a numerical study of the mediterranean sea circulation abstract a primitive equation ocean model that makes use of a curvilinear orthogonal grid and a sigma coordinate system was used to simulate the mediterranean sea the model was forced with monthly climatological values of wind stress heat and salinity flux with the help of the curvilinear horizontal grid the larger scales of the entire mediterranean sea are modeled and the topography around the narrow and shallow straits of gibraltar is also reasonably well represented the resulting model inflow and outflow seems to mimic the real mediterranean often in considerable detail levantine intermediate water is formed in the levantine basin and exits through the strait of sicily and the strait of gibraltar deep water formation processes are clearly represented by the model the model results indicate that in the western mediterranean the wind stress is very important in establishing the summer northward shift of the atlantic inflow lateral boundary runoff surface salinity and heat fluxes are necessar

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

the martian subsurface as a potential window into the origin of life few traces of earth s geologic record are preserved from the time of life s emergence over 3 800 million years ago consequently what little we understand about abiogenesis the origin of life on earth is based primarily on laboratory experiments and theory the best geological lens for understanding early earth might actually come from mars a planet with a crust that s overall far more ancient than our own on earth surface sedimentary environments are thought to best preserve evidence of ancient life but this is mostly because our planet has been dominated by high photosynthetic biomass production at the surface for the last 2 500 million years or more by the time oxygenic photosynthesis evolved on earth mars had been a hyperarid frozen desert with a surface bombarded by high energy solar and cosmic radiation for more than a billion years and as a result photosynthetic surface life may never have occurred on mars therefore one must question whether searching for evidence of life in martian surface sediments is the best strategy this perspective explores the possibility that the abundant hydrothermal environments on mars might provide more valuable insights into life s origins ancient hydrothermal deposits formed in the martian subsurface may be the best targets for finding evidence for ancient life on mars and clues about the origin of life on earth

deep crustal carbonate rocks exposed by meteor impact on mars mars may have once had a co2 rich atmosphere but carbonate rocks that could provide evidence for such conditions are sparse spectral analyses of rocks exposed from deep within an impact crater reveal that carbonate deposits may be extensive on mars but are buried under layers of younger volcanic rocks

comparison of warm and wet and cold and icy scenarios for early mars in a 3 d climate model we use a 3 d general circulation model to compare the primitive martian hydrological cycle in warm and wet and cold and icy scenarios in the warm and wet scenario an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice free northern ocean precipitation shows strong surface variations with high rates around hellas basin and west of tharsis but low rates around margaritifer sinus where the observed valley network drainage density is nonetheless high in the cold and icy scenario snow migration is a function of both obliquity and surface pressure and limited episodic melting is possible through combinations of seasonal volcanic and impact forcing at surface pressures above those required to avoid atmospheric collapse 0 5 bar and moderate to high obliquity snow is transported to the equatorial highland regions where the concentration of valley networks is highest snow accumulation in the aeolis quadrangle is high indicating an ice free northern ocean is not required to supply water to gale crater at lower surface pressures and obliquities both h2o and co2 are trapped as ice at the poles and the equatorial regions become extremely dry the valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41 8 obliquity but uncorrelated with precipitation produced by the warm and wet simulation because our simulations make specific predictions for precipitation patterns under different climate scenarios they motivate future targeted geological studies

timing of water plume eruptions on enceladus explained by interior viscosity structure water plume eruptions on saturn s icy moon enceladus are delayed relative to the peak tidal stresses simulations suggest the delay can be explained by the moon s interior structure and the presence of a subsurface ocean at the south pole of saturn s icy moon enceladus eruptions of water vapour and ice emanate from warm tectonic ridges1 2 3 4 observations in the infrared5 and visible6 spectra have shown an orbital modulation of the plume brightness which suggests that the eruption activity is influenced by tidal forces however the observed activity seems to be delayed by several hours with respect to predictions based on simple tidal models6 7 here we simulate the viscoelastic tidal response of enceladus with a full three dimensional numerical model8 9 and show that the delay in eruption activity may be a natural consequence of the viscosity structure in the south polar region and the size of the putative subsurface ocean by systematically comparing simulations of variations in normal stress along faults with plume brightness data we show that the observed activity is reproduced for two classes of interior models with contrasting thermal histories a low viscosity convective region above a polar sea extending about 45 60 from the south pole at a depth below the surface as small as 30 km or a convecting ice shell of 60 70 km in thickness above a global ocean our analysis further shows that the eruption activity is controlled by the average normal stress applied across the cracks thus providing a constraint on the eruption mechanism

inversion of reflection seismograms by differential semblance analysis algorithm structure and synthetic examples1 seismograms predicted from acoustic or elastic earth models depend very non linearly on the long wavelength components of velocity this sensitive dependence demands the use of special variational principles in waveform based inversion algorithms the differential semblance variational principle is well suited to velocity inversion by gradient methods since its objective function is smooth and convex over a large range of velocity models an extension of the adjoint state technique yields an accurate estimate of the differential semblance gradient non linear conjugate gradient iteration is quite successful in locating the global differential semblance minimum which is near the ordinary least squares global minimum when coherent data noise is small several examples based on the 2d primaries only acoustic model illustrate features of the method and its performance

