the age of the medusae fossae formation evidence of hesperian emplacement from crater morphology stratigraphy and ancient lava contacts abstract the medusae fossae formation mff covering about 2 1 10 6 km 2 with an estimated volume of 1 4 10 6 km 3 and straddling the equatorial region of mars east of tharsis has historically been mapped and dated as amazonian in age analysis of the mff using a range of new observations from recent mission data at multiple resolutions reveals evidence that the formation is older than previously hypothesized with parts of the mff having formed in the hesperian and parts having been reworked and reformed throughout the amazonian up to the present ancient outcroppings of the mff edged with jagged yardangs became a mold for embaying hesperian aged lavas the erosion of the mff left solidified lava casts in the embaying lava unit this lava edge morphology permits the identification of ancient contacts between the mff and hesperian aged lava terrain additionally the flanking fan of the hesperian aged apollinaris patera volcano embays the formation at its foot indicating that parts of the mff were formed in the hesperian erosion has erased and inverted many of the superposed craters in the region showing that very young amazonian ages derived from impact crater size frequency distributions are resurfacing ages and not emplacement ages we find abundant evidence that the formation is extremely mobile and continuously reworked we conclude that a significant part of the mff may have originally been emplaced in the hesperian these observations place new constraints on the mode of origin of the mff

the dispersal of pyroclasts from apollinaris patera mars implications for the origin of the medusae fossae formation the medusae fossae formation mff has long been thought to be of amazonian age but recent studies propose that a significant part of its emplacement occurred in the hesperian and that many of the amazonian ages represent modification erosional and redepositional ages on the basis of the new formational age we assess the hypothesis that explosive eruptions from apollinaris patera might have been the source of the medusae fossae formation in order to assess the likelihood of this hypothesis we examine stratigraphic relationships between apollinaris patera and the mff and analyze the relief of the mff using topographic data we predict the areal distribution of tephra erupted from apollinaris patera using a mars global circulation model gcm combined with a semi analytical explosive eruption model for mars and compare this with the distribution of the mff we conclude that apollinaris patera could have been responsible for the emplacement of the medusae fossae formation

constraints on the martian lithosphere from gravity and topography data localized spectral admittances of the large martian volcanoes are modeled by assuming that surface and subsurface loads are elastically supported by the lithosphere in order to model the case where the load density differs from that of the crust a new method for calculating gravity anomalies and lithospheric deflections is developed the modeled gravity anomalies depend upon the elastic thickness crustal thickness load density and crustal density and these parameters were exhaustively sampled in order to determine their effect on the misfit between the observed and modeled admittance function we find that the densities of the martian volcanoes are generally well constrained with values of 3200 100 kg m 3 which is considerably greater than those reported previously these higher densities are consistent with those of the martian basaltic meteorites which are believed to originate from the tharsis and elysium volcanic provinces the crustal density is constrained only beneath the elysium rise to be 3270 150 kg m 3 if this value is representative of the northern lowlands then pratt compensation is likely responsible for the approximately 6 km elevation difference between the northern and southern hemispheres the elastic thicknesses of the major martian volcanoes when subsurface loads are ignored are found to be the following elysium rise 56 20 km olympus mons 93 40 km alba patera 66 20 km and ascraeus mons 105 40 km we have also investigated the effects of subsurface loads allowing the bottom load to be located either in the crust as dense intrusive material or in the mantle as less dense material we found that all volcanoes except pavonis are better modeled with the presence of less dense material in the upper mantle which is indicative of either a mantle plume or a depleted mantle composition an active plume beneath the major volcanoes is consistent with recent analyses of cratering statistics on olympus mons and the elysium rise which indicate that some lava flows are as young as 10 30 myr as well as with the crystallization ages of the shergottites of which some are as young as 180 myr

analysis of the bedding landslide due to the presence of the weak intercalated layer in the limestone analysis and research results show that the sliding plane of jiudingshan landslide is along the weak intercalated layer clay filled in the limestone and the sliding block is separated by the tension crack on the slope crest the earlier study results show that for the rough ups and downs structural plane when i is greater than 2 0 the shear strength of the structural surface is intensely close to the strength of the filling by the earlier theory this failure must be through the clay filling in this study the failure is back analyzed and the shear strength of the infilling is tested by the laboratory direct shear tests for which samples were retrieved in the field the failure cannot be explained by the laboratory results of shear strength parameters to simulate the field conditions the real strength parameters of sliding surface are measured by the in situ shear tests for the weak intercalated layer by the in situ tests it is shown that the failure initiates along the contacts between the clay infilling and the limestone boundaries but not through the clay itself though the contact surface is the interface of the clay limestone the cohesion is not 0 and it is not negligible too

