a strong seasonal dependence in the martian hydrogen exosphere hubble space telescope hst and mars express mex observed unexpected rapid changes in the martian hydrogen exosphere involving a decrease in scattered lyman intensity in fall 2007 solar longitude ls 331 345 these changes detected were speculated to be a combination of seasonal variation and or dust storms and lower atmospheric dynamics here we present hst observations of mars in 2014 over a broad range of heliocentric distances and seasons ls 138 232 which indicate a factor of 3 5 change in martian lyman brightness associated with a factor 5 4 variation of hydrogen escape flux in the absence of global dust storms and significant solar variability we thus conclude that seasonal effects have a strong influence on the hydrogen exosphere which in turn has major implications for the processes that control water supply to the martian upper atmosphere and the history of water escape from mars

the normality of el nino the amplitude of the el nino southern oscillation enso would be normally distributed if the coupled pacific ocean atmosphere were a linear system forced by gaussian weather noise moment estimates of skewness and kurtosis demonstrate that this is not the case for monthly mean anomalies in pacific sea surface temperatures during 1950 97 the noted predominance of el nino events compared to la nina events is related to the high skewness in the eastern pacific skewness and kurtosis both exhibit an intriguing geographical variation from positive in the eastern to negative in the western pacific we have also examined nino 3 indices generated by three climate models having widely different complexity these exhibit a wide range of skewness and kurtosis values rather different from those found for the observations skewness and kurtosis can be used to diagnose non linear processes and provide powerful tools for validating models and for testing observed sea surface temperatures for the presence of possible climate change

hydrogen isotope evidence for loss of water from mars through time 1 the high d h of the martian atmosphere 5 6 terrestrial is considered strong evidence for the loss of martian water to space the timing and magnitude of the loss of water from mars can be constrained by measurements of d h in martian meteorites previous studies of martian meteorites have shown a large range in d h from terrestrial values to as high as the current martian atmosphere here we show that the ancient 4 ga mars meteorite alh84001 has a d h 4 terrestrial and that the young 0 17 ga shergotty meteorite has a d h 5 6 terrestrial we also find that the young los angeles shergottite has zoning in d h that can be correlated to igneous growth zoning strongly suggesting assimilation of d enriched water during igneous crystallization near the martian surface in contrast to previous studies we find higher and less variable d h ratios in these three meteorites our results suggest a two stage evolution for martian water a significant early loss of water to space prior to 3 9 ga followed by only modest loss to space in the last 4 billion years the current martian atmospheric d h has remained essentially unchanged for the last 165 ma

a probabilistic case for a large missing carbon sink on mars after 3 5 billion years ago abstract mars has a thin 6 mbar co2 atmosphere currently there is strong evidence for paleolakes and rivers formed by warm climates on mars including after 3 5 billion years ga ago which indicates that a co2 atmosphere thick enough to permit a warm climate was present at these times since mars no longer has a thick co2 atmosphere it must have been lost one possibility is that martian co2 was lost to space oxygen escape rates from mars are high enough to account for loss of a thick co2 atmosphere if co2 was the main source of escaping o but here using h isotope ratios o escape calculations and quantification of the surface o sinks on mars we show for the first time that o escape from mars after 3 5 ga must have been predominantly associated with the loss of h2o not co2 and therefore it is unlikely that 250 mbar martian co2 has been lost to space in the last 3 5 ga because such results require highly unfavored o loss scenarios it is possible that the presence of young rivers and lakes on mars could be reconciled with limited co2 loss to space if crater chronologies on mars are sufficiently incorrect that all apparently young rivers and lakes are actually older than 3 5 ga or if climate solutions exist for sustained runoff on mars with atmospheric co2 pressure

jarosite occurrence in the deccan volcanic province of kachchh western india spectroscopic studies on a martian analog locality the sulfate mineral jarosite is considered a key indicator of hydrous acidic and oxidizing conditions on the surface of early mars here we report an analog terrestrial locality hosting jarosite from matanumadh kachchh western india using detailed spectroscopic studies on weathered basalts of the deccan volcanic province and overlying tuffaceous shales and sandstones of the matanumadh formation hyperspectral data in the visible near infrared 350 2500 nm to midinfrared 4000 400 cm 1 region of the electromagnetic spectrum and x ray diffraction patterns have been acquired on samples collected from the field to detect and characterize the hydrous sulfate and phyllosilicate phases present at the studied site hydrous sulfates occur in association with al rich phyllosilicates kaolinite that overlie a zone of fe mg smectites in altered basalts jarosite is found within both saprolitic clay horizons altered from the basalt and within variegated sandstone and shale clay units overlying the saprolite it mostly occurs as secondary veins with or without gypsum jarosite is also seen as coatings on kaolinite clasts of varying shapes and sizes within the tuffaceous variegated sandstone unit we argue that the overall geological setting of the matanumadh area with this unusual mineral assemblage developing within altered basalts and in the overlying sedimentary sequence mimics the geological environment of many of the identified jarosite localities on mars and can be considered as a martian analog from this perspective

the case against vast glaciation in valles marineris mars abstract the valles marineris of mars form the largest system of interconnected canyons in the solar system where morphological mineralogical and structural evidence of widespread glaciation has been recently reported however neither precipitation models nor global water budgets can account for such a colossal fill and the hypothesis has thus far remained unchallenged by additional scrutiny here we present the first thorough case against a valles marineris glaciation by describing new evidence that precludes the existence of a glacier most crucially we review high resolution imaging science experiment hirise images of chaos terrain in candor chasma previously interpreted as remnant glacial ice and identify layered boulder rich scarps bearing no similarity to scarps of massive ice in promethei terra or the north polar layered deposits we also find no significant differences in the structure morphology and composition of chaos terrain in candor and the chryse planitia region which suggests candor s chaos like chryse s is fractured highland terrain we also review several other key supports for the glacial hypothesis including the coincidence of an apparent glacial trimline with the water bearing mineral jarosite and the apparent presence of glacial features including kettle holes and sandur plains these too are found to have more plausible explanations with non glacial origins including tectonic reorganisation groundwater sapping and chaotic fracturing we conclude that the valles marineris glacial hypothesis is inconsistent with both observed morphology and our understanding of the ancient martian climate and we find no evidence to support its existence

predicted diurnal variation of the deuterium to hydrogen ratio in water at the surface of mars caused by mass exchange with the regolith regolith on mars exchanges water with the atmosphere on a diurnal basis and this process causes significant variation in the abundance of water vapor at the surface while previous studies of regolith atmosphere exchange focus on the abundance recent in situ experiments and remote sensing observations measure the isotopic composition of the atmospheric water we are therefore motivated to investigate isotopic water exchange between the atmosphere and the regolith and determine its effect on the deuterium to hydrogen ratio d h of the atmosphere we model transport of water in the regolith and regolith atmosphere exchange by solving a transport equation including regolith adsorption condensation and diffusion the model calculates equilibrium fractionation between hdo and h 2o in each of these processes the fractionation in adsorption is caused by the difference in the latent heat of adsorption and that of condensation is caused by the difference in the vapor pressure together with a simple bulk aerodynamic boundary layer model we simulate the diurnal variation of the d h near the planetary surface we find that the d h can vary by 300 1400 diurnally in the equatorial and mid latitude locations and the magnitude is greater at a colder location or season the variability is mainly driven by adsorption and desorption of regolith particles and its diurnal trend features a drop in the early morning a rise to the peak value during the daytime and a second drop in the late afternoon and evening tracing the water vapor flow into and out from the regolith the predicted d h variation can be tested with in situ measurements as such our calculations suggest stable isotope analysis to be a powerful tool in pinpointing regolith atmosphere exchange of water on mars

spatial and temporal features of enso meridional scales 1 the spatial and temporal features of the el nino southern oscillation enso meridional scales are investigated using the hadley center global sea ice and sea surface temperature hadisst data for the period of 1950 2007 the results show that the meridional scales of the enso warm and cold events are asymmetric and exhibit interdecadal changes the meridional extent of the sea surface temperature anomalies ssta during la nina years is wider than that during el nino years this is because strengthened trades and thus strengthened upwelling and meridional currents during la nina events more effectively spread ssta away from the equator with the walker circulation weakening in recent decades which tends to reduce upwelling and meridional currents over the central and eastern equatorial pacific the meridional scales of both el nino and la nina events also decrease citation zhang w j li and f f jin 2009 spatial and temporal features of enso meridional scales geophys res lett 36 l15605

volatiles in the martian crust and mantle clues from the nwa 6162 shergottite abstract martian meteorites of various petrogeneses retain a record of volatiles on mars from the hydrosphere crustal water to the mantle sputtering of the martian atmosphere by solar wind after the loss of mars magnetic field enriched it in deuterium which exchanged with martian crustal water recent studies show that the hydrogen isotopic composition of the martian crustal water reservoir varies from 3000 to 7000 but requires better constraints melt inclusion glasses maskelynite and fusion crust from the depleted olivine phyric shergotite nwa 6162 were analyzed using nanosims providing a unique insight into the hydrogen isotopic and volatile elemental content of both the martian crustal water reservoir and the mantle source the h2o s and cl contents of the melt inclusion glasses are 0 3137 14 239 and 16 967 ppm respectively d values vary from 560 to 6137 the water content positively correlates with the d values in both the melt inclusion glasses and maskelynite in a two end member mixing trend one end member is the magmatic water with a d value of 0 and the other end member is the martian crustal water with d ranging from 5000 to 6000 nwa 6162 a depleted olivine phyric shergottite originated from a different mantle source to the enriched lherzolitic shergottites however both types of shergottites exchanged with martian crustal water with the same d values indicating a homogeneous martian crustal water hydrogen isotopic composition 5000 6000 most melt inclusion glasses from nwa 6162 have low water content 0 234 ppm except for two enriched locations as micron sized bands and dendrites the low water content in most melt inclusion glasses the dendritic shaped water enriched areas in melt inclusions and the martian crustal water diffusion profile recorded in maskelynite collectively suggest short lived water rock interactions in the nwa 6162 parent rock that was probably induced by impact furthermore a great contribution up to 98 of surface cl accompanying d enriched water was recorded in the melt inclusions supported by the positive correlation between cl and h2o the presence of sulfide and s rich hot spots and low d end member of the magmatic water indicate that the degassing during post entrapment crystallization and ascent of the melt inclusion is negligible h2o s and cl contents of the martian mantle reservoir are estimated to be 0 1 3 0 5 15 and 0 5 4 ppm respectively after the correction of fractional crystallization of the melt inclusions and contribution from the martian surface reservoir the martian mantle reservoir estimated from nwa 6162 was water s and cl poorer than the earth s interior

