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

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

greenland meltwater as a significant and potentially bioavailable source of iron to the ocean the micronutrient iron is thought to limit primary production in large regions of the global ocean meltwater measurements suggest that the greenland ice sheet serves as a significant source of potentially bioavailable iron to the surrounding coastal ocean

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

calcium carbonate as ikaite crystals in antarctic sea ice 1 we report on the discovery of the mineral ikaite caco3 6h2o in sea ice from the southern ocean the precipitation of caco3 during the freezing of seawater has previously been predicted from thermodynamic modelling indirect measurements and has been documented in artificial sea ice during laboratory experiments but has not been reported for natural sea ice it is assumed that caco3 formation in sea ice may be important for a sea ice driven carbon pump in ice covered oceanic waters without direct evidence of caco3 precipitation in sea ice its role in this and other processes has remained speculative the discovery of caco3 6h2o crystals in natural sea ice provides the necessary evidence for the evaluation of previous assumptions and lays the foundation for further studies to help elucidate the role of ikaite in the carbon cycle of the seasonally sea ice covered regions

a laboratory based dielectric model for the radar sounding of the martian subsurface abstract for the last decade the sharad radar on board nasa s mars reconnaissance orbiter and the marsis radar on board esa s mars express have sounded the surface and subsurface of mars from orbit to search for and characterise water ice reservoirs when associated with dielectric models the regolith composition in terms of dust ice and voids of the surface and subsurface can be extracted from these data these models describe the electromagnetic properties of the material as a function of its chemical and physical properties with the goal of improving the currently available dielectric models for martian icy regolith we conducted laboratory measurements of the dielectric properties of the jsc mars 1 martian soil simulant mixed with water ice varying the water ice mass fraction from 0 to 76 our measurements were performed between 50 mhz and 2 ghz at ambient temperature and at 243 k the samples had porosities between 40 and 72 based on these we propose a model that relates the dielectric constant of the sounded material to its volume fraction of water ice and or of jsc mars 1 its porosity and its temperature tuned to the relevant frequencies our dielectric model can be used to estimate the volume fraction of water ice from the radar sounding data of sharad and marsis it is similarly relevant for the interpretation of data from the wisdom radar which will be part of the science payload of the exomars 2020 rover

carbon dynamics in sea ice a winter flux time series 1 a winter time series of the inorganic carbon system above within and beneath the landfast sea ice of the southern beaufort sea confirmed that sea ice is an active participant in the carbon cycle of polar waters eddy covariance measurements above the ice identified significant vertical co2 fluxes mostly upward away from the ice but with short periods of downward fluxes as well a novel in situ method revealed extremely high pco2 values within the ice that are not inconsistent with theory the total carbon content of the ice increased slightly through the winter season and increasing variability in the vertical profiles as spring began indicated that the inorganic carbon became mobile as the ice began to melt during early winter as the ice formed inorganic carbon concentrations in the surface waters increased dramatically along with salinity partly because of rejection from the ice and partly from advective mixing brine drainage was apparently not sufficient to initiate convection and the excess carbon remained in the surface waters into the summer

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

the percolation phase transition in sea ice sea ice exhibits a marked transition in its fluid transport properties at a critical brine volume fraction p c of about 5 percent or temperature t c of about 5 c for salinity of 5 parts per thousand for temperatures warmer than t c brine carrying heat and nutrients can move through the ice whereas for colder temperatures the ice is impermeable this transition plays a key role in the geophysics biology and remote sensing of sea ice percolation theory can be used to understand this critical behavior of transport in sea ice the similarity of sea ice microstructure to compressed powders is used to theoretically predict p c of about 5 percent

