the role of fungi in the diagenetic alteration of spar calcite fungi may play a far more important role in carbonate diagenesis than has been previously suspected this can be demonstrated by placing known species of fungi on crystals of iceland spar calcite such experiments show that fungi can 1 cause sparmicritization through dissolution 2 produce spiky calcite through dissolution 3 trap and bind loose particles of calcite and 4 promote the growth of new calcite crystals although not observed in this series of experiments fungi can bore into substrates and cause sparmicritization the activity of fungi involves a complex interplay of substrate destruction and construction without the intervention of vast quantities of fluid

regression of martian north polar cap 1990 1997 hubble space telescope observations abstract hubble space telescope imaging of mars from december 13 1990 through april 17 1997 has resulted in the synoptic monitoring of parts of four consecutive martian north polar cap regressional cycles spanningls 335 65 tols 144 56 the 1990 1993 observations were obtained with the wide field planetary camera 1 wfpc1 instrument while subsequent observations from 1994 to 1997 were obtained with the improved optics of the wide field planetary camera 2 wfpc2 mars observations were obtained from the ultraviolet 218 nm to the near infrared 1042 nm which has allowed us to constrain the effects of clouds and dust particulates on cap edge measurements hst observations of the polar cap regressions afterls 0 are fairly consistent from year to year with some variations possible beforels 0 the 1991 observations atls 35 25 andls 59 88 in the longitude range 270 280 possibly support a standstill in cap retreat at a latitude 70 n the standstill in cap retreat reported in previous years at a latitude 67 n was not observed in 1992 1997 comparison with previous ground based and spacecraft observations suggests that interannual variations may be significant they may be due to interannual atmospheric changes such as global dust storm activity lambert albedos of the north polar cap in red and violet bandpasses are similar to those reported before

rhinegraben horizontal stylolites indicating stress regimes of earlier stages of rifting abstract buchner f 1981 rhinegraben horizontal stylolites indicating stress regimes of earlier stages of rifting in j h illies editor mechanism of graben formation tectonophysics 73 113 118 tectonic stylolites horizontal columns and their statistical distribution in middle triassic and jurassic limestones on both flanks of the rhinegraben are described and their relation to the rhinegraben taphrogenesis is discussed a generation of pre middle miocene nne striking horizontal stylolites and a subsequent generation of post lower miocene nw striking horizontal stylolites have been recognized the first generation stylolites indicates a horizontal compression in the nne ssw direction while the second generation indicates a compression in the nw se direction average maxima of joints parallel to the two horizontal stylolite maxima were found joints and their corresponding horizontal stylolites were formed under the same stress regime

impact of forest tree species on feldspar weathering rates abstract an in situ experimental approach was used to test the impact of several forest tree species on weathering of a plagioclase used as a test mineral tree species were norway spruce scots pine sessil oak pedunculated oak and european beech the experiment was carried out by putting a fixed mass of test mineral into the soil under different tree species stands located in the same conditions test minerals were inserted into soils at various depths 0 5 15 40 cm and then maintained over two periods 3 and 9 years at the end of their incubation period test minerals were collected weighed and analysed mass losses of test minerals were highest for bags inserted under litters 0 cm depth at 0 and 5 cm depth dissolution rates significantly decreased over the 9 years of the experiment there was a significant positive linear relation between specific surface area of test minerals and their mass losses test mineral evolution in mass and specific surface area was strongly dependent on environmental conditions mostly soil ph and soil type test minerals which were inserted into soil layers of low acidity ph 4 5 had very low mass losses and specific surface area increments coniferous species promoted mass losses more significantly than broadleaved species did tree species provoked more or less mass losses through modifications in the acidity of the soil

mars south polar spring and summer behavior observed by tes seasonal cap evolution controlled by frost grain size thermal emission spectrometer tes observations of the recession phase of mars south polar cap are used to quantitatively map this recession in both thermal and visual appearance geographically nonuniform behavior interior to the cap is characterized by defining several small regions which exemplify the range of behavior for most of the cap while temperatures remain near the co2 frost point albedos slowly increase with the seasonal rise of the sun then drop rapidly as frost patches disappear over a period of 20 days a cryptic region remains dark and mottled throughout its cold period tes observations are compared with first order theoretical spectra of solid co2 frost with admixtures of dust and h2o the tes spectra indicate that the cryptic region has much larger grained solid co2 than the rest of the cap and that the solid co2 here may be in the form of a slab the mountains of mitchel remain cold and bright well after other areas at comparable latitude apparently as a result of unusually small size of the co2 frost grains we found little evidence for a significant presence of h2o although co2 grain size may be the major difference between these regions incorporated dust is also required to match the observations a self cleaning process carries away the smaller dust grains comparisons with viking observations indicate little difference in the seasonal cycle 12 martian years later the observed radiation balance indicates co2 sublimation budgets of up to 1250 kg m 2 regional atmospheric dust is common localized dust clouds are seen near the edge of the cap prior to the onset of a regional dust storm and interior to the cap during the storm

freshwater oncolites created by industrial pollution onondaga lake new york abstract onondaga lake is a moderately saline eutrophic lake characterized by waters rich in calcium sodium chloride and bicarbonate large quantities of caco3 that are precipitated in the lake result from excess calcium supplied as calcium chloride wastes produced by soda ash manufacturing to lake waters that are at or near saturation with respect to caco3 from solution of carbonate rocks in the drainage basin beaches along the leeward northeastern shore of the lake are composed almost entirely of oncolites ranging from a few millimeters to several centimeters in maximum dimension offshore in 1 2 m of water the oncolites are biscuit shaped concretions as much as 15 cm in diameter the oncolites consist mainly of low magnesium calcite but dissolution of the carbonate with dilute acid results in a mass of blue green algal filaments of the same approximate size and shape as the original oncolite most oncolites have an obvious nucleus the most common nucleus is the hollow stem and cortication tubules of charophytes charophytes do not occur in onondaga lake today although they are common in other limestone bedrock lakes in central new york state charophytes probably were eliminated by the marked increases in salinity of the lake that resulted from the introduction of soda ash manufacturing on the lake shores around 1880 which means that growth of the oncolites began at least 100 years ago

mass balance of mars residual south polar cap from ctx images and other data abstract erosion of pits in the residual south polar cap rspc of mars concurrent with deposition and fluctuating cap boundaries raises questions about the mass balance and long term stability of the cap determining a mass balance by measurement of a net gain or loss of atmospheric co 2 by direct pressure measurements haberle r m et al 2014 secular climate change on mars an update using one mars year of msl pressure data american geophysical union fall abstract 3947 although perhaps the most direct method has so far given ambiguous results estimating volume changes from imaging data faces challenges and has previously been attempted only in isolated areas of the cap in this study we use 6 m pixel context imager ctx data from mars year 31 to map all the morphologic units of the rspc expand the measurement record of pit erosion rates and use high resolution images to place limits on vertical changes in the surface of the residual cap we find the mass balance in mars years 9 31 to be 6 to 4 km 3 y or roughly 0 039 to 0 026 of the mean atmospheric co 2 mass y the indeterminate sign results chiefly from uncertainty in the amounts of deposition or erosion on the upper surfaces of deposits as opposed to scarp retreat erosion and net deposition in this period appear to be controlled by summertime planetary scale dust events the largest occurring in my 9 another smaller one in my 28 the rates of erosion and the deposition observed since my 9 appear to be consistent with the types of deposits and erosional behavior found in most of the residual cap however small areas 100 y of depositional and or erosional conditions different from those occurring in the period since my 9 although these environmental differences could be subtle

reconciling different observations of the co2 ice mass loading of the martian north polar cap 1 the grs measurements of the peak mass loading of the north polar co2 ice cap on mars are about 60 lower than those calculated from mgs tes radiation data and those inferred from the mola cap thicknesses however the grs data provide the most accurate measurement of the mass loading we show that the tes and mola data can be reconciled with the grs data if 1 subsurface heat conduction and atmospheric heat transport are included in the tes mass budget calculations and 2 the density of the polar deposits is 600 kg m 3 the latter is much less than that expected for slab ice 1600 kg m 3 and suggests that processes unique to the north polar region are responsible for the low cap density

breakdown of mineral grains by earthworms and beetle larvae feeding experiments were conducted quantitatively to examine the breakdown of mineral grains by earthworm eisenia feida and larva of beetle protaetia lugubris insperata crushed and sieved test minerals of k feldspar and or quartz were mixed with artificial humus that contained no mineral grains the mixture was fed to the soil animals in the plastic containers after 1 4 and 7 day experimental durations the ingested mineral grains were collected from the casts excreted by the soil animals in each container even 1 day after feeding of mineral grains the casts of soil animals contained finer rounded mineral grains that were not included in the initial prepared mineral samples

