environmental perturbations caused by the impacts of asteroids and comets we review the major impact associated mechanisms proposed to cause extinctions at the cretaceous tertiary geological boundary we then discuss how the proposed extinction mechanisms may relate to the environmental consequences of asteroid and comet impacts in general our chief goal is to provide relatively simple prescriptions for evaluating the importance of impacting objects over a range of energies and compositions but we also stress that there are many uncertainties we conclude that impacts with energies less than about 10 mt are a negligible hazard for impacts with energies above 10 mt and below about 104 mt i e impact frequencies less than one in 6 104 years corresponding to comets and asteroids with diameters smaller than about 400 m and 650 m respectively blast damage earthquakes and fires should be important on a scale of 104 or 105 km which corresponds to the area damaged in many natural disasters of recent history however tsunami excited by marine impacts could be more damaging flooding a kilometer of coastal plain over entire ocean basins in the energy range of 104 105 mt intervals up to 3 105 years corresponding to comets and asteroids with diameters up to 850 m and 1 4 km respectively water vapor injections and ozone loss become significant on the global scale in our nominal model such an impact does not inject enough submicrometer dust into the stratosphere to produce major adverse effects but if a higher fraction of pulverized rock than we think likely reaches the stratosphere stratospheric dust causing global cooling would also be important in this energy range thus 105 mt is a lower limit where damage might occur beyond the experience of human history the energy range from 105 to 106 mt intervals up to 2 106 years corresponding to comets and asteroids up to 1 8 and 3 km diameter is transitional between regional and global effects stratospheric dust sulfates released from within impacting asteroids and soot from extensive wild fires sparked by thermal radiation from the impact can produce climatologically significant global optical depths of the order of 10 moreover the ejecta plumes of these impacts may produce enough no from shock heated air to destroy the ozone shield between 106 and 107 mt intervals up to 1 5 107 years corresponding to comets and asteroids up to 4 and 6 5 km diameter dust and sulfate levels would be high enough to reduce light levels below those necessary for photosynthesis ballistic ejecta reentering the atmosphere as shooting stars would set fires over regions exceeding 107 km and the resulting smoke would reduce light levels even further at energies above 107 mt blast and earthquake damage reach the regional scale 106 km tsunami cresting to 100 m and flooding 20 km inland could sweep the coastal zones of one of the world s ocean basins fires would be set globally light levels may drop so low from the smoke dust and sulfate as to make vision impossible at energies approaching 109 mt 108 years the ocean surface waters may be acidified globally by sulfur from the interiors of comets and asteroids the cretaceous tertiary impact in particular struck evaporate substrates that very likely generated a dense widespread sulfate aerosol layer with consequent climatic effects the combination of all of these physical effects would surely represent a devastating stress on the global biosphere

benthic metazoan biomass community structure and bioturbation at three contrasting deep water sites on the northwest european continental margin size structure taxonomic composition and bioturbation potential of benthic metazoan communities were examined at three contrasting sites on the northwest european continental margin as part of a wider study of biogeochemical cycling in the deep sea benthic boundary layer sampling was conducted in the hatton rockall basin 1100 m depth on the north feni ridge 1920 m and in the south rockall trough 3580 m on two cruises bracketing the expected 1998 spring phytodetrital flux density and biomass of epibenthic megafauna declined with depth and were consistent with previous data from the deep northeast atlantic aggregations of the hexactinellid sponge pheronema carpenteri occurred at 1100 m the percentage contribution of suspension feeders to megafaunal biomass at the lower slope sites was much higher than expected for these depths macrofauna sensu stricto were consistently undersampled by a box corer relative to an hydraulically damped multiple corer estimated macrofaunal densities declined with depth polychaete trophic group structure was very different at the three sites with more small carnivores at 1100 m surface deposit and interface feeders at 1920 m and a higher representation of subsurface deposit feeders at 3580 m meiofaunal densities were low in comparison with published data from comparable depths in the northeast atlantic meiofaunal numbers increased at all three sites from may to july 1998 the increase at 1920 m was statistically significant and was associated with the greatest phytodetrital accumulation observed during the study period the relative contribution of the mega macro and meiofauna to benthic metazoan biomass did not vary consistently with depth and no trend was apparent in a review of data from other studies in the north atlantic depth related patterns in community size structure recorded from previous north atlantic studies were not all replicated suggesting the importance of local hydrodynamics and other environmental factors there was no obvious link between faunal parameters and biodiffusion coefficients or mixing modes estimated from radiotracer profiles diffusion analogue 210pbexcess profiles recorded at 3580 and 1100 m resulted from a combination of macrofaunal and megafaunal sediment mixing some of it advective at 1920 m a combination of deep megafaunal subduction and near surface concentration of macrofaunal feeding activity produced subsurface radiotracer peaks the poorly known burrowing megafauna probably play a significant role in bioturbation at all three sites

petrology and chemistry of two large granite clasts from the moon abstract pristine granite clasts in apollo 14 breccias 14321 and 14303 have estimated masses of 1 8 and 0 17 g respectively the 14321 clast is 60 k feldspar and 40 quartz with traces of extremely mg poor mafic silicates and ilmenite the 14303 clast is roughly 33 plagioclase 32 k feldspar 23 quartz 11 pyroxene and 1 ilmenite pyroxene and ilmenite are moderately mg rich plagioclase and pyroxene are strongly zoned both clasts are severely brecciated but monomict pristine both have abundant graphic intergrowths of k feldspar with quartz unlike the majority of similar earth rocks both clasts are devoid of hydrous phases the bulk composition of the 14321 clast is similar to those of several other lunar granitic samples but the 14303 clast is unique it bears as close a resemblance to kreep as it does to other lunar granites silicate liquid immiscibility may explain why the granites are low in ree relative to kreep

a statistical study of gravity waves in the polar regions based on operational radiosonde data gravity waves in the lower polar stratosphere are examined using operational radiosonde observations gathered from 33 stations over a period of 10 years both the potential and kinetic energies of the gravity waves vary annually and reach maxima in winter in the arctic and in spring in the antarctic in the antarctic spring a region of large gravity wave energy propagates downward following the movement of a zone of high static stability associated with southern hemispheric warming moreover the enhanced energy region and the high stability zone coincide in the horizontal plane and move gradually from 135 e 50 s to 45 w 70 s over the south pole the vertical and horizontal directions of wave propagation are examined using hodograph analysis in the vertical most gravity waves transfer energy upward in the arctic while the percentage of downward energy propagation is relatively high in winter and spring in the antarctic horizontally gravity waves propagate westward relative to the mean wind in the arctic while in the antarctic the dominant direction varies from station to station the correlation between gravity wave energy in the lower stratosphere and the mean wind is also examined in the arctic gravity wave energy is highly correlated with the surface wind though in the antarctic it correlates with the stratospheric wind these results suggest that gravity waves observed in the arctic are forced by topography whereas in antarctica some sources may exist in the stratosphere one such source candidate is likely to be the polar night jet

numerical simulation of impact cratering on granular material a new numerical code based on the distinct element method dem is developed to study the impact cratering processes on granular material this code has a potential advantage to simulate the cratering process on granular material since the movement of discrete particles can be treated to show the physical plausibility of this code we conduct 3 d numerical simulations of vertical impact into granular material targets that consist of 384 000 particles and compare the results with those from experimental studies it is shown that the excavation stage of cratering derived from experimental studies is represented well by our simulation the size of the crater cavity and the ejecta velocity and angle distributions are consistent with those obtained in laboratory experiments the impact simulation code developed in this study is thus suggested to be useful for the analysis of the impact cratering process on granular material

trapped waves in the edge region of stratospheric polar vortices 1 a global distribution and seasonal variability of short period 2 days disturbances in the lower and middle stratosphere are investigated using 6 hourly european centre for medium range weather forecasts reanalysis data over 15 years 1979 1993 two dimensional spectral analysis and a recently developed lagrangian mean diagnostic are used for the analysis it is shown that the short period disturbances are most active around the polar night jet in each winter hemisphere they have a wavelike structure in the longitudinal direction with typical zonal wavelengths of 1 700 2 000 km i e zonal wave number 10 12 and a latitudinally evanescent structure with a half width of about 1 500 km suggesting that they are waves trapped in the edge region of the polar vortex where the latitudinal gradient of isentropic potential vorticity is maximized the trapped waves have a nearly barotropic structure over a depth greater than 10 km because the polar vortex in the northern hemisphere is much deformed and not symmetric around the pole dynamical characteristics of the trapped waves in the southern hemisphere alone are investigated by applying a lag correlation analysis to the reanalysis data the characteristics of trapped waves are fairly dependent on the state of the polar vortex such as zonal wind speed and its vertical shear they have a significant westward intrinsic phase velocity from june through october when the polar vortex is most stable this indicates that the trapped waves during this period have their own dynamics contrary to the filaments being passively advected by the large scale flow