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

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

regional geological and tectonic structures of the north sea area from potential field modelling the spatial distribution of large scale crustal domains and their boundaries are investigated in the north sea area by combining gravity magnetic and seismic data the north sea is situated on the plates of three continents avalonia laurentia and baltica which collided during the caledonian orogeny in the middle palaeozoic the location and continuation of the collisional sutures are debated we apply filters and transformations to potential field data to focus on the crystalline crust and uppermost mantle on a regional scale in order to extract new information on continental sutures the transformations reveal intrinsic features of crustal transitions between the caledonian plates and their relation to later extensional structures the transformations include the hough transform applied to the gravity field calculation of fractional derivatives and integrals of the gravity and magnetic fields the pseudogravity field and the horizontal gradient field as well as upward continuation the results indicate a fundamental difference between the lithosphere of avalonia laurentia and baltica the location of the mesozoic rift system the central graben and viking graben may have been partly determined by the presence of the sutures between these three plate indicative of extensional reactivation of compressional structures a significant lineament across the entire north sea between scotland and north germany indicates that the lower crust of baltica provenance may extend as far south westward as to this lineament comparison of the power spectra of the gravity field in five selected areas shows significant differences in the long wavelength components between the areas north and south of the lineament corresponding to differences in crustal properties this lineament could represent the suture between lithosphere of caledonian origin avalonia versus lithosphere of precambrian origin baltica in the lower crust and upper mantle if this is the case the lineament is the missing link in the reconstruction of the triple plate collision

equations for determining the gas and brine volumes in sea ice samples on a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite de salinite et de temperature dans des gammes de temperatures entre 2 c et 30 c inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace on donne aussi des equations qui permettent le calcul du volume de gaz et d eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

temperature and heat flow density along european transcontinental profiles abstract the project geothermal atlas of europe for the first time gives a compilation of geothermal data for the whole of europe along two transcontinental profiles temperatures at different depths and heat flow density are studied the geothermal field is characterized by large scale and small scale anomalies which are connected with the main tectonics of europe and possibly also with convective heat transport the relationship between the near surface heat flow density and the depth of the crust mantle boundary is different for the various tectonic units extrapolation of temperature for greater depths should start from the deepest possible level for which the temperature distribution is known as the temperature at a depth of 3 km is quite well established for the most of europe these data can be used as a basis for estimating the temperature depth distribution within the earth s crust

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

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

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

the evolution of a submarine landform record following recent and multiple surges of tunabreen glacier svalbard this study focuses on the glacial landform record associated with recent surge events of tunabreen a calving tidewater glacier in tempelfjorden spitsbergen submarine geomorphology and recent te

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

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

influence of glacial water and carbonate minerals on wintertime sea ice biogeochemistry and the co2 system in an arctic fjord in svalbard the effect of freshwater sources on wintertime sea ice co2 processes was studied from the glacier front to the outer tempelfjorden svalbard in sea ice glacier ice brine and snow march april 2012 was mild and the fjord was mainly covered with drift ice in contrast to the observed thicker fast ice in the colder april 2013 this resulted in different physical and chemical properties of the sea ice and under ice water data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in april 2012 contained on average 54 of frozen in glacial meltwater this was five times higher than in april 2013 where the ice was frozen seawater in april 2012 the largest excess of sea ice total alkalinity at carbonate ion co32 and bicarbonate ion concentrations hco3 relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral enriched glacial water in april 2013 the excess of these variables was mainly due to ikaite dissolution as a result of sea ice processes dolomite dissolution increased sea ice at twice as much as ikaite and calcite dissolution implying different buffering capacity and potential for ocean co2 uptake in a changing climate

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

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

increased co2 uptake due to sea ice growth and decay in the nordic seas 1 the uptake rates of atmospheric co2 in the nordic seas are among the highest in the world s oceans this has been ascribed mainly to a strong biological drawdown but chemical processes within the sea ice itself have also been suggested to play a role the importance of sea ice for the carbon uptake in the nordic seas is currently unknown we present evidence from 50 localities in the arctic ocean that dissolved inorganic carbon is rejected together with brine from growing sea ice and that sea ice melting during summer is rich in carbonates model calculations show that melting of sea ice exported from the arctic ocean into the east greenland current and the nordic seas plays an important and overlooked role in regulating the surface water partial pressure of co2 and increases the seasonal co2 uptake in the area by approximately 50

