gullies and landslides on the moon evidence for dry granular flows 1 high resolution images from chandrayaan 1 terrain mapping camera and lunar reconnaissance orbiter camera reveal landslides and gully formation on the interior wall of a 7 km diameter simple crater emplaced in schrodinger basin on the farside of the moon these features occur on the steep upper crater wall where the slope is 35 the gullies show a typical alcove channel fan morphology some gullies incise bedrock where impact related faults are present slope failure along the concentric faults also led to formation of landslides dark slope streaks are abundant at the bright gully regions especially near the fan and channel deposits spectral characteristics inferred from data obtained by hyperspectral imager and moon mineralogy mapper on board chandrayaan 1 show that the gullies and landslides are characterized by high optical immaturity and devoid of prominent spectral absorption features related to water or hydroxyl molecules suggesting youthful dry granular flows mass movements on the crater wall led to the formation of arcuate ridges and ponding of fine grained sediments on the crater floor runout flows from small impact craters on the slopes indicate that impact induced seismic shaking was responsible for the downslope mass movements crater size frequency distributions suggest a minimum age of 18 2 ma for the gullies and 2 ma for the landslides while age of the host crater ejecta was inferred to be about 175 ma the gullies and landslides also occur on the interior wall of other impact craters elsewhere on the moon and probably formed by similar processes

the unique geomorphology and physical properties of the vestalia terra plateau abstract we produced a geologic map of the av 9 numisia quadrangle of asteroid vesta using dawn spacecraft data to serve as a tool to understand the geologic relations of surface features in this region these features include the plateau vestalia terra a hill named brumalia tholus and an unusual dark ribbon material crossing the majority of the map area stratigraphic relations suggest that vestalia terra is one of the oldest features on vesta despite a model crater age date similar to that of much of the surface of the asteroid cornelia numisia and drusilla craters reveal bright and dark material in their walls and both cornelia and numisia have smooth and pitted terrains on their floors suggestive of the release of volatiles during or shortly after the impacts that formed these craters cornelia fabia and teia craters have extensive bright ejecta lobes while diogenitic material has been identified in association with the bright teia and fabia ejecta hydroxyl has been detected in the dark material within cornelia numisia and drusilla three large pit crater chains appear in the map area with an orientation similar to the equatorial troughs that cut the majority of vesta analysis of these features has led to several interpretations of the geological history of the region vestalia terra appears to be mechanically stronger than the rest of vesta brumalia tholus may be the surface representation of a dike fed laccolith the dark ribbon feature is proposed to represent a long runout ejecta flow from drusilla crater

planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

shock effects in plagioclase feldspar from the mistastin lake impact structure canada shock metamorphism caused by hypervelocity impact is a poorly understood process in feldspar due to the complexity of the crystal structure the relative ease of weathering and chemical variations making optical studies of shocked feldspars challenging understanding shock metamorphism in feldspars and plagioclase in particular is vital for understanding the history of earth s moon mars and many other planetary bodies we present here a comprehensive study of shock effects in andesine and labradorite from the mistastin lake impact structure labrador canada samples from a range of different settings were studied from in situ central uplift materials to clasts from various breccias and impact melt rocks evidence of shock metamorphism includes undulose extinction offset twins kinked twins alternate twin deformation and partial to complete transformation to diaplectic plagioclase glass in some cases isotropization of alternating twin lamellae was observed planar deformation features pdfs are notably absent in the plagioclase even when present in neighboring quartz grains it is notable that various microlites twin planes and compositionally different lamellae could easily be mistaken for pdfs and so care must be taken a pseudomorphous zeolite phase levyne ca was identified as a replacement mineral of diaplectic feldspar glass in some samples which could in some instances also be potentially mistaken for pdfs we suggest that the lack of pdfs in plagioclase could be due to a combination of structural controls relating to the crystal structure of different feldspars and or the presence of existing planes of weakness in the form of twin and cleavage planes

erosional modification and gully formation at meteor crater arizona insights into crater degradation processes on mars hydrogeological modification of meteor crater produced a spectacular set of gullies throughout the interior wall in response to rainwater precipitation snow melting and possible groundwater discharge the crater wall has an exceptionally well developed centripetal drainage pattern consisting of individual alcoves channels and fans some of the gullies originate from the rim crest and others from the middle crater wall where a lithologic transition occurs broad gullies occur along the crater corner radial faults deeply incised alcoves are well developed on the soft coconino sandstone exposed on the middle crater wall beneath overlying dolomite in general the gully locations are along crater wall radial fractures and faults which are favorable locales of erosion due to preferential rock breakup from faulting and groundwater flow discharge these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow causing erosion and crater degradation channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor caves exposed on the lower crater level point to percolation of surface runoff and selective discharge through fractures on the crater wall in addition lake sediments on the crater floor provide significant evidence of a past pluvial climate when the water table was higher and groundwater may have seeped from springs on the crater wall although these hydrological processes continue at meteor crater today conditions at the crater are much more arid than they were soon after impact reflecting a climatic shift this climate shift and the hydrological modifications observed at meteor crater provide insights for landscape sculpturing on mars during various parts of its history

on the average absolute transport of the deep western boundary currents east of abaco island the bahamas abstract data obtained from a line of absolute current profiler pegasus and ctd stations at 26 5 n east of abaco island in the northern bahamas are used to estimate the average transport and overall level of variability of the deep below 800 m southward flow associated with the so called deep western boundary current dwbc at this latitude from april 1985 to september 1987 a total of 11 sections were made along a line extending from near the island boundary to 85 km offshore as part of the subtropical atlantic climate studies stacs program in all but two cases when pegasus data were obtained over the total depth absolute velocities were determined from 0 to about 3000 db while ctd derived relative velocities were determined over the total depth using the combined datasets it is possible to reference the relative geostrophic velocity with pegasus data thereby obtaining an estimate of the absolute southward transport of the deep flow the average value of transport determined in this man

how old are young lunar craters 1 the accurate definition of the lunar cratering chronology is important for deriving absolute model ages across the lunar surface and throughout the solar system images from the lunar reconnaissance orbiter narrow angle cameras and wide angle camera and the selene kaguya terrain camera provide new opportunities to investigate crater size frequency distributions csfds on individual geological units at lunar impact craters we report new csfd measurements for the copernican aged craters north ray tycho and copernicus which are crucial anchor points for the lunar cratering chronology we also discuss possible reasons for an age discrepancy observed between the impact melt and ejecta units our csfds for north ray and tycho crater ejecta deposits are consistent with earlier measurements however for copernicus crater and one of its rays we find significantly lower cumulative crater frequencies than previous studies our new results for copernicus crater fit the existing lunar absolute chronologies significantly better than the previous counts our derived model ages of the ejecta blankets of north ray tycho and copernicus agree well with radiometric and exposure ages of the apollo 16 17 and 12 landing sites respectively and are generally consistent with a constant impact rate over the last 3 ga however small variations of the impact rate cannot be resolved in our data and require further investigations

spectral and photogeologic mapping of schrodinger basin and implications for post south pole aitken impact deep subsurface stratigraphy abstract schrodinger basin provides a window into the stratigraphy of the lunar crust adjacent to the south pole aitken basin region that we have probed with lunar reconnaissance orbiter moon mineralogy mapper m 3 and crater scaling relationships the composition of materials that make up the basin wall impact melt and peak ring provide a cross section of the lunar crust which reveals products of the lunar magma ocean subsequent magmatism and reworking of those components into a megaregolith large hectometer to kilometer size areas of anorthite rich material anorthosite low ca pyroxene material a noritic unit and olivine rich material troctolite or dunite are exposed with a few areas of intermediate composition the schrodinger impact excavated 20 km into an orthopyroxene plagioclase noritic lunar crust which is exposed in the basin walls rim and proximal ejecta and dominates the composition of materials that make up the basin floor substantially later in lunar history two spatially and chronologically isolated volcanic eruptions occurred on the basin floor two large craters east of schrodinger excavated a compositionally gabbroic subsurface unit that was not tapped by schrodinger this indicates a compositional crustal facies change which may be from spa ejecta but could reflect heterogeneity in the original lunar crust

origin of a unique impact melt rock the l chondrite ramsdorf we have studied a unique impact melt rock the ramsdorf l chondrite using optical and scanning microscopy and electron microprobe analysis ramsdorf contains not only clast poor impact melt begemann and wlotzka 1969 but also a chondritic portion 60 g with what appears at low magnification to be a normal well defined chondritic texture however detailed studies at high magnification show that 90 vol of the crystals in the chondritic portion were largely melted by the impact the chondrules lack normal microtextures and are ghosts of the original features the only relics from the precursor chondrules are olivine crystals which have the highest melting temperature 1620 c pyroxene rich chondrules were so extensively melted that no phenocrysts were preserved and the melt crystallized in situ before significant mixing with exterior olivine rich melts fine grained pyroxene chondrule ghosts have sharper boundaries with the matrix than porphyritic olivine and pyroxene chondrule ghosts probably because pyroxene rich melts are significantly more viscous complex textures that formed by injection of melt along cracks and fractures in relic olivines suggest that the chondritic portion of ramsdorf formed directly from petrologic type 3 4 material by strong shock we infer that ramsdorf was largely melted by shock pressures of 75 90 gpa and that chondrule ghosts and relic olivine phenocrysts were locally preserved by rapid cooling quenching was not due to the addition of cold clasts into the melt but to heterogeneous shock heating that only caused internal melting of large olivines and pyroxenes ramsdorf appears to be one of the most heavily shocked meteorites that has retained some trace of its original texture