annual climate variability in the holocene interpreting the message of ancient trees abstract over vast areas of the world s landmasses where climate beats out a strong seasonal rhythm tree growth keeps unerring time in their rings trees record many climate melodies played in different places and different eras recent years have seen a consolidation and expansion of tree ring sample collections across the traditional research areas of north america and europe and the start of major developments in many new areas of eurasia south america and australasia from such collections are produced networks of precisely dated chronologies records of various aspects of tree growth registered continuously year by year across many centuries their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space with their extensive coverage high temporal resolution and rigid dating control dendroclimatic reconstructions contribute significantly to our knowledge of late holocene climates most importantly on timescales ranging from 1 to 100 years in special areas of the world where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved work building chronologies covering many millennia continues apace very recently trees have provided important new information about major modes of general circulation dynamics linked to the el nino southern oscillation and the north atlantic oscillation and about the effect of large volcanic eruptions as for assessing the significance of 20th century global warming the evidence from dendroclimatology in general supports the notion that the last 100 years have been unusually warm at least within a context of the last two millennia however this evidence should not be considered equivocal the activities of humans may well be impacting on the natural growth of trees in different ways making the task of isolating a clear climate message subtly difficult

dust and ice deposition in the martian geologic record abstract the polar layered deposits of mars demonstrate that thick accumulations of dust and ice deposits can develop on the planet if environmental conditions are favorable these deposits appear to be hundreds of millions of years old and other deposits of similar size but of greater age in nonpolar regions may have formed by similar processes possible relict dust deposits include from oldest to youngest noachian intercrater materials including arabia mantle deposits noachian to early hesperian south polar pitted deposits early hesperian hellas and argyre basin deposits late hesperian electris deposits and the amazonian medusae fossae formation these deposits typically are hundreds of meters to a couple kilometers thick and cover upward of a million or more square kilometers the apparent persistence of dust sedimentation at the south pole back to the early hesperian or earlier and the early growth of tharsis during the late noachian and perhaps earlier indicates that extensive polar wandering is unlikely following the middle noachian a scenario for the overall history of dust and perhaps ice deposition on mars includes widespread voluminous accumulations perhaps planetwide during the noachian as impacts volcanism and surface processes generated large amounts of dust the arabia deposits may have formed as ice availability and dust accumulation waned during the early hesperian thick dust sedimentation became restricted to the south pole and the deep hellas and argyre basins the north polar sedimentary record prior to the amazonian is largely obscured deposits at electris and medusae fossae may have resulted from local sources of fine grained material perhaps volcanic eruptions

shallow radar sharad sounding observations of the medusae fossae formation mars the sharad shallow radar sounding radar on the mars reconnaissance orbiter detects subsurface reflections in the eastern and western parts of the medusae fossae formation mff the radar waves penetrate up to 580 m of the mff and detect clear subsurface interfaces in two locations west mff between 150 and 155 e and east mff between 209 and 213 e analysis of sharad radargrams suggests that the real part of the permittivity is 3 0 which falls within the range of permittivity values inferred from marsis data for thicker parts of the mff the sharad data cannot uniquely determine the composition of the mff material but the low permittivity implies that the upper few hundred meters of the mff material has a high porosity one possibility is that the mff is comprised of low density welded or interlocked pyroclastic deposits that are capable of sustaining the steep sided yardangs and ridges seen in imagery the sharad surface echo power across the mff is low relative to typical martian plains and completely disappears in parts of the east mff that correspond to the radar dark stealth region these areas are extremely rough at centimeter to meter scales and the lack of echo power is most likely due to a combination of surface roughness and a low near surface permittivity that reduces the echo strength from any locally flat regions there is also no radar evidence for internal layering in any of the sharad data for the mff despite the fact that tens of meters scale layering is apparent in infrared and visible wavelength images of nearby areas these interfaces may not be detected in sharad data if their permittivity contrasts are low or if the layers are discontinuous the lack of closely spaced internal radar reflectors suggests that the mff is not an equatorial analog to the current martian polar deposits which show clear evidence of multiple internal layers in sharad data