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

the effect of land plants on weathering rates of silicate minerals abstract land plants and their associated microbiota directly affect silicate mineral weathering in several ways by generation of chelating ligands by modifying ph through production of co2 or organic acids and by altering the physical properties of a soil particularly the exposed surface areas of minerals and the residence time of water in laboratory experiments far from equilibrium 1 mm oxalate a strong chelator of al has a negligible effect on the dissolution rate of alkali feldspars but some effect on calcic feldspars and olivine by analogy to oxalate the overall effect of organic ligands on the weathering rate of silicate minerals in nature is likely to be small except perhaps in microenvironments adjacent to roots and fungal hyphae the effect of ph on silicate mineral dissolution rate depends on ph below ph 4 5 the rate increases with decreasing ph in the circumneutral region the rate is ph independent and at ph values above around 8 the rate increases with increasing ph vegetation should thus cause an increase in weathering rate through the ph effect only where the ph is below 4 5 as an overall generalization the effect of plants on weathering rate through changes in soil solution chemistry is probably small for granitic rocks it may be greater for more mafic rocks it is the release of ca and mg from mafic rocks that has the greatest influence on the global co2 budget the effect of changes in soil physical properties on weathering rate can be major by binding fine particles plants can greatly increase weathering rates in areas of high physical erosion where erosion rates are lower the effect of plants is less clear on long timescales plants may decrease chemical weathering by binding secondary products and isolating unweathered minerals from meteoric water a major unknown in estimating the effect of the advent of land plants on weathering rates is the nature thickness particle size distribution permeability of the regolith on the pre silurian continents the indirect effect of vegetation through changing the regional distribution of precipitation may be as important as the direct effects

the polar deposits of mars the tantalizing prospect of a readable record of martian climatic variations has driven decades of work toward deciphering the stratigraphy of the martian polar layered deposits and understanding the role of the residual ice caps that cover them spacecraft over the past decade have provided a massive infusion of new data into mars science polar science has benefited immensely due to the near polar orbits of most of the orbiting missions and the successful landing of the phoenix spacecraft in the northern high latitudes topographic thermal radar hyperspectral and high resolution imaging data are among the datasets that have allowed characterization of the stratigraphy of the polar layered deposits in unprecedented detail additionally change within the residual ice caps has been monitored with spacecraft instruments for several years these new data have provided a golden opportunity to understand the interplay between the martian orbit climate and polar ice

crossover analysis of mars orbiter laser altimeter data in its first 15 months of continuous operation the mars orbiter laser altimeter mola instrument aboard mars global surveyor ranged to mars over 330 million times generating more than 5000 orbital profiles with a ranging precision of 0 4 m over smooth terrain the accuracy of the profiles depends on knowledge of the spacecraft position orientation and observation time which are subject to errors we model these errors via the analysis of over 24 million altimetric crossovers a quasiperiodic once per revolution adjustment of the ground tracks as a function of time in three locally orthogonal directions minimizes the altimetric residuals via least squares using a sparse matrix technique computational effort scales linearly with the number of crossovers and only marginally with the number of parameters orbital errors mainly result from poor modeling of spacecraft thrusting events in the absence of tracking seasonal effects likely due to changing thermal environment as well as residual miscalibrations are evident in the pointing solutions incorporating multiple parameters per revolution significantly improves crossover residuals and resolves pointing aberrations during orbital transitions from night to day altimetry from the adjusted tracks generates a topographic model whose accuracy is typically better than 1 m vertically with respect to the center of mass of mars the centroid position of each mola shot is typically accurate to 100 m horizontally terrain models from accurately located lidar data can be gradient shaded to illuminate geological structures with 1 in 1000 slopes that are invisible to cameras temporal changes in elevation e g frost deposition ablation at decimeter levels may also be assessed using crossovers but results must be interpreted with caution due to uncertainties in range walk correction

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

exposed water ice discovered near the south pole of mars the mars odyssey thermal emission imaging system themis has discovered water ice exposed near the edge of mars southern perennial polar cap the surface h2o ice was first observed by themis as a region that was cooler than expected for dry soil at that latitude during the summer season diurnal and seasonal temperature trends derived from mars global surveyor thermal emission spectrometer observations indicate that there is h2o ice at the surface viking observations and the few other relevant themis observations indicate that surface h2o ice may be widespread around and under the perennial co2 cap

planet four terrains discovery of araneiforms outside of the south polar layered deposits abstract we present the results of a systematic mapping of seasonally sculpted terrains on the south polar region of mars with the planet four terrains p4t online citizen science project p4t enlists members of the general public to visually identify features in the publicly released mars reconnaissance orbiter context camera ctx images in particular p4t volunteers are asked to identify 1 araneiforms including features with a central pit and radiating channels known as spiders 2 erosional depressions troughs mesas ridges and quasi circular pits characteristic of the south polar residual cap sprc which we collectively refer to as swiss cheese terrain and 3 craters in this work we present the distributions of our high confidence classic spider araneiforms and swiss cheese terrain identifications in 90 ctx images covering 11 of the south polar regions at latitudes 75 n we find no locations within our high confidence spider sample that also have confident swiss cheese terrain identifications previously spiders were reported as being confined to the south polar layered deposits spld our work has provided the first identification of spiders at locations outside of the spld confirmed with high resolution hirise high resolution imaging science experiment imaging we find araneiforms on the amazonian and hesperian polar units and the early noachian highland units with 75 of the identified araneiform locations in our high confidence sample residing on the spld with our current coverage we cannot confirm whether these are the only geologic units conducive to araneiform formation on the martian south polar region our results are consistent with the current co 2 jet formation scenario with the process exploiting weaknesses in the surface below the seasonal co 2 ice sheet to carve araneiform channels into the regolith over many seasons these new regions serve as additional probes of the conditions required for channel creation in the co 2 jet process

a topographically forced asymmetry in the martian circulation and climate large seasonal and hemispheric asymmetries in the martian climate system are generally ascribed to variations in solar heating associated with orbital eccentricity as the orbital elements slowly change over a period of 10 4 years characteristics of the climate such as dustiness and the vigour of atmospheric circulation are thought to vary as should asymmetries in the climate for example the deposition of water ice at the northern versus the southern pole such orbitally driven climate change might be responsible for the observed layering in mars polar deposits by modulating deposition of dust and water ice most current theories assume that climate asymmetries completely reverse as the angular distance between equinox and perihelion changes by 180 here we describe a major climate mechanism that will not precess in this way we show that mars global north south elevation difference forces a dominant southern summer hadley circulation that is independent of perihelion timing the hadley circulation a tropical overturning cell responsible for trade winds largely controls interhemispheric transport of water and the bulk dustiness of the atmosphere the topography therefore imprints a strong handedness on climate with water ice and the active formation of polar layered deposits more likely in the north

the mars observer laser altimeter investigation the primary objective of the mars observer laser altimeter mola investigation is to determine globally the topography of mars at a level suitable for addressing problems in geology and geophysics secondary objectives are to characterize the 1064 nm wavelength surface reflectivity of mars to contribute to analyses of global surface mineralogy and seasonal albedo changes to assist in addressing problems in atmospheric circulation and to provide geodetic control and topographic context for the assessment of possible future mars landing sites the principal components of mola are a diode pumped neodymium doped yttrium aluminum garnet laser transmitter that emits 1064 nm wavelength laser pulses a 0 5 m diameter telescope a silicon avalanche photodiode detector and a time interval unit with 10 ns resolution mola will provide measurements of the topography of mars within approximately 160 m footprints and a center to center along track foot print spacing of 300 m along the mars observer subspacecraft ground track the elevation measurements will be quantized with 1 5 m vertical resolution before correction for orbit and pointing induced errors mola profiles will be assembled into a global 0 2 deg x 0 2 deg grid that will be referenced to mars center of mass with an absolute accuracy of approximately 30 m other data products will include a global grid of topographic gradients corrected individual profiles and a global 0 2 deg x 0 2 deg grid of 1064 nm surface reflectivity

formation of gypsum and bassanite by cation exchange reactions in the absence of free liquid h2o implications for mars 1 smectites and hydrated mg sulfate minerals have been identified in close association at various locations on the martian surface the hydration states of sulfates and smectites are dependent on temperature and relative humidity rh and therefore these minerals have the potential to affect cycling and bioavailability of h2o on mars we have conducted x ray powder diffraction experiments to investigate cycling of h2o within mixtures of ca bearing smectites and hydrated mg sulfate minerals under conditions of varying rh similar to those that exist at or just beneath the martian surface our experiments show that under conditions of varying rh cation exchange reactions occur between these two potential components of the martian regolith producing gypsum caso4 2h2o and bassanite caso4 0 5h2o in the absence of free liquid h2o cation exchange reactions were accompanied by significant loss of porosity warping of the sample surface and in some cases volume expansion the formation of ca sulfate minerals in these experiments provides evidence for the development of thin films of h2o at mineral surfaces and suggests that similar processes may operate at the arid surface of mars humidity driven cation exchange reactions between smectites and hydrated mg sulfate minerals may therefore play a role in shaping the present day martian surface and could have provided a transient source of h2o and nutrients e g major and trace elements and possibly organic micro macronutrients for putative microorganisms

stromatolitic bioherms and microphytolites from the late proterozoic draken conglomerate formation spitsbergen abstract the late proterozoic draken conglomerate formation akademikerbreen group in eastern spitsbergen displays several prominent stromatolitic bioherms in its lowermost beds the dolomitic bioherms are comprised principally of columnar stromatolites cf gymnosolenoides but include cross bedded microphytolitic grainstones the excellent exposures of the bioherms and microphytolitic grainstones along the margin of petrovbreen glacier and the exquisite preservation of structural and microscopic details permit the documentation and interpretation of these sedimentary and biological associations locally favorable ecologic circumstance or chance colonization initiated stromatolitic mat development which then became self perpetuating to form bioherms until rapid siliciclastic influx overwhelmed the mat building populations intermediate energy conditions in concert with microbial activity and inorganic processes generated the microphytolitic grainstones the interpretation of the biological and sedimentological interactions within these biohermal carbonates microphytolitic grainstones and siliciclastic rocks affords new insights into proterozoic paleoenvironments