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

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

geology of the northeastern flank of apollinaris mons mars constraints on the erosional history from morphology topography and crater populations abstract we have utilized themis mola ctx and hirise data sets to investigate the morphologic and topographic characteristics of the northeast flank of apollinaris mons a region with evidence for significant erosion of volcanic deposits using arcgis software we mapped the geology of the northeast flank and obtained age estimates using crater size frequency distributions from crater counts of the eight mapped units three apollinaris mons upper mid and lower flank units represent volcanic flank materials in various states of preservation the late noachian early hesperian upper flank unit is massive and contains joint like vertical structures along the scarp faces of two large plateaus whose upper surfaces likely represent the original surface or near surface deposits of apollinaris mons downslope facing plateau scarps have up to 500 m of relief positioned below this unit are the mid flank and lower flank units each representing eroded surfaces within apollinaris mons flank materials that have stabilization ages between the late hesperian to early amazonian mantling material in the region contains cavities and boxwork like textures that resemble patterns in terrestrial eroded pyroclastic flow deposits dome shaped mounds west of the mapping region have morphologic similarities to terrestrial fumarolic mounds or possibly inverted impact craters both the texture and features suggest widespread pyroclastic deposits adjacent to apollinaris mons using mola gridded topography we estimate that 308 km3 of materials have been eroded along the flanks of the volcano statistical and histogram data from the thickness values of eroded materials shows that up to 300 m of material has been removed from the majority of flank surfaces assuming steady state erosion of flank surfaces we estimate an area normalized loss rate of 0 859 nm yr for northeast apollinaris mons this erosion rate is within the long term range for mars 0 01 10 nm yr as estimated from mer landing site geology by golombek et al 2006

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

influence of melting icebergs on distribution characteristics and transport of marine particles in an east greenland fjord a detailed study of distribution of suspended sediments in an east greenland fjord with a high iceberg production rate reveals the existence of intermediate nepheloid layers inls observed inls extended from the head to the mouth of the fjord at water depths between 100 and 400 m particulate organic carbon and nitrogen chlorophyll a and nutrient measurements and observation by microscope and energy dispersive x ray analyses were used to characterize marine particles particles in the inls are composed of glacial flour including 50 m quartz and feldspar grains with angular and sharp edges considered to be released from melting icebergs in situ photographs show large aggregates 1 mm at high concentration 300 particles per liter in and below inls these aggregates in comparison with the dispersed particle size distribution demonstrate that smaller size particles e g clay settle effectively along with larger single size grains in kangerlugssuaq fjord the mass transport of marine particles was governed by the subsurface iceberg melting producing observed inls rather than the surface meltwater plume this suggests that the subsurface water temperature controls release of iceberg debris and the existence of warm subsurface water as well as the spread of cold and fresh water in the surface layer needs to be considered to evaluate the occurrence of ice rafted debris layers including heinrich layers this study provides the field evidence of a modern analogue on ocean conditions that could form iceberg rafted layers

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

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

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

thermal evolution of permeability and microstructure in sea ice 1 the fluid permeability k of sea ice constrains a broad range of processes such as the growth and decay of seasonal ice the evolution of summer ice albedo and biomass build up such processes are critical to how sea ice and associated ecosystems respond to climate change however studies of k and its dependence on brine porosity and microstructure are sparse here we present a multifaceted theory for k which closely captures laboratory and field data x ray computed tomography provides an unprecedented look at the brine phase and its connectivity we find that sea ice displays universal transport properties remarkably similar to crustal rocks yet over a much narrower temperature range our results yield simple parameterizations for fluid transport in terms of temperature and salinity and permit more realistic representations of sea ice in global climate and biological models

