adaptation of prestack migration to multi offset ground penetrating radar gpr data in adapting the prestack migration technique used in seismic imaging to the inversion of ground penetrating radar gpr from time to depth sections we show that the theoretical integral formulation of the inversion can be applied to electromagnetic problems albeit with three assumptions the first two assumptions concern the electromagnetic characteristics of the medium primarily that the medium must be perfectly resistive and non dispersive and the third concerns the antennae radiation pattern which is taken to be 2d the application of this adaptation of the inversion method is confirmed by migrating actual gpr measurements acquired on the test site of the laboratoire central des ponts et chaussees the results show good agreement with the geometry of the structures in the medium and confirm that the possible departure from the assumption of a purely resistive medium has no visible effect on the information concerning the geometry of scattering and reflecting structures the field experiments also show that prestack migration processing is sufficiently robust with regard to the assumption of a non dispersive medium the assumption of a 2d antennae radiation pattern however produces artefacts that could be significant for laterally heterogeneous media nevertheless where the medium is not highly laterally heterogeneous the migration gives a clear image of the scattering potential due to the geometry of structural contrasts in the medium the scatterers are well focused from diffraction hyperbolae and well localized spatial geometry has limited dimensional accuracy and positions are located with a maximum error equal to the minimum wavelength of the signal bandpass objects smaller than one wavelength can nevertheless be detected and well focused if their dielectric contrasts are sufficiently high as in the case of iron or water in gneiss gravels furthermore the suitability of multi offset protocols to estimate the electromagnetic propagating velocity and to decrease the non coherent noise level of measurements is confirmed our velocity estimation is based on the semblance calculation of multi offset migrated images and we confirmed the relevance of this quantification method using numerical data the signal to noise ratio is improved by summing multi offset results after the addition of random noise on measurements thus the adaptation of prestack migration to multi offset radar measurements significantly improves the resolution of the scattering potential of the medium limitations associated with the methods used here suggest that 3d algorithms should be applied to strongly laterally heterogeneous media and further studies concerning the waveform inversion are necessary to obtain information about the electric nature of the medium

resolving a late oligocene conundrum deep sea warming and antarctic glaciation abstract changes in ice volume and resulting changes in sea level were determined for the late oligocene 26 23 ma astronomical timescale ats by applying 18 o to sea level calibrations to deep sea 18 o records from odp sites 689 690 929 1090 and 1218 our results show that maximum global ice volume occurred during two late oligocene 18 o events oi2c 24 4 ma and mi1 23 0 ma inferred glacioeustatic lowering with volumes up to 25 greater than the present day east antarctic ice sheet eais ice volume during glacial minima was on the order of about 50 of the present day eais this is supported by late oligocene stratigraphic records from antarctica that contain evidence of cold climates and repeated episodes of glaciation at sea level and grounding lines of glacial ice on the antarctic continental shelf in the ross sea and prydz bay in contrast composite deep sea 18 o records show a significant decrease 1 between 26 7 and 23 5 ma which have long been interpreted as bottom water warming combined with deglaciation of antarctica however a close examination of individual 18 o records indicates a clear divergence after 26 8 ma between records from southern ocean locations i e ocean drilling program sites 689 690 744 and those of other ocean basins high 18 o values 2 9 3 3 from these southern ocean 18 o records are consistent with an ice sheet on the east antarctic continent equivalent to present day values and cold bottom water temperatures 2 0 c these differences suggest a reduction in deep water produced near the antarctic continent i e proto antarctic bottom water proto aabw which were quickly entrained and mixed with warmer and presumably more saline bottom water originating from lower latitudes expansion of a warmer deep water mass and the weakening of the proto aabw may explain the large intra basinal isotopic gradients that developed among late oligocene benthic 18 o records these conclusions are also supported by ocean modeling suggesting a reduction of deep water formed in the southern ocean strengthening of deep water from the northern hemisphere and decreasing temperatures in high southern latitudes occurred as the drake passage opened to deep water low 18 o values reported from deep sea locations other than the southern ocean are shown to bias estimates of antarctic ice volume calling for a re evaluation of the notion that antarctic ice volume was significantly reduced during the late oligocene

the last 1 million years of the extinct genus discoaster plio pleistocene environment and productivity at site u1476 mozambique channel abstract a detailed paleoenvironment reconstruction from the mozambique channel western indian ocean based on the calcareous nannoplankton assemblages was conducted for the interval between 2 85 and 1 85 myr this study covers the period during which the successive extinction of the last five species of discoasters occurred new productivity data obtained from the abundances of the discoaster species discoaster brouweri d triradiatus d pentaradiatus d surculus and d tamalis and other indicative calcareous nannoplankton taxa showed abundance variations which were at paced with the 100 41 and 23 kyr astronomical periodicities a shift in the productivity and water column stratification proxies occurred at 2 4 ma after the onset of the northern hemisphere glaciation here we propose that the variability recorded at international ocean discovery program site u1476 reflects the interplay between forcing associated with warm tropical pacific and cold southern ocean influences the former is shown by consistent occurrence of warm water taxa calcidiscus leptoporus oolithotus spp rhabdosphaera clavigera syracosphaera spp umbellosphaera spp typical of indonesian throughflow surface waters on the other hand the occurrence of coccolithus pelagicus indicates the influence of cold nutrient rich sub antarctic surface waters a more mixed water column initiated at 2 4 ma and a consequent productivity increase led to the gradual reduction of the discoaster species until their extinction at 1 91 ma this period was characterized by the low values of the florisphaera profunda index and high abundances of upper photic zone flora indicative of nutrient rich surface water conditions high productivity at the location during this period could have also been amplified by localized upwelling events driven by the mozambique channel eddies

alternating southern and northern hemisphere climate response to astronomical forcing during the past 35 m y earth s climate has undergone different intervals of gradual change as well as abrupt shifts between climate states here we aim to characterize the corresponding changes in climate response to astronomical forcing in the icehouse portion of the cenozoic from the latest eocene to the present as a tool we use a 35 m y long 18 o benthic record compiled from different high resolution benthic isotope records spliced together what we refer to as a megasplice we analyze the climate response to astronomical forcing during four 800 k y long time windows during the mid miocene climatic optimum ca 15 5 ma global climate variability was mainly dependent on southern hemisphere summer insolation amplified by a dynamic antarctic ice sheet 2 5 m y later relatively warm global climate states occurred during maxima in both southern hemisphere and northern hemisphere summer insolation at that point the antarctic ice sheet grew too big to pulse on the beat of precession and the southern hemisphere lost its overwhelming influence on the global climate state likewise we juxtapose response regimes of the miocene ca 19 ma and oligocene ca 25 5 ma warming periods despite the similarity in 18 o benthic values and variability we find different responses to precession forcing while miocene warmth occurs during summer insolation maxima in both hemispheres oligocene global warmth is consistently triggered when earth reaches perihelion in the northern hemisphere summer this pattern is in accordance with previously published paleoclimate modeling results and suggests an amplifying role for northern hemisphere sea ice

geological modelling from field data and geological knowledge part ii modelling validation using gravity and magnetic data inversion the analysis of multiple data sets is required to select a realistic 3d geological model among an infinite number of possibilities an inverse method that aims at describing the 3d geometry of geological objects is presented the method takes into account the geology and the physical properties of rocks while respecting the topological properties of an a priori model the a priori model is built from the geological data set and its geometry is largely dependent upon assumptions about inaccessible geology at depth this method referred to as total litho inversion is a generalized 3d inversion that results in quantifying the lithology and the distribution of rock property in a probabilistic way its application is demonstrated through i a simple synthetic case and ii the relative distribution characterization of granites and diorites in an orogenic domain

neogene siliciclastic deposition and climate variability on a carbonate margin australian northwest shelf abstract the bare formation represents a unique episode of neogene siliciclastic deposition on the carbonate dominated australian northwest shelf nws seismic interpretation coupled with age control from international ocean discovery program iodp expedition 356 sites u1462 u1463 and u1464 allow us to constrain the timing of siliciclastic deposition and the associated sedimentary processes the bare formation is preceded by middle to late miocene shelf exposure and karstification 12 ma elongate sandbars deposits with small lobate deltas developed during the late miocene fluvial deposition increased markedly in the zanclean 5 3 3 6 ma resulting in development of a large wave dominated delta with evidence of channels comprising the thickest component of the bare formation siliciclastic input decreased in the piacenzian 3 6 2 58 ma leading to margin retreat and final termination in the early pleistocene 2 39 ma the results correlate with regional climate and sedimentary records from sites u1463 and u1464 which indicate an arid middle to late miocene on the nws followed by a humid interval in the zanclean and a return to arid conditions during the piacenzian we suggest that fluctuation of surface runoff patterns in the continental hinterland was the primary control on bare formation evolution sedimentary and climate transitions are linked to reorganization of indian ocean paleoceanography accompanying northward migration of the australian continent and progressive restriction of the indonesian throughflow