gravity wave generation around the polar vortex in the stratosphere revealed by 3 hourly radiosonde observations at syowa station intensive radiosonde observations were performed at syowa station 69 0 s 39 6 e over about 10 days in each of march june october and december 2002 to examine inertia gravity wave characteristics in the antarctic lower stratosphere based on the 3 hourly observation data two dimensional i e vertical wavenumber versus frequency spectra of wind fluctuations were examined utilizing a double fourier transform method clear signals of gravity waves whose phases propagate upward suggesting downward energy propagation are detected in june and october when the polar night jet pnj was present on the other hand downward phase propagation i e upward energy propagation components are dominant in all months there is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in december when the background wind was weak whereas large spectral densities are distributed over lower frequency regions in june and october these spectral characteristics are consistent with the results obtained using a gravity wave resolving global circulation model gcm by sato et al dynamical characteristics are examined separately for upward and downward propagating gravity waves in june using a hodograph analysis method as a result it is found that upward and downward propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities this fact suggests that these gravity waves are generated from the same source with a similar mechanism when the wave packets were observed both the local rossby number and the residual in the nonlinear balance equation estimated using ncep ncar reanalysis data are large around the pnj situated slightly to the lower latitudes of syowa station therefore it is likely that the observed inertia gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced pnj and propagate toward syowa station the possibility of spontaneous gravity wave generation around the pnj is confirmed by comparison with the gcm simulation by sato et al

feldspathic lunar meteorites pecora escarpment 02007 and dhofar 489 contamination of the surface of the lunar highlands by post basin impacts abstract pca pecora escarpment 02007 and dhofar 489 are both meteorites from the feldspathic highlands of the moon pca 02007 is a feldspathic breccia consisting of lithified regolith from the lunar surface it has concentrations of both incompatible and siderophile elements that are at the high end of the ranges for feldspathic lunar meteorites dhofar 489 is a feldspathic breccia composed mainly of impact melted material from an unknown depth beneath the regolith concentrations of incompatible and siderophile elements are the lowest among brecciated lunar meteorites among 19 known feldspathic lunar meteorites all of which presumably originate from random locations in the highlands concentrations of incompatible elements like sm and th tend to increase with those of siderophile elements like ir feldspathic meteorites with high concentrations of both suites of elements are usually regolith breccias iridium derives mainly from micrometeorites that accumulate in the regolith with duration of surface exposure micrometeorites have low concentrations of incompatible elements however so the correlation must reflect a three component system we postulate that the correlation between sm and ir occurs because the surface of the feldspathic highlands terrane has become increasingly contaminated with time in sm rich material from the procellarum kreep terrane that has been redistributed across the lunar surface by impacts of moderate sized post basin impacts the most sm rich regolith breccias among feldspathic lunar meteorites are about 3 enriched compared to the most sm poor breccias but this level of enrichment requires only a few percent sm rich material typical of the procellarum kreep terrane the meteorite data suggest that nowhere in the feldspathic highlands are the concentrations of k rare earths and th measured by the lunar prospector mission at the surface representative of the underlying bedrock all surfaces covered by old regolith as opposed to fresh ejecta are at least slightly contaminated dhofar 489 is one of 15 paired lunar meteorite stones from oman total mass of meteorite 1037 g on the basis of its unusually high mg fe ratio the meteorite is likely to have originated from northern feldspathic highlands

trace element fractionation by impact induced volatilization sims study of lunar hasp samples impact is a dominant process acting on the surfaces of planetary bodies and is the major process that modifies the physical and chemical nature of planetary materials on atmosphere free bodies once volcanic activity has ceased elements with relatively high volatilities are readily mobilized during impact hasp high alumina silica poor compositions are thought to be generated by impact induced volatilization processes on the moon the high al si ratio of hasp is believed to be the result of preferential loss of sio 2 relative to al 2 o 3 here we report sims analyses for hasp glass beads and devitrified glasses from the apollo 14 regolith to assess the behavior of li be b ree sr y and zr during impact events we compare the behavior of these trace elements to the behavior of major and minor elements analyzed by the electron microprobe the hasp samples we studied fall into two compositional groups with one group apparently derived from kreepy lunar lithologies and the other from anorthosite the kreepy hasp beads have an estimated mass loss of 28 compared to their kreepy protolith we estimate that 44 of sio 2 and 35 of feo were lost during impact induced volatilization the mass loss estimate for the anorthositic protolith to produce anorthositic hasp is more uncertain because of the uncertainty of the protolith composition however an estimate of approximately 25 appears reasonable with 38 loss of silica clearly impact processes in the early stages of planetary evolution are important in the modification of geochemical signatures and ordinarily geochemically coherent elements may be decoupled because of different volatilities

general aspects of a t213l256 middle atmosphere general circulation model 1 a high resolution middle atmosphere general circulation model gcm developed for studying small scale atmospheric processes is presented and the general features of the model are discussed the gcm has t213 spectral horizontal resolution and 256 vertical levels extending from the surface to a height of 85 km with a uniform vertical spacing of 300 m gravity waves gws are spontaneously generated by convection topography instability and adjustment processes in the model and the gcm reproduces realistic general circulation in the extratropical stratosphere and mesosphere the oscillations similar to the stratopause semiannual oscillation and the quasi biennial oscillation qbo in the equatorial lower stratosphere are also spontaneously generated in the gcm although the period of the qbo like oscillation is short 15 months the relative roles of planetary waves large scale gws and small scale gws in maintenance of the meridional structures of the zonal wind jets in the middle atmosphere are evaluated by calculating eliassen palm diagnostics separately for each of these three groups of waves small scale gws are found to cause deceleration of the wintertime polar night jet and the summertime easterly jet in the mesosphere while extratropical planetary waves primarily cause deceleration of the polar night jet below a height of approximately 60 km the meridional distribution and propagation of small scale gws are shown to affect the shape of the upper part of mesospheric jets the phase structures of orographic gws over the south andes and gws emitted from the tropospheric jet stream are discussed as examples of realistic gws reproduced by the t213l256 gcm

chemical gradient at diffusive interfaces in magma chambers the results of high pressure experiments on diffusion and soret separation in natural silicate melts show that the diffusive behaviour between natural silicic and mafic magmas can be approximately modelled as if the system were a binary mixture of sio2 and other components such as mgo feo cao steady state compositional profiles across a diffusive interface between silicic and mafic magma layers are calculated on the basis of phenomenological relationships for the fluxes of chemical species and heat in the binary mixtures using the experimental data of diffusion and soret coefficients in natural silicate melts the compositional profiles show a curvature with a minimum sio2 value within the interface due to the soret effect and temperature dependence of diffusion coefficient the compositional gradient at the lower half of the diffusive interface is similar to that resulting from the soret separation of a mafic melt regardless of the composition of the silicic magmas these results suggest that picritic magma can be formed in the interfacial region between the mafic and silicic magma layers the compositional gradient explains chemical variation of mafic to picritic inclusions in a mixed andesite of the abu volcano group japan

lunar rock rain diverse silicate impact vapor condensates in an apollo 14 regolith breccia abstract apollo 14 regolith breccia 14076 long known to be uniquely endowed with high alumina silica poor hasp material of evaporation residue origin has been found to contain a diverse suite of complementary condensates dubbed gasp gas associated spheroidal precipitates gasp occurs in two forms as glassy or extremely fine grained quenched melt spheroids mostly less than 5 m across and as quenched textured clasts up to 200 m across in two of the clasts origin by aggregation of spheroidal gasp is confirmed by the presence of relict spheroids gasp is distinctively depleted in the same refractory major oxides that are characteristically enriched in hasp al 2 o 3 and cao among the larger gasp spheroids al 2 o 3 is seldom 1 wt among the clasts excluding two instances of apparent contamination by na and k rich substrate derived melt bulk al 2 o 3 averages 0 3 wt depletion of al 2 o 3 and cao is also manifested by pyroxene compositions in some clasts e g in the largest clast en 82 wo 0 45 with 0 07 wt al 2 o 3 although gasp bulk compositions are nearly pure sio 2 mgo feo they are nonetheless highly diverse spheroid compositions range in mg from 7 to 84 mol and in feo sio 2 weight ratio from 0 002 to 0 67 bulk compositions and textures of many gasp spheroids suggest that liquid immiscibility occurred prior to quenching implying that these materials were some time after condensation at temperatures of 1680 c textural evidence for immiscibility includes lobate boundaries between silicic and mafic domains and a general tendency for quenched mafic silicates to be concentrated into a few limited patches rather than evenly dispersed the parent melt of the largest clast s pyroxene is inferred to have formed as a partial melt within the parent aggregation of gasp matter compositionally near the pyroxene cristobalite melt eutectic and thus at 1500 c a few gasp spheroids show possible signs of in flight collision coalescence but aggregation of the much larger clasts probably took place in mushy puddles on the lunar surface little mixing took place between these gasp puddles and the related hasp probably because gasp condensation did not commence until after an intermediate stage during which while neither net evaporation nor net condensation took place expansion of the vapor cloud carried the eventual gasp matter well apart from the hasp considering the characteristic length scale of lunar regolith mixing the concentration of both gasp and hasp into this single unique regolith sample 14076 is most consistent with a parent crater size diameter of 10 100 km i speculate that the 14076 regolith may have been unusually situated almost directly uprange from an unusually oblique large impact mercurian analogs of the 14076 impact condensates may have significant implications for remote sensing

