike circulations are also predicted in the large eddy simulation finally a simulation that examines atmosphere surface interactions near big crater is discussed predicted surface wind stress patterns are consistent with aeolian processes inferred through mars orbiter camera imagery of big crater located near the mpf landing site c 2001 academic press

aeolian features and processes at the mars pathfinder landing site the mars pathfinder landing site contains abundant features attributed to aeolian or wind processes these include wind tails drift deposits duneforms of various types ripplelike features and ventifacts the first clearly seen on mars many of these features are consistant with formation involving sand size particles although some features such as dunes could develop from saltating sand size aggregates of finer grains the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline rather than aggregates excluding the ventifacts the orientations of the wind related features correlate well with the orientations of bright wind steaks seen on viking orbiter images in the general area they also correlate with wind direction predictions from the nasa ames general circulation model gcm which show that the strongest winds in the area occur in the northern hemisphere winter and are directed toward 209

the seasonal behavior of water ice clouds in the tharsis and valles marineris regions of mars mars orbiter camera observations abstract the mars global surveyor mars orbiter camera was used to obtain global maps of the martian surface with equatorial resolution of 7 5 km pixel in two wavelength ranges blue 400 450 nm and red 575 625 nm the maps used were acquired between march 15 1999 ls 110 and july 31 2001 ls 205 corresponding to approximately one and a quarter martian years using the global maps cloud area in km2 has been measured daily for water ice clouds topographically corresponding to olympus mons ascraeus mons pavonis mons arsia mons alba patera the western valles marineris canyon system and for other small surface features in the region seasonal trends in cloud activity have been established for the three tharsis volcanoes olympus mons and alba patera olympus ascraeus and pavonis mons show cloud activity from about ls 0 220 with a peak in cloud area near ls 100 one of our most interesting observational results is that alba patera shows a double peaked feature in the cloud area with peaks at ls 60 and 140 and a minimum near ls 100 arsia mons shows nearly continuous cloud activity the altitudes of several of these clouds have been determined from the locations of the visual cloud tops and optical depths were measured for a number of them using the disort code of stamnes et al 1988 appl opt 27 2502 2509 several aspects of the observations e g cloud heights effects of increased dust on cloud activity are similar to simulations in richardson et al 2002 j geophys res 107 5064 a search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours unambiguous evidence for other periodicities was not found

observations of martian ice clouds by the mars global surveyor thermal emission spectrometer the first martian year successful operation of the mars global surveyor spacecraft beginning in september 1997 ls 184 has permitted extensive observations over more than a martian year initially thin normal optical depth 0 06 at 825 cm 1 ice clouds and hazes were widespread showing a distinct latitudinal gradient with the onset of a regional dust storm at ls 224 ice clouds vanished in the southern hemisphere to reappear gradually after the decay of the storm the zonally averaged cloud opacities show little difference between the beginning and end of the first martian year a broad low latitude cloud belt with considerable longitudinal structure was present in early northern summer apparently characteristic of the northern summer season it vanished between ls 140 and 150 the latitudinal extent of this feature is apparently controlled by the ascending branch of the hadley circulation the most opaque clouds optical depth 0 6 were found above the summits of major volcanic features these showed spatial structure possibly associated with wave activity variety among low lying late morning clouds suggests localized differences in circulation and microclimates limb observations showed extensive optically thin optical depth 0 04 stratiform clouds at altitudes up to 55 km considerable latitude and altitude variations were evident in ice clouds in early northern spring ls 25 near 30 km thin clouds extended from just north of the equator to 45 n nearly to the north polar vortex a water ice haze was present in the north polar night ls 30 at altitudes up to 40 km because little dust was present this probably provided heterogeneous nucleation sites for the formation of co2 clouds and snowfall at altitudes below 20 km where atmospheric temperatures dropped to the co2 condensation point the relatively invariant spectral shape of the water ice cloud feature over space and time indicates that ice particle radii are generally between 1 and 4 m