medusae fossae formation new perspectives from mars global surveyor 1 the nature and origin of the medusae fossae formation mff on mars has been debated since the return of the first viking images the mff s young age distinctive surface texture and lack of obvious source have prompted multiple hypotheses for its origin this study uses data from the mars global surveyor mgs mission to examine the mff at all available scales we discuss and quantify observations from mars orbiter laser altimeter mola topography and mars orbiter camera moc images to better constrain the origin of the mff topographic grid estimates yield a present extent of 2 1 106 km2 and a volume of 1 4 106 km3 however remnant yardang deposits observed far from the thicker lobes of mff material suggest that it may have once covered up to 5 106 km2 we do not find compelling evidence for extensive fluvial reworking of the mff however in several regions buried channels are apparent in the mff because the formation is draped over underlying topography layering is apparent at all scales from submeter to hundreds of meters with variable resistance to weathering continuity of layers appears to be local to regional but not likely formation wide yardangs form both parallel and bidirectional patterns with resistant layers and jointing probably influencing their orientations a comparative study of mff regional topography and surface expression indicates that the mff is quantitatively dissimilar to martian polar layered deposits the material is most likely a friable and irregularly consolidated air fall deposit of probable volcanic origin

occurrence and origin of rhythmic sedimentary rocks on mars sedimentary rocks preserved on the surface of mars represent a natural archive of past climate conditions although the details of their formation often remain poorly constrained the recent detection of rhythmic bedding patterns in the arabia terra region suggests the influence of orbital variations on sedimentary deposition here we detail a number of new sites which exhibit quasiperiodic stratigraphic variations demonstrating their occurrence throughout the equatorial region of the planet we characterize these recorded signals as well as the local geomorphic context and structural attributes two cyclic units are identified within gale crater the landing site of the mars science laboratory mission enabling estimation of possible formation timescales for the geologic units that may be studied in situ by the rover we find a general lack of fluvial features in connection with rhythmic geologic units contrasting these sites with the aperiodic deltaic stratigraphy found at eberswalde crater possible formation scenarios and their climatic implications are discussed for the diverse set of quasiperiodic sedimentary units we propose multiple depositional pathways for recording cyclic climate changes including repeated evaporitic precipitation from groundwater discharge in topographic lows as well as largely anhydrous accumulation of atmospheric dust for deposits outside of confined basins the preservation of orbital signals in sediments distributed across a wide range of geographic settings suggests a pervasive influence on martian climate conditions through time

ignimbrites of amazonis planitia region of mars a series of postulated ignimbrite units is mapped in the amazonis memnonia and aeolis quadrangles of mars the units cover about 2 2 106 km2 within a broad but discontinuous and irregular belt trending east west along the highland lowland boundary the ignimbrites overlie parts of the western and southern aureole materials of olympus mons but are embayed in places by the lava plains of the lowlands stratigraphic relations between the basalt flows from the tharsis montes region and the ignimbrites are not clearly defined crater counts suggest that the younger ignimbrites postdate the lava flows crater counts per square kilometer for the ignimbrites range from 7 29 1 95 10 4 to 6 36 2 01 10 5 for craters larger than 1 km in diameter the ignimbrite materials form thick 100 m extensive relatively flat sheets that are smooth to grooved or gently undulating grooved surfaces appear to be yardangs and in most places are not alined with prevailing wind directions the seven mapped ignimbrite units are characterized by morphologic expression stratigraphic position and crater counts similarities to ignimbrites in the pancake range of central nevada include 1 rounded patches of smooth high albedo nonwelded material superposed on jointed low albedo welded material 2 local complementary joint sets in welded materials and 3 thick flow sheets of great areal extent that follow but subdue underlying topography four major eruptive centers occur in areas where units are thickest and where a dominant nnw sse structural trend is expressed locally by unit margins elongate collapse features and normal faulting a minimum volume of 3 85 106 km3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations

observations of the north polar region of mars from the mars orbiter laser altimeter elevations from the mars orbiter laser altimeter mola have been used to construct a precise topographic map of the martian north polar region the northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5 kilometer deep hemispheric depression that is contiguous with the area into which most outflow channels emptied polar cap topography displays evidence of modification by ablation flow and wind and is consistent with a primarily h2o composition correlation of topography with images suggests that the cap was more spatially extensive in the past the cap volume of 1 2 3 10 6 to 1 7 3 10 6 cubic kilometers is about half that of the greenland ice cap clouds observed over the polar cap are likely composed of co 2 that condensed out of the atmosphere during northern hemisphere winter many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography

a comparison of volcanic eruption processes on earth moon mars io and venus the silicate planets and satellites display a wide range of physical chemical and atmospheric characteristics which may influence the nature of volcanism a major geological process common to the evolution of the surfaces of these bodies consideration of the process of magma ascent and eruption from first principles allows predictions to be made concerning volcanic eruption styles and expected landforms and deposits on each planetary body examination of actual land forms and deposits in light of these predictions leads to a better understanding of the nature of volcanic eruption processes and outlines outstanding problems