preferred orientation distribution of shock induced planar microstructures in quartz and feldspar shocked quartz and feldspar grains commonly exhibit planar microstructures such as planar fractures planar deformation features and possibly microtwins which are considered to have formed by shock metamorphism their orientation and frequency are typically reported to be randomly distributed across a sample the goal of this study is to investigate whether such microstructures are completely random within a given sample or whether their orientation might also retain information on the direction of the local shock wave propagation for this work we selected samples of shatter cones which were cut normal to the striated surface and the striation direction from three impact structures keurusselka finland and charlevoix and manicouagan canada these samples show different stages of pre impact tectonic deformation additionally we investigated several shocked granite samples selected at different depths along the drill core recovered during the joint iodp icdp chicxulub expedition 364 mexico in this case thin sections were cut along two orthogonal directions one parallel and one normal to the drill core axis all the results refer to optical microscopy and universal stage analyses performed on petrographic thin sections our results show that such shock related microstructures do have a preferred orientation but also that relating their orientation with the possible shock wave propagation is quite challenging and potentially impossible this is largely due to the lack of dedicated experiments to provide a key to interpret the observed preferred orientation and to the lack of information on postimpact orientation modifications especially in the case of the drill core samples

introduction to atlantic meridional overturning circulation amoc a striking conclusion of the intergovernmental panel on climate change 2007 report is the crucial role that the atlantic meridional overturning circulation amoc may play in anthropogenic climate change however these ipcc coupled climate simulations show a broad range of uncertainty in the magnitude and timing of amoc transport change ranging from none to nearly complete collapse within the 21st century the potential consequences of large changes in the characteristics of amoc have motivated the creation in the united states of an interagency program and implementation plan to develop monitoring and prediction capabilities for the amoc this program parallels the development of substantial monitoring efforts by european south american and african countries notably the uk rapid and rapid watch programs the papers contained in this volume are derived from presentations at the first u s atlantic meridional overturning circulation amoc meeting held 4 6 may 2009 to review the us implementation plan and its coordination with other monitoring activities the atlantic meridional overturning circulation consists of multiple components illustrated in an attached figure water enters the south atlantic at upper and intermediate depths through both western and eastern routes where eddy transport is especially important and is transported northward across the equator where it recirculates within the northern subtropical and subpolar gyres the northern end is defined by the sinking regions of the nordic seas and the labrador sea where the waters that eventually form the upper and lower branches of north atlantic deep water are conditioned high surface salinities the result of high net evaporation in the tropics and subtropics including the mediterranean sea and presence of regions of the arctic ocean that remain ice free even in winter allow for the rapid cooling and thus densification of surface water this dense surface water becomes the source of deep water formation in the sinking regions in addition to transporting mass the amoc transports roughly half of the total amount of heat carried northward through the northern subtropics down the temperature gradient by the ocean in contrast in the southern hemisphere amoc transports heat up gradient from the cool circumpolar current to the warm tropics paleoevidence suggests that amoc heat transport in the two hemispheres has varied over time in ways intimately tied to millennial changes in the earth s climate in one example the abrupt younger dryas spell of cold weather over the north atlantic which began 13 000 years ago has generally been linked to a millennial shutdown of the amoc as a result of massive freshwater discharge from the north american continent the current amoc monitoring array consists of a series of instrumented transects located across key passages see cunningham et al 2010 for a recent review in the arctic and sub arctic transects cross fram strait denmark strait and the faroe channel connecting greenland iceland and the united kingdom as well as the entrance to the labrador sea further south and extending outwards from the east coast of north america there are a series of monitoring arrays including arrays of the canadian atlantic zone monitoring program deployments of the rapid western atlantic variability experiment wave line w at 39 n as well as the rapid moc moored array the latter spans the entire atlantic basin along 26 5 n at tropical latitudes we have the meridional overturning variability experiment move array at 16 n while in the southern hemisphere a corresponding basin spanning transect is being established at the latitude of cape of good hope complemented by arrays at drake passage

moored observations of western boundary current variability and thermohaline circulation at 26 5 n in the subtropical north atlantic abstract a 5 8 year time series of moored current meter observations is used with hydrographic section data cme model results and gridded wind fields over the north atlantic to describe the mean structure and variability of circulation and volume transports east of abaco bahamas at 26 5 n a mean antilles current with 5 sv of northward transport is confined against the bahamas boundary in the upper 800 m and combines with approximately 19 sv of florida current transport to balance the sverdrup interior circulation and does not contribute to interhemispheric exchange the mean transport of the deep western boundary current dwbc off the bahamas is approximately 40 sv of which 13 sv compensates the upper branch of the thermohaline circulation requiring a 27 sv deep recirculation robust annual and semiannual cycles of meridional are found in both moored observations and model results with remarkable agreement in amplitude 13 sv and phase maximum northward transports occur in winter and summer

the first description and confirmation of the vista alegre impact structure in the parana flood basalts of southern brazil abstract the vista alegre structure centered at 25 57 s and 52 41 w has been recently proposed as a meteorite impact structure the 9 5 km diameter structure is located in the parana state of southern brazil within the parana basin which contains one of the largest and most extensive flood basalt provinces on earth the parana flood basalts belong to the serra geral formation and are temporally related to the opening of the south atlantic ocean having been dated at about 133 132 ma tholeiitic basalts dominate the western portion of parana state with some minor rhyodacites morphologically vista alegre has a prominent circular outline in the form of an incomplete ring of escarpments and an inner depression the presence of a central uplift is not obvious but it is inferred by the occurrence of deformed sandstone blocks near the center of the structure these sandstones are possibly related to the triassic piramboia formation and or to the cretaceous botucatu formation these units are normally at stratigraphic depths of about 700 800 m below the present surface in this portion of the parana basin the structure appears to be in an advanced erosion stage and its interior is occupied by a soil cover several meters thick extensively used for agriculture as a result there are limited outcrops in the interior of the structure all of polymict breccias some of them melt bearing we report the extensive occurrence of shatter cones in the form of fine grained rock clasts within the polymict breccias the shatter cone bearing breccias occur at different locations within the structure separated by several kilometers the nested shatter cones range in size from about 0 5 to 20 cm for individual cones and up to half a meter for complete assemblages the shatter cones formed in fine grained parana flood basalt and might be the first examples of shatter cones in such a rock type in addition planar deformation features pdfs were found in quartz grains within sedimentary rock clasts of the polymict breccia these findings confirm the impact origin of the vista alegre structure

a novel topographic parameterization scheme indicates that martian gullies display the signature of liquid water martian gullies resemble gullies carved by water on earth yet are thought to have formed in an extremely cold 50 c and dry humidity 100 precipitable micrometers surface environment cf mellon et al 2004 despite more than a decade of observations no consensus has emerged as to whether liquid water is required to form martian gullies with some recent studies favouring dry co2 driven processes that this argument persists demonstrates the limitations of morphological interpretations made from 2d images especially when similar looking landforms can form by very different processes to overcome this we have devised a parameterization scheme based on statistical discriminant analysis and hydrological terrain analysis of meter scale digital topography data which can distinguish between dry and wet surface processes acting on a landscape applying this approach to new meter scale topographic datasets of earth the moon and mars we demonstrate that martian gullied slopes are dissimilar to dry gullied slopes on earth and the moon but are similar to both terrestrial debris flows and fluvial gullies we conclude that liquid water was integral to the process by which martian gullies formed finally our work shows that quantitative 3d analyses of landscape have great potential as a tool in planetary science enabling remote assessment of processes acting on planetary surfaces

long term monitoring of martian gully formation and evolution with mro hirise abstract gully landforms are commonly taken as evidence for surface liquid water in the recent geological history of mars repeat observations with the high resolution imaging science experiment hirise instrument on the mars reconnaissance orbiter demonstrate widespread activity in gullies in the southern hemisphere particularly in those with the freshest morphologies this activity includes substantial channel incision and large scale mass movements and constitutes ongoing gully formation rather than degradation of older landforms new apron deposits that are bright dark and neutrally toned have all been observed the timing of gully activity is seasonally controlled and occurs during the period when seasonal frost is present and defrosting these observations support a model in which currently active gully formation is driven mainly by seasonal co 2 frost gullies in the northern hemisphere are far less active than those in the south this may be due to the current timing of perihelion near the northern winter solstice integrated over time activity like that observed within the past few years appears capable of forming all of the martian gully landforms on timescales of millions of years additionally the current style and rate of activity is able to erase meter to decameter scale surface features that might have been uniquely produced by other processes during the last obliquity high 0 4 ma although it is impossible to rule out a past role for water in the formation of martian gullies a model in which gullies form only through currently active processes with little or no liquid water is consistent with our observations