lunar and martian meteorite delivery services launch mechanisms for lunar and martian meteorites have been investigated by integrating physical modeling constraints geochemical cosmic ray exposure cre constraints and petrologic constraints the potential source region for lunar meteorites is remarkably small compared to the final crater volume cre constraints indicate that most launches start at depths of 3 2 m and cratering theory implies derivation of suitably accelerated objects from a subvolume with diameter only about 0 3 the final crater diameter the shallow depth provenance is probably related to shock wave interference enhanced by the lunar regolith s extremely low compressional wave velocity cre constraints alone imply that four to five separate launch events are represented among the eight well studied lunar meteorites most of the lunar meteorites are regolith breccias which tend to show only limited compositional diversity within any kilometer scale region of the moon several others are polymict breccias which also show relatively subdued compositional diversity compared to igneous rocks the observed diversity among these samples in terms of abundances of mare basalt and kreep and in mg mg fe ratio implies that among eight well studied lunar meteorites only two potential source crater pairings are plausible between asuka 881757 y 793169 most probable and between y 793274 eet875721 altogether these eight lunar meteorites apparently represent at least six separate source craters including three in the past 105 years and five in the past 106 years cre constraints imply that snc meteorites are launched from systematically greater depths than lunar meteorites sncs are also systematically bigger and all nine well studied sncs are uncommonly young by martian standards mafic igneous rocks comparison between viking and apollo results reveals that rocks the size of common meteorites are remarkably scarce in the martian regolith probably due to pervasive weathering a plausible explanation for these trends is that most old small and shallow rocks on mars have been weakened by a two stage process of brecciation followed by pervasive weathering to the point where they seldom survive the stresses of spallation off the planet the scarcity of source crater pairing among the lunar meteorites implies that these objects can be launched from craters much smaller than previously estimated and tends to support the suggestion of rabinowitz 1993 astrophys j 407 412 427 that present day cratering rates for the earth moon region may be higher than previously estimated

spherule layers records of ancient impacts abstract a large extraterrestrial object striking earth at cosmic velocity melts and vaporizes silicate materials which can condense into highly spheroidal sand size particles that get deposited hundreds to thousands of kilometers from the point of impact these particles known as impact spherules have been detected in great abundance in a relatively small number of thin discrete layers ranging in age from less than a million years to 3 47 billion years unaltered impact spherules consist entirely of glass microtektites or a combination of glass and crystals grown in flight microkrystites impact spherule layers form very rapidly and can be very extensive even global in extent e g the cretaceous tertiary k t boundary layer so they form excellent time stratigraphic markers because they are always found in a stratigraphic context spherule layers are probably superior to terrestrial craters and related structures for assessing the environmental and biotic effects of large impacts a reco

new lunar meteorites impact melt and regolith breccias and large scale heterogeneities of the upper lunar crust we have analyzed nine highland lunar meteorites lunaites using mainly inaa several of these rocks are difficult to classify dhofar 081 is basically a fragmental breccia but much of its groundmass features a glassy fluidized texture that is indicative of localized shock melting also much of the matrix glass is swirly brown suggesting a possible regolith derivation we interpret dar al gani dag 400 as an extremely immature regolith breccia consisting mainly of impact melt breccia clasts we interpret dhofar 026 as an unusually complex anorthositic impact melt breccia with scattered ovoid globules that formed as clasts of mafic subophitic impact melt the presence of mafic crystalline globules in a lunar material even one so clearly impact heated suggests that it may have originated as a regolith our new data and a synthesis of literature data suggest a contrast in al2o3 incompatible element systematics between impact melts from the central nearside highlands where apollo sampling occurred and those from the general highland surface of the moon impact melts from the general highland surface tend to have systematically lower incompatible element concentration at any given al2o3 concentration than those from apollo 16 in the case of dhofar 026 both the bulk rock and a comparatively al poor composition 14 wt al2o3 7 g g sm extrapolated for the globules manifest incompatible element contents well below the apollo 16 trend impact melts from luna 20 57e distribute more along the general highland trend than along the apollo 16 trend siderophile elements also show a distinctive composition for apollo 16 impact melts ni ir averaging 1 8x chondritic in contrast lunaite impact melt breccias have consistently chondritic ni ir impact melts from luna 20 and other apollo sites show average ni ir almost as high as those from apollo 16 the prevalence of this distinctive ni ir ratio at such widely separated nearside sites suggests that debris from one extraordinarily large impact may dominate the megaregolith siderophile component of a nearside region 2300 km or more across highland polymict breccia lunaites and other kreep poor highland regolith samples manifest a strong anticorrelation between al2o3 and mg the magnesian component probably represents the chemical signature of the mg suite of pristine nonmare rocks in its most pure form unaltered by the major kreep assimilation that is so common among apollo mg suite samples the average composition of the ferroan anorthositic component is now well constrained at al2o3 29 30 wt implying about 17 19 wt modal mafic silicates in good agreement with the composition predicted for flotation crust over a ferroan magma ocean warren 1990

soret separation of mid ocean ridge basalt magma chemical differentiation of an initially homogeneous mid ocean ridge basalt morb liquid has been experimentally observed in a temperature gradient above the liquidus the magnitude of this effect in producing differences in composition is comparable to that of crystal liquid fractionation for a given temperature difference however the chemical changes produced by the two processes soret and crystal liquid fractionation are different soret separations resemble those observed in a third process silicate liquid immiscibility this similarity is a reflection of the fact that the soret separable components are the same network former network modifier structural components which segregate during silicate liquid immiscibility

present day and past last 25000 years marine pollen signal off western iberia abstract the comparison between modern terrestrial and marine pollen signals in and off western iberia shows that marine pollen assemblages give an integrated image of the regional vegetation colonising the adjacent continent present day mediterranean and atlantic forest communities of iberia are well discriminated by south and north marine pollen spectra respectively results from total pollen concentration together with recognized conceptual models of fine particle dynamics in the iberian margin have allowed us to establish the present day pattern of pollen dispersion in this region the 25 000 year long record of continental pollen and marine 18 o of globigerina bulloides ice rafted detritus ird and neogloboquadrina pachyderma s proxies from the galician margin composite core md99 2331 and md03 2697 show that vegetation cover in north western iberia has responded contemporaneously to the climate variability of the north atlantic the vegetation response to the well known north atlantic heinrich events 2 and 1 h2 and h1 is however complex and characterised by two vegetation phases at low and mid altitudes of north western iberia the beginning of each heinrich event is marked on land by an important pine forest reduction and the expansion of heathers which are synchronous with the heaviest planktic 18 o values and the maxima of n pachyderma s suggesting that these first phases were cold and wet pinus forest expansion characterising the second phase of each heinrich event indicates a less cold episode associated during h1 with an increase of dryness as suggested by the development of semi desert associations the comparison of our galician margin multi proxy record with several pollen sequences from in and off iberia allows us to demonstrate that h1 event is the marine equivalent of the oldest dryas on the continent the occurrence of temperate trees during the last glacial maximum lgm and the rapid expansion of deciduous quercus during the bolling allerod period in our galician margin composite sequence show that not only the southern but also north western iberia was a refugium zone for deciduous trees during the last glacial period especially at low and mid altitude zones furthermore the comparison between southern and northern marine and terrestrial sequences allows us to confirm that vegetation responded to the bolling allerod warming the younger dryas cold event and the holocene more quickly in low and mid altitudes of north western iberia and in the south than in the high altitude northern region most likely as the result of the higher density of refugia for temperate trees in these zones during the lgm