the gravitational signature of martian volcanoes by modeling the elastic flexure of the martian lithosphere under imposed loads we provide a systematic study of the old and low relief volcanoes 3 2 ga 0 5 to 7 4 km and the younger and larger prominent constructs within the tharsis and elysium provinces 3 2 ga 0 5 to 7 4 km and the younger and larger constructs clustered in the tharsis and elysium provinces 3 ga 5 8 to 21 9 km the observed topography is used to define the load and to derive a simulated gravity field that is compared to the observed gravity the bulk density of the lava that composes all volcanoes is found to be 3 200 kg m 3 which is representative of iron rich basalts as sampled by the martian basaltic meteorites the elastic part of the lithosphere that is the part maintaining loads over geologic time is found to have been thin when the small old volcanoes formed which implies that the lithosphere was hot early in geologic history conversely larger volcanoes are found to have been emplaced on a cold and thicker elastic lithosphere

rafted pumice a new model for the formation of the medusae fossae formation mars abstract the medusae fossae formation mff mars could be deposits of materials originally formed as hyaloclastites erupted from vents which formed the basal units of olympus mons volcano and subsequently collapsed as landslides to form the aureole materials these low density hyaloclastites subsequently floated on the northern sea as pumice rafts and drifted to the southwest where they encountered the boundary of the southern highlands to form the mff

effect of glacial drainage water on the co2 system and ocean acidification state in an arctic tidewater glacier fjord during two contrasting years in order to investigate the effect of glacial water on the co2 system in the fjord we studied the variability of the total alkalinity at total dissolved inorganic carbon ct dissolved inorganic nutrients oxygen isotopic ratio d18o and freshwater fractions from the glacier front to the outer tempelfjorden on spitsbergen in winter 2012 january march and april and 2013 april and summer fall 2013 september the two contrasting years clearly showed that the influence of freshwater mixing and haline convection affected the chemical and physical characteristics of the fjord the seasonal variability showed the lowest calcium carbonate saturation state x and ph values in march 2012 coinciding with the highest freshwater fractions the highest x and ph were found in september 2013 mostly due to co2 uptake during primary production overall we found that increased freshwater supply decreased x ph and at on the other hand we observed higher at relative to salinity in the freshwater end member in the mild and rainy winter of 2012 1142 lmol kg21 compared to at in 2013 526 lmol kg21 observations of calcite and dolomite crystals in the glacial ice suggested supply of carbonate rich glacial drainage water to the fjord this implies that winters with a large amount of glacial drainage water partly provide a lessening of further ocean acidification which will also affect the air sea co2 exchange

first estimates of the contribution of caco3 precipitation to the release of co2 to the atmosphere during young sea ice growth 1 we report measurements of ph total alkalinity air ice co2 fluxes chamber method and caco3 content of frost flowers ff and thin landfast sea ice as the temperature decreases concentration of solutes in the brine skim increases along this gradual concentration process some salts reach their solubility threshold and start precipitating the precipitation of ikaite caco3 6h2o was confirmed in the ff and throughout the ice by raman spectroscopy and x ray analysis the amount of ikaite precipitated was estimated to be 25 mol kg 1 melted ff in the ff and is shown to decrease from 19 to 15 mol kg 1 melted ice in the upper part and at the bottom of the ice respectively co2 release due to precipitation of caco3 is estimated to be 50 mol kg 1 melted samples the dissolved inorganic carbon dic normalized to a salinity of 10 exhibits significant depletion in the upper layer of the ice and in the ff this dic loss is estimated to be 2069 mol kg 1 melted sample and corresponds to a co2 release from the ice to the atmosphere ranging from 20 to 40 mmol m 2 d 1 this estimate is consistent with flux measurements of air ice co2 exchange our measurements confirm previous laboratory findings that growing young sea ice acts as a source of co2 to the atmosphere caco3 precipitation during early ice growth appears to promote the release of co2 to the atmosphere however its contribution to the overall release by newly formed ice is most likely minor

wintertime warming of an arctic shelf in response to large scale atmospheric circulation 1 observations on the west spitsbergen shelf have shown that the dynamic response of the shelf to wind forcing has a profound effect on the heat content of the water hydrographic and atmospheric data have been analysed with respect to the relative importance of surface heat fluxes and advective processes on ocean temperature during the arctic winter of 2005 06 periods of sustained along shelf winds generated upwelling and cross shelf exchange causing extensive flooding of the coastal waters with warm atlantic water from the west spitsbergen current the winter temperature of the west spitsbergen shelf reverted to that typical of fall interrupting the normal cycle of sea ice formation in the region

