precessional climate cyclicity in late cretaceous early tertiary marine sediments a high resolution chronometer of cretaceous tertiary boundary events we report well dated late cretaceous and early tertiary precessional climatic cycles recorded by rhythmic carbonate maxima and minima in south atlantic deep sea sites spectral analyses of digitized sediment color a suitable carbonate proxy show prominent regularities in the spacing marl carbonate beds magnetostratigraphic dating over a number of magnetic chrons constrains the duration of the cycles which can be detected over at least 20 myr of sedimentation at 7 coring locations their mean absolute period of23 5 4 4kyr agrees closely with the predicted late cretaceous precessional period of 20 8 kyr because they can be matched to a physical forcing mechanism with a known repeat time the cycles offer a new high resolution tool to measure rates of climate change before and after the cretaceous tertiary k t boundary from counts of carbonate cycles we derive the position of the k t boundary within c29r at 350 kyr after the base of the reversal the constancy of cycle thickness linearly related to sedimentation rate and amplitude up to the boundary clay does not give evidence for climate instability preceding the boundary orbital chronometry records a step function decrease in sediment accumulation rate at the cretaceous tertiary boundary that is consistent with a geologically instantaneous event

the dominant intraseasonal mode of intraseasonal south asian summer monsoon from june through september the intraseasonal variability of the asian summer monsoon is dominated by the so called monsoon intraseasonal oscillation miso this paper provides a comprehensive description of the miso based on outgoing longwave radiation olr data the miso is characterized by alternating active periods in which the primary rain area of the asian summer monsoon that stretches from the northern arabian sea east southeastward almost all the way to the northwest pacific intertropical convergence zone is relatively intense and break periods in which the heaviest rainfall shifts from south asia to the central and eastern equatorial indian ocean the miso is attended by well defined but weak sea surface temperature sst perturbations whose phase is indicative of a negative feedback upon the atmospheric perturbations meridional profile of variables on the various regression maps shown in this paper averaged along a set of tilted axes parallel to the west northwest to east southeast wnw ese sloping lines in empirical orthogonal function 1 of olr have been made and it is found that the strongest westerly 850 hpa wind anomalies are located two grid points 5 of latitude to the south of the reference latitude at the 150 hpa level the meridional profile of divergence is closely aligned with the olr profile sst profile is lowest at approximately 2 5 of latitude to the south of the minimum olr and 2 5 to the north of the strongest westerly 850 hpa wind anomalies the sea level pressure profiles and the midlower tropospheric geopotential height profiles are almost in phase it is observed that in most years there are two three bands of intensified and suppressed rainfall that cross the reference line from south to north northward propagating at the interval of 30 60 days over south asia the degree of correspondence between the miso and active and break spells of the indian summer monsoon rainfall is also documented

end permian catastrophe by a bolide impact evidence of a gigantic release of sulfur from the mantle our studies in southern china have revealed a remarkable sulfur and strontium isotope excursion at the end of the permian along with a coincident concentration of impact metamorphosed grains and kaolinite and a significant decrease in manganese phosphorous calcium and microfossils foraminifera these data suggest that an asteroid or a comet hit the ocean at the end of permian time and caused a rapid and massive release of sulfur from the mantle to the ocean atmosphere system leading to significant oxygen consumption acid rain and the most severe biotic crisis in the history of life on earth

dielectric properties of jovian satellite ice analogs for subsurface radar exploration a review the first european mission dedicated to the exploration of jupiter and its icy moons jupiter icy moons explorer juice will be launched in 2022 and will reach its final destination in 2030 the main goals of this mission are to understand the internal structure of the icy crusts of three galilean satellites europa ganymede and callisto and ultimately to detect europa s subsurface ocean which is believed to be the closest to the surface among those hypothesized to exist on these moons juice will be equipped with the 9 mhz subsurface penetrating radar rime radar for icy moon exploration which is designed to image the ice down to a depth of 9 km moreover a parallel mission to europa which will host onboard reason radar for europa assessment and sounding ocean to near surface equipped with 9mhz and 60mhz antennas has been recently approved by nasa the success of these experiments strongly relies on the accurate prediction of the radar performance and on the optimal processing and interpretation of radar echoes that in turn depend on the dielectric properties of the materials composing the icy satellite crusts in the present review we report a complete range of potential ice types that may occur on these icy satellites to understand how they may affect the results of the proposed missions first we discuss the experimental results on pure and doped water ice in the framework of the jaccard theory highlighting the critical aspects in terms of a lack of standard laboratory procedures and inconsistency in data interpretation we then describe the dielectric behavior of extraterrestrial ice analogs like hydrates and icy mixtures carbon dioxide ice and ammonia ice building on this review we have selected the most suitable data to compute dielectric attenuation velocity vertical resolution and reflection coefficients for such icy moon environments with the final goal being to estimate the potential capabilities of the radar missions as a function of the frequency and temperature ranges of interest for the subsurface sounders we present the different subsurface scenarios and associated radar signal attenuation models that have been proposed so far to simulate the structure of the crust of europa and discuss the physical and geological nature of various dielectric targets potentially detectable with rime finally we briefly highlight several unresolved issues that should be addressed in near future to improve our capability to produce realistic electromagnetic models of icy moon crusts the present review is of interest for the geophysical exploration of all solar system bodies including the earth where ice can be present at the surface or at relatively shallow depths

why the western pacific subtropical high has extended westward since the late 1970s the western pacific subtropical high wpsh is closely related to asian climate previous examination of changes in the wpsh found a westward extension since the late 1970s which has contributed to the inter decadal transition of east asian climate the reason for the westward extension is unknown however the present study suggests that this significant change of wpsh is partly due to the atmosphere s response to the observed indian ocean western pacific iwp warming coordinated by a european union s sixth framework programme understanding the dynamics of the coupled climate system dynamite five agcms were forced by identical idealized sea surface temperature patterns representative of the iwp warming and cooling the results of these numerical experiments suggest that the negative heating in the central and eastern tropical pacific and increased convective heating in the equatorial indian ocean maritime continent associated with iwp warming are in favor of the westward extension of wpsh the sst changes in iwp influences the walker circulation with a subsequent reduction of convections in the tropical central and eastern pacific which then forces an enso gill type response that modulates the wpsh the monsoon diabatic heating mechanism proposed by rodwell and hoskins plays a secondary reinforcing role in the westward extension of wpsh the low level equatorial flank of wpsh is interpreted as a kelvin response to monsoon condensational heating while the intensified poleward flow along the western flank of wpsh is in accord with sverdrup vorticity balance the iwp warming has led to an expansion of the south asian high in the upper troposphere as seen in the reanalysis