distribution and state of h2o in the high latitude shallow subsurface of mars abstract a quantitative model of the state distribution and migration of water in the shallow martian regolith is presented reported results are confined to the region of the planet greater than 40 lat the calculations take into account 1 expected thermal variations at all depths latitudes and times resulting from seasonal and astronomically induced insolation variations 2 variations in atmospheric ph2o and pco2 resulting from polar insolation variations and regolith adsorptive equilibria 3 feedback effects related to latent heat and albedo variations resulting from condensation of atmospheric constituents 4 two possible regolith mineralogies 5 variable total h2o content of the regolith 6 kinetics of h2o transport through the martian atmosphere and regolith and 7 equilibrium phase partitioning of h2o between the condensed adsorbed and vapor phases results suggest that the adsorptive capacity of the regolith is important in controlling the state and distribution of high latitude h2o unweathered mafic silicates favor the development of shallow ground ice at all temperate and polar latitudes while heavily weathered clay like regolith materials leads to a deeper ground ice interface and far more extensive quantities of adsorbed h2o the capacity of the high latitude regolith for storage of h2o and the total mass of h2o exchanged between the atmosphere polar cap and subsurface over an obliquity cycle is found to be relatively independent of mineralogy the maximum exchanged volume is found to be 3 0 104 km3 of ice per cycle implications for the history of the polar caps and the origin of the layered terrain are discussed results also suggest that seasonal thermal waves act to force adsorbed h2o into the solid phase over a wide variety of latitude obliquity conditions seasonal phase cycling of regolith h2o is most common at high latitudes and obliquities such phase behavior is highly dependent on regolith mineralogy in a highly weathered regolith adsorbed h2o is annually forced into the solid phase at all latitudes 40 at obliquities greater than approximately 25 seasonal adsorption freezing cycles which are predicted here may produce geomorphologic signatures not unlike those produced by terrestrial freeze thaw cycles

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh

seasonal activity and morphological changes in martian gullies abstract recent studies of martian dune and non dune gullies have suggested a seasonal control on present day gully activity the timing of current gully activity especially activity involving the formation or modification of channels which commonly have been taken as evidence of fluvial processes has important implications regarding likely gully formation processes and necessary environmental conditions in this study we describe the results of frequent meter scale monitoring of several active gully sites by the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro the aim is to better assess the scope and nature of current morphological changes and to provide improved constraints on timing of gully activity on both dune and non dune slopes our observations indicate that 1 gully formation on mars is ongoing today and 2 the most significant morphological changes are strongly associated with seasonal frost and defrosting activity observed changes include formation of all major components of typical gully landforms although we have not observed alcove formation in coherent bedrock these results reduce the need to invoke recent climate change or present day groundwater seepage to explain the many martian gullies with pristine appearance

tes premapping data slab ice and snow flurries in the martian north polar night in the 1970s mariner and viking spacecraft observations of the north polar region of mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures for co 2 sublimation for the past few decades the scientific community has speculated as to the nature of these martian polar cold spots thermal emission spectrometer tes thermal spectral data have shown these cold spots to result largely from fine grained co 2 and have constrained most of these cold spots to the surface or near surface cold spot formation is strongly dependent on topography forming preferentially near craters and on polar slopes tes data combined with mars orbiter laser altimeter mola cloud data suggest atmospheric condensates form a small fraction of the observed cold spots tes observations of spectra close to a blackbody indicate that another major component of the polar cap is slab co 2 ice these spectrally bland regions commonly have a low albedo the cause is uncertain but may result from most of the light being reflected toward the specular direction from the slab ice being intrinsically dark or from it being transparent regions of the cap where the difference between the brightness temperatures at 18 m t 18 and 25 m t 25 is less than 5 are taken to indicate deposits of slab ice slab ice is the dominant component of the polar cap at latitudes outside of the polar night

plant induced weathering of a basaltic rock experimental evidence abstract the active role of higher plants in the weathering of silicate minerals and rocks is still a question for debate the present work aimed at providing experimental evidence of the important role of a range of crop plants in such processes in order to quantitatively assess the possible effect of these diverse plant species on the weathering of a basaltic rock two laboratory experiments were carried out at room temperature these compared the amounts of elements released from basalt when leached with a dilute salt solution in the presence or absence of crop plants grown for up to 36 days for si ca mg and na plants resulted in an increase in the release rate by a factor ranging from 1 to 5 in most cases ca and na seemed to be preferentially released relative to other elements suggesting that plagioclase dissolved faster than the other constituents of the studied basalt negligible amounts of fe were released in the absence of plants as a consequence of the neutral ph and atmospheric po2 that were maintained in the leaching solution however the amounts of fe released from basalt in the presence of plants were up to 100 to 500 fold larger than in the absence of plants for banana and maize the kinetics of dissolution of basalt in the absence of plants showed a constantly decreasing release rate over the whole duration of the experiment 36 days no steady state value was reached both in the absence and presence of banana plants however in the latter case the rates remained at a high initial level over a longer period of time up to 15 days before starting to decrease for fe the maximum rate of release was reached beyond 4 days and this rate remained high up to 22 days of growth of banana the possible mechanisms responsible for this enhanced release of elements from basalt in the presence of plants are discussed although these mechanisms need to be elucidated the present results clearly show that higher plants can considerably affect the kinetics of dissolution of basalt rock therefore they need to be taken into account when assessing the biogeochemical cycles of elements that are major nutrients for plants such as ca mg and k but also micronutrients such as fe and nonessential elements such as si and na

martian north polar cap recession 2000 mars orbiter camera observations abstract the wide angle cameras of the mars orbiter camera moc on the mars global surveyor have recorded the 2000 recession of the seasonal co 2 cap in the north polar region from l s 330 to 90 in stark contrast to the asymmetric behavior of the south seasonal cap the seasonal north cap remains relatively circular and uniform until mid spring when the retreat reaches the circum polar dune field which is the one major nonuniformity in the cap the recession of cap edge latitude versus areocentric longitude l s is very well represented as a linear function until late spring there is no evidence for the plateau or standstill in the recession curve that has been observed in some prior years the lambert albedo of the seasonal frost deposits in the north polar region demonstrates the increase with insolation first observed by paige in 1985 increasing to approximately 0 57 at l s 40 the north polar cap near solstice visually appears smaller than that observed by moc at the start of mapping in 1999 but later images acquired in summer show the residual cap returning to its more usual shape the most likely explanation for these changes in albedo is precipitation and subsequent removal of dust on the cap as a result of frequent dust storms near the cap edge

ranging performance of satellite laser altimeters topographic mapping of the earth moon and planets can be accomplished with high resolution and accuracy using satellite laser altimeters these systems employ nanosecond laser pulses and microradian beam divergences to achieve submetre vertical range resolution from orbital altitudes of several hundred kilometres in this paper the authors develop detailed expressions for the range and pulsewidth measurement accuracies and use the results to evaluate the ranging performances of several satellite laser altimeters currently under development by nasa for launch during the next decade the analysis includes the effects of the target surface characteristics spacecraft pointing jitter and waveform digitizer characteristics the results show that ranging accuracy is critically dependent on the pointing accuracy and stability of the altimeter especially over high relief terrain where surface slopes are large at typical orbital altitudes of several hundred kilometres single shot accuracies of a few centimetres can be achieved only when the pointing jitter is on the order of 10 mu rad or less

hirise observations of gas sublimation driven activity in mars southern polar regions i erosion of the surface the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro has imaged the sublimation of mars seasonal co2 polar cap with unprecedented detail for one complete martian southern spring in some areas of the surface beneath the conformal coating of seasonal ice radiallyorganized channels are connected in spidery patterns the process of formation of this terrain erosion by gas from subliming seasonal ice has no earthly analog the new capabilities high resolution color and stereo images of hirise enable detailed study of this enigmatic terrain two sites are analyzed in detail one within an area expected to have translucent seasonal co2 ice and the other site outside that region stereo anaglyphs show that some channels grow larger as they go uphill implicating gas rather than liquid as the erosive agent dark fans of material from the substrate are observed draped over the seasonal ice and this material collects in thin to thick layers in the channels possibly choking off gas flow in subsequent years resulting in inactive crisscrossing shallow channels in some areas there are very dense networks of channels with similar width and depth and fewer fans emerging later in the season are observed subtle variations in topography affect the channel morphology a new terminology is proposed for the wide variety of erosional features observed

graben width controlling syn rift sedimentation the palaeogene southern upper rhine graben as an example eocene to early oligocene syn rift deposits of the southern upper rhine graben urg accumulated in restricted environments sedimentation was controlled by local clastic supply from the graben flanks as well as by strong intra basinal variations in accommodation space due to differential tectonic subsidence that in turn led to pronounced lateral variations in depositional environment three large scale cycles of intensified evaporite sedimentation were interrupted by temporary changes towards brackish or freshwater conditions they form three major base level cycles that can be traced throughout the basin each of them representing a stratigraphic sub unit a relatively constant amount of horizontal extension l in the range of 4 5 km has been estimated for the urg from numerous cross sections the width of the rift lf however varies between 35 and more than 60 km resulting in a variable crustal stretching factor between the bounding masterfaults apart from block tilting tectonic subsidence was therefore largely controlled by changes in the initial rift width l0 the along strike variations of the graben width are responsible for the development of a deep trough like evaporite basin potash basin in the narrowest part of the southern urg adjacent to shallow areas in the wider parts of the rift such as the colmar swell in the north and the rhine bresse transfer zone that delimits the urg to the south under a constant amount of extension the along strike variation in rift width is the principal factor controlling depo centre development in extensional basins