atlantic ocean baroclinic heat flux at 24 to 26 n the spatially varying interior geostrophic baroclinic heat flux component of the total meridional oceanic heat flux near 24 n in the atlantic ocean is examined using four transatlantic hydrographic sections including the october 1957 discovery ii igy section the september 1981 atlantis section the august 1992 hesperides section the february 1998 ronald h brown section and the 1982 levitus and the lozier owens curry climatologies the 1992 section is complemented by shorter western boundary sections obtained concurrently during the trident cruise we find an average southward baroclinic heat flux of 0 9 0 3 pw with an annual cycle amplitude of 0 3 pw more than 90 of the annual cycle is captured within 30 of the western boundary

testing the water hypothesis quantitative morphological analysis of terrestrial and martian mid latitude gullies abstract although martian gullies resemble terrestrial counterparts two conflicting hypotheses exist for their formation still invoke fluvial processes on the one hand or lubricated co 2 flows on the other in this work we compared the quantitative morphology of terrestrial gullies known to have formed by liquid water and mid latitude martian gullies in the martian southern hemisphere we also compared these results with measurements of martian dry ravines adjacent to the gullies our results show a similarity between martian and terrestrial gully formation supporting the hypothesis that liquid water was involved in their erosion our results show dry ravines differ morphologically from gullies further suggesting fluidised flows as a likely origin of the latter variations in the relationships across various terrestrial and martian gullies indicate the significance of local environmental and geological conditions our work supports the idea that martian gullies may not have been formed by just one single process but may have evolved through a more complex interaction of processes and environment

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

temperature and salinity variability in the deep western boundary current abstract a ten year time series 1984 1993 of repeat hydrographic sections from offshore abaco island the bahamas 26 5 n is used to define the mean and time dependent characteristics of the deep western boundary current dwbc the dwbc flow is divided into four vertical layers based on chlorofluorocarbon cfc concentration and formation regions upper layer cfc core 3 9 5 0 c second layer classical labrador sea water 3 2 3 9 c third layer cfc minimum 2 4 3 2 c deepest layer cfc core 1 85 2 4 c time series analysis of mean layer properties and their anomalies showed that the temperature and salinity of each layer did not increase or decrease monotonically with time variations in temperature and salinity were characterized by 2 3 yr period oscillations variability between years is illustrated by subtracting repeat sections of temperature and salinity along levels of both constant pressure and constant potential density to determine an original water mass modificati

recent shallow moonquake and impact triggered boulder falls on the moon new insights from the schrodinger basin shallow moonquakes are thought to be of tectonic origin however the geologic structures responsible for these moonquakes are unknown here we report sites where moonquakes possibly occurred along young lobate scarps in the schrodinger basin our analysis of lunar reconnaissance orbiter and chandrayaan 1 images revealed four lobate scarps in different parts of the schrodinger basin the scarps crosscut small fresh impact craters 1500 boulders associated with trails and bouncing marks their origins are largely controlled by recent impact events ejecta rays and secondary crater chains from a 14 km diameter impact crater traversed schrodinger and triggered significant boulder falls about 17 ma therefore a combination of recent shallow moonquakes and impact events triggered the boulder falls in the schrodinger basin

decadal changes in water mass characteristics at 24 n in the subtropical north atlantic ocean abstract three transatlantic hydrographic sections across 24 n through the center of the subtropical gyre are analyzed for evidence of decadal changes in water mass characteristics in the main thermocline there has been a steady increase in salinity from 1957 to 1981 to 1992 the salinity at a given potential temperature between 12 c and 17 c has increased at a nearly constant rate of 0 010 per decade at constant potential density salinity and temperature both increased at rates of 0 018 per decade and 0 065 c per decade in the intermediate waters between 800 and 1500 dbar salinity has increased as well on average by as much as 0 025 from 1981 to 1992 either on constant potential temperature or constant density surfaces these changes cannot be due to vertical heaving of a constant water mass structure and they cannot be easily explained in terms of horizontal shifts in the subtropical gyre water mass structure throughout the water column down to 2000 dbar and across the zonal extent of the 24 n

flow through discovery gap abstract a narrow gap discovery gap in the east azores fracture zone at 37 n in the eastern atlantic provides a channel for the exchange of bottom water between the madeira and iberian abyssal basins a detailed survey defines its length 150 km width 10 50 km depth of sills near 4800 m and sediment thickness 0 500 m year long measurements of deep flow are made from six moorings and ten current meters mean flows are about 5 cm s 1 these data are supplemented by 10 days of float tracking near 4700 m and numerous density profiles within and around the gap a persistent southwest northeast flow of dense water is found in discovery gap and the flux of water colder than a potential temperature of 2 05 c is measured to be 0 21 04 106 m3 s 1 this discharge spreads over an area of about 1011 m2 beyond the gap exit where it is warmed both by geothermal heating and by mixing with overlying water an estimate of 1 5 to 4 cm2 s 1 is derived for the diapycnal diffusivity similar to values dete

historical variability in atlantic meridional baroclinic transport at 26 5 n from boundary dynamic height observations the strength of the atlantic meridional overturning circulation moc at 26 5 n may be inferred from the combination of florida straits transport derived from cable measurements ekman transport estimated from wind stress climatologies and mid ocean geostrophic shear traditionally obtained from hydrographic sections with application of mass balance to the section to yield the mid ocean barotropic flow the recent rapid monitoring project has provided time series information for the mid ocean geostrophic shear since 2004 this work presents methods to assemble a comparable dataset from ctd end stations and boundary mooring temperature and pressure time series to estimate the past variability from 1980 to 2005 variability in the end station derived transport anomalies suggests that the moc has fluctuated by more than 10 sv encompassing all moc estimates reported in the literature interannual changes in moc transport are masked by this variability and calculated trends in layer transports are not statistically significant more extensive datasets of ctd casts and moored temperature records at the western boundary do show significant changes with warming in the thermocline and long term freshening of the deep waters between the 1980s and 2005 these changes are associated with stronger southward flow in the upper waters and weaker southward flow in the deep waters and suggest a decrease in the moc strength of 2 4 sv any such decrease however is masked by the scale of variability in layer transports derived from the historical database of ctd end stations

ancient multiring basins on the moon revealed by clementine laser altimetry analysis of laser altimetry data from clementine has confirmed and extended our knowledge of nearly obliterated multiring basins on the moon these basins were formed during the early bombardment phase of lunar history have been filled to varying degrees by mare lavas and regional ejecta blankets and have been degraded by the superposition of large impact craters the mendel rydberg basin a degraded three ring feature over 600 kilometers in diameter on the lunar western limb is about 6 kilometers deep from rim to floor only slightly less deep than the nearby younger and much better preserved orientale basin 8 kilometers deep the south pole aitken basin the oldest discernible impact feature on the moon is revealed as a basin 2500 kilometers in diameter with an average depth of more than 13 kilometers rim crest to floor this feature is the largest deepest impact crater yet discovered in the solar system several additional depressions seen in the data may represent previously unmapped ancient impact basins

the mean circulation east of the bahamas as determined from a recent measurement program and historical xbt data abstract observational evidence from a two ship synoptic survey from one year long current measurements at four sites and from two independent long term expendable baththermograph xbt data sets is combined to describe the circulation east of the bahamas the results indicate that a weak antilles current actually exists at mid depths about 300 100 m with a northward transport along this boundary of about 4 106 m3 s 1 however both the dynamic height fields and water mass distributions suggest that this current does not represent return flow from the gyre wire sverdrup recirculation but instead is part of the northwestern gulf stream recirculation system west of about 50 w the near surface flow east of the bahamas is more complicated and consists of two isolated anticyclonic circulation cells along the boundary the most intense of these is centered just northeast of abaco island in the northern bahamas the southern weaker cell is centered at about 24 n 71 w in the area just north of puerto r

geologic settings of martian gullies implications for their origins 1 martian gullies are found on steep slopes of all origins on all sorts of terrains of all ages scattered across nearly all of mars gullies are observed on all manner of substrates layered massive shattered rubble with or without nearby mantling deposits gullies are most common in the southern midlatitudes but also occur in the northern hemisphere in near polar terrain on equatorial volcanoes and on northern plains most gullies in the southern hemisphere are on south facing slopes but they occur on slopes of all orientations gullies are among the youngest features on mars but locally are overlain by eolian deposits and cut by faults old or eroded gullies are rare and those found have been partially stripped from slopes leaving no rock debris behind most gully deposits contain no detectable rocks these data are inconsistent with published hypotheses of gully formation including seeps and breakouts of water or brine hydrothermal activity cryovolcanism and breakouts from liquid carbon dioxide the data are consistent with gullies being dry flows of eolian material dust and silt comparable to climax snow avalanches on earth eolian sedimentation should be correlated little with underlying geology cause of slope age of terrain type of terrain or the nature of the rocks eolian sedimentation should be correlated with wind deceleration which will cause suspended sediment to drop and areas with common gullies are those with strong wind deceleration predicted by global circulation model in such areas sediment will be deposited preferentially in the lee of obstacles for the gully rich areas of the southern midlatitudes winds blow from the nnw so that sediment is deposited on sse facing slopes i e poleward these predictions are in accord with observations