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

constraining the cause of the end guadalupian extinction with coupled records of carbon and calcium isotopes abstract a negative c 13 excursion in carbonate sediments near the guadalupian lopingian middle late permian boundary has been interpreted to have resulted from a large carbon cycle disturbance during the end guadalupian extinction event ca 260 ma however the carbon isotope data alone are insufficient to uniquely determine the type and magnitude of perturbation to the global carbon cycle calcium isotopes can be used to further constrain the cause of a carbon isotope excursion because the carbon and calcium cycles are coupled via caco3 burial in this study we present coupled carbon and calcium isotope records from three guadalupian lopingian g l sections in china penglaitan and chaotian and turkey koserelik tepe the c 13 and ca 44 40 records differ among our studied sections and do not co vary in the same manner no section shows c 13 and ca 44 40 changes consistent with massive rapid volcanic co2 emissions or methane clathrate destabilization additionally many sections with large 3 changes in c 13 exhibit o 18 evidence for diagenetic alteration only one section exhibits a large excursion in the ca 44 40 of limestone but the absence of a similar excursion in the ca 44 40 of conodont apatite suggests that the limestone excursion reflects a mineralogical control rather than a perturbation to the global calcium cycle hence we interpret the large isotopic changes observed in some sections to have resulted from local burial conditions or diagenetic effects rather than from a large carbon and calcium cycle disturbance perturbations to the global carbon and calcium cycles across the g l transition were much less intense than the disturbances that occurred across the subsequent permian triassic boundary this finding is consistent with the much smaller magnitude of the end guadalupian extinction relative to the end permian

dependence of simulation of boreal summer tropical intraseasonal oscillations on the simulation of seasonal mean the link between realism in simulation of the seasonal mean precipitation and summer tropical intraseasonal oscillations and their dependence on cumulus parameterization schemes is investigated using the florida state university global spectral model fsugsm forty member model ensemble simulations of the northern summer season are generated for three different cumulus parameterization schemes namely arakawa schubert naval research laboratory nrl zhang and mcfarlane national center for atmospheric research ncar and emanuel massachusetts institute of technology mit the mit scheme simulates the regional pattern of seasonal mean precipitation over the indian monsoon region well but has large systematic bias in simulating the precipitation over the western pacific and the maritime continent although the simulation of details of regional distribution of precipitation over the indian monsoon region by the nrl and ncar schemes is not accurate they simulate the spatial pattern of precipitation over the tropical indo pacific domain closer to observation the nrl scheme seems to captures the observed northward and eastward propagation of intraseasonal precipitation anomalies realistically however the simulations of the ncar and mit schemes are dominated by a westward propagating component the westward propagating mode seen in the model as well as observations is indicated to be an equatorial rossby wave modified by the northern summer mean flow an examination of the relationship between simulation of the model climatology and eastward propagating character of monsoon intraseasonal oscillations isos in a limited sample shows that the scheme that simulates better seasonal mean pattern of rainfall over the tropical indo pacific domain also simulates better intraseasonal variance and more realistic eastward propagation of monsoon isos among the parameters known to be important for meridional propagation of the summer monsoon isos the meridional gradient of mean humidity in the lower atmosphere seems to be crucial in determining the northward propagation in the equatorial indian ocean between 10 s and 10 n for better prediction of the seasonal mean indian monsoon therefore the model climatology should have minimum bias not only over the indian monsoon region but also over the entire indo pacific basin

ice age ice sheet rheology constraints from the last glacial maximum form of the laurentide ice sheet state ot the art thermomechanical models of the modern greenland ice and the ancient laurenticle ice sheet that covered canada at the last glacial maximum lgm are not able to explain simultaneously the observed forms of these cryospheric structures when the same anisotropy enhanced version of the conventional glen flow law is employed to describe their rheology the lgm laurenticle ice sheet predicted to develop in response to orbital climate forcing is such that the ratio of its thickness to its horizontal extent is extremely large compared to the aspect ratio inferred on the basis of surface geomorphological and solid earth geophysical constraints we show that if the glen flow law representation of the rheology is replaced with a new rheology based upon very high quality laboratory measurements of the stress strain rate relation then the aspect ratios of both the modern greenland ice sheet and the laurenticle ice sheet that existed at the lgm are simultaneously explained with little or no retuning of the flow law

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

high resolution simulation of the boreal summer intraseasonal oscillation in met office unified model the present study investigates the fidelity and resolution sensitivity of met office unified model global atmosphere 3 0 in simulating the intra seasonal oscillation iso of the east asia and western north pacific summer monsoon two sets of model simulations at horizontal resolutions of n216 60km and n96 130km forced by observed daily high resolution sea surface temperature are examined and compared with the observations diagnostic results show that the model can well reproduce the gross spatio temporal features of observed summer iso over the east asia and western north pacific in terms of period dominant reof mode variance northward propagation cycle evolution and vertical structure the intra seasonal change in intensity and position of western north pacific subtropical high and upper troposphere westerly jet associated with the northward propagating isos are also reasonably captured in the model moreover increasing horizontal resolution improves most aspects of the iso simulation especially the intensity and northward propagation of the iso related convection and circulation systems further analysis indicates that the improvement as resolution increases is related to the weakening in background state of east asian summer monsoon which is due to the realistic simulation of land sea thermal contrast at higher resolution model this study suggests that enhanced model resolution can have some beneficial impacts on the iso simulation

an mjo simulated by the nicam at 14 and 7 km resolutions this study discloses detailed madden julian oscillation mjo characteristics in the two 30 day integrations of the global cloud system resolving nonhydrostatic icosahedral atmospheric model nicam using the allseason real time multivariate mjo index of wheeler and hendon the model anomaly is derived by excluding the observed climatology because the simulation is sufficiently realistic results show that the mjo has a realistic evolution in amplitude pattern geographical locations eastward propagation and baroclinic and westwardtilted structures in the central indian ocean convection develops with the low level easterly wind anomaly then matures where the low level easterly and westerly anomalies meet anomalous moisture tilts slightly with height in contrast over the western pacific the convection grows with a low level westerly anomaly moisture fluctuations leading convection in eastward propagation tilt clearly westward with height the frictional moisture convergence mechanism operates to maintain the mjo such success can be attributed to the explicit representation of the interactions between convection and large scale circulations the simulated event however grows faster in phases 2 and 3 and peaks with 30 higher amplitude than that observed although the 7 km version shows slight improvement the fast growth phases are induced by the fast growing low level convergence in the indian ocean and the strongly biased itcz in the west pacific when the model undergoes a spinup the simulated olr has a substantial bias in the tropics possible solutions to the deficiencies are discussed

a rotated eof analysis of global sea surface temperature variability with interannual and interdecadal scales abstract spatiotemporal variability of preferred global scale sea surface temperature anomaly patterns is documented applying a varimax rotated empirical orthogonal function r eof analysis to monthly mean sst anomalies the present study focuses especially on the interdecadal variability of leading r eof modes it is first found that temporal variability of r eof1 has a quasi periodicity of 2 5 years and coincides quite well with the occurrence of the enso event hence this mode can be identified with the enso mode and distinguished from the other modes dominated by interdecadal variability the authors find that r eof2 typically shows the dominance of interdecadal variability and signals of the enso phenomenon are removed this mode is characterized by increasing indian ocean sst and decreasing central north pacific sst around 40 50 n in the recent ten or more years a further indication is that both r eof3 and r eof4 which show the dominance of interdecadal variability are fundamentally regarded a