interannual and seasonal changes in the south seasonal polar cap of mars observations from my 28 31 using marci the mars color imager marci camera on the mars reconnaissance orbiter provides daily synoptic coverage that allows monitoring of seasonal cap retreat and interannual changes that occur between mars years my and over the southern summer we present the first analysis of this data for the southern seasonal cap evolution observed in my 28 29 30 and 31 2 2007 to 07 2013 observation over multiple mars years allows us to compare changes between years as well as longer term evolution of the high albedo deposits at the poles seasonal cap retreat is similar in all years and to retreats observed in other years by both optical and thermal instruments the cryptic terrain has a fairly consistent boundary in each year but numerous small scale variations occur in each my observed additionally numerous small dark deposits are identified outside the classically identified cyptic region including inca city and other locations not previously noted the large water ice outlier is observed to retain seasonal frost the longest outside the polar dome and is also highly variable in each my the development of the cryptic anti cryptic hemispheres is inferred to occur due to albedo variations that develop after dust venting starts and may be caused by recondensation of co2 ice on the brightest and coldest regions controlled by topographic winds ground ice may play a role in which regions develop cryptic terrain as there is no elevation control on either cryptic terrain or the late season brightest deposits

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

hirise observations of gas sublimation driven activity in mars southern polar regions ii surficial deposits and their origins abstract the high resolution imaging science experiment hirise onboard mars reconnaissance orbiter mro has been used to monitor the seasonal evolution of several regions at high southern latitudes and in particular the jet like activity which may result from the process described by kieffer jgr 112 e08005 doi 10 1029 2006je002816 2007 involving translucent co 2 ice in this work we mostly concentrate on observations of the inca city 81 s 296 e and manhattan 86 s 99 e regions in the southern spring of 2007 two companion papers hansen et al this issue and portyankina et al this issue discuss the surface features in these regions and specific models of the behaviour of co 2 slab ice respectively the observations indicate rapid on set of activity in late winter initiating before hirise can obtain adequately illuminated images ls 2 titus et al 2007 agu abstract p41a 0188 these deposits originate from araneiform structures spiders boulders on ridges cracks on slopes and along linear cracks in the slab ice on flatter surfaces the type of activity observed can often be explained qualitatively by considering the local topography some dark fans are observed to shorten enormously in length on a timescale of 18 days we consider this to be strong evidence that outgassing was in progress at the time of hirise image acquisition and estimate a total particulate emission rate of 30 g s 1 from a single typical jet feature brighter deposits at inca city become increasingly hard to detect after ls 210 in the inca city region the orientations of surficial deposits are topographically controlled the deposition of dark material also appears to be influenced by local topography suggesting that the ejection from the vents is at low velocity 1 and that a ground hugging flow process a sort of cryo fumarole may be occurring the failure up to this point to obtain a clear detection of outgassing though stereo imaging is consistent with low level transport the downslope orientation of the deposits may result from the geometry of the vent or from catabatic winds at many sites more than one ejection event appears to have occurred suggesting re charging of the sources around ls 230 the brightness of the surface begins to drop rapidly on north facing slopes and the contrast between the dark deposits and the surrounding surface reduces this indicates that the co 2 ice slab is being lost completely in some areas at around this time by ls 280 at inca city the ice slab has effectively gone crism band ratios and themis brightness temperature measurements are consistent with this interpretation

observations of the northern seasonal polar cap on mars i spring sublimation activity and processes abstract spring sublimation of the seasonal co2 northern polar cap is a dynamic process in the current mars climate phenomena include dark fans of dune material propelled out onto the seasonal ice layer polygonal cracks in the seasonal ice sand flow down slipfaces and outbreaks of gas and sand around the dune margins these phenomena are concentrated on the north polar erg that encircles the northern residual polar cap the mars reconnaissance orbiter has been in orbit for three mars years allowing us to observe three northern spring seasons activity is consistent with and well described by the kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer the crest of the dune the interface of the dune with the interdune substrate and through polygonal cracks in the ice pressurized gas flows through these vents and carries out material entrained from the dune furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially organized channels araneiform terrain albeit not permanent properties of the seasonal co2 ice layer are derived from timing of seasonal events such as when final sublimation occurs modification of dune morphology shows that landscape evolution is occurring on mars today driven by seasonal activity associated with sublimation of the seasonal co2 polar cap

the instability of a south polar cap on mars composed of carbon dioxide abstract if the martian south polar cap were composed of solid carbon dioxide would it be sufficiently stable against collapse under its own weight this question is examined in the light of new experiments on the creep of solid carbon dioxide and new high resolution topographic mapping of the south polar cap the conclusion from a simple model is that with the strongest of three flow laws compatible with the measurements co 2 is strong enough to support a cap of this material with thickness about 1800 m for 10 7 years or more which is the age suggested by the cratering record however none of the three possible flow laws will allow a 3000 m cap the thickness suggested by stereogrammetry to survive for 10 7 years indicating that the south polar ice cap is probably not composed of pure co 2 ice

morphologie des constructions microbiennes en contexte de fan delta oligocene exemple du rift rhenan europe occidentale abstract at the eocene oligocene boundary a first paroxysmal phase of subsidence created the rhine rift graben system a lacustrine basin with variable salinity was formed in the graben in the southern part of this basin a large fan delta developed extending northward along the graben axis microbial ecosystems settled on the fringe of the lake in the paludal zone they formed carbonate encrustations on living plants or detrital vegetal remains littoral carbonate facies occur as algal bioherms and stromatolitic reefs in the distal lacustrine zone a discrete nodular texture within the sediment reveals the microbial origin of micrite and gives the limestone a breccial pattern all these facies illustrate the lateral zonation of the different types of constructions from fluvio deltaic to lacustrine in certain cases the microbial coating on plants permits to reconstruct seasonal rhythms and the processes of substratum colonisation

the rhinegraben extension subsidence and shoulder uplift abstract we apply a numerical model of the thermal evolution of a continental lithosphere undergoing extensional deformation to the rhinegraben using reasonable parameters the results of computations are in agreement with the present configuration of the rift and of its shoulders as well as with their evolution since the oligocene contrasting evolutions are reconstructed in the northern and southern rhinegraben whereas the northern history is accounted for by a simple model of homogeneous stretching of the lithosphere the history of the southern rhinegraben cannot be explained without introducing two main periods of heterogeneous stretching the results are locally supported by structural analyses of extensional patterns factors of extension average 1 2 in the axial portion of the rhinegraben and 1 15 for the whole rift section suggesting that the total amount of e w extension reaches 6 km

mars and earth comparison of cold climate features abstract on earth glacial and periglacial features are common in areas of cold climate on mars the temperature of the present day surface is appropriate for permafrost and the presence of water is suspected from data relating to the outgassing of the planet from remote sensing measurements over the polar caps and elsewhere on the martian surface and from recognition of fluvial morphological features such as channels these observations and the possibility that ice could be in equilibrium with the atmosphere in the high latitudes north and south of 40 latitude suggest that glacial and periglacial features should exist on the planet morphological studies based mainly on viking pictures indicate many features that can be attributed to the action of ice among these features are extensive talus aprons debris avalanches flows that resemble glaciers or rock glaciers ridges that look like moraines various types of patterned ground scalloped scarps and chaotically collapsed terrain that could be attributed to thermokarst processes and landforms that may reflect the interaction of volcanism and ice

radar evidence of subglacial liquid water on mars the presence of liquid water at the base of the martian polar caps has long been suspected but not observed we surveyed the planum australe region using the marsis mars advanced radar for subsurface and ionosphere sounding instrument a low frequency radar on the mars express spacecraft radar profiles collected between may 2012 and december 2015 contain evidence of liquid water trapped below the ice of the south polar layered deposits anomalously bright subsurface reflections are evident within a well defined 20 kilometer wide zone centered at 193 e 81 s which is surrounded by much less reflective areas quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity 15 matching that of water bearing materials we interpret this feature as a stable body of liquid water on mars

the stability of ground ice in the equatorial region of mars consideration of the partial pressure of h2o in the martian atmosphere and the range of mean annual temperatures at the martian surface suggests that the occurrence of ground ice in equilibrium with the atmosphere is restricted to latitudes poleward of 40 however there is a growing body of morphologic evidence that indicates that substantial quantities of ground ice may have been present in the equatorial regolith throughout martian geologic time the accepted explanation for this apparent contradiction has been that the h2o found near the equator is a relic emplaced very early in martian geologic history 3 5 b y ago and under substantially different climatic conditions it is generally believed that this fossil ground ice layer has been preserved to the present day by the diffusion limiting properties of a relatively shallow layer 10 m of fine grained regolith to evaluate this hypothesis the lifetime of a 200 m layer of ground ice buried below 100 m of ice free regolith has been examined for the latitudes between 30 on mars twelve model pore size distributions representative of silt and clay type soils found on earth were selected to simulate the pore structure of the martian regolith the parallel pore model of gaseous diffusion was then used to calculate the flux of escaping h2o molecules from the buried ground ice layer the potential effects of such factors as depth of burial the martian geothermal gradient regolith porosity adsorption surface diffusion and climatic change were also considered based on our analysis the most important factors affecting the stability of equatorial ground ice appear to be 1 soil structure 2 the magnitude of the geothermal gradient and 3 the climatic desorption of co2 from the regolith we conclude that while the conditions necessary for the long term survival of ground ice may exist in isolated regions within the equatorial regolith on the global scale it appears unlikely that a fossil ground ice layer has been preserved throughout martian geologic history if massive ground ice does presently exist in the equatorial regolith then its presence may imply the existence of some continuous or periodic process of replenishment