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

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

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

crust stratigraphy and heterogeneities of the first kilometers at the dichotomy boundary in western elysium planitia and implications for insight lander abstract insight landed on mars on november 26 2018 in western elysium planitia the mars crust beneath the lander is subject to complex geologic history next to the great topographic and crustal dichotomy of mars understanding this part of the martian crust in the subsurface would aid future investigations of the internal structure of the planet based on seismic datasets collected by the seismic experiment for interior structure seis instrument here we investigate the subsurface structure and composition from the analysis of mineralogy and morphology of exposures in impact craters as well as on scarps and knobs in the general region of elysium planitia using a combination of orbital datasets we identify exposures of subsurface materials with distinct composition and physical properties we find olivine and pyroxene detections associated with small impact craters 1 5 7 km rim in the vicinity of insight lander as well as in the transition unit and elysium volcanic unit fe mg phyllosilicates have been identified in the central peak of the 51 km diameter kalpin crater and on knobs in the transition unit between the dichotomy and the plains in addition eroded meter scale layered unit subject to erosion has been identified in six impact craters to the north east of the landing site including kalpin crater massive bedrock and layered weak materials co occur in the transition unit indicating a complex origin these results together suggest both materials with altered composition and layered deposit occur as distinct geologic units beneath the basaltic lava flow units through analogy with terrestrial sedimentary rocks or clay bearing sediments we suggest physically weak materials exist beneath the lava flow units in the general region of elysium planitia the spatial distribution and continuity of these materials are unclear due to the lack of exposures within the lava flow unit where the insight lander is located these subsurface materials of distinct physical properties may result in increased attenuation or reverberations of seismic waves to be collected by seis the findings suggest a close investigation of the potential effects of subsurface stratigraphy on seismic data would help inform future data interpretation and understanding of the internal structure of mars

physical and biogeochemical properties in landfast sea ice barrow alaska insights on brine and gas dynamics across seasons 1 the impacts of the seasonal evolution of sea ice physical properties on ice ocean biogeochemical exchanges were investigated in landfast ice at barrow alaska from january through june 2009 three stages of brine dynamics across the annual cycle have been identified based on brine salinity brine volume fraction and porous medium rayleigh number ra these are sea ice bottom layer convection full depth convection and brine stratification we further discuss the impact of brine dynamics on biogeochemical compounds in sea ice stable isotopes of water d 18o nutrients no3 po43 nh4 microalgae chlorophyll a and inert gas argon in general full depth convection events favor exchanges between sea ice and seawater while brine stratification limits these exchanges however argon responds differently to brine dynamics than the other biogeochemical compounds analyzed in this study this contrast is attributed to the impact of bubble nucleation on inert gas transport compared to the other biogeochemical compounds we present a scenario for argon bubble formation and evolution in sea ice and suggest that a brine volume fraction approaching 7 5 10 is required for inert gas bubbles to escape from sea ice to the atmosphere

inputs of glacially derived dissolved and colloidal iron to the coastal ocean and implications for primary productivity 1 glacial meltwaters draining shield bedrock under the greenland ice sheet gis contain 0 4 m total dissolved fe tdfe with an average flow weighted concentration of 53 nm the concentrations of 0 03 and 0 03 0 4 m fe vary over the ablation period with weighted means for each of these fractions being respectively 22 4 nm and 30 8 nm these concentrations are lower estimates as an adjacent larger glacier a more representative source of glacial meltwater had higher dissolved fe concentrations and reactions of meltwaters with proglacial sediments could also enhance dissolved fe concentrations this source of tdfe is additional to the reactive oxyhydr oxide phases identified by raiswell et al 2006 that are also introduced to adjacent polar seas from glaciers the fe concentrations in the shield bedrock underlying the gis are lower than those of other crustal rocks 4 0 cf 6 2 but we argue that these fe concentrations are not limiting on the total dissolved fe concentrations we measure the biogeochemical weathering processes operating on the subglacial debris and suspended sediment in our catchment are likely to be similar to those in other glaciated catchments therefore the meltwater fe concentrations reported here can be used to give a first estimate of global fluxes of meltwater dissolved fe to coastal polar waters a lower estimate of the global flux of tdfe from glacial meltwaters is 75 106 moles fe a this glacial meltwater input of fe to adjacent polar waters will be greatest around greenland where there are highest annual meltwater discharges however the greatest impact of this source of glacial meltwater fe is anticipated to be in antarctic high nutrient low chlorophyll hnlc waters where phytoplankton productivity is typically limited by availability of fe for antarctic waters the estimated meltwater fe tdfe input is about 10 of that suggested to come from sea ice melting but glacial inputs continue throughout the austral summer ablation period after sea ice melt is complete

