refugia from asteroid impacts on early mars and the early earth impacts of asteroids and comets posed a major hazard to the continuous existence of early life on mars as on earth the chief danger was presented by globally distributed ejecta including transient thick rock vapor atmospheres on earth much of the thermal radiation is absorbed by boiling the oceans any surviving life is either in deep water or well below the surface global thermal excursions are buffered by the heat capacity of the oceans but when impacts are large enough to vaporize the oceans l028 j thermal buffering serves only to prolong the disaster for thousands of years while the oceans rain out without oceans thermal buffering does not occur on mars relatively small impacts 1026 j frequently heat the surface everywhere to the melting point however owing to the low martian escape velocity the most energetic ejecta including the rock vapor more easily escape to space while massive quantities of less energetic ejecta are globally distributed survival in deep subsurface environments is more likely on mars because 1 mars lower background heat flow and lower gravity allow deeper colonies and 2 the thermal heat pulse from a major impact is briefer only thermophile organisms could have survived impacts of asteroids large enough to leave heat or boil the entire terrestrial ocean studies of terrestrial microorganisms indicate that the last common ancestor may have been thermophile and the survivor of such a catastrophe this organism should be distinguished from the first common ancestor an additional refugium is ejection of rock to space by impacts and thier return to a habitable planet

brittle failure of ice ice exhibits either ductile or brittle behavior depending upon the conditions under which it is loaded glaciers for instance are loaded by gravity under deviatoric stresses of 0 1 mpa or lower at temperatures of interest they flow through dislocation creep at strain rates of the order of 10 9 s 1 or lower patterson 1994 sheets of sea ice another terrestrially important ice feature are loaded predominantly by wind under global compressive stresses similar in magnitude to the shear stresses within glaciers richter menge and elder 1998 these bodies deform through a combination of creep and fracture the latter process manifested by oriented leads or open cracks and by compressive shear faults which often form as conjugate sets that traverse a large fraction of the arctic basin kwok 1999 schulson 2002 the cold icy crust of europa an extraterrestrial feature which may shield an ocean beneath within which a form of life may exist or may once have existed reynolds et al 1987 hoppa et al 1999 pappalardo et al 1999 greenberg et al 2000 kargel et al 2000 is loaded by the motion of diurnal tides and by non synchronous rotation greenberg and weidenschilling 1984 the crust deforms in a brittle manner as evident from the networks of cracks that lace through it greeley et al 2000 of the two kinds of ice deformation creep is probably the better known by readers of the geological and geophysical literature and is certainly the more fully explored and better understood the interested reader may wish to consult a number of excellent reviews of the subject e g see duval et al 1983 weertman 1983 durham and stern 2001 fracture in comparison has only recently been systematically examined the motivation with respect to terrestrial mechanics schulson 2001 comes largely

a model dye comparison experiment in the tidal mixing front zone on the southern flank of georges bank 1 a process oriented model dye comparison experiment was conducted to examine the ability of a numerical ocean model to simulate the observed movement of dye across the tidal mixing front on the southern flank of georges bank during 22 26 may 1999 the experiment was made using the unstructured grid finite volume coastal ocean model fvcom with varying horizontal resolution the results indicate that the observed cross isobath movement of the dye patch was primarily controlled by meso scale temporal and spatial variability of the water temperature and salinity fields onset of vertical stratification tended to slow down an upward stretching of the dye column and trapped the dye within the bottom mixed layer to reach a convergent numerical solution that reproduced the observed lateral turbulent dispersion of dye the fvcom grid required a horizontal resolution of 500 m in the dye study region within the tidal mixing front of georges bank the movement of the center of the dye patch was mainly driven by the ensemble velocity integrated over the dye volume with a first order contribution from vertical shear of the dye s horizontal velocity

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

impact excavation and the search for subsurface life on mars because of the ubiquity of subsurface microbial life on earth examination of the subsurface of mars could provide an answer to the question of whether microorganisms exist or ever existed on that planet impact craters provide a natural mechanism for accessing the deep substrate of mars and exploring its exobiological potential based on equations that relate impact crater diameters to excavation depth we estimate the observed crater diameters that are required to prospect to given depths in the martian subsurface and we relate these depths to observed microbiological phenomena in the terrestrial subsurface simple craters can be used to examine material to a depth of 270 m complex craters can be used to reach greater depths with craters of diameters 300 km required to reach depths of 6 km or greater which represent the limit of the terrestrial deep subsurface biosphere examination of the ejecta blankets of craters between 17 5 and 260 km in diameter would provide insights into whether there is an extant or whether there is evidence of an extinct deep subsurface microbiota between 500 and 5000 m prior to committing to large scale drilling efforts at depths 500 m some crater excavations are likely to be more important than others from an exobiological point of view we discuss examples of impacts into putative intracrater paleolacustrine sediments and regions associated with hydrothermal activity we compare these depths to the characteristics of subsurface life on earth and the fossil microbiological record in terrestrial impact craters