lithological correction of chemical weathering proxies based on k rb and mg contents for isolation of orbital signals in clastic sedimentary archives abstract the extraction of palaeoenvironmental palaeoclimatic signals from the chemical composition of siliciclastic sediments is valuable for the reconstruction of past environments particularly in continental basins here we test novel weathering proxies which are less sensitive to lithological control than the previously used raw element ratios k al k ti and k rb 1 local enrichment factors of k al mg al and k rb i e the element ratios corrected for grain size and matrix composition using local background functions al si fe and ca as explanatory variables and ordinary regression and 2 robust regression residuals of those element ratios based on isometric log ratio coordinates of the most relevant lithogenic elements ca fe rb si zr in the chemical composition chemical weathering proxies can be obtained from departures of chemical composition of sedimentary profiles from relationships with other chemical elements in particular those with grain size control the resulting weathering proxies were examined for the miocene deposits from the most basin the czech republic which recorded one of the major warm episodes of the cenozoic time the miocene climatic optimum the performance of weathering proxies has been checked by 1 comparison of individual proposed proxies in one drill core hk930 2 detailed analysis of orbital signals in the relevant compositional functions in hk930 and 3 lateral correlation of three cores hk930 du7 and do565 of the same basin the novel proxies show lateral stability and orbital signatures of short eccentricity obliquity and precession confirming their usefulness in palaeoenvironmental studies corrections for grain size and carbonate contents should help to isolate climatic content from the weathering proxies although in the studied sediments it weakened the precession component in the orbital signal as grain size proxies and other compositional data also carried orbital signals we propose to consider these proxy ideas in palaeoclimatic reconstructions based on chemical weathering proxies

three dimensional density structure of la soufriere de guadeloupe lava dome from simultaneous muon radiographies and gravity data muon imaging has recently emerged as a powerful method to complement standard geophysical tools in the understanding of the earth s subsurface muon measurements can yield a radiography of the average density along the muon path allowing to image large volumes of a geological body from a single observation point here we jointly invert muon data from three simultaneous telescope acquisitions together with gravity data to estimate the three dimensional density structure of the la soufriere de guadeloupe lava dome our unique datas et allows us to achieve an unprecedented spatial resolution with this novel technique the retrieved density model reveals an extensive low density anomaly where the most active part of the volcanic hydrothermal system is located supporting previous studies that indicate this region as the most likely to be involved in a partial edifice collapse

variation in the eastern north pacific subtropical gyre california current system during the middle to late miocene as inferred from radiolarian assemblages abstract the california current has influenced the primary productivity along the california margin which plays a significant role in global carbon cycles although previous studies have explored the response of the california current to climate change since the pliocene comparatively little is known about that during the middle and late miocene when the paleoclimate changed significantly here we present variations of the california current based on new data of radiolarian fossil assemblages integrated with previously published data from the middle to late miocene and show that the california current was strengthened from 12 3 to 10 5 ma 9 0 to 8 2 ma and 7 2 to 6 9 ma at odp site 1021 the biogenic opal declined during periods of increased strength of the california current from the middle to late miocene at site 1021 in offshore area these data suggest that the biogenic opal decreased at site 1021 in offshore area due to the deep nutricline depth by the strengthened california current r mode cluster analyses divided into three major assemblages surface warm cool surface to thermocline and intermediate deep water taxa the pronounced faunal changes of radiolarian assemblages to the dominance of intermediate deep water taxa might reflect an initiation of the modern type california current system since ca 10 5 ma in the early late miocene due to the tectonic changes e g partial closing of tropical gateways and uplift of the himalaya and the rocky mountains and or significant high latitude cooling

the 1975 1977 crisis of la soufriere de guadeloupe f w i a still born magmatic eruption on july 8 1976 eruptive activity broke out at la soufriere de guadeloupe f w i after about one year of increasing seismic activity seismic activity continued to increase until august 1976 reaching more than 1500 events a 200 fold increase over the preceding quiet period of a few years and an energy output of about 1017 ergs in a day a total of 26 major phreatic eruptions similar to the july 8 outburst took place during an eight months period the steam blasts that characterized the eruptions gave rise to particle and sometimes block charged plumes that deposited an estimated 106 m3 of solids the h2o rich gases emitted during the blasts presumably contained other gases h2s so2 co2 that were partly adsorbed on solid particles all material was erupted at temperatures of the order of 100 to 200 c the observation of vertical migration of earthquake foci in less than a few hours and over about 6 km depth and of abnormal variations of the geomagnetic field indicate a deep energy source for the phreatic eruptions a small proportion of the gases adsorbed on solid particles had a magmatic origin however most of the steam and the tephra seemed to originate from superficial levels of a hydrothermal system similar phreatic eruptions have occurred several times in recorded history in the case of la soufriere the origin of the phreatic eruptions is best described by an abnormal energy input versus steady state from a crustal magma chamber the occurrence of truly magmatic eruptions is presumably inhibited by an extensive hydrothermal system the abrupt release of more power from the magma chamber could have resulted in an explosive pyroclastic eruption substantial improvement of the guadeloupe volcano observatory has followed the 1975 1977 crisis permanent telemetered geophysical networks and regular geochemical observations have provided a five year data base of the volcano behavior in its noneruptive state which can be compared to crisis situations

correlation of late miocene to early pliocene sequences between the mediterranean and north atlantic ocean drilling program odp site 982 in the north atlantic contains a complete latest miocene to early pliocene section that was tuned to the astronomical timescale by correlating the record of gamma ray attenuation gra bulk density to summer insolation at 65 n and the benthic 18o signal to orbital obliquity for the interval from 4 6 to 7 5 ma the astronomical tuning of the site 982 record permits a direct bed to bed correlation to the cyclostratigraphy of messinian sections in the mediterranean krijgsman et al 1999a 2001 the benthic 18o signal at site 982 records a latest miocene glacial period that lasted from 6 26 to 5 50 ma and consisted of 18 glacial to interglacial oscillations that were controlled by the 41 kyr cycle of obliquity although the intensification of glaciation at 6 26 ma may have contributed to the restriction of the mediterranean it preceded the depositional onset of the lower evaporite unit at 5 96 ma by some 300 kyr the transition from stage tg12 to tg11 at 5 5 ma marks the end of the latest miocene glacial period and precedes the miocene pliocene boundary by 170 kyr although benthic 18o values are relatively low and 18o of bulk carbonate reaches a minimum at the miocene pliocene boundary at 5 33 ma there is no single event that would indicate deglaciation and sea level rise as the cause of the reflooding of the mediterranean we conclude that glacioeustatic changes alone were not responsible for either the start or end of evaporite deposition during the messinian suggesting that tectonic or local climate changes in the mediterranean region were the dominant cause s

interpretation of seismic pulse duration in terms of a propagating rupture a method and case histories abstract extended earthquake source models in which a rupture migrates in a fault plane radiate signals whose duration show a directional variation analysis of spectral corner frequencies may be used to estimate the parameters of an extended source but an alternative method is by the direct measurement of teleseismic body wave pulse durations on broad band seismograms this time domain approach is shown to have certain advantages including easier estimation of confidence limits and treatment of interfering arrivals a method is described for testing the compatibility of observed pulse durations with possible source geometries derived from a propagating rupture model this establishes the identity of or non existence of compatible source geometries the results provide evidence to help discriminate between source directivity and anelastic attenuation and between the fault and auxiliary planes p pp pcp or other phases observed at only a small number of stations can provide sufficiently wide directional sampling of the focal sphere to place tight constraints on the parameters of commonly assumed rupture models more constraint is imposed if the s wave radiation is also sampled for example with sp or direct s accurate measurement of durations is neither realistic nor essential a confidence of 30 in pulse duration is typical but better measurements are possible if the instrument phase response is removed from the observed seismogram a synthetic example is used to demonstrate these points and real examples studied by previous authors are re examined in more detail to assess the value of this approach in the analysis of extended sources

local and regional trends in plio pleistocene δ18o records from benthic foraminifera we present new orbital resolution pliocene pleistocene benthic stable oxygen isotope 18ob records from ocean drilling program sites 1264 and 1267 from walvis ridge in the southeast atlantic we compare long term 250 kyr interbasin 18ob gradients between pacific and north atlantic regional stacks as well as intra and interbasin gradients from the perspective of walvis ridge the 18ob values from sites 1264 and 1267 are almost always higher than deep north atlantic and pacific sites with large gradients 0 5 emerging abruptly at 2 4 ma and persisting until 1 3 ma from this we infer the presence of a new water mass which resulted from the influence of dense 18o enriched nordic sea overflow waters via the abyssal east atlantic meanwhile long term average 18ob values in the north atlantic appear to have remained within 0 0 25 lower than in the pacific however the magnitude of this difference is sensitive to the inclusion of records from the equatorial west atlantic these results together with constraints based on temperature salinity and density suggest an influence of the seawater 18o 18osw versus salinity relationship of source waters on 18ob values within the atlantic in particular the abrupt emergence at 2 4 ma of higher 18ob values at sites 1264 and 1267 relative to north atlantic records appears to require a low latitude surface water 18osw signal this implies a connection between northward heat transport and deep water export into the abyssal east atlantic hence our results have implications for the interpretation of 18ob records and highlight the potential for 18ob to constrain deep atlantic water mass sources and pathways during the plio pleistocene

crossover and peaks in the pleistocene climate spectrum understanding from simple ice age models the power spectrum provides a compact representation of the scale dependence of the variability in time series at multi millennial time scales the spectrum of the pleistocene climate is composed of a set of narrow band spectral modes attributed to the regularly varying changes in insolation from the astronomical change in earth s orbit and rotation superimposed on a continuous background generally attributed to stochastic variations quantitative analyses of paleoclimatic records indicate that the continuous part comprises a dominant part of the variance it exhibits a power law dependency typical of stochastic self similar processes but with a scale break at the frequency of glacial interglacial cycles here we discuss possible origins of this scale break the connection between the continuous background and the narrow bands and the apparently modest spectral power above the continuum at these scales we demonstrate that the observed scale break around 100 ka can have a variety of different origins and does not imply an internal time scale of correlation as implied by the simplest linear stochastic model