variational assimilation of ocean tomographic data twin experiments in a quasi geostrophic model the possibility of using tomography data as a constraint in variational data assimilation is explored by performing twin experiments realistic travel time data are generated in a quasi geostrophic model applied to the western mediterranean sea after checking the robustness of the method with this dataset a sensitivity study analyses the propagation of information by the model and tests the effect of different parameters such as the starting point of the optimization or the length of the assimilation period it appears that the variational method is well adapted to the nature of tomographic data that provide at the same time high time resolution and space integrals the results clearly show the ability of this dataset to recover the temporal evolution of heat content in each layer and improve various components of the circulation described by the model tomography must then be considered as an important source of information that may contribute with altimetry or local in situ measurement to the description of the ocean state and its evolution copyright 2002 royal meteorological society

evidence of ancient life at 207 m depth in a granitic aquife the results of electron microscopy investigations of calcite precipitated in a water conducting fracture in a ca 1800 ma granitic rock from 207 m below sea level at the island of aspo on the southeastern baltic coast of sweden are compared with measurements of carbon oxygen and sulfur isotope composition of the calcite and embedded pyrite parts of the calcite had extremely low 13c values indicative of biological activity and contained bacteria like microfossils occurring in colonies and as typical biofilms x ray microanalysis demonstrated these fossils to be enriched in carbon our results provide evidence for ancient life in deep granitic rock aquifers and suggest that the modern microbial life found there is intrinsic modeling historical and present geochemical processes in deep granitic aquifers should therefore preferably include biologically catalyzed reactions the results also suggest that the search for life on other planets e g mars should include subsurface material

u rich archaean sea floor sediments from greenland indications of 3700 ma oxygenic photosynthesis abstract 3700 ma metamorphosed pelagic shale from west greenland contains up to 0 4 wt reduced carbon with 13c values down to 25 6 pdb peedee belemnite the isotopic signature and mode of occurrence suggest that the carbon derived from planktonic organisms the pb isotopic composition shows that the shale had high primary u th this indicates that organic debris produced a local reducing environment which precipitated u transported to the site of sedimentation by oxidized ocean water the existence of highly productive plankton that fractionated c isotopes strongly and set up oxidation contrast in the environment suggests that oxygenic photosynthesis evolved before 3700 ma

migration velocity analysis from locally coherent events in 2 d laterally heterogeneous media part i theoretical aspects we present a new method based on migration velocity analysis mva to estimate 2 d velocity models from seismic reflection data with no assumption on reflector geometry or the background velocity field classical approaches using picking on common image gathers cigs must consider continuous events over the whole panel this interpretive step may be difficult particularly for applications on real data sets we propose to overcome the limiting factor by considering locally coherent events a locally coherent event can be defined whenever the imaged reflectivity locally shows lateral coherency at some location in the image cube in the prestack depth migrated volume obtained for an a priori velocity model locally coherent events are picked automatically without interpretation and are characterized by their positions and slopes tangent to the event even a single locally coherent event has information on the unknown velocity model carried by the value of the slope measured in the cig the velocity is e

active formation of chaos terrain over shallow subsurface water on europa the galileo spacecraft revealed a number of chaos regions on jupiter s moon europa where the surface terrain appears to have been disrupted from below in many places the surface contains sharp edged blocks or rafts of ice that have at some point been flipped or rotated some characteristics of these regions have been hard to explain such as the fact that the archetypal conamara chaos stands above its surroundings and contains matrix domes schmidt et al apply lessons learned from analogous processes within earth s subglacial volcanoes and ice shelves to an analysis of archival data that suggests chaos terrain forms above liquid water lenses that are perched only 3 kilometres deep within the ice shell the data suggest that ice water interactions and freeze out give rise to the varied morphology of chaos terrains implying that more water is involved than has been previously appreciated for instance the sunken topography of thera macula a large chaos area may indicate that europa is actively resurfacing over a lens comparable in volume to north america s great lakes europa the innermost icy satellite of jupiter has a tortured young surface1 2 3 4 and sustains a liquid water ocean1 2 3 4 5 6 below an ice shell of highly debated thickness1 2 3 4 5 7 8 9 10 quasi circular areas of ice disruption called chaos terrains are unique to europa and both their formation and the ice shell thickness depend on europa s thermal state1 2 3 4 5 7 8 9 10 11 12 13 14 15 16 17 no model so far has been able to explain why features such as conamara chaos stand above surrounding terrain and contain matrix domes10 18 melt through of a thin few kilometre shell3 7 8 is thermodynamically improbable and cannot raise the ice10 18 the buoyancy of material rising as either plumes of warm pure ice called diapirs1 9 10 11 12 13 14 15 or convective cells16 17 in a thick 10 kilometres shell is insufficient to produce the observed chaos heights and no single plume can create matrix domes10 18 here we report an analysis of archival data from europa guided by processes observed within earth s subglacial volcanoes and ice shelves the data suggest that chaos terrains form above liquid water lenses perched within the ice shell as shallow as 3 kilometres our results suggest that ice water interactions and freeze out give rise to the diverse morphologies and topography of chaos terrains the sunken topography of thera macula indicates that europa is actively resurfacing over a lens comparable in volume to the great lakes in north america