structure of an internal bore and dissipating gravity current as revealed by raman lidar abstract detailed moisture observations from a ground based raman lidar and special radiosonde data of two disturbances associated with a dissipating gust front are presented a synthesis of the lidar data with conventional meteorological data in conjunction with theoretical calculations and comparison to laboratory studies leads to the conclusion that the disturbances seen in both the lidar and accompanying barograph data represent a weak gravity current and an associated undular bore the disturbances display excellent coherence over hundreds of kilometers upstream of the lidar site bore formation occurs at the leading edge of the gust front coincidentally with the rapid weakening of the gravity current analysis suggests that the bore was generated by the collapse of the gravity current into a stable nocturnal inversion layer and subsequently propagated along this wave guide at nearly twice the speed of the gravity current the raman lidar provided detailed measurements of the vertical structure o

toward a parameterization of global scale organic carbon mineralization kinetics in surface marine sediments an empirical function is derived for predicting the rate depth profile of particulate organic carbon poc degradation in surface marine sediments including the bioturbated layer the rate takes the form of a power law analogous to the middelburg function the functional parameters were optimized by simulating measured benthic o2 and no3 fluxes at 185 stations worldwide using a diagenetic model the novelty of this work rests with the finding that the vertically resolved poc degradation rate in the bioturbated zone can be determined using a simple function where the poc rain rate is the governing variable although imperfect the model is able to fit 71 of paired o2 and no3 fluxes to within 50 of measured values it further provides realistic geochemical concentration depth profiles no3 penetration depths and apparent first order poc mineralization rate constants the model performs less well on the continental shelf due to the high heterogeneity there when applied to globally resolved maps of rain rate the model predicts a global denitrification rate of 182 88 tg yr 1 of n and a poc burial rate of 107 52 tg yr 1 of c with a mean carbon burial efficiency of 6 1 these results are in very good agreement with published values our proposed function is conceptually simple requires less parameterization than multi g type models and is suitable for non steady state applications it provides a basis for more accurately simulating benthic nutrient fluxes and carbonate dissolution rates in earth system models

mars global digital dune database and initial science results 1 a new mars global digital dune database mgd3 constructed using thermal emission imaging system themis infrared ir images provides a comprehensive and quantitative view of the geographic distribution of moderate to large size dune fields area 1 km2 that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of mars mgd3 extends from 65 n to 65 s latitude and includes 550 dune fields covering 70 000 km2 with an estimated total volume of 3 600 km3 this area when combined with polar dune estimates suggests moderate to large size dune field coverage on mars may total 800 000 km2 6 times less than the total areal estimate of 5 000 000 km2 for terrestrial dunes where availability and quality of themis visible vis or mars orbiter camera narrow angle moc na images allow we classify dunes and include dune slipface measurements which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification for dunes located within craters the azimuth from crater centroid to dune field centroid referred to as dune centroid azimuth is calculated and can provide an accurate method for tracking dune migration within smooth floored craters these indicators of wind direction are compared to output from a general circulation model gcm dune centroid azimuth values generally correlate to regional wind patterns slipface orientations are less well correlated suggesting that local topographic effects may play a larger role in dune orientation than regional winds

persistent dust cloud activity on mars near echus chasma in 1978 abstract clouds were recorded by viking cameras during five out of six observations over the same side canyon of echus chasma during a period of over 3 1 2 months in 1978 although these clouds were different from one another in appearance all were bright through a red filter and are believed to be at least partially composed of dust two of them were also imaged in violet light in which they were also bright therefore they may also have contained condensate a plausible explanation for the formation of the dust clouds is drainage winds which are also known to be active to the west in the tharsis region during this season in this case winds may have been flowing downslope from the north rim of tithonium chasma