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

extended orbitally forced palaeoclimatic records from the equatorial atlantic ceara rise abstract we extend existing high resolution oligocene miocene proxy records from ocean drilling program odp leg 154 the extended record spans the time interval from 17 86 to 26 5 ma the data are age calibrated against a new astronomical solution that affords a re evaluation of the intricate interaction between orbital milankovitch forcing of the climate and ocean system and the fidelity with which this forcing is recorded in oxygen and carbon stable isotope measurements from benthic foraminifera and associated lithological proxy records of magnetic susceptibility colour reflectance and the measured sand fraction our records show a very strong continual imprint of the earth s obliquity cycle modulate in amplitude every 41 ka a very strong eccentricity signal in the carbon isotope records and a strong but probably local imprint of climatic precession on the coarse fraction and magnetic susceptibility records our data allowed us to evaluate how the interaction of long multi million year beats in the earth s eccentricity and obliquity are implicated in the waxing and waning of ice sheets presumably on antarctica our refined age model confirms the revised age of the oligocene miocene boundary previously established by analysis of the lithological data and allows a strong correlation with the geomagnetic time scale by comparison with data from odp site 1090 southern ocean

japanese volcanoes visualized with muography high energy muons that are generated via the reaction between primary cosmic rays and the earth s atmosphere can be used to map out the density distribution in shallow parts of a volcano s interior

the nucleation and rupture process of the 1981 gulf of corinth earthquakes from deconvolved broad band data summary source parameters of the largest three normal faulting earthquakes ms6 6 6 3 6 4 in the 1981 gulf of corinth greece sequence are determined using deconvolved broad band data recorded by arrays and single stations and a 2 d finite source model such a model enables the spatial extent rupture velocity and stress drop of the earthquakes to be determined and geological observations of surface slip can be included as a further constraint on the waveform modelling all three earthquakes were shallow lo km with low stress drops 30 bars and exhibited source complexity the correspondence between the complexity of the earthquake sources and that of the mapped fault breaks implies that the segmentation of surface faulting in greece is representative of faulting at depth tiny initial pulses which correlate across the arrays are seen in the seismograms from the gulf of corinth earthquakes at most stations these initial subevents 1 per cent of the total moment are interpreted as the breaking of small asperities which initiated the main rupture and are used to constrain the attenuation correction t 0 2 s

investigation of mantle discontinuities from a single deep earthquake converted phases have been identified in the p wave coda of teleseismic seismograms from a single large mw 6 8 deep 360 km earthquake south of honshu japan standard array techniques slantstacking applied to broadband data from the global broadband network the german regional seismic network grsn and the grafenberg grf array and synthetic seismogram modeling reveal that these unusual phases are s to p conversions from under the seismic source timing of the converted phase indicates that subduction has had little if any effect on the depth of the 660 km discontinuity this study shows that upper mantle seismic structure can be constrained from single events using the presently available broadband seismic data and applying array techniques to network data

cyclostratigraphic calibration of the famennian stage late devonian illinois basin usa abstract the late devonian biosphere was affected by two of the most severe biodiversity crises in earth s history the kellwasser and hangenberg events near the frasnian famennian f f and the devonian carboniferous d c boundaries respectively current hypotheses for the causes of the late devonian extinctions are focused on climate changes and associated ocean anoxia testing these hypotheses has been impeded by a lack of sufficient temporal resolution in paleobiological tectonic and climate proxy records while there have been recent advances in astronomical calibration that have improved the accuracy of the frasnian time scale and part of the famennian the time duration of the entire famennian stage remains poorly constrained during the late devonian a complete late frasnian early carboniferous succession of deep shelf deposits accumulated in the epieric sea in illinois basin of the central north american mid continent a record of this sequence is captured in three overlapping cores h 30 sullivan and h 32 the h 30 core section spans the f f boundary the sullivan section spans almost all of the famennian and the h 32 section sampled spans the interval of the upper famennian and the d c boundary to have the best chance of capturing milankovitch cycles 2000 rock samples were collected at minimum 5 cm interval across the entire sequence magnetic susceptibility ms was measured on each sample and the preservation of climatic information into the ms signal was verified through geochemical analyses and low temperature magnetic susceptibility acquisition to estimate the duration of the famennian stage we applied multiple spectral techniques and tuned the ms signal using the highly stable 405 kyr cycle for sullivan and the obliquity cycle for the h 30 and h 32 cores based on the correlation between the cores we constructed a famennian floating astronomical time scale which indicates a duration of 13 5 0 5 myr an uncertainty of 0 5 myr was estimated for the uncertainties arising from the errors in the stratigraphic position of the f f and d c boundaries and the 405 kyr cycle counting interpolated from the high resolution u pb radiometric ages available for the devonian carboniferous boundary we recalibrated the frasnian famennian boundary numerical age to 372 4 0 9 ma

an astronomically dated record of earth s climate and its predictability over the last 66 million years much of our understanding of earth s past climate comes from the measurement of oxygen and carbon isotope variations in deep sea benthic foraminifera yet long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the cenozoic era and to study their dynamics here we present a new highly resolved astronomically dated continuous composite of benthic foraminifer isotope records developed in our laboratories four climate states hothouse warmhouse coolhouse icehouse are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of cenozoic climate dynamics

absolute gravity change associated with magma mass movement in the conduit of asama volcano central japan revealed by physical modeling of hydrological gravity disturbances the gravity signal originating from magma mass movement in a volcanic conduit is retrieved from the hydrologically disturbed absolute gravity data obtained at asama volcano central japan in 2004 using a three dimensional hydrological model we improve the hydrological model of the previous study using realistic soil parameters and boundary conditions to better estimate the spatiotemporal land water distributions and the consequent hydrological gravity disturbances the newly estimated gravity disturbances agree with the absolute gravity values observed by fg5 gravimeters in 2004 2009 within about 2 6 gal by additionally accounting for the excess discharge of groundwater mass associated with a sloping impermeable surface below the discharge area after the gravity disturbance of 20 gal amplitude is subtracted from the absolute gravity data observed during the 2004 eruptive event the gravity residual of 5 gal amplitude shows a significant decrease in synchronization with eruptions because the ascending magma mass in the conduit affects the upward attraction force to the gravimeters installed on the flank of asama volcano the magma head altitude to which the residual gravity is converted assuming a homogeneous linear density in the conduit shows a comprehensive agreement of the time variation in the magma head with those in other volcanic observations such as gas emission rate and earthquake frequency by correcting the hydrological gravity disturbances using this hydrological model and simultaneously obtained meteorological data in real time spatiotemporal variations in the magma mass can be instantaneously monitored at asama volcano even before eruptions during future volcanic events

astronomically paced changes in deep water circulation in the western north atlantic during the middle eocene abstract north atlantic deep water nadw currently redistributes heat and salt between earth s ocean basins and plays a vital role in the ocean atmosphere co2 exchange despite its crucial role in today s climate system vigorous debate remains as to when deep water formation in the north atlantic started here we present datasets from carbonate rich middle eocene sediments from the newfoundland ridge revealing a unique archive of paleoceanographic change from the progressively cooling climate of the middle eocene well defined lithologic alternations between calcareous ooze and clay rich intervals occur at the 41 kyr beat of axial obliquity hence we identify obliquity as the driver of middle eocene 43 5 46 ma northern component water ncw the predecessor of modern nadw variability high resolution benthic foraminiferal 18 o and 13 c suggest that obliquity minima correspond to cold nutrient depleted western north atlantic deep waters we thus link stronger ncw formation with obliquity minima in contrast during obliquity maxima deep western boundary currents were weaker and warmer while abyssal nutrients were more abundant these aspects reflect a more sluggish ncw formation this obliquity paced paleoceanographic regime is in excellent agreement with results from an earth system model in which obliquity minima configurations enhance ncw formation

electrical tomography of la soufriere of guadeloupe volcano field experiments 1d inversion and qualitative interpretation the soufriere of guadeloupe lava dome consists of several 3d domains of relatively unaltered massive andesite separated by major radial fractures that reach at least up to about half of the dome s height more than 20 000 geo electrical measurements made on the top and the flanks of the lava dome are used to construct the first geophysical image of the internal structure of this active volcano the main features of the apparent conductivity structure of the lava dome are high conductivity regions associated with the strongly altered material of present and fossil hydrothermal zones local 1d inversions of data subsets belonging to regions where the geological structure is supposed laterally invariant confirm the structures observed in the pseudo sections the relatively stable units lie above a basal inclined layer of highly conductive geological materials interpreted to be more altered and thus characterised by reduced internal friction and probably increased pore pressure past and current hydrothermal fluid circulation through these fractures has promoted rock alteration and particularly along the base of the dome that likely contributes to the instability of parts of the edifice

checklist for the use of potassium concentrations in siliciclastic sediments as paleoenvironmental archives weathering indices quantify the release of mobile elements from source units of soils and sediments they have been employed in geosciences for more than three decades but their performance in sedimentary archives can still be improved by deciphering other forcing factors than climatic from the most common alkali and alkaline earth metals included in the weathering indices k seems to be most suitable for deciphering paleoclimate records of temperate to subtropical non arid climates assuming the interpretation respects the complex of controlling factors on sediment geochemistry as a case study normalised k concentrations in siliciclastic sediments of the most basin miocene period central europe are revisited here and variations compared with modern fluvially transported solids existing knowledge on manifold controls of k concentrations in sediments is summarised and used to propose list of possible controlling factors in particular al si and zr rb as grain size proxies ti al as provenance proxy relevant for k concentration in parent rocks and k rb as a measure for possible effects of metasomatism the k al or k ti element ratios may be efficient in chemostratigraphic correlations in siliciclastic basins and efficient proxies for chemical weathering in the source area the proposals in this work should stimulate future studies to overcome the underrepresentation of continental sediments in paleoclimate reconstructions