ascent and eruption of a lunar high titanium magma as inferred from the petrology of the 74001 2 drill core abstract an analysis of the orange glasses and crystallized beads from the 68 cm deep 74001 2 core has been conducted to understand the processes occurring during ascent and eruption of the apollo 17 orange glass magma equilibrium between melt and metal blebs fe85ni14co1 within the core along with cr contents in olivine phenocrysts suggest there was an oxidation of c and a reduction of the melt at an o fugacity of iw 1 3 and 1320 c to form co gas at 200 bars or 4 km depth this was followed by development of more oxidized conditions during ascent also during ascent there was formation of euhedral homogeneous fo81 olivine crystals and spinel crystals with higher al and mg contents than the smaller spinels in the crystallized beads both the metal blebs and al rich spinels were trapped inside the fo81 olivine phenocrysts as they grew prior to eruption the composition of the orange glasses are homogeneous throughout the core except for a few distinct glasses at the top that appear to have been mixed in by micrometeorite reworking a few glassy melt inclusions of orange glass composition trapped in the fo81 phenocrysts contain 600 100 ppm s and 50 ppm cl compared to the 200 ppm s and 50 ppm cl in the orange glass melt when quenched these inclusions therefore document the addition of 400 ppm s to the co rich volcanic gas during the eruption the size and distribution of different volcanic beads in the apollo 17 deposit indicate a mode of eruption in which the orange glasses and partially crystallized beads formed further away from the volcanic vent where cooling rates were faster progressively larger and more numerous crystals in the black beads reflect slower cooling rates at higher optical densities in the volcanic plume the development of a brown texture in the orange glasses at the bottom of the core where the black beads dominate is interpreted to result from devitrification by subsolidus heating either as the orange glasses fell back through the hot plume or after deposition on the surface the change from domination by orange glasses to black beads in the core probably reflects a decrease in gas content over time which consequently would increase the plume optical density and favor slower cooling rates

energy enhancements of gravity waves in the antarctic lower stratosphere associated with variations in the polar vortex and tropospheric disturbances 1 gravity waves in the antarctic lower stratosphere are examined using original operational radiosonde data obtained at syowa station 69 0 s 39 6 e with fine vertical resolution in the lower stratosphere the temporal variation in gravity wave energy depends on height in the height region of 13 15 km just above the tropopause the seasonal variation in gravity wave energy is not evident the wave energy is rather enhanced when the absolute value of potential vorticity in the upper troposphere becomes small over syowa station this fact implies that tropospheric disturbances affect the dynamical processes of gravity waves there however the gravity wave energy in the height region of 15 25 km shows clear seasonal variation having a maximum in spring the time variation in gravity wave energy is examined in detail in terms of the polar vortex by using the equivalent latitude coordinate energy enhancements occur when the edge of the polar vortex approaches syowa station and the enhancements are especially large when the polar vortex breaks down in spring these results suggest that height variation in the background atmosphere leads to the difference of wave characteristics between the two height regions the enhancements of wave energy are partly explained as modification of the wave structure by the background wind speed and the static stability but it is also likely that enhancements of wave activity contribute to the energy enhancement at the edge of the polar vortex in spring

gravity wave characteristics in the lower atmosphere at south pole a 4 year 1993 1996 temperature and wind data set obtained from over 2000 high resolution balloon soundings at south pole is used to study gravity wave characteristics in the troposphere and lower stratosphere extensive analyses of energy density spectra and static stability are performed to present a comprehensive view of the gravity wave characteristics in the lower atmosphere at south pole our results show that the gravity waves are ubiquitous and often fairly strong at south pole even though the generation mechanisms are not clear gravity wave characteristics are in general similar to those obtained at other high latitude southern hemisphere stations potential energies vary between about 0 5 j kg and 5 j kg with season and altitude variations in kinetic energies are not well correlated with potential energy variations and range from 1 j kg to 11 j kg we observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations especially in the stratosphere in general the gravity waves in the stratosphere are stronger weaker in austral spring fall wave activity in the troposphere has little seasonal dependence stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere the probability of wave instability is 13 7 in the troposphere and 5 4 in the stratosphere this is due to the less stable stratification in the troposphere where the buoyancy period averages 8 3 min compared to 4 9 min in the stratosphere dynamic shear instability is more likely to occur than convective instability 11 versus 2 6 in the troposphere and 4 7 versus 0 7 in the stratosphere due to the prevailing strong wind shear the instability probabilities vary seasonally with the austral winter exhibiting the highest probability of instabilities dynamic and convective instabilities combined in both the troposphere and stratosphere

spinel bearing spherules condensed from the chicxulub impact vapor plume formation of the giant chicxulub crater off mexico s yucatan peninsula coincided with deposition of the global ir rich cretaceous tertiary k t stratigraphic boundary layer at ca 65 ma the boundary is marked most sharply by abundant spherules containing unaltered grains of magnesioferrite spinel here we predict for the first time the sequential condensation of solids and liquids from the plume of vaporized rock expected from oblique k t impacts we predict highly oxidizing plumes that condense silicate liquid droplets bearing spinel grains whose compositions closely match those marking the actual boundary systematic global variations in spinel composition are consistent with higher condensation temperatures for spinels found at atlantic and european sites than for those in the pacific

a statistical approach to estimate the 3d size distribution of spheres from 2d size distributions size distribution of rigidly embedded spheres in a groundmass is usually determined from measurements of the radii of the two dimensional 2d circular cross sections of the spheres in random flat planes of a sample such as in thin sections or polished slabs several methods have been devised to find a simple factor to convert the mean of such 2d size distributions to the actual 3d mean size of the spheres without a consensus we derive an entirely theoretical solution based on well established probability laws and not constrained by limitations of absolute size which indicates that the ratio of the means of measured 2d and estimated 3d grain size distribution should be 4 785 actual 2d size distribution of the radii of submicron sized pure fe 0 globules in lunar agglutinitic glass determined from backscattered electron images is tested to fit the gamma size distribution model better than the log normal model numerical analysis of 2d size distributions of fe 0 globules in 9 lunar soils shows that the average mean of 2d 3d ratio is 0 84 which is very close to the theoretical value these results converge with the ratio 0 8 that hughes 1978 determined for millimeter sized chondrules from empirical measurements we recommend that a factor of 1 273 reciprocal of 0 785 be used to convert the determined 2d mean size radius or diameter of a population of spheres to estimate their actual 3d size

modeling the ries steinheim impact event and the formation of the moldavite strewn field using detailed geological petrographic geochemical and geographical constraints we have performed numerical modeling studies that relate the steinheim crater apparent diameter da 3 8 km the ries crater da 24 km in southern germany and the moldavite tektite strewn field in bohemia and moravia czech republic lusatia east germany and lower austria the moldavite strewn field extends from 200 to 450 km from the center of the ries to the east northeast forming a fan with an angle of 57 an oblique impact of a binary asteroid from a west southwest direction appears to explain the locations of the craters and the formation and distribution of the moldavites the impactor must have been a binary asteroid with two widely separated components some 1 5 and 0 15 km in diameter respectively we carried out a series of three dimensional hydrocode simulations of a ries type impact the results confirm previous results suggesting that impacts around 30 50 from the horizontal are the most favorable angles for near surface melting and consequently for the formation of tektites finally modeling of the motion of impact produced tektite particles through the atmosphere produces in the downrange direction a narrow angle distribution of the moldavites tektites in a fan like field with an angle of 75 an additional result of modeling the motion of melt inside and outside the crater is the preferred flow of melt from the main melt zone of the crystalline basement downrange towards the east northeast rim this explains perfectly the occurrence of coherent impact melt bodies some tens of meters in size in a restricted zone of the downrange rim of the ries crater the origin of these melt bodies which represent chemically a mixture of crystalline basement rocks similar to the main melt mass contained as melt particles 0 5 m in size in the suevite do not occur at any other portion of the ries crater rim and remained enigmatic until now although the calculated distribution of moldavites still deviates to some degree from the known distribution our results represent an important step toward a better understanding of the origin and distribution of the high velocity surface melts and the low velocity deep seated melt resulting from an oblique impact on a stratified target