finding the steady state of a general circulation model through data assimilation application to the north atlantic ocean an attempt is made to find a steady state of a general circulation model consistent with error estimates of the north atlantic hydrography during 1981 1985 and with wind and thermodynamic boundary conditions the quadratic misfit of the model state from the data is minimized using the general circulation model together with its adjoint a state which is steady within limits of estimated observational error is found but no such state is simultaneously consistent with the observed hydrographic and surface flux fields model dynamics are able to sharpen gradients which were overly smooth in the mapped data producing a meridional overturning cell with a maximum value of about 21 sv at equilibrium the model must produce its own water masses and has a strong tendency to go toward wintertime conditions the consequence is an estimated model surface temperature systematically lower than in the hydrography which comes from all seasons the western boundary current thermocline is also both colder and fresher than the mapped hydrography and the overall meridional heat transport is low about 0 6 1015 w the results suggest that the concept of a realistic steady state north atlantic circulation has reached the end of its utility that models with realistic property fluxes and divergences must have much higher resolution and that the open ocean boundary conditions must be formulated as control variables

overview of the spirit mars exploration rover mission to gusev crater landing site to backstay rock in the columbia hills spirit landed on the floor of gusev crater and conducted initial operations on soil covered rock strewn cratered plains underlain by olivine bearing basalts plains surface rocks are covered by wind blown dust and show evidence for surface enrichment of soluble species as vein and void filling materials and coatings the surface enrichment is the result of a minor amount of transport and deposition by aqueous processes layered granular deposits were discovered in the columbia hills with outcrops that tend to dip conformably with the topography the granular rocks are interpreted to be volcanic ash and or impact ejecta deposits that have been modified by aqueous fluids during and or after emplacement soils consist of basaltic deposits that are weakly cohesive relatively poorly sorted and covered by a veneer of wind blown dust the soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover mobilization of soluble species has occurred within at least two soil deposits examined the presence of monolayers of coarse sand on wind blown bedforms together with even spacing of granule sized surface clasts suggests that some of the soil surfaces encountered by spirit have not been modified by wind for some time on the other hand dust deposits on the surface and rover deck have changed during the course of the mission detection of dust devils monitoring of the dust opacity and lower boundary layer and coordinated experiments with orbiters provided new insights into atmosphere surface dynamics

widespread surface weathering on early mars a case for a warmer and wetter climate abstract early mars 3 ga underwent aqueous alteration as evidenced by fluvial lacustrine morphologies and the recent discovery of widespread hydrous clays despite compelling evidence for diverse and localized aqueous environments the possibility for sustained liquid water globally on the martian surface and over geological timescales is still highly debated instead a durably cold and dry mars scenario is often proposed by studying specific fe mg and al rich clay stratigraphies on mars by means of a planetary scale orbital investigation we present new evidence that mars experienced an early era 3 7 ga of widespread aqueous alteration consistent with surface weathering

3d angle decomposition for elastic reverse time migration abstractwe have developed three approaches for 3d angle decomposition using elastic reverse time migration the first approach uses time and space lag common image point gathers computed from elastic wavefields this method facilitates computing angle gathers at sparse and possibly irregularly distributed points in the image the second approach transforms extended time lag images to the angle domain using slant stacks along 4d surfaces instead of using slant stacks along 2d straight lines the third approach transforms space lag common image gathers to the angle domain the three proposed methods solve a system of equations that handles dipping reflectors and they yield angle gathers that are more accurate compared with those obtained via alternative existing methods we have developed our methods using 2d and 3d synthetic and field data examples and found that they provide accurate opening and azimuth angles and they can handle steeply dipping reflectors and converted wave modes

a decade of acoustic thermometry in the north pacific ocean 1 over the decade 1996 2006 acoustic sources located off central california 1996 1999 and north of kauai 1997 1999 2002 2006 transmitted to receivers distributed throughout the northeast and north central pacific the acoustic travel times are inherently spatially integrating which suppresses mesoscale variability and provides a precise measure of ray averaged temperature daily average travel times at 4 day intervals provide excellent temporal resolution of the large scale thermal field the interannual seasonal and shorter period variability is large with substantial changes sometimes occurring in only a few weeks linear trends estimated over the decade are small compared to the interannual variability and inconsistent from path to path with some acoustic paths warming slightly and others cooling slightly the measured travel times are compared with travel times derived from four independent estimates of the north pacific 1 climatology as represented by the world ocean atlas 2005 woa05 2 objective analysis of the upper ocean temperature field derived from satellite altimetry and in situ profiles 3 an analysis provided by the estimating the circulation and climate of the ocean project as implemented at the jet propulsion laboratory jpl ecco and 4 simulation results from a high resolution configuration of the parallel ocean program pop model the acoustic data show that woa05 is a better estimate of the time mean hydrography than either the jpl ecco or the pop estimates both of which proved incapable of reproducing the observed acoustic arrival patterns the comparisons of time series provide a stringent test of the large scale temperature variability in the models the differences are sometimes substantial indicating that acoustic thermometry data can provide significant additional constraints for numerical ocean models