mars time variable gravity and its determination simulated geodesy experiments 1 the seasonal carbon dioxide co2 cycle on mars results in a time variable global redistribution of mass these large scale variations are associated with changes in the gravity field mainly in the two zonal gravity coefficients and which have been recently evaluated from doppler tracking data of the mars global surveyor mgs spacecraft in the present study we calculated these variations from the mass redistribution obtained from outputs of two general circulation models gcm as well as from co2 thickness measurements by the high energy neutron detector hend instrument on board the mars odyssey spacecraft and compared them to the observations tracking observations provide one of the most direct measures of the global scale atmospheric mass cycle however the associated uncertainties are relatively large partly because the low degree zonals obtained from a single orbiter tracking analysis are contaminated by higher degree harmonics which are shown to have nonnegligible seasonal variations thus we investigated possibilities to improve the determination of the time variable gravity field by means of simulated geodesy experiments additional radio tracking of a second spacecraft with suitable orbital characteristics was shown to be able to separate the higher degree geodetic signatures radio links between landers on the martian surface and a near polar orbiter can further better estimate especially the even zonals

on the mystery of the perennial carbon dioxide cap at the south pole of mars a perennial ice cap has long been observed near the south pole of mars the surface of this cap is predominantly composed of carbon dioxide ice the retention of a co 2 ice cap results from the surface energy balance of the latent heat solar radiation surface emission subsurface conduction and atmospheric sensible heat while models conventionally treat surface co 2 ice using constant ice albedos and emissivities such an approach fails to predict the existence of a perennial cap here we explore the role of the insolation dependent ice albedo which agrees well with viking mars global surveyor and mars express albedo observations using a simple parameterization within a general circulation model in which the albedo of co 2 ice responds linearly to the incident solar insolation we are able to predict the existence of a perennial co 2 cap at the observed latitude and only in the southern hemisphere further experiments with different total co 2 inventories planetary obliquities and surface boundary conditions suggest that the location of the residual cap may exchange hemispheres favoring the pole with the highest peak insolation

cold jets in the martian polar caps 1 mars seasonal polar caps display dark ice local darker spots aligned elongate patches and radially dendritic forms that reverse albedo contrast the unexpected variety and sequence of these features are explained on the basis of processes involving co2 dust sand and h2o these processes are largely related to the atmosphere being near its saturation temperature and they have few terrestrial analogies in the simplest case the 1 m thick seasonal cap initially dusty cleans itself and becomes translucent after sunrise and is impermeable over extensive regions except for local vents the slab ice sublimates at the base and is levitated on high pressure gas causing humidity exchange with deeper layers subslab gas converging toward the vents erodes channels in the soil and ejects this material in high velocity jets recent spectral observations indicate great variety in the details

breaking ground pedological geological and ecological implications of soil bioturbation abstract soil and its biota are fundamental components of the critical zone earth s living skin that most directly sustains life within that zone geologically rapid soil and saprolite displacement by biota particularly invertebrate meso and macrofauna affects a large proportion of earth s soils this was first recognised by late 19th century observers on both sides of the atlantic ocean who regarded bioturbation as fundamental to soil formation throughout much of the 20th century however the agronomical focus of soil scientists and the dominant paradigm of landscape evolution relegated bioturbation as a result many aspects of bioturbation are still not widely appreciated only in the last few decades has a re evaluation commenced in a range of disciplines primary effects of bioturbation which we quantify herein include soil production from saprolite the formation of surface mounds soil burial and downslope transport rates of bioturbation can be as rapid as sustained maximum rates of tectonic uplift in concert with surface geomorphic processes bioturbation alters fundamental properties of soil including particle size distribution porosity the content of carbon and other nutrients and creep flux rate the precise influence of biotic mixing is regulated by its depth function earth s incredibly diverse soil biota also perform a number of functions at a range of spatial and temporal scales that extend beyond soil to landscape evolution ecosystem engineering niche construction and carbon cycling understanding these linkages which have operated since the evolution of trees in the devonian period is of growing importance as we seek a fuller picture of earth s history to predict and manage its future

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

overview of the mars global surveyor mission the mars global surveyor spacecraft was placed into mars orbit on september 11 1997 and by march 9 1999 had slowly circularized through aerobraking to a sun synchronous near polar orbit with an average altitude of 378 km the science payload includes the mars orbiter camera mars orbiter laser altimeter thermal emission spectrometer ultrastable oscillator for radio science experiments and magnetometer electron reflectometer package in addition the spacecraft accelerometers and horizon sensors were used to study atmospheric dynamics during aerobraking observations are processed to standard products by the instrument teams and released as documented archive volumes on 6 month centers by the planetary data system significant results have been obtained from observations of the interior surface and atmosphere for example mars does not now have an active magnetic field although strong remanent magnetization features exist in the ancient crust these results imply that an internal dynamo ceased operation early in geologic time altimetry and gravity data indicate that the crust is thickest under the south pole thinning northward from the cratered terrain to the northern plains analysis of altimetry data demonstrates that mars is egg shaped with gravitational equipotential contours that show that channel systems in the southern highlands drained to the north largely to the chryse trough a closed contour in the northern plains is consistent with the existence of a great northern ocean emission spectra of low albedo regions show that basaltic rocks dominate spectral signatures on the southern highlands whereas basaltic andesites dominate the northern lowlands the bright regions show nondiagnostic spectra similar to that of dust in the atmosphere signatures of aqueous minerals e g clays carbonates and sulfates are noticeably absent from the emission spectra high spatial resolution images show that the surface has been extensively modified by wind and that layering is nearly ubiquitous implying that a complex history of events is recorded in surface and near surface materials altimetry data imply that both permanent caps are composed of water ice and dust with seasonal covers of carbon dioxide frost finally the altimetry data coupled with thousands of atmospheric profiles are providing new boundary conditions and dynamic controls for the generation and testing of more realistic dynamic models of the global circulation of the atmosphere

possible precipitation of ice at low latitudes of mars during periods of high obliquity most of the old cratered highlands of mars are dissected by branching river valleys that appear to have been cut by running water1 2 yet liquid water is unstable everywhere on the martian surface in the equatorial region where most of the valleys are observed even ice is unstable3 4 it has been suggested therefore that mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water5 here we suggest instead that during periods of very high obliquities ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapour equatorwards at low latitudes the water vapour would saturate the atmosphere and condense onto the surface where it would accumulate until lower obliquities prevailed the mechanism is efficient only at the very high obliquities that occurred before formation of tharsis very early in the planet s history but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet s history partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system

no signature of clear co2 ice from the cryptic regions in mars south seasonal polar cap the seasonal polar ice caps of mars are composed mainly of co2 ice a region of low 30 albedo has been observed within the south seasonal cap during early to mid spring the low temperature of this cryptic region has been attributed to a clear slab of nearly pure co2 ice with the low albedo resulting from absorption by the underlying surface here we report near infrared imaging spectroscopy of the south seasonal cap the deep and broad co2 absorption bands that are expected in the near infrared with a thick transparent slab of co2 ice are not observed models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a co2 ice layer which could be linked to atmospheric circulation patterns the strength of the co2 absorption increases after mid spring so part of the dust is either carried away or buried more deeply in the ice layer during the co2 ice sublimation process

sedimentology and isotopic composition of upper palaeocene to eocene non marine stromatolites eastern ebro basin ne spain stromatolites are abundant in upper palaeocene to eocene fluvial deposits from the eastern ebro basin whereas they are scarce in the lacustrine facies the fluvial stromatolites display a variety of growth forms oncoids domes laminated crusts and locally irregular bioherms these morphologies are related to the hydrological behaviour of the fluvial systems elongate domes dome heads and ovoid to subspherical oncoids accreted in flowing water laminated crusts and small sized cylindrical to lenticular oncoids formed during low discharge and ponding phases in the lacustrine environments only small sized ovoid oncoids occur the main characteristics of the ebro basin non marine stromatolites are 1 laminations and concentric banding exhibited by all morphologies 2 the occurrence of well preserved cyanobacterial filaments in several laminae suggesting that these microbiotas are the major contributors in growth 3 the asymmetrical growth of cortices in domes and oncoids with polar thickening on the upper side suggesting in situ growth under low energy conditions 13c values of carbonate stromatolites range from 11 3 o late palaeocene to 4 4 o middle late eocene during the late palaeocene under tectonically quiescent conditions the 13c values mainly reflect the influence of soil derived co2 during the eocene the progressive uplift of the surrounding catchment areas led to an increase of exposures of mesozoic rocks consequently the 13c values of the eocene stromatolites reflect the influence of the co2 derived from the dissolution of mesozoic marine carbonates there is a 2 5 o shift in 18o values of stromatolites from the late palaeocene to middle late eocene which is consistent with the variation in 18o of precipitation due to changes in altitude of the catchment area during this time the isotopic values of all middle upper eocene laminated crust samples show distinct covariant trends suggesting that these stromatolites were formed either in ponding zones of fluvial channels or in disconnected pools developed during low discharge episodes