longitudinally dependent ozone increase in the antarctic polar vortex revealed by balloon and satellite observations the horizontal structure of processes causing increases in ozone in the antarctic polar vortex was examined using data measured in 2003 from an ozonesonde observation campaign at syowa station 39 68e 69 08s and from the improved limb atmospheric spectrometer ii ilas ii onboard the advanced earth observing satellite ii the ilas ii data are daily and distributed uniformly at 14 points in the zonal direction mostly at polar latitudes the antarctic ozone hole that developed in 2003 was one of the largest recorded the period of focus in this study is 26 september through 24 october when a strong polar vortex was situated in the stratosphere an ozone mixing ratio contour 1 0 ppmv moved downward near a height of 20 km during the period of focus this increase in ozone is likely to result from downward transport of ozone rich air originating from lower latitudes by brewer dobson circulation first the descent rate of the mixing ratio contour was estimated by taking the geometric height as the vertical coordinate for the deep vortex interior around 20 km a significant longitudinal dependence was observed an analysis using ecmwf operational data shows that this dependence can be approximately explained by longitudinally dependent vertical movements of the isentropes caused by a zonal wavenumber 1 quasi stationary planetary wave with amplitude and phases varying on a seasonal time scale next the descent rate was calculated around 500 k around 20 km by taking the potential temperature isentrope as the vertical coordinate the longitudinal dependence was still present using this coordinate meaning that the ozone mixing ratio and its increase are not constant on the isentropic layer even in the interior of the polar vortex a backward trajectory analysis showed that air parcels with large ozone mixing ratios were mostly transported from the polar vortex boundary region this result suggests that lateral transport mixing is important even before the breakup of the polar vortex results from a tracer tracer correlation analysis of o3 and long lived constituent n2o were also consistent with this inference the contribution of lateral mixing to the increase in ozone was estimated at about 17 6 4 that of the brewer dobson circulation around 20 km using the calculated descent rates the results of this study also imply that lagrangian downward motions in the vortex interior are not correctly estimated without accounting for lateral mixing even if the polar vortex is dynamically stable

the nature and origin of rims on lunar soil grains abstract space weathering processes that operate in the lunar regolith modify the surfaces of lunar soil grains transmission electron microscope analysis of the lunar soil grains from the fine size fraction of several lunar soils show that most grains are surrounded by thin 60 200 nm thick rims the microstructure and chemical compositions of the rims can be used to classify rims into four broad categories amorphous inclusion rich multiple and vesicular amorphous rims are noncrystalline generally lack crystalline inclusions show evidence for preferential sputtering of cations and are produced largely by solar wind irradiation damage inclusion rich rims contain abundant nanometer sized grains of fe metal as randomly dispersed inclusions or as distinct layers embedded in an amorphous silica rich matrix inclusion rich rims are compositionally distinct from their host grains and typically contain accumulations of elements that are not indigenous to the host inclusion rich rims are formed largely by the deposition of impact generated vapors with a contribution from the deposition of sputtered ions a continuum in the chemical and microstructural properties exists between typical amorphous rims and typical inclusion rich rims multiple rims consist of a distinct radiation damaged layer up to 50 nm thick that is overlain by vapor deposited material of comparable thickness vesicular rims are compositionally similar to their hosts and are characterized by an abundance of small the formation of rims on lunar soils is complex and involves several processes whose effects may be superimposed from this study it is shown that one process does not dominate and that the relative importance of vapor deposition is comparable to radiation damage in the formation of rims on lunar silicate grains the presence of rims on lunar soil grains particularly those with nanometer sized fe metal inclusions may have a major influence on the optical and magnetic properties of lunar soils

wintertime temperature maximum at the subtropical stratopause in a t213l256 gcm 1 a wintertime temperature maximum can be observed at the subtropical stratopause but does not appear in the radiative equilibrium temperature distribution this structure was well simulated using a high resolution general circulation model and examined in detail the stratopause temperature is latitudinally maximized in the winter subtropics because of a strong downwelling of the meridional circulation from summer tropics to winter subtropics passing above the stratopause its strong meridional flow consists of two parts a strong poleward flow in the winter subtropics with nearly vertically aligned contours of absolute angular momentum m and a strong cross equatorial flow toward winter hemisphere above the tropical stratopause with nearly horizontally aligned m contours the strong poleward flow in the winter subtropics is driven by a large eliassen palm e p flux convergence in a small absolute vorticity region the large e p flux convergence is due to extratropical planetary waves and asymmetric inertial instability on the other hand the strong cross equatorial flow is induced along the m contour to satisfy mass continuity with the strong poleward flow in the winter subtropics and exists in the easterly phase of s sao with a small latitudinal gradient of m the easterly of s sao during its mature phase acts as a corridor for cross equatorial meridional circulation while cross equatorial meridional circulation contributes to driving the easterly of s sao in its development phase

in quest of lunar regolith breccias of exotic provenance a uniquely anorthositic sample from the fra mauro apollo 14 highlands polymict samples can be used to establish mass balance constraints regarding the bulk composition of the lunar crust and to gauge the degree of regional heterogeneity in the composition of the lunar crust the most ideally polymict type of sample is finely mixed regolith lunar soil or its lithified equivalent regolith breccia fortunately lunar regolith breccias can occasionally be found at great distances from their points of origin most of the known lunar meteorites are regolith breccias we are searching for examples of exotic regolith samples among the apollo regolith breccia collection most of the 21 apollo regolith breccias analyzed for this study strongly resemble the local soils over which they were collected nine regolith breccias from apollo 16 are surprisingly mature compared to previously analyzed apollo 16 regolith breccias and six of the seven from apollo 16 station 5 have lower more local soil like mg ratios than previously analyzed regolith breccias from this station several of the apollo 14 regolith breccias investigated show significantly highermg and lower al than the local soils the most interesting sample we have investigated is 14076 1 from a lithology that constitutes roughly half of a 2 0 g pebble the presence of spherules indicates a regolith derivation for 14076 1 yet its highly aluminous 30 wt al2o3 composition is clearly exotic to the 1 6 km traverse surface over which the apollo 14 samples were collected this sample resembles soils from the descartes apollo 16 highlands far more than it does any other polymict sample from the fra mauro apollo 14 region the i sfeo maturity index is extremely low but this may be a result of thermal annealing a variety of siderophile elements occur in 14076 1 at typical regolith concentrations the chemistry of the second most aluminous regolith sample from apollo 14 14315 can only be roughly approximated as a mixture of local regolith and 14076 1 like material however the low a priori statistical probability for long distance horizontal transport by impact cratering along with the relatively high contents of incompatible elements in 14076 1 despite its high al content suggest that this regolith breccia probably originated within a few hundred kilometers of the appollo 14 site if so its compositional resemblance to ferroan anorthosite tends to suggest that the regional crust is or originally was far richer in ferroan anorthosite than implied by the meager statistics for pristine rocks from this site thus 14076 1 tends to strengthen the hypothesis that ferroan anorthosite originated as the flotation crust of a global magmasphere

lunar mg suite thermobarometry and petrogenesis of parental magmas using compilations of internally consistent thermodynamic data on minerals and advances in quantifying the energetics of crystalline solid solutions we have recalculated the pressures and temperatures of equilibration of troctolite sample 76535 and a number of spinel cataclasites the five phase assemblage olivine orthopyroxene clinopyroxene cr spinel plagioclase which occurs in symplectite assemblages in 76535 gives equilibration temperatures from 800 900 c and pressures from 200 to 250 mpa indicating a deep 40 50 km crustal source spinel cataclasite assemblages give minimum pressures of 100 mpa mg suite magmas were apparently intruded throughout the lunar crust early in lunar history the textures and equilibration temperatures in many mg suite samples are consistent with sub solidus recrystallization and the mg rich minerals of some refractory troctolites and dunites may be residues of a crustal melting process or products of subsolidus elemental redistribution the sm nd age of 4 26 0 06 ga of troctolite 76535 most likely represents the time of sub solidus recrystallization and or partial melting in an attempt to identify the primary source material for the mg suite magmas a variety of models were tested using the melts and magfox codes a good fit between mineral compositions and crystallization sequences is obtained by 20 batch melting at 0 5 gpa of an average whole moon composition with an mg of 0 85 melts formed by batch melting at higher pressures and melts formed by poly baric partial fusion over the pressure range from 2 0 to 0 3 gpa were either too poor in mg and or crystallized clinopyroxene before orthopyroxene mixing with 10 20 urkreep which is required to satisfy the ree constraints of the mg suite reduces the mg of the parental magmas and requires a whole moon mg closer to that of the terrestrial mantle

formation of apollo 17 orange and black glass beads size frequency distributions of the cross sections of orange and black glass beads in the 125 250 m fraction of soil 74220 have been determined cross section medians of black vitrophyric and orange glassy beads in the 125 250 m fraction are 0 16 mm and 0 14 mm respectively the vitrophyric beads contain skeletal olivine crystals mantled by ilmenite some beads contain fragments and euhedral crystals of endogeneous olivine free flight cooling rates and the critical cooling rate for crystallization have been determined with a synthetic melt of orange glass composition the critical cooling rate is approximately 100 c s the free flight cooling rate of droplets 0 16 mm in diameter is approximately 1080 c s it is inferred that apollo 17 orange melt droplets were erupted together with a large mass of hot gas and or formed a dense cloud of heat radiating droplets