migration velocity analysis using pre stack wave fields using both image and data domains to perform velocity inversion can help us resolve the long and short wavelength components of the velocity model usually in that order this translates to integrating migration velocity analysis into full waveform inversion the migration velocity analysis part of the inversion often requires computing extended images which is expensive when using conventional methods as a result we use pre stack wavefield the double square root formulation extrapolation which includes the extended information subsurface offsets naturally to make the process far more efficient and stable the combination of the forward and adjoint pre stack wavefields provides us with update options that can be easily conditioned to improve convergence we specifically use a modified differential semblance operator to split the extended image into a residual part for classic differential semblance operator updates and the image born modelling part which provides reflections for higher resolution information in our implementation we invert for the velocity and the image simultaneously through a dual objective function applications to synthetic examples demonstrate the features of the approach

fluvial sedimentary deposits on mars ancient deltas in a crater lake in the nili fossae region 1 new spacecraft observations in the nili fossae region of mars reveal two valley networks 80 and 200 km long that each formed distributary fans as they entered an ancient 40 km diameter impact crater an outlet channel on the eastern crater rim lying at an elevation above the fans suggests these fans formed as subaqueous deltas in a crater lake water flowing in the valley networks entered the crater and deposited the fans and ponded to a maximum depth of about 450 m the lake then overtopped and breached the crater rim incising it and dropping the lake level by 100 m geological evidence combined with the volume of water necessary to fill the crater suggests the duration of flow through this system was prolonged the existence of the deposits described here implies that the early martian environment supported overland flow and ponding of water for an extended period of time

exchange through the strait of gibraltar to measure the exchange between the atlantic and mediterranean through the strait of gibraltar an array of current meter moorings was deployed for a year in the strait during 1985 1986 a novel aspect of these measurements is the inclusion of conductivity as well as temperature and pressure sensors on each current meter so that the salinity of the flows could be monitored continuously these salinity measurements determine the water mass characteristics of the flows crossing the sill they allow definition of the 37 psu isohaline as the interface between inflowing fresher atlantic water and outflowing saltier mediterranean water and they enable time series to be developed for the depth of this interface for the upper layer inflow and for the lower layer outflow from these measurements the time averaged outflow of mediterranean water is estimated to be 0 68sv 1sv 1 106m3s 1 and the outflow salinity transport defined to be the outflow times the salinity excess above a basic atlantic water salinity of 36 1 psu is estimated to be 1 50 103m3s 1 1sv 1psu 1 103m3s 1 equivalent to a net evaporation over the mediterranean basin of 52cm y 1 extrapolated measurements of the inflow from current meters generally deployed below 100m depth yield an estimate for the time averaged inflow of 0 93sv which is believed to be unrealistically high in view of the better measured outflow and net evaporation thus a more realistic estimate of the inflow is 0 72sv equal to the sum of the outflow and net evaporation as required by the mass budget for the mediterranean sea such estimates of the exchange are smaller by almost a factor of 2 than previous values for the exchange by lacombe and richez 1982 the exchange across the gibraltar sill is found to be due in nearly equal parts to the mean currents and to the tidal fluctuations the mean currents are smaller than had been expected reaching a peak value of only about 60 cm s 1 in the deep outflow over the sill the tidal exchange is due to a strong correlation over the tidal period between the depth of the interface and the strength of the inflowing currents for the m2 tide at the sill the amplitude of the interface depth is 51 m and the amplitude of the tidal currents is 1 2m s 1 furthermore the inflow and interface depth have similar phases as a consequence the upper layer is deep on the inflowing tide so that a large slug of atlantic water crosses the sill into the mediterranean on the outflowing tide the interface is shallow so that a large slug of mediterranean water crosses the sill into the atlantic similar processes occur for the s2 o1 and k1 tides though the amplitude are smaller in this manner tidal oscillations lead to a time averaged exchange of water masses across the gibraltar sill the inflow and outflow defined to be the instantaneous transports above and below the 37psu isohaline interface exhibit m2 tidal amplitudes of 2 3 sv and 1 3sv respectively thus the tides are large enough to reverse the mean upper layer inflow and lower layer outflow daily averaged inflow and outflow transports exhibit low frequency fluctuations with standard deviations of 0 37sv and 0 22sv respectively such low frequency fluctuations have been shown previously to be associated with barotropic flows through the strait of gibraltar compensating for sea level variations over the mediterranean due to atmospheric pressure fluctuations candela winant and bryden 1989 finally from these measurements there appear to be little fortnightly or annual period fluctuations in the exchange through the strait of gibraltar