comment on superplastic deformation of ice experimental observations by d l goldsby and d l kohlstedt knowledge of the rheological properties of ice at devia toric stresses lower than 0 1 mpa is of great interest whenmodeling the flow of glaciers and ice sheets in spite of thedifficulty of obtaining convincing results in the laboratory thereis now agreement on a flow law with a stress exponent lowerthan 2 mellor and testa 1969 duval 1973 alley 1992 duval and castelnau 1995 this result is also supported byborehole deformation measurements dahl jensen and gun destrup 1987 and bubbly ice densification modeling lipenkovet al 1997

textures and fabrics in the grip ice core a comprehensive study of textures and fabrics has been carried out on the greenland ice core project grip ice core crystal sizes and c axis orientations have been measured on thin sections with conventional techniques yielding new information on the growth rotation and recrystallization of ice crystals in the greenland ice sheet normal grain growth is found to persist to a depth of 700 m in the core where the onset of polygonization due to increasing strain prevents a further increase in grain size in the holocene ice smaller crystals are observed in the wisconsin ice larger crystals are found in the eemian ice and the crystal size is found to vary with climatic parameters in these periods this dependence which probably results from variable impurity content in the ice persists to a depth of 2930 m coarse grained ice probably resulting from rapid growth of crystals at comparatively high temperatures is found in the lowest 100 m of the core the data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet a significant strengthening is not observed at the holocene wisconsin transition the fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m the evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth stretched fabrics in coarse grained ice in the lowest 100 m could be due to tensional stresses this ice is unlikely to be undergoing any significant horizontal deformation at the present time

convection in ice i shells and mantles with self consistent grain size 1 the viscosity of ice i is grain size dependent for temperature and stress conditions appropriate for ice i shells and mantles of large and midsized icy satellites satellite thermal evolution heat flux critical shell thickness for convection brittle ductile transition temperature and potential for surface deformation are therefore grain size dependent using measured grain sizes from terrestrial ice sheets experiencing temperature and strain rate conditions similar to convecting ice shells in icy satellites we develop two end member models of grain size and its evolution in the absence of non water ice impurities grain size in a convecting ice shell of a large icy satellite will evolve over time to an equilibrium value which we determine to be between 30 and 80 mm because of dynamic recrystallization such large grains imply viscous ice so convection in an ice shell thinner than 35 km in a large icy satellite such as ganymede and callisto would be sluggish at best and may cease after a few convective overturns if it starts soluble ions and silicate microparticles may keep grains small however of order 1 5 mm and permit convection in shells as thin as 30 km in large icy satellites the dynamic recrystallization model provides a plausible upper limit on grain size in a geodynamically evolved ice shell whereas grain sizes from dust contaminated terrestrial ice cores provide a plausible lower limit on grain size in an icy satellite on the basis of these constraints grain sizes in evolved ice shells of large water ice satellites in the absence of tidal forcing should be of order 1 mm to 10 cm

the carbon isotope excursion on gssp candidate section of lopingian guadalupian boundary an isotopic stratigraphically well documented outcrop in penglaitan guangxi province south china has been proposed as a candidate gssp for the lopingian guadalupian boundary correlatable outcrops from the west wing tieqiao section and east wing penglaitan section of the laibin syncline exhibit synchronous excursions in carbon isotopes the isotopic excursions 13c show the best placement of the boundary may lie at the base of bed 6k which coincides with the clarkina postbitteri conodont zone and with eustatic change 13c increases during the uppermost guadalupian jinogondolella granti conodont zone from the top of 3c to the base of 6i a 13c peak value of 5 is located at the transition between these two conodont zones and is suggested as a proxy for the transition from transgression to regression a gradual depletion of carbon isotopes occurs in the c postbitteri zone from bed 6e to 7b and this gradual 13c excursion also suggests the sequences around the guadalupian lopingian boundary at the candidate section are conformable during the middle later c postbitteri zone a 3 5 dramatic 13c depletion is recorded at the tieqiao section but only a 2 depletion at the deeper facies penglaitan section synchronous with conodont zones that mark eustatic changes

rate controlling processes in the creep of polar ice influence of grain boundary migration associated with recrystallization abstract information on the deformation modes and recrystallization processes in polar ice sheets was obtained thanks to the analysis of the ice structure along two deep ice cores from greenland and antarctica it is shown that the deformation of polar ice at low stresses is produced by intracrystalline slip accommodated by grain boundary migration gbm a deformation model based on an equilibrium between work hardening and recovery processes has been developed the decrease in dislocation density is due to both gbm associated with grain growth and the formation of boundaries by recrystallization the value of the dislocation density along the byrd and grip ice cores obtained thanks to the model is about 1 10 11 m 2 this value is in agreement with data from synchrotron x ray diffraction on samples taken along the core this deformation model can account for the deformation of polar ice at low stresses it is shown that the flow law with a stress exponent lower than 2 can be related to the efficiency of gbm as a recovery process

palynofacies analysis of sediments from the cote d ivoire ghana transform margin preliminary correlation with some regional events in the equatorial atlantic abstract analyses of the palynofacies and sporomorph thermal alteration indices tai of sediments from ocean drilling program odp sites 959 to 962 in the cote d ivoire ghana transform margin west africa were undertaken to 1 determine the source and depositional conditions of the organic matter in the sediments 2 refine a paleobathymetric curve derived from other data for site 959 which drilled the most continuous sedimentary sequence from pleistocene to albian and 3 interpret the paleothermal history of the area twelve types of dispersed organic matter were identified amorphous organic matter aom marine palynomorphs algae resins black debris yellow brown fragments black brown fragments cuticles plant tissue wood sporomorphs and fungi the relative abundances of these organic matter components at each site were analyzed using cluster analysis resulting in the identification of seven palynofacies assemblages at site 959 five each at sites 960 and 961 and four at site 962 amorphous organic matter which is chiefly marine derived black debris and wood have played the most significant role in defining palynofacies assemblages the palynofacies assemblages show some correlation with lithologic units sediment sources and depositional environments previous palynofacies studies in passive margins have demonstrated that changes in the ratio of aom to terrestrial organic matter are related primarily to proximal distal positions of depositional environments relative to the shoreline however this assumption does not always hold true for a transform margin where tectonic factors play an important role in the organic matter distribution at least in the early stages of evolution lithofacies ccd paleodepths for the north atlantic trace fossil association benthic foraminifera and palynofacies data were the criteria used for reconstructing a paleobathymetric curve for site 959 a cyclicity in the organic matter distribution of the upper miocene to lower pliocene pelagic sediments could be related to fluctuations in productivity of biosiliceous and calcareous organisms and sedimentation rates a drastic increase in the amount of aom and a decrease in black debris and wood in the carbonate and clastic rocks lithologic unit iv overlying the tectonized albian sediments lithologic unit v at sites 959 and 960 coincide with the presence of an unconformity qualitative color analysis of palynomorphs was undertaken for all sites although the main focus was on site 959 where detailed organic geochemical data were available at site 959 tai values indicate an immature stage of organic maturation 2 except for the claystone samples between 1012 52 and 1036 5 mbsf and one limestone sample at 1043 4 mbsf reaching peak levels of 2 58 to 3 0 in the tectonized albian sediments below the unconformity these tai values show a positive correlation with the tmax values derived from rock eval pyrolysis data the highest values recorded in the basal tectonized units at all the sites sites 960 962 have mean values between 2 25 and 3 13 may be related to high heat flow during the intracontinental to syntransform basin stage in the region