is enso a cycle or a series of events 1 after early ideas that saw el ninos as isolated events the advent of coupled models brought the conception of enso as a cycle in which each phase led to the next in a self sustained oscillation twenty two years of observations that represent the el nino and la nina peaks east pacific sst and the memory of the system zonal mean warm water volume suggest a distinct break in the cycle in which the coupled system is able to remain in a weak la nina state for up to two years so that memory of previous influences would be lost similarly while the amplitude of anomalies persists from the onset of a warm event through its termination there is no such persistence across the la nina break these observations suggest that el ninos are in fact event like disturbances to a stable basic state requiring an initiating impulse not contained in the dynamics of the cycle itself

robust characteristics method for modelling multiphase visco elasto plastic thermo mechanical problems abstract we have extended our previous 2d method gerya t v yuen d a 2003 characteristics based marker in cell method with conservative finite differences schemes for modeling geological flows with strongly variable transport properties phys earth planet interiors 140 295 320 which is a combination of conservative finite differences with marker in cell techniques to include the effects of visco elasto plastic rheology self gravitation and a self consistently derived evolving curvilinear planetary surface this code is called i2elvis and can solve a new class of computationally challenging problems in geodynamics such as shear localization with large strains crustal intrusion emplacement of magmas bending of realistic visco elasto plastic plates and core formation by vigorous shell tectonics activities related to a global rayleigh taylor instability of a metal layer formed around silicate rich lower density primordial core during planetary accretion we discuss in detail the computational strategy required the rheological constraints to be satisfied at each time step and spatial location we show analytical benchmarks and examples drawn from comparing between numerical and analogue experiments in structural geology subducting slab bending with a visco elasto plastic rheology and equilibrium spherical configurations from self gravitation we have also tested possibilities of future applications by addressing 3d geometries based on multigrid method and including inertial effects in the momentum equation with tracers in order to simulate meteoritic impact events and eventually earthquake instabilities

water on mars insights from apatite in regolith breccia northwest africa 7034 abstract determining the source of planetary water from the hydrogen isotope compositions of crustal samples is complicated by the overprinting of isotopically diverse source material by geologic and atmospheric processes as mars has no plate tectonics crustal material which may have isotopically exchanged with the martian atmosphere is not recycled into the mantle keeping the water reservoirs in the mantle and atmosphere mostly isolated buffered by the crust as the only known martian samples that are regolith breccias with a composition representative of the average crust of mars northwest africa nwa 7034 and its paired stones provide an important opportunity to investigate the water content and hydrogen isotope composition of the martian crust in particular apatites in distinct clasts as well as the brecciated matrix of nwa 7034 record a complex history including magmatic and impact processes and exchange with crustal fluids

retention of an atmosphere on early mars the presence of valley networks and indications of high erosion rates in ancient terrains on mars suggest that mars was warm and wet during heavy bombardment various processes that could occur on early mars were integrated into a self consistent model to determine what circumstances might lead to warm temperatures during and at the end of heavy bombardment included were weathering and burial of co2 as carbonates impact erosion sputtering and recycling of co2 back into the atmosphere by burial and heating the models suggest that despite losses from the atmosphere by weathering and impact erosion mars could retain a 0 5 to 1 bar atmosphere at the end of heavy bombardment partly because weathering temporarily sequesters co2 in the ground and protects it from impact erosion while the impact rate is declining and impact erosion is becoming less effective because of the low output of the early sun surface temperatures can be above freezing only for a very efficient greenhouse such as that suggested by forget and pierrehumbert 1997 with weak greenhouse models temperatures are below freezing throughout heavy bombardment and such a large amount of co2 is left in the atmosphere at the end of heavy bombardment that it is difficult to eliminate subsequently to arrive at the present surface inventory with strong greenhouse models temperatures are well above freezing during heavy bombardment and drop to close to freezing at the end of heavy bombardment at which time the atmosphere contains 0 5 to 1 bar of co2 this can be largely eliminated subsequently by sputtering and low temperature weathering such a model is consistent with the change in erosion rate and the declining rate of valley formation at the end of heavy bombardment conditions that favor warm temperatures at the end of heavy bombardment are an efficient greenhouse low weathering rates low impact erosion rates and a smaller fraction of heat lost by conduction as opposed to transport of lava to the surface

elasticity yielding and episodicity in simple models of mantle convection we explore the implications of refinements in the mechanical description of planetary constituents on the convection modes predicted by finite element simulations the refinements consist in the inclusion of incremental elasticity plasticity yielding and multiple simultaneous creep mechanisms in addition to the usual visco plastic models employed in the context of unified plate mantle models the main emphasis of this paper rests on the constitutive and computational formulation of the model we apply a consistent incremental formulation of the non linear governing equations avoiding the computationally expensive iterations that are otherwise necessary to handle the onset of plastic yield in connection with episodic convection simulations we point out the strong dependency of the results on the choice of the initial temperature distribution our results also indicate that the inclusion of elasticity in the constitutive relationships lowers the mechanical energy associated with subduction events

oceans on mars an assessment of the observational evidence and possible fate the edges of the northern plains and interpreted to be shorelines remaining from these former standing bodies of water we examine the elevations and geologic relations along these contacts in detail and find little support for their interpretation as shorelines some contacts are clearly of volcanic origin and all have significant variations in elevation better support for the former presence of water over large parts of the northern plains is provided by the vastitas borealis formation vbf most of the post noachian fill within the northern basin is ridged plains of lower hesperian age interpreted to be volcanic in origin overlying the ridged plains is the vbf a thin veneer of material of upper hesperian age the vbf may have been deposited from large floods support for this interpretation is the similarity in age between the outflow channels and the vbf the presence of the vbf at the lower ends of the outflow channels and identification of numerous features in the outcrop areas of the vbf that are suggestive of basal melting of an ice sheet to cover all the area over which the vbf is exposed would require 2 3 10 7 km 3 of water spread over the entire surface of mars this volume is equal to a global layer global equivalent layer or gel 156 m deep we find no support for the larger estimates of ocean volumes that range up to 3 10 8 km 3 and which imply comparable amounts of water per unit area as are currently present on the surface of the earth under present climatic conditions on mars an ocean would freeze in a geologically short time period 10 4 years then would sublimate away at rates strongly dependent on the presence or absence of debris on the ice surface the present vbf is interpreted as a sublimation residue from the ponded outflow channel effluents the fate of a volume of water thought to have been emplaced by the outflow channels 2 3 10 7 km 3 is largely accounted for by the presence of other existing reservoirs on the planet an approximately 20 30 m gel of water is estimated to be in the present polar caps and a 50 m gel may have escaped to space since the hesperian leaving 80 m gel unaccounted for this amount may be partly trapped in other volatile rich deposits on the surface and a significant amount could have reentered the groundwater system by south polar basal melting and been progressively cold trapped at the base of a growing cryosphere on the basis of our assessment of the hesperian aged deposits we predict that testing of the clifford and parker 2001 hypothesis that a noachian aged ocean covered up to one third of the surface of mars will be made very difficult by the enhanced degradation rates in the noachian and subsequent geological events in the northern lowlands index terms 6225 planetology solar system objects mars 4267 oceanography general paleoceanography 5407 planetary sciences atmospheres evolution 5470 planetary sciences surface materials and properties 1635 global change oceans 4203 keywords mars oceans channels shorelines hesperian

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

strong water isotopic anomalies in the martian atmosphere probing current and ancient reservoirs we measured maps of atmospheric water h2o and its deuterated form hdo across the martian globe showing strong isotopic anomalies and a significant high deuterium hydrogen d h enrichment indicative of great water loss the maps sample the evolution of sublimation from the north polar cap revealing that the released water has a representative d h value enriched by a factor of about 7 relative to earth s ocean vienna standard mean ocean water vsmow certain basins and orographic depressions show even higher enrichment whereas high altitude regions show much lower values 1 to 3 vsmow our atmospheric maps indicate that water ice in the polar reservoirs is enriched in deuterium to at least 8 vsmow which would mean that early mars 4 5 billion years ago had a global equivalent water layer at least 137 meters deep

interactive feedback between enso and the indian ocean abstract a feedback process of the indian ocean sst on enso is investigated by using observed data and atmospheric gcm it is suggested that warming in the indian ocean produces an easterly wind stress anomaly over indonesia and the western edge of the pacific during the mature phase of el nino the anomalous easterly wind in the western pacific during el nino helps a rapid termination of el nino and a fast transition to la nina by generating upwelling kelvin waves thus warming in the indian ocean which is a part of the el nino signal operates as a negative feedback mechanism to enso this indian ocean feedback appears to operate mostly for relatively strong el ninos and results in a la nina one year after the mature phase of the el nino this 1 yr period of phase transition implies a possible role of indian ocean enso coupling in the biennial tendency of the enso atmospheric gcm experiments show that indian ocean sst forcing is mostly responsible for the easterly wind anomalies in the western pacific

observations of warm water volume changes in the equatorial pacific and their relationship to el nino and la nina abstract this paper describes observed changes in surface winds sea surface temperature sst and the volume of water warmer than 20 c wwv in the equatorial pacific ocean for the period 1980 99 the purpose is to test recent hypotheses about the relationship between variations in wwv and the el nino southern oscillation enso cycle the results confirm inferences based on theory models and previous empirical analyses using proxy data namely sea level that enso involves a recharge and discharge of wwv along the equator and that the cyclic nature of enso results from a disequilibrium between zonal winds and zonal mean thermocline depth the authors also find that the magnitude of enso sst anomalies is directly related to the magnitude of zonal mean wwv anomalies furthermore for a given change in equatorial wwv the corresponding warm el nino sst anomalies are larger than the corresponding cold la nina anomalies this asymmetry between the warm and cold phases of the enso cycle implies differences

evidence from the mars express high resolution stereo camera for a frozen sea close to mars equator it is thought that the cerberus fossae fissures on mars were the source of both lava and water floods two to ten million years ago evidence for the resulting lava plains has been identified in eastern elysium but seas and lakes from these fissures and previous water flooding events were presumed to have evaporated and sublimed away here we present high resolution stereo camera images from the european space agency mars express spacecraft that indicate that such lakes may still exist we infer that the evidence is consistent with a frozen body of water with surface pack ice around 5 degrees north latitude and 150 degrees east longitude in southern elysium the frozen lake measures about 800 x 900 km in lateral extent and may be up to 45 metres deep similar in size and depth to the north sea from crater counts we determined its age to be 5 2 million years old if our interpretation is confirmed this is a place that might preserve evidence of primitive life if it has ever developed on mars