optimal surface temperature reconstructions using terrestrial borehole data 1 we derive an optimal northern hemisphere mean surface temperature reconstruction from terrestrial borehole temperature profiles spanning the past five centuries the pattern of borehole ground surface temperature gst reconstructions displays prominent discrepancies with instrumental surface air temperature sat estimates during the 20th century suggesting the presence of a considerable amount of noise and or bias in any underlying spatial sat signal the vast majority of variance in the borehole dataset is efficiently retained by its two leading eigenvectors a sizable share of the variance in the first eigenvector appears to be associated with non sat related bias in the borehole data a weak but detectable sat signal appears to be described by a combination of the first two eigenvectors exploiting this eigendecomposition application of optimal signal estimation methods yields a hemispheric borehole sat reconstruction that is largely consistent with instrumental data available in past centuries and is indistinguishable in its major features from several published long term temperature estimates based on both climate proxy data and model simulations

internal structure and early thermal evolution of mars from mars global surveyor topography and gravity topography and gravity measured by the mars global surveyor have enabled determination of the global crust and upper mantle structure of mars the planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy a region of crust that thins progressively from south to north and encompasses much of the southern highlands and tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and arabia terra the strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history the thickness of the elastic lithosphere increases with time of loading in the northern plains and tharsis the northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing

widespread excess ice in arcadia planitia mars the distribution of subsurface water ice on mars is a key constraint on past climate while the volumetric concentration of buried ice pore filling versus excess provides information about the process that led to its deposition we investigate the subsurface of arcadia planitia by measuring the depth of terraces in simple impact craters and mapping a widespread subsurface reflection in radar sounding data assuming that the contrast in material strengths responsible for the terracing is the same dielectric interface that causes the radar reflection we can combine these data to estimate the dielectric constant of the overlying material we compare these results to a three component dielectric mixing model to constrain composition our results indicate a widespread decameters thick layer that is excess water ice 104 km3 in volume the accumulation and long term preservation of this ice is a challenge for current martian climate models

on the secular retention of ground water and ice on mars tropical ground ice on mars undergoes long term sublimation and likely exospheric escape without restriction of sublimation the cryosphere would eventually breach leading to massive loss of any underlying groundwater we seek to understand the conditions under which the ground ice seal groundwater and subsurface habitability are preserved using multi reservoir models for the evolution of deuterium to hydrogen ratios d h we derive a median estimate of the hesperian amazonian h2o loss of 60 m interquartile range 30 120 m global equivalent layer gel neglecting magmatic degassing most of the loss may have been early with consequent low loss in the modern cold and dry climate we modeled global h2o transport within mars following an assumed abrupt transition to modern conditions at 3 ga sublimation is retarded in order of decreasing priority by higher obliquity smaller porosity higher tortuosity lower heat flow and smaller pore radius higher obliquity reduces h2o loss by decreasing tropical surface temperatures and raising global atmospheric water vapor time variable obliquities do not overly influence outcomes as long as the total duration 30 obliquity is 1 gyr with no interval longer than a few hundred myr decreased solar luminosity or a thicker co2 atmosphere can also retard loss of subsurface h2o whereas lower atmospheric water vapor accelerates sublimation if mars post noachian crustal h2o inventory was a few hundred meters gel or more then the modest loss since then implies that the cryospheric seal has been maintained following top down freezing and that groundwater likely exists globally on mars today

density and lithospheric structure at tyrrhena patera mars from gravity and topography data the tyrrhena patera highland volcano mars is associated with a relatively well localized gravity anomaly and we have carried out a localized admittance analysis in the region to constrain the density of the volcanic load the load thickness and the elastic thickness at the time of load emplacement the employed admittance model considers loading of an initially spherical surface and surface as well as subsurface loading is taken into account our results indicate that the gravity and topography data available at tyrrhena patera is consistent with the absence of subsurface loading but the presence of a small subsurface load cannot be ruled out we obtain minimum load densities of 2960 kg m 3 minimum load thicknesses of 5 km and minimum load volumes of 0 6 106 km3 photogeological evidence suggests that pyroclastic deposits make up at most 30 of this volume such that the bulk of tyrrhena patera is likely composed of competent basalt best fitting model parameters are a load density of 3343 kg m 3 a load thickness of 10 8 km and a load volume of 1 7 106 km3 these relatively large load densities indicate that lava compositions are comparable to those at other martian volcanoes and densities are comparable to those of the martian meteorites the elastic thickness in the region is constrained to be smaller than 27 5 km at the time of loading indicating surface heat flows in excess of 24 mw m 2