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

svalbard glacier elevation changes and contribution to sea level rise 1 we compare satellite altimetry from the ice cloud and land elevation satellite icesat 2003 2007 to older topographic maps and digital elevation models 1965 1990 to calculate long term elevation changes of glaciers on the svalbard archipelago results indicate significant thinning at most glacier fronts with either slight thinning or thickening in the accumulation areas except for glaciers that surged which show thickening in the ablation area and thinning in the accumulation areas the most negative geodetic balances occur in the south and on glaciers that have surged while the least negative balances occur in the northeast and on glaciers in the quiescent phase of a surge cycle geodetic balances are related to latitude and to the dynamical behavior of the glacier the average volume change rate over the past 40 years for svalbard excluding austfonna and kvitoya is estimated to be 9 71 0 55 km3 yr 1 or 0 36 0 02 m yr 1 w equivalent for an annual contribution to global sea level rise of 0 026 mm yr 1 sea level equivalent

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

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

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

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

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

sea ice mass balance monitoring in an arctic fjord a sea ice mass balance monitoring study including ice extent and thickness observations was started at kongsfjorden 798 n 128 e svalbard in 2003 the inner part of kongsfjorden is usually covered by seasonal fast ice 1 m thick initially forming between december and march and persisting until june ice extent is visually observed from the mountain zeppelinfjellet and documented by ice maps and photographs several times a week ice and snow thickness is measured regularly at four sites from drillholes time series of ice extent in four areas east of ny alesund total area 120 km 2 were calculated for 2003 05 by combining extent with thickness data ice mass time series were calculated as also observed earlier than 2003 in other studies the fast ice varies interannually in extent and thickness among the factors which control the fast ice evolution are physical and meteorological parameters and the geographical setting of kongsfjorden with its coastline and a group of islands in its inner part having a protective effect this study is ongoing and a major aim is to identify and quantify connections between the kongsfjorden fast ice evolution and climate parameters

co2 system development in young sea ice and co2 gas exchange at the ice air interface mediated by brine and frost flowers in kongsfjorden spitsbergen in march and april 2010 we investigated the development of young landfast sea ice in kongsfjorden spitsbergen svalbard we sampled the vertical column including sea ice brine frost flowers and sea water to determine the co2 system nutrients salinity and bacterial and ice algae production during a 13 day interval of ice growth apart from the changes due to salinity and brine rejection the sea ice concentrations of total inorganic carbon c t total alkalinity a t co2 and carbonate ions co3 2 in melted ice were influenced by dissolution of calcium carbonate caco3 precipitates 25 55 mol kg 1 and played the largest role in the changes to the co2 system the c t values were also influenced by co2 gas flux bacterial carbon production and primary production which had a small impact on the c t the only exception was the uppermost ice layer in the top 0 05 m of the ice there was a co2 loss of 20 mol kg 1 melted ice 1 mmol m 2 from the ice to the atmosphere frost flowers on newly formed sea ice were important in promoting ice air co2 gas flux causing a co2 loss to the atmosphere of 140 800 mol kg 1 d 1 melted frost flowers 7 40 mmol m 2 d 1