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

a comparison of numerical surface topography calculations in geodynamic modelling an evaluation of the sticky air method summary calculating surface topography in geodynamic models is a common numerical problem besides other approaches the so called sticky air approach has gained interest as a free surface proxy at the top boundary the often used free slip condition is thereby vertically extended by introducing a low density low viscosityfluid layer this allows the air crust interface to behave in a similar manner to a true free surface we present here a theoretical analysis that provides the physical conditions under which the sticky air approach is a valid approximation of a true free surface two cases are evaluated that characterize the evolution of topography on different timescales 1 isostatic relaxation of a cosine perturbation and 2 topography changes above a rising plume we quantitatively compare topographies calculated by six different numerical codes using finite difference and finite element techniques using three different topography calculation methods i direct calculation of topography from normal stress ii body fitting methods allowing for meshing the topography and iii lagrangian tracking of the topography on an eulerian grid it is found that the sticky air approach works well as long as the term st ch hst l 3 is sufficiently small where st and hst are the viscosity and thickness of the sticky air layer and ch and l are the characteristic viscosity and length scale of the model respectively spurious lateral fluctuations of topography as observed in some marker based sticky air approaches may effectively be damped by an anisotropic distribution of markers with a higher number of markers per element in the vertical than in the horizontal direction

the hypanis valles delta the last highstand of a sea on early mars one of the most contentious hypotheses in the geological history of mars is whether the northern lowlands ever contained an oceanic water body arguably the best evidence for an ocean comes from the presence of sedimentary fans around mars dichotomy boundary which separates the northern lowlands from the southern highlands here we describe the palaeogeomorphology of the hypanis valles sediment fan the largest sediment fan complex reported on mars area 970 km2 this has an extensive catchment 4 6 x 105 km2 incorporating hypanis and nanedi valles that we show was active during the late noachian early hesperian period 3 7 ga the fan comprises a series of lobe shaped sediment bodies connected by multiple bifurcating flat topped ridges we interpret the latter as former fluvial channel belts now preserved in inverted relief meter scale thick sub horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins the inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of hypanis valles and descend 500 m in elevation the progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water assuming the elevation of the northern plains basin floor is stable we interpret the hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system at its location at the dichotomy boundary the hypanis valles fan system is topographically open to chryse planitia an extensive plain that opens in turn into the larger northern lowlands basin we conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least chryse planitia given the open topography it is plausible that the hypanis fan system records the existence last highstand and retreat of a large sea in chryse planitia and perhaps even an ocean that filled the northern plains of mars

mangala valles mars a reassessment of formation processes based on a new geomorphological and stratigraphic analysis of the geological units abstract mangala valles has always been viewed as the typical outflow channel formed by catastrophic floods of water a new analysis has shown that the geomorphological traces of fluvial or lacustrine processes within mangala valles can be better explained by fluid lava flooding the channels and filling pre existing impact craters as for the circum chryse outflow channels where no clear source of water or mechanism able to replenish water at its hydraulic head is observed there is no geologic trace of a sudden removal of a volume of water ice necessary to carve mangala valles neither maars nor rootless cones typical volcanic features indicative of interaction between lava and ground ice were found past works suggested that the formation of mangala valles occurred in late amazonian age when the climate of mars was similar to that seen today that is absolutely not liquid water friendly the present work shows how the origin of mangala valles may go back to noachian or even pre noachian when other studies have concluded that the climate was not liquid water friendly even assuming limited periods of obliquity favourable to liquid water in the history of mars which is at odds with the widespread presence of unaltered olivine and jarosite it is very difficult to find plausible mechanisms of aquifer recharge or signs of catastrophic water release at the notch of mangala valles that could feed the multiple episodes or even a single episode of fluvial flooding suggested in the literature this evidence and other analysis will show that the presence of water and eventually ground ice is not incontrovertible in the equatorial regions and should not be given for granted as commonly done so far in the literature the geomorphological analysis of the mars reconnaissance orbiter mro images provided in this paper combined with themis and mola data show how mangala fossa from which mangala valles originated as a breakout is an erosional channel formed by the flow of lava in a original tube coming from daedalia planum rather than a tectonic graben or the sign of a dike rupturing to the surface

a proposed mechanism for the asymmetric duration of el nino and la nina el nino and la nina exhibit significant asymmetry not only in their spatial structure but also in their duration most el ninos terminate rapidly after maturing near the end of the calendar year whereas many la ninas persist into the following year and often reintensify in boreal winter through atmospheric general circulation model experiments it is shown that the nonlinear response of atmospheric deep convection to the polarity of equatorial pacific sea surface temperature anomalies causes an asymmetric evolution of surface wind anomalies over the far western pacific around the mature phase of el nino and la nina because of the eastward displacement of precipitation anomalies in the equatorial pacific during el nino compared to la nina surface winds in the western pacific are more affected by sst forcing outside the equatorial pacific which acts to terminate the pacific event

the sources of water in martian meteorites clues from hydrogen isotopes abstract h isotope measurements of carbonate phosphate feldspathic and mafic glasses and post stishovite silica phase in the shergottites zagami shergotty sau 005 dag 476 alha 77005 and eeta 79001 as well as in chassigny and alh 84001 show that all these phases contain deuterium enriched water of extraterrestrial origin the minerals and glasses analyzed may contain an initial primary hydrogen component but their isotopic composition was modified to varying degrees by three different processes interaction with a fractionated exchangeable water reservoir on mars hydrogen devolatilization by impact melting and terrestrial contamination positive correlations between d and water abundance in feldspathic glass and post stishovite silica in zagami shergotty and sau 005 is indicative of mixing of a high d component 3000 4000 and a less abundant low d component 0 the high d component is primarily derived from the martian exchangable reservoir but may also have been influenced by isotopic fractionation associated with shock induced hydrogen loss the low d component is either a terrestrial contaminant or a primary magmatic component the negative correlation between d and water abundances in mafic and feldspathic glasses in alh 84001 alha 77005 and eeta 79001 is consistent with the addition of a low d terrestrial contaminant to a less abundant high deuterium martian component the low d of magmatic glass in melt inclusions suggests that the d of martian parent magma was low and that the initial h isotope signature of mars may be similar to that of earth

mars in the aftermath of a colossal impact abstract the abundance of highly siderophile elements hses inferred for mars mantle from martian meteorites implies a late veneer lv mass addition of 0 8 wt with broadly chondritic composition late accretion to mars by a differentiated ceres sized 1000 km diameter object can account for part of the requisite lv mass and geochronological constraints suggests that this must have occurred no later than ca 4480 ma here we analyze the outcome of the hypothetical lv giant impact to mars with smoothed particle hydrodynamics simulations together with analytical theory results show that in general about 50 of the impactor s metallic core shatters into 10 m fragments that subsequently fragment into sub mm metallic hail at re accretion this returns a promising delivery of hses into martian mantle compared to either a head on and hit and run collision in both cases 10 myr a dense pre noachian co2 atmosphere should lower the escape efficiency of hydrogen by ir emission a more detailed hydrodynamic atmospheric model of this early hydrogen atmosphere is warranted to examine its effect on pre noachian mars

investigation of water vapor on mars with pfs sw of mars express abstract new insight into the seasonal diurnal and spatial distribution of water vapor on mars has been obtained from analyzing the spectra of the short wavelength channel sw of the planetary fourier spectrometer pfs onboard mars express the processed dataset recorded between january 2004 and april 2005 covers the seasons from l s 331 of mars year 26 to l s 196 of the following year in this period the mean column density around vernal equinox was 8 2 pr m the maximum values during northern summer were about 65 pr m located around 75 n latitude with a longitudinally inhomogeneous distribution regarding the atmospheric transport the majority of polar water vapor remains in the north polar region while only about a quarter is transported southward geographically there are two water vapor maxima visible over arabia terra and the tharsis plateau that are most likely caused both by atmosphere ground interaction and by atmospheric circulation a comparison with other instruments generally shows a good agreement only the spicam results are systematically lower compared to the results from the pfs long wavelength channel the results of this work are slightly higher a strong discrepancy is visible northward of about 50 n during the northern summer that is possibly explained by a non uniform vertical h 2 o mixing in particular a confinement of the water to the lower few kilometers yields a much better agreement between the retrieved column densities of the two pfs channels

asymmetry in zonal phase propagation of enso sea surface temperature anomalies 1 it is often emphasized in the literature that the phase propagation of el nino sea surface temperature sst anomalies along the equator changed from westward to eastward after a mid to late 1970s climate regime shift in the pacific theories have been developed to explain this change of phase propagation in terms of changes in background state on which el nino events develop those theories also suggest that the direction of la nina anomaly phase propagation should have changed from westward to eastward as well however the direction of la nina sst anomaly phase propagation did not change after the mid to late 1970s instead la nina ssts continued to exhibit westward phase propagation along the equator a feature overlooked in both observational analyses and theories this paper highlights the asymmetry in zonal phase propagation between el nino and la nina sea surface temperature anomalies since 1980 and discusses the implications of that asymmetry for understanding el nino southern oscillation enso dynamics

on the variety of coastal el nino events we examine the connection between interannual anomalies of sea surface temperature sst in the central and far eastern equatorial pacific associated with basin scale and coastal el ninos variations of the sst anomalies in these two regions are largely coherent meaning coastal el ninos mostly occur together with the commonly studied basin scale el ninos of particular interest for this study though is the understanding of the coastal el ninos that are not accompanied by basin scale el ninos or that follow basin scale el ninos such coastal el ninos can have catastrophic societal consequences in western south america we identify seven coastal el ninos during 1979 2017 namely 1983 1987 1998 2008 2014 2015 and 2017 these coastal el ninos are driven by different mechanisms the coastal el ninos in 1983 1987 and 1998 occurred after basin scale el ninos a unique feature of such extreme basin scale el ninos like in 1982 1983 1986 1987 and 1997 1998 is an equatorially centered intertropical convergence zone during its decaying phase as a result positive sst anomalies persist and sometimes even strengthen in the eastern pacific in the subsequent boreal spring early summer leading to coastal el ninos the coastal el ninos in 2014 and 2015 on the other hand resulted from westerly wind bursts in the western pacific that forced downwelling kelvin waves and a thermocline depression in the far eastern pacific the formation of coastal el ninos in 2008 and 2017 were associated with westerly surface wind anomalies in the eastern equatorial pacific and largely driven by ocean surface heat flux anomalies these two coastal el ninos occur during the warm phase of the seasonal cycle so that warm ssts are amplified and or the warm season is extended along the west coast of south america thus there is a wide variety of the coastal el ninos in terms of evolution mechanism and timing

viscoelastic mantle convection and lithospheric stresses summary accurate predictions of stress distribution in the lithosphere are of major importance for approaching more realistic numerical models of the mantle lithosphere system since stress fields in the lithosphere computed in convection models differ substantially between viscous and viscoelastic rheologies it is essential to employ a viscoelastic rheology when accurate stresses are to be predicted in mantle convection models involving the lithosphere this difference in stress distribution and magnitude has important implications for accurate modelling of stress dependent processes like power law creep shear heating and plasticity a further requirement for computation of accurate stress fields is to ensure numerically divergence free solutions in the boussinesq approximation we present the technical background required for implementation of numerically incompressible solutions and for implementation of a maxwell viscoelastic rheology in the frame of the finite element method fem we employ the jaumann invariant stress derivative in our implementation and demonstrate that the choice of the invariant stress derivative is irrelevant for geodynamic simulations we discuss potential numerical advantages of a viscoelastic rheology when large viscosity variations are applied in thermal convection models due to the physical transition from effectively viscous to elastic behaviour in a viscoelastic model the introduction of viscosity cut offs generally applied in viscous models can be avoided