northwestward propagation of the intraseasonal oscillation in the western north pacific during the boreal summer structure and mechanism abstract the convection of the intraseasonal timescale in the western north pacific during the boreal summer tends to propagate northwestward in the philippine sea to near 20 n and then continues propagating westward the formation of enhanced convection in the western north pacific is a result of the merging of a convective system moving eastward along the equator and a westward propagating low level convergence anomaly which is located to the east of a vortex in the subtropics a positive feedback between the anomalous circulation and convection leads to a rapid enhancement of the system the strengthened southwesterly associated with the vortex enhances evaporation over the oceans e g the eastern indian ocean the bay of bengal and the south china sea and transports moisture northeastward the moisture converges at the northwestern corner of the convection and results in a potentially unstable atmosphere the result is the northwestward propagation of the coupled circulation convection system in

vertical and lateral propagation characteristics of intraseasonal oscillation from the tropical lower troposphere to upper mesosphere 1 using a mesosphere stratosphere troposphere mst radar and a rayleigh lidar collocated at the indian tropical station gadanki 13 5 n 79 2 e european centre for medium range weather forecasts ecmwf re analysis data and the horizontal wind velocities measured by the thermosphere ionosphere mesosphere energetics and dynamics timed doppler interferometer tidi instrument onboard the timed satellite the present study makes a report on the lateral and vertical propagation characteristics of an intraseasonal oscillation iso 20 40 day period band propagating from the lower troposphere to the upper mesosphere region during the winter november december january and february months of the years 2004 2005 it is found that the iso had its origin in the tropical lower troposphere and propagated laterally and vertically to the upper mesosphere through the subtropical latitudes by partial refraction and reflection processes about the subtropical westerly jet corresponding enhancements in the wavelet spectrum of outgoing long wave radiation olr noaa interpolated indicate that convective forces in the lower troposphere are one of the main sources for the generation of the iso from the phase of the iso in the horizontal winds as observed by the mst radar it is found that the iso propagated upward from the lower troposphere up to near the tropopause where it got sharply attenuated from the ecmwf data it is observed that the iso was refracted to the subtropical latitudes through the tropical tropopause from where it got radiated upward into the stratosphere the phase propagation of the filtered winds shows that the iso arched back toward the tropical latitudes and propagated to the mesospheric region

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

reply to comment by p duval and m montagnat on superplastic deformation of ice experimental observations 1 in a recent paper we reported the results of a detailed experimental investigation of the rheological properties of ice goldsby and kohlstedt 2001 one of the innovative aspects of our investigation was the use of fine grained samples that enabled us to explore deformation not only by grain size insensitive mechanisms involving grain matrix dislocation processes but also by grain size sensitive flow mechanisms involving grain boundary sliding gbs an exciting discovery in our research was an extensive creep regime in which gbs contributes substantially to the flow of ice most importantly this deformation regime in which basal slip is accommodated by gbs referred to in our paper as the superplastic flow regime governs the flow of ice over a wide range of temperature grain size and stress conditions found in glaciers ice sheets and icy planetary interiors 2 in their comment on our paper duval and montagnat 2002 repeat the objection that they had raised previously montagnat and duval 2000 concerning our conclusion that superplastic deformation controls the flow of glaciers and ice sheets they assert that gbs as a significant creep mechanism is not compatible with observations on the development of fabrics and microstructures in ice sheets special emphasis is placed instead on the role of grain boundary migration as a recovery process in glacier ice they then continue by arguing that basal slip accommodated by grain boundary migration gbm rather than by gbs is the dominant deformation mechanism in ice 3 in this reply we extend the results presented in detail by goldsby and kohlstedt 1997 and goldsby and kohlstedt 2001 to further demonstrate that gbs is a very important deformation process in natural ice bodies our reasoning is based on three points 1 the microstructures reported for samples from large natural ice bodies are remarkably similar to those observed in samples deformed in the laboratory in the superplastic flow regime 2 our constitutive equation for ice is in excellent agreement with the flow behavior determined from field measurements on glaciers and ice sheets 3 contrary to the assertion of montagnat and duval 2000 and duval and montagnat 2001 fabric development is fully compatible with deformation in the superplastic regime described in our paper in addition we note that while gbm associated with dynamic recrystallization is an important recovery mechanism in ice it is not a deformation mechanism and hence cannot accommodate basal slip

preferred crystallographic orientation development during the plastic and superplastic flow of calcite rocks abstract grain size sensitive flow of fine grained rocks such as are often found in mylonitic shear zones is commonly inferred to be accomplished by grain boundary sliding so that no preferred crystallographic orientation is expected to develop pre existing fabrics are supposed to weaken and grain shapes to remain equant however many fine grained mylonites commonly exhibit marked preferred crystallographic orientation whilst displaying a stable but weak grain shape fabric we have examined preferred crystallographic orientation and shape fabric development during the flow of synthetic ultrafine grained 700 c the strong crystal plastic fabric develops more slowly but is not eliminated through the broad transition into true superplastic flow this is interpreted to reflect an important role of intracrystalline plasticity in the accommodation of grain boundary sliding from experiments designed to investigate the extent of survival or modification of an initial twinning fabric through recrystallization and subsequent hot working it was shown that although the microstructure could be totally annealed the early formed fabric survived even subsequent high temperature crystal plastic or superplastic flow this may explain the frequent occurrence of strong low temperature fabrics in calcite ultramylonites

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

deformation properties of subfreezing glacier ice role of crystal size chemical impurities and rock particles inferred from in situ measurements to improve understanding of the deformation properties of subfreezing polycrystalline glacier ice and in particular the role of crystal size chemical impurities and rock particle impurities we analyze in situ strain rates of the basal layers of meserve glacier antarctica strain rates were monitored on the walls of a subglacial tunnel where down flow shear stress is relatively uniform and ice properties were measured texture fabric and impurity content we propose a simple empirical model describing strain rate variations due to variations in crystal size and impurity content and we use all relevant meserve data to constrain model parameters we conclude that there is a direct dependence of strain rate on crystal size which reflects an important role for a grain size sensitive deformation mechanism such as grain boundary sliding or diffusion chemical impurities are found to enhance the grain size sensitive deformation and are found to be an important control on strain rate variations in the very impure ices of meserve glacier however the per molar sensitivity of strain rate to chemical impurity content is shown to be very low such that in the ice age ices of the greenland ice sheet there is probably an immeasurable contribution of chemical impurities to strain rate enhancement though we cannot exclude chemical enhancements as high as 1 3 there our analyses detect no direct rheologic effect of rock particles in the meserve ices which suggests that rock content is not directly responsible for the low viscosity of dirty basal layers