introduction to the 4th mars polar science and exploration conference special issue five top questions in mars polar science abstract as an introduction to this icarus special issue for the 4th mars polar science and exploration conference we discuss five key questions in mars polar science gleaned from plenary discussions and presentations held at the conference these questions highlight major unknowns in the field 1 what are the physical characteristics of the polar layered deposits pld and how are the different geologic units within beneath and surrounding the pld related 2 how old are the pld and what are their glacial fluvial depositional and erosional histories 3 what are the mass and energy budgets of the pld and what processes control these budgets on seasonal and longer timescales 4 what chronology compositional variability and record of climatic change is expressed in the stratigraphy of the pld 5 how have volatiles and dust been exchanged between polar and non polar reservoirs and how has this exchange affected the past and present distribution of surface and subsurface ice

long term observations of southern winters on mars estimations of column thickness mass and volume density of the seasonal co2 deposit from hend odyssey data 1 in this paper we have analyzed neutron spectroscopy data gathered by the high energy neutron detector hend instrument on board mars odyssey for two martian years of orbital mapping we focused on the observations of the martian southern seasonal cap for this period of time nuclear methods based on numerical modeling allow us to derive an estimation of the distribution of co2 frost column density and mass from the temporal variations of neutron flux between summer and winter seasons we have estimated the seasonal behavior of both the column density and mass of co2 frost comparison between two martian years revealed minor 10 interannual variations of co2 thickness at the south pole during the middle of southern winter it was found that maximal mass of the southern seasonal cap is achieved at ls 160 and is equal to 6 6 0 6 1015 kg we found that this result corresponds well with previous hend results nasa ames gcm predictions gamma ray spectrometer estimates and estimations from gravity models based on mgs and mars odyssey tracking data in our analysis we also compared to processed mola data linear thicknesses of snow depths to measure the value of the volume density of the southern seasonal cap and we found that it may vary in the range 400 1250 kg m3

sediment ingestion by worms and the production of bio clays a study of macrobiologically enhanced weathering and early diagenetic processes the experiments reported here show that a range of early diagenetic clay minerals can develop within ingested sand in the guts of creatures at a rate that is at least 2 or 3 orders of magnitude greater than in an abiotic environment early diagenesis in marine environments may be strongly influenced by the occurrence of sediment ingestion and excretion by animals using a set of artificial marine experiments and the common lugworm arenicola marina i t is shown that sediment ingestion by macrobiota represents a new way in which to precipitate clay minerals or bio clays significant quantities of clay minerals can be the product of biological interaction within sediment tanks were constructed with artificially layered sediment and natural seawater the experiments were conducted at room temperature for a total duration of 9 months the silicate material fed to the worms was an unweathered and thus clay mineral free basalt from iceland less than 2 lm fractions from original control and faecal samples were periodically analysed using x ray diffraction xrd and fourier transform infrared spectroscopy ftir faecal casts underwent mineral alteration as denoted by loss of primary minerals especially plagioclase new minerals in faecal casts from the lugworms included kaolinite illite quartz and possibly chlorite inorganic weathering of similar parent basalt would probably produce an identical mineral assemblage but many more times slowly than with the macrobiotic mechanism demonstrated here

martian global scale co2 exchange from time variable gravity measurements 1 the martian co2 cycle causes variations in the gravity field that can be detected by an orbiting spacecraft the time variable c20 and c30 reported from the radio tracking analysis of mars global surveyor are used to calculate the seasonal changes in the polar cap masses as well as in the global atmospheric pressure the results show a good agreement with the model dependent solutions of general circulation models and co2 thickness observations of the high energy neutron detector on board mars odyssey

residual south polar cap of mars stratigraphy history and implications of recent changes abstract the residual south polar cap rspc of mars includes a group of different depositional units of co 2 ice undergoing a variety of erosional processes complete summer coverage of the rspc by 6 m pixel data of the context imager ctx on mars reconnaissance orbiter mro has allowed mapping and inventory of the units in the rspc unit maps and estimated thicknesses indicate the total volume of the rspc is currently 3 and represents less than 3 of the total mass of the current mars atmosphere scarp retreat rates in the co 2 ice derived from comparison of high resolution imaging science experiment hirise data with earlier images are comparable to those obtained for periods up to 3 mars years earlier these rates combined with sizes of depressions suggest that the oldest materials were deposited more than 125 mars years ago most current erosion is by backwasting of scarps 1 12 m in height this backwasting is initiated by a series of scarp parallel fractures in the older thicker unit these fractures form about every mars year in thinner younger materials they form less frequently some areas of the older thicker unit are lost by downwasting rather than by the scarp retreat a surprising finding from the hirise data is the scarcity of visible layering of rspc materials a result quite distinct from previous interpretations of layers in lower resolution images layers 0 1 m thick are exposed on the upper surfaces of some areas but their timescale of deposition is not known late summer albedo changes mapped by the ctx images indicate local recycling of ice although the amounts may be morphologically insignificant compact reconnaissance imaging spectrometer for mars crism data show that the primary material of all the different forms of the rspc is co 2 ice with only small admixtures of water ice and dust

evolution of mars northern polar seasonal co2 deposits variations in surface brightness and bulk density small scale variations of seasonal ice are explored at different geomorphic units on the northern polar seasonal cap npsc we use seasonal rock shadow measurements combined with visible and thermal observations to calculate density over time the coupling of volume density and albedo allows us to determine the microphysical state of the seasonal co2 ice we find two distinct end members across the npsc 1 snow deposits may anneal to form an overlying slab layer that fractures these low density deposits maintain relatively constant densities over springtime 2 porous slab deposits likely anneal rapidly in early spring and fracture in late spring these high density deposits dramatically increase in density over time the end members appear to be correlated with latitude

seasonality of present day martian dune gully activity martian slope gullies are argued to be evidence for recent liquid water flow on the surface of mars to explain the source of water a wide range of environmental conditions and processes has been invoked however a lack of information about the environmental context or timing of gully activity makes it difficult to evaluate the theories here we present new observations of extensive gully modification over the past 6 mars years within dune gullies with slope gully morphology observed activity within 18 gullies in 7 dune fields constrains timing to winter which is consistent with observed slope gully activity these observations show that fluvial processes are unlikely to cause present day martian dune gully activity and imply that co 2 frost accumulation may play the dominant role

how the martian residual south polar cap develops quasi circular and heart shaped pits troughs and moats the martian residual south polar cap rspc is a 1 10 m thick deposit of permanent co 2 ice perched on the much larger h 2o ice cap the co 2 ice is dissected into mesas by erosional landforms that can be broadly classified as i quasi circular pits ii heart shaped pits iii linear troughs and iv moats we use hirise 25 50 cm px images taken at a cadence of days to months to track meter scale changes in the rspc in order to investigate the mechanisms that lead to the development of these four distinct morphologies for the first time we report the development of dark fans on the sides of the co 2 mesas and the fracturing and deterioration of the initially smooth upper surface of co 2 mesas we interpret these features as indicating the sublimation and subsequent escape of co 2 from the interiors of mesas which undermines structural support of mesa tops causing them to collapse the collapse of mesa tops along with uneven deposition of co 2 ice creates steep scarps that erode during the summer due to preferential sunlight absorption during the winter co 2 deposition acts to smooth topography creating gently sloping ramps we propose that the interplay between the steep scarps and gentle slopes leads to either quasi circular pits heart shaped pits linear troughs or moats depending on local conditions

ground ice on mars inventory distribution and resulting landforms abstract most 90 of the estimated original volume of outgassed water on mars cannot be satisfactorily accounted for by exospheric escape or storage in the atmosphere as frost or in the permanent north polar ice cap the balance may be stored as ground ice in the martian cryosphere a zone of permanently frozen ground that is protected from the atmosphere by a debris cover ground ice can exist throughout the entire cryosphere but it need not fill it if the ground ice does fill the cryosphere then excess water can exist in a confined aquifer the theoretical distribution of ground ice can be tested by identification of forms on the martian surface that may be related to the presence of subsurface ice the observed features that are most likely to reflect ground ice are thermokarst like pits and debris flows landforms with ambivalent origins include polygonally patterned ground lobate ejecta blankets craters with central pits and curvilinear features the most persuasive morphologic evidence for ground ice is thermokarst pits and debris flows the thermokarst pits are primarily located in the volcanic regions of tharsis and elysium the association of ice related features with these volcanic areas suggests that these forms are not directly latitude dependent activation by orbital variations could produce periodic multiple episodes of melting that are dependent upon latitude the presence of ice related features in both hemispheres and the equatorial region of mars indicates that ground ice may be or have been present over the entire planet as predicted by the cryosphere model