mjo related oceanic kelvin waves and the enso cycle a study with the ncep global ocean data assimilation system 1 the surface wind anomalies associated with the madden julian oscillation mjo appear to play a critical role during the onset and termination phases of enso the characteristics of the mjo related oceanic kelvin waves have not been systematically studied due to a lack of ocean reanalysis that resolves intraseasonal variability this study uses the operational ocean reanalysis for the period 1982 2003 produced by the state of art global ocean data assimilation system at ncep to explore the relationship between sst anomalies of enso and mjo related oceanic kelvin waves the first four extended empirical orthogonal functions of the depth of 20c isotherm are used to represent the dominant oceanic kelvin waves the wave activity is measured by seasonal variance of oceanic kelvin waves svkw at 130w svkw peaks are associated with the onset stage of warm enso events since they occur during the transition period and tend to produce positive tendency in nino3 4 and heat content and lead mature phases by 5 11 months mjo related oceanic kelvin wave activity is also shown to impact the growth and termination of warm events the consistent relationships do not occur in cold events a real time monitoring tool using svkw index is proposed to support the official enso forecast at ncep citation seo k h and y xue 2005 mjo related oceanic kelvin waves and the enso cycle a study with the ncep global ocean data assimilation system geophys res lett 32 l07712 doi 10 1029 2005gl022511

shear zone and nappe formation by thermal softening related stress and temperature evolution and application to the alps we present the results of two dimensional thermo mechanical numerical simulations of the formation of kilometre scale shear zones and tectonic nappes which are generated by thermal softening during horizontal shortening this model is thermo mechanically coupled and conserves energy by converting mechanical work into heat the results show that in homogeneous material the temperature increase in shear zones caused by viscous heating can be 100 c the characteristic width of the thermally perturbed part of the deforming zone is three times larger than the width of the corresponding shear zone because of diffusive heating of the wall rock therefore temperature variations initiated by shear heating may be difficult to identify based on petrological inferences of field data during lithospheric shortening with a bulk rate of 2 5 10 15 s 1 a nappe forms in the crust at a depth of 45 km peak temperatures in the nappe reach 600 c 100 c increase due to shear heating significant shear heating occurs only locally and is not active continuously in time along the entire crustal shear zone peak values of the maximal principal stress locally reach 2 5 gpa in the nappe peak values of temperature and maximal principal stress increase locally to 770 c 300 c increase due to shear heating and 3 8 gpa respectively if the applied bulk shortening rate is 5 10 15 s 1 and if higher effective viscosities for the crust are applied in the model lithosphere high differential stresses 500 mpa and significant stress deviations from the lithostatic pressure 50 occur only locally and are transient the highest average effective viscosity of the model lithosphere is 2 1022 pa s which is in agreement with the estimates for the continental lithosphere a characteristic feature of the presented dynamic nappe model is a significant stress decrease and cooling within a hundred thousand to 2 million years these rates of decompression and cooling are discussed in the context of microstructural and metamorphic observations the results also show that differential stresses in mature shear zones can be several hundred mpa smaller than at the onset of shear zone formation which suggests that estimates based on microstructural analysis of rocks in ductile shear zones provide minimum values the presented model could explain the formation of coherent alpine nappes with inferred high pressure 1 5 2 5 gpa and ultrahigh pressure 3 gpa conditions in 40 60 km depth at the base of an orogenic wedge

the imprint of atmospheric evolution in the d h of hesperian clay minerals on mars the deuterium to hydrogen d h ratio in strongly bound water or hydroxyl groups in ancient martian clays retains the imprint of the water of formation of these minerals curiosity s sample analysis at mars sam experiment measured thermally evolved water and hydrogen gas released between 550 c and 950 c from samples of hesperian era gale crater smectite to determine this isotope ratio the d h value is 3 0 0 2 times the ratio in standard mean ocean water smow the d h ratio in this 3 billion year old mudstone that is half that of the present martian atmosphere but substantially higher than that expected in very early mars indicates an extended history of hydrogen escape and desiccation of the planet

the annual cycle modulation of meridional asymmetry in enso s atmospheric response and its dependence on enso zonal structure previous studies documented that a distinct southward shift of central pacific low level wind anomalies occurringduringtheensodecayingphaseiscausedbyaninteractionbetweenthewesternpacificannualcycleand el nino southern oscillation enso variability the present study finds that the meridional movement of the central pacificwindanomalies appears only duringtraditional eastern pacific el nino ep el nino eventsrather than in central pacific el nino cp el nino events in which sea surface temperature sst anomalies are confined to the central pacific the zonal structure of enso related sst anomalies therefore has an important effectonmeridionalasymmetryintheassociatedatmosphericresponseanditsmodulationbytheannualcycle in contrasttoepelninoevents thesstanomaliesofcpelninoeventsextendfartherwesttowardthewarmpool regionwithitsclimatological warmssts inthewarmpool region relativelysmallsstanomaliesarethusable to excite convection anomalies on both sides of the equator even with a meridionally asymmetric sst background state therefore almost meridionally symmetric precipitation and wind anomalies are observed over the central pacific during the decaying phase of cp el nino events the sst anomaly pattern of la nina events is similar to cp el nino events with a reversed sign accordingly no distinct southward displacement of the atmospheric response occurs over the central pacific during the la nina decaying phase these results have important implications for enso climate impacts over east asia since the anomalous low level anticyclone over the western north pacific is an integral part of the annual cycle modulated enso response

deuterium and 37 chlorine rich fluids on the surface of mars evidence from the enriched basaltic shergottite northwest africa 8657 abstract apatite a major hydrous mineral in martian meteorites has the potential to reveal history of volatiles on mars here we report the h and cl isotopic systematics of apatite from the enriched basaltic shergottite nwa 8657 to better understand the processes influencing volatiles at or near the martian sub surface the apatite in nwa 8657 has the highest reported d value up to 6509 of any phosphates in martian meteorites the positive correlation between the h2o contents 72 2251 ppm and d values 3965 6509 as well as between the cl contents 1 28 6 17 wt and 37cl values 1 7 4 0 in nwa 8657 apatite are consistent with mixing between volatiles derived from the martian mantle and meteoric water fluid the d and 37cl enrichment of apatite in nwa 8657 implies isotopic exchange with sub surficial fluids during post crystallization hydrothermal event s plain language summary mars was probably a wet and warm world during its earliest geological history supported by many lines of evidence present day mars is cold and arid although recent remote sensing data support the existence of subsurface glaciers and seasonal fluid activities at some locations in this study our aim was to use ground truth about the potential water rock interaction on or near surface environments on recent mars via measuring the h and cl isotopic compositions of apatite from a geologically young meteorite from mars the enriched basaltic shergottite nwa 8657 the petrography and mineral chemistry of apatite and other associated phases e g merrillite maskelynite mesostasis and pyroxene were documented prior to in situ h and cl isotopes analysis the water contents of apatite merrillite maskelynite mesostasis and pyroxene are positively correlated with the d values all of the datasets can be reconciled in terms of mixing between two endmembers a d poor 0 mantle reservoir and a d rich 5920 500 near surface underground water reservoir moreover apatite in nwa 8657 displays 37cl enriched 1 1 in average characteristics these signatures are consistent with d and 37cl rich fluid assisted isotopic exchange in recent near surface environment on mars

the role of reversed equatorial zonal transport in terminating an enso event abstractthis study shows the sudden basinwide reversal of anomalous equatorial zonal transport above the thermocline at the peaking phase of enso triggers rapid termination of enso events the anomalous equatorial zonal transport is controlled by the concavity of anomalous thermocline meridional structure across the equator during the developing phase of enso opposite zonal transport anomalies form in the western central and central eastern equatorial pacific respectively both are driven by the equatorial thermocline anomalies in response to zonal wind anomalies over the western central equatorial ocean at this stage the anomalous zonal transport in the east enhances enso growth through zonal sst advection in the mature phase of enso off equatorial thermocline depth anomalies become more dominant in the eastern pacific because of the reflection of equatorial signals at the eastern boundary as a result the meridional concavity of the thermocline anomalies is reversed in the east this change reve

a unified oscillator model for the el nino southern oscillation the delayed oscillator the western pacific oscillator the recharge discharge oscillator and the advective reflective oscillator have been proposed to interpret the oscillatory nature of the el nino southern oscillation enso all of these oscillator models assume a positive ocean atmosphere feedback in the equatorial eastern and central pacific the delayed oscillator assumes that the western pacific is an inactive region and wave reflection at the western boundary provides a negative feedback for the coupled system to oscillate the western pacific oscillator emphasizes an active role of the western pacific in enso the recharge discharge oscillator argues that discharge and recharge of equatorial heat content cause the coupled system to oscillate the advective reflective oscillator emphasizes the importance of zonal advection associated with wave reflection at both the western and eastern boundaries motivated by the existence of these different oscillator models a unified oscillator model is formulated and derived from the dynamics and thermodynamics of the coupled ocean atmosphere system consistent with enso anomaly patterns observed in the tropical pacific this oscillator model considers sea surface temperature anomalies in the equatorial eastern pacific zonal wind stress anomalies in both the equatorial central pacific and the equatorial western pacific and thermocline depth anomalies in the off equatorial western pacific if the western pacific wind forced response is neglected thermocline and zonal wind stress anomalies in the western pacific are decoupled from the coupled system and the unified oscillator reduces to the delayed oscillator if wave reflection at the western boundary is neglected the unified oscillator reduces to the western pacific oscillator the mathematical form of the recharge discharge oscillator can also be derived from this unified oscillator most of the physics of the advective reflective oscillator are implicitly included in the unified oscillator and the negative feedback of wave reflection at the eastern boundary is added to the unified oscillator with appropriate model parameters chosen to be consistent with those of previous oscillator models the unified oscillator model oscillates on interannual timescales

mantle convection modeling with viscoelastic brittle lithosphere numerical methodology and plate tectonic modeling the earth s tectonic plates are strong viscoelastic shells which make up the outermost part of a thermally convecting predominantly viscous layer brittle failure of the lithosphere occurs when stresses are high in order to build a realistic simulation of the planet s evolution the complete viscoelastic brittle convection system needs to be considered a particle in cell finite element method is demonstrated which can simulate very large deformation viscoelasticity with a strain dependent yield stress this is applied to a plate deformation problem numerical accuracy is demonstrated relative to analytic benchmarks and the characteristics of the method are discussed