on convection in ice i shells of outer solar system bodies with detailed application to callisto it has been argued that the dominant non newtonian creep mechanisms of water ice make the ice shell above callisto s ocean and by inference all radiogenically heated ice i shells in the outer solar system stable against solid state convective overturn conductive heat transport and internal melting oceans are therefore predicted to be or have been widespread among midsize and larger icy satellites and kuiper belt objects alternatively at low stresses where non newtonian viscosities can be arbitrarily large convective instabilities may arise in the diffusional creep regime for arbitrarily small temperature perturbations for callisto ice viscosities are low enough that convection is expected over most of geologic time above the internal liquid layer for plausible ice grain sizes a few mm the alternative for early callisto a conducting shell over a very deep ocean 450 km is not compatible with callisto s present partially differentiated state moreover if convection is occurring today the stagnant lid would be quite thick 100 km and compatible with the lack of active geology nevertheless callisto s steady state heat flow may have fallen below the convective minimum for its ice i shell late in solar system history in this case convection ends the ice shell melts back at its base and the internal ocean widens considerably the presence of such an ocean of order 200 km thick is compatible with callisto s moment of inertia but its formation would have caused an 0 25 radial expansion the tectonic effects of such a late slow expansion are not observed so convection likely persists in callisto possibly subcritically ganymede due to its greater size rock fraction and full differentiation has a substantially higher heat flow than callisto and has not reached this tectonic end state titan if differentiated and triton should be more similar to ganymede in this regard pluto like callisto may be near the tipping point for convective shutdown but uncertainties in its size and rock fraction prevent a more definitive assessment

strain history of ice shells of the galilean satellites from radar detection of crystal orientation fabric 1 orbital radar sounding has been suggested as a means of determining the subsurface thermal and physical structure of the outer ice i shells of the galilean satellites at radar frequencies the dielectric permittivity of single and polycrystalline water ice i is anisotropic crystal orientation fabric cof which is indicative of strain history can be unambiguously detected by comparing the received power of dual co polarization linear polarization parallel and perpendicular to the orbit radar data regions with crystal orientations dictated by the local strain field fabric form in terrestrial ice masses where accumulated strain and temperature are high similar to conditions expected in a convecting outer ice i shell on europa ganymede or callisto we use simulations of solid state ice shell convection to show that crystal orientation fabric can form in the warm convecting sublayer of the ice shells for plausible grain sizes changes in received power from parallel and perpendicular polarizations in the ice shells due to fabric could be detected if multi polarization data is collected with proper instrument design radar sounding could be used to shed light on the strain history of the satellites ice shells in addition to their present day internal structures

a negative carbon isotope anomaly associated with the earliest lopingian late permian mass extinction abstract palaeozoic life was severely affected in a pair of mass extinction events at the beginning earliest lopingian 260 million years ago and the end 251 million years ago of the late permian however the biological and geochemical record of the earliest lopingian crisis remains poorly constrained we present analyses of strata in south china showing that a negative anomaly of stable carbon isotope ratios accompanied an abrupt extinction of marine faunas at the beginning of the late permian similar to patterns observed at the end permian and the end cretaceous 65 million years ago extinction events

stability of the astronomical frequencies over the earth s history for paleoclimate studies the expected changes over the past 500 million years in the principal astronomical frequencies influencing the earth s climate may be strong enough to be detectable in the geological records and such effects have been inferred in several cases calculations suggest that the shortening of the earth moon distance and of the length of the day back in time induced a shortening of the fundamental periods for the obliquity and climatic precession from 54 to 35 41 to 29 23 to 19 and 19 to 16 thousand years over the last half billion years at the same time the precessional constant increased from 50 to 61 arc seconds per year the changes in the frequencies of the planetary system due to its chaotic motion are much smaller their influence on the changes of the periods of climatic precession obliquity and eccentricity of the earth s orbit around the sun can be neglected eccentricity periods used for quaternary climate studies may therefore be considered to have been more or less constant for pre quaternary times

the guadalupian lopingian boundary permian in a pelagic sequence from panthalassa recognized by integrated conodont and radiolarian biostratigraphy abstract guadalupian lopingian sedimentary rocks are widely distributed in accretionary complexes in japan but the guadalupian lopingian boundary g lb is not well documented from these pelagic sediments to identify the g lb and to better correlate an extinction event that occurred around the guadalupian lopingian boundary we examined the conodont biostratigraphy from a permian pelagic chert sequence in the gujo hachiman section gifu southwest japan age diagnostic conodonts including clarkina postbitteri postbitteri were found in this section the biostratigraphic occurrences of these age diagnostic conodonts can pinpoint the g l transitional zone in the gujo hachiman section by comparison with well studied sections from south china including the gssp section the transitional zone was recognized by the first occurrence horizons of both clarkina postbitteri hongshuiensis and c p postbitteri the g lb has been placed at or above the first occurrence horizon of the radiolarians albaillella yamakitai or albaillella cavitata in previous studies from china and japan we detected the first occurrence horizon of a yamakitai below the base of the g l transitional zone in the upper capitanian the conodont biostratigraphy is consistent with the radiolarian biostratigraphy in this section which can be correlated to relevant sections in china

the mid capitanian middle permian mass extinction and carbon isotope record of south china abstract conodont c isotope and fossil and facies data are presented for the capitanian middle permian mass extinction record seen in platform carbonates maokou and wuchiaping formations of south china where limestones interdigitate with the volcanic succession of the emeishan large igneous province the maokou formation provides an extinction record marked by the loss of keriothecal walled fusulinaceans and a turnover in calcareous algae in sections within the emeishan province this crisis occurs at the base of the oldest record of volcanism from the jinogondolella altudaensis conodont zone of mid capitanian age around the periphery of the emeishan province this extinction level lies within the upper part of the maokou formation at a level where platform carbonate deposition was frequently interrupted by thick volcanic ash depositional events the assemblages of the uppermost maokou formation are characterised by typical late permian taxa although these levels still lie within the middle permian guadalupian series disaster taxa such as earlandia and diplosphaerina are locally prolifically abundant in the aftermath of the mass extinction the crisis is particularly noteworthy amongst photosynthetic taxa such as calcareous algae and fusulinaceans that probably harboured photosymbionts therefore a kill mechanism involving cooling from explosive volcanism and potentially acid rain from sulphate aerosols appears appropriate a composite 13ccarb curve calibrated against a high resolution conodont biostratigraphy reveals a major intra capitanian negative excursion of 5 superimposed on typically heavy 4 5 middle permian values this curve can also be recognised in panthalassan seamount carbonates of japan although this requires reassignment of apparently upper permian limestones to the middle permian in both china and japan the capitanian mass extinction occurs during the early stage of this major intra capitanian negative excursion assuming typical platform carbonate accumulation rates the records of the maokou formation suggest 13ccarb values fell at 0 01 kyr suggesting a catastrophic origin such as gas hydrate destabilisation is unlikely although a volcanic source is possible

asian summer monsoon simulated by a global cloud system resolving model diurnal to intra seasonal variability 1 interaction of convection and circulation is key to the asian summer monsoon but difficult to represent in global models here we report results from simulations for the summer of 2004 by a global cloud system resolving model nicam at both 14 and 7 km horizontal resolution nicam simulates the observed monsoon circulation patterns and the northward propagation of precipitation the 7 km run simulates summer mean precipitation maxima in narrow bands along the western ghats himalayan foothills the arakan yoma highlands and the annamite range precipitation 1 is modulated by orography 2 is affected by synoptic scale systems and 3 displays a pronounced diurnal cycle especially over indo china with its strong weak signal propagating westward eastward in the wet dry phase of the intraseasonal oscillation this set of simulations captures these intraseasonal changes of the indian monsoon with high fidelity from june to early july nicam exhibits a positive bias in precipitation over the indian ocean common to atmospheric models with prescribed sea surface temperature this calls for the inclusion of ocean atmosphere coupling process to improve monsoon simulation skills