satellite altimetry the marine geoid and the oceanic general circulation for technical reasons the general circulation of the ocean has historically been treated as a steady laminar flow field the recent availability of extremely highaccuracy and high precision satellite altimetry has provided a graphic demonstration that the ocean is actually a rapidly time evolving turbulent flow field to render the observations quantitatively useful for oceanographic purposes has required order of magnitude improvements in a number of fields including orbit dynamics gravity field estimation and atmospheric variability with five years of very high quality data now available the nature of oceanic variability on all space and time scales is emerging including new findings about such diverse and important phenomena as mixing coefficients the frequency wavenumber spectrum and turbulent cascades because the surface elevation is both a cause and consequence of motions deep within the water column oceanographers soon will be able to provide general circulation numerical models tested against and then combined with the altimeter data these will be complete three dimensional timeevolving estimates of the ocean circulation permitting greatly improved estimates of oceanic heat carbon and other property fluxes

image warping waveform tomography imaging the change in physical parameters in the subsurface requires an estimate of the long wavelength components of the same parameters in order to reconstruct the kinematics of the waves propagating in the subsurface one can reconstruct the model by matching the recorded data with modeled waveforms extrapolated in a trial model of the medium alternatively assuming a trial model one can obtain a set of images of the reflectors from a number of seismic experiments and match the locations of the imaged interfaces apparent displacements between migrated images contain information about the velocity model and can be used for velocity analysis a number of methods are available to characterize the displacement between images in this paper we compare shot domain differential semblance image difference penalized local correlations and image warping we show that the image warping vector field is a more reliable tool for estimating displacements between migrated images and leads to a more robust velocity analysis procedure by using image warping we can redefine the differential semblance optimization problem with an objective function that is more robust against cycle skipping than the direct image difference we propose an approach that has straightforward implementation and reduced computational cost compared with the conventional adjoint state method calculations we also discuss the weakness of migration velocity analysis in the migrated shot domain in the case of highly refractive media when the born modelling operator is far from being unitary and thus its adjoint migration operator poorly approximates the inverse

experimental delta formation in crater lakes and implications for interpretation of martian deltas 1 the morphology of delta deposits in crater lakes on mars is indicative of upstream e g flow discharge and sediment properties and downstream e g basin characteristics parameters from which the hydrological conditions at the time of formation can be inferred to investigate the influences of these parameters on delta morphology we experimentally created deltas in crater shaped basins by feeding a range of constant flow discharges over a feeder channel of various sand textures we reproduced three categorically different types of deltas including most of the types that have been identified on mars our most striking observation is that water level behavior itself a unique function of flow discharge basin size and hypsometry and basin floor permeability can explain most delta morphologies observed on mars stepped retrograding deltas formed during water level rise prograding deltas formed during water level still stand and during water level fall deltas were partially destroyed by erosion on mars numerous retrograding and prograding deltas were preserved most of them without indications of channel incisions or other fluvial modification we conclude that the main difference between a single foreset prograding delta and a multiple foreset retrograding delta is the behavior of the water level in the basin these simple delta morphologies cannot be reconciled with long duration hydrological activity because that would imply crater lake fluctuations due to inherent complex water level histories along with complex sediment delivery histories our experiments and numerical verifications demonstrate that such deltas preferentially form during one aqueous event which parsimoniously argues for short duration hydrological activity

serpentinization and the origin of hydrogen gas in kansas hydrogen gas occurs in ten kansas wells near the mid continent rift system since 1982 two wells have yielded small amounts of gases containing an average of 29 37 mole h2 the remainder being chiefly n2 with only traces of hydrocarbons isotopic compositions for hydrogen dgrd 740 to 836 pmil imply near ambient about 10 c equilibration temperatures for the gases which are among the most deuterium depleted in nature and resemble the h2 rich gases described from ophiolites in oman isotopic values for the kansas n2 differ slightly from those of the atmosphere but not enough to rule out an atmospheric origin because they are low in ch4 and co2 expected byproducts of biogenic activity the gases are probably abiogenic in origin the existence of such gases near a major rift system containing mafic rocks and not far from known kimberlites is consistent with an origin from reactions involving fe 2 oxidation for example during serpentinization because the gases may be associated with kimberlites and deep seated rifting mantle outgassing is possible but such an origin would be difficult to reconcile with the low isotopic temperatures the h2 gases from kansas and elsewhere seem to be too low in pressure to have commercial value however neither the kansas gases nor those from other h2 occurrences have been adequately examined to assess their importance as potential resources

a sawtooth like timeline for the first billion years of lunar bombardment abstract we revisit the early evolution of the moon s bombardment our work combines modeling based on plausible projectile sources and their dynamical decay rates with constraints from the lunar crater record radiometric ages of the youngest lunar basins and the abundance of highly siderophile elements in the lunar crust and mantle we deduce that the evolution of the impact flux did not decline exponentially over the first billion years of lunar history but also there was no prominent and narrow impact spike 3 9 gy ago unlike that typically envisioned in the lunar cataclysm scenario instead we show the timeline of the lunar bombardment has a sawtooth like profile with an uptick in the impact flux near 4 1 gy ago the impact flux at the beginning of this weaker cataclysm was 5 10 times higher than the immediately preceding period the nectaris basin should have been one of the first basins formed at the sawtooth we predict the bombardment rate since 4 1 gy ago declined slowly and adhered relatively close to classic crater chronology models neukum and ivanov 1994 overall we expect that the sawtooth event accounted for about one fourth of the total bombardment suffered by the moon since its formation consequently considering that 12 14 basins formed during the sawtooth event we expect that the net number of basins formed on the moon was 45 50 from our expected bombardment timeline we derived a new and improved lunar chronology suitable for use on pre nectarian surface units according to this chronology a significant portion of the oldest lunar cratered terrains has an age of 4 38 4 42 gyr moreover the largest lunar basin south pole aitken is older than 4 3 gy and therefore was not produced during the lunar cataclysm