northeast monsoon rainfall variability over the southern peninsular india associated with multiyear la nina events the present study examines the variability of northeast monsoon nem rainfall over the southern peninsular india spi associated with multiyear la nina events using observations and coupled model inter comparison project phase 5 cmip5 models the analysis is carried out for nem season october december of two successive la nina years referred to as the first and second year during the period 1900 2010 observations show that despite noticeable weakening in the equatorial pacific cooling from the first year to the second year strong la nina teleconnections and the rainfall deficiency over the spi region remains the same in most of the multiyear la nina events 70 in the first year zonally protracted low level cyclonic circulation over the north indian ocean nio region induces northwesterly wind anomalies over spi region negative moisture anomalies corroborated by northwesterlies and subsidence cause deficient rainfall over this region on the other hand the western flank of nio cyclonic circulation is pushed towards indian longitudes in the second year inducing dry northerlies over spi region development of low level divergent flow over the western tropical indian ocean and eastward migration of convergence zone from bay of bengal are found to be responsible for the shift in circulation pattern these anomalous circulations together with low moisture content are responsible for deficit nem rainfall in the second year differences in circulation patterns noted in the first and second year are associated with changes in the la nina related sst patterns over the equatorial pacific and modulation of the upper lower level convergence divergence zones analysis reveals that most of the cmip5 models have tendency to simulate excess rainfall over the spi region in 70 100 of multiyear la nina events unlike in the observations 30 of events the possible reasons for the simulation of such positive rainfall anomalies are explored in the present study

martian low temperature alteration materials in shock melt pockets in tissint constraints on their preservation in shergottite meteorites we apply an array of in situ analytical techniques including electron and raman microscopy electron and ion probe microanalysis and laser ablation mass spectrometry to the tissint martian meteorite in order to find and elucidate a geochemical signature characteristic of low temperature alteration at or near the martian surface tissint contains abundant shock produced quench crystallized melt pockets containing water in concentrations ranging from 73 to 1730 ppm water content is positively correlated with cl content the isotopic composition of hydrogen in the shock produced glass ranges from d 2559 to 4422 water is derived from two distinct hydrogen reservoirs the martian near surface 500 and the martian mantle 100 in one shock melt pocket comprising texturally homogeneous vesiculated glass the concentration of h in the shock melt decreases while simultaneously becoming enriched in d attributable to the preferential loss of h over d to the vesicle while the pocket was still molten while igneous sulfides are pyrrhotite in composition fe 0 88 0 90 s the iron to sulfur ratios of spherules in shock melt pockets are elevated up to fe 1 70 s which we attribute to shock oxidation of igneous pyrrhotite and the formation of hematite at high temperature the d and cl enrichment and higher oxidation of the pockets as indicated by hematite support a scenario in which alteration products formed within fractures or void spaces within the rock the signature of these alteration products is preserved within shock melt now glass which formed upon collapse of these fractures and voids during impact shock thermal modeling of tissint shock melt pockets using the heat program demonstrates that the shock melt pockets with the greatest potential to preserve a signature of aqueous alteration are small isolated from other regions of shock melt vesicle free and glassy

season dependent predictability and error growth dynamics for la nina predictions the spring predictability barrier spb is a well known characteristic of enso prediction which has been widely studied for el nino events however due to the nonlinearity of the coupled ocean atmosphere system and the asymmetries between el nino and la nina it is worthy to investigate the spb for la nina events and reveal their differences with el nino this study investigates the season dependent predictability of sea surface temperature sst for la nina events by exploring initial error growth in a perfect model scenario within the community earth system model the results show that for the prediction through the spring season the prediction errors caused by initial errors have a season dependent evolution and induce an spb for la nina events two types of initial errors that often yield the spb phenomenon are identified the first are type 1 initial errors showing positive sst errors in the central eastern equatorial pacific accompanied by a large positive error in the upper layers of the eastern equatorial pacific the second are type 2 errors presenting an sst pattern with positive errors in the southeastern equatorial pacific and a west east dipole pattern in the subsurface ocean the type 1 errors exhibit an evolving mode similar to the growth phase of an el nino like event while the type 2 initially experience a la nina like decay and then a transition to the growth phase of an el nino like event both types of initial errors cause positive prediction errors for nino3 sst and under predict the corresponding la nina events the resultant prediction errors of type 1 errors are owing to the growth of the initial errors in the upper layers of the eastern equatorial pacific for the type 2 errors the prediction errors originate from the initial errors in the subsurface layers of the western equatorial pacific these two regions may represent the sensitive areas of targeted observation for la nina prediction in addition the type 2 errors in the equatorial regions are enlarged by the recharge process from 10 n in the central pacific during the eastward propagation therefore the off equatorial regions around 10 n in the central pacific may represent another sensitive area of la nina prediction additional observations may be prioritized in these identified sensitive areas to better predict la nina events

oceans on mars formed early the geometry of putative ancient shorelines on mars suggests that these features were deformed by the growth of a massive volcanic region a finding that has implications for the climate geology and hydrology of early mars the geometry of putative ancient shorelines on mars suggests that these features were deformed by the growth of a massive volcanic region a finding that has implications for the climate geology and hydrology of early mars

enso prediction using an enso trigger and a proxy for western equatorial pacific warm pool movement the zonal windstress anomaly in the far western equatorial pacific 130 160 e is a precursor to el nino and la nina episodes a linear combination of this windstress with the el nino index nino3 4 can be used to predict enso successfully cross verified prediction results for nino3 4 compare favorably with those of leading enso prediction models the model is improved slightly if the time trend in sea surface temperature sst near the eastern edge of the western pacific warm pool is included in the linear combination physically this trend is related to zonal equatorial ocean flow which advects the warm pool the trend therefore aids prediction since it is a precursor to warm pool position and hence enso variability

spontaneous development of arcuate single sided subduction in global 3 d mantle convection models with a free surface we present temporally evolving 3 d global mantle convection models with single sided subduction and a free surface in both 3 d cartesian and fully spherical geometry special focus is given to the spontaneous development of three dimensional structures at the surface and in the upper mantle we find that an arcuate shape is the natural form for trenches and slabs cartesian models are used first to study the dynamic evolution of subduction zones spreading ridges and interconnected transform features these experiments highlight the strong variation of spontaneously developing arcuate slab curvature and subduction polarity along the trench strike the spontaneous development of spreading ridges leads to lateral offsets between separated segments that are characterized by normal transform motion spherical models then allow insights into the evolution of plate tectonics on a sphere investigated are the spontaneous evolution of slab geometry trench motion and subduction induced mantle flow two new dynamical features are discovered back slab spiral flow and slab tunneling

pacific east asian teleconnection part ii how the philippine sea anomalous anticyclone is established during el nino development the anomalous philippine sea anticyclone psac conveys impacts of el nino to east asian climate during the mature and decay of an el nino from the winter to ensuing summer it is shown that the anomalous psac forms in fall about one season prior to the peak el nino its strength increases with the el nino intensity and its sign reverses during a la nina the psac formation concurs with abnormal deepening of the east asian trough and with increasing number of northward recurvature of tropical storms in the western pacific the psac establishment is abrupt coupling with a swing from a wet to dry phase of an intraseasonal oscillation iso and often concurrent with early retreat of the east asian summer monsoon the iso becomes inactive after psac establishment the development of the psac is attributed to combined effects of the remote el nino forcing tropical extratropical interaction and monsoon ocean interaction the developing el nino induces off equatorial as cending rossby wave responses and land surface cooling in northeast asia both deepen the east asian trough in fall and induces vigorous tropical extratropical exchange of air mass and heat which enhances the cold air outbreak and initiation of the psac through exciting descending rossby waves the el nino induced indonesian subsidence generates low level anticyclonic vorticity over south asia which is advected by mean monsoon westerly instigating the anomalous psac the iso interacting with the underlying ocean plays a critical role in the abrupt establishment of psac the wind evaporation entrainment feedback tends to amplify suppress iso before after winter northeasterly monsoon commences suggesting the roles of atmosphere ocean inter action and the seasonal march of background winds in changing the philippine sea iso intensity and maintaining psac

canyon formation constraints on the discharge of catastrophic outburst floods of earth and mars catastrophic outburst floods carved amphitheater headed canyons on earth and mars and the steep headwalls of these canyons suggest that some formed by upstream headwall propagation through waterfall erosion processes because topography evolves in concert with water flow during canyon erosion we suggest that bedrock canyon morphology preserves hydraulic information about canyon forming floods in particular we propose that for a canyon to form with a roughly uniform width by upstream headwall retreat erosion must occur around the canyon head but not along the sidewalls such that canyon width is related to flood discharge we develop a new theory for bedrock canyon formation by megafloods based on flow convergence of large outburst floods toward a horseshoe shaped waterfall the model is developed for waterfall erosion by rock toppling a candidate erosion mechanism in well fractured rock like columnar basalt we apply the model to 14 terrestrial channeled scablands washington snake river plain idaho and asbyrgi canyon iceland and nine martian near ares vallis and echus chasma bedrock canyons and show that predicted flood discharges are nearly 3 orders of magnitude less than previously estimated and predicted flood durations are longer than previously estimated from less than a day to a few months results also show a positive correlation between flood discharge per unit width and canyon width which supports our hypothesis that canyon width is set in part by flood discharge despite lower discharges than previously estimated the flood volumes remain large enough for individual outburst floods to have perturbed the global hydrology of mars

dating martian climate change abstract geological evidence indicates that low latitude polygonally patterned grounds on mars generally thought to be the product of flood volcanism are periglacial in nature and record a complex signal of changing climate by studying the martian surface stratigraphically in terms of the geometrical relations between surface landforms and the substrate rather than genetically by form analogy with earth we have identified dynamic surfaces across one fifth of martian longitude new stratigraphical observations in the elysium amazonis plains have revealed a progressive surface polygonisation that is destructive of impact craters across the region this activity is comparable to the climatically driven degradation of periglacial landscapes on earth but because it affects impact craters the martian chronometer it can be dated here we show that it is possible to directly date this activity based on the fraction of impact craters affected by polygon formation nearly 100 of craters of all diameters are superposed by polygonal sculpture considering the few 100 ma age of the substrate this suggests that the process of polygon formation was active within the last few million years surface polygonisation in this region often considered to be one of the signs of young plains forming volcanism on mars is instead shown to postdate the majority of impact craters seen we therefore conclude that it is post depositional in origin and an artefact of thermal cycling of near surface ground ice stratigraphically controlled crater counts present the first way of dating climate change on a planet other than earth a record that may tell us something about climate change on our own planet parallel climate change on these two worlds an ice age mars coincident with earth s glacial quaternary period might suggest a coupled system linking both we have previously been unable to generalise about the causes of long term climate change based on a single terrestrial example with the beginnings of a chronology for climate change on our nearest planetary neighbour we can