gravity waves appearing in a high resolution gcm simulation global characteristics of gravity waves in the lower stratosphere are examined using a gcm with high resolution in both the horizontal t106 corresponding to about 120 km and the vertical 600 m the bottom boundary condition of the model is that of an aquaplanet with perpetual february sea surface temperature the simulated gravity waves are in good agreement with mesosphere stratosphere troposphere mst radar observations at a middle latitude on the gravity wave structure and on the frequency spectra as a function of height the frequency spectra of simulated wind and temperature fluctuations are also examined as a function of latitude large values of spectral density are observed at frequencies higher than the inertial frequency f in a weak wind region around 20 km which is consistent with the characteristics of internal gravity waves an isolated peak is observed near f for horizontal wind spectra at latitudes higher than 108 while the energy is distributed in a wide range of frequency at lower latitudes where f approaches zero further analysis is performed of those fluctuations having periods shorter than 24 h and those having vertical wavelengths smaller than 5 km these are frequently analyzed as gravity waves using observation data the distribution of energy and momentum fluxes in the latitude height section is examined the result indicates that short period waves mostly propagate upward and poleward from the equatorial region the wave energy reaches about 508 lat at the 27 km altitude a negative positive maximum of vertical flux of meridional momentum y9w9 is seen above the subtropical jet in the northern southern hemisphere for small vertical scale gravity waves this is consistent with the preferred equatorward propagation of the wave indicated by a statistical analysis based on mst radar observations the ratio of potential to kinetic energy maximizes over the equator and decreases poleward the eliassen palm flux divergence associated with gravity waves is decelerative above the subtropical jet albeit small

the effects of space weathering on apollo 17 mare soils petrographie and chemical characterization the lunar soil characterization consortium a group of lunar sample and remote sensing scientists has undertaken the extensive task of characterization of the finest fractions of lunar soils with respect to their mineralogical and chemical makeup these compositional data form the basis for integration and modeling with the reflectance spectra of these same soil fractions this endeavor is aimed at deciphering the effects of space weathering of soils on airless bodies with quantification of the links between remotely sensed reflectance spectra and composition a beneficial byproduct is an understanding of the complexities involved in the formation of lunar soil several significant findings have been documented in the study of the 2x whereas the abundance of agglutinitic glass increases by only 10 15 this is evidence for a large contribution from surface correlated nanophase fe0 to the is feo values particularly in the 10 m size fraction the surface nanophase fe0 is present largely as vapor deposited patinas on the surfaces of almost every particle of the mature soils and to a lesser degree for the immature soils keller et al 1999a it is reasoned that the vapor deposited patinas may have far greater effects upon reflectance spectra of mare soils than the agglutinitic fe0

near surface temperatures on mercury and the moon and the stability of polar ice deposits abstract in order to assess the thermal stability of polar ice deposits we present model calculated temperatures of flat surfaces and surfaces within bowl shaped and flat floored polar impact craters on mercury and the moon our model includes appropriate insolation cycles realistic crater shapes multiple scattering of sunlight and infrared radiation and depth and temperature dependent regolith thermophysical properties unshaded water ice deposits on the surface of either body are rapidly lost to thermal sublimation a subsurface water ice deposit is stable within 2 latitude of the moon s poles meter thick water ice deposits require billions of years to sublime if located in the permanently shaded portions of flat floored craters within 10 latitude of the poles of mercury and 13 latitude of the poles of the moon results for craters associated with radar features on mercury are consistent with the presence of stable water ice deposits if a thin regolith layer thermally insulates deposits at lower latitudes and within smaller craters a regolith cover would also reduce losses from diffusion ion sputtering impact vaporization and h ly and is implied independently by the radar observations permanently shaded areas near the moon s poles are generally colder than those near mercury s poles but the moon s obliquity history its orbit through earth s magnetospheric tail and its radar opaque regolith may limit the volume and radar detectability of ice deposits there

three dimensional structure of mass weighted isentropic time mean meridional circulations abstractthe present study develops a diagnostic framework for investigating the three dimensional 3 d structure of mass weighted isentropic time mean t mim meridional circulations and conducts a preliminary analysis of the winter hemispheres the t mim meridional velocity can unfold in the zonal direction time averaged two dimensional 2 d mass weighted isentropic zonal means furthermore the t mim velocity can be decomposed into the unweighted isentropic time mean utm velocity and the temporal eddy correlated transport velocity the so called bolus velocity the bolus velocity greatly contributes to the 2 d extratropical direct circulation in the troposphere and to the brewer dobson circulation in the stratosphere the 3 d bolus velocity seems to reflect the geographical distributions of baroclinic instability wave activity in the boreal winter both low level equatorward flows and upper level poleward flows are located around the north pacific and north atlantic storm tracks in the austral w

understanding oblique impacts from experiments observations and modeling natural impacts in which the projectile strikes the target vertically are virtually nonexistent nevertheless our inherent drive to simplify nature often causes us to suppose most impacts are nearly vertical recent theoretical observational and experimental work is improving this situation but even with the current wealth of studies on impact cratering the effect of impact angle on the final crater is not well understood although craters rims may appear circular down to low impact angles the distribution of ejecta around the crater is more sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts experimental studies established that crater dimensions depend only on the vertical component of the impact velocity the shock wave generated by the impact weakens with decreasing impact angle as a result melting and vaporization depend on impact angle however these processes do not seem to depend on the vertical component of the velocity alone finally obliquity influences the fate of the projectile in particular the amount and velocity of ricochet are a strong function of impact angle

atmos atlas 3 observations of long lived tracers and descent in the antarctic vortex in november 1994 observations of the long lived tracers n2o ch4 and hf obtained by the atmospheric trace molecule spectroscopy atmos instrument in early november 1994 are used to estimate average descent rates during winter in the antarctic polar vortex of 0 5 to 1 5 km month in the lower stratosphere and 2 5 to 3 5 km month in the middle and upper stratosphere descent rates inferred from atmos tracer observations agree well with theoretical estimates obtained using radiative heating calculations air of mesospheric origin n2o 5 ppbv was observed at altitudes above about 25 km within the vortex strong horizontal gradients of tracer mixing ratios the presence of mesospheric air in the vortex in early spring and the variation with altitude of inferred descent rates indicate that the antarctic vortex is highly isolated from midlatitudes throughout the winter from approximately 20 km to the stratopause the 1994 antarctic vortex remained well isolated between 20 and 30 km through at least mid november

basaltic magmatism on the moon a perspective from volcanic picritic glass beads abstract it is widely accepted that basaltic magmas are products of partial fusion of periodotite within planetary mantles as such they provide valuable insights into the composition structure and processes of planetary interiors those compositions which approach primary melt compositions provide the most direct information about planetary interiors and serve as a starting point to understand basaltic evolution within the collection of lunar samples returned by the apollo and luna missions are homogeneous picritic glass beads of volcanic origin these picritic glasses are our closest approximations to primary magmas as such these glass beads provide a unique perspective concerning the origin of mare basalts the characteristics of the lunar interior and processes in the early differentiation of the moon we have obtained trace element data for these picritic glasses using sims techniques these data and literature isotopic and experimental data on the picritic glasses are placed within the framework of mare basaltic magmatism the volcanic glasses are very diverse in their trace element characteristics for example they have a wide range of ree pattern shapes and concentrations like the crystalline mare basalts all picritic glasses have a negative eu anomaly unlike the crystalline mare basalts there is little correlation between the size of the eu anomaly and overall ree concentrations trace element differences among the various glasses suggests that a kreep component was incorporated into their mantle source this implies large scale mixing of the lunar magma ocean derived cumulate pile subtle differences among glasses suggest that local mixing of sources may also have been an important process preservation of subtle chemical differences in the picritic glasses and crystalline basalts may be interpreted as indicating that they were produced by small to moderate degrees of partial melting and that the lunar mantle did not experience extensive melting during episodes of mare volcanism several lines of evidence are consistent with the view that the picritic glasses were derived from mantle sources that were compositionally distinct from the sources for crystalline mare basalts these are parallel but no common liquid lines of descent chemical differences between picritic glasses and the more primitive crystalline mare basalts experimental studies indicating that the picritic glasses are multiply saturated at depths greater than that of the mare basalts differences in lead isotopic data and the mode of eruption i e fire fountaining for glass beads these data also provide circumstantial evidence that suggests that the picritic glasses were derived from a source somewhat more volatile rich than that of the mare basalts several petrogenetic models are suggested by the trace element characteristics of the picritic glasses 1 1 partial melting of heterogeneous lunar mantle at depths greater than 300 km to produce the parental magmas picritic for both the mare basalts and picritic glasses picritic magmas represented by glass beads were erupted to the surface with small degrees of fractional crystallization while mare basalts were produced by larger degrees of fractional crystallization 15 30 of similar but not identical picritic magmas 2 2 picritic magmas represented by the glass beads were generated at depths greater than 400 km in a volatile enriched relative to the mare basalt source heterogeneous mantle while mare basalts are fractional crystallization products of picritic magmas generated at depths of less than 400 km 3 3 the picritic magmas represented by the glass beads represent polybaric melting that initiated at depths of at least 1000 km a primitive mantle component or less processed cumulate mantle components may have been involved in the generation of the picritic glasses in any of these models