an overview of the pge concentrations in the shetland ophiolite complex extremely anomalous platinum group element pge concentrations are known at one site cliff in the shetland ophiolite complex systematic pge analysis of all the mafic and ultramafic igneous and alteration lithologies in the ophiolite has revealed many lower grade anomalous pge occurrences throughout the cumulate ultramafic sequence and their distribution is described here more sites with pge enrichments as anomalous as those at cliff have not been found at cliff the anomalous values of over 60 ppm pt pd are restricted to a chromite rich sulphide bearing dunite forming a small part of a 200 m dunite lens in mantle harzburgite close to the basal thrust of the ophiolite lower values of up to 6 4 ppm pt pd occur in chromite poor sulphide rich dunites also within this dunite lens the only other chromite rich dunite lens in the cliff area also has detected pt and pd but with low pt pd values of 200 ppb in contrast harzburgites metasediments underlying the basal thrust serpentinites from the basal thrust and internal faults are all barren of pt and pd detection limit 20 ppb in the cliff area therefore detected pge values are restricted to magmatic chromite rich dunite lenses pge analyses of drill core from beneath the disused chromite quarries at cliff are low 227 ppb pt pd indicating that the extremely anomalous pge values are very restricted this supports the idea that pge concentrated magmatically within the dunite lens at cliff may have been remobilized locally to produce extremely anomalous pge values in an alteration zone only a few metres in diameter elsewhere in the ophiolite anomalous pt pd values of up to 4 ppm occur in chromite rich sulphide bearing dunite within the dunite unit which stratigraphically overlies the harzburgite pt pd concentrations of up to 1 ppm are present in the pyroxenites and wehrlites of the upper part of the ultramafic sequences high level wehrlites and pyroxenites within the gabbro unit representing late ultramafic differentiates contain lower levels of pge of up to 310 ppb pt pd the gabbros all have less than 20 ppb pt and pd this distribution indicates that the pge concentrations occur in specific primary magmatic lithologies and pathfinder analysis shows that they are associated with ni cu au and cr pge have not been found above detection limits in fault zones away from primary pge mineralization sites and it is concluded that pge are not significantly hydrothermally reconcentrated at cliff remobilization may have occurred over short distances of only a few metres at most

determination of the wind induced detachment threshold for granular material on mars using wind tunnel simulations experimental results are presented of wind induced grain detachment under mars simulation conditions a simple force balance equation is applied to quantify the wind shear stress required for removal of glass spheres from a sand bed the transport of fine grained martian dust is simulated by the detachment of hollow glass spheres which resemble low mass density dust aggregates observed to form during simulations when using mars analogue material the results agree well with observations of dust removal and wind speed measurements made by the nasa viking landers at the martian surface this work supports the suggestion that dust aggregate fragmentation allows wind induced dust entrainment at substantially lower wind shear than that of solid sand grains and has direct application to the study of global dust transport and martian climatology

impact of gravity waves on the middle atmosphere of mars a non orographic gravity wave parameterization based on global climate modeling and mcs observations the impact of gravity waves gw on diurnal tides and the global circulation in the middle upper atmosphere of mars is investigated using a general circulation model gcm we have implemented a stochastic parameterization of non orographic gw into the laboratoire de meteorologie dynamique lmd mars gcm lmd mgcm following an innovative approach the source is assumed to be located above typical convective cells urn x wiley jgre media jgre21298 jgre21298 math 0001250 pa and the effect of gw on the circulation and predicted thermal structure above 1 pa urn x wiley jgre media jgre21298 jgre21298 math 000250 km is analyzed we focus on the comparison between model simulations and observations by the mars climate sounder mcs on board mars reconnaissance orbiter during martian year 29 mcs data provide the only systematic measurements of the martian mesosphere up to 80 km to date the primary effect of gw is to damp the thermal tides by reducing the diurnal oscillation of the meridional and zonal winds the gw drag reaches magnitudes of the order of 1 m s sol above 10 urn x wiley jgre media jgre21298 jgre21298 math 0003 pa in the northern hemisphere winter solstice and produces major changes in the zonal wind field from tens to hundreds of m s while the impact on the temperature field is relatively moderate 10 20 k it suggests that gw induced alteration of the meridional flow is the main responsible for the simulated temperature variation the results also show that with the gw scheme included the maximum day night temperature difference due to the diurnal tide is around 10 k and the peak of the tide is shifted toward lower altitudes in better agreement with mcs observations

severe downslope windstorm calculations in two and three spatial dimensions using anelastic interactive grid nesting a possible mechanism for gustiness abstract the clark nonhydrostatic anelastic code is extended to allow for interactive grid nesting in both two and three spatial dimensions tests are presented which investigate the accuracy of three different quadratic interpolation formulae which are used to derive boundary conditions for the fine mesh model application of the conservation condition of kurihara and others is shown to result in significant improvements in the treatment of interactive nesting a significant improvement in the solutions for interactive versus parasitic nesting is also shown in the context of forced gravity wave flow this result for the anelastic system is in agreement with the earlier results of phillips and shukla who considered the hydrostatic shallow water system of equations the interactive nesting model is applied to the simulation of the severe downslope windstorm of 11 january 1972 in boulder using both two and three spatial dimensions the three dimensional simulation results in a gustiness signature in the