impact melt hygrometer for mars the case of shergottite elephant moraine eeta 79001 we report volatile concentrations and hydrogen isotope compositions of impact melts and minerals in eeta 79001 we observed chemical changes in pyroxene maskelynite or feldspathic glass and merrillite in contact with or inside impact melts all pyroxene grains analyzed here are inside or close to impact melt pockets and contain 10 41 ppm h 2o and enriched in d d 1729 to 3707 with the highest values found in a grain enclosed in an impact melt pocket maskelynite or feldspathic glass contains 6 3 to 98 ppm h 2o with d values of 1604 to 3938 the high h 2o and d values were obtained in those enclosed inside or in contact with the impact melts whereas low h 2o content 4 ppm and terrestrial like d h value d of 90 82 were found in one maskelynite grain away from impact melts contains rims of 5 m thickness of merrillite grains next to impact melts display na depletion by 0 9 wt and the sides in contact with impact melts show mg enrichment by 0 5 wt however the h 2o and d values of merrillite interiors 39 242 ppm h 2o and d of 1682 to 3884 do not show correlation with their proximity to the impact melts rather d and 1 h 2o of merrillite form a negative trend different from that of impact melt pockets and maskelynite suggesting post crystallization or late crystallization interactions with the crustal fluids the impact melt pockets in eeta 79001 contain 121 646 ppm h 2o 4 3 13 ppm f 13 50 ppm cl 707 2702 ppm s and the d values of 3368 to 4639 the correlations between h 2o f cl p 2o 5 and d values of impact melts and feldspathic glass are consistent with mixing between a volatile rich and high d 3000 to 5000 endmember and a volatile poor and low d endmember the volatile poor and low d endmember is consistent with magmatic volatiles stored in silicates the volatile rich and high d endmember represents pre impact alteration materials by subsurface water alteration from the subsurface water equilibrated with the present day like martian atmosphere occurred after the crystallization of the rock 170 ma and before impact launch 0 7 ma our conclusion is different from the previous suggestion of an isotopically distinct subsurface water reservoir with a d value of 1000 to 2000 in eeta 79001 although heterogeneous subsurface water on mars is possible the previous study was likely biased by a limited number of analyses n 2 and possible terrestrial contamination the d value of the subsurface source in eeta 79001 is 4200 similar to those in the tissint meteorite crystallization at 600 ma impact launch at 0 7 ma and lar 06319 crystallization at 200 ma impact launch at 3 ma suggesting stable water chemistry for the subsurface environment in the last 600 myrs

mars formation and fate of a frozen hesperian ocean abstract late hesperian aged circum tharsis floods interpreted to have formed by catastrophic release of groundwater cut large channels and debouched significant quantities of water into the northern lowlands of mars the floods are thought by many to have formed an ocean of significant volume and depth encircled by contacts that have been interpreted as shorelines models of catastrophic groundwater release require a thick and continuous cryosphere with mean annual temperatures well below freezing much like those today in this environment the bodies of liquid formed by individual outflow events would have been very short lived undergoing rapid freezing we investigate the case where floods repeatedly flowed into the northern lowlands under climatic conditions that resemble those of the present day the water from each flood froze in a geologically short period of time to form an ice layer successive ice layers accumulated to form an ocean sized body of ice that filled the basin up to the 3650 contour thereby enclosing a 110 m global equivalent layer gel of water subsequent to the filling of the basin the ice slowly sublimated into the atmosphere to be lost to space or to accumulate in various surface and near surface cold traps such as the polar layered deposits where is this excess water today the presence of the thick global cryosphere meant that only minor amounts of water were lost from the surface back into the global groundwater system approximately 20 30 m gel of water is estimated to be at or near the surface today and exchanging with the atmosphere on geologic time scales this includes the polar layered deposits and deposits elsewhere at depths less than approximately 80 m below the exchangeable reservoir is a non exchangeable reservoir of unknown capacity present day loss rates to space fall far short of those needed to eliminate the mid hesperian ice ocean and those needed to cause the observed doubling of the d h of the exchangeable reservoir since the mid hesperian the discrepancy implies earlier loss rates must have been higher assuming a linear increase in loss rates because of the higher early euv output of the sun we estimate that for a present inventory of 30 m gel 42 m gel remains to be accounted for possibilities include greater dependence of losses of euv than assumed and enhanced losses during periods of high obliquity in addition large volumes of ice may be present near the surface at high latitudes outside the polar layered deposits as indicated by recent discoveries of ice layers in cliffs

interannual and interdecadal variability of ocean temperature along the equatorial pacific in conjunction with enso in this paper the leading modes of ocean temperature anomalies ota along the equatorial pacific ocean are analyzed and their connection with el nino southern oscillation enso and interdecadal variation is investigated the first two leading modes of ota are connected with the different phases of the canonical enso and display asymmetric features of enso evolution the third leading mode depicts a tripole pattern with opposite variation of ota above the thermocline in the central pacific to that along the thermocline in the eastern and western pacific this mode is found to be associated with so called enso modoki insignificant correlations of this mode with the first two leading modes suggest that enso modoki may be a mode that is independent to the canonical enso and also has longer time scales compared with the canonical enso the fourth mode reflects a warming cooling tendency above below the thermocline since 2000 both the first and second modes have a large contribution to the interdecadal change in thermocline during 1979 2012 also the analysis also documents that both enso and ota shifted into higher frequency since 2000 compared with that during 1979 1999 interestingly the enso modoki related ota mode does not have any trend or significant interdecadal shift during 1979 2012 in addition it is shown that first four eof modes seem robust before and after 1999 2000 suggesting that the interdecadal shift of the climate system in the tropical pacific is mainly a frequency shift and the changes in spatial pattern are relatively small although the mean states over two periods experienced some significant changes

wind stress curl and enso discharge recharge in the equatorial pacific discharge and recharge of the warm water volume wwv above the 20 c isotherm in an equatorial pacific ocean box extending across the pacific from 156 e to the eastern ocean boundary between latitudes 5 s and 5 n are key variables in enso dynamics a formula linking wwv anomalies zonally integrated wind stress curl anomalies along the northern and southern edges of the box and flow into the western end of the box is derived and tested using monthly data since 1993 consistent with previous work a wwv balance can only be achieved if the 20 c isotherm surface is not a material surface that is warm water can pass through it for example during el nino part of the wwv anomaly entering the box is cooled so that it is less than 20 c and therefore passes out of the bottom of the box the 20 c isotherm surface the observations suggest that the anomalous volume passing through the 20 c isotherm is approximately the same as t the anomalous wwv entering the western end of the box therefore the observed wwv anomaly can be regarded as being driven by the anomalous wind stress curl along the northern and southern edges of the box the curl anomaly changes the wwv both by divergent meridional flow at the edges of the box and vortex stretching that is the sverdrup balance does not hold in the upper ocean a typical amplitude for the rate of change of wwv for the 5 s 5 n box is 9 6 sv sv 10 6 m 3 s 1 the wind stress curl anomaly and the transport anomaly into the western end of the box are highly correlated with the el nino index nino 3 4 the average sea surface temperature anomaly ssta over the region 5 s 5 n 170 120 w and nino 3 4 leads minus the wwv anomaly by one quarter of a cycle based on the preceding results a simple discharge recharge coupled enso model is derived only water warmer than about 27 5 28 c can give rise to deep atmospheric convection so unlike past discharge recharge oscillator models the west central rather than eastern equatorial sstas are emphasized the model consists of two variables t the ssta averaged over the region of strong enso air sea interaction in the west central pacific equatorial strip 5 s 5 n 156 e 140 w and d the 20 c isotherm depth anomaly averaged over the

dielectric map of the martian northern hemisphere and the nature of plain filling materials 1 a number of observations suggest that an extended ocean once covered a significant part of the martian northern hemisphere by probing the physical properties of the subsurface to unprecedented depth the marsis mars express provides new geophysical evidences for the former existence of a late hesperian ocean the vastitas borealis formation located inside a putative shoreline of the ancient ocean has a low dielectric constant compared with that of typical volcanic materials we show that the measured value is only consistent with low density sedimentary deposits massive deposits of ground ice or a combination of the two in contrast radar observations indicate a distribution of shallow ground ice in equilibrium with the atmosphere in the south polar region we conclude that the northern plains are filled with remnants of a late hesperian ocean fed by water and sediments from the outflow channels about 3 gy ago

weakened interannual variability in the tropical pacific ocean since 2000 abstractan interdecadal shift in the variability and mean state of the tropical pacific ocean is investigated within the context of changes in el nino southern oscillation enso compared with 1979 99 the interannual variability in the tropical pacific was significantly weaker in 2000 11 and this shift can be seen by coherent changes in both the tropical atmosphere and ocean for example the equatorial thermocline tilt became steeper during 2000 11 which was consistent with positive negative sea surface temperature anomalies increased decreased precipitation and enhanced suppressed convection in the western central and eastern tropical pacific which reflected an intensification of the walker circulation the combination of a steeper thermocline slope with stronger surface trade winds is proposed to have hampered the eastward migration of the warm water along the equatorial pacific as a consequence the variability of the warm water volume was reduced and thus enso amplitude also decreased

potential impact of the tropical indian ocean indonesian seas on el nino characteristics diagnostics performed with twentieth century 1861 2000 ensemble integrations of the geophysical fluid dynamics laboratory climate model version 2 1 cm2 1 suggest that during the developing phase el nino events that co occur with the indian ocean dipole zonal mode iodzm class 1 are stronger than those without class 2 also during class 1 events coherent sea surface temperature sst anomalies develop in the indonesian seas that closely follow the life cycle of iodzm this study investigates the effect of these regional sst anomalies equatorial indian ocean and indonesian seas on the amplitude of the developing el nino an examination of class 1 minus class 2 composites suggests two conditions that could lead to a strong el nino in class 1 events i during january ocean atmosphere conditions internal to the equatorial pacific are favorable for the development of a stronger el nino and ii during may june coinciding with the development of regional sst anomalies an abrupt increase in westerly wind anomalies is noticeable over the equatorial western pacific with a subsequent increase in thermocline and sst anomalies over the eastern equatorial pacific this paper posits the hypothesis that under favorable conditions in the equatorial pacific regional sst anomalies may enable the development of a stronger el nino owing to a wealth of feedbacks in cm2 1 solutions from a linear atmosphere model forced with may june anomalous precipitation and anomalous sst from selected areas over the equatorial indo pacific are examined consistent with our earlier study the net kelvin wave response to contrasting tropical indian ocean heating anomalies cancels over the equatorial western pacific in contrast indonesian seas sst anomalies account for about 60 80 of the westerly wind anomalies over the equatorial western pacific and also induce anomalous precipitation over the equatorial central pacific it is argued that the feedback between the precipitation and circulation anomalies results in an abrupt increase in zonal wind anomalies over the equatorial western pacific encouraged by these results the authors further examined the processes that cause cold sst anomalies over the indonesian seas using an ocean model sensitivity experiments suggest that local wind anomalies through stronger surface heat loss and evaporation and subsurface upwelling are the primary causes the present results imply that in coupled models a proper representation of regional air sea interactions over the equatorial indo pacific warm pool may be important to understand and predict the amplitude of el nino