impact dust not the cause of the cretaceous tertiary mass extinction most of the 3 mm thick globally distributed chicxulub ejecta layer found at the cretaceous tertiary k t boundary was deposited as condensation droplets from the impact vapor plume a small fraction of this layer 14 g was submicrometer size dust the global mass and grain size distribution of the clastic debris indicate that stratospheric winds spread the debris from north america over the pacific ocean to europe and little debris reached high southern latitudes these findings indicate that the original k t impact extinction hypothesis the shutdown of photosynthesis by submicrometer size dust is not valid because it requires more than two orders of magnitude more fine dust than is estimated here furthermore estimates of future impact hazards which rely upon inaccurate impact dust loadings are greatly overstated

space weathering on airless planetary bodies clues from the lunar mineral hapkeite physical and chemical reactions occurring as a result of the high velocity impacts of meteorites and micrometeorites and of cosmic rays and solar wind particles are major causes of space weathering on airless planetary bodies such as the moon mercury and asteroids these weathering processes are responsible for the formation of their regolith and soil we report here the natural occurrence of the mineral hapkeite a fe2si phase and other associated fe si phases iron silicides in a regolith breccia clast of a lunar highland meteorite these fe si phases are considered to be a direct product of impact induced vapor phase deposition in the lunar soil all part of space weathering we have used an in situ synchrotron energy dispersive single crystal x ray diffraction technique to confirm the crystal structure of hapkeite as similar to the structure of synthetic fe2si this mineral hapkeite is named after bruce hapke of the university of pittsburgh who predicted the presence and importance of vapor deposited coatings on lunar soil grains some 30 years ago we propose that this mineral and other fe si phases are probably more common in the lunar regolith than previously thought and are directly related to the formation of vapor deposited nanophase elemental iron in the lunar soils

interannual variability of the vertical descent rate in the antarctic polar vortex to investigate a descent rate in the antarctic polar vortex we analyzed the long lived trace gas data derived from the halogen occultation experiment on board the upper atmosphere research satellite during the 6 year period from 1992 to 1997 by comparing the antarctic fall february and march and spring september and october methane profiles we estimated the middle stratospheric descent for each of the six winters large year to year variations are seen 1 2 1 8 km month 1 at 0 6 ppmv which consist of a biennial oscillation and a decreasing trend for the period analyzed the descent rate is larger in the even years 1992 1994 and 1996 than in the odd years 1993 1995 and 1997 dynamical fields for the 6 years are also analyzed using the united kingdom meteorological office assimilation data the differences between the even and odd years are clear in the midwinter in the even years the downward and poleward movement of the westerly jet occurs earlier the thermal wind relation infers that this event is associated with the development of a warm pool around the antarctic stratopause resulting from adiabatic heating due to the downward motion of air planetary wave activity over the winter season is more vigorous in the even years than in the odd years suggesting a close relationship between the mean flow and planetary waves

the frequency of compound chondrules and implications for chondrule formation the properties of compound chondrules and the implications that they have for the conditions and environment in which chondrules formed are investigated formulae to calculate the probability of detecting compound chondrules in thin sections are derived and applied to previous studies this reinterpretation suggests that at least 5 of chondrules are compounds a value that agrees well with studies in which whole chondrules were removed from meteorites the observation that adhering compounds tend to have small contact arcs is strengthened by application of these formulae while it has been observed that the secondaries of compound chondrules are usually smaller than their primaries these same formulae suggest that this could be an observation bias it is more likely than not that thin section analyses will identify compounds with secondaries that are smaller than their primaries a new model for chondrule collisional evolution is also developed from this model it is inferred that chondrules would have formed on average in areas of the solar nebula that had solids concentrated at least 45 times over the canonical solar value

influence of tropical convection on the southern hemisphere ozone maximum during the winter to spring transition 1 during the southern hemisphere sh winter a zonally asymmetric maximum in column ozone develops south of australia which amplifies from august through october this ozone maximum lies in the band 50 60 s and extends from the southern indian ocean to the eastern pacific it is proposed that the location of the ozone maximum is due to the geographical distribution of outflow from tropical convection in the upper troposphere and lower stratosphere utls which is concentrated over the southern indian ocean this southward flow of tropical air creates subtropical anticyclones in the utls and provides the angular momentum for the entrance to the australian westerly jet the ozone rich troughs in synoptic waves breaking on the jet contribute to the monthly mean ozone maximum poleward of the jet as indonesian convection contracts zonally and shifts eastward during sh spring so do the australian jet and ozone maximum in addition extratropical planetary waves become more active from august through october convective outflow surges lead to amplification of subtropical anticyclones which often extend into the lower stratosphere and merge with stalling planetary wave ridges amplification of these ozone rich ridges over the high latitude south pacific contributes to the eastward shift of the ozone maximum the utls over the southern indian ocean appears to be a sensitive region where tropical convection can influence extratropical planetary waves via excitation of subtropical anticyclones and propagation of rossby wave activity through the connecting westerly waveguide

igneous rims on low feo and high feo chondrules in ordinary chondrites abstract many ordinary chondrite oc chondrules are surrounded by rims that show evidence of appreciable melting and can be called igneous these rims formed after the melting and solidification of the host chondrule we studied thirteen igneous rims on low feo chondrules fa or fs 10 mol in ordinary chondrites of petrographic type 3 5 by electron microprobe analysis and scanning electron microscopy in both sets olivine and pyroxene compositions of the rims are similar to or moderately higher in feo than those in the host igneous rims around low feo chondrules show evidence of large degree 80 melting including 1 resorbed chondrule surfaces 2 rounded metal troilite nodules and feldspathic mesostasis 3 euhedral and subhedral morphology of olivine and pyroxene and limited ranges in grain sizes and 4 a rarity of relict grains most low feo chondrules have olivine as their major phase but pyroxene is commonly the predominant phase in their rims rims on high feo chondrules generally have smaller grain sizes and exhibit lower degrees of melting than rims around low feo chondrules mg rich relict grains are observed in high feo rims most low feo chondrules have matrix like rims around the igneous rims but matrix like rims are rare around rims on high feo chondrules there is a continuum between igneous rims and enveloping secondaries of compound chondrules the existence of both sets of objects supports the view that in the oc region most mm size grain assemblages experienced more than one melting event the precursors melted to produce the igneous rims on low feo chondrules differ from those that comprise the rims on high feo chondrules a sizeable fraction of the precursors of low feo rims are from the host chondrule most high feo rims appear to consist largely of melted matrix like materials if the rim precursors are mainly independent the similar fa and fs contents in mafic minerals of rims and host chondrules indicate that 1 oc nebular subregions bounded in space and or in time were dominated by well mixed solids 2 many chondrules experienced multiple heating events during a short period and were then withdrawn from the chondrule forming region and 3 chondrules formed at different times were mixed before agglomeration to form chondrites if the host chondrules were the main source of the low feo rim materials the fact that pyroxene is generally more abundant than in the host suggests that sio 2 normative matrix was also an important ingredient and or that kinetics favored pyroxene crystallization in the rim rims around high feo chondrules were heated to lower temperatures than rims around low feo chondrules the rarity of matrix like rims around high feo igneous rims may indicate that the dust chondrule ratio was lower where they formed