a shift in heavy and clay mineral provenance indicates a middle miocene onset of a perennial sea ice cover in the arctic ocean during the arctic coring expedition acex a 428 m thick sequence of upper cretaceous to quaternary sediments was penetrated the mineralogical composition of the upper 300 m of this sequence is presented here for the first time heavy and clay mineral associations indicate a major and consistent shift in provenance from the barents kara western laptev sea region characterized by presence of common clinopyroxene to the eastern laptev east siberian seas in the upper part of the section characterized by common hornblende amphibole sea ice originating from the latter source region must have survived at least one summer melt cycle in order to reach the acex drill site if considering modern sea ice trajectories and velocities this shift in mineral assemblages probably represents the onset of a perennial sea ice cover in the arctic ocean which occurred at about 13 ma thus suggesting a coeval freeze in the arctic and antarctic regions

analysis of broadband seismograms from the chile eru area broadband seismograms recorded at the graefenberg grf array in germany are analyzed these data from the chile peru area have often a very complicated signature we have attempted to identify pp using theoretical seismograms a third phase besides p and pp which may have higher frequencies was discovered in a number of broadband records interpretations that relate this phase to the source or the structure are discussed our preferred interpretation is an s to p conversion at the bottom of the descending plate

joint inversion of p wave velocity and density application to la soufriere of guadeloupe hydrothermal system we present the result of a 3 d gravity and p wave traveltime joint inversion applied to the hydrothermal system of la soufri ere of guadeloupe the joint inversion process is used here to overcome the different resolution limitations attached to the two data sets p wave traveltimes were obtained from three active seismic surveys that were conducted from 2001 to 2007 gravity data collected during a microgravity campaign is described in a companion paper we use a joint inversion process based on a bayesian formulation and a deterministic iterative approach the coupling between slowness and density is introduced through a supplementary constraint in the misfit function that tries to minimize the distance between parameter values and a theoretical relationship this relationship is derived from measurements on samples representative of mt pel ee of martinique and la soufri ere volcanoes we chose a grid discretization that leads to an under determined problem that we regularize using spatial exponential covariance between the nodes parameters our results are compared to geophysical electromagnetic results obtained using resistivity and vlf surveys they confirm the presence of highly contrasted dense fast and light slow zones in la soufri ere dome and crater basement our images suggest however that some non conductive zones may be massive andesite bodies rather than argilized zones and that these bodies may have deeper roots than hypothesized

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

comment on systematic determination of earthquake rupture directivity and fault planes from analysis of long period p wave spectra by l m warren and p m shearer summary warren and shearer describe a method of estimating the duration of p pulses radiated by earthquakes on the assumption that the source is a unilateral fracture the estimates are made in the frequency domain the estimates obtained by warren and shearer for seven of the earthquakes are compared to durations estimated here in the time domain the time domain measurements being made on broad band seismograms 0 1 4 0 hz derived by filtering from short period recordings overall the time domain method indicates that the pulse duration of the earthquakes studied here range from 2 0 to 7 6 s whereas the estimates from the results of warren and shearer range from 7 1 to 9 8 s this suggests that the method of warren and shearer cannot resolve pulse lengths less than about 7 s the suggestion is supported by the estimates of the duration of rupture fault length speed of rupture implied by the results of warren and shearer for although the estimated fault length ranges from 0 8 km to over 40 km most rupture durations are around 8 s

arctic perennial ice cover over the last 14 million years knowledge of the long term history of the perennial ice is an important issue that has eluded study because the cenozoic core material needed has been unavailable until the recent arctic coring expedition acex detrital fe oxide mineral grains analyzed by microprobe from the last 14 ma 164 m of the acex composite core on the lomonosov ridge were matched to circum arctic sources with the same mineral and 12 element composition these precise source determinations and estimates of drift rates were used to determine that these sand grains could not be rafted to the acex core site in less than a year thus the perennial ice cover has existed since 14 ma except for the unlikely rapid return to seasonal ice between the average sampling interval of about 0 17 ma both north america and russia contributed significant fe grains to the acex core during the last 14 ma

orbital forcing and abrupt events in a continental weathering proxy from central europe most basin czech republic 17 7 15 9 ma recorded beginning of the miocene climatic optimum abstract we describe orbital forcing in siliciclastic lacustrine sediments deposited in central europe ca 50 5 n and 13 5 e the most basin the czech republic between 17 7 and 15 9 ma i e before the miocene climatic optimum mco and in its early stage chemical element analysis combined with magneto and cyclostratigraphy produced a consistent stratigraphy for the studied basin fill the palaeoenvironmental record is mainly based on variations of the chemical weathering intensity in the lake catchment normalised potassium concentration k al or k ti the most basin sedimentary profile is specific by relatively high deposition rates typically 20 cm kyr sampling density corresponded to temporal resolution of 1 2 kyr and sensitivity to a regional continental climate for age control we used the atnts2012 for younger sediments and an alternative age of the onset of c5dn chron and the end of c5dr 1r short chron in the earliest studied interval the chemical weathering intensity in the catchment was controlled by precession while between 17 5 and 17 15 ma short eccentricity was mainly driving chemical weathering intensity after 17 05 ma i e just before the onset of the mco and in the period of persistent high eccentricity between 16 95 and 16 7 ma chemical weathering intensity reached its precession controlled maxima in the subsequent period of the persistent low eccentricity at 16 65 ma the orbital signal nearly vanished in the most basin abrupt but temporary environmental change occurred in the interval between 16 5 and 16 35 ma polarity chron c5cn 2n within two cycles of high eccentricity its trigger is uncertain but it might have been local or regional the obtained composite record was compared with marine 13c and 18o data showing certain global control of the most basin deposits the most basin record thus shows climatic events of the pre mco and early mco period in terrestrial settings of central europe with changes at 17 05 16 65 and 16 5 ma possibly representing triggers of the mco

astronomical forcing and sedimentary noise modeling of lake level changes in the paleogene dongpu depression of north china abstract challenges in interpreting continental sequence stratigraphy and typically uncertain geochronology hinder the understanding of paleolake evolution and hydrocarbon exploration in terrestrial basins the dongpu depression in north china is a lacustrine basin with abundant hydrocarbon resources an accurate chronology for the paleogene stratigraphy in the dongpu depression is lacking and the mechanism of lake level variation remains unclear in this study we utilize high resolution gamma ray logs to conduct a cyclostratigraphic analysis of the shahejie formation which is a paleogene succession in the dongpu depression characterized by sandstones and dark mudstones interbedded with thin salt rocks time series analysis reveals evidence for 405 kyr eccentricity cycles in the gamma ray series which is supported by statistical modeling of optimal sedimentation rates tuning of the gamma ray data to this 405 kyr eccentricity cyclicity enables a 14 7 myr long astronomical time scale to be constructed this astrochronology is anchored to the astronomical age of the dongying formation shahejie formation boundary 28 86 ma in the bohai bay basin thus providing an absolute timescale for the studied interval that extends from 28 86 ma to 43 59 ma using this anchored astrochronology we show that a recently established sedimentary noise model for inferring sea level change in marginal marine settings can be used to similarly infer lake level fluctuations in terrestrial basins in particular sedimentary noise modeling of the tuned gamma ray series reveals high resolution changes in sedimentary noise that are indicative of lake level variations linked to million year scale i e 4 8 myr 2 4 myr and 1 2 myr astronomical forcing these inferred changes in lake level are supported by previously published sequence stratigraphic interpretations moreover an evolutionary correlation coefficient ecoco analysis of the gamma ray series also indicates recurrent distortions in sedimentation that may be linked to lake level changes this study provides new methods for the assessment of paleolake level variations as well as insights into the connection between astronomical forcing and lake evolution across long timescales in terrestrial basins

the pwaves from the amchitka island explosions summary there is evidence that the equivalent seismic sources of the amchitka island explosions longshot milrow and cannikin depart significantly from the simple model of a point compressional source in a layered elastic medium consequently modelling the observed seismograms using standard source models may not be the most efficient method of determining source properties here an alternative to modelling is used to obtain information on the seismic sources due to the explosions broad band bb estimates of the p signals are obtained from the short period sp seismograms corrected for attenuation and interpreted in terms of p pp and radiation from secondary sources the main conclusions are i bb estimates of the radiated displacement from the explosions can be obtained with only a small reduction in the signal to noise ratio seen on sp seismograms ii observations of differences in pulse amplitudes and spectra are not necessarily due to differences in anelastic attenuation iii p and pp at a given station may differ in shape so that notches in the signal spectrum may not be related to source depth iv there is evidence of arrivals that others have identified as due to slapdown but which could be interpreted as an overshoot to pp v direct interpretation of the estimated ground displacement is a better procedure for determining the seismic source properties of explosions than modelling sp seismograms using idealised models as a starting point