new morphological mapping and interpretation of ejecta deposits from orientale basin on the moon abstract orientale basin is one of the youngest and best preserved multi ring impact basins in the solar system the structure is 950 km across and is located on the western edge of the nearside of the moon the interior of the basin which possesses three distinct rings and a post impact mare fill has been studied extensively using modern high resolution datasets exterior to these rings orientale has an extensive ejecta blanket that extends out radially for at least 800 km from the basin rim in all directions and covers portions of both the nearside and farside of the moon these deposits known as the hevelius formation were first mapped using photographic data from the lunar orbiter iv probe in this study we map in detail the morphology of each distinct facies observed within the orientale ejecta blanket using high resolution lunar reconnaissance orbiter lro wide angle camera wac and narrow angle camera nac images and lunar orbiter laser altimeter lola elevation data we identified 5 unique facies within the ejecta blanket facies a is identified as a region of hummocky plains located in a low lying topographic region between the outer rook and cordillera rings this facies is interpreted to be a mix of crater derived impact melt and km scale blocks of ballistic ejecta and host rock broken up during the modification stage and formation of the cordillera ring facies b is an inner facies marked by radial grooves extending outward from the direction of the basin center this facies is interpreted as the continuous ballistic ejecta blanket facies c consists of inner and outer groupings of flat smooth surfaced deposits isolated in local topographic lows facies d displays characteristic sinuous ridges and lobate extensions facies c and d are interpreted to be impact melt rich materials which manifest as flows and ponds our observations suggest that these facies were emplaced subsequent to the ballistic ejecta blanket most likely during the modification stage of crater formation and flowed and ponded in topographically low lying regions facies e consists of distinct crater chains emanating radially from the basin center and extending from 700 to 1000 km from the center of orientale this facies is considered to be chains of secondary craters formed from large blocks of ballistic ejecta our mapping effort shows that the individual ejecta facies were influenced and controlled to varying degrees by pre existing slopes and topography at the basin scale the overall downslope direction toward the lunar lowlands to the east and southeast of the basin center resulted in large impact melt flows 100 s of kilometers in length while the regional upslope trends in the west and northwest inhibited the development of extensive impact melt flows on a smaller scale it can be observed that ground hugging ejecta collected behind and flowed around high topographic obstacles while diverting into topographic low regions e g around uplifted pre existing crater rims but down into pre existing crater floors the dispersion of the various ejecta facies mapped here also indicates both a direction and an angle for the impact event that formed orientale basin the bilateral distribution of both ballistic and impact melt rich ejecta deposits across a line running northeast southwest suggests the impact occurred from the northeast toward the southwest careful mapping of the secondary impact crater chains facies e shows the development of a forbidden zone lacking these impacts to the northeast as well as a concentration of the longest secondary crater chains to the northwest and southeast perpendicular to the aforementioned line of bilateral ejecta distribution this distribution of secondary impact craters contrasts with the circularity of the basin and suggests that orientale basin was formed by 25 45 impact from the northeast

martian gullies a comprehensive review of observations mechanisms and insights from earth analogues upon their discovery in 2000 martian gullies were hailed as the first proof of recent i e less than a few million years flowing liquid water on the surface of a dry desert planet many processes have been proposed to have formed martian gullies ranging from liquid water seepage from aquifers melting of snow ice and frost to dry granular flows potentially lubricated by co2 terrestrial analogues have played a pivotal role in the conception and validation of gully formation mechanisms comparison with the terrestrial landscape argues for gully formation by liquid water debris flows originating from surface melting however limited knowledge of sediment transport by sublimation is a critical factor in impeding progress on the co2 sublimation hypothesis we propose avenues towards resolving the debate a laboratory simulations targeting variables that can be measured from orbit b applications of landscape evolution models c incorporation of the concept of sediment connectivity d using 3d fluid dynamic models to link deposit morphology and flow rheology and e a more intense exchange of techniques between terrestrial and planetary geomorphology including quantitative and temporal approaches finally we emphasize that the present may not accurately represent the past and that martian gullies likely formed by a combination of processes

the equilibrium size frequency distribution of small craters reveals the effects of distal ejecta on lunar landscape morphology abstract small craters of the lunar maria are observed to be in a state of equilibrium in which the rate of production of new craters is on average equal to the rate of destruction of old craters crater counts of multiple lunar terrains over decades consistently show that the equilibrium cumulative size frequency distribution sfd per unit area of small craters of radius r is proportional r 2 and that the total crater density is a few percent of so called geometric saturation which is the maximum theoretical packing density of circular features while it has long been known that the primary crater destruction mechanism for these small craters is steady diffusive degradation there are few quantitative constraints on the processes that determine the degradation rate of meter to kilometer scale lunar surface features here we combine analytical modeling with a monte carlo landscape evolution code known as the cratered terrain evolution model to place constraints on which processes control the observed equilibrium size frequency distribution for small craters we find that the impacts by small distal ejecta fragments distributed in spatially heterogeneous rays is the largest contributor to the diffusive degradation which controls the equilibrium sfd of small craters other degradation or crater removal mechanisms such cookie cutting ejecta burial seismic shaking and micrometeoroid bombardment likely contribute very little to the diffusive topographic degradation of the lunar maria at the meter scale and larger

impact fragmentation of lonar crater india implications for impact cratering processes in basalt impact fragmentation is an energetic process that has affected all planetary bodies to understand its effects in basalt we studied lonar crater which is a rare terrestrial simple impact crater in basalt and analogues to kilometer scale simple craters on mars the lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder the cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges suggesting simple and complex fragmentation the general shape of the fragments is compact platy bladed and elongated with an average edge angle of 100 the size distribution of cobble to boulder sized fragments is similar to the fracture spacing distribution in the upper crater wall indicating the provenance of those large fragments its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target whereas the small fragments from deeper level the petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments the presence of fe mg phyllosilicates smectites both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration the seismic images reveal a thickness variation in the ejecta blanket segregation of boulders fractures and faults in the bedrock beneath the crater rim the fracturing fragmentation and fluvial degradation of lonar crater have important implications for mars

granular avalanches on the moon mass wasting conditions processes and features seven lunar crater sites of granular avalanches are studied utilizing high resolution images 0 42 1 3 m pixel from the lunar reconnaissance orbiter camera one in kepler crater is examined in detail all the sites are slopes of debris extensively aggraded by frictional freezing at their dynamic angle of repose four in craters formed in basaltic mare and three in the anorthositic highlands diverse styles of mass wasting occur and three types of dry debris flow deposit are recognized 1 multiple channel and lobe type with coarse grained levees and lobate terminations that impound finer debris 2 single surge polylobate type with sub parallel arrays of lobes and fingers with segregated coarse grained margins and 3 multiple ribbon type with tracks reflecting reworked substrate minor levees and no coarse terminations the latter type results from propagation of granular erosion deposition waves down slopes dominantly of fine regolith and it is the first recognized natural example dimensions architectures and granular segregation styles of the two coarse grained deposit types are like those formed in natural and experimental avalanches on earth although the timescale of motion differs due to the reduced gravity influences of reduced gravity and fine grained regolith on dynamics of granular flow and deposition appear slight but we distinguish for the first time extensive remobilization of coarse talus by inundation with finer debris the few sites show no clear difference attributable to the contrasting mare basalt and highland megaregolith host rocks and their fragmentation this lunar study offers a benchmarking of deposit types that can be attributed to formation without influence of liquid or gas

the seismically active lobate scarps and coseismic lunar boulder avalanches triggered by 3 january 1975 mw 4 1 shallow moonquake

crater degradation on the lunar maria topographic diffusion and the rate of erosion on the moon landscape evolution on the moon is dominated by impact cratering in the post maria period in this study we mapped 800 m to 5 km diameter craters on 30 of the lunar maria and extracted their topographic profiles from digital terrain models created using the kaguya terrain camera we then characterized the degradation of these craters using a topographic diffusion model because craters have a well understood initial morphometry these data provide insight into erosion on the moon and the topographic diffusivity of the lunar surface as a function of time the average diffusivity we calculate over the past 3 ga is 5 5 m2 myr with this diffusivity after 3 ga a 1 km diameter crater is reduced to approximately 52 of its initial depth and a 300 m diameter crater is reduced to only 7 of its initial depth and craters smaller than 200 300 m are degraded beyond recognition our results also allow estimation of the age of individual craters on the basis of their degradation state provide a constraint on the age of mare units and enable modeling of how lunar terrain evolves as a function of its topography

construction of the adjoint mit ocean general circulation model and application to atlantic heat transport sensitivity we first describe the principles and practical considerations behind the computer generation of the adjoint to the massachusetts institute of technology ocean general circulation model gcm using r giering s software tool tangent linear and adjoint model compiler tamc the tamc s recipe for fortran line by line generation of adjoint code is explained by interpreting an adjoint model strictly as the operator that gives the sensitivity of the output of a model to its input then the sensitivity of 1993 annual mean heat transport across 29on in the atlantic to the hydrography on january 1 1993 is calculated from a global solution of the gcm the kinematic sensitivity to initial temperature variations is isolated showing how the latter would influence heat transport if they did not affect the density and hence the flow over 1 year the heat transport at 29on is influenced kinematically from regions up to 20 o upstream in the western boundary current and up to 5 o upstream in the interior in contrast the dynamical influences of initial temperature and salinity perturbations spread from as far as the rim of the labrador sea to the 29on section along the western boundary the sensitivities calculated with the adjoint compare excellently to those from a perturbation calculation with the dynamical model perturbations in initial interior salinity influence meridional overturning and heat transport when they have propagated to the western boundary and can thus influence the integrated east west density difference our results support the notion that boundary monitoring of meridional mass and heat transports is feasible