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

the microstructure of polar ice part ii state of the art an important feature of natural ice in addition to the obvious relevance of glaciers and ice sheets for climate related issues is its ability to creep on geological time scales and low deviatoric stresses at temperatures very close to its melting point without losing its polycrystalline character this fact together with its strong mechanical anisotropy and other notable properties makes natural ice an interesting model material for studying the high temperature creep and recrystallization of rocks in earth s interior after having reviewed the major contributions of deep ice coring to the research on natural ice microstructures in part i of this work faria et al 2014 here in part ii we present an up todate view of the modern understanding of natural ice microstructures and the deformation processes that may produce them in particular we analyze a large body of evidence that reveals fundamental flaws in the widely accepted tripartite paradigm of polar ice microstructure also known as the three stage model cf part i these results prove that grain growth in ice sheets is dynamic in the sense that it occurs during deformation and is markedly affected by the stored strain energy as well as by air inclusions and other impurities the strong plastic anisotropy of the ice lattice gives rise to high internal stresses and concentrated strain heterogeneities in the polycrystal which demand large amounts of strain accommodation from the microstructural analyses of ice cores we conclude that the formation of many and diverse subgrain boundaries and the splitting of grains by rotation recrystallization are the most fundamental mechanisms of dynamic recovery and strain accommodation in polar ice additionally in fine grained high impurity ice layers e g cloudy bands strain may sometimes be accommodated by diffusional flow at low temperatures and stresses or microscopic grain boundary sliding via microshear in anisotropic ice sheared at high temperatures grain boundaries bulged by migration recrystallization and subgrain boundaries are endemic and very frequent at almost all depths in ice sheets evidence of nucleation of new grains is also observed at various depths provided that the local concentration of strain energy is high enough which is not seldom the case as a substitute for the tripartite paradigm we propose a novel dynamic recrystallization diagram in the three dimensional state space of strain rate temperature and mean grain size which summarizes the various competing recrystallization processes that contribute to the evolution of the polar ice microstructure dedicated to sepp kipfstuhl on occasion of his 60th birthday

physical and structural properties of the greenland ice sheet project 2 ice core a review substantial data sets have been collected on the relaxation characteristics density grain size c axis fabrics and ultrasonic velocities of the greenland ice sheet project 2 gisp2 core to its contact with bedrock at 3053 4 m changes in all these properties paralleled closely those found in cores from byrd station antarctica and dye 3 greenland density increased progressively with depth to a maximum of 0 921 mg m3 at about 1400 m at which depth the ice became bubble free below about 2000 m in situ densities began to decrease in response to increasing ice sheet temperatures since drilling much of the ice core has undergone significant volume expansion relaxation due to microcracking and the exsolving of enclathratized gases especially in the brittle ice zone between 650 and 1400 m grain size increased linearly to about 1000 m thereafter remaining fairly constant until the younger dryas event at 1678 m where a twofold to threefold decrease in grain size occurred these grain size changes were accompanied by a progressive clustering of crystal c axes toward the vertical including a small increase in c axis concentration across the younger dryas holocene boundary increased dust levels in the wisconsin ice have contributed to the maintenance of a fine grained texture which with its strong vertical c axis fabric persisted to nearly 3000 m however beginning at about 2800 m layers of coarse grained ice intermixed with the much finer grained matrix ice are observed below 3000 m the ice became very coarse grained this change attributed to annealing recrystallization at elevated temperatures in the ice sheet was accompanied by a dispersed or ring like redistribution of the c axes about the vertical ultrasonic measurements of vertical and horizontal p wave velocities made at 10 m intervals along the entire length of the gisp2 core fully confirmed the results of the crystallo optical observations a return to fine grained ice coincided with the first appearance of brown silty ice 13 m above bedrock bedrock material consisted of 48 cm of till including boulders and cobbles overlying gray biotite granite comprising the true bedrock there is evidence that disturbed structure in the gisp2 cores begins little more than 70 of the way through the ice sheet this disturbance increases with depth until it becomes large enough to cast suspicion on features lasting centuries or more in the bottom 10 of the ice sheet

intraseasonal variations of the yangtze rainfall and its related atmospheric circulation features during the 1991 summer the intraseasonal variations of the yangtze rainfall over eastern china and its related atmospheric circulation characteristics during the 1991 summer are examined based on the gauge observed rainfall and the ncep ncar reanalysis data wavelet analysis shows that during the 1991 summer the active and break sequences of rainfall over the middle and lower yangtze basin are mainly regulated by an oscillatory mode with a period of 15 35 days an investigation of the circulation features suggests that the 15 35 day oscillation is associated with an anomalous low level cyclone anticyclone appearing alternatively over the northern south china sea scs and the philippine sea and related to a northeastward southwestward shift of the western pacific subtropical anticyclone over the scs leading to a lower tropospheric divergence convergence over the yangtze basin in the upper troposphere the 15 35 day oscillation exhibits a dipole anomaly characterized by an anomalous cyclone anticyclone over eastern china and an anomalous anticyclone cyclone over the northern tibetan plateau resulting in a southwestward shrinking northeastward extending of the south asian anticyclone and forming a convergence divergence over eastern china such a coupled anomalous flow pattern between the lower and upper troposphere favors large scale descending ascending motion and hence reduced enhanced rainfall over the yangtze basin dynamically the intraseasonal variations in the yangtze rainfall are mainly determined by the coupling between the low level relative vorticity and the upper level divergence in the middle troposphere the 15 35 day oscillation of the subtropical high is originated over the central north pacific north of hawaii then propagates westward to the scs philippine sea and finally modulates the intraseasonal variations of the yangtze rainfall

long period seismology on europa 1 physically consistent interior models 1 in order to examine the potential of seismology to determine the interior structure and properties of europa it is essential to calculate seismic velocities and attenuation for the range of plausible interiors we calculate a range of models for the physical structure of europa as constrained by the satellite s composition mass and moment of inertia we assume a water ice shell a pyrolitic or a chondritic mantle and a core composed of pure iron or iron plus 20 weight percent of sulfur we consider two extreme mantle thermal states hot and cold given a temperature and composition we determine density seismic velocities and attenuation using thermodynamical models while anelastic effects will be negligible in a cold mantle and the brittle part of the ice shell strong dispersion and dissipation are expected in a hot convective mantle and the bulk of the ice shell there is a strong relationship between different thermal structures and compositions the hot mantle may maintain temperatures consistent with a liquid core made of iron plus light elements for the cold scenarios the possibility of a solid iron core cannot be excluded and it may even be favored the depths of the ocean and core mantle boundary are determined with high precision 10 km and 40 km respectively once we assume a composition and thermal structure furthermore the depth of the ocean is relatively insensitive 4 km to the core composition used