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

middle to late miocene stepwise climate cooling evidence from a high resolution deep water isotope curve spanning 8 million years 1 we present high resolution 2 3 kyr benthic foraminiferal stable isotopes in a continuous well preserved sedimentary archive from the west pacific ocean ocean drilling program site 1146 which track climate evolution in unprecedented resolution over the period 12 9 to 8 4 ma we developed an astronomically tuned chronology over this interval and integrated our new records with published isotope data from the same location to reconstruct long term climate and ocean circulation development between 16 4 and 8 4 ma this extended perspective reveals that the long eccentricity 400 kyr cycle is prominently encoded in the 13c signal over most of the record reflecting long term fluctuations in the carbon cycle the 18o signal closely follows variations in short eccentricity 100 kyr and obliquity 41 kyr in particular the obliquity cycle is prominent from 14 6 to 14 1 ma and from 9 8 to 9 2 ma when high amplitude variability in obliquity is congruent with low amplitude variability in short eccentricity the 18o curve is additionally characterized by a series of incremental steps at 14 6 13 9 13 1 10 6 9 9 and 9 0 ma which we attribute to progressive deep water cooling and or glaciation episodes following the end of the miocene climatic optimum on the basis of 18o amplitudes we find that climate variability decreased substantially after 13 ma except for a remarkable warming episode at 10 8 10 7 ma at peak insolation during eccentricity maxima 100 and 400 kyr this transient warming associated with a massive negative carbon isotope shift is reminiscent of intense global warming events at eccentricity maxima during the miocene climatic optimum

orbital time scale records of asian eolian dust from the sea of japan since the early pliocene abstract a high resolution potassium content record of sediments from integrated ocean drilling program iodp site u1422 drilled in the northern sea of japan was employed to yield an astronomical timescale for this 205 m thick sedimentary archive the k content was quantified using the natural gamma radiation ngr data routinely measured on dv joides resolution the u1422 k wt series shows an increasing trend with time which parallels the growth of north hemisphere ice sheets since 4 ma as revealed by the global benthic foraminifer s oxygen isotope stack lr04 we propose that k content variations reflect changes in the relative contributions of asian eolian dust and volcanic weathering products in response to changes in global ice volume using the shipboard age model constrained by palaeomagnetism and nanofossils datums we tuned the u1422 k content variations to the lr04 stack our tuned age model for site u1422 goes back to 3 9 ma the studied record indicates that asian dust generation is enhanced during periods of global cooling the synchronous variations between the u1422 k record and the lr04 stack also suggest that global cooling played a dominant role in promoting the central asian aridification since 3 9 ma while the uplift of tibetan plateau plays a secondary role considering many disagreements still exists between the timing and amplitude of the qinghai tibetan uplift and the evolution of central asian aridity since the early pliocene

on the probability of mistaking an earthquake for an explosion using the simplicity of p abstract the observation that p waves from an earthquake are generally more complex than those from an underground explosion was first noted in the 1960s this difference in p wave character may still be the only way of identifying small earthquakes close to the detection threshold of a given station network however there are certain earthquakes that produce simple seismograms the frequency at which such earthquakes are mistaken for explosions using the complexity criterion is known as the false alarm rate a simple seismogram can be defined as having only one large amplitude phase that can be caused by several mechanisms we examine the proportion of simple seismograms produced by a randomly oriented double couple source buried in three different crustal structures observed at a single station at a range of epicentral distances the model predicts that if the hypocenter of a small earthquake near the detection threshold is in a region with thick sediments then the false alarm rate at a single station can be as high as 50 in the teleseismic distance range 30 to 90 the results suggest that the false alarm rate is minimized if 1 array stations are used 2 the station is at a large epicentral distance 3 the source region structure has few layers or 4 the disturbance is recorded at more than one station

high resolution imaging in the inhomogeneous crust with cosmic ray muon radiography the density structure below the volcanic crater floor of mt asama japan we have developed a novel radiographic imaging method to survey the inhomogeneous structure of the crust as an example we performed measurements at mt asama volcano and studied the feasibility of using an azimuthally isotropic flux of cosmicray muons in the energy range up to a few tev the principle of the technique is that by measuring muon absorption along different nearly horizontal paths through a solid body one can deduce the density distribution in the interior of the object a muon detector with an area of 4000 cm 2 was installed in a 1 m deep instrument vault located about 1 km from the summit crater of mt asama muon tracks within emulsion layers in the detector were analyzed by 3d image processing to determine the level of energy absorption along different ray paths through the summit crater region a typical angular resolution of the muon detector of 10 milliradians mrad corresponds to a spatial resolution of 10 m at a distance of 1 km the measurements would be ideal for studying the shallow structure of the crust at sites which cannot be well resolved because of their strong structural heterogeneity and potential difficulty to be accessed and which therefore cannot have their structure determined by conventional electromagnetic or seismic techniques the present method can also provide three dimensional images of the subsurface by making measurements from two or more different points in this work we have radiographically imaged a few hundred meters below the crater floor of mt asama japan and have detected a dense region which corresponds to the position and shape of a lava mound created during the last eruption urabe b watanabe n murakami m topographic change of the summit crater of asama volcano during the 2004 eruption derived from airborne synthetic aperture radar sar measurements bulletin of geographical survey institute 53 1 6 2006 right below the lava mound we found a low density region that suggests a drain back induced porous conduit urabe b watanabe n murakami m topographic change of the summit crater of asama volcano during the 2004 eruption derived from airborne synthetic aperture radar sar measurements bulletin of geographical survey institute 53 1 6 2006 the density contrast was resolved with a precision of 1 3 this method

a model for episodic degassing of an andesitic magma intrusion 1 episodic magmatic degassing has been observed at numerous volcanoes especially those of intermediate composition it can span timescales from years to decades here we propose a physical model for the degassing of a shallow magma intrusion to explain this phenomenon the magma cools by convection which leads to melt crystallization volatile exsolution and magma overpressure when the pressure reaches a critical value wall rocks fracture and the exsolved gas escapes the intrusion then returns to the initial lithostatic pressure and a new cooling crystallization degassing cycle occurs a series of such cycles leads to episodic degassing the trend and timescale of the degassing process are mainly governed by magma cooling two degassing regimes are exhibited an early phase with a high frequency of gas pulses and a later phase with a lower gas pulse frequency the transition between these two regimes is caused by the viscosity increase when the magma crystallinity exceeds the crystal percolation threshold we find that the time to this transition is dependent on magma volume to a first approximation where observations are available from sustained geochemical surveillance the model provides constraints on key aspects of the subsurface magmatic system with estimation of the volume of an intrusion and tensile strength of the surrounding rocks it therefore represents a relevant tool for volcanic surveillance and hazard assessment

degassing at la soufriere de guadeloupe volcano lesser antilles since the last eruptive crisis in 1975 77 result of a shallow magma intrusion in the 15 years following the last crisis of phreatic type in 1975 77 the hydrothermal and seismic activity of la soufriere de guadeloupe has displayed an episodic behavior superimposed on a long term decay as inferred from seismicity and degassing monitored through fumarolic emissions and cl content in thermal springs in particular the evolution of the cl content can be explained by a succession of magmatic gas injections into the hydrothermal system this episodic supply of gas may be associated to the thermodynamic evolution of a batch of magma intruded at shallow depth around 1976 progressive magma cooling crystallization gas exsolution and pressure buildup lead to cyclic failure of host rock around the intrusion and episodic release of gas with a decreasing frequency as cooling proceeds this physical model allows to reproduce the pattern of degassing activity of la soufriere including the decreasing frequency of cl pulses with time our preferred forward model of cl pulses involves a magma intrusion volume in the range 0 01 0 52 km 3 and a tensile strength of the surrounding rock in the range 0 1 0 6 mpa these results reinforce the hypothesis of a shallow magma intrusion triggering the 1975 77 crisis and provide an explanation for the degassing and seismic activities observed until 1992

radiographic imaging below a volcanic crater floor with cosmic ray muons we present a novel application of cosmic ray muon radiography to image the shallow density structure beneath asama volcano japan we use a single detector emulsion cloud chamber set up in an underground vault at an elevation of 2250 m on the eastern flank of asama 310 m below the summit of the edifice and 1 km away from the crater the results point to two high density anomalies located between the original pre 2004 eruption crater floor and post 2004 eruption crater profile a third low density anomaly is imaged immediately below the pre 2004 eruption crater floor the spatial extent of each density anomaly is about 100 to 200 m to know if this method applied to other volcanoes would produce contrasting results we performed the measurement in 1944 usu lava dome we confirmed a bulbous shape measuring approximately 300 m in diameter and narrowing downwards the diameter of the uppermost part of the conduit is estimated at 100 15 m at an elevation of 260 m a s l and 50 15 m at an elevation of 217 m a s l demonstrating a resolution that is significantly better than that typically achieved with seismic tomography based on picks of first arrival times from earthquakes or artificial sources

cosmic ray muon imaging of magma in a conduit degassing process of satsuma iwojima volcano japan 1 muon radiography can provide essentially a cross section through the object parallel to the plane of the detector on which the average density along all the muon paths is projected somewhat like x ray radiography very recently the use of emulsion films has given us a clue for visualization of the interior of volcanoes to image a larger volcano in shorter time we need a larger detector to collect more muon events however the time required for imaging will be proportional to the detection area in order to overcome this problem we developed a portable assembly type cosmic ray muon telescope module to image the density distribution of magma in the conduit of mt iwodake volcano japan a muon detector with an area of 1 m2 was set up at the foot of the volcano we mapped differentially absorbed cosmic ray muons which depend on the varying thickness and density beneath the crater floor we successfully imaged density distribution in the conduit as well as the conduit shape assuming the density anomaly is localized in the vent area the observed location of the magma head is consistent with the degassing model of rhyolitic systems proposed by k kazahaya et al in 2002

increased seasonality through the eocene to oligocene transition in northern high latitudes a profound global climate shift took place at the eocene oligocene transition approximately 33 5 million years ago when cretaceous early palaeogene greenhouse conditions gave way to icehouse conditions during this interval changes in the earth s orbit and a long term drop in atmospheric carbon dioxide concentrations resulted in both the growth of antarctic ice sheets to approximately their modern size and the appearance of northern hemisphere glacial ice however palaeoclimatic studies of this interval are contradictory although some analyses indicate no major climatic changes others imply cooler temperatures increased seasonality and or aridity climatic conditions in high northern latitudes over this interval are particularly poorly known here we present northern high latitude terrestrial climate estimates for the eocene to oligocene interval based on bioclimatic analysis of terrestrially derived spore and pollen assemblages preserved in marine sediments from the norwegian greenland sea our data indicate a cooling of approximately 5 degrees c in cold month winter mean temperatures to 0 2 degrees c and a concomitant increased seasonality before the oi 1 glaciation event these data indicate that a cooling component is indeed incorporated in the delta 18 o isotope shift across the eocene oligocene transition however the relatively warm summer temperatures at that time mean that continental ice on east greenland was probably restricted to alpine outlet glaciers