image domain velocity inversion and event location for microseismic monitoring abstractmicroseismic event locations obtained from seismic monitoring data sets are often a primary means of determining the success of fluid injection programs such as hydraulic fracturing for oil and gas extraction geothermal projects and wastewater injection event locations help the decision makers to evaluate whether operations conform to expectations or parameters need to be changed and may be used to help assess and reduce the risk of induced seismicity however obtaining accurate event location estimates requires an accurate velocity model which is not available at most injection sites common velocity updating techniques require picking arrivals on individual seismograms this can be problematic in microseismic monitoring particularly for surface acquisition due to the low signal to noise ratio of the arrivals we have developed a full wavefield adjoint state method for locating seismic events while inverting for p and s wave velocity models that optimally focus multiple complementary ima

martian surface mineralogy from observatoire pour la mineralogie l eau les glaces et l activite on board the mars express spacecraft omega mex global mineral maps 1 after 2 years of operation the observatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer on board mars express has acquired data coverage of the martian surface with spatial resolution varying between 300 m and 4 8 km depending on the pericenter altitude of the spacecraft s elliptical orbit we report the global surface distributions of some minerals using the omega observations in the visible and near infrared vnir wavelength domains 0 35 2 5 m global maps of ferric phases mafic minerals pyroxenes and olivines and hydrated minerals have been derived from spectral parameters the limits of detection in terms of abundance for some minerals of different grain size distributions are given the distribution of pyroxenes is in general agreement with the mineral maps of previous telescopic and space observations the fe3 absorption feature in the visible wavelength region is present everywhere on the surface the spectra of the bright regions compare with anhydrous nanophase ferric oxides terrains with water bearing minerals cover a very small fraction of the martian surface olivine mg rich compositions is detected in more extensive regions of the pyroxene rich zones than previously reported olivine with higher iron content and or larger grain size 100 m is only detected in isolated areas the mineralogy of the northern low albedo regions is discussed in the light of these mineral maps chemical alteration or oxidation during extrusion producing a coating or varnish of anhydrous ferric phases over a dark basaltic surface best accounts for the vnir spectral properties of these regions although a glassy composition resulting from impact is also considered

a differential semblance criterion for inversion of multioffset seismic reflection data mean square error leading to least squares inversion of multioffset reflection seismograms is insensitive to velocity trend information except in the immediate vicinity of a kinematically correct model in contrast differential semblance retains sensitivity to velocity trend changes over a wide range of models the differential semblance criterion combines mean square error with the mean square differences of inverted models from data sets at neighboring shot positions or offsets or slownesses differential semblance compares model estimates at nearby acquisition parameters which are similar even when the model velocity trends are incorrect because the method inverts the data so that the estimated model amplitudes are meaningful simple differences between the unstacked model estimates give a reliable measure of velocity error a mathematical investigation indicates that the differential semblance criterion is smooth and convex over a large range of velocity models numerical simulation using synthetic data sets verifies this contention

basin scale ocean circulation from combined altimetric tomographic and model data the ocean stores and transports vast quantities of heat fresh water carbon and other materials and its circulation plays an important role in determining both the earth s climate and fundamental processes in the biosphere understanding the development of climate and important biological cycles therefore requires detailed knowledge of ocean circulation and its transport properties this cannot be achieved solely through modelling but must involve accurate observations of the spatio temporal evolution of the global oceanic flow field estimates of oceanic flow are currently made on the basis of space borne measurements of the sea surface and monitoring of the ocean interior satellite altimetry and acoustic tomography are complementary for this purpose1 as the former provides detailed horizontal coverage of the surface and the latter the requisite vertical sampling of the interior high quality acoustic tomographic2 and altimetric3 data are now available to test the combined power of these technologies for estimating oceanic flows here we demonstrate that with the aid of state of the art numerical models it is possible to recover from these data a detailed spatio temporal record of flow over basin scale volumes of fluid our present results are restricted to the mediterranean sea but the method described here provides a powerful tool for studying oceanic circulation worldwide

a fracture history on enceladus provides evidence for a global ocean 1 the region surrounding the south pole of saturn s moon enceladus shows a young pervasively fractured surface that emanates enough heat to be detected by the cassini spacecraft to explain the elevated heat and eruptive icy plumes originating from large cracks informally called tiger stripes in the surface many models implicitly assume a global liquid ocean beneath the surface here we show that the fracture patterns in the south polar terrain spt of enceladus are inconsistent with contemporary stress fields but instead formed in a temporally varying global stress field related to nonsynchronous rotation of a floating ice shell above a global liquid ocean this finding increase to at least three the number of outer planet satellites likely to possess a subsurface liquid water layer