feldspars as a source of nutrients for microorganisms phosphorus and nitrogen are essential macronutrients necessary for the survival of virtually all living organisms in groundwater systems these nutrients can be quite scarce and can represent limiting elements for growth of subsurface microorganisms in this study we examined silicate sources of these elements by characterizing the colonization and weathering of feldspars in situ using field microcosms we found that in carbon rich anoxic groundwaters where p and n are scarce feldspars that contain inclusions of p minerals such as apatite are preferentially colonized over similar feldspars without p a microcline from s dakota which contains 0 24 p 2 o 5 but 1 mu mol g nh 4 super was heavily colonized and deeply weathered a similar microcline from ontario which has no detectable p or nh 4 super was barren of attached organisms and completely unweathered after one year anorthoclase 0 28 p 2 o 5 approximately 1 mu mol g nh 4 super was very heavily colonized and weathered whereas plagioclase specimens 0 01 p 1 mu mmol g nh 4 super were uncolonized and unweathered in addition the observed weathering rates are faster than expected based on laboratory rates we propose that this system is particularly sensitive to the availability of p and the native subsurface microorganisms have developed biochemical strategies to aggressively scavenge p or some other essential nutrient such as fe super 3 from resistant feldspars the result of this interaction is that only minerals containing p will be significantly colonized and these feldspars will be preferentially destroyed as the subsurface microbial community scavenges a limiting nutrient

mars high resolution gravity fields from mro mars seasonal gravity and other dynamical parameters abstract with 2 years of tracking data collection from the mro spacecraft there is noticeable improvement in the high frequency portion of the spherical harmonic mars gravity field the new jpl mars gravity fields mro110b and mro110b2 show resolution near degree 90 additional years of mgs and mars odyssey tracking data result in improvement for the seasonal j 3 gravity changes which compares well to global circulation models and odyssey neutron data and mars rotation and precession 7594 10 mas year once atmospheric dust is accounted for in the spacecraft solar pressure model solutions for mars solar tide are consistent between data sets and show slightly larger values k2 0 164 0 009 after correction for atmospheric tide compared to previous results further constraining core models an additional 4 years of mars range data improves the mars ephemeris determines 21 asteroid masses and bounds solar mass loss dgmsun dt

stromatolites the challenge of a term in space and time abstract several definitions of stromatolites are discussed and kalkowsky s most important statements about stromatolites are translated from german to english a new definition for stromatolites is proposed namely stromatolites are laminated rocks the origin of which can clearly be related to the activity of microbial communities which by their morphology physiology and arrangement in space and time interact with the physical and chemical environment to produce a laminated pattern which is retained in the final rock structure unconsolidated laminated systems clearly related to the activity of microbial communities and often called recent stromatolites or living stromatolites are defined as potential stromatolites the main microbial activities which are important in the formation of potential stromatolites and stromatolites are described and examples of stromatolites of various types including iron stromatolites are also described

biogenic structures and micrite in stalactites from grand cayman island british west indies stalactites from modern and old caves developed in the bluff formation of grand cayman island contain laminae and bulbous masses of micrite intercalated with sparry calcite the micrite as well as some of the sparry calcite around it contains small up to 25 m long ovate to spherical bodies that have a high concentration of either manganese or iron such bodies may be of bacterial origin the micrite contains numerous calcified filaments that are probably of algal origin calcification of the filaments occurred either during life or shortly after death of the algae the algae played an important role in trapping and binding the micrite furthermore the algae may be directly or indirectly responsible for the formation of much of the micrite

an improved solution of the gravity field of mars gmm 2b from mars global surveyor a spherical harmonic solution of the mars gravity field to degree and order 80 goddard mars model 2b gmm 2b has been developed using x band tracking data of mars global surveyor mgs from october 1997 to february 2000 and altimeter crossovers formed from the mars orbiter laser altimeter mola data between march and december 1999 during the mapping mission mgs was located in a near polar 92 9 inclination and near circular orbit at a mean altitude of 400 km the tracking data from this orbit provide a detailed global and high resolution view of the gravity field of mars mars gravity solutions are stable to 60 60 even without application of a kaula power law constraint the valles marineris is resolved distinctly with lows reaching 450 mgals olympus mons and its aureole are both separately resolved and the volcano has a peak anomaly of 2950 mgals the global correlation of the gmm 2b gravity coefficients with mola derived topography is 0 78 through degree 60 and the correlation remains above 0 6 through degree 62 the global gravity anomaly error predicted from the gmm 2b error covariance through 60 60 is 11 mgal the global geoid error from gmm 2b through 60 60 is 1 8 m mgs orbit quality using gmm 2b as measured by overlapping orbital arcs is 1 m in the radial direction and 10 m in total position

winter and spring evolution of northern seasonal deposits on mars from omega on mars express the omega visible near infrared imaging spectrometer on mars express has observed the retreat of the northern seasonal deposits during martian year 27 28 from the period of maximum extension close to the northern winter solstice to the end of the retreat at l s 95 we present the temporal and spatial distributions of both co 2 and h 2o ices and propose a scenario that describes the winter and spring evolution of the northern seasonal deposits during winter the co 2 rich condensates are initially transparent and could be in slab form a water ice annulus surrounds the sublimating co 2 ice extending over 6 of latitude at l s 320 decreasing to 2 at l s 350 and gradually increasing to 4 5 at l s 50 this annulus first consists of thin frost as observed by the viking lander 2 and is then overlaid by h 2o grains trapped in the co 2 rich ice layer and released during co 2 sublimation by l s 50 h 2o ice spectrally dominates most of the deposits in order to hide the still several tens of centimeters thick co 2 ice layer in central areas of the cap we propose the buildup of an optically thick top layer of h 2o ice from ice grains previously embedded in the co 2 ice and by cold trapping of water vapor from the sublimating water ice annulus the co 2 ice signature locally reappears between l s 50 and 70 what emerges from our observations is a very active surface atmosphere water cycle these data provide additional constraints to the general circulation models simulating the martian climate copyright 2011 by the american geophysical union

global duricrust on mars analysis of remote sensing data global remote sensing data for mars are analyzed to obtain a simple self consistent model for the surface layer the data sets discussed include radar cross section measurements at several wavelengths radio whole disk thermal emission observations at two wavelengths the global distribution of thermal inertia deviations of diurnal temperatures from those of a homogeneous model and thermal spectral estimates of surface rock abundance and of the thermal inertia of the nonrocky component of the surface the data sets which most constrain the interpretation are the rock abundance map and the correlation of thermal inertia with radar cross section these require the rock abundance to not vary significantly from place to place and simultaneously require the density and thermal inertia of the fines to vary in a consistent manner the simplest model which can explain all of the data involves a global case hardened crust duricrust which varies spatially in its degree of formation in general low thermal inertia regions have a poorly developed crust and highinertia regions have a well developed crust there are however regions that consist of coarse particles and which do not fit this model e g chryse this model is consistent with the ages of low inertia regions and with aeolian mechanisms for their development the duricrust is thought to form via the mobilization of salt ions within a layer of water adsorbed within the regolith and its formation may be associated with the exchange of water between the regolith and atmosphere which occurs on the 105 and 106 year time scale

a new dry hypothesis for the formation of martian linear gullies long narrow grooves found on the slopes of martian sand dunes have been cited as evidence of liquid water via the hypothesis that melt water initiated debris flows eroded channels and deposited lateral levees however this theory has several short comings for explaining the observed morphology and activity of these linear gullies we present an alternative hypothesis that is consistent with the observed morphology location and current activity that blocks of co2 ice break from over steepened cornices as sublimation processes destabilize the surface in the spring and these blocks move downslope carving out leveed grooves of relatively uniform width and forming terminal pits to test this hypothesis we describe experiments involving water and co2 blocks on terrestrial dunes and then compare results with the martian features furthermore we present a theoretical model of the initiation of block motion due to sublimation and use this to quantitatively compare the expected behavior of blocks on the earth and mars the model demonstrates that co2 blocks can be expected to move via our proposed mechanism on the earth and mars and the experiments show that the motion of these blocks will naturally create the main morphological features of linear gullies seen on mars

giant subtidal stromatolites forming in normal salinity waters we report here the discovery of giant lithified subtidal columnar stromatolites 2 m high growing in 7 8 m of clear oceanic water in current swept channels between the exuma islands on the eastern bahama bank they grow by trapping ooid and pelletal carbonate sand and synsedimentary precipitation of carbonate cement within a field of giant megaripples the discovery is important to geologists and biologists because similar organo sedimentary structures built by a combination of cementation and the trapping of sediment by microbes were the dominant fossil types during the precambrian stromatolites are thought to have been responsible for the production of free oxygen and thus the evolution of animal life1 2 until the discovery of small lithified subtidal columnar stromatolites in the bahamas3 the only subtidal marine examples known to be living while undergoing lithification were in the hypersaline waters of hamelin pool at shark bay western australia4 7 shark bay stromatolites range from intertidal to the shallow subtidal with the larger columns reaching 1 m in height the shark bay stromatolites have strongly influenced geological interpretation by analogy many ancient stromatolites have been considered to have grown in intertidal and or hypersaline conditions8 although hypersalinity was not a necessity for growth during the precambrian because grazing metazoan life had not then evolved

daily temperature variations on mars the viking infrared thermal mapper irtm has measured the infrared brightness temperature of mars for more than a full martian year the daily variation of the 20 m brightness temperature can be predicted to within 5 k for most of the martian surface during any season if the radiometric albedo and the thermal inertia of the model are allowed to increase with increasing atmospheric dust opacity however for approximately 32 of the martian surface area no values of thermal inertia or albedo can fit the thermal observations these temperature anomalies isolate one large region on mars which connects the low thermal inertia regions of arabia tharsis and elysium the anomalies do not correlate with elevation geologic units morphology or atmospheric dust content all regions with lambert albedo less than 0 18 can be well fit with the standard thermal model but all areas with albedo greater than 0 28 are anomalous there is a strong inverse correlation between the magnitude of the anomaly and the thermal inertia this correlation indicates that some surface property is responsible for the anomaly in the anomalous region the observed temperatures are warmer in the morning cooler late in the afternoon and decrease more slowly during the night than the viking model temperatures of all the physical processes likely to occur on mars but not included in the viking thermal model only a layered soil can explain the observations a low thermal inertia layer covering a high thermal inertia material will heat up quickly in the morning and cool down quickly in the afternoon at night the high thermal inertia material will moderate the temperature a possible interpretation for the layering deduced from the irtm observations is a layer of aeolian deposited dust about one thermal skin depth thick 1 to 4 cm covering a duricrust because dust accumulates in some areas after every global dust storm the duricrust must be actively forming a one thermal skin depth dust layer covering a duricrust is compatible with viking lander observations irtm spectral observations and viking orbiter imaging