cosmic muon imaging of hidden seismic fault zones rainwater permeation into the mechanical fractured zones in itoigawa shizuoka tectonic line japan abstract we have developed a novel radiographic imaging method to survey the seismic fault hidden beneath the surface by measuring the rainfall permeation around the fault zone with cosmic ray muon radiography as an example we performed measurements in itoigawa shizuoka tectonic line istl japan and studied the feasibility of using this method in this method muons after passing through a fault zone are measured for different depths after major rain fall events when large amount of rain permeated gravitationally into the mechanical fractured zone around the fault gouge the average density increases hence decreasing the number of muon events the principle of the technique is that by measuring the time dependent changes in muon absorption along different paths through the fault one can image the permeable region in the interior of the object a muon detector with an area of 3969 cm 2 was located 6 m from the fault outcrop in unesco itoigawa geopark the outcrop is geologically well studied and the direction of the fault is approximately determined by linear extrapolation from the site but is not parallel to the istl an angular resolution of the muon detector of 100 milliradians mrad corresponds to a spatial resolution of 10 m at a distance of 100 m the measurements would be ideal for studying the vertical or near vertical strike slip faults which cannot be well resolved by the conventional standard seismic reflection acquisition and processing that are designed to image reflectors that are close to horizontal in this work we have radiographically imaged the fault zone up to 50 m below the surface a systematic delay in response to the rain fall events was observed with increasing depth only along the fault zone which corresponds to the position and direction of the seismic fault estimated from the geometry of the fault outcrop applying the same method to another direction we discovered a new permeable region that is parallel to the istl this permeable region indicates a major seismic fault that is thought to be located along the istl

imaging the conduit size of the dome with cosmic ray muons the structure beneath showa shinzan lava dome japan 1 we developed a radiographic technique to image a subsurface conduit shape using cosmic ray muons the test measurement was performed in showa shinzan lava dome located in hokkaido japan as an example a muon detector with an area of 6000 cm2 was set up at the foot of the lava dome muon tracks recorded in nuclear emulsion films in the detector were analyzed to determine the level of energy absorption along different ray paths through subsurface beneath the lava dome a typical angular resolution of the muon detector of 10 mrad corresponds to a spatial resolution of 10 m at a distance of 1 km which is difficult to be addressed with seismological technique we mapped differentially absorbed cosmic ray muons which depend upon the varying thickness and density beneath the dome we successfully imaged the conduit shape and determined a conduit diameter of 102 15 m assuming the observed high absorption region beneath the dome is localized in the vent area

density muon radiography of la soufriere of guadeloupe volcano comparison with geological electrical resistivity and gravity data density muon radiography is a new method to determine the average density of geological bodies by measuring the attenuation produced by rocks on the flux of cosmic muons we present such density radiographies obtained for the soufri ere of guadeloupe lava dome both in the north south and east west planes these radiographies reveal the highly heterogeneous density structure of the volcano with low density regions corresponding to recognized hydrothermally altered areas the main structures observed in the density radiographies correlate with anomalies in electrical resistivity cross sections and a density model obtained from gravity data

evolution of middle to late cretaceous oceans a 55 m y record of earth s temperature and carbon cycle a new 55 m y global compilation of benthic foraminifera 13 c and 18 o for the middle to late cretaceous shows that there was widespread formation of bottom waters with temperatures 20 c during the cretaceous greenhouse world these bottom waters filled the silled north atlantic and probably originated as thermocline or intermediate waters in the tropical oceans carbon burial during the cretaceous oceanic anoxic events produced a positive 13 c shift in global carbon reservoirs but this is not particularly large especially by comparison with the remarkable late paleocene carbon maximum the interbasin 13 c gradient was unusually large during the cretaceous hot greenhouse probably because the north atlantic sills prevented the free exchange of waters in the deep basin the hot greenhouse ended when the equatorial atlantic gateway opened sufficiently to flood the deep north atlantic with relatively cool polar waters formed in the southern ocean

observations of q from the northwest pacific subduction zone recorded at teleseismic distances twenty seven earthquakes in the northwest pacific with mb 5 4 are used to study upper mantle attenuation the data were recorded at seismometer arrays in australia canada india and scotland the short period instruments used in the arrays are sufficiently broadband and the signal to noise enhancement resulting from beamforming the data is good enough that seismic noise is above system noise out to between 3 and 5 hz and in some cases to 8 hz the instrument response has been removed and a power law 2 farfield source correction has been assumed and applied the remaining fall off in the spectra above 1 hz which is above the corner frequency fc is assumed to be due to attenuation including losses due both to anelasticity and to scattering an 3 spectral fall off preferred by some would result in lower estimates of attenuation conservative estimates of the average attenuation along the whole path have been made from the spectral fall off despite the imperfect knowledge of the source spectra the high sensitivity of spectral amplitudes to attenuation at high frequencies yields quite reliable and stable attenuation estimates the scatter in the data is small resulting in estimates of mean t t av with an average standard error of only 21 where t av is defined as the ratio of the travel time t to the effective mean quality factor q av only 14 of the 64 measurements show a t av above 0 5 sec within the given error bounds all estimates of t av and q av refer to p wave attenuation only the results for t av from the northwest pacific subduction zone cannot be explained simply by the traditional high q subducting slab in a low q upper mantle a low q region in the uppermost 100 km approximately of the subduction zone has been identified source corrected t av yield upper mantle q av estimates of about 1200 for predominantly oceanic paths australia and india and 1500 for mixed continental and oceanic paths canada and scotland

response of the himalayan glacial cycles to multiple equilibrium of climate system a review abstract the astronomical theory of milankovitch supports the waxing and waning of ice sheets and polar glaciers by orbital forcing excluding the fact that small changes in solar radiation flux are difficult to reconcile with the amplitude of glacial cycles the numerical model explaining the 100 kyr problem has now revealed that the phase locking mechanism of orbital forcing has started to modulate the climatic transitions since 1 2 myr back and remained locked till present climatic state rial et al 2013 however the true evidence to confirm it is not present the present study is an attempt to comprehend the concept of synchronization of summer insolation modulation and internal climate forcing responsible for glacial interglacial termination present in and around the himalaya tibet and worldwide we present geographical evidences of glaciations from the himalayan tibet region pointing out that responses i e 18 24 kyr and 60 70 kyr bp glaciation events are similar to the progression in climatic data and glaciations cycles for the last 100 kyr the compelling evidence presents a possible explanation towards synchronized modulation of 100 kyr orbital cycles with 41 kyr obliquity cycles coincidently resulting in unprecedentedly large glaciation around the last glacial cycle 60 70 kyr bp and the last glacial maxima 18 24 kys bp by considering the influence of internal and external factors on glacier mechanism we underline the most probable cause of 41 kyr cycle obliquity as the foremost driver of glaciations in the himalaya and tibet on longer timescales we provide several lines of evidence to establish the possible connection of glaciation events and orbital cycles with the help of geographical and geological records consistent with the fact that resonance might be faded through time but the effect of frequency modulation still persists in the system

reconstruction of the chaotic behavior of the solar system from geologic records abstract astronomical solutions for planetary orbits beyond several tens of million years myr ago have large uncertainties due to the chaotic nature of the solar system mainly myr scale cycles related with the earth mars secular resonance our only accessible archive for unraveling the earth s orbital variations in the geologic past are sedimentological records yet their reliability and uncertainties are still debated here we describe myr scale orbital signals of early mesozoic monsoon records from two different sedimentary settings lake level records of the equatorial pangea and biogenic silica burial flux of deep sea panthalassa along with a marine carbon isotope compilation although most of the dominant multi myr cycles are not exactly of the same frequency 1 8 myr cycles during 216 210 ma are detected from the two mutually independent sedimentary settings and differ from available astronomical solutions this finding provides not only convincing evidence for the chaotic nature of the solar system in the geological past but also additional constraints on astronomical models on the other hand besides the orbital cycles tectonic forcing and consequent climatic perturbations could also have affected the proxies on multi myr timescales during episodes of large igneous province emplacement such as siberian trap volcanism 252 245 ma wrangellia 233 225 ma central atlantic magmatic province 202 200 ma and karoo ferrar volcanism 184 180 ma if we can distinguish orbital signals from other effects such as tectonic and volcanic processes the multi myr cycles in geologic records have the potential to reconstruct the chaotic evolution of the solar system

volcano flank instability in the lesser antilles arc diversity of scale processes and temporal recurrence 1 the 1997 boxing day collapse a remarkable feature of the ongoing eruption of soufriere hills on montserrat has prompted new interest in the study of volcano stability in the lesser antilles building on a few cases documented in the literature we have now identified at least 47 flank collapse events on volcanoes of the caribbean arc where this type of behavior is characteristic and repetitive about 15 events occurred on active volcanoes within the last 12 000 years in the northern part of the arc flank collapses are repetitive do not exceed 1 km3 in volume occur in all directions and are promoted by intense hydrothermal alteration and well developed fracturing of the summit part of the edifices in contrast infrequent but large sector collapses with volumes up to tens of km3 are typical of the southern volcanoes they are always directed to the west as a result of the high overall slopes of the islands toward the deep back arc grenada basin because caribbean islands are small a large part of the resulting debris avalanches have flowed into the sea thus contributing voluminous and sudden inputs of volcaniclastic sediments to the grenada basin deposits from such submarine flows have been identified during the recent aguadomar and caraval oceanographic cruises and traced to their source structures on land edifice collapses have a major influence on subsequent volcanic activity but also are of high concern because of their tsunamigenic potential