modelled stress distributions at the dome summit south borehole law dome east antarctica a comparison of anisotropic ice flow relations in this study we compare the anisotropic flow relations for polycrystalline ice of azuma and goto azuma 1996 thorsteinsson 2002 placidi and others 2010 and budd and others 2013 observations from the dome summit south dss ice coring site at law dome east antarctica are used to model the vertical distribution of deviatoric stress components at the borehole site the flow relations in which the anisotropic rheology is parameterized by a scalar function so that the strain rate and deviatoric stress tensor components are collinear provide simple shear and vertical compression deviatoric stress profiles that are most consistent with laboratory observations of tertiary creep in combined stress configurations those flow relations where 1 the anisotropy is derived from the magnitude of applied stresses resolved onto the basal planes of individual grains and 2 the macroscopic deformation is obtained via homogenization of individual grain responses provide stress estimates less consistent with laboratory observations this is most evident in combined simple shear and vertical compression flow regimes where shear is dominant our results highlight the difficulties associated with developing flow relations which incorporate a physically based description of microdeformation processes in particular this requires that all relevant microdeformation recrystallization and recovery processes are adequately parameterized

a modeling study of the episodic cross frontal water transport over the inner shelf of the south atlantic bight abstract physical processes that control the episodic cross frontal transport over the inner shelf of the south atlantic bight were examined using a 3d primitive turbulent closure equation model the model results showed that significant cross frontal water exchange occurred under upwelling favorable wind conditions through the detachment of isolated low salinity lenses at the outer edge of the front the formation of isolated lenses was a 3d feature associated with complex nonlinear processes it depended on 1 the amount of multiple river discharges 2 direction and magnitude of the wind and 3 tidal mixing as the total amount of river discharges increased stronger winds were required to form the isolated lenses when the river discharges were larger tidal mixing tended to delay the occurrence of isolated lenses through 1 increasing the cross shelf gradients of density and surface elevation and thus enhancing the along shelf current and reducing the along shelf variation of salinity and 2 streng

bacterial mats from crater lake oregon and their relationship to possible deep lake hydrothermal venting crater lake is located in a caldera on mt mazama a volcanic centre in the oregon cascades which has been active for more than 400 000 years1 the 594 m deep lake is a consequence of a climactic eruption which occurred 6 845 50 years ago however caldera volcanism took place as recently as 4 000 years ago1 it has been suggested that some of the physical and chemical features of the lake result from hydrothermal inputs2 7 here we present submersible observations of the bottom of crater lake which reveal communities of bacteria that are usually associated with anomalously warm saline waters the bacteria seem to derive energy from the oxidation of ferrous iron to fuel their metabolism we propose that the mats are indicators of diffuse hydrothermal venting into the deep lake

standardizing the nomenclature of martian impact crater ejecta morphologies the mars crater morphology consortium recommends the use of a standardized nomenclature system when discussing martian impact crater ejecta morphologies the system utilizes nongenetic descriptors to identify the various ejecta morphologies seen on mars this system is designed to facilitate communication and collaboration between researchers crater morphology databases will be archived through the u s geological survey in flagstaff where a comprehensive catalog of martian crater morphologic information will be maintained

low salinity plume detachment under non uniform summer wind off the changjiang estuary abstract in the past two physical mechanisms baroclinic instability bi and strong asymmetric tidal mixing satm during the spring tidal period were proposed for the offshore detachment of the low salinity plume over the inner shelf of the east china sea ecs these two mechanisms were re examined using both observations and a fully three dimensional 3 d high resolution unstructured grid free surface primitive equation finite volume community ocean model fvcom the observed currents and salinities showed that the plume was characterized by a two layer system in which the upper layer is mainly driven by the river discharge induced buoyancy flow and the lower layer is predominantly controlled by tidal mixing and rectification the satm mechanism was based on the model run without calibration against observed currents and salinity around the plume region so that it should be applied with caution to a realistic condition observed on the inner shelf of the ecs the bi mechanism was derived under a condition without consideration of tidal mixing although bi could still occur along the frontal zone when tides were included it was unable to produce a single large detached low salinity lens observed on the inner shelf of the ecs the process oriented model experiment results suggest that for a given river discharge and realistic tidal flow the spatially non uniform southwesterly surface wind during the southeast monsoon dominant summer could increase frontal spatial variability and thus produce a significant offshore detachment of low salinity water on the inner shelf of east china sea