simulation of the atmospheric thermal circulation of a martian volcano using a mesoscale numerical model mesoscale 100 km atmospheric phenomena are ubiquitous on mars as revealed by mars orbiter camera images numerical models provide an important means of investigating martian atmospheric dynamics for which data availability is limited but the resolution of general circulation models which are traditionally used for such research is not sufficient to resolve mesoscale phenomena to provide better understanding of these relatively small scale phenomena mesoscale models have recently been introduced here we simulate the mesoscale spiral dust cloud observed over the caldera of the volcano arsia mons by using the mars regional atmospheric modelling system our simulation uses a hierarchy of nested models with grid sizes ranging from 240 km to 3 km and reveals that the dust cloud is an indicator of a greater but optically thin thermal circulation that reaches heights of up to 30 km and transports dust horizontally over thousands of kilometres

field and laboratory observations of bed stress and associated nutrient release in a tidal estuary abstract nutrient release driven by sediment resuspension in a shallow coastal estuarine system is examined with field observations of bed stress and bed elevation coupled with laboratory erosion experiments on sediment cores two field experiments were conducted over near cohesive muddy sand sediments in the great bay estuary new hampshire in the first deployment boundary layer development during typical summer tidal forcing was observed while the second deployment occurred under enhanced wind forcing of tropical storm irene in situ bed stress and erosion depths were estimated with a profiling acoustic doppler velocimeter sediment cores were subjected to eromes erosion chamber experiments to determine erosion depth and nutrient release as a function of applied shear stress results show erosion depths are consistent with in situ observations over shear stresses ranging from 0 10 n m 2 incipient motion to 0 35 n m 2 resuspension events erosion chamber experiments showed that ammonium release up to 2 mmol m 2 increased with bed stress in both spring and summer however phosphate release was more variable with no phosphate release during resuspension in spring and a variable phosphate flux ranging 0 5 2 mmol m 2 in summer increased hydrodynamic forcing during a storm event in the summer generated shear stresses up to 0 58 n m 2 during flood tides that exceeded the threshold for sediment motion and resulted in erosion of the seabed eromes results predict there was concomitant release of nutrients into the water column from the muddy sediments of the bay and the release of dissolved inorganic nitrogen and phosphate was up to 10 and 65 respectively of the summer monthly riverine input of these nutrients results indicate qualitatively that in shallow tidally dominated estuaries fine grained sediment beds may be a source of nutrients that are particularly important during storms that enhance near bed shear stresses

the bushveld complex south africa formation of platinum palladium chrome and vanadium rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large relatively slowly cooling subsiding magma chamber platinum group element pge deposits in the bushveld complex and other layered intrusions form when large incompletely solidified magma chambers undergo central subsidence in response to crustal loading resulting in slumping of semi consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides oxides olivine and pyroxene and less dense layers enriched in plagioclase the most economic pge cr and v reefs form in large multiple replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification the depth of emplacement has to be relatively shallow as otherwise ductile crust would not be able to flex and collapse in smaller intrusions cooling rates are faster subsidence is less pronounced and where it occurs the cumulate may be largely solidified resulting in insignificant mush mobility and mineral sorting layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower but the reefs can be relatively thicker an additional factor controlling the pge cr and v prospectivity of intrusions is their location within cratons intra cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large layered igneous bodies furthermore intrusions sited within cratons are more readily preserved because cratons are underlain by thick buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust

mars surface pressure tides and their behavior during global dust storms simulations of mars atmospheric tides with the nasa ames mars general circulation model are presented and analyzed in an annual simulation diurnal and semidiurnal tides in the model s surface pressure field are shown to compare well with tides observed by the viking landers throughout the mars year focused simulations of global dust storms during the northern winter season show a semidiurnal tide that responds very strongly to the increased dust load during the storms again matching well with observations analysis of the structure and behavior of this tide during global storms verifies that it is dominated by the gravest symmetric hough mode h22 as has been noted previously however it is shown here that additional symmetric and asymmetric modes play an important role in accounting for the structure of the tide and its variation during the dust storms the phase advance observed between the viking lander sites earlier semidiurnal phase at the higher latitude site is explained by the presence of these higher order modes finally decomposition of the semidiurnal tide during a global dust storm into its component hough modes shows that the amplitude of the h22 mode mirrors changes in the observed overhead visible dust opacity while variations in higher order modes are indicative of the zonal and possibly longitudinal distribution of airborne dust