physical properties of martian meteorites porosity and density measurements martian meteorites are fragments of the martian crust these samples represent igneous rocks much like basalt as such many laboratory techniques designed for the study of earth materials have been applied to these meteorites despite numerous studies of martian meteorites little data exists on their basic structural characteristics such as porosity or density information that is important in interpreting their origin shock modification and cosmic ray exposure history analysis of these meteorites provides both insight into the various lithologies present as well as the impact history of the planets surface we present new data relating to the physical characteristics of twelve martian meteorites porosity was determined via a combination of scanning electron microscope sem imagery image analysis and helium pycnometry coupled with a modified archimedean method for bulk density measurements our results show a range in porosity and density values and that porosity tends to increase toward the edge of the sample preliminary interpretation of the data demonstrates good agreement between porosity measured at 100 and 300 magnification for the shergottite group while others exhibit more variability in comparison with the limited existing data for martian meteorites we find fairly good agreement although our porosity values typically lie at the low end of published values surprisingly despite the increased data set there is little by way of correlation between either porosity or density with parameters such as shock effect or terrestrial residency further data collection on additional meteorite samples is required before more definitive statements can be made concerning the validity of these observations

radar images of mars full disk images of mars have been obtained with the use of the very large array vla to map the radar reflected flux density the transmitter system was the 70 m antenna of the deep space network at goldstone california the surface of mars was illuminated with continuous wave radiation at a wavelength of 3 5 cm the reflected energy was mapped in individual 12 minute snapshots with the vla in its largest configuration fringe spacings as small as 67 km were obtained the images reveal near surface features including a region in the tharsis volcano area over 2000 km in east west extent that displayed no echo to the very low level of the radar system noise the feature called stealth is interpreted as a deposit of dust or ash with a density less than about 0 5 gram per cubic centimeter and free of rocks larger than 1 cm across the deposit must be several meters thick and may be much deeper the strongest reflecting geological feature was the south polar ice cap which was reduced in size to the residual south polar ice cap at the season of observation the cap image is interpreted as arising from nearly pure co 2 or h 2o ice with a small amount of martian dust less than 2 percent by volume and a depth greater than 2 to 5 m only one anomalous reflecting feature was identified outside of the tharsis region although the elysium region was poorly sampled in this experiment and the north pole was not visible from earth

tornetrask tree ring width and density ad 500 2004 a test of climatic sensitivity and a new 1500 year reconstruction of north fennoscandian summers this paper presents updated tree ring width trw and maximum density mxd from tornetrask in northern sweden now covering the period ad 500 2004 by including data from relatively young trees for the most recent period a previously noted decline in recent mxd is eliminated non climatological growth trends in the data are removed using regional curve standardization rcs thus producing trw and mxd chronologies with preserved low frequency variability the chronologies are calibrated using local and regional instrumental climate records a bootstrapped response function analysis using regional climate data shows that tree growth is forced by april august temperatures and that the regression weights for mxd are much stronger than for trw the robustness of the reconstruction equation is verified by independent temperature data and shows that 63 64 of the instrumental inter annual variation is captured by the tree ring data this is a significant improvement compared to previously published reconstructions based on tree ring data from tornetrask a divergence phenomenon around ad 1800 expressed as an increase in trw that is not paralleled by temperature and mxd is most likely an effect of major changes in the density of the pine population at this northern tree line site the bias introduced by this trw phenomenon is assessed by producing a summer temperature reconstruction based on mxd exclusively the new data show generally higher temperature estimates than previous reconstructions based on tornetrask tree ring data the late twentieth century however is not exceptionally warm in the new record on decadal to centennial timescales periods around ad 750 1000 1400 and 1750 were equally warm or warmer the 200 year long warm period centered on ad 1000 was significantly warmer than the late twentieth century p 0 05 and is supported by other local and regional paleoclimate data the new tree ring evidence from tornetrask suggests that this medieval warm period in northern fennoscandia was much warmer than previously recognized

an improved jpl mars gravity field and orientation from mars orbiter and lander tracking data abstract the mars gravity field resolution is mostly determined by the lower altitude mars reconnaissance orbiter mro tracking data with nearly four years of additional mro and mars odyssey tracking data since the last jpl released gravity field mro110c and lander tracking from the mer opportunity rover the gravity field and orientation of mars have been improved the new field mro120d extends the maximum spherical harmonic degree slightly to 120 improves the determination of the higher degree coefficients as demonstrated by improved correlation with topography and reduces the uncertainty in the corresponding mars orientation parameters by up to a factor of two versus previously combined gravity and orientation solutions the new precession solution is 7608 3 2 1 mas yr and is consistent with previous results but with a reduced uncertainty by 40 the love number solution k2 0 169 0 006 also shows a similar result to previous studies