tropical intraseasonal variability in the mri 20km60l agcm this study documents the detailed characteristics of the tropical intraseasonal variability tisv in the mri 20km60l agcm that uses a variant of the arakawa schubert cumulus parameterization mean states power spectra propagation features leading eof modes horizontal and vertical structures and seasonality associated with the tisv are analyzed results show that the model reproduces the mean states in winds realistically and in convection comparable to that of the observations however the simulated tisv is less realistic it shows low amplitudes in convection and low level winds in the 30 60 day band filtered anomalies have standing structures power spectra and lag correlation of the signals do not propagate dominantly either in the eastward direction during boreal winter or in the northward direction during boreal summer a combined eof ceof analysis shows that winds and convection have a loose coupling that cannot sustain the simulated tisv as realistically as that observed in the composited mature phase of the simulated mjo the low level convergence does not lead convection clearly so that the moisture anomalies do not tilt westward in the vertical indicating that the low level convergence does not favor the eastward propagation the less realistic tisv suggests that the representation of cumulus convection needs to be improved in this model

spike of pyrosynthetic polycyclic aromatic hydrocarbons associated with an abrupt decrease in δ13c of a terrestrial biomarker at the cretaceous tertiary boundary at caravaca spain the first vertical high resolution record of polycyclic aromatic hydrocarbons pahs of pyrosynthetic origin and the corresponding 13 c profile of a terrestrial biomarker across the cretaceous tertiary k t boundary at caravaca spain reveals the following in comparison with adjacent cretaceous marlstones the first thin horizon 0 to 0 5 cm 0 the k t boundary of the boundary clay layer is 1 enriched as much as 112 to 154 fold in typical pyrosynthetic pahs such as coronene benzo g h i perylene and benzo e pyrene and 2 shows an abrupt 13 c decrease of 1 4 1 8 in terrestrial higher plant derived n c 29 alkane the spike of pyrosynthetic pahs associated with an abrupt decrease in 13 c value of a terrestrial biomarker is interpreted to reflect the prevalence of extensive fires with subsequent 13 c decrease in atmospheric co 2 it is estimated that the geologically instantaneous combustion of 18 24 of the terrestrial above ground biomass would be necessary to account for the measured negative isotopic shift at the k t boundary on the basis of carbon mass balance between terrestrial above ground biomass and atmosphere

a renewed argument for crystal size control of ice sheet strain rates at present it is generally believed that crystal size has no direct influence on strain rate in the ice sheets and that the fraction of strain rate enhancement there which is not ascribable to c axis fabric is due to impurity content here we challenge this view because it is not consistent with recent results from analyses of deformation at meserve glacier and instead ascribe residual enhancement in the ice sheets to variations in crystal size we resurrect the idea that variations of crystal size can be an important part of the total shear enhancement in the ice sheets though agree with paterson that this effect is generally dominated by variations of crystal fabric we propose that the enhanced shear strain rate of ice age ice in southern greenland as inferred from tilt of the dye 3 borehole can be explained as a result of combined fabric variations and crystal size variations with these two ice properties accounting for roughly 70 and 30 of the average enhancement respectively permitting a grain size dependence of ice viscosity also resolves the quandary concerning closure and tilt of the agassiz ice cap borehole

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

pattern of marine mass extinction near the permian triassic boundary in south china the meishan section across the permian triassic boundary in south china is the most thoroughly investigated in the world a statistical analysis of the occurrences of 162 genera and 333 species confirms a sudden extinction event at 251 4 million years ago coincident with a dramatic depletion of 13ccarbonate and an increase in microspherules

20 50 day oscillation of summer yangtze rainfall in response to intraseasonal variations in the subtropical high over the western north pacific and south china sea the spatio temporal variability in summer rainfall within eastern china is identified based on empirical orthogonal function eof analysis of daily rain gauge precipitation data for the period 1979 2003 spatial coherence of rainfall is found in the yangtze basin and a wavelet transform is applied to the corresponding principal component to capture the intraseasonal oscillation iso of yangtze rainfall the ensemble mean wavelet spectrum representing statistically significant intraseasonal variability shows a predominant oscillation in summer yangtze rainfall with a period of 20 50 days a 10 20 day oscillation is pronounced during june and july this finding suggests that the 20 50 day oscillation is a major agent in regulating summer yangtze rainfall composite analyses reveal that the 20 50 day oscillation of summer yangtze rainfall arises in response to intraseasonal variations in the western north pacific subtropical high wnpsh which in turn is modulated by a rossby wave like coupled circulation convection system that propagates northward and northwestward from the equatorial western pacific when an anomalous cyclone associated with this rossby wave like system reaches the south china sea scs and philippine sea the wnpsh retreats northeastward due to a reduction in local pressure under these conditions strong monsoonal southwesterlies blow mainly toward the scs philippine sea while dry conditions form in the yangtze basin with a pronounced divergent flow pattern in contrast the movement of an anomalous anticyclone over the scs philippine sea results in the southwestward extension of the wnpsh consequently the tropical monsoonal southwesterlies veer to the northeast over the scs and then converge toward the yangtze basin producing wet conditions therefore the 20 50 day oscillation of yangtze rainfall is also manifest as a seesaw pattern in convective anomalies between the yangtze basin and the scs philippine sea a considerable zonal shift in the wnpsh is associated with extreme dry wet episodes in the yangtze basin with an abrupt eastward westward shift in the wnpsh generally leading the extreme negative positive yangtze rainfall anomaly by a 3 8 period of the 20 50 day oscillation this finding may have implications for improving extended range weather forecasting in the yangtze basin

the 30 50 day variation of convective activity over the western pacific ocean with emphasis on the northwestern region abstract coherent 30 50 day oscillations between regions north and south of 20 n were observed using the latitude time y t diagram of a convective index ic along 140 e over the entire 1979 summer may september the oscillation in the northern region exhibits a relatively regular north south movement of deep convective clouds while the oscillation in the southern region shows enhancement or suppression fluctuations of broad and intensive deep convective clouds with a period of 30 50 days the southward northward movement of the midlatitude oscillation coincides with the suppression enhancement of the tropical deep convective clouds the midlatitude deep convective clouds are usually maintained by the divergent circulation and are associated with fronts the empirical orthogonal function eof analysis of velocity potential at 200 mb shows that the north south 30 50 day oscillation of deep convective clouds over the northwestern pacific is a response of the regional weather system to the eastwar

dynamic recrystallization and texture development in ice as revealed by the study of deep ice cores in antarctica and greenland the preferred c axis orientation of ice from polar ice sheets develops essentially as a result of intracrystalline slip but dynamic recrystallization appears to alter the kinetics of the development of deformation textures and is at high temperature at the origin of recrystallization textures the purpose of this work is to obtain a better understanding of recrystallization processes that occur in polar ice sheets and to clarify the relationship between dynamic recrystallization and textures the study was based on two deep ice cores from greenland and antarctica the greenland ice core project grip and vostok ice cores the structure along the grip core displays normal grain growth in the first 100 m of the ice sheet and rotation recrystallization and migration recrystallization near the bottom only grain growth and rotation recrystallization appear to occur in the vostok ice core the transition between these recrystallization regimes was studied estimating for interglacial ice the evolution with depth of the dislocation density this calculation has shown the efficiency of grain boundary migration for the absorption of dislocations at vostok the highest value of the dislocation density is found at a depth of about 1000 m and the continuous decrease in the dislocation density below this depth is related to the increase of the grain boundary migration rate it is shown that the driving force required to initiate migration recrystallization is not reached in interglacial ice at vostok the observed textures were compared with those predicted by the self consistent approach recrystallization textures are interpreted by assuming that the less stressed grains i e the best oriented for basal slip are favored by the size advantage of subgrains the recrystallization textures are compared with those of other materials