numerical modeling of mars dust devils albedo track generation 1 dust devil tracks are abundant on mars and can significantly change the regional surface albedo possibly altering regional scale atmospheric circulations however little is understood about the formation of these features besides their correlation with dust devils the mars regional atmospheric modeling system mrams is used here to explicitly simulate the formation of a dust devil track the example dust devil 200 m in diameter studied in detail here generates a track approximately 1 5 km long 75 m wide and 1 8 m in depth which compares well with observed real world tracks valuable insight is gleaned from the study of the formation of this simulated track which may be used to better interpret the linkage between observed dust devil tracks and the atmospheric and surface conditions that spawned them

dust devils on mars columnar cone shaped and funnel shaped clouds rising 1 to 6 kilometers above the surface of mars have been identified in viking orbiter images they are interpreted as dust devils confirming predictions of their occurrence on mars and giving evidence of a specific form of dust entrainment

cloud tracked winds for the first mars global surveyor mapping year we have measured winds using cloud motion in consecutive mars global surveyor mgs mars orbiter camera moc wide angle global map swaths taken during the first mapping year l s 135 360 111 we present a total of 11 200 wind vectors collected in the north polar region during l s 135 195 late summer early fall and l s 20 55 mid spring and in the south polar region during l s 337 10 late summer early fall for cases with good coverage we also present the derived mean zonal and meridional winds and the associated eddies the speed of the zonal winds in 60 n 70 n increases at 0 6 m s l s in late northern summer and that in 60 s 70 s increases at a rate of 0 7 m s l s in late southern summer the latitudinal distribution of zonal wind within 50 n 75 n from mid northern summer to early northern fall indicates that winds at higher latitudes are generally weaker than those at lower latitudes but the rate of increase with time is faster at higher latitudes there is a cyclonic gyre in the 90 w 0 30 e sector in the north polar region there are large scale waves in the weekly mean meridional wind and in the biweekly mean eddy momentum flux and eddy kinetic energy fields in the north polar region from mid to late summer the cloud tracked winds in the north are generally consistent with winds calculated by general circulation model at the water condensation level derived from mgs thermal emission spectrometer tes observations but appear stronger than the gradient winds derived from tes assuming no flow at the surface

large eddy simulation of the convective atmospheric boundary layer abstract large eddy simulations of a free convective atmospheric boundary layer with an overlying capping inversion are considered attention is given to the dependence of the results upon the various factors influencing the simulation the subgrid model the domain size and the mesh resolution by providing artificial constraints upon the convection the results also provide extra insight into the underlying dynamics the gross features of the boundary layer such as the overall energy budget are not sensitive to the details of the simulations but a number of important factors are revealed it has been found that near the surface the subgrid diffusivity must be larger than is usually supposed in order for the vertical velocity skewness to have the correct sign this region of the flow has a significant subgrid scale heat flux and it seems that the subgrid model requires improvement in such cases a revised model which under statically unstable conditions allows the mixing length of the subgrid scale tu

character of the ug2 chromitite and host rocks and petrogenesis of its pegmatoidal footwall northeastern bushveld complex the ug2 chromitite and its immediate footwall have been mapped at the centimeter scale in a characteristic section exposed in a wall in the middelpunt mine northeast bushveld complex in this region the ug2 chromitite and its coarse grained footwall rocks are underlain and overlain by plagioclase pyroxenite the ug2 chromitite itself is a massive 70 cm thick layer composed of 75 to 90 percent chromite with plagioclase as the dominant interstitial mineral immediately beneath the chromitite is the so called mixed layer a previously undescribed but distinct mappable layer 50 to 70 cm thick consisting of chromite bearing pegmatoidal pyroxenite and chromitite intimately mixed at scales of centimeters to decimeters the mixture is chaotic with no megascopic fabric and contains in bulk about 15 percent chromite the contact between the mixed layer and overlying chromitite is well defined but sinuous at scales of centimeters to decimeters based on observations of drill core and outcrop the mixed layer appears to exist throughout the central sector of the eastern bushveld and may be ubiquitous throughout the entire complex the mixed layer usually rests directly on the ug2 pegmatoid which is a well known and widespread pegmatoidal plagioclase pyroxenite the pegmatoid is much coarser grained than the underlying pyroxenite but the two lithologic units are similar in terms of mineral modes and compositions the contact between them is irregular at scales of decimeters to meters with vertical fingers of pegmatoid extending into the pyroxenite the mixed layer and ug2 pegmatoid contain rare lenses of massive anorthosite encased by continuous centimeter thick rims of chromitite a model is proposed to account for the footwall sequence of the ug2 chromitite in this model the ug2 pegmatoid formed when hydrous interstitial melt percolated up through the partially molten crystal pile accumulated beneath the preexisting compacted massive chromitite and metasomatized and partially melted the pyroxenite protolith which upon cooling recrystallized to a coarse grained rock on the basis of published experiments illustrating the effect of water on melting in mafic systems it is shown how the hydrous melt was able to penetrate the pyroxene bearing assemblages below the chromitite but unable to partially melt the chromitite itself which in consequence remained relatively impermeable the anorthosite lenses in the pegmatoid mark local areas of relatively high degrees of hydration partial melting with the anorthosite representing the crystalline residue the mixed layer formed by gradual collapse of the base of the ug2 chromitite into the less dense relatively fluid footwall the mixed layer and ug2 pegmatoid are diagnostic of the ug2 chromitite and the three lithologic units should be considered a single petrologic unit