current separation and upwelling over the southeast shelf of vietnam in the south china sea 1 the high resolution unstructured grid finite volume community ocean model fvcom was used to examine the physical mechanisms that cause current separation and upwelling over the southeast shelf of vietnam in the south china sea scs process oriented experiments suggest that the southwesterly monsoon wind is a key physical mechanism for upwelling in that area but not a prerequisite to cause current separation with no wind forcing current separation in summer can occur as a result of the encounter of a southward along shelf coastal current from the north and northeastward buoyancy driven and stratified tidal rectified currents from the southwest the southward current can be traced upstream to the hong river in the gulf of tonkin this current is dominated by semigeostrophic dynamics and is mostly confined to the narrow shelf along the northern vietnamese coast the northeastward currents are generated by tidal rectification and are intensified by the mekong river discharge and southwesterly monsoon wind forcing the dynamics controlling this current are fully nonlinear with significant contributions from advection and vertical turbulent mixing upwelling in the current separation zone can be produced by a spatially uniform constant wind field and can be explained using simple wind induced ekman transport theory this finding differs from previous theory in which the regional dipole wind stress curl is claimed as a key mechanism for current separation and upwelling in this coastal region our scs fvcom driven by the wind stress river discharge and tides is capable of reproducing the location and tongue like offshore distribution of temperature as those seen in satellite derived sea surface temperature imagery

copernicus crater central peak lunar mountain of unique composition olivine is identified as the major mafic mineral in a central peak of copernicus crater information on the mineral assemblages of such unsampled lunar surface material is provided by near infrared reflectance spectra 0 7 to 2 5 micrometers obtained with earth based telescopes the composition of the deep seated material comprising the copernicus central peak is unique among measured areas other lunar terra areas and the wall of copernicus exhibit spectral characteristics of mineral assemblages comparable to the feldspathic breccias returned by the apollo missions with low calcium orthopyroxene being the major mafic mineral

the scaling of complex craters the empirical relation between the transient crater diameter dg and final crater diameter dr of complex craters and basins is estimated using cumulative terrace widths central uplift diameters continuous ejecta radii and transient crater reconstructions determined from lunar and terrestrial impact structures the ratio dg dr is a power law function of dr decreasing uniformly from unity at the diameter of the simple complex crater morphology transition to about 0 5 for large multiring basins like imbrium on the moon the empirical constants in the dg dr relation are interpreted physically to mean that the position of the final rim relative to the transient crater and hence the extent of collapse is controlled or greatly influenced by the properties of the zone of dissociated material produced by the impact shock the continuity of the dg dr relation over the entire spectrum of morphologic types from complex craters to multiring basins implies that the rims of all these structures form in the same tectonic environment despite morphologic differences

an estimate of the cross frontal transport at the shelf break of the east china sea with the finite volume coastal ocean model 1 the finite volume coastal ocean model fvcom is used to estimate the onshore cross frontal transport at the shelf break of the east china sea boundary conditions of fvcom are provided by the princeton ocean model simulating ocean currents in the yellow sea and east china sea realistically one advantage of this study is that the unstructured triangular cell grid of fvcom resolves complex bottom topography that may trigger kuroshio frontal waves it is anticipated that these nonlinear frontal waves enhance the exchange of seawater between the kuroshio and shelf regions kuroshio frontal waves in the model are excited around the location where the bottom slope changes abruptly and have the phase speed and amplitude consistent with those observed in the east china sea in addition the model reproduces the onshore transport associated with growing frontal waves in the upper and lower layers on the basis of passive tracer experiments the annually averaged onshore transport integrated along the shelf break is estimated to be 0 85 106 m3 s

possible ancient oceans on mars evidence from mars orbiter laser altimeter data high resolution altimetric data define the detailed topography of the northern lowlands of mars and a range of data is consistent with the hypothesis that a lowland encircling geologic contact represents the ancient shoreline of a large standing body of water present in middle mars history the contact altitude is close to an equipotential line the topography is smoother at all scales below the contact than above it the volume enclosed by this contact is within the range of estimates of available water on mars and a series of extensive terraces parallel the contact in many places