the cyclostratigraphy intercomparison project cip consistency merits and pitfalls abstract cyclostratigraphy is an important tool for understanding astronomical climate forcing and reading geological time in sedimentary sequences provided that an imprint of insolation variations caused by earth s orbital eccentricity obliquity and or precession is preserved milankovitch forcing numerous stratigraphic and paleoclimate studies have applied cyclostratigraphy but the robustness of the methodology and its dependence on the investigator have not been systematically evaluated we developed the cyclostratigraphy intercomparison project cip to assess the robustness of cyclostratigraphic methods using an experimental design of three artificial cyclostratigraphic case studies with known input parameters each case study is designed to address specific challenges that are relevant to cyclostratigraphy case 1 represents an offshore research vessel environment as only a drill core photo and the approximate position of a late miocene stage boundary are available for analysis in case 2 the pleistocene proxy record displays clear nonlinear cyclical patterns and the interpretation is complicated by the presence of a hiatus case 3 represents a late devonian proxy record with a low signal to noise ratio with no specific theoretical astronomical solution available for this age each case was analyzed by a test group of 17 20 participants with varying experience levels methodological preferences and dedicated analysis time during the cip 2018 meeting in brussels belgium the ensuing analyses and discussion demonstrated that most participants did not arrive at a perfect solution which may be partly explained by the limited amount of time spent on the exercises 4 5 hours per case however in all three cases the median solution of all submitted analyses accurately approached the correct result and several participants obtained the exact correct answers interestingly systematically better performances were obtained for cases that represented the data type and stratigraphic age that were closest to the individual participants experience this experiment demonstrates that cyclostratigraphy is a powerful tool for deciphering time in sedimentary successions and importantly that it is a trainable skill finally we emphasize the importance of an integrated stratigraphic approach and provide flexible guidelines on what good practices in cyclostratigraphy should include our case studies provide valuable insight into current common practices in cyclostratigraphy their potential merits and pitfalls our work does not provide a quantitative measure of reliability and uncertainty of cyclostratigraphy but rather constitutes a starting point for further discussions on how to move the maturing field of cyclostratigraphy forward

three dimensional computational axial tomography scan of a volcano with cosmic ray muon radiography 1 cosmic ray muon radiography can measure the density distribution within a volcano unidirectional radiography shows a precise cross sectional view of a conduit and a magma body through a volcano parallel to the plane of the detector however it only resolves the average density distribution along individual muon paths precise size and shape of underground structure such as a conduit or a magma body provide clear and pervasive information on understanding dynamics of volcanic eruption here we show a highly resolved three dimensional tomographic image of an active volcano asama in japan specifically we developed a portable power effective muon radiography telescope that can be operated stable with a realistically sized solar panel so as to place it around an active volcano where commercial electric power is not available the resulting image below the crater floor shows that a local low density region accumulates sufficient gas pressure to cause vulcanian eruption the present muon computational axial tomography scan has a resolving power with a resolution of 100 m allowing it to see great detail in volcanoes

global perturbation of the carbon cycle at the onset of the miocene climatic optimum the miocene climatic optimum mco ca 17 14 7 ma represents one of several major interruptions in the long term cooling trend of the past 50 m y to date the processes driving high amplitude climate variability and sustaining global warmth during this remarkable interval remain highly enigmatic we present high resolution benthic foraminiferal and bulk carbonate stable isotope records in an exceptional continuous carbonate rich sedimentary archive integrated ocean drilling program site u1337 eastern equatorial pacific ocean which offer a new view of climate evolution over the onset of the mco a sharp decline in delta o 18 and delta c 13 at ca 16 9 ma contemporaneous with a massive increase in carbonate dissolution demonstrates that abrupt warming was coupled to an intense perturbation of the carbon cycle the rapid recovery in delta c 13 at ca 16 7 ma similar to 250 k y after the beginning of the mco marks the onset of the first carbon isotope maximum within the long lasting monterey excursion these results lend support to the notion that atmospheric pco 2 variations drove profound changes in the global carbon reservoir through the mco implying a delicate balance between changing co2 fluxes rates of silicate weathering and global carbon sequestration comparison with a high resolution delta c 13 record spanning the onset of the cretaceous oceanic anoxic event 1a similar to 120 m y ago reveals common forcing factors and climatic responses providing a long term perspective to understand climate carbon cycle feedbacks during warmer periods of earth s climate with markedly different atmospheric co2 concentrations

earthquake depth estimation using the f trace and associated probability determining the depths of seismic disturbances is of great importance when monitoring compliance with the comprehensive nuclear test ban treaty ctbt in plate tectonic studies and in seismic hazard assessments we have developed a semiautomated method that uses the output from the f detector a processing technique that detects correlated signals crossing a seismometer array as a tool for identifying candidate depth phases and hence estimating hypocenter depth the f trace can be interpreted approximately in terms of probability this can be used to help interpret signals and identify candidate depth phases here a method of calculating f probability traces that optimally highlight candidate depth phases is presented the values of the probability trace at the predicted times for pp and sp for a given depth are then weighted and summed over several high quality medium aperture array stations a clear maximum in the trace sum function with depth is interpreted as the probable hypocenter depth results for earthquakes from the lop nor and hindu kush regions indicate that this method of depth estimation is effective for many earthquakes with magnitude greater than about m b 4 0 and depths greater than around 10 km the method is best suited as a tool to be used by analysts to estimate the depths of individual seismic disturbances of special interest or groups of earthquakes in regions where there is a good azimuthal distribution of medium aperture array stations

continuous simulations over the last 40 million years with a coupled antarctic ice sheet sediment model abstract much of the knowledge of antarctic ice sheet variations since its inception 34 ma derives from marine sediments on the continental shelf deposited in glacimarine or sub ice environments by advancing and retreating grounded ice and observed today by seismic profiling and coring here we apply a 3 d coupled ice sheet and sediment model from 40 ma to the present with the goal of directly linking ice sheet variations with the sediment record the ice sheet model uses vertically averaged ice dynamics and parameterized grounding line flux the sediment model includes quarrying of bedrock sub ice transport and marine deposition atmospheric and oceanic forcing are determined by uniform shifts to modern climatology in proportion to records of atmospheric co2 deep sea core 18o and orbital insolation variations the model is run continuously over the last 40 myr at coarse resolution 80 or 160 km modeling post eocene ice landscape evolution and off shore sediment packages in a single self consistent simulation strata and unconformities are tracked by recording times of deposition within the model sediment stacks which can be compared directly with observed seismic profiles the initial bedrock topography is initialized to 34 ma geologic reconstructions or an iterative procedure is used that yields independent estimates of paleo bedrock topography preliminary results are compared with recognized cenozoic ice sheet variations modern sediment distributions and seismic profiles and modern and paleo bedrock topographies

the enigma of oligocene climate and global surface temperature evolution falling atmospheric co2 levels led to cooling through the eocene and the expansion of antarctic ice sheets close to their modern size near the beginning of the oligocene a period of poorly documented climate here we present a record of climate evolution across the entire oligocene 33 9 to 23 0 ma based on tex86 sea surface temperature sst estimates from southwestern atlantic deep sea drilling project site 516 paleolatitude 36 s and western equatorial atlantic ocean drilling project site 929 paleolatitude 0 combined with a compilation of existing sst records and climate modeling in this relatively low co2 oligocene world 300 to 700 ppm warm climates similar to those of the late eocene continued with only brief interruptions while the antarctic ice sheet waxed and waned ssts are spatially heterogenous but generally support late oligocene warming coincident with declining atmospheric co2 this oligocene warmth especially at high latitudes belies a simple relationship between climate and atmospheric co2 and or ocean gateways and is only partially explained by current climate models although the dominant climate drivers of this enigmatic oligocene world remain unclear our results help fill a gap in understanding past cenozoic climates and the way long term climate sensitivity responded to varying background climate states

antarctic ice sheet sensitivity to obliquity forcing enhanced through ocean connections deep sea geological records indicate that antarctic ice sheet growth and decay is strongly influenced by the earth s astronomical variations known as milankovitch cycles and that the frequency of the glacial interglacial cycles changes through time here we examine the emergence of a strong obliquity axial tilt control on antarctic ice sheet evolution during the miocene by correlating the antarctic margin geological records from 34 to 5 million years ago with a measure of obliquity sensitivity that compares the variance in deep sea sediment core oxygen isotope data at obliquity timescales with variance of the calculated obliquity forcing our analysis reveals distinct phases of ice sheet evolution and suggests the sensitivity to obliquity forcing increases when ice sheet margins extend into marine environments we propose that this occurs because obliquity driven changes in the meridional temperature gradient affect the position and strength of the circum antarctic easterly flow and enhance or reduce ocean heat transport across the antarctic continental margin the influence of obliquity driven changes in ocean dynamics is amplified when marine ice sheets are extensive and sea ice is limited our reconstruction of the antarctic ice sheet history suggests that if sea ice cover decreases in the coming decades ocean driven melting at the ice sheet margin will be amplified the sensitivity of the antarctic ice sheet to obliquity increases when ice sheet margins are exposed to the ocean suggests an analysis of sediment core oxygen isotope records