large rock slides in impact craters on the moon and mercury abstract impact craters are the most common surface features on the moon and mercury on these two bodies we recognized and mapped large landslides on the walls of impact craters through visual inspection of high resolution imagery we compiled an inventory of 60 landslides on the moon and a second inventory of 58 landslides on mercury adopting categories used to catalog terrestrial mass movements we classified the landslides on the moon and mercury as rock slides we determined the probability density distribution of their planimetric area and we compared the distributions with similar distributions for terrestrial and martian landslides using data from the literature we found that rock slides mapped in impact craters on the moon are on average larger than analogous rock slides on mercury the relationship between the area of the individual rock slides and the area of the hosting crater suggests that rock slides on mercury initiate in smaller craters we hypothesize that the above findings are an effect of the weaker surface gravity of the moon compared to that of mercury and or an effect of the rock material properties

the south pole region of the moon as seen by clementine the clementine mission has provided the first comprehensive set of high resolution images of the south pole region of the moon within 5 of latitude of the pole an area of an estimated 30 000 square kilometers remained in shadow during a full lunar rotation and is a promising target for future exploration for ice deposits the schrodinger basin 320 kilometers in diameter centered at 75 s is one of the two youngest least modified great multiring impact basins on the moon a large maar type volcano localized along a graben within the schrodinger basin probably erupted between 1 and 2 billion years ago

estimated decadal changes in the north atlantic meridional overturning circulation and heat flux 1993 2004 results from a global 1 model constrained by least squares to a multiplicity of datasets over the interval 1992 2004 are used to describe apparent changes in the north atlantic ocean meridional overturning circulation and associated heat fluxes at 26 n the least squares fit is both stable and adequately close to the data to make the analysis worthwhile changes over the 12 yr are spatially and temporally complex a weak statistically significant trend is found in net north atlantic volume flux above about 1200 m which drops slightly 0 19 0 05 sv yr 1 1s v 10 6 m 3 s 1 but with a corresponding strengthening of the outflow of north atlantic deep water and inflow of abyssal waters the slight associated trend in meridional heat flux is very small and not statistically significant the month to month variability implies that single section determinations of heat and volume flux are subject to serious aliasing errors

model tests on flow slide of lunar regolith simulant a significant fraction of lunar exploration is concerned with the lunar regolith over the last three decades theoretical and experimental effort has been directed towards investigating the mechanical parameters and chemical composition of lunar regolith however the properties of lunar regolith flow have received only limited attention even though there have been reports of lunar avalanches in this paper the flow evolution of a lunar regolith simulant at various inclined angles was investigated in a rectangular shaped flume constructed of plexiglas the objective of this paper is to study the flow patterns of lunar regolith simulant by using a fast shutter speed 1 140 s ccd camera 640 480 pixels configurations of the flow under the action of different chute angles are captured in addition the engineering strains of the different chute angles are also calculated the research results help to investigate the real lunar regolith flow slide to some extent

a hydrological analysis of terrestrial and martian gullies implications for liquid water on mars abstract understanding the role and amounts of liquid water involved in martian gully formation is critical in studies of the martian hydrosphere and climate we performed hydrological analyses using the manning and darcy weisbach equations in order to infer flow velocities and discharge rates from channels at two gully sites in noachis terra mars the results of these analyses were compared with analogous hillside gullies in australia we found the velocities and discharge rates for the terrestrial gullies to be comparable to velocities and discharge rates of some small martian gully channels in contrast velocity and discharge in some larger martian gullies were almost an order of magnitude higher equating with catastrophic flows on earth we postulate that the larger gully channels were more likely formed by a number of smaller flows in a similar manner observed in some terrestrial gullies a scenario that does not require vast amounts of liquid water to be stable under martian conditions in addition we found that post fluvial channel widening may have acted on the martian gullies probably by dry mass wasting leading to larger channels than were originally carved by liquid water future hydrological analyses of martian gullies will lead to a greater understanding of the relative importance of dry mass wasting compared to liquid water erosion

shock veins in the central uplift of the manicouagan impact structure context and genesis we describe the development of shock veins that penetrate the anorthositic central uplift of the manicouagan impact structure they occur as thin 2 5 mm wide linear micro fault systems that can be traced for several meters in length and which predominantly trend radially from the point of impact the shock veins are distinguished by the development of maskelynite along vein margins and stishovite in vein matrices which are otherwise absent in non veined regions these phases define a shock excursion of up to 30 gpa in contrast to bulk shock effects of 12 gpa defined by development of shatter cones planar fractures and planar deformation features in various minerals the shock veins at manicouagan share many similarities with vein systems developed in meteorites they also provide an in situ context with which to better understand meteoroid source and lofting conditions in addition to containing high pressure phases the shock veins exhibit evidence for high temperature partial melting of host silicate clasts with the generation of flow textured fragments and glasses the formation of microcrystallites and dendrites from some melts indicates rapid cooling we propose a two stage generation mechanism comprising an initial high pressure shock excursion estimated to last 0 5 s based on projectile size considerations followed by a longer high temperature pulse of a few seconds duration we suggest that the shock excursion is initiated by target heterogeneities that cause distortions in the hemispherically propagating shock front this results in radially oriented tearing and vein formation with shock amplification occurring via intra vein shock reverberation high speed displacement along the veins is driven by stress release on rarefaction which results in frictional melting via adiabatic heating

the arrival of recently formed labrador sea water in the deep western boundary current at 26 5 n the deep western boundary current dwbc of the north atlantic is a principal conduit between the formation region for labrador sea water lsw and the oceanic interior to the south time series 1985 1997 of hydrographic properties obtained in the dwbc at 26 5 n show that prior to 1994 temperature salinity and transient tracer properties within the lsw density range showed little indication of recently formed parcels properties characteristic of a newer version of lsw cooler fresher and higher tracer concentrations were observed beginning in 1994 and continuing through 1997 longer time series of temperature and salinity developed from a regional data base show both the 1994 and a 1980 1981 event in the abaco region both events are consistent with anomalies in the labrador sea that occurred some 10 years earlier the 10 year transit time from the labrador sea to 26 5 n is less than the 18 year transit time inferred from earlier studies

geologic map of the northern hemisphere of vesta based on dawn framing camera fc images abstract the dawn framing camera fc has imaged the northern hemisphere of the asteroid 4 vesta at high spatial resolution and coverage this study represents the first investigation of the overall geology of the northern hemisphere 22 90 n quadrangles av 1 2 3 4 and 5 using these unique dawn mission observations we have compiled a morphologic map and performed crater size frequency distribution csfd measurements to date the geologic units the hemisphere is characterized by a heavily cratered surface with a few highly subdued basins up to 200 km in diameter the most widespread unit is a plateau cratered highland unit similar to although of lower elevation than the equatorial vestalia terra plateau large scale troughs and ridges have regionally affected the surface between 180 e and 270 e these tectonic features are well developed and related to the south pole veneneia impact saturnalia fossae trough unit elsewhere on the hemisphere they are rare and subdued saturnalia fossae cratered unit in these pre rheasilvia units we observed an unexpectedly high frequency of impact craters up to 10 km in diameter whose formation could in part be related to the rheasilvia basin forming event the rheasilvia impact has potentially affected the northern hemisphere also with s n small scale lineations but without covering it with an ejecta blanket post rheasilvia impact craters are small

a monitoring design for the atlantic meridional overturning circulation 1 current hydrographic data can provide snapshots but no continuous timeseries of the meridional overturning circulation moc using output from two eddy permitting numerical ocean models we test the feasibility of a monitoring system for the moc in the north atlantic the results suggest that a relatively simple arrangement using moorings placed across a longitude depth section and the zonal wind stress is able to capture most of the moc strength and vertical structure as a function of time being closely related to the transport of energy to the north atlantic measuring the moc would open the prospect of having continuous information about a key element of northern hemisphere climate

maskelynite formation via solid state transformation evidence of infrared and x ray anisotropy we present the results of a combined study of shocked labradorite from the lonar crater india using optical microscopy micro raman spectroscopy nuclear magnetic resonance nmr spectroscopy high energy x ray total scattering experiments and micro fourier transform infrared micro ftir spectroscopy we show that maskelynite of shock class 2 is structurally more similar to fused glass than to crystalline plagioclase however there are slight but significant differences preservation of original preimpact igneous zoning anisotropy at infrared wavelengths x ray anisotropy and preservation of some intermediate range order which are all consistent with a solid state transformation from plagioclase to maskelynite