tidal modulation on the changjiang river plume in summer 1 tide effects on the structure of the near field changjiang river plume and on the extension of the far field plume have often been neglected in analysis and numerical simulations which is the focus of this study numerical experiments highlighted the crucial role of the tidal forcing in modulating the changjiang river plume without the tidal forcing the plume results in an unrealistic upstream extension along the jiangsu coast with the tidal forcing the vertical mixing increases resulting in a strong horizontal salinity gradient at the northern side of the changjiang river mouth along the jiangsu coast which acts as a dynamic barrier and restricts the northward migration of the plume furthermore the tidal forcing produces a bidirectional plume structure in the near field and the plume separation is located at the head of the submarine canyon a significant bulge occurs around the head of the submarine canyon and rotates anticyclonically which carries a large portion of the diluted water toward the northeast and merges into the far field plume a portion of the diluted water moves toward the southeast which is mainly caused by tidal rectification this bidirectional plume structure is more evident under certain wind conditions during the neap tide with the reduced tidal energy the near field plume extends farther offshore and the bulge becomes less evident these dynamic behaviors are maintained and are fundamentally important in the region around the river mouth even under the summer monsoon and the shelf currents although in the far field the wind forcing and shelf currents eventually dominate the plume extension

a habitat for psychrophiles in deep antarctic ice microbes some of which may be viable have been found in ice cores drilled at vostok station at depths down to approximately 3 600 m close to the surface of the huge subglacial lake vostok two types of ice have been found the upper 3 500 m comprises glacial ice containing traces of nutrients of aeolian origin including sulfuric acid nitric acid methanosulfonic acid msa formic acid sea salts and mineral grains ice below approximately 3 500 m comprises refrozen water from lake vostok accreted to the bottom of the glacial ice nutrients in the accretion ice include salts and dissolved organic carbon there is great interest in searching for living microbes and especially for new species in deepest antarctic ice i propose a habitat consisting of interconnected liquid veins along three grain boundaries in ice in which psychrophilic bacteria can move and obtain energy and carbon from ions in solution in the accretion ice with an age of a few 10 4 years and a temperature a few degrees below freezing the carbon and energy sources in the veins can maintain significant numbers of cells per cubic centimeter that are metabolizing but not multiplying in the 4 x 10 5 year old colder glacial ice at least 1 cell per cm 3 in acid veins can be maintained with fluorescence microscopy tuned to detect nadh in live organisms motile bacteria could be detected by direct scanning of the veins in ice samples

variations in the onset diameter for martian layered ejecta morphologies and their implications for subsurface volatile reservoirs we investigated regional variations in the onset diameter of craters displaying a single layer ejecta morphology within 30 latitude using viking imagery our results generally agree with those of previous studies which show onset diameters of 5 to 6 km in the equatorial region but we have identified localized regions with unusually small onset diameters the largest region is located in solis and thaumasia planae the 3 5 km onset diameter range in this area indicates a near surface ice rich reservoir depth 110 m this unusual concentration of near surface ice may have resulted from magmatic driven uplifts associated with the tharsis rise which modified parts of a regional aquifer drainage basin system and resulted in the transfer and concentration of subsurface volatiles in this region

saltwater intrusion into the changjiang river a model guided mechanism study 1 the changjiang river cr is divided into a southern branch sb and a northern branche nb by chongming island as the river enters the east china sea observations reveal that during the dry season the saltwater in the inner shelf of the east china sea flows into the cr through the nb and forms an isolated mass of saltwater in the upstream area of the sb the physical mechanism causing this saltwater intrusion has been studied using the high resolution unstructured grid finite volume coastal ocean model fvcom the results suggest that the intrusion is caused by a complex nonlinear interaction process in relation to the freshwater flux upstream tidal currents mixing wind and the salt distribution in the inner shelf of the east china sea the tidal rectification resulting from the interaction of the convergence or divergence of tidal momentum flux and bottom friction over abrupt topography produces a net upstreamward volume flux from nb to sb with river discharge the net water transport in the nb is driven through a momentum balance of surface elevation gradient forcing horizontal advection and vertical diffusion in the dry season reducing the surface elevation gradient forcing makes tidal rectification a key process favorable for the saltwater intrusion a northerly wind tends to enhance the saltwater intrusion by reducing the seaward surface elevation gradient forcing rather than either the baroclinic pressure gradient forcing or the wind driven ekman transport a convergence experiment suggests that high grid resolution 100 m or less is required to correctly resolve the net water transport through the nb particularly in the narrow channel on the northern coast of chongming island