observation of a deep convection regime with acoustic tomography in the winter of 1991 1992 a convection experiment was conducted in the western mediterranean gulf of lions combining a variety of observational techniques an essential component was an acoustic tomography array consisting of six moorings designed to observe the time evolution of the large scale processes believed to be relevant in a convection regime here two dimensional slice inversions in three directions from the central mooring are used to estimate the volume of convected water and the mean convection depth and to observe the preconditioning and restratification processes before and after the convection the near surface layer is well sampled by the acoustics which show cooling and subsequent entrainment of the warmer levantine intermediate water liw from below in agreement with mixedlayer calculations during the 2 months prior to the main convection event the total heat loss of the large scale field is in approximate agreement with the surface heat fluxes showing that little net warm water advection takes place from outside the convection region the implied confinement of water by the local circulation should be an important factor in setting the location and extent of the deep convection patch the volume of water modified by convection in this winter is estimated to correspond to an area of order 60 km radius and 1500 m depth it is argued that the homogenized area implies an annual mean deep water replenishment of 0 3 sv the restratification by the return of less dense water in the surface and liw layers occurs first by rapid capping in the near surface region thereafter the southern and eastern parts of the region restratify in the deeper layers on a 40 day timescale while a dense core of 50 60 km diameter remains in the northwest until the end of the experiment

hydrous minerals on mars as seen by the crism and omega imaging spectrometers updated global view 1 the surface of mars has preserved the record of early environments in which its basaltic crust was altered by liquid water these aqueous environments have survived in the form of hydrological morphologies and alteration minerals including clays and hydrated salts because these minerals probe on earth aqueous environments compatible with biotic activity understanding their formation processes on mars is of great exobiological relevance and also offers insight into earth s now erased ancient water environments using remote sensing we conducted a large scale investigation of the distribution composition age and geomorphic settings of hydrous minerals on mars providing a sharpened global view of the early aqueous environments and their evolution with time aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on mars 4 gyr however very diverse aqueous environments have also been found which suggest widespread complex aqueous settings from the surface to kilometric depths and spanning over 1 gyr by building a robust statistical sample of detections the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on mars and provide context for more localized in depth analyses collectively these trends suggest that at least transient conditions have existed on mars which may have been favorable for pre biotic to biotic activity

mean sea level and surface circulation variability of the mediterranean sea from 2 years of topex poseidon altimetry we describe the circulation and mean sea level variations of the mediterranean sea from 2 years of topex poseidon altimetric data it is first shown that the response of the mediterranean sea to atmospheric pressure forcing is close to an inverse barometer except at high frequencies which means that the adjustment is accompanied by a flow through the straits of sicily and gibraltar we then use topex poseidon to study the mean sea level variations representing steric effects and integrated large scale changes of the mass of the mediterranean sea we observe an annual cycle with a fast drop during winter steric effects account for about half of the observed variations the remaining signal is believed to be driven by evaporation minus precipitation e p forcing and internal hydraulic control in the straits of gibraltar using suboptimal space time objective analysis the classic components of the mediterranean surface circulation are recovered despite low signal to noise ratio the rms of sea level variability is less than 10 cm the variable mediterranean circulation is seen as a complex combination of mesoscale and large scale variations the surface circulation is more complex in the eastern basin than in the western basin in the east it is composed of subbasin scale gyres such as the so called mersa matruh and shikmona gyres which do not have an obvious recurrence period we also observe an intensification of the large scale cyclonic winter circulation in the western and in the ionian basins several mesoscale structures such as the alboran gyres and the ierepetra gyre show a clear seasonal cycle with a maximum in summer the good qualitative and quantitative agreement of the results with previous data from the mediterranean illustrates the improved accurary of topex poseidon over its predecessors

noise removal by migration of time shift images abstractwhen using seismic data to image complex structures the reverse time migration rtm algorithm generally provides the best results when the velocity model is accurate with an inexact model moveouts appear in common image gathers cigs which are either in the surface offset domain or in subsurface angle domain thus the stacked image is not well focused in extended image gathers the strongest energy of a seismic event may occur at non zero lag in time shift or offset shift gathers based on the operation of rtm images produced by the time shift imaging condition the non zero lag time shift images exhibit a spatial shift we propose an approach to correct them by a second pass of migration similar to zero offset depth migration the proposed approach is based on the local poststack depth migration assumption after the proposed second pass migration the time shift cigs appear to be flat and can be stacked the stack enhances the energy of seismic events that are defocused at zero time lag

silica deposits in the nili patera caldera on the syrtis major volcanic complex on mars the martian surface features abundant volcanoes and evidence for past liquid water extant or relict martian volcanic hydrothermal systems have therefore been sought in the pursuit of evidence for habitable environments the mars exploration rover spirit detected deposits highly enriched in silica with accessory minerals suggesting formation by hydrothermal leaching of basaltic rocks by low ph solutions however extensive erosion has obscured the context of the formation environment of these deposits silica deposits have also been identified remotely but also with limited contextual clues to their formation aqueous alteration products of basalt and volcanic ash are the most likely sources here we report the detection from orbit of hydrated silica deposits on the flanks of a volcanic cone in the martian syrtis major caldera complex near infrared observations show dozens of localized hydrated silica deposits as a result of the morphology of these deposits and their location in and around the cone summit we suggest that the deposits were produced by a volcanically driven hydrothermal system the cone and associated lava flows post date early hesperian volcano formation we conclude that if a relict hydrothermal system was associated with the silica deposits it may preserve one of the most recent habitable microenvironments on mars