microstructure mapping a new method for imaging deformation induced microstructural features of ice on the grain scale this work presents a method of mapping deformation related sublimation patterns formed on the surface of ice specimens at microscopic resolution 3 4 mm pixel 1 the method is based on the systematic sublimation of a microtomed piece of ice prepared either as a thick or a thin section the mapping system consists of an optical microscope a ccd video camera and a computer controlled xy stage about 1500 images are needed to build a high resolution mosaic map of a 4 5 9 cm section mosaics and single images are used to derive a variety of statistical data about air inclusions air bubbles and air clathrate hydrates texture grain size shape and orientation and deformation related features subgrain boundaries slip bands subgrain islands and loops pinned and bulged grain boundaries the most common sublimation patterns are described and their relevance for the deformation of polar ice is briefly discussed

high resolution simulation of mean convection and its intraseasonal variability over the tropics in the mri jma 20 km mesh agcm abstract tropical mean convection and its organization on different spatiotemporal scales in a simulation using the meteorological research institute japan meteorological agency mri jma global atmospheric general circulation model agcm at 20 km resolution tl959l60 has been investigated comparison with two lower resolution simulations of 120 km tl159l40 and 180 km tl95l40 shows that convection climatological fields and moist stability over the indian ocean and south pacific convergence zone are better represented in tl959l60 than in lower resolution simulations however the simulated three dimensional structure of the walker and hadley cells and the vertical structure of convective heating do not show marked improvement relative to lower resolution simulations the amplitude and phase speed of convectively coupled equatorial waves show that although the kelvin waves the observed hierarchical structure of cloud clusters associated with the madden julian oscillation mjo convection and th

volcanism mass extinction and carbon isotope fluctuations in the middle permian of china the 260 million year old emeishan volcanic province of southwest china overlies and is interbedded with middle permian carbonates that contain a record of the guadalupian mass extinction sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations these show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae the temporal coincidence of these two phenomena supports the idea of a cause and effect relationship the crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean atmosphere carbon cycle

tempo of the end permian event high resolution cyclostratigraphy at the permian triassic boundary the permian triassic p t boundary is marked by the most severe mass extinction in the geologic record high resolution cyclostratigraphy on a 10 4 yr scale across the p t boundary in a core from the carnic alps austria revealed significant cycles in the ratio 40 10 4 7 2 3 m identified with milankovitch cycles of 412 100 40 20 k y eccentricity 1 and 2 obliquity and precession wavelet analysis indicates continuity of deposition across the boundary with an average accumulation rate of 10 cm k y the dramatic faunal changes at the p t boundary can be constrained within an interval of 60 k y possibly 8 k y with the accompanying sharp negative global carbonisotope shift within 30 k y suggesting a catastrophic cause

deformation of debris ice mixtures mixtures of rock debris and ice are common in high latitude and high altitude environments and are thought to be widespread elsewhere in our solar system in the form of permafrost soils glaciers and rock glaciers these debris ice mixtures are often not static but slide and creep generating many of the landforms and landscapes associated with the cryosphere in this review a broad range of field observations theory and experimental work relevant to the mechanical interactions between ice and rock debris are evaluated with emphasis on the temperature and stress regimes common in terrestrial surface and near surface environments the first order variables governing the deformation of debris ice mixtures in these environments are debris concentration particle size temperature solute concentration salinity and stress a key observation from prior studies consistent with expectations is that debris ice mixtures are usually more resistant to deformation at low temperatures than their pure end member components however at temperatures closer to melting the growth of unfrozen water films at ice particle interfaces begins to reduce the strengthening effect and can even lead to profound weakening using existing quantitative relationships from theoretical and experimental work in permafrost engineering ice mechanics and glaciology combined with theory adapted from metallurgy and materials science a simple constitutive framework is assembled that is capable of capturing most of the observed dynamics this framework highlights the competition between the role of debris in impeding ice creep and the mitigating effects of unfrozen water at debris ice interfaces

permo triassic boundary superanoxia and stratified superocean records from lost deep sea pelagic cherts of japan and british columbia canada recorded a long term and worldwide deep sea anoxic oxygen depleted event across the permo triassic or paleozoic and mesozoic boundary 251 2 million years ago the symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean panthalassa became totally stratified for nearly 20 million years across the boundary the timing of onset climax and termination of the oceanic stratification correspond to global biotic events including the end guadalupian decline the end permian extinction and mid triassic recovery

a model for the boreal summer intraseasonal oscillation abstract the tropical intraseasonal oscillation iso exhibits pronounced seasonality the boreal summer iso is more complex than its winter counterpart due to the coexistence of equatorial eastward off equatorial westward and northward propagating low frequency modes and their interactions based on observational evidence and results obtained from numerical experiments a mechanism is proposed for the boreal summer iso in which the northern hemisphere summer monsoon nhsm circulation and moist static energy distribution play essential roles with a climatological july mean basic state the life cycle of model low frequency waves consists of four processes an equatorial eastward propagation of a coupled kelvin rossby wave packet an emanation of moist rossby waves in the western pacific a westward propagation and amplification of the rossby waves in south asian monsoon regions and a reinitiation of the equatorial disturbances over the central indian ocean the life cycle spans about one month and p

putative ice flows on europa geometric patterns and relation to topography collectively constrain material properties and effusion rates europa s surface exhibits numerous small dome like and lobate features some of which have been attributed to fluid emplacement of ice or slush on the surface we perform numerical simulations of non newtonian flows to assess the physical conditions required for these features to result from viscous flows our simulations indicate that the morphology of an ice flow on europa will be at least partially influenced by pre existing topography unless the thickness of the flow exceeds that of the underlying topography by at least an order of magnitude three classes of features can be identified on europa first some possibly most putative flow like features exhibit no influence from the pre existing topography such as ridges although their thicknesses are generally on the same order as those of ridges therefore flow processes probably cannot explain the formation of these features second some observed features show modest influence from the underlying topography these might be explained by ice flows with wide ranges of parameters ice temperatures 230 k effusion rates 10 7 m 3 year 1 and a wide range of grain sizes although surface uplift e g by diapirism and in situ disaggregation provide an equally compelling explanation third several observed features are completely confined by pre existing topographic structures on at least one side these are the best known candidates for flow features on europa if these features resulted from solid ice flows then temperatures 260 k and grain sizes 2 m are required such small grain sizes seem unlikely low viscosity flows such as ice slurries or brines provide a better explanation for these features our results provide theoretical support for the view that many of europa s lobate features have not resulted from solid ice flows