climate cycling on early mars caused by the carbonate silicate cycle abstract for decades scientists have tried to explain the evidence for fluvial activity on early mars but a consensus has yet to emerge regarding the mechanism for producing it one hypothesis suggests early mars was warmed by a thick greenhouse atmosphere another suggests that early mars was generally cold but was warmed occasionally by impacts or by episodes of enhanced volcanism these latter hypotheses struggle to produce the amounts of rainfall needed to form the martian valleys but are consistent with inferred low rates of weathering compared to earth here we provide a geophysical mechanism that could have induced cycles of glaciation and deglaciation on early mars our model produces dramatic climate cycles with extended periods of glaciation punctuated by warm periods lasting up to 10 myr much longer than those generated in other episodic warming models the cycles occur because stellar insolation was low and because co 2 outgassing is not able to keep pace with co 2 consumption by silicate weathering followed by deposition of carbonates while co 2 by itself is not able to deglaciate early mars in our model we assume that the greenhouse effect is enhanced by substantial amounts of h 2 outgassed from mars reduced crust and mantle our hypothesis can be tested by future mars exploration that better establishes the time scale for valley formation

hydrogen isotopic composition of the martian mantle inferred from the newest martian meteorite fall tissint the hydrogen isotopic composition of planetary reservoirs can provide key constraints on the origin and history of water on planets the sources of water and the hydrological evolution of mars may be inferred from the hydrogen isotopic compositions of mineral phases in martian meteorites which are currently the only samples of mars available for earth based laboratory investigations previous studies have shown that d values in minerals in the martian meteorites span a large range of 250 to 6000 the highest hydrogen isotope ratios likely represent a martian atmospheric component either interaction with a reservoir in equilibrium with the martian atmosphere such as crustal water or direct incorporation of the martian atmosphere due to shock processes the lowest d values may represent those of the martian mantle but it has also been suggested that these values may represent terrestrial contamination in martian meteorites here we report the hydrogen isotopic compositions and water contents of a variety of phases merrillites maskelynites olivines and an olivine hosted melt inclusion in tissint the latest martian meteorite fall that was minimally exposed to the terrestrial environment we compared traditional sample preparation techniques with anhydrous sample preparation methods to evaluate their effects on hydrogen isotopes and find that for severely shocked meteorites like tissint the traditional sample preparation techniques increase water content and alter the d h ratios toward more terrestrial like values in the anhydrously prepared tissint sample we see a large range of d values most likely resulting from a combination of processes including magmatic degassing secondary alteration by crustal fluids shock related fractionation and implantation of martian atmosphere based on these data our best estimate of the d value for the martian depleted mantle is 116 94 which is the lowest value measured in a phase in the anhydrously prepared section of tissint this value is similar to that of the terrestrial upper mantle suggesting that water on mars and earth was derived from similar sources the water contents of phases in tissint are highly variable and have been affected by secondary processes considering the h2o abundances reported here in the driest phases most likely representing primary igneous compositions and appropriate partition coefficients we estimate the h2o content of the tissint parent magma to be 0 2 wt

abrupt climate transition of icy worlds from snowball to moist or runaway greenhouse ongoing and future space missions aim to identify potentially habitable planets in our solar system and beyond planetary habitability is determined not only by a planet s current stellar insolation and atmospheric properties but also by the evolutionary history of its climate it has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate silicate cycle and low concentrations of greenhouse gases examples for such planetary bodies are the icy moons europa and enceladus and certain icy exoplanets orbiting g and f stars we find that the stellar fluxes that are required to overcome a planet s initial snowball state are so large that they lead to significant water loss and preclude a habitable planet specifically they exceed the moist greenhouse limit at which water vapour accumulates at high altitudes where it can readily escape or the runaway greenhouse limit at which the strength of the greenhouse increases until the oceans boil away we suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable earth like state icy planets and moons could become habitable as their host stars brighten and their ice melts climate simulations instead show a rapid transition from a snowball to an inhospitable greenhouse climate with significant water loss

why were some la ninas followed by another la nina this paper investigates why some la nina events are followed by another la nina and some others are not we propose two preconditions that result in continuation of a la nina the first one is that la nina must be a strong event a major la nina this ensures that the reflected rossby wave signal at the eastern boundary of the pacific has a strong westward propagating cold ocean temperature anomaly over the off equatorial region the off equator cold anomaly may not be conducive to the equatorial recharge process and as a result may favor the persistence of cold ocean subsurface temperature anomaly and prevent the transition from la nina to el nino the second precondition is whether there are eastward propagating downwelling kelvin waves during the decay phase of a major la nina eastward propagating downwelling kelvin waves could lead to demise for a tendency for a follow up la nina the equatorial kelvin wave activities are associated with fluctuations of surface wind in the equatorial far western pacific the analysis suggests that both the surface wind in the equatorial far western pacific and the recharge discharge of the equatorial pacific are indicators for occurrence or no occurrence of a follow up la nina event

topography and geoid induced by a convecting mantle beneath an elastic lithosphere summary in the absence of seismological measurements observations of the topography and gravity fields of solid planets are the primary constraints on their internal structure to compute the synthetic geoid and topography induced by the dynamics of planetary interiors we introduce a 3 d numerical tool describing mantle convection beneath an elastic lithosphere although the energy conservation is treated in the whole spherical domain the deformation aspect is solved using a hybrid technique finite volume method for the viscous flow spectral method for elastic deformation the mechanical coupling is achieved via the imposition of the traction at the surface of the viscous flow as a basal boundary condition for the elastic deformation we present both response functions and full thermal convection cases computed with our new method for planetary bodies of varying dimensions the filtering effect of the lithosphere on the dynamic topography and geoid is specific for each planetary body justifying the importance of such a tool furthermore since our approach specifically focuses on the mechanical coupling at the base of the lithosphere it will permit future more elaborate rheological treatments it also enables to discriminate between the radial and tangential components of the viscous traction the latter is found to have a significant influence on the elastic deformation the effect on geoid is prominent more specifically while a thin elastic lithosphere is usually considered to play little role on the dynamic topography and geoid of venus a 35 per cent reduction is obtained for geoid height in the numerical example we propose on a planet with thicker elastic lithosphere such as mars the consequence of this filtering effect is to rule out the possibility of a dynamical support for the tharsis rise even for the lowest admissible values of elastic thickness in this region

preconditions for el nino and la nina onsets and their relation to the indian ocean 1 el nino la nina onset is a challenging problem of enso prediction in this study we introduce two precursors of el nino and la nina onsets one is the equatorial heat content and the other is the western pacific wp wind when the two precursors are considered together both the el nino and la nina onsets can be highly predictable in particular the persistence of the wp wind is more important for the onset than sporadic wind events the persistent wp westerly easterly wind tends to be concurrent with the indian ocean sst cooling warming the indian ocean sst anomaly is partly correlated to an enso event during the previous winter we demonstrate that an asymmetric relation between the indian ocean sst and enso can result in asymmetric progress of onset in the opposite enso phases

towards a self consistent plate mantle model that includes elasticity simple benchmarks and application to basic modes of convection one of the difficulties with self consistent plate mantle models capturing multiple physical features such as elasticity non newtonian flow properties and temperature dependence is that the individual behaviours cannot be considered in isolation for instance if a viscous mantle convection model is generalized naively to include hypo elasticity then problems based on earth like rayleigh numbers exhibit almost insurmountable numerical stability issues due to spurious softening associated with the co rotational stress terms if a stress limiter is introduced in the form of a power law rheology or yield criterion these difficulties can be avoided in this paper a novel eulerian finite element formulation for visco elastic convection is presented and the implementation of the co rotational stress terms is addressed the salient dimensionless numbers of visco elastic plastic flows such as weissenberg deborah and bingham numbers are discussed in a separate section in the context of geodynamics we present an eulerian formulation for slow temperature dependent visco elastic plastic flows a consistent tangent incremental formulation of the governing equations is derived numerical and analytical solutions demonstrating the effect of visco elasticity co rotational terms are first discussed for simplified benchmark problems for flow around cylinders we identify parameter ranges of predominantly viscous and visco plastic and transient behavior the influence of locally high strain rates on the importance of elasticity and non newtonian effects is also discussed in this context for the case of simple shear we investigate in detail the effect of different co rotational stress rates and the effect of power law creep the results show that the effect of the co rotational terms is insignificant if realistic stress levels are considered e g deviatoric invariant smaller than 1 10 of the shear modulus say we also consider the basic convection modes of stagnant lid episodic resurfacing and mobile lid convection as applicable to a cooling planet the simulations show that elasticity does not have a significant effect on global parameters such as the nusselt number and the qualitative nature of the basic convection pattern our simple benchmarks show however also that elasticity plays a significant role for instabilities on the local scale of an individual subduction zone

effects of lithosphere on the long wavelength gravity anomalies and their implications for the formation of the tharsis rise on mars 1 the tharsis rise represents the most significant long wavelength gravity and topography anomalies on mars two competing models have been proposed to explain the origin of these anomalies in the first model the tharsis rise is attributed to loading of volcanic construction on the lithosphere while in the second model these anomalies are explained as dynamic effects of a one plume thermal structure below the tharsis rise in this study we seek to distinguish between these two models by formulating a generalized viscoelastic loading model that determines responses to loads at different depths with this new formulation we found that the instantaneous viscous flow loading formulation used to compute responses from a plume may significantly overestimate the geoid anomalies if the elastic thickness of the tharsis lithosphere is 150 km as inferred from gravity and topography data we suggest that the one plume structure if currently existing below the tharsis rise may be responsible for only a small fraction 10 of the tharsis geoid anomalies and that other processes including surface loading of volcanic construction may be the primary cause of the geoid anomalies the plume structure is inefficient in producing geoid anomalies because the long wavelength components of the plume structure are confined to a 300 km layer below the lithosphere in which the geoid response is minimal future studies on gravity and topography at different wavelengths may put constraints on possible contribution of a plume to the elevated tharsis topography

ancient geologic events on mars revealed by zircons and apatites from the martian regolith breccia nwa 7034

the dorsa argentea formation and the noachian hesperian climate transition abstract the dorsa argentea formation daf a set of geomorphologic units covering 1 5 million square kilometers in the south circumpolar region of mars has been interpreted as the remnants of a large south polar ice sheet that formed near the noachian hesperian boundary and receded in the early hesperian determining the extent and thermal regime of the daf ice sheet as well as the mechanism and timing of its recession can therefore provide insight into the ancient martian climate and the timing of the transition from a presumably thicker co2 atmosphere to the present climate we used the laboratoire de meteorologie dynamique lmd early mars global climate model gcm and the university of maine ice sheet model umism glacial flow model to constrain climates allowing development of a south polar ice sheet of daf like size and shape in addition we modeled basal melting of this ice sheet in amounts and locations consistent with observed glaciofluvial landforms a large asymmetric region of ice stability surrounding the south pole is a robust feature of gcm simulations with spin axis obliquity of 15 or 25 and a 600 1000 mb co2 atmosphere the shape results from the large scale south polar topography of mars and the strong dependence of surface temperature on altitude under a thicker atmosphere of the scenarios considered in this study the extent of the modeled daf ice sheet in umism simulations most closely matches that of the daf when the surface water ice inventory of mars is a 137 m global equivalent layer gel and spin axis obliquity is 15 in climates warmed only by co2 significant basal melting does not occur except when the ice inventory is larger than plausible estimates for early mars in this case the extent of the south polar ice sheet is also much larger than that of the daf and basal melting is more widespread than observed landforms indicate when an idealized greenhouse gas warms the surface by at least 20 c near the poles relative to co2 alone the stable extent of the ice sheet is less than that of the daf units but widespread basal melting occurs with maxima in the locations where eskers are currently observed we therefore conclude that warming by a gas other than co2 alone was necessary to enable the construction of glaciofluvial landforms in the daf previously published crater exposure ages of eskers in the daf indicate that eskers were being exposed as activity was ceasing in the equatorial valley networks suggesting that the warming that allowed basal melting at the edges of the daf ice sheet were broadly contemporaneous with those in which the valley networks were carved finally elevated tharsis topography is required to produce an ice sheet with the shape of the daf thus our results are not consistent with the daf and the valley networks forming before the emplacement of tharsis as recently suggested