structural effects of meteorite impact on basalt evidence from lonar crater india received 31 january 2005 revised 17 august 2005 accepted 26 august 2005 published 8 december 2005 1 lonar crater is a simple bowl shaped near circular impact crater in the 65 myr old deccan volcanic province in india as lonar crater is a rare terrestrial crater formed entirely in basalt it provides an excellent opportunity to study the impact deformation in target basalt which is common on the surfaces of other terrestrial planets and their satellites the present study aims at documenting the impact deformational structures in the massive basalt well exposed on the upper crater wall where the basalt shows upward turning of the flow sequence resulting in a circular deformation pattern three fracture systems radial concentric and conical fractures are exposed on the inner crater wall on the fracture planes plumose structures are common uplift and tilting of the basalt sequence and formation of the fractures inside the crater are clearly related to the impact event and are different from the preimpact structures such as cooling related columnar joints and fractures of possible tectonic origin which are observed outside the crater slumping is common throughout the inner wall and listric faulting displaces the flows in the northeastern inner wall the impact structures of lonar crater are broadly similar to those at other simple terrestrial craters in granites and clastic sedimentary rocks and even small scale experimental craters formed in gabbro targets as lonar crater is similar to the strength controlled laboratory craters impact parameters could be modeled for this crater provided maximum depth of fracture formation would be known citation kumar p s 2005 structural effects of meteorite impact on basalt evidence from lonar crater india j geophys res 110 b12402 doi 10 1029 2005jb003662

shock metamorphic features and their zoning and orientation in the precambrian rocks of the manicouagan structure quebec canada abstract the manicouagan structure of impact origin is located in eastern quebec about 300 km north of the st lawrence river the complex is of triassic age the shock deformation of the more important rock forming minerals of the autochthonous or at least parautochthonous rocks within the structure is described four zones of shock metamorphism are delineated based on the deformation features of plagioclase 1 plagioclase without planar features 2 plagioclase with planar features 3 first occurrence of plagioclase with partial isotropization and 4 first occurrence of plagioclase with total isotropization these four zones are more or less concentric and indicate a general increase in the grade of shock metamorphism towards the centre of the structure however several small areas probably underlain by allochthonous rocks appear not to fit this general picture biotite and garnet show evidence of a shock orientation of their deformation features an impact origin for the structure is favoured the impact possibly triggering volcanism

imaging of lunar surface maturity the physical evolution of the lunar surface with exposure to the space environment is termed maturation and maturity is the degree to which a particular lunar soil possesses quantitative characteristics consistent with that exposure several quantitative measures or indices of maturity have been proposed and employed including the abundance of solar wind gas abundance of various types of agglutinates various measures of grain size and is feo among the changes attendant with space exposure are striking changes in the optical characteristics of soils mature lunar soils are dark red and exhibit reduced spectral contrast relative to immature soils this paper presents an optical maturity index that quantifies the spectral effects of maturation we show that this optical maturity index correlates with other maturity indices about as well as the accepted maturity indices correlate among themselves and is only weakly coupled to composition the modest correlations among maturity indices suggest important controls on individual maturity indices other than age uncorrelated variations in the rates of accumulation of individual indicators or variations in depths over which indicators are emplaced in addition to mixing these effects conspire to reduce the equivalence of maturity and duration of surface exposure optical maturity illustrates some of these effects showing that ejecta of large and small craters mature at different rates and that the interiors and ejecta of large craters exhibit systematically different optical maturities the same or analogous effects are likely to influence other maturity indices

impact spallation processes on the moon a case study from the size and shape analysis of ejecta boulders and secondary craters of censorinus crater abstract impact spallation is a fundamental process responsible for formation of ejecta boulders from impact craters although theoretical spallation models were developed about three decades ago only limited geological observations have been made so far to test these models the 3 8 km censorinus crater on the moon provides an excellent opportunity for studying the impact spallation processes associated with a fresh simple crater formed by oblique impact using the lunar reconnaissance orbiter narrow angle camera images we prepared the ejecta boulder distribution map of censorinus crater and measured the boulder sizes and shapes mapping of about 242 000 ejecta boulders enabled us to document the size distribution of boulders both radial and concentric to the impact crater larger size boulders dominate the crater rim areas while they become smaller away from the crater the boulder distribution exhibits a radial asymmetry suggesting censorinus is a oblique impact in which the uprange ejecta have smaller ranges with larger concentration of boulders near the southwestern crater rim while the downrange ejecta are in general characterized by smaller boulders with high spatial dispersion the cumulative size frequency distribution csfd of boulders shows a highly variable fragmentation history in which the uprange boulders suffered more complex fragmentation the ejecta boulders also exhibit a variety of shapes that are gleaned from their axial ratios and edge angle characteristics there is a general decrease of axial ratios away from the crater rim rectangular boulders dominate the crater rim and they become more equant away from the crater in addition to the boulder sizes the boulder shape distribution also exhibits a mild asymmetry in response to the oblique impact small size fresh impact craters 84 000 craters are abundant on the censorinus ejecta and post date censorinus these craters are found in two morphologic types in which a large majority of craters have subdued ejecta rayless craters while some possess bright rayed ejecta bright rayed craters the csfd of rayless craters show a steep power law slope with a b value of 4 0 similar to the secondary craters produced by the impact of ejecta from primary craters we therefore interpret the rayless craters as the secondary craters of censorinus on the other hand the csfd of bright rayed craters have smaller power law slope b value 2 7 which is a characteristic of primary craters and thus provide 3 ma age for censorinus crater when the characteristics of censorinus boulders are compared with the theoretical spallation models that are sensitive to the petrophysical properties of the target lunar highland the models generally agree with the censorinus boulders however the observed shape and size characteristics of the censorinus boulders are found to be more complex than the theoretical spallation models the ejecta boulders suffered more complex fragmentation and asymmetric distribution in response to the oblique impact the spallation models accounting oblique impacts have not yet been developed therefore our censorinus boulder observations can be used to develop and validate the new theoretical spallation models for the effects of oblique impacts

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

the canary basin contribution to the seasonal cycle of the atlantic meridional overturning circulation at 26 n this study examines the seasonal cycle of the atlantic meridional overturning circulation amoc and its eastern boundary contributions the cycle has a magnitude of 6 sv as measured by the rapid mocha wbts project array at 26 n which is driven largely by the eastern boundary the eastern boundary variations are explored in the context of the regional circulation around the canary islands there is a 3 month lag between maximum wind forcing and the largest eastern boundary transports which is explained in terms of a model for rossby wave generated at the eastern boundary two dynamic processes take place through the lanzarote passage lp in fall the recirculation of the canary current and the northward flow of the intermediate poleward undercurrent in contrast during the remaining seasons the transport through the lp is southward due to the canary upwelling current these processes are linked to the seasonal cycle of the amoc

the nature distribution and genesis of the coesite and stishovite associated with the pseudotachylite of the vredefort dome south africa abstract the vredefort dome represents the uplift centre of a well known 2 00 ga old impact structure of unusually large magnitude shock features like shatter cones planar features and high pressure silica polymorphs are common the present study deals with the description mode of occurrence field distribution and post shock metamorphic alteration of coesite and stishovite which were poorly documented up to now these minerals occur as unusually large crystals in the quartzite of the wall rock in contact with very thin pseudotachylite veins in the pseudotachylite itself which can be interpreted as a friction and or a shock recovery melt fine needles of kyanite are ubiquitous it is proposed that these thin pseudotachylites a type formed during the transit of the shock wave they preceded the development of thick pseudotachylite and microbreccia veins b type which formed during the tensional period which immediately followed from comparison with the model of formation of high pressure polymorphs in porous sandstone it is suggested that higher pressure and stress was concentrated along the a type veins at the arrival of the shock front at this time the quartz was transformed into a high pressure phase which was probably poorly crystalline behind the shock front that is during the rarefaction the pressure was progressively released and the polymorphs crystallized from this initial high pressure phase stishovite crystallized first followed by coesite the high pressure conditions may have lasted an unusually long time due to the magnitude of the vredefort impact this long time probably about one second may account for the large size of the coesite and stishovite crystals most of the high pressure silica polymorphs are corroded to a variable degree by secondary quartz and preserved only in a restricted area of the impact structure this alteration is attributed to post shock metamorphism due to the temperature of the rock before impact plus the heat left after shock recovery some of the evidence put forward by authors against the impact model is discussed according to the facts arising from this investigation it is concluded that an origin by impact remains the simplest and most realistic model to explain the origin of the vredefort dome

slowing of the atlantic meridional overturning circulation at 25 n the atlantic meridional overturning circulation carries warm upper waters into far northern latitudes and returns cold deep waters southward across the equator its heat transport makes a substantial contribution to the moderate climate of maritime and continental europe and any slowdown in the overturning circulation would have profound implications for climate change a transatlantic section along latitude 25 n has been used as a baseline for estimating the overturning circulation and associated heat transport here we analyse a new 25 n transatlantic section and compare it with four previous sections taken over the past five decades the comparison suggests that the atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004 whereas the northward transport in the gulf stream across 25 n has remained nearly constant the slowing is evident both in a 50 per cent larger southward moving mid ocean recirculation of thermocline waters and also in a 50 per cent decrease in the southward transport of lower north atlantic deep water between 3 000 and 5 000 m in depth in 2004 more of the northward gulf stream flow was recirculating back southward in the thermocline within the subtropical gyre and less was returning southward at depth