structure and eastward extension of the changjiang river plume in the east china sea 1 the hydrographic structure and offshore extension of freshwater plume discharged from the changjiang also known as the yangtze river in the northern east china sea were investigated by analyzing conductivity temperature depth ctd data and drifter trajectories collected during the summers of 1997 and 1998 from june to early september when southerly winds prevail the plume tends to move northeast in the chinese coastal area and then separates from the coastal zone to travel eastward over 400 km offshore across the western shelf of the northern east china sea during other seasons when northerly winds prevail the plume is confined to the chinese coast in the summer the plume in the midshelf confined to a thin surface layer 10 to 15 m thick extends eastward in the form of patches of low salinity water rather than spreading as a tongue shaped pattern from the changjiang mouth the eastward movement of patches in the western shelf is primarily due to upwelling favorable southerly winds upon reaching the vicinity of cheju do an island in the middle of northern east china sea the patches are advected to the korea tsushima strait by either the cheju warm current or a northward flowing mean current of the kuroshio branch current and then finally flow into the east japan sea

the effects of sulfuric acid on the mechanical properties of ice single crystals ice single crystals of various orientations containing various concentrations of h 2 so 4 up to 11 5 ppm were cut from large pucks of laboratory grown ice constant strain rate compression tests were performed on the doped ice crystals both at 20 c at an axial strain rate of 1 10 5 s 1 and at 10 c at 1 10 6 s 1 the stress strain curves showed a linearly rising stress with increasing strain followed by a sharply declining stress after reaching a peak with further strain the sharp decline in stress slowed the tests clearly showed for the first time that this naturally occurring impurity dramatically decreases both the peak stress and the subsequent flow stress of ice single crystals the decrease in the peak strength was related to the square root of the concentration of h 2 so 4 up to 11 5 ppm suggesting that the solubility limit of h 2 so 4 in ice is at least 11 5 ppm the sulfuric acid also appeared to increase the ductility of the ice preliminary examination of a doped ice single crystal by synchrotron x ray topography suggested that sulfuric acid dramatically increases the grown in dislocation density

separation of the kuroshio water and its penetration onto the continental shelf west of kyushu the separation of kuroshio water west of kyushu and its penetration onto the continental shelf of the east china sea were investigated by analyzing trajectories of satellite tracked surface drifters deployed during 1989 1996 conductivity temperature and depth ctd data collected in the eastern east china sea in december 1993 and late april early may 1995 were also analyzed composite trajectories of 172 drogued drifters provided direct evidence of the separation of the northeastward flowing kuroshio into two parts at the western mouth of the deep trough southwest of kyushu the kuroshio main stream turns to the east toward the tokara strait and a northward flowing branch current penetrates onto the shelf across the continental slope west of the trough analysis of the ctd data and drifter trajectories concurrently observed shows that the branch current was part of the inshore kuroshio just upstream before its separation during the periods of ctd observations the separated inshore kuroshio water intruded northward in a tongue shape along the shelf break of the trough and penetrated onto the shelf after crossing obliquely the western continental slope of the trough the water that penetrated onto the shelf continued to flow northward toward the korea strait the main path of this water was easily traced by its high salinity which is characteristic of the inshore kuroshio water application of an inverse method to the observed ctd data also supports the separation and penetration of the kuroshio and calculates the volume transport of the northward branch to be about 4 0 106 m3 s for the two different surveys the tongue shaped intrusion of the inshore kuroshio water onto the outer shelf may take place in close association with the eastward turning of the kuroshio main stream and it might be caused by the vorticity adjustment created by the eastward turning of the kuroshio

geometric properties of martian impact craters preliminary results from the mars orbiter laser altimeter the mars orbiter laser altimeter mola acquired high spatial and vertical resolution topographic data for 18 tracks across the northern hemisphere of mars during the fall of 1997 it sampled 98 minimally degraded impact craters between the latitudes of 80 n and 12 s the best fitting depth d versus diameter d power law relationship for these craters is d 0 14 d0 90 for simple varieties and d 0 25 d0 49 for complex structures the simple to complex transition diameter is 8 km 0 5 km the cross sectional shape of the crater cavities was determined by fitting a power function to each profile variation in the exponent n suggest the craters flatten with increasing diameter and impact energy the ejecta thickness is skewed suggesting that use of existing empirical expressions for the expected radial decay of ejecta thickness is inappropriate for mars in most cases