space weathering on the moon patina on apollo 17 samples 75075 and 76015 we studied patinas on lunar rocks 75075 and 76015 from the apollo collection using a multi disciplinary approach including scanning electron microscopy sem energy dispersive x ray spectrometry eds transmission electron microscopy tem wavelength dispersive x ray wds mapping mossbauer spectroscopy spectral reflectance and microspectrophotometry based on sem petrography we have defined three textural types of patina glazed fragmental and classic cratered the presence of classic patina is diagnostic of lunar samples that have been exposed directly to the space weathering environment it is characterized by the presence of microcraters and glass pancakes and is the patina type studied by earlier workers classic patina is found on 76015 but not on 75075 glazed patina is found on both 76015 and 75075 whereas fragmental patina is found only on 75075 the glazed and fragmental patinas on 75075 were probably formed as a result of relatively large nearby impacts and although these two types of patina are not strictly the result of direct exposure to the space weathering environment they are important because they affect the optical properties of the rocks field emission gun sem fe sem of classic patina on 76015 shows evidence of possible solar wind sputtering erosion transmission electron microscope studies of 76015 reveal the presence of impact generated deposits and solar flare particle tracks which like microcraters and pancakes are diagnostic of direct exposure to space weathering processes the outermost surface of the 76015 patina consists of an amorphous rim very much like the rims found on individual lunar soil grains this amorphous patina rim probably formed by similar processes of impact generated vapor condensation and possible sputter deposition wavelength dispersive x ray element maps of polished thin sections of 75075 and 76015 indicate that patina compositions are poor indicators of the compositions and mineralogies of the rocks underlying them on average the reflectance spectra of patinas on both samples are slightly darker than those of their unweathered equivalents microreflectance measurements show that a thick patina can dramatically alter the optical properties of the rock on which it forms the backscatter mossbauer bams spectrum of a patina covered surface of 76015 is very similar to that of an unweathered surface indicating that the mossbauer signal is generated from beneath the patina because bams sees through surface space weathering effects to the underlying rock this technique has great potential for use in robotic missions to other planetary bodies

the petrogenesis of impact basin melt rocks in lunar meteorite shisr 161 this study explores the petrogenesis of shisr 161 an immature lunar regolith breccia meteorite with low abundances of incompatible elements a feldspathic affinity and a significant magnesian component our approach was to identify all clasts 0 5 mm in size in a thin section characterize their mineral and melt components and reconstruct their bulk major and minor element compositions trace element concentrations in representative clasts of different textural and compositional types indicate that the clast inventory of shisr 161 is dominated by impact melts that include slowly cooled cumulate melt rocks with mafic magnesian mineral assemblages minor exotic components are incompatible element rich melt spherules and glass fragments and a gas associated spheroidal precipitate our hypothesis for the petrologic setting of shisr 161 is that the crystallized melt clasts originate from the upper 1 km of the melt sheet of a 300 to 500 km diameter lunar impact basin in the moon s feldspathic highlands this hypothesis is based on size requirements for cumulate impact melts and the incorporation of magnesian components that we interpret to be mantle derived the glassy melts likely formed during the excavation of the melt sheet assemblage by an impact that produced a 15 km diameter crater the assembly of shisr 161 occurred in a proximal ejecta deposit of this excavation event a later impact into this ejecta deposit then launched shisr 161 from the moon our geochemical modeling of remote sensing data combined with the petrographic and chemical characterization of shisr 161 reveals a preferred provenance on the moon s surface that is close to pre nectarian riemann fabry basin

impact induced thermal effects in the lunar and mercurian regoliths while the moon and mercury are similar objects in a geomorphologic sense they also possess important differences particularly in the context of small scale impact phenomena not only is the surface of mercury notably hotter than that of the moon but the impact flux is also more intense at mercury due to higher impact velocities and a greater spatial density of micrometeoroids by extrapolating the terrestrial micrometeoroid flux to the moon and mercury it is found that the impact rate at mercury is 5 5 times greater and the mean impact velocity more than 60 percent higher than at the moon a model of impact melting and vaporization applied to the lunar and mercurian environments indicates that almost 14 times more impact melt and over 20 times more vapor are generated per unit time in the mercurian regolith although the surface temperature plays a role in determining the melt and vapor volumes the difference in impact velocity appears to be markedly more important average craters formed by identical projectiles under the two velocity distributions on the two planets should be very similar in size because differences in the kinetic energy of the average impactors will be offset by the differences in gravitational acceleration as a result variations in regolith mixing should depend more on the actual impact rates than on disparities in excavated volumes each average impact on mercury however will produce more than twice as much impact melt as its lunar counterpart introducing more glass into the mercurian regolith although substantial quantities of impact vapor are produced on both planets mixing of the regolith should occur quickly enough in each case to spread the deposited vapor over large surface areas the resulting vapor coatings should be negligibly small for most purposes a much larger agglutinate population should exist on mercury and individual agglutinates should be similar to those of the lunar highlands reflectance spectra and visual albedos indicate that the mercurian crust possesses relatively small quantities of fe perhaps similar to those of apollo 16 light and dark matrix breccias laboratory studies have demonstrated that as the magnetic fractions which are correlated with agglutinate abundances of soils derived from these breccias increase the differences in 0 565 mm visible light reflectivity between the soils diminish should the regional variations in fe content of the mercurian crust be similar to those of these apollo 16 samples then the intense agglutination environment could account for the lack of optical contrast across the mercurian surface at the same time the very large fraction of impact glass in the regolith would imply that most pyroxenes have been fused and incorporated into these glasses seriously attenuating the fe2 crystal field absorption near 0 9 mm supporting this picture are the most recently published spectral observations of mercury which provide little or no evidence of such an absorption feature

stratigraphy of the lunar highland crust depths of burial of lunar samples from cooling rate studies current models of lunar crustal stratigraphy are based primarily on models of impact cratering coupled with what is known about the distribution of rock types in the ejecta blankets associated with the large multiring basins these models postulate an upper crust rich in the ferroan anorthosite component underlain by a more mafic noritic lower crust spudis 1993 we attempted to test these models by determining the depth at which various lunar plutonic rocks formed despite intense brecciation and shock many lunar highland samples retain vestiges of a prior magmatic history for example pyroxene samples preserve a record of their thermal history in such phenomena as cation ordering and exsolution textures by computer simulation of the growth of exsolution lamellae in augite and pigeonite we deduced cooling rates and from these estimated a depth of burial on the basis of a simple model for the thermal evolution of the lunar crust despite the fairly large uncertainties in the calculations it is clear that the ferroan anorthosite samples we studied formed at a depth between 10 and 20 km whereas some members of highland magnesian and alkali suites formed as cumulates in magma chambers intruded into the uppermost layers of the crust as yet there is no evidence to indicate that crystalline rocks from the lower half of the lunar crust are present in the samples returned by the apollo missions most samples derived from the lower crust appear to be impact melts oflow k fra mauro noritic composition

time variations of descent in the antarctic vortex during the early winter of 1997 1 we analyzed long lived chemical constituents observed by the improved limb atmospheric spectrometer ilas on board the advanced earth observing satellite adeos to study the stratospheric descent in the southern hemisphere polar vortex the ilas n2o distribution inside the polar vortex exhibited clear downward motion in february to june 1997 average descent for the 5 months is estimated to be 2 1 1 7 km month 1 in the middle stratosphere in late april to june when planetary waves are relatively active the vertical velocity displays time variations with a period of about 10 days these time variations also synchronize with both time variations of the temperature time change t and the eliassen palm flux divergence df in high latitudes moreover a correlation coefficient map in the latitude height cross section between the vertical velocity and the temperature time change reveals an interesting four box pattern suggesting warming below 10 hpa and cooling above 10 hpa in the polar region 70 90 s and an opposite distribution in midlatitudes 40 70 s when large descent is observed inside the polar vortex it is just like the meridional circulation in response to df induced by planetary waves which was first illustrated by matsuno s stratospheric sudden warming theory

computations of diabatic descent in the stratospheric polar vortex a radiation model together with national meteorological center temperature observations was used to compute daily net heating rates in the northern hemisphere nh for the arctic late fall and winter periods of both 1988 1989 and 1991 1992 and in the southern hemisphere sh for the antarctic fall and winters of 1987 and 1992 the heating rates were interpolated to potential temperature surfaces between 400 k and 2000 k and averaged within the polar vortex the boundary of which was determined by the maximum gradient in potential vorticity the averaged heating rates were used in a one dimensional vortex interior descent model to compute the change in potential temperature with time of air parcels initialized at various values as well as to compute the descent in log pressure coordinates in the nh vortex air parcels which were initialized at 18 km on november 1 descended about 6 km by march 21 while air initially at 25 km descended 9 km in the same time period this represents an average descent rate in the lower stratosphere of 1 3 to 2 km per month air initialized at 50 km descended 27 km between november 1 and march 21 in the sh vortex parcels initialized at 18 km on march 1 descended 3 km while air at 25 km descended 5 7 km by the end of october this is equivalent to an average descent in the lower stratosphere of 0 4 to 0 9 km per month during this 8 month period air initialized at 52 km descended 26 29 km between march 1 and october 31 in both the nh and the sh computed descent rates increased markedly with height the descent for the nh winter of 1992 1993 and the sh winter of 1992 computed with a three dimensional trajectory model using the same radiation code was within 1 to 2 km of that calculated by the one dimensional model thus validating the vortex averaging procedure the computed descent rates generally agree well with observations of long lived tracers thus validating the radiative transfer model