platinum group elements in silicate rocks of the lower critical and main zones at union section western bushveld complex concentration patterns of platinum group elements pge in the lower critical and main zones of the bushveld complex are modelled by a process of metal collection by segregating sulphide melt followed by fractional crystallization of monosulphide solid solution mss separation of os ir ru rh enriched mss cumulate ore and pt pd enriched residual sulphide melt is inferred to have occurred by upward percolation of interstitial silicate melt entraining sulphide melt whereas mss crystals are entrapped by early crystallizing chromite this process resulted in os ir ru rh enrichment of the chromitites and an upward increasing trend of pt pd os ir ru crystallization of platinum group minerals pgm from s undersaturated sulphide melt or from coalescing noble metal clusters are alternative possibilities to explain the observed pge patterns but remain difficult to model at present remobilization of pt and pd by percolating late magmatic hydrous fluids could have resulted in metal enrichment of pre existing magmatic sulphides but this model is not supported by the metal budget of the reefs and the field data there is no evidence for solid substitution of pge into oxides and silicates

the formation of internal bores in the atmosphere a laboratory model summary recently several atmospheric observations have been interpreted as internal undular bores or internal solitary waves evolving from internal bores that propagate along low level temperature inversions it has been speculated that such disturbances are generated by some type of gravity current such as cold fronts sea breeze fronts and thunderstorm outflows interacting with an existing temperature inversion in this paper we describe a systematic laboratory study in a water channel of internal bores and their generation by the movement of gravity currents through a two layer model of the atmosphere we compare the results of our laboratory experiments with previous theories and numerical simulations and with several detailed atmospheric observations of internal bores at different stages of development

modeling the martian seasonal water cycle ever since the observations of percival lowell the annual cycle of martian water has been a fascinating topic in planetary exploration observations by the viking orbiter supplemented by earth based microwave and infrared observations have given us a reasonable picture of this cycle we are now also able to model the cycle using our mars climate model a simplified atmospheric general circulation model designed specifically for this purpose we find that a thin adsorbing layer of the martian regolith plays a fundamental role in the water cycle limiting the lower atmospheric relative humidity and preventing the formation of widespread ice deposits at low latitudes we are thus able to estimate a large scale average value of the specific soil surface area of this regolith water which evaporates from the permanent north polar ice cap during summer is returned by a process of repeated evaporation and precipitation on the retreating seasonal cap the following spring so that the global inventory of water outside the polar caps ranges within narrow limits there is a small net annual deposition of water ice at the south polar cap which is always at dry ice temperatures if ice on the residual south polar cap is exposed during the summer it rapidly sublimes generating vapor amounts similar to those observed in northern summer recovery to normal dry conditions in the southern atmosphere occurs very rapidly in the next year such an event could explain the otherwise anomalous earth based pre viking observations of a wet southern summer if southern ice deposits at lower latitudes are exposed the vapor can be transferred irreversibly through the strong hadley cell to the north polar cap we therefore speculate that the asymmetry of mars current orbit is responsible for the asymmetry of the present water distribution with extensive permanent water ice deposits located only in the colder aphelion summer northern hemisphere