velocity inversion by differential semblance optimization differential semblance optimization dso is an approach to inversion of reflection seismograms which avoids the severe convergence difficulties associated with nonlinear least squares inversion the method exploits both moveout and amplitude characteristics of reflections we have implemented a version appropriate to plane wave p tau seismograms and layered constant density acoustic earth models theoretical and numerical analyses of this version of dso indicate that stable and reasonably accurate estimates of both velocity trend and reflectivity can be derived to test dso further we applied it to a marine data set from the gulf of mexico where the method produced results which compare favorably to well log information the method can be extended to incorporate laterally heterogeneous velocity models

3d angle gathers from reverse time migration reverse time migration rtm based on directly solving the two way wave equation provides a natural way to deal with large lateral velocity variations and imposes no dip limitations on the seismic images it has become a standard migration tool for subsalt imaging in the gulf of mexico in addition the adoption of wide azimuth waz data acquisition provides better subsurface illumination and more azimuthal information which significantly aids imaging beneath complex overburdens because waz data are richer in the propagation directions of the waves recorded rtm and waz acquisition go hand in hand

fluid mixing and the deep biosphere of a fossil lost city type hydrothermal system at the iberia margin subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle i e serpentinite however geosphere biosphere interactions in serpentinite hosted subseafloor mixing zones remain poorly constrained here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a cretaceous lost city type hydrothermal system at the magma poor passive iberia margin ocean drilling program leg 149 hole 897d brucite calcite mineral assemblages precipitated from mixed fluids ca 65 m below the cretaceous paleo seafloor at temperatures of 31 7 4 3 c within steep chemical gradients between weathered carbonate rich serpentinite breccia and serpentinite mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity dense microbial colonies are fossilized in brucite calcite veins that are strongly enriched in organic carbon up to 0 5 wt of the total carbon but depleted in 13c 13ctoc 19 4 we detected a combination of bacterial diether lipid biomarkers archaeol and archaeal tetraethers analogous to those found in carbonate chimneys at the active lost city hydrothermal field the exposure of mantle rocks to seawater during the breakup of pangaea fueled chemolithoautotrophic microbial communities at the iberia margin possibly before the onset of seafloor spreading lost city type serpentinization systems have been discovered at midocean ridges in forearc settings of subduction zones and at continental margins it appears that wherever they occur they can support microbial life even in deep subseafloor environments

microseismic image domain velocity inversion marcellus shale case study abstractseismic monitoring at injection wells relies on generating accurate location estimates of detected micro seismicity event location estimates assist in optimizing well and stage spacings assessing potential hazards and establishing causation of larger events the largest impediment to generating accurate location estimates is an accurate velocity model for surface based monitoring the model should capture 3d velocity variation yet rarely is the laterally heterogeneous nature of the velocity field captured another complication for surface monitoring is that the data often suffer from low signal to noise levels making velocity updating with established techniques difficult due to uncertainties in the arrival picks we use surface monitored field data to demonstrate that a new method requiring no arrival picking can improve microseismic locations by jointly locating events and updating 3d p and s wave velocity models through image domain adjoint state tomography this approach creates a co

role of biomineralization as an ultraviolet shield implications for archean life cyanobacteria isolated from the krisuvik hot spring iceland were mineralized in an iron silica solution and irradiated with high levels of ultraviolet light analysis of the rates of photosynthesis chlorophyll a content and phycocyanin autofluorescence revealed that these mineralized bacteria have a marked resistance to uv compared to nonmineralized bacteria naturally occurring sinters composed of iron silica biominerals collected from

a serpentinite hosted ecosystem the lost city hydrothermal field the serpentinite hosted lost city hydrothermal field is a remarkable submarine ecosystem in which geological chemical and biological processes are intimately interlinked reactions between seawater and upper mantle peridotite produce methane and hydrogen rich fluids with temperatures ranging from 40 to 90 c at ph 9 to 11 and carbonate chimneys 30 to 60 meters tall a low diversity of microorganisms related to methane cycling archaea thrive in the warm porous interiors of the edifices macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the mid atlantic ridge but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems

the global frequency wavenumber spectrum of oceanic variability estimated from topex poseidon altimetric measurements two years of altimetric data from the topex poseidon spacecraft have been used to produce preliminary estimates of the space and time spectra of global variability for both sea surface height and slope the results are expressed in terms of both degree variances from spherical harmonic expansions and in along track wavenumbers simple analytic approximations both in terms of piecewise power laws and pade fractions are provided for comparison with independent measurements and for easy use of the results a number of uses of such spectra exist including the possibility of combining the altimetric data with other observations predictions of spatial coherences and the estimation of the accuracy of apparent secular trends in sea level