impact of sea ice processes on the carbonate system and ocean acidification at the ice water interface of the amundsen gulf arctic ocean 1 from sea ice formation in november 2007 to onset of ice melt in may 2008 we studied the carbonate system in first year arctic sea ice focusing on the impact of calciumcarbonate caco3 saturation states of aragonite xar and calcite xca at the ice water interface uiw based on total inorganic carbon ct and total alkalinity at and derived ph co2 carbonate ion co3 22 concentrations and x we investigated the major drivers such as brine rejection caco3 precipitation bacterial respiration primary production and co2 gas flux in sea ice brine frost flowers and uiw we estimated large variability in seaice ct at the top mid and bottom ice changes due to caco3 and co2 gas flux had large impact on ct in the whole ice core from march to may bacterial respiration was important at the bottom ice during all months and primary production in may it was evident that the sea ice processes had large impact on uiw resulting in a five times larger seasonal amplitude of the carbonate system relative to the upper 20 m during ice formation co2 increased by 30 mmol kg 21 co 3 22 decreased by 50 mmol kg 21 and the xar decreased by 0 8 in the uiw due to co2 enriched brine from solid caco3 conversely during ice melt co3 22 increased by 90 mmol kg 21 in the uiw and x increased by 1 4 between march and may likely due to caco3 dissolution and primary production we estimated that increased ice melt would lead to enhanced oceanic uptake of inorganic carbon to the surface layer

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

acceleration in thinning rate on western svalbard glaciers 1 geodetic measurements indicate that a number of glaciers in western svalbard ranging in size from 5 1000 km2 are losing mass at an accelerating rate the average thinning rate for midtre lovenbreen the glacier with the best data coverage has increased steadily since 1936 thinning rates for 2003 2005 are more than 4 times the average for the first measurement period 1936 1962 and are significantly greater than presented previously on slakbreen thinning rates for the latest measurement period 1990 2003 are more than 4 times that of the period 1961 1977 thinning of several glaciers along a previously measured airborne lidar profile in wedel jarls land has also increased doubling between the period 1990 1996 and 1996 2002 our results imply an increased sea level contribution from svalbard in addition the mass loss is an important influence on measured rates of rebound on western svalbard and should be factored into analysis of grace results

antarctic sea ice carbon dioxide system and controls 1 in austral summer from december 2008 to january 2009 we investigated the sea ice carbon dioxide co2 system and co2 controls in the amundsen and ross seas antarctica we sampled seawater brine and sea ice for the measurements of total alkalinity at total inorganic carbon dic ph inorganic nutrients particulate organic carbon poc and nitrogen pon chlorophyll a pigments salinity and temperature large variability in all measured parameters was observed in time and space due to the complex sea ice dynamics we discuss the controls of the sea ice co2 system such as brine rejection biological processes calcium carbonate caco3 precipitation dissolution and co2 exchange most 80 to 90 of the dic loss was due to brine rejection which suggests that the sea ice acted as an efficient dic sink from 0 8 and 2 6 mol m 2 yr 1 9 6 31 g c m 2 yr 1 the remaining change in dic was to a large extent explained by net biological production the at dic ratio in the sea ice was higher than in the under ice water uiw with ratios reaching 1 7 which indicated caco3 precipitation and concomitant dic loss in the sea ice elevated at dic ratios and carbonate concentrations were also observed in the uiw which reflect the solid caco3 rejected from the ice during melt the potential for uptake of atmospheric co2 in the mixed layer increased by approximately 56 atm due to the combined effect of caco3 precipitation during ice formation and ice melt in summer

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

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

inorganic carbon transport during sea ice growth and decay a carbon pump in polar seas 1 during sea ice formation in polar areas brine rejection increases the density in the underlying water column and thereby contributes to the formation of deep and intermediate water masses in the world ocean here we present evidence that dissolved inorganic carbon tco2 is rejected together with brine from growing sea ice and that low temperatures may result in a significant change in the ratio of tco2 and alkalinity in arctic sea ice compared with surface waters model calculations show that this sea ice driven carbon pump affects surface water partial pressure of co2 significantly in polar seas and potentially sequesters large amounts of co2 to the deep ocean