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

explosive volcanism in the tharsis region global evidence in the martian geologic record 1 a global equatorial set of layered deposits on mars has been reexamined with mars global surveyor data the stratigraphy morphology and erosional characteristics of units separated by thousands of kilometers are remarkably similar to each other and consistent with a widespread episodic subaerial source of fine grained material this study is the first to propose a genetic link between many units that have traditionally been considered on a local or regional level including the medusae fossae formation valles marineris interior deposits chaotic terrain terra meridiani and arabia materials mapping relationships suggest that all of these units are post noachian in age and formation may have continued until the recent past thinning of deposits with increasing distance from the tharsis rise suggests that much of these materials may be volcanic ash flows and air fall from explosive eruptions in the tharsis region analogous to those produced by terrestrial plinian eruptions contemporary martian winds would preferentially transport ash from an eruption plume near tharsis east or west along the equator depending on the season erosion has removed much of the original volcanic ash and only isolated layered stacks remain sometimes in topographic depressions that inhibit erosion modeling indicates that widespread dispersion of ash after an eruption is easily attainable in present or past atmospheric conditions consistent with the hypothesis that the far reaching deposits may be composed of ash from past explosive eruptions in the vicinity of tharsis

air ground temperature coupling and subsurface propagation of annual temperature signals 1 borehole based reconstructions of ground surface temperature gst have been widely used as indicators of paleoclimate these reconstructions assume that heat transport within the subsurface is conductive climatic interpretations of gst reconstructions also assume that gst is strongly coupled to surface air temperature sat on timescales of decades and longer we examine these two assumptions using records of sat and subsurface temperature time series from fargo north dakota prague czech republic cape henlopen state park delaware and cape hatteras national seashore north carolina the characteristics of downward propagating annual temperature signals at each site clearly indicate that heat transport can be described as one dimensional conduction in a homogeneous medium extrapolations of subsurface observations to the ground surface yield estimates of annual gst signals and allow comparisons to annual sat signals all annual gst signals are modestly attenuated and negligibly phase shifted relative to sat the four sites collectively demonstrate that differences between annual gst and sat signals arise in both summer and winter seasons in amounts dependent on the climatic setting of each site index terms 1645 global change solid earth 1875 hydrology unsaturated zone 3322 meteorology and atmospheric dynamics land atmosphere interactions 3344 meteorology and atmospheric dynamics paleoclimatology 3367 meteorology and atmospheric dynamics theoretical modeling keywords heat transport air ground termperature coupling paleoclimate

proxy based northern hemisphere surface temperature reconstructions sensitivity to method predictor network target season and target domain abstract results are presented from a set of experiments designed to investigate factors that may influence proxy based reconstructions of large scale temperature patterns in past centuries the factors investigated include 1 the method used to assimilate proxy data into a climate reconstruction 2 the proxy data network used 3 the target season and 4 the spatial domain of the reconstruction estimates of hemispheric mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach the experiments compare results based on the global multiproxy dataset used by mann and coworkers with results obtained using the extratropical northern hemisphere nh maximum latewood tree ring density set used by briffa and coworkers mean temperature reconstructions are compared for the full nh tropics and extratropics land and ocean and ext

constraints on the composition of the martian south polar cap from gravity and topography abstract the polar caps of mars have long been acknowledged to be composed of unknown proportions of water ice solid co 2 dry ice and dust gravity and topography data are here analyzed over the southern cap to place constraints on its density and hence composition using a localized spectral analysis combined with a lithospheric flexure model of ice cap loading the best fit density of the volatile rich south polar layered deposits is found to be 1271 kg m 3 with 1 limits of 1166 and 1391 kg m 3 the best fit elastic thickness of this geologically young deposit is 140 km though any value greater than 102 km can fit the observations the best fit density implies that about 55 dry ice by volume could be sequestered in these deposits if they were completely dust free alternatively if these deposits were completely free of solid co 2 the dust content would be constrained to lie between about 14 and 28 by volume the bulk thermal conductivity of the polar cap is not significantly affected by these maximum allowable concentrations of dust however even if a moderate quantity of solid co 2 were present as horizontal layers the bulk thermal conductivity of the polar cap would be significantly reduced reasonable estimates of the present day heat flow of mars predict that dry ice beneath the thicker portions of the south polar cap would have melted depending on the quantity of solid co 2 in these deposits today it is even possible that water ice could melt where the cap is thickest if independent estimates for either the dust or co 2 content of the south polar cap could be obtained and if radar sounding data could determine whether this polar cap is presently experiencing basal melting or not it would be possible to use these observations to place tight constraints on the present day heat flow of mars