modeling megathrust earthquakes across scales one way coupling from geodynamics and seismic cycles to dynamic rupture abstract taking the full complexity of subduction zones into account is important for realistic modelling and hazard assessment of subduction zone seismicity and associated tsunamis studying seismicity requires numerical methods that span a large range of spatial and temporal scales we present the first coupled framework that resolves subduction dynamics over millions of years and earthquake dynamics down to fractions of a second using a two dimensional geodynamic seismic cycle sc method we model 4 million years of subduction followed by cycles of spontaneous megathrust events at the initiation of one such sc event we export the self consistent fault and surface geometry fault stress and strength and heterogeneous material properties to a dynamic rupture dr model coupling leads to spontaneous dynamic rupture nucleation propagation and arrest with the same spatial characteristics as in the sc model it also results in a similar material dependent stress drop although dynamic slip is significantly larger the dr event shows a high degree of complexity featuring various rupture styles and speeds precursory phases and fault reactivation compared to a coupled model with homogeneous material properties accounting for realistic lithological contrasts doubles the amount of maximum slip introduces local pulse like rupture episodes and relocates the peak slip from near the downdip limit of the seismogenic zone to the updip limit when an sc splay fault is included in the dr model the rupture prefers the splay over the shallow megathrust although wave reflections do activate the megathrust afterwards

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

asymmetry in summertime atmospheric circulation anomalies over the northwest pacific during decaying phase of el nino and la nina the present study has revealed the asymmetric characteristics of summertime atmospheric circulation anomalies over the indo pacific for el nino and la nina as well as the possible mechanism during the summer when el nino has dissipated there are basin wide warming over the tropical indian ocean tio and cooling over the equatorial central and eastern pacific cep the northwest pacific nwp anticyclone is maintained by a combined effect of the tio warming and equatorial cep cooling the impact of tio warming is via the kelvin wave induced divergence mechanism and the effect of cep cooling is by stimulating a rossby wave response to its northwest correspondingly there are lower upper level convergence divergence over the tio and divergence convergence over the nwp the tropical atmospheric waves and large scale circulation anomalies could couple together and maintain the anticyclone however for la nina there are easterly wind anomalies over the equatorial western pacific and the anomalous nwp cyclone nwpc is weak and shifts northwestward which are largely different from el nino the equatorial cep cooling plays a dominant role in the maintenance of nwpc the negative rainfall anomalies induced by cep cooling force the anticyclonic wind anomalies over the wp as a rossby wave response which further cause the lower upper level convergence divergence over the mc and nwp the resultant convergence leads to the enhanced convection there inducing the nwpc as a rossby wave response besides the equatorial easterly wind anomalies trigger the upwelling oceanic kelvin wave and maintain the cep cooling as the bjerknes feedback

fluids during diagenesis and sulfate vein formation in sediments at gale crater mars we model the fluids involved in the alteration processes recorded in the sheepbed member mudstones of yellowknife bay ykb gale crater mars as revealed by the mars science laboratory curiosity rover investigations we compare the gale crater waters with fluids modeled for shergottites nakhlites and the ancient meteorite alh 84001 as well as rocks analyzed by the mars exploration rovers and with terrestrial ground and surface waters the aqueous solution present during sediment alteration associated with phyllosilicate formation at gale was high in na k and si had low mg fe and al concentrations relative to terrestrial groundwaters such as the deccan traps and other modeled mars fluids and had near neutral to alkaline ph ca and s species were present in the 10 3 to 10 2 concentration range a fluid local to gale crater strata produced the alteration products observed by curiosity and subsequent evaporation of this groundwater type fluid formed impure sulfate and silica rich deposits veins or horizons in a second separate stage of alteration partial dissolution of this sulfate rich layer in yellowknife bay or beyond led to the pure sulfate veins observed in ykb this scenario is analogous to similar processes identified at a terrestrial site in triassic sediments with gypsum veins of the mercia mudstone group in watchet bay uk

origins of biases in cmip5 models simulating northwest pacific summertime atmospheric circulation anomalies during the decaying phase of enso abstractpresent study documents the biases of summertime northwest pacific nwp atmospheric circulation anomalies during the decaying phase of enso and investigates their plausible reasons in 32 coupled model intercomparison project phase 5 models based on an inter model empirical orthogonal function eof analysis of el nino southern oscillation enso related 850hpa wind anomalies the dominant modes of biases are extracted the first eof mode explaining 21 3 of total inter model variance is characterized by a cyclone over the nwp indicating a weaker nwp anticyclone the cyclone appears to be a rossby wave response to unrealistic equatorial western pacific wp sea surface temperature sst anomalies related to excessive equatorial pacific cold tongue in the models on one hand the cold sst biases increase the mean zonal sst gradient which further intensifies warm zonal advection favoring the development and persistence of equatorial wp sst anomalies on the other hand they reduce the anomalou

tracing martian surface interactions with the triple o isotope compositions of meteoritic phosphates abstract the triple oxygen isotope compositions of phosphate grains in six martian meteorites have been measured by secondary ion mass spectrometry sims and combined together with their chlorine isotope and halogen concentrations have been used to constrain hydrosphere lithosphere interactions on mars these samples include three enriched shergottites zagami roberts massif 04262 and larkman nunatak 12011 one depleted shergottite tissint an orthopyroxenite allan hills 84001 and a regolith breccia northwest africa 7533 the phosphates measured here have a range in 18 o 18o 16o sample 18o 16o standard 1 103 from 1 0 to 6 8 and could be a result of indigenous mantle values mixing with martian water or replacement reactions taking place on the surface of mars three samples have a 17 o 17 o 1000 1 18 o 1000 0 528 1 in equilibrium with the martian mantle alh 84001 tissint and zagami while three samples lar 12011 rbt 04262 and nwa 7533 have an elevated positive 17 o outside of analytical uncertainty of the martian fractionation line mfl the phosphates in the latter group also have positive and negative 37 cl 37cl 35cl sample 37cl 35cl standard 1 103 and enrichments in halogens not seen in the rest of the sample suite perchlorate formation on earth fractionates cl in both positive and negative directions and generates a correlated positive 17 o further perchlorate has been detected in wt amounts on the martian surface thus these results strongly suggest the presence of multiple cl isotope reservoirs on the martian surface that have interacted with the samples studied here over the last ca 2 ga of geologic time the weighted average of 17 o measurements from phosphate grains n 13 in nwa 7533 which are the explicit result of exchange reactions on the martian surface yields a statistically robust mean value of 1 39 0 19 2 mswd 1 5 p 0 13 this value likely represents an accurate estimate for an oxidized surface reservoir on mars

an inversion of gravity and topography for mantle and crustal structure on mars analysis of the gravity and topography of mars presently provides our primary quantitative constraints on the internal structure of mars we present an inversion of the long wavelength harmonic degree 10 gravity and topography of mars for lateral variations of mantle temperature and crustal thickness our formulation incorporates both viscous mantle flow which most prior studies have neglected and isostatically compensated density anomalies in the crust and lithosphere our nominal model has a 150 km thick high viscosity surface layer over an isoviscous mantle with a core radius of 1840 km it predicts lateral temperature variations of up to a few hundred degrees kelvin relative to the mean mantle temperature with high temperature under tharsis and to a lesser extent under elysium and cool temperatures elsewhere surprisingly the model predicts crustal thinning beneath tharsis if correct this implies that thinning of the crust by mantle shear stresses dominates over thickening of the crust by volcanism the major impact basins hellas argyre isidis chryse and utopia are regions of crustal thinning as expected utopia is also predicted to be a region of hot mantle which is hard to reconcile with the surface geology an alternative model for utopia treats it as a mascon basin the utopia gravity anomaly is consistent with the presence of a 1 2 to 1 6 km thick layer of uncompensated basalt in good agreement with geologic arguments about the amount of volcanic fill in this area the mantle thermal structure is the dominant contributor to the observed geoid in our inversion the mantle also dominates the topography at the longest wavelengths but shorter wavelengths harmonic degrees 4 are dominated by the crustal structure because of the uncertainty about the appropriate numerical values for some of the model s input parameters we have examined the sensitivity of the model results to the planetary structural model core radius and core and mantle densities the mantle s viscosity stratification and the mean crustal thickness the model results are insensitive to the specific thickness or viscosity contrast of the high viscosity surface layer and to the mean crustal thickness in the range 25 to 100 km models with a large core radius or with an upper mantle low viscosity zone require implausibly large lateral variations in mantle temperature

asymmetric evolution of el nino and la nina the recharge discharge processes and role of the off equatorial sea surface height anomaly observed oceanic and atmospheric anomalies in the tropical pacific are analyzed to understand the symmetric and asymmetric characteristics between el nino and la nina evolutions it is noted that the evolutions are largely symmetric for el nino and la nina prior to and in their mature phase but become asymmetric afterwards it is further demonstrated that this asymmetry is due to the fact that on average the discharge process associated with el nino is stronger than the recharge counterpart associated with la nina the symmetric and asymmetric evolution for different phases of el nino southern oscillation enso is consistent with the associated recharge and discharge processes that are linked with the evolution of anomalous ocean surface current and gradient of sea surface height anomalies sshas it is suggested that the evolution of the meridional gradient of sshas in the central and eastern equatorial pacific is different between el nino and la nina years due to relatively different rates of the ssha changes on and off the equator during the decay of a warm event the equatorial ssha quickly switches from positive to negative meanwhile the off equator areas are occupied by positive sshas such changes on the equator and in the off equatorial regions make the concavity of the meridional ssha favorable for growth and persistence of westward surface zonal current anomaly in the equatorial pacific then for the enso phase transition during the decay of a cold event the slow decrease of the negative ssha on the equator combined with the disappearance of the negative ssha in the off equatorial regions makes the meridional concavity reverse easily and is unfavorable for the steady growth of the eastward surface zonal current anomaly and for the phase transition thus the asymmetric evolution of enso is associated with both the atmosphere and ocean anomalies on the equator and off the equator