volcanism on farside of the moon new evidence from antoniadi in south pole aitken basin abstract the lunar surface is characterized by asymmetric distribution of its volcanic deposits the nearside contains about 90 of the mare basalts while there are a few on the farside with some are in the south pole aitken spa basin which is the largest and oldest impact basin on the moon although the mare volcanism on the nearside of the moon has been very well characterized our understanding of the farside is relatively poor our geological mapping using lunar reconnaissance orbiter lro and chandrayaan 1 moon mineralogy mapper m3 data of 143 km antoniadi impact basin provides new insights into volcanic processes in the southern spa antoniadi has excavated the spa floor as deep as 9 km distribution of secondary craters around antoniadi shows that the basin was formed by oblique impact with the direction of 50 counter clockwise from 178 e longitude our geological mapping has found for the first time several volcanic cones 0 2 2 5 km diameter in association with the mare basalt flows as per morphological classification these are c e n and p type volcanic cones with abundant volcanic fragments in their summit areas the base and summit diameters of these cones are similar to those of marius hills on the nearside of the moon the cumulative size frequency distributions of the summit fragments provide a range of power index values between 3 and 9 suggesting the involvement of dynamic fragmentation of the volcanic materials during the eruptive processes the grabens in the basin floor show evidence for fissure eruption of the mare basalts the graben near the central peak exposes about 140 m thick basalt sequence containing a minimum of five individual lava layers the crater size frequency distributions of the mare deposits suggest an age of 1 6 ga for the flows in the central part of the basin while 2 6 ga for those on the outer floor near the basin wall indicating the episodic volcanism in the basin the young volcanism of 1 6 ga is reported for the first time from spa the m3 data reveal that the basin materials contain abundant low ca pyroxene while the mare basalts with high ca pyroxene we calculated the liquidus density of mare basalts based on feo and tio2 content which suggest a range of density from 2 7 to 2 8 g cm3 which would be lower than a gross lunar crust this would imply the emplacement of basaltic lavas through dikes by simple magma buoyancy or over pressurization of magma chambers if they present at the crust mantle boundary when the magma density is greater than the host crust the 1 6 ga old volcanism in antoniadi suggests that the mantle beneath the spa has been conducive for young magmatism possibly due to presence of kreep like material in the mantle

the geology of 433 eros the global high resolution imaging of asteroid 433 eros by the near earth asteroid rendezvous near shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small s type asteroid eros displays a variety of surface features and evidence of a substantial regolith large scale facets grooves and ridges indicate the presence of at least one global planar structure directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object as with other small objects impact craters dominate the overall shape as well as the small scale topography of eros depth diameter ratios of craters on eros average 0 13 but the freshest craters approach lunar values of 0 2 ejecta block production from craters is highly variable the majority of large blocks appear to have originated from one 7 6 km crater shoemaker the interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of phobos this lack of mechanical boundaries and the abundant evidence of regolith in nearly every high resolution image suggests a gradation in the porosity and fracturing with depth the density of small craters is deficient at sizes below 200 m relative to predicted slopes of empirical saturation this characteristic which is also found on parts of phobos and lunar highland areas probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith eros displays a variety of regolith features such as debris aprons fine grained ponded deposits talus cones and bright and dark streamers on steep slopes indicative of efficient downslope movement of regolith these processes serve to mix materials in the upper loose fragmental portion of the asteroid regolith in the instance of ponded materials and crater wall deposits there is evidence of processes that segregate finer materials into discrete deposits the near observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the near shoemaker spacecraft

comparison of small lunar landslides and martian gullies some lunar crater wall landslides strongly resemble martian gullies despite the lack of geologically active water on the moon today or in the past the lunar features indicate that alcove channel apron morphology attributed on mars to seepage of liquid water can also form via a dry landslide mechanism therefore a more stringent test than just an alcove channel apron morphology is necessary to differentiate dry landslides from water carved gullies

the record of miocene impacts in the argentine pampas argentine pampean sediments represent a nearly continuous record of deposition since the late miocene 10 ma previous studies described five localized concentrations of vesicular impact glasses from the holocene to late pliocene two more occurrences from the late miocene are reported here one near chasico ch with an 40ar 39ar age of 9 24 0 09 ma and the other near baha blanca bb with an age of 5 28 0 04 ma in contrast with andesitic and dacitic impact glasses from other localities in the pampas the ch and bb glasses are more mafic they also exhibit higher degrees of melting with relatively few xenoycrysts but extensive quench crystals in addition to evidence for extreme heating 1700 c shock features are observed e g planar deformation features pdfs and diaplectic quartz and feldspar in impact glasses from both deposits geochemical analyses reveal unusually high levels of ba 7700 ppm in some samples which is consistent with an interpretation that these impacts excavated marine sequences known to be at depth these two new impact glass occurrences raise to seven the number of late cenozoic impacts for which there is evidence preserved in the pampean sediments this seemingly high number of significant impacts over a 10 6 km 2 area in a time span of 10 myr is consistent with the number of bolides larger than 100 m expected to enter the atmosphere but is contrary to calculated survival rates following atmospheric disruption the pampean record suggests therefore that either atmospheric entry models need to be reconsidered or that the earth has received an enhanced flux of impactors during portions of the late cenozoic evidence for the resulting collisions may be best preserved and revealed in rare dissected regions of continuous low energy deposition such as the pampas additionally the rare earth element ree concentrations of the target sediments and impact melts associated with the chasic event resemble the hna k australites of similar age this suggests the possibility that those enigmatic tektites could have originated as high angle distal ejecta from an impact in argentina thereby accounting for their rarity and notable chemical and physical differences from other australasian impact glasses

petrography geochemistry and hf nd isotope evolution of drill core samples and target rocks from the el gygytgyn impact crater ne chukotka arctic russia el gygytgyn in northeast chukotka russia is a 3 6 ma 18 km diameter impact structure the impact crater was recently drilled in the framework of a project sponsored by the international continental scientific drilling program icdp target rocks at the el gygytgyn area are dominated by the felsic members of the late cretaceous okhotsk chukotka volcanic belt ocvb such a target lithology is unique among terrestrial impact craters thereby providing the opportunity to study shock metamorphism in siliceous volcanic rocks here we present a petrographic geochemical and isotopic study of the section of the drill core underneath the lacustrine sediments extending from 316 m to 517 m below the lake bottom blb the drill core stratigraphy includes 80 m of suevite and a cross section through a volcanic suite which consists of 1 a middle section 390 423 mblb with dominant felsic tuffs and a few mafic members and 2 a welded rhyolitic dacitic ignimbrite 423 517 mblb the melt fragments embedded in the suevite are interpreted as being impact related by comparison with impact glasses from the crater and in opposition to the target rock which does not include similar melts a suevitic dyke crosscuts the lower section of the core at the depth 471 40 mblb evidence for shock metamorphism is concentrated in the upper 10 m of the drill core and almost limited to the suevitic breccia the geochemical and isotope nd and hf composition of samples from the target and the drill core reveals relationships to the berlozhya magmatic assemblage bma arguing for similar source magmas the primitive upper mantle pum normalized trace element plot of rocks investigated here confirms a subduction related signature as previously proposed for rocks from both ocvb and bma

ocean gyre circulation changes associated with the north atlantic oscillation abstract observational evidence is presented for interannual to interdecadal variability in the intensity of the north atlantic gyre circulation related to the atmospheric north atlantic oscillation nao patterns a two point baroclinic pressure difference between the subtropical and subpolar gyre centers an oceanic analogue to the much used sea level pressure slp based atmospheric nao indices is constructed from time series of potential energy anomaly pea derived from hydrographic measurements in the labrador basin and at station s near bermuda representing the upper 2000 db eastward baroclinic mass transport between the two centers the transport index indicates a gulf stream and north atlantic current that gradually weakened during the low nao period of the 1960s and then intensified in the subsequent 25 years of persistently high nao to a record peak in the 1990s the peak to peak amplitude difference was 15 20 megatons per second mt s 1 with a 43 yr mean of about 60 mt s 1 a change of 25 33

impact induced seismic activity on asteroid 433 eros a surface modification process high resolution images of the surface of asteroid 433 eros revealed evidence of downslope movement of a loose regolith layer as well as the degradation and erasure of small impact craters less than 100 meters in diameter one hypothesis to explain these observations is seismic reverberation after impact events we used a combination of seismic and geomorphic modeling to analyze the response of regolith covered topography particularly craters to impact induced seismic shaking applying these results to a stochastic cratering model for the surface of eros produced good agreement with the observed size frequency distribution of craters including the paucity of small craters