effects of tides on freshwater and volume transports in the changjiang river plume 1 effects of tides on the changjiang river plume are investigated using a numerical model of the east china and yellow seas in the absence of tides the buoyancy driven coastal current downstream of the river mouth is a surface trapped plume attached to the coast in the presence of tides however the plume shifts away from the coast and features a bottom boundary layer the freshwater transport by the coastal current accounts for only 35 of the changjiang river discharge without tides but increases to 80 with tides tidal currents stabilize the plume bulge near the river mouth and force the plume water to move in the direction of tidal currents thus increasing the downstream freshwater transport in contrast tidal residual currents are weak and make little contributions to the total freshwater transport tidal mixing reduces the plume s buoyancy but increases its thickness so that the freshwater transport is insensitive to the strength of turbulent mixing volume transport in the tidal affected buoyancy coastal current exceeds the river discharge by 4 to 12 times as opposed to 2 3 fold amplification in the plume without tides tidal mixing between the plume and ambient shelf waters produces higher salinity classes in the plume so that the volume flux in the downstream coastal current increases to discharge the freshwater released from the changjiang river

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve

north polar region craterforms on mars geometric characteristics from the mars orbiter laser altimeter abstract this study focuses on topographic characterization of ice associated north polar region impact craters and several enigmatic polar craterforms using new information from the mars orbiter laser altimeter mola an instrument aboard the mars global surveyor mgs orbiter we find that for ice associated craters the topography reveals several surprising results not previously apparent from orbital images alone first geometric properties for several impact craters associated with ice and frost deposits suggest that cavity infill is as high as 80 of reconstructed preerosion levels second craters associated with ice also demonstrate unique cavity geometries relative to their nonpolar counterparts finally in some cases ice associated impact features are anomalously deep on the basis of depths modeled from the best available scaling laws we suggest that burial of these impact features by either episodic advance of the polar cap margin or by continuous deposition at the highest rates previously estimated for the north polar region of mars has occurred subsequent stripping has exhumed the features leaving behind cavity infill deposits and a few of these display topographic levels above the surrounding preimpact surface in at least one case cavity interior deposits show layering with a typical thickness of 10 m suggesting episodic deposition and ablation of materials as in the polar layered terrain in addition to ice associated craters we investigated the topography of several enigmatic polar craterforms in particular a few craterforms within 150 km of the permanent north polar cap appear to resemble simple effusive lava shield volcanoes found on earth their geometric properties cannot be reconciled with previous suggestions that they were manifestations of martian hydromagmatic processes i e maar volcanism mola s initial measurements of impact craters and other craterforms in the north polar latitudes of mars support the concept of a geologically recent surface with evidence of effusive volcanism and enhanced sedimentation in addition the measured impact crater depths for ice associated craters suggest at least a few cases of enhanced excavation and thus a possibly weaker target relative to the typical northern hemisphere plains

layered ejecta craters and the early water ice aquifer on mars a model for emplacement of deposits of impact craters is presented that explains the size range of martian layered ejecta craters between 5 km and 60 km in diameter in the low and middle latitudes the impact model provides estimates of the water content of crater deposits relative to volatile content in the aquifer of mars these estimates together with the amount of water required to initiate fluid flow in terrestrial debris flows provide an estimate of 21 by volume 7 6 x 10 7 km 3 of water ice that was stored between 0 27 and 2 5 km depth in the crust of mars during hesperian and amazonian time this would have been sufficient to supply the water for an ocean in the northern lowlands of mars the existence of fluidized craters smaller than 5 km diameter in some places on mars suggests that volatiles were present locally at depths less than 0 27 km deposits of martian craters may be ideal sites for searches for fossils of early organisms that may have existed in the water table if life originated on mars

the alteration of lateral circulation under the influence of human activities in a multiple channel system changjiang estuary abstract extensive coastal engineering activities including channel dredging and constructions of large infrastructure have greatly altered hydrodynamics in the changjiang estuary while the changes in longitudinal circulation have been well documented limited studies have focused on the alteration in lateral circulation and its impact on estuarine circulation in the changjiang estuary lateral circulation in an estuary plays an important role in modulating estuarine circulation sediment transport and morphological change different from many of previous numerical studies we utilize an unstructured grid numerical model configured in a way to allow inundation over dikes and tidal flats numerical model experiments show significant changes in lateral circulation and stratification along the north passage in response to the altered geometry and bathymetry due to the channel deepening and the dike construction both the channel deepening and the dike construction led to an enhanced stratification further analysis suggests that the along channel the lateral and the vertical including up and downwelling and vertical mixing effects are all important in modulating the intra tidal stratification destratification process the channel deepening enhances both the lateral and the vertical effects around the high water slack the construction of dikes that completely blocks the lateral water exchange between the north passage and surrounding tidal flats changes the system from a multiple channel system into a single channel system with dike construction the estuarine circulation tends to have a horizontally sheared pattern with weaker friction and a stronger stratification