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

absence of silicic volcanism on mars implications for crustal composition and volatile abundance on earth eruptions of silicic magmas with volumes of 1 100 km3 are generally associated with stratovolcanoes or composite cones whereas larger 100 1000 km3 ignimbrite deposits are erupted from resurgent calderas and related structures small volumes of silicic rocks are generated by differentiation within basic magma chambers associated with stratovolcanoes but large silicic deposits are largely confined to areas where the granitic crust is thicker than 25 km as mantle derived magmas rise through the thick granitic crust fractional crystallization and assimilation of hydrous crustal rocks concentrate volatiles and sio2 in the magma yielding explosive silicic eruptions on mars under similar chemical conditions ignimbrite eruptions could take place over a broader range of physical conditions than on earth but no large volume ignimbrite deposits can be identified positively explosive basic to ultrabasic eruptions may be responsible for small cinder conelike features on mars and perhaps for the ancient flank scoured paterae such eruptions may have been driven by near surface water ice magma interactions or volatile rich magmas the paterae represent a unique style of volcanism that stopped 2 b y ago we suggest that the volatiles associated with these features were derived from mantle sources and that the cessation of patera formation may coincide with the termination of the period of maximum planetary degassing volcanism since 2 b y ago has been dominantly effusive except for minor explosive ash events such as those which blanketed part of the summit of hecates tholus we propose that such eruptions were driven by volatiles generated by differentiation of a magma chamber similar to icelandic explosive eruptions the apparent lack of large scale silicic volcanism on mars is circumstantial evidence that mars is deficient in volatiles and lacks a granitic crust

explosive volcanic eruptions on mars tephra and accretionary lapilli formation dispersal and recognition in the geologic record explosive volcanic eruptions potentially involving large amounts of magmatic and entrained water are thought to have been very important in the noachian and hesperian periods earlier in mars history and basaltic plinian eruptions are likely to have occurred throughout martian history previous treatments of explosive volcanic plumes on mars have simply extrapolated plume models for the earth s atmosphere to mars taking account of known limitations to the applicability of this approach which suggest that convective plumes may be capable of reaching only 20 km height on mars we introduce the concept of inertial plumes capable of carrying clasts to much greater heights and dropping them into the lower atmosphere over a wide area atmospheric circulation patterns guarantee wide dispersal and thick deposits of tephra resulting from both types of eruption the presence of large amounts of water in convecting explosive eruption plumes can also lead to condensation of water on small particles and the consequent accretion of other particles as the smaller particles fall through the plume producing accretionary lapilli formation of accretionary lapilli significantly alters the spatial distribution and grain sizes of pyroclastic fall deposits from those involving discrete juvenile clasts with negligible clast interactions we model the eruption and dispersal of tephra and the formation of accretionary lapilli on mars under current atmospheric conditions and explore the consequences of this for the geometry and grain size of deposits formed from explosive eruption plumes we show that explosive eruptions can produce thick widespread deposits of ash and lapilli similar to those thought to have produced mantling deposits in several regions of mars we develop a detailed example that shows that local hydrovolcanic explosive eruptions and solely magmatic eruptions originating from the nearby apollinaris patera could have emplaced tephra and accretionary lapilli in the columbia hills region of the mars exploration rover gusev site if the atmospheric pressure was higher early in mars history than now eruptions would have led to somewhat more extensive pyroclast dispersal than under current conditions

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

hirise images of yardangs and sinuous ridges in the lower member of the medusae fossae formation mars abstract hirise images of the lower member of the medusae fossae formation mff were used to identify characteristics of two specific landforms that are well expressed in this particular geologic unit yardangs and sinuous ridges yardangs are wind eroded ridges that are usually confined to arid environments where the bedrock materials can be easily eroded by windblown sand yardangs are common in the lower member of mff where many individual yardangs show evidence of a caprock unit overlying a more friable unit most consistent with an ignimbrite origin for these mff deposits heights of the yardangs in the lower member materials are generally less than a few tens of meters in contrast to yardangs in the thicker middle member mff materials to the east of the study area the yardangs may form in materials comprised of discrete depositional units and there is good evidence that at least a dozen such depositional events contributed to the emplacement of the lower member of mff the lower member yardang heights indicate aeolian erosion has removed at least 19 000 km 3 of lower member mff materials sinuous ridges are elongate positive relief landforms that have been attributed to a variety of possible fluvial flow processes on mars sinuous ridges are very common within exposures of the lower member of mff multiple ridge types are present but all forms seen at hirise scale are most consistent with some form of aqueous channel flow rather than other possible origins the results from this initial examination of hirise images indicate the potential utility of comparing yardangs and sinuous ridges in the lower member to other members of mff although it remains to be determined if sinuous ridges are abundant in the younger mff members