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

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

mars orbiter laser altimeter pulse width measurements and footprint scale roughness the mars orbiter laser altimeter mola measured the pulse width and energy of altimetric laser returns during the course of two mars years of operations as secondary science objectives mola obtains the footprint scale roughness and the bidirectional reflectivity of mars mola underwent extensive preflight calibration and pulse measurements were monitored continuously in flight but anomalous values of roughness have been inferred a calibration of pulse widths using inflight data yields a slope corrected roughness over 75 m diameter footprints that may be used for quantitative geomorphic surface characterization required for example for landing site selection the recalibration uses a total least squares estimation of pulse characteristics that generalizes the method of abshire et al 2000 this method utilizing the timing at voltage threshold crossings and the area between crossings accounts for observation errors and shows that surface roughness as small as 1 m can be resolved

the thermal stability of near surface ground ice on mars the existence of subsurface water ice on mars has been predicted in several theoretical studies1 5 but there are no definitive observations of its present distribution geomorphic features on the surface of mars have been widely interpreted as evidence for the presence of ground ice6 12 but many of these features are found at near equatorial latitudes where thermal models have predicted that near surface water ice should not be stable under present climate conditions3 13 14 here i present the results of thermal calculations which show that observed geographic variations in the thermal and reflectance properties of martian soils significantly affect subsurface temperatures my results indicate that in certain regions ground ice deposits could exist much closer to the surface and much closer to the equator than previously thought in the future these deposits could be a valuable resource for human exploration15

periodic climate change on mars review of evidence and effects on distribution of volatiles abstract the polar regions of mars preserve in both their layering and their topography a record of recent climate changes because of the coincidence of the growth of the northern seasonal cap with global dust storms dust may be currently accumulating on the northern cap but conditions at the poles will alternate with the precessional cycle deposition is also modulated by changes in eccentricity and obliquity which interact complexly affecting initiation of global dust storms the stability of volatiles at the surface and global wind regimes formation of spiral valleys and low undulations on the surface of the layered deposits may result from prefential sublimation of volatiles on sunward facing slopes and condensation on the adjacent flats with the rates also modulated by astronomically caused insolation variations lack of impact craters on the surface and lack of interruption of the layers by impact scars suggest that the polar deposits are no more than a few million years old older deposits may have been periodically removed as indicated by etch pitted terrain at the south pole and by superposition relations around the periphery of the present layered deposits evidence of ancient periodic climate changes that occurred before formation of the present layered terrain is fragmentary but includes pedestal craters parallel moraine like ridges and etched ground at high latitudes perturbation of the orbital motions also results in adsorption and desorption of volatiles in the regolith which leads to variations in atmospheric pressure and partial dehydration of the equatorial near surface materials

plant impact on the biogeochemical cycle of silicon and related weathering processes abstract the contribution of plants to the biogeochemical cycle of si and related weathering processes was studied in an equatorial rainforest ecosystem congo where the biologic turnover of si is high 58 to 76 kg ha y litterfall leaves a soil profile and groundwaters were analysed phytoliths and organic matter have a similar distribution with depth in the soil profile the model of a bicompartmental distribution of organic matter is applied to phytolith distribution and shows that about 92 of the biogenic silica input is rapidly recycled while about 8 of the biogenic silica input supplies a stable pool of phytoliths with a lower turnover reprecipitation of silica was observed at the base of the soil profile indicating a local geochemical environment that is oversaturated with respect to amorphous silica a balance in biogeochemical cycle of si requires that the vegetation absorb dissolved silicon released from weathering of minerals which otherwise would be available for mineral neoformation or export from the profile towards regional drainages plant uptake of si increases the chemical weathering rate without increasing the denudation rate this study shows that the uptake storage and release of si by the vegetation have to be taken into account when using dissolved si for tracing chemical weathering dynamics

depth distribution and density of co2 deposition on mars observations by the mars orbiter laser altimeter have been used to detect subtle changes of the polar surface height during the course of seasonal cycles that correlate with the expected pattern of co2 deposition and sublimation using altimetric crossover residuals from the mars orbiter laser altimeter we show that while zonally averaged data capture the global behavior of co2 exchange there is a dependence of the pattern on longitude at the highest latitudes the surface height change is as high as 1 5 2 m peak to peak and it decreases equatorward decomposition of the signal into harmonics in time allows inspection of the spatial pattern and shows that the annual component is strongly correlated with the residual south polar cap deposits and to a lesser extent with the north polar cap in the north the second harmonic semiannual component correlates with the location of the ice deposits the phases of the annual cycles are in agreement with observations by the thermal emission spectrometer of the timing of the annual disappearance of co2 frost from the surface at the high latitudes at lower latitudes frost sublimation crocus date predates the mean depositional minima as expected these global scale volumetric measurements of the distribution of condensed co2 can be combined with measurements of the deposited column mass density derived from the neutron spectrometer on board mars odyssey to yield an estimate of the density of the seasonally exchanging material of 0 5 0 1 g cm 3 these constraints should be considered in models of the martian climate system and volatile cycles

co2 snow depth and subsurface water ice abundance in the northern hemisphere of mars observations of seasonal variations of neutron flux from the high energy neutron detector hend on mars odyssey combined with direct measurements of the thickness of condensed carbon dioxide by the mars orbiter laser altimeter mola on mars global surveyor show a latitudinal dependence of northern winter deposition of carbon dioxide the observations are also consistent with a shallow substrate consisting of a layer with water ice overlain by a layer of drier soil the lower ice rich layer contains between 50 and 75 weight water indicating that the shallow subsurface at northern polar latitudes on mars is even more water rich than that in the south

rootless cones on mars a consequence of lava ground ice interaction fields of small cratered cones on mars are interpreted to have formed by rootless eruptions due to explosive interaction of lava with ground ice contained within the regolith beneath the flow melting and vaporization of the ice and subsequent explosive expansion of the vapour act to excavate the lava and construct a rootless cone around the explosion site similar features are found in iceland where flowing lava encountered water saturated substrates the martian cones have basal diameters of c 30 1000 m and are located predominantly in the northern volcanic plains high resolution mars orbiter camera images offer significant improvements over viking data for interpretation of cone origins a new model of the dynamics of cone formation indicates that very modest amounts of water ice are required to initiate and sustain the explosive interactions that produced the observed features this is consistent with the likely low availability of water ice in the martian regolith the scarcity of impact craters on many of the host lava flows indicates very young ages suggesting that ground ice was present as recently as less than 10 l00 ma and may persist today rootless cones therefore act as a spatial and temporal probe of the distribution of ground ice on mars which is of key significance in understanding the evolution of the martian climate the location of water in liquid or solid form is of great importance to future robotic and human exploration strategies and to the search for extraterrestrial life

co2 frost cap thickness on mars during northern winter and spring 1 the thickness of seasonal co2 frost that covers the north pole of mars during the winter and spring seasons is studied using gamma ray and neutron data measured using the gamma ray spectrometer suite of instruments aboard mars odyssey the resultant seasonal variation of co2 ice frost thickness for latitudes greater than 85 is in close agreement within 9 at maximum with those predicted using all three major mars general circulation models presently in use these observed co2 ice results are significantly different from those inferred from the mars obiter laser altimeter experiment aboard mars global surveyor mgs a possible explanation is that the density of the co2 ice frost cap is considerably lower than that inferred from observed variations of the mgs orbit other significant results are that the thermal neutron counting rates provide evidence for variations in the abundance of noncondensable components of the polar atmosphere of mars and that the basement terrain below the seasonal cover of co2 frost within about 10 of the pole is nearly 100 water ice

the use of laser altimetry in the orbit and attitude determination of mars global surveyor altimetry from the mars observer laser altimeter mola an instrument on board the mars global surveyor mgs spacecraft has been analyzed for the period of the mgs science phasing orbit 1 spo 1 mission phase altimeter ranges have been used to improve significantly the orbit and attitude knowledge of the spacecraft by the use of crossover constraint equations derived from short passes of the mola data these constraint equations differ from traditional crossover constraints and exploit the small footprint associated with laser altimetry the rationale for using this technique with laser altimetry over sloping terrain is laid out and evidence of the resulting benefit is presented