insights into complex layered ejecta emplacement and subsurface stratigraphy in chryse planitia mars through an analysis of themis brightness temperature data layered ejecta craters on mars have been interpreted to indicate the presence of volatiles in the substrate making them important targets for the investigation of sites of astrobiological significance if the ejecta are associated with the presence of water in the substratum specific surface grain size trends are expected in this study we explore the distribution of grain sizes in the layered ejecta of impact craters located in chryse planitia using thermal emission imaging system themis thermal infrared data ejecta grain size trends in conjunction with ejecta mobility and lobateness values are applied to assess the degree of surface flow of the ejecta and in turn to constrain the plausible volatile abundance cohesion and fine particle content of the target materials craters with a larger fraction of small grain sizes in their ejecta showed greater ejecta mobility and lobateness consistent with a water rich and or a low cohesion target craters displaying decreasing grain size with increasing radius had smaller diameters and lower ejecta mobility and lobateness indicating only a minimal component of surface ejecta flow ejecta grain size trends varied with crater diameter from which the presence of vertical compositional stratigraphy in chryse planitia is inferred and interpreted our observations are synthesized into a number of plausible geologic scenarios for chryse planitia

martian impact craters correlations of ejecta and interior morphologies with diameter latitude and terrain abstract the premise of this study is that global analysis of crater morphologies can discriminate between the effects of impact energy atmosphere and subsurface volatiles based on the correlation between morphology and latitude diameter and terrain this study focuses on seven ejecta and nine interior morphologies associated with 3819 craters 8 km in diameter distributed across the entire martian surface this data set is sufficiently large to provide statistically viable results on a global scale the results of the analyses indicate that changes in ejecta and interior morphology correlate with increases in crater diameter excavation depths corresponding to these diameters are calculated from depth diameter relationships and are compared to the theoretical distribution of subsurface volatiles the different ejecta morphologies can be described by impact into material with varying proportions of volatiles and the latidudinal variations seen for rampart crater morphologies correlate well with the proposed latitude depth relationship for ice and brines across the planet many of the interior structres show distributions indicative of terrain dependent influences for example the concentrations of central pit craters around ancient impact basins and on alba patera suggest that volatiles preferentially collect in these areas however central peak and peak ring interior morphologies show little relationship to planetary properties and probably result from changes in impact energy thus many of the unique morphologies associated with martian impact craters result from the presence of subsurface volatiles

sources of nutrients and energy for a deep biosphere on mars hydrothermal vents appear to be the tip of the subsurface biosphere in the ocean crust the primary prducers in this biosphere are prokaryotes that tolerate a wide variety of physical and chemical conditions and are versatile in their use of inorganic compounds to drive metabolism a synthesis of chemical and mineralogical data from martian meteorites and measurements of the martian surface suggest that conditions similar to those that make life possible in earth s oceanic crust namely water carbon nutrients appropriate temperatures and gradients in redox conditions also occur within mars chemolithoautotrophic microorganisms capable of living below the seafloor on earth would probably survive in some regions of the martian subsurface

physical mechanisms for the offshore detachment of the changjiang diluted water in the east china sea 1 physical mechanisms for the summertime offshore detachment of the changjiang diluted water cdw into the east china sea are examined using the high resolution unstructured grid finite volume coastal ocean model fvcom the model results suggest that isolated low salinity water lens detected west of cheju island can be formed by 1 a large scale adjustment of the flow field to the changjiang discharge and 2 the detachment of anticyclonic eddies as a result of baroclinic instability of the cdw front adding the changjiang discharge intensifies the clockwise vorticity of the subsurface current originating from the taiwan warm current flowing along the 50 m isobath and thus drives the low salinity water in the northern coastal area of the changjiang mouth offshore over a submerged plateau that extends toward cheju island given a model horizontal resolution of less than 1 0 km the cdw front becomes baroclinically unstable and forms a chain of anticyclonic and cyclonic eddies the offshore detachment of anticyclonic eddies can carry the cdw offshore this process is enhanced under northward winds as a result of the spatially nonuniform interaction of wind induced ekman flow and eddy generated frontal density currents characteristics of the model predicted eddy field are consistent with previous theoretical studies of baroclinic instability of buoyancy driven coastal density currents and existing satellite imagery the plume stability is controlled by the horizontal ekman number in the changjiang this number is much smaller than the criterion suggested by a theoretical analysis