geochemical evidence for magmatic water within mars from pyroxenes in the shergotty meteorite observations of martian surface morphology have been used to argue that an ancient ocean once existed on mars1 it has been thought that significant quantities of such water could have been supplied to the martian surface through volcanic outgassing but this suggestion is contradicted by the low magmatic water content that is generally inferred from chemical analyses of igneous martian meteorites2 here however we report the distributions of trace elements within pyroxenes of the shergotty meteorite a basalt body ejected 175 million years ago from mars3 as well as hydrous and anhydrous crystallization experiments that together imply that water contents of pre eruptive magma on mars could have been up to 1 8 we found that in the shergotty meteorite the inner cores of pyroxene minerals which formed at depth in the martian crust are enriched in soluble trace elements when compared to the outer rims which crystallized on or near to the martian surface this implies that water was present in pyroxenes at depth but was largely lost as pyroxenes were carried to the surface during magma ascent we conclude that ascending magmas possibly delivered significant quantities of water to the martian surface in recent times reconciling geologic and petrologic constraints on the outgassing history of mars

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

evidence for a low bulk crustal density for mars from gravity and topography knowledge of the average density of the crust of a planet is important in determining its interior structure the combination of high resolution gravity and topography data has yielded a low density for the moon s crust yet for other terrestrial planets the resolution of the gravity field models has hampered reasonable estimates by using well chosen constraints derived from topography during gravity field model determination using satellite tracking data we show that we can robustly and independently determine the average bulk crustal density directly from the tracking data using the admittance between topography and imperfect gravity we find a low average bulk crustal density for mars 2582 209 kg m 3 this bulk crustal density is lower than that assumed until now densities for volcanic complexes are higher consistent with earlier estimates implying large lateral variations in crustal density in addition we find indications that the crustal density increases with depth

correction to localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution 1 in the paper localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution by patrick j mcgovern sean c solomon david e smith maria t zuber mark simons mark a wieczorek roger j phillips gregory a neumann oded aharonson and james w head journal of geophysical research 107 e12 5136 doi 10 1029 2002je001854 2002 the thickness of the lithosphere and lithospheric heat flow for a number of regions of mars and as functions of time were inferred on the basis of gravity topography admittance spectra observed admittances derived from spherical harmonic expansions localized with the scheme of simons et al 1997 were compared with those predicted from models for the flexural response to lithospheric loading e g turcotte et al 1981 gravity was calculated according to the finite amplitude scheme of wieczorek and phillips 1998 estimates for the thickness of the elastic lithosphere te at the time of loading for each region were converted to equivalent thermal gradient dt dz and heat flux q by means of an elastic plastic stressenvelope formalism mcnutt 1984 here we describe a correction required in the calculation of the modeled gravity anomalies we report new estimates of te load density rl dt dz and q from corrected model admittances and we discuss the implications of the new results 2 the source of the required correction is a difference in reference radius values as defined by mcgovern et al 2002 the planetary shape was taken to equal the radius from the center of mass of mars to the martian surface expressed as a spherical harmonic expansion and referenced to the mean equatorial radius req 3396 km

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

seasonal and static gravity field of mars from mgs mars odyssey and mro radio science abstract we present a spherical harmonic solution of the static gravity field of mars to degree and order 120 gmm 3 that has been calculated using the deep space network tracking data of the nasa mars missions mars global surveyor mgs mars odyssey ody and the mars reconnaissance orbiter mro we have also jointly determined spherical harmonic solutions for the static and time variable gravity field of mars and the mars k 2 love numbers exclusive of the gravity contribution of the atmosphere consequently the retrieved time varying gravity coefficients and the love number k 2 solely yield seasonal variations in the mass of the polar caps and the solid tides of mars respectively we obtain a mars love number k 2 of 0 1697 0 0027 3 the inclusion of mro tracking data results in improved seasonal gravity field coefficients c 30 and for the first time c 50 refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic c 30 for 1 5 solar cycles 16 years this gravity model shows improved correlations with mola topography up to 15 larger at higher harmonics l 60 80 than previous solutions