meddies and decadal changes at the azores front from 1980 to 2000 twenty years of time series observations from the deep sea mooring kiel276 are used to obtain information on the frequency and propagation of meddies mediterranean water eddies on long term changes in flow properties and on a possible relation to the north atlantic oscillation the mooring was set at the nominal position 33 n 22 w at a water depth of more than 5200 m in the northern canary basin it is located near the southern boundary of the azores current ac which is part of the north atlantic subtropical gyre and also in the large scale mediterranean water mw tongue originating from the strait of gibraltar the amplitudes of time varying vertical quasi geostrophic modes and the correlation of current and temperature changes at levels in the mw and the north atlantic central water above are used to identify meddies a total of 10 meddies passed the mooring during the period 1980 2000 half of the events can be related to earlier observations directional changes in meddy related velocities are used to estimate speeds and directions of meddy propagation directions of propagation are very homogeneous with all the 10 meddies observed propagating with a southward velocity component within a sector of 90 and typical speeds are 2 3 cm s meddy occurrence was uneven in time with six meddies found during the first four years and only four meddies during the remaining 16 years decadal changes show the annual mean and the fluctuating kinetic energy levels at the site changing from lower values in the 1980s to high values in the 1990s this change appears to be correlated with variations in the north atlantic oscillation nao index with a delay in oceanic response of about 3 years a conceptual model of ac meanders is used to identify meander signals in the upper layer time series the ac axis appears to be closer to the site during the 1990s than during the preceding decade and indicates a southward or southwestward displacement of the ac with increasingly positive values of the nao index meddy frequency is lower when the ac gets closer from the north a reduction in meddy occurrence in the region just south of the ac is possibly caused by the shear induced blocking of some meddies crossing the front from the north

shock induced amorphous textures in plagioclase manicouagan quebec canada the textural relationships and structural states of optically isotropic labradorite from the manicouagan quebec impact structure have been examined by light optical and transmission electron tem microscopy two distinct diaplectic glasses have been recognized based on their contrasting morphology timing and the inferred modes of formation the earliest isotropic bands and grain scale isotropism maskelynite optically exhibit a gradational in situ transformation from crystalline plagioclase with preservation of relict textures twins grain boundaries the same transformation from crystalline to amorphous structure is observed in tem to occur heterogeneously at scales on the order of the unit cell the progressive transformation of optical properties reflects an increase in the volume fraction and eventual coalescence of these amorphous units this maskelynite type diaplectic glass is interpreted to form in the solid state directly from crystalline material during the compressional phase of the shock wave the other isotropic material occurs in spatially discrete tensiongashes and planar deformation features pdfs that overprint the maskelynite type glass this second type of diaplectic glass pdf type is developed homogeneously within a given glass band and exhibits sharp crystal glass boundaries in contrast to the gradational boundaries of the maskelynite type glass pdf type glass is interpreted to form by melting in tensional release zones during passage of the rarefaction wave these observations emphasize the ability of naturally shocked rocks to preserve subtle evidence of variations in the shock process from highly transient events

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

the origin of lunar crater rays abstract lunar rays are filamentous high albedo deposits occurring radial or subradial to impact craters the nature and origin of lunar rays have long been the subjects of major controversies we have determined the origin of selected lunar ray segments utilizing earth based spectral and radar data as well as feo tio 2 and optical maturity maps produced from clementine uvvis images these include rays associated with tycho olbers a lichtenberg and the messier crater complex it was found that lunar rays are bright because of compositional contrast with the surrounding terrain the presence of immature material or some combination of the two mature compositional rays such as those exhibited by lichtenberg crater are due entirely to the contrast in albedo between ray material containing highlands rich primary ejecta and the adjacent dark mare surfaces immaturity rays are bright due to the presence of fresh high albedo material this fresh debris was produced by one or more of the following 1 the emplacement of immature primary ejecta 2 the deposition of immature local material from secondary craters 3 the action of debris surges downrange of secondary clusters and 4 the presence of immature interior walls of secondary impact craters both composition and state of maturity play a role in producing a third combination class of lunar rays the working distinction between the eratosthenian and copernican systems is that copernican craters still have visible rays whereas eratosthenian aged craters do not compositional rays can persist far longer than 1 1 ga the currently accepted age of the copernican eratosthenian boundary hence the mere presence of rays is not a reliable indication of crater age the optical maturity parameter should be used to define the copernican eratosthenian boundary the time required for an immature surface to reach the optical maturity index saturation point could be defined as the copernican period

impact fracturing and structural modification of sedimentary rocks at meteor crater arizona 1 meteor crater provides a rare opportunity to study impact deformation of sedimentary target rocks and isolate those features from preexisting tectonic deformation and impact generated reactivation of preexisting tectonic features this study reports over 2500 new measurements of orientations of bedding faults and fractures in crater walls and in surrounding bedrock target rocks are characterized by horizontal bedding planes that are cut by at least three prominent sets of preimpact tectonic fracture systems the crater rim is also cut by three distinct groups of fractures radial concentric and conical fractures when the crater rim is restored to preimpact condition the radial and concentric fractures resemble preimpact fracture populations indicating that crater wall deformation and rim uplift were partly accommodated by activation of preexisting fractures in contrast the conical fractures are dissimilar to the preimpact fractures and apparently formed as a direct result of impact deformation some of the preimpact fractures were transformed into tear faults during the impact event and motion along those faults appears to have controlled the geometry of the impact deformational features the crater rim is thus square in plan view rather than circular faults occurring in the crater diagonals are prominent ones allowing greater vertical displacement the deformation pattern of meteor crater is different from that at lonar crater which was excavated in basalt with fewer preimpact fractures the differences between deformation at meteor crater and lonar crater may reflect the same disparities seen in simple craters produced in different target lithologies on mars and other planetary surfaces

olivine rich exposures in the south pole aitken basin abstract the distribution and the geological context of the olivine rich exposures in the south pole aitken spa basin on the moon were investigated based on the spectral data obtained from the spectral profiler sp and multiband imager mi onboard the japanese lunar explorer kaguya selene the olivine rich exposures are found only in the peak rings or central peaks of the schrodinger basin and zeeman crater which are located in the outer region of the spa basin and not in the center region on a localized scale the olivine rich materials are exposed on landslide features on the crater walls or sloped wall of the central peaks or the peak rings another observational finding is the co existence of olivine rich and plagioclase rich materials on a kilometer scale spanning most of the olivine rich sites in the schrodinger basin pyroxene rich materials are found in fresh craters outside the peak rings or the central peaks with olivine rich materials based on these results the following scenario are proposed 1 the impact to form the spa basin melted a large amount of the lunar upper mantle and crust and distributed the melted materials to the outer region 2 local differentiation of melted materials hid the olivine rich materials in the center region of the spa basin 3 later impacts that formed the schrodinger and zeeman craters excavated and exposed the olivine rich materials to the surface again and 4 space weathering and regolith gardening obscured the olivine rich spectra at the exposure sites but recent small scale impacts or landslides on the sloped wall exposed fresh olivine rich materials allowing the identification of the olivine rich exposures by spectral remote sensing this suggests that several different scale events play an important role in forming the surface distributions of originally deep seated materials on the moon as well as on other planetary bodies

tissintite ca na alsi2o6 a highly defective shock induced high pressure clinopyroxene in the tissint martian meteorite tissintite is a new vacancy rich high pressure clinopyroxene with a composition essentially equivalent to plagioclase it was discovered in maskelynite shocked plagioclase and is commonly observed included within or in contact with shock melt pockets in the tissint meteorite a depleted olivine phyric shergottite fall from mars the simple composition of tissintite an58 69 and its precursor plagioclase an59 69 together with the limited occurrence both spatially only in maskelynite less than 25 m of a shock melt pocket and in terms of bulk composition make tissintite a goldilocks phase it formed during a shock event severe enough to allow nucleation and growth of vacancy rich clinopyroxene from a melt of not too calcic and not too sodic plagioclase composition that was neither too hot nor too cold with experimental calibration these limitations on occurrence can be used to place strong constraints on the thermal history of a shock event the kinetics for nucleation and growth of tissintite are probably slower for more sodic plagioclase precursors so tissintite is most likely to occur in depleted olivine phyric shergottites like tissint and other highly shocked meteorites and lunar and terrestrial rocks that consistently contained calcic plagioclase precursors in the appropriate compositional range for a shock of given intensity tissintite ca 0 45 na 0 31 0 24 al 0 97 fe 0 03 mg 0 01 si 1 80 al 0 20 o6 is a c2 c clinopyroxene containing 42 60 mol of the ca eskola component by far the highest known the cell parameters are 9 21 17 a b 9 09 4 a c 5 20 2 a 109 6 9 v 410 8 a 3 z 4z 4 the density is 3 32 g cm 3 and we estimate a cell volume for the ca eskola end member pyroxene of 411 13 a 3 which is consistent with a previous estimate and therefore supports the importance of this component in clinopyroxenes from ultra high pressure metamorphic rocks from the earth s upper mantle at least in c2 c clinopyroxenes as sodic as tissintite the a and b cell parameters as a function of vacancy concentration intersect at 0 3 vacancies pfu much lower than the ca eskola end member 0 5 an inversion of anisotropy suggesting an elastic instability that drives clinopyroxene toward a disordered trigonal structure closely related to that of wadeite it may mark the boundary beyond which the breakdown of vacancy rich clinopyroxene to a wadeite structured phase stishovite becomes stable although this was not observed in tissint