the pretoria saltpan a 200 000 year southern african lacustrine sequence abstract the pretoria saltpan is a circular crater 1130 m in diameter and is situated some 40 km n of pretoria lat 25 34 30 long 28 04 59 e a recent tube sampling and core drilling programme has revealed an infilling consisting of some 90 m of fine lacustrine sediments chiefly organic muds underlain below 30 m depth by micrites which rest upon a further 61 m of coarse clastic debris granite bedrock was encountered at 151 m broad sedimentary zones correspond with major phases in the evolution of the crater lake superimposed cyclical patterns of accumulation reflect environmental changes on millenial to seasonal timescales 14c age determinations on algal debris from the upper 20 m of the core indicate a mean rate of sedimentation of about 1 m 2000 yr suggesting that the lacustrine sequence may span almost 200 000 yr over this period major environmental changes are apparent from sedimentological chemical mineralogical and isotopic analyses of the core and studies of the pollen spectra and diatom assemblages present within it this long continental sequence is therefore providing a high resolution palaeoenvironmental record for southern mid latitudes over much the same period as is covered by the vostok ice core in antarctica

physical processes controlling the formation evolution and perturbation of the low salinity front in the inner shelf off the southeastern united states a modeling study physical processes that control the formation evolution and perturbation of the low salinity front over the inner shelf of the south atlantic bight have been examined using a fully three dimensional primitive equation and turbulent closure model the model was forced by semidiurnal tides m2 s2 and n2 climatological means of multiple river discharges and upwelling favorable wind this model has provided a reasonable simulation of the fortnightly and monthly variations of semidiurnal tides computed amplitudes and phases of tides show good agreement with observational data available at tidal gauge stations along the coast spatial structures of buoyancy currents are significantly modified by stratified tidal rectification as a result the southward residual current intensifies significantly at the front and reduces or reverses close to the coast a weak velocity area forms in the downstream region of each river which blocks the low salinity water to form multiple tongue like domes in the inner shelf for a given springtime climatological upwelling favorable wind isolated low salinity lenses can form episodically in two steps at first a geometrically controlling wave like frontal shape develops at the outer edge of the frontal zone as a result of the interaction between tides multiple river discharges and upwelling favorable wind then isolated low salinity lenses form at the crest when water on the shoreward side of the crest is displaced by relatively high salinity water advected from the upstream trough south of the crest and diffused upward from the deeper region wind induced upwelling is noticeable to compensate for the water loss due to the near surface offshore ekman transport but it does not play a critical role in the formation of isolated lenses under the climatological conditions of river discharges and upwelling favorable winds over the inner shelf of the south atlantic bight

offshore detachment process of the low salinity water around changjiang bank in the east china sea abstract a patchlike structure of low salinity water detached from the chanjiang diluted water cdw is frequently observed in the east china sea ecs in this study the offshore detachment process of cdw into the ecs is examined using a three dimensional numerical model the model results show that low salinity water is detached from the cdw plume by the intense tide induced vertical mixing during the spring tide period when the tidal current becomes stronger during the spring tide thickness of the bottom mixed layer in the sloping bottom around changjiang bank reaches the mean water depth implying that the stratification is completely destroyed in the entire water column as a result the offshore detachment of cdw occurs in the sloping side of the bank where the tidal energy dissipation is strong enough to overcome the buoyancy effect during this period on the other hand the surface stratification is retrieved during the neap tide period because the tidal current becomes substantially weaker

a numerical study on the changjiang diluted water in the yellow and east china seas 1 a numerical simulation is performed using the princeton ocean model pom to investigate the behavior of the changjiang diluted water cdw and to evaluate the freshwater budget in the yellow and east china seas in addition the major process controlling the behavior of the cdw is discussed the simulated cdw distributions are fairly consistent with the observed distributions showing a remarkable seasonal variation the cdw extends to the northeast toward the tsushima korea straits during summer while it hugs the chinese coast to the southwest within a narrow band in winter tracer experiment is carried out to track the freshwater originating only from the changjiang and to evaluate the freshwater budget in the yellow and east china seas the result shows that about 68 percent of the changjiang discharge is transported through the tsushima korea straits and that about 27 percent is transported through the taiwan strait in autumn and winter to investigate the main process controlling the behavior of the cdw mentioned above another experiment is carried out without wind forcing it is found that the eastward extension of the cdw is strongly constrained by the taiwan tsushima warm current system over the shelf regime the wind is however responsible for the northeastward extension of the cdw in summer in addition the southwestward extension at the taiwan strait during winter is done by strong northeasterly monsoon the experiment without wind forcing shows that freshwater transport through the tsushima korea straits increases to 90 percent of the total changjiang discharge