a lower to middle eocene astrochronology for the mentelle basin australia and its implications for the geologic time scale the geologic time scale for the cenozoic era has been notably improved over the last decades by virtue of integrated stratigraphy combining high resolution astrochronologies biostratigraphy and magnetostratigraphy with high precision radioisotopic dates however the middle eocene remains a weak link the so called eocene time scale gap reflects the scarcity of suitable study sections with clear astronomically forced variations in carbonate content primarily because large parts of the oceans were starved of carbonate during the eocene greenhouse international ocean discovery program iodp expedition 369 cored a carbonate rich sedimentary sequence of eocene age in the mentelle basin site u1514 offshore southwest australia the sequence consists of nannofossil chalk and exhibits rhythmic clay content variability here we show that iodp site u1514 allows for the extraction of an astronomical signal and the construction of an eocene astrochronology using 3 cm resolution x ray fluorescence xrf core scans the xrf derived ratio between calcium and iron content ca fe tracks the lithologic variability and serves as the basis for our u1514 astrochronology we present a 16 million year long 40 56 ma nearly continuous history of eocene sedimentation with variations paced by eccentricity and obliquity we supplement the high resolution xrf data with low resolution bulk carbon and oxygen isotopes recording the long term cooling trend from the paleocene eocene thermal maximum petm ca 56 ma into the middle eocene ca 40 ma our early eocene astrochronology corroborates existing chronologies based on deep sea sites and italian land sections for the middle eocene the sedimentological record at u1514 provides a single site geochemical backbone and thus offers a further step towards a fully integrated cenozoic geologic time scale at orbital resolution

northern chile earthquake of 1980 may 26 evidence of unilateral fracture summary p seismograms recorded in europe from some of the earthquakes that occur at depths of around 100 km in northern chile show three prominent arrivals p bp and pp bp being interpreted as a conversion of downward radiated s to p at a discontinuity in wavespeed beneath the source on broad band seismograms the duration of the p pulse is around 5s that of bp around 2s and that of pp around 12s these differences in duration have been interpreted as doppler effects due to the motion of the source of seismic radiation this being assumed to be a near unilateral fracture propagating downwards on a steeply dipping fault plane for the downward radiated pulses p and bp the source is travelling towards the observer whereas for the upward radiated pulse pp the source is receding from the observer the near unilateral fracture interpretation of the differences in pulse duration is based on data from the earthquake of 1976 november 30 recorded on effectively one azimuth 30 40 which is towards europe to give further support to the interpretation requires data from a wider range of azimuths but this is not available for the 1976 earthquake however data from the northern chile earthquake of 1980 may 26 are available from four stations covering an azimuthal range of 180 eskdalemuir scotland eka azimuth 31 6 blacknest england bna azimuth 35 6 gauribidanur india gba azimuth 95 2 and warramunga australia wra azimuth 212 0 the 1980 earthquake which appears to have a very similar mechanism to that of the 1976 earthquake is investigated here to see if the observations are consistent with the near unilateral fracture mechanism the first motion of p and pp where these can be observed and the general form of the broad band seismograms are consistent with the presence of a nodal plane dipping steeply towards the east p is observed to be small relative to the surface reflection pp at eka bna and gba where p leaves the source close to a node and p is large relative to pp at wra where p leaves the source away from the node and the take off of pp is close to a node taking the steeply dipping nodal plane to be the fault plane the fault dimensions and fracture speeds compatible with the pulse durations are estimated using one of the compatible solutions fault length 40 km maximum width 18 km fracture speed 0 5p wavespeed maximum dimension oriented downdip seismograms are computed and compared to the observed the computed seismograms simulate the pulse durations and relative amplitudes of most of the main pulses the detailed form of the main pulses is not modelled possibly because the fault model used is oversimplified the complexity of the observed pulses presumably indicates that the distribution of slip on the fault plane varies less smoothly than assumed in the model to determine the detailed distribution and time history of slip on the fault requires data from a larger number of well distributed stations than is available here however if it is accepted that the pulse durations of p bp and pp given are reliable and that hp is an s to p conversion at a boundary below the source then the conclusion seems to be inescapable that the source was a near unilateral fracture propagating downwards on a steeply dipping fault plane

a new scenario for the last magmatic eruption of la soufriere of guadeloupe lesser antilles in 1530 a d evidence from stratigraphy radiocarbon dating and magmatic evolution of erupted products la soufriere of guadeloupe is a dangerous volcano characterized over the last decade by moderate seismic and fumarolic unrest in the last 15 000 years it has experienced phreatic and magmatic eruptions and unusually numerous flank collapse events sometimes associated with a magmatic eruption we propose a new age of 1530 a d and a new eruptive scenario for the last magmatic eruption on the basis of a novel statistical analysis of radiocarbon age dates and new field and geochemical data this eruption is the only magmatic eruption likely to have occurred in guadeloupe during the last 1400 years the eruption mainly involved an andesitic magma which in the first phase of the eruption partially mixed with a slightly more differentiated magma stored in a small and shallow magma chamber ascent of magma to the surface generated a partial collapse of the hydrothermally altered edifice that increased the magma discharge and led to a sub plinian phase with scoria fallout and column collapse pyroclastic flows followed by near vent pyroclastic scoria fountains the eruption ended with growth of a lava dome our revised interpretation of the last magmatic eruption of la soufriere constitutes the most likely key to a future magmatic eruption scenario for this volcano which displays strong evidence of unrest since 1992

an experiment of muon radiography at mt etna italy interactions of conduit geometry with gas liquid flows control volcanic activity implying that the evaluation of volcanic hazards requires quantitative understanding of the inner structure of the volcano the more established geophysical imaging techniques suffer from inherent ambiguity may require spatially dense measurements in active areas and may not provide sufficient spatial resolution in the uppermost part of the conduit system it is thus desirable to develop new imaging techniques allowing a better spatial resolution of a volcano s upper feeding system with reduced ambiguity and a low level of risk for operators muon particles can be utilized to image the internal density distribution of volcanic structures the principle of muon radiography is essentially the same as x ray radiography except for substituting penetrating particles in place of photons muons are more attenuated by higher density parts inside the target and thus information about its inner structure are obtained from the differential muon absorption we report on a muon imaging experiment that was conducted at mt etna in 2010 the target structure was one of the summit craters of the volcano this experiment was performed using a muon telescope suitably designed to withstand the harsh conditions in the summit zone of a high volcano we found a marked difference between synthetic and observed attenuation of muons through the target this discrepancy is likely due to the bias on the observed flux arising from false muon tracks they are caused by low energy particles that by chance hit simultaneously the two matrixes of the telescope leading to detection of a false positive we separated the useful from the unwanted signal through a first order model of the background noise the resulting signal is compared with the corresponding synthetic flux eventually we found regions of higher and lower than expected muon flux that are possibly related to inner features of the target crater

detecting a mass change inside a volcano by cosmic ray muon radiography muography first results from measurements at asama volcano japan 1 a visual detection and monitoring of volcanic eruptions is the most essential information in february 2 2009 asama volcano japan erupted and a large amount of volcanic ash was ejected from the vent we have observed the activity at asama since october 12 2008 for eruption monitoring we used cosmic ray muon radiography muography a new volcano monitoring system recently developed by tanaka et al 2009 we measured a quantitative mass loss inside the crater during the eruption event although no changes were found below the crater the measured value of 30 780 tons is consistent with a model calculation of volcanic ash flow as observed on february 2 2009 the obtained radiographic image suggests that a boiling liquid expanding vapor explosion occurred and a part of an old lava mound was exploded this picture is consistent with the analytical result of the volcanic ash ejected on february 2 2009

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

middle miocene climate cooling linked to intensification of eastern equatorial pacific upwelling during the middle miocene earth s climate transitioned from a relatively warm phase miocene climatic optimum to a colder mode with reestablishment of permanent ice sheets on antarctica thus marking a fundamental step in cenozoic cooling carbon sequestration and atmospheric co2 drawdown through increased terrestrial and or marine productivity have been proposed as the main drivers of this fundamental transition we integrate high resolution 1 3 k y benthic stable isotope data with x ray fluorescence scanner derived biogenic silica and carbonate accumulation estimates in an exceptionally well preserved sedimentary archive recovered at integrated ocean drilling program site u1338 to reconstruct eastern equatorial pacific productivity variations and to investigate temporal links between high and low latitude climate change over the interval 16 13 ma our records show that the climatic optimum 16 8 14 7 ma was characterized by high amplitude climate variations marked by intense perturbations of the carbon cycle episodes of peak warmth at southern hemisphere insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean a switch to obliquity paced climate variability after 14 7 ma concurred with a general improvement in carbonate preservation and the onset of step wise global cooling culminating with extensive ice growth over antarctica ca 13 8 ma we find that two massive increases in opal accumulation ca 14 0 and ca 13 8 ma occurred just before and during the final and most prominent cooling step supporting the hypothesis that enhanced siliceous productivity in the eastern equatorial pacific contributed to co2 drawdown

astronomic calibration of the late oligocene through early miocene geomagnetic polarity time scale at ocean drilling program odp site 1090 subantarctic south atlantic benthic foraminiferal stable isotope data from cibicidoides and oridorsalis span the late oligocene through early miocene f24 16 ma at a temporal resolution of f5 ky over the same interval a magnetic polarity stratigraphy can be unequivocally correlated to the geomagnetic polarity time scale gpts thereby providing direct correlation of the isotope record to the gpts in an initial age model we use the newly derived age of the oligocene miocene o m boundary of 23 0 ma of shackleton et al geology 28 2000 447 revised to the new astronomical calculation la2003 of laskar et al icarus in press to recalculate the spline ages of cande and kent j geophys res 100 1995 6093 we then tune the site 1090 y 18 o record to obliquity using la2003 in this manner we are able to refine the ages of polarity chrons c7n through c5cn 1n the new age model is consistent within one obliquity cycle with previously tuned ages for polarity chrons c7n through c6bn from shackleton et al geology 28 447 450 2000 when rescaled to la2003 the results from site 1090 provide independent evidence for the revised age of the oligocene miocene boundary of 23 0 ma for early miocene polarity chrons c6aar through c5cn our obliquity scale age model is the first to allow a direct calibration to the gpts the new ages are generally within one obliquity cycle of those obtained by rescaling the cande and kent j geophys res 100 1995 6093 interpolation using the new age of the o m boundary 23 0 ma and the

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher