a new look at the saturn system the voyager 2 images voyager 2 photography has complemented that of voyager i in revealing many additional characteristics of saturn and its satellites and rings saturn s atmosphere contains persistent oval cloud features reminiscent of features on jupiter smaller irregular features track out a pattern of zonal winds that is symmetric about saturn s equator and appears to extend to great depth winds are predominantly eastward and reach 500 meters per second at the equator titan has several haze layers with significantly varying optical properties and a northern polar collar that is dark at short wavelengths several satellites have been photographed at substantially improved resolution enceladus surface ranges from old densely cratered terrain to relatively young uncratered plains crossed by grooves and faults tethys has a crater 400 kilometers in diameter whose floor has domed to match tethys surface curvature and a deep trench that extends at least 270 around tethys circumference hyperion is cratered and irregular in shape iapetus bright trailing hemisphere includes several dark floored craters and phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours within saturn s rings the birth of a spoke has been observed and surprising azimuthal and time variability is found in the ringlet structure of the outer b ring these observations lead to speculations about saturn s internal structure and about the collisional and thermal history of the rings and satellites

the 1815 tambora ash fall implications for transport and deposition of distal ash on land and in the deep sea tambora volcano lies on the sanggar peninsula of sumbawa island in the indonesian archipelago during the great 1815 explosive eruption the majority of the erupted pyroclastic material was dispersed and subsequently deposited into the indian ocean and java sea this study focuses on the grain size distribution of distal 1815 tambora ash deposited in the deep sea compared to ash fallen on land grain size distribution is an important factor in assessing potential risks to aviation and human health and provides additional information about the ash transport mechanisms within volcanic umbrella clouds grain size analysis was performed using high precision laser diffraction for a particle range of 0 2 m 2 mm diameter the results indicate that the deep sea samples provide a smooth transition to the land samples in terms of grain size distributions despite the different depositional environments even the very fine ash fraction 10 m is deposited in the deep sea suggesting vertical density currents as a fast and effective means of transport to the seafloor the measured grain size distribution is consistent with an improved atmospheric gravity current sedimentation model that takes into account the finite duration of an eruption in this model the eruption time and particle fall velocity are the critical parameters for assessing the ash component depositing while the cloud advances versus the ash component depositing once the eruption terminates with the historical data on eruption duration maximum 24 h and volumetric flow rate of the umbrella cloud 1 5 2 5 1011 m3 s as input to the improved model and assuming a combination of 3 h plinian phase and 21 h co ignimbrite phase it reduces the mean deviation of the predicted versus observed grain size distribution by more than half 9 4 to 3 7 if both ash components are considered

thermal structure and dynamics of saturn s northern springtime disturbance saturn s slow seasonal evolution was disrupted in 2010 2011 by the eruption of a bright storm in its northern spring hemisphere thermal infrared spectroscopy showed that within a month the resulting planetary scale disturbance had generated intense perturbations of atmospheric temperatures winds and composition between 20 and 50 n over an entire hemisphere 140 000 kilometers the tropospheric storm cell produced effects that penetrated hundreds of kilometers into saturn s stratosphere to the 1 millibar region stratospheric subsidence at the edges of the disturbance produced beacons of infrared emission and longitudinal temperature contrasts of 16 kelvin the disturbance substantially altered atmospheric circulation transporting material vertically over great distances modifying stratospheric zonal jets exciting wave activity and turbulence and generating a new cold anticyclonic oval in the center of the disturbance at 41 n

rapid releases of metal salts and nutrients following the deposition of volcanic ash into aqueous environments deposition of volcanic ash into aqueous environments leads to dissolution of adsorbed metal salts and aerosols increasing the bioavailability of key nutrients volcanogenic fertilization events could increase marine primary productivity leading to a drawdown of atmospheric co2 here we conduct flow through experiments on unhydrated volcanic ash samples from a variety of locations and sources measuring the concentrations and fluxes of elements into de ionized water and two contrasting ocean surface waters comparisons of element fluxes show that dissolution of adsorbed surface salts and aerosols dominates over glass dissolution even in sustained low ph conditions these surface ash leachates appear unstable decaying in situ even if kept unhydrated volcanic ash from recent eruptions is shown to have a large fertilization potential in both fresh and saline water fluorine concentrations are integral to bulk dissolution rates and samples with high f concentrations display elevated fluxes of some nutrients particularly fe si and p bio limiting micronutrients are released in large quantities suggesting that subsequent biological growth will be limited by macronutrient availability importantly acidification of surface waters and high fluxes of toxic elements highlights the potential of volcanic ash leachates to poison aqueous environments in particular large ph changes can cause undersaturation of caco3 polymorphs damaging populations of calcifying organisms deposition of volcanic ash can both fertilize and or poison aqueous environments causing significant changes to surface water chemistry and biogeochemical cycles

palaeoenvironmental reconstruction and biostratinomic analysis of the jurassic yanliao lagerstatte in northeastern china abstract the middle upper jurassic yanliao lagerstatte contains numerous exceptionally preserved fossils of aquatic and land organisms including insects salamanders dinosaurs pterosaurs and mammaliaforms despite extensive study of the diversity and evolutionary implications of the biota the palaeoenvironmental setting and taphonomy of the fossils remain poorly understood we reconstruct both the palaeoenvironment of the daohugou area one of the most famous yanliao fossil areas and the biostratinomy of the fossils we use high resolution stratigraphic data from field investigation and excavations to document in detail the stratigraphic succession lithofacies facies associations and biostratinomic features of the lagerstatte our results show that frequent volcanic eruptions generated an extensive volcaniclastic apron and lake s in the studied area the frequent alternation of thin lacustrine deposits and thick volcaniclastic apron deposits indicates either that the studied area was located in the marginal regions of a single lake where the frequent influx of volcaniclastic apron material caused substantial fluctuations in lake area and thus the frequent lateral alternation of the two facies or that many short lived lakes developed on the volcaniclastic apron most terrestrial insects were preserved in the laminated normally graded siltstone claystone and tuff facies that form many thin intervals with deposits of graded sandstone siltstone and tuff in between within each interval the terrestrial insects occur in many laminae associated with abundant aquatic organisms but are particularly abundant in some laminae that directly underlie tuff of fallout origin most of these terrestrial insects are interpreted to have been killed in the area adjacent to the studied palaeolake s during volcanic eruptions their carcasses were transported by influxes of fresh volcaniclastic material primarily meteoric runoff and possibly minor distal pyroclastic flow into the palaeolake s and were buried in palaeolake deposits prior to extended decay probably due to a combination of rapid vertical settling ash fall and water turbulence

tephra beds in deep sea cores off northern new zealand implications for the history of taupo volcanic zone mayor island and white island volcanoes twenty piston cores were collected from water depths of 650 3300 m from offshore bay of plenty north island new zealand they contain tephra from 11 okataina volcanic centre and 4 taupo volcanic centre rhyolite eruptions during the last 50 kyr that produce a tephrostratigraphic framework across the tectonically and volcanically complex region of southern havre trough alderman trough and the bay of plenty continental shelf this allows correlation between offshore and onshore sequences up to 200 km from source volcanoes covering much of marine isotope stages 3 and 2 the framework temporally constrains poorly dated and newly recognised volcanic events macroscopic tephra layers from the peralkaline mayor island volcano are documented for the first time at pre 50 post 50 40 5 37 4 22 2 and 14 2 ka in addition to the well known 7 ka tuhua event these macroscopic layers represent some of the most explosive events from this volcano and provide new marker horizons they are dispersed up to 90 km north east to east of the edifice minor tephra dispersal is also recorded at 17 8 25 5 35 and pre 50 ka the tephra contain high sio2 73 75 5 wt glass and subordinate basaltic components and each tephra represents a distinct magma batch that can be fingerprinted the mayor island tephra form two temporal trends toward less evolved magma compositions punctuated by a large caldera forming event at 36 ka the historically active andesitic white island volcano does not have widely dispersed tephra and the oldest primary deposit found is 21 ka five pre 50 ka rhyolite eruptions from an unknown taupo volcanic zone source provide evidence for explosive activity in a time interval poorly documented on land the cores demonstrate the patchy and uneven preservation of large magnitude tephra falls caused by local faulting bioturbation and ponding in bathymetrically complex regions reworked tephra layers are common and often lack indicative lithological features such units could easily be misinterpreted as primary events without micro beam geochemical analyses of glass shards

hydrometeor enhanced tephra sedimentation constraints from the 18 may 1980 eruption of mount st helens 1 uncertainty remains on the origin of distal mass deposition maxima observed in many recent tephra fall deposits in this study the link between ash aggregation and the formation of distal mass deposition maxima is investigated through reanalysis of tephra fallout from the mount st helens 18 may 1980 msh80 eruption in addition we collate all the data needed to model distal ash sedimentation from the msh80 eruption cloud four particle size subpopulations were present in distal fallout with modes at 2 2 4 2 5 9 and 8 3 settling rates of the coarsest subpopulation closely matched predicted single particle terminal fall velocities sedimentation of particles 100 m was greatly enhanced predominantly through aggregation of a particle subpopulation with modal diameter 5 9 0 2 19 3 m mammatus on the msh80 cloud provided a mechanism to transport very fine ash particles with predicted atmospheric lifetimes of days to weeks from the upper troposphere to the surface in a matter of hours in this mechanism ash particles initiate ice hydrometeor formation high in the troposphere subsequently the volcanic cloud rapidly subsides as mammatus develop from increased particle loading and cloud base sublimation rapid fallout occurs as the cloud passes through the melting level in a process analogous to snowflake aggregation aggregates sediment en masse and form the distal mass deposition maxima observed in many recent volcanic ash fall deposits this work provides a data resource that will facilitate tephra sedimentation modeling and allow model intercomparisons

saturn s atmosphere at 1 10 kilometer resolution we present images of saturn from the final phases of the cassini mission including images with 0 5 km per pixel resolution as high as any saturn images ever taken notable features are puffy clouds resembling terrestrial cumulus shadows indicating cloud height dome and bowl shaped cloud structures indicating upwelling and downwelling in anticyclones and cyclones respectively and filaments which are thread like clouds that remain coherent over distances of 20 000 km from the coherence of the filaments we give upper bounds on the diffusivity and kinetic energy dissipation a radiative transfer analysis by sanz requena et al 2018 indicates that methane band imagery is most useful in determining cloud and haze properties in the 60 250 mbar pressure range our methane band imagery finds haze in this pressure range covering 64 74 planetocentric latitude filaments lie within the haze and cumulus clouds lie below it but pressure levels are uncertain below the 250 mbar level

holocene climate variability in sicily from a discontinuous stalagmite record and the mesolithic to neolithic transition abstract fabric and stable isotopic composition of a holocene stalagmite cr1 from a cave in northern sicily record changes in paleorainfall in the early holocene high 13c stable isotope values in the calcite deposited from ca 8500 to ca 7500 yr ago are interpreted as reflecting periods of high rainfall the wet phase was interrupted by two periods of multi century duration characterized by relatively cool and dry winters centered at ca 8200 and ca 7500 yr ago highlighted by low 13c and 18o values a high variability of 13c values is recorded from ca 7500 to ca 6500 yr ago and indicates that the transition from a pluvial early holocene to the present day climate conditions was punctuated by decadal scale periods of relatively dry winters in northern sicily the traditional elements of the neolithic appear at ca 7700 yr ago it is possible that changes in rainfall influenced the passage from hunter gathering to farming and sheep herding economies

saturn s zonal winds at cloud level we present an analysis of new cloud motion measurements in saturn s atmosphere from voyager 1 and 2 images and define a nominal zonal wind velocity vs latitude profile for the cloud top level that can be used as reference for the upcoming cassini mission improvements over previous studies include i twice the number of wind vectors used ii independent measurements of cloud tracers iii extended latitudinal coverage iv strict error control and evaluation and v a new zonal averaging methodology mean zonal wind velocities are given for the latitude range 81 to 71 planetographic in steps of 0 5 with a gap between 0 and 10 due to ring shadowing this research also includes the study of the morphology and motions of cloud systems in the equator and in the southern hemisphere which have not been described previously we give an ephemeris motion equation for several long lived features that could be observable if they survive until cassini arrives on saturn the long term behavior of the zonal wind profile is studied by comparing it with a complete set of wind velocities compiled from historical and modern ground based and hst observations significant changes are noted in the equatorial jet between this set and the nominal voyager profile we discuss in detail the possible origin for such differences

enhanced airborne dispersal of silicic tephras during the onset of northern hemisphere glaciations from 6 to 0 ma records of explosive volcanism and climate change in the subpolar north atlantic a 6 m y long composite marine record of explosive silicic volcanism from five ocean drilling program sites in the subpolar north atlantic was compared with several marine records of global and local paleoclimate proxies benthic d 18 o and ice rafted debris records coarsening and high frequency of occurrence of icelandic tephras were recorded in 3 6 3 ma sediments suggesting that these tephras were dispersed farther from the source by enhanced westerly winds over the subpolar north atlantic the 40 ar 39 ar ages were determined by laser probe on k feldspar and biotite phenocrysts of tephras that were erupted from the jan mayen volcanic system compared to the tuned paleomagnetic age model the 40 ar 39 ar dating 0 618 6 0 007 ma to 4 90 6 0 05 ma yields a new age model that postdates by 155 k y the inception of ice rafting on the iceland plateau during the cold marine isotope stage m2 i e 3 3 3 14 ma

ground based observations of saturn s north polar spot and hexagon ground based observations of two conspicuous features near the north pole of saturn the polar vortex and the hexagonal wave structure were made from july 1990 to october 1991 10 years after their discovery during this period the polar spot drifted in longitude relative to system iii by 0 0353 per day on average superimposed on this mean motion the spot also underwent short term rapid excursions in longitude of up to 14 at rates of up to 1 per day the spot also exhibited irregular variations in its latitude location a combination of these data together with those obtained by voyager 1 and 2 in 1980 and 1981 shows that the spot drifted 0 0577 per day for the 11 year interval from 1980 to 1991 the large lifetime of both features indicates that they are insensitive to the strong variations in the seasonal heating of the cloud layers in the upper polar atmosphere

comparison of lake and land tephra records from the 2015 eruption of calbuco volcano chile tephra layers in lake sediment cores are regularly used for tephrostratigraphy as isochronous features for dating and recording eruption frequencies however their value for determining volcanic eruption size and style may be complicated by processes occurring in the lake that modify the thickness and grain size distributions of the deposit to assess the reliability of data from lake cores we compare tephra deposited on land during the 2015 eruption of calbuco volcano in chile to records in sediment cores from three lakes of different sizes that are known to have received primary fall deposits in general the thickness and granulometry of the deposit in lake cores and nearby terrestrial sections are very similar as anticipated however cores sampled close to here within 300 m of fluvial inflows were affected by sediment deposition from the lake s catchment they differed from primary deposits not only in their greater thickness and organic content but also in poor sorting and lack of grading cores 850 m away from the inlet were not affected we consider our results in the context of the particle settling regime as well as each lake s location bathymetry and catchment area we find that the particle settling regime is important in more distal settings where the ash particles are small and particle settling occurs in density plumes rather than as individual particles we conclude that lake cores can be useful for physical volcanology providing consideration is given to eruption parameters such as particle size and mass flux as well as lake features such as bathymetry and catchment area

hydrological change in southern europe responding to increasing north atlantic overturning during greenland stadial 1 greenland stadial 1 gs 1 was the last of a long series of severe cooling episodes in the northern hemisphere during the last glacial period numerous north atlantic and european records reveal the intense environmental impact of that stadial whose origin is attributed to an intense weakening of the atlantic meridional overturning circulation in response to freshening of the north atlantic recent high resolution studies of european lakes revealed a mid gs 1 transition in the climatic regimes the geographical extension of such atmospheric changes and their potential coupling with ocean dynamics still remains unclear here we use a subdecadally resolved stalagmite record from the northern iberian peninsula to further investigate the timing and forcing of this transition a solid interpretation of the environmental changes detected in this new accurately dated stalagmite record is based on a parallel cave monitoring exercise this record reveals a gradual transition from dry to wet conditions starting at 12 500 y before 2000 a d in parallel to a progressive warming of the subtropical atlantic ocean the observed atmospheric changes are proposed to be led by a progressive resumption of the north atlantic convection and highlight the complex regional signature of gs 1 very distinctive from previous stadial events

high temperature emplacement and liquefaction of shallow water caldera forming eruption products early miocene tateyamazaki dacite in the oga peninsula ne japan abstract the early miocene tateyamazaki dacite infills a 3 2 km diameter caldera it comprises poorly sorted massive biotite bearing dacite pumice lapilli tuff in which huge blocks of densely welded dacite lapilli tuff basaltic andesite lava and other lithologies are commonly set dense blocks are variably cracked and intruded by the host lapilli tuff sparse blocks of bedded lapilli tuff and tuff are variably disaggregated to intermingle with the host rocks or are plastically deformed into irregular shapes rootless tuff veins millimeters to 30 cm thick are developed within the host rocks mainly dipping at 10 30 and are locally branched and mutually cut to form a network where thicker they are stratified and locally carry accidental fragments accidental lapilli up to 2 or 3 cm wide and 30 cm long are locally set in near vertical and variably sinuous arrays although poorly defined they are reminiscent of fluid escape structures the host pumice lapilli tuff however retains in part a thermal remnant magnetization trm vector stable at temperatures above 280 c blocks in the caldera fill also retain trm but the vectors are rotated significantly from those of the host pumice lapilli tuff and the adjacent volcanic rocks tateyamazaki dacite is thus likely to have been emplaced at high temperatures and intermingled with shattered basement rocks and ambient water to be partly liquefied within the caldera immediately after or during the caldera forming eruption

responses to rapid warming at termination 1a at gerzensee central europe primary succession albedo soils lake development and ecological interactions the transition from the oldest dryas to the bolling around 14 685 cal yr bp was a period of extremely rapid climatic warming from a single core of lake marl taken at gerzensee switzerland we studied the transition in stable isotopes of oxygen and carbon on bulk sediment and charophyte remains as well as on monospecific samples of ostracods after pisidium a in addition pollen chironomids and cladocera were analyzed the 18o record serves as an estimate of mean air temperature and by correlation to the one from ngrip in greenland it provides a timescale the timing of responses the statistically significant zone boundaries of the biostratigraphies are telescoped at the rapid increase of about 3 in 18o at the onset of bolling biotic responses may have occurred within sampling resolution 8 to 16 years although younger zone boundaries are less synchronous gradual and longer lasting responses include complex processes such as primary or secular succession during the late glacial interstadial of bolling and allerod two stronger and two weaker cool phases were found biological processes involved in the responses occurred on levels of individuals e g pollen productivity of populations increases or decreases immigration or extinction and on the ecosystem level species interactions such as facilitation or competition abiotic and biotic interactions include pedogenesis nitrogen fixation nutrient cycling catchment hydrology water chemistry of the lake and albedo controlled by the transition from tundra to forest for the swiss plateau this major change in vegetation induced a change in the mammal fauna which in turn led to changes in the tool making by paleolithic people

settling driven convection a mechanism of sedimentation from stratified fluids convection driven by sediment particles may play an important role in sedimentation from the base of buoyant hypopycnal plumes for example fluvial plumes in stratified estuaries and lakes black smokers on the ocean floor volcanic clouds and coastal currents in addition to the well known double diffusive convection mechanism another mode of convective instability development is by settling across the density interface we performed laboratory experiments to investigate this fingering convective instability mechanism and its effect on particle distribution in the water column and deposition at the bed a simple theoretical model of finger formation at a fluid density interface is developed based on an analogy with thermal plume formation at a flat heated plate this model which involves a thickening interface layer that becomes gravitationally unstable relative to the ambient fluid is in good agreement with measurements of finger size and instability wavelength from visualization experiments since fingering at the density interface drives larger scale convection in the fluid below a mass balance model of the lower layer assuming strong mixing i e uniform sediment concentration is successfully applied to predict sediment concentration in the water column and deposition at the bed strong mixing can be assumed since convective velocities are usually much greater than the particle fall velocities as convection proceeds the sediment concentrations in the two layers approach each other and convection will die out using the model equations we develop analytical expressions for the time when convection ceases and the portion of sediment remaining in the water column

three dimensional volcanic aerosol dispersal a comparison between multiangle imaging spectroradiometer misr data and numerical simulations 1 the three dimensional reconstruction of volcanic plumes is a central goal to enhance our understanding on dispersal processes in this paper we use data from the multiangle imaging spectroradiometer misr on board nasa s terra spacecraft combined with a stereo matching retrieval procedure we show the potential of misr in capturing important features of volcanic plumes like column height optical depth type and shape of the finest particles of two highly explosive eruptions occurring on mount etna in 2001 and 2002 this work tests how tephra dispersal models reconstruct the 3 d shape of volcanic clouds we compare misr data with fall3d an eulerian model for the transport and deposition of volcanic ash and aerosols coupled with the weather research and forecasting mesoscale meteorological model agreement between simulations and misr data is good regarding both events although it could be improved by increasing the accuracy of the meteorological data a better constraint on volcanological input parameters like the height of the eruptive column and improving our understanding of processes such as aggregation phenomena and volcanic cloud microphysics

eruption fed particle plumes and volcaniclastic deposits at a submarine volcano nw rota 1 mariana arc 1 nw rota 1 is an active submarine volcano in the mariana arc with a summit depth of 517 m and an explosively erupting volcanic vent southwest of the summit at a depth of 530 560 m during a period of ongoing explosive eruptions particle plumes surrounded the volcano and at least 3 3 107 m3 of volcaniclastic material was deposited on the southern flank particle plumes over the summit were magmatic hydrothermal in origin characterized by 3he enrichment hydrothermal precipitates and low ph values plumes at multiple depths below the summit surrounded the volcano and were composed overwhelmingly of fresh glassy shards of basalt rare anhydrite particles were present but there was a complete absence of other hydrothermal components in the deep plume samples these short lived anhydrite particles indicate the source of the deep plumes is from within or very near the eruptive vent and the mechanism for transport down the flanks of the volcano must be far faster than settling of individual particles the deep plumes most likely originated from sediment gravity flows generated by explosive eruptions or slope failure and landslides of unstable materials that had accumulated near the eruptive vent suspended sediments detach from the volcano slopes at multiple depths and are transported laterally up to tens of kilometers where they contribute to fall out deposits in distal sediments these observations link mechanisms for the transport of volcanic ash in the submarine environment to the types of deposits common in volcaniclastic aprons and fine ash layers in distal sediments

environments at the mis 3 2 transition in the northern alps and their foreland abstract this paper reviews the current state of knowledge about environmental changes at the mis 3 2 transition in the northern alps and their foreland covering the time frame from 35 to 25 ka lake and peat deposits cave sediments loess and glacial deposits are presented and the response of their biotic and abiotic proxies to climate change is discussed during late mis 3 interstadial conditions albeit weak occurred at c 36 32 ka at climatically favourable sites small patches of trees mainly pinus and some betula existed together with some shrubs the environmental conditions during late mis 3 are also reflected by a boreal brown soil horizon a cambisol called lohne soil found in many loess sequences subsequently the environmental conditions became harsher as shown by the proxy data from c 30 ka onwards the absence of pedogenesis sensu stricto and the plant assemblages point to an arctic climate in the northern alpine foreland accentuating glaciers advanced beyond the northern limit of the alps around the mis 3 2 boundary and reached their maximum extent in the foreland at about 25 ka

subaqueous eruption and emplacement of ot2 in the middle miocene iizuka formation noto peninsula japan abstract ot2 okada tuff 2 is one of six rhyolitic tuff beds that occur in a middle miocene marine diatomite lower iizuka formation and are known as the okada tuff ot2 is well sorted and thins and thickens infilling channels 1 3 m across and 0 30 cm deep with a thickness up to 30 cm small channels 10 30 cm across and 1 10 cm deep are commonly superimposed within wider channels a thin diatomite layer is ripped from the substrate up to a level immediately above the small channels the basal part beneath the ripped up diatomite layer is dominated by ash components with vague wavy stratifications above the ripped up diatomite layer diatomite clasts are dispersed and pumice lapilli increase upward in amount and size with local interruption at a middle lower level by a poorly defined pumice lapilli poor thin layer many glass and pumice shards are blocky with curviplanar surfaces and jigsaw cracks presumably produced by phreatomagmatic explosions the poorly defined two layers of ot2 are interpreted to be ash turbidites individually produced by discrete phreatomagmatic explosions lenticular bedforms and channels indicate that the currents were fully turbulent and unsteady fed by the submarine eruptions upward coarsening of pumice probably represents settling lag of hot pumice ot2 perhaps provides potential diagnostic features to identify eruption fed turbidites

timing and dynamics of the last deglaciation from european and north african δ13c stalagmite profiles comparison with chinese and south hemisphere stalagmites abstract the last deglaciation and its climatic events such as the bolling allerod ba and the younger dryas yd have been clearly recorded in the 13 c profiles of three stalagmites from caves from southern france to northern tunisia the three 13 c records dated by thermal ionization mass spectrometric uranium thorium method tims show great synchroneity and similarity in shape with the chinese cave 18 o records and with the marine tropical records leading to the hypothesis of an in phase between 15 5 and 16 ka 0 5 ka postglacial warming in the northern hemisphere up to at least 45 n the ba transition appears more gradual in the speleothem records than in the greenland records and the allerod seems warmer than the bolling showing here close similarities with other marine and continental archives a north south gradient is observed in the ba trend it cools in greenland and warms in our speleothem records several climatic events are clearly recognizable a cooler period at about 14 ka older dryas od the intra allerod cold period at about 13 3 ka the yd cooling onset between 12 7 and 12 9 0 3 ka similar to the ba the yd displays a gradual climate amelioration just after its onset at 12 75 0 25 ka up to the preboreal and is punctuated by a short climatic event at 12 15 ka even though the southern hemisphere stalagmite records seem to indicate that the postglacial warming started about 3 ka 1 8 ka earlier in new zealand 41 s and about 1 to 2 ka earlier in south africa 24 1 s large age uncertainties essentially due to slow growth rates make the comparison still perilous the overall 13 c speleothem record seems to follow a baseline temperature increase controlled by the increase in insolation and punctuated by cold events possibly due to the n america freshwater lake discharges

haze and cloud structure of saturn s north pole and hexagon wave from cassini iss imaging abstract in this paper we present a study of the vertical haze and cloud structure in the upper two bars of saturn s northern polar atmosphere using the imaging science subsystem iss instrument onboard the cassini spacecraft we focus on the characterization of latitudes from 53 to 90 n the observations were taken during june 2013 with five different filters vio bl1 mt2 cb2 and mt3 covering spectral range from the 420 nm to 890 nm in a deep methane absorption band absolute reflectivity measurements of seven selected regions at all wavelengths and several illumination and observation geometries are compared with the values produced by a radiative transfer model the changes in reflectivity at these latitudes are mostly attributed to changes in the tropospheric haze this includes the haze base height from 600 200 mbar at the lowest latitudes to 1000 300 mbar in the pole its particle number density from 20 2 particles cm3 to 2 0 5 particles cm3 at the haze base and its scale height from 18 0 1 km to 50 0 1 km we also report variability in the retrieved particle size distribution and refractive indices we find that the hexagonal wave dichotomizes the studied stratospheric and tropospheric hazes between the outer equatorward regions and the inner polar regions this suggests that the wave or the jet isolates the particle distribution at least at tropospheric levels

cloud features and zonal wind measurements of saturn s atmosphere as observed by cassini vims 1 we present an analysis of data about saturn s atmosphere from cassini s visual and infrared mapping spectrometer vims focusing on the meteorology of the features seen in the 5 m spectral window we present vims mosaics and discuss the morphology and general characteristics of the features backlit by saturn s thermal emission we have also constructed a zonal wind profile from vims feature tracking observation sequences using an automated cloud feature tracker comparison with previously constructed profiles from voyager and cassini imaging data reveals broad similarities suggesting minimal vertical shear of the zonal wind however areas of apparent wind shear are present in the vims zonal wind profile at jet stream cores in particular our analysis shows that the equatorial jet reaches speeds exceeding 450 m s 1 similar to speeds obtained during the voyager era this suggests that recent inferences of relatively slower jet speeds of 275 375 m s 1 are confined to the upper troposphere and that the deep 1 bar jet has not experienced a significant slowdown our measurements of the numerous dark spotted features seen in the vims mosaics reveals that most of these features have diameters less than 1000 km and reside in confined zonal bands between jet stream cores we propose that these spot features are vortices and that vims and imaging science subsystem are sensing the same vortices at two different pressure levels the local structure at the zonal jet streams remains complex as vims may be sensing cloud features that are deeper than the nh3 cloud deck

speleothems from the earliest quaternary snapshots of paleoclimate and landscape evolution at the northern rim of the alps abstract ancient cave systems in the northern calcareous alps today located well above the timberline at altitudes of 2400 2500 m host u rich speleothems that preserved growth layers on the microscopic scale of presumably annual origin two flowstone samples were dated to 2 019 0 037 0 069 ma and 1 730 0 032 0 068 ma respectively using u pb isochron techniques these ages are corroborated by the late pliocene to early pleistocene pollen spectrum extracted from one of the samples we use a multiproxy approach and exploit laminated speleothem sequences to tie high resolution stable isotope data to a floating lamina counted chronology o isotope values of growth intervals when calcite deposition was close to isotopic equilibrium are low compared to modern and holocene speleothems from other alpine caves and are inconsistent with the current altitudinal setting of the caves a vegetated but geomorphologically stable alpine catchment i e 2000 m asl no peri glacial processes combined with a deep seated cave the thickness of the vadose zone might have exceeded 1000 m is required in order to reconcile the isotopic data with the pollen record and the petrographic evidence furthermore the data can be used to constrain the rate for quaternary rock uplift to 0 8 mm annum for this frontal part of the european alps collectively the data suggest that these speleothems formed both during interglacials mis 59 or 61 and interglacial glacial transitions mis 75 74 or 77 76 but the seasonal precipitation pattern was arguably markedly different from today s provided that the highly regular microscopic laminae are indeed annual lamina counts suggest a minimum length of ca 6 ka for interglacials during the earliest pleistocene

late ordovician chatfieldian catastrophic volcanism and abrupt carbonate platform interior subsidence a tectonic link across a taconian foreland basin quebec embayment due to inherited crustal weakness the late ordovician trenton group of new york state and equivalent strata in south central canada peripheral to the quebec embayment form a regional carbonate platform succession within the taconian foreland basin the upper and lower group boundaries record geodynamically controlled changes in regional subsidence whereas a higher order allocyclic stratigraphy traced south along the foreland interior of the eastern united states may identify shorter term eustatic controls a tectonomagmatic event extending across the foreland basin is recorded a few million years prior to the regional collapse of the foreland platform in the quebec embayment within the lower c spiniferus graptolite zone platform margin retreat 50 km in southern quebec is contemporaneous with a shale rich limestone succession that thins 30 10 m westward over 300 km into the ottawa embayment eastern ontario west of the appalachian structural front this stratigraphic record coincides with catastrophic volcanism within the once distant volcanic arc terranes as recorded by a bentonite traced geophysically from the platform margin to the michigan basin core from the ottawa embayment demonstrates western directed transport of lithic bearing ash the lithic material representing reworked deep water sedimentary and or volcaniclastic sediment was entrained by eruption of calc alkaline felsic to basaltic andesitic and trachyandesitic magmatic sources the above geological history documents a short period of diminishing influence of subsidence moving into the platform interior an event that enhanced briefly cross platform oceanographic circulation as recorded by elevated shale abundance and change in macrofaunal assemblages short lived differential subsidence of the continental crust in this region in response to distal tectonism may have been predicated by inherited weakness of a shallowly buried intracratonic 400km precambrian fault system manifest today by the ottawa bonnechere graben the resulting thin 10 to 30 m stratigraphic record of the tectonomagmatic event is of similar thickness to high order allostratigraphic patterns within the taconic foreland interior of the eastern united states because there is a heterogeneous distribution of precambrian fault systems underlying the taconian foreland interior of eastern laurentia differential structural response of the foreland interior can be anticipated the apparent regional allostratigraphy may contain subtle facies differences along the strike of the foreland basin that reflect this tectonic component

large kinetic isotope effects in modern speleothems the application of stable isotopes in speleothem records requires an understanding of the extent to which speleothem calcite isotopic compositions refl ect the compositions of the cave waters from which they precipitate to test for equilibrium precipitation modern speleothem calcite was grown on glass plates so that the carbon and oxygen isotope composition of the calcite and the water from which it precipitated could be directly compared the plates were placed on the tops of three actively growing stalagmites that occupy a 1 m 2 area in harrison s cave barbados west indies only some of the plate 13 c values and none of the plate 18 o values correspond to equilibrium values indicating signifi cant kinetic isotope effects during speleothem calcite growth we investigate herein mechanisms that may account for the kinetic isotope effects on each plate speleothem calcite was deposited with distinct 18 o and 13 c compositions that increase progressively away from the growth axis with up to 6 6 13 c and 1 7 18 o enrichments the positive 13 c

palaeoclimate records 60 8 ka in the austrian and swiss alps and their forelands abstract the european alps and their forelands provide a range of different archives and climate proxies for developing climate records in the time interval 60 8 thousand years ka ago we review quantitative and semi quantitative approaches for reconstructing climatic variables in the austrian and swiss sector of the alpine region within this time interval available quantitative to semi quantitative climate records in this region are mainly based on fossil assemblages of biota such as chironomids cladocerans coleopterans diatoms and pollen preserved in lake sediments and peat the analysis of oxygen isotopes in speleothems and lake sediment records the reconstruction of past variations in treeline altitude the reconstruction of past equilibrium line altitude and extent of glaciers based on geomorphological evidence and the interpretation of past soil formation processes dust deposition and permafrost as apparent in loess palaeosol sequences palaeoclimate reconstructions in the alpine region are affected by dating uncertainties increasing with age the fragmentary nature of most of the available records which typically only incorporate a fraction of the time interval of interest and the limited replication of records within and between regions furthermore there have been few attempts to cross validate different approaches across this time interval to confirm reconstructed patterns of climatic change by several independent lines of evidence based on our review we identify a number of developments that would provide major advances for palaeoclimate reconstruction for the period 60 8 ka in the alps and their forelands these include 1 the compilation of individual fragmentary records to longer and continuous reconstructions 2 replication of climate records and the development of regional reconstructions for different parts of the alps 3 the cross validation of different proxy types and approaches and 4 the reconstruction of past variations in climate gradients across the alps and their forelands furthermore the development of downscaled climate model runs for the alpine region 60 8 ka and of forward modelling approaches for climate proxies would expand the opportunities for quantitative assessments of climatic conditions in europe within this time interval

convective instability in sedimentation linear stability analysis 1 convective sedimentation in a stably stratified saltwater is studied using the linear stability analysis convective sedimentation is known to occur due to the double diffusive mechanism and the settling driven mechanism in this study a semi empirical closure of sediment diffusivity based on the long range hydrodynamics effect is adopted the sediment phase can act as either the slow or fast diffusing agent in the double diffusive system for the given salt diffusivity moreover the settling driven effect is proportional to the square of the sediment diameter via stoke settling law we consider sediment concentration grain size in the upper freshwater layer to be in the range of 0 1 to 39 4 g l 2 to 60 m which is on top of a saltwater layer with salinity 35 ppt linear stability analysis allows us to identify the dominant mechanism that triggers the instability the growth rate and the resulting characteristic finger width model results suggest that for fine sediment with grain diameter smaller than 10 m settling velocity 0 09 mm s double diffusive mechanism controls the instability and the resulting sediment finger size is of millimeter scale for the given threshold of growth rate of o 0 01 s 1 the minimum sediment concentration is about 8 15 g l for grain size greater than or around 10 m the settling driven mechanism dominates and instabilities occur at sediment concentration as low as o 0 1 g l with centimeter scale fingers our findings may contribute to a better understanding on the observed rapid sediment removal in the plume of small mountainous rivers

trace element behaviour in seawater during etna s pyroclastic activity in 2001 concurrent effects of nutrients and formation of alteration minerals abstract the eruption of etna in sicily on 13 july 2001 marked the most intense activity of the volcano in the last 300 years the eruption occurred while the oceanographic cruise ansic 01 was being conducted to the east of sicily presenting a unique opportunity for the investigation of the chemical effects on the marine system during a period of significant 1 g m 2 ash deposition comparison of trace element data with measured concentrations from the oceanographic cruise juvenile 99 carried out two years before indicates large enrichments of v cr mn fe co cu and pb we attribute this behaviour to leaching of freshly erupted volcanic ash according to trace element concentrations measured in suspended particulate matter spm the exception is pb which is likely to be influenced by another possibly anthropogenic source trace element behaviour in the water column and during leaching experiments suggests that trace element distributions are driven by the occurrence of alteration minerals on glass surfaces given that the main trace element source in seawater appears to come from the soluble ash fraction trace element solubility is likely to be increased by organic complexation which accelerates the alteration of ash particles organic substances suitable for complex trace elements are probably formed during the lysis of phytoplankton cells produced during an increase in marine primary productivity associated with the volcanic fertilisation of surface waters

the saturnian ribbon feature a baroclinically unstable model images of saturn from the two voyager spacecraft showed few discrete atmospheric features in the low contrast latitudinal banding over the planet one unusual feature however was a narrow dark oscillatory structure encircling the planet in the light zone at 45 to 50 north this paper presents a description of this dark structure which we call the ribbon feature a wavelength of 5710 260 km is obtained from moderate resolution images which were used to produce a 360 image of the feature higher resolution image pairs were used to examine the local circulation which shows counterclockwise rotation north of the ribbon and clockwise rotation south of it the zonal circulation measurements show that it is located in a 120 m sec 1 westerly jet but with a small 5 m sec 1 meridional velocity the infrared spectrometer results from voyager showed the greatest thermal wind sheer in this latitude region the regions adjacent to the ribbon are of similar brightness except for the uv 3400 a filter images where the northern part of this zone is lighter than the southern section from this observation we have estimated that the disturbance associated with the ribbon feature extends to at least the 200 mbar level a study of a 120 section of the ribbon feature and the associated latitudinal thermal gradient by l a sromovsky h e revercomb r j krauss and v e suomi 1983 j geophys res 88 8650 8666 led them to suggest that it was produced by some form of baroclinic instability this proposal is considered here with other alternative types of instability we conclude that the ribbon feature could arise from a baroclinic instability we then develop a numerical model of such an instability that is consistent with the observed wavelength the vertical extent of the ribbon and the local latitudinal thermal profile

submarine deposits from pumiceous pyroclastic density currents traveling over water an outstanding example from offshore montserrat iodp 340 pyroclastic density currents have been observed to both enter the sea and to travel over water for tens of kilometers here we identified a 1 2 m thick stratified pumice lapilli ash cored at site u1396 offshore montserrat integrated ocean drilling program iodp expedition 340 as being the first deposit to provide evidence that it was formed by submarine deposition from pumice rich pyroclastic density currents that traveled above the water surface the age of the submarine deposit is ca 4 ma and its magma source is similar to those for much younger soufriere hills deposits indicating that the island experienced large magnitude subaerial caldera forming explosive eruptions much earlier than recorded in land deposits the deposit s combined sedimentological characteristics are incompatible with deposition from a submarine eruption pyroclastic fall over water or a submarine seafloor hugging turbidity current derived from a subaerial pyroclastic density current that entered water at the shoreline the stratified pumice lapilli ash unit can be subdivided into at least three depositional units with the lowermost one being clast supported the unit contains grains in five separate size modes and has a 12 phi range particles are chiefly subrounded pumice clasts lithic clasts crystal fragments and glass shards pumice clasts are very poorly segregated from other particle types and lithic clasts occur throughout the deposit fine particles are weakly density graded we interpret the unit to record multiple closely spaced 2 d hot pyroclastic density currents that flowed over the ocean releasing pyroclasts onto the water surface and settling of the various pyroclasts into the water column our settling and hot and cold flotation experiments show that waterlogging of pumice clasts at the water surface would have been immediate the overall poor hydraulic sorting of the deposit resulted from mixing of particles from multiple pulses of vertical settling in the water column attesting to complex sedimentation slow settling particles were deposited on the seafloor together with faster descending particles that were delivered at the water surface by subsequent pyroclastic flows the final sediment pulses were eventually deflected upon their arrival on the seafloor and were deposited in laterally continuous facies this study emphasizes the interaction between products of explosive volcanism and the ocean and discusses sedimentological complexities and hydrodynamics associated with particle delivery to water

construction of a tephra based multi archive coherent chronological framework for the last deglaciation in the mediterranean region abstract proxy records from different climate archives such as ice cores speleothems or sediment cores are essential to define the sequence of events over to the last deglaciation however multi archive comparison and compilation of data necessary to assess the robustness of climate models are rapidly limited by inconsistencies between archives chronology here we present the development and validation of the datice chronological integration tool for the construction of multi archive coherent chronologies this chronology building tool first developed to date ice cores only can now integrate deposition like archives such as sediment cores and speleothems independently or coherently the robustness of this dating method resides in its capacity to build coherent chronologies for multiple archives with a proper calculation of chronological uncertainties using this tool we were able to construct a coherent chronology for the last deglaciation in the mediterranean region based on volcanic tephra layers correlation in terrestrial and marine sediment cores we confirm the synchronicity within chronological errors of the sequence of events characterizing the last deglaciation between greenland and the mediterranean region independently of any climatic alignment assumptions using this chronological framework we however highlight some regional expression of this transition period in term of vegetation cover over the mediterranean region

high frequency explosive volcanic eruptions in a late jurassic volcanic arc the ameghino formation antarctic peninsula abstract ash layers in the lower tithonian longing member ameghino formation on the antarctic peninsula are derived from the fallout of tephra associated with explosive eruptions these layers are preserved in a complete and continuous sedimentary record formed in a deep anoxic marine environment with high background sedimentation rates allowing rapid burial and preservation absence of bioturbation precluded the thin ash beds from mixing with enclosing sediment the average interval between explosive eruptions in the volcanic arc of the antarctic peninsula during the early tithonian is estimated at between 700 and 1000 years the highest frequency of explosive volcanic events ever defined in ancient marine rocks this frequency is comparable to that of explosive eruptions in some presently active volcanic arcs this indicates that deposition in some deep marine settings can produce records sufficiently complete to determine accurate frequencies of explosive eruptions in ancient magmatic arcs the apparent lull in the volcanic activity in the antarctic peninsula during this time inferred from dating of volcanic rocks from the arc itself is not supported by the marine record in the adjacent basin and must be due to a bias of sampling

volcanic triggering of late pliocene glaciation evidence from the flux of volcanic glass and ice rafted debris to the north pacific ocean abstract mass accumulation rates mar of different components of north pacific deep sea sediment provide detailed information about the timing of the onset of major northern hemisphere glaciation that occurred at 2 65 ma an increase in explosive volcanism in the kamchatka kurile and aleutian arcs occurred at this same time suggesting a link between volcanism and glaciation sediments recovered by piston coring techniques during odp leg 145 provide a unique opportunity to undertake a detailed test of this possibility here we use volcanic glass as a proxy for explosive volcanism and ice rafted debris ird as a proxy for glaciation the mar of both glass and ird increase markedly at 2 65 ma further the flux of the volcanic glass increased just prior to the flux of ice rafted material suggesting that the cooling resulting from explosive volcanic eruptions may have been the ultimate trigger for the mid pliocene glacial intensification

new physical characterization of the fontana lapilli basaltic plinian eruption nicaragua the fontana lapilli deposit was erupted in the late pleistocene from a vent or multiple vents located near masaya volcano nicaragua and is the product of one of the largest basaltic plinian eruptions studied so far this eruption evolved from an initial sequence of fluctuating fountain like events and moderately explosive pulses to a sustained plinian episode depositing fall beds of highly vesicular basaltic andesite scoria sio2 53 wt samples show unimodal grain size distribution and a moderate sorting that are uniform in time the juvenile component predominates 96 wt and consists of vesicular clasts with both sub angular and fluidal elongated shapes we obtain a maximum plume height of 32 km and an associated mass eruption rate of 1 4 108 kg s 1 for the plinian phase estimates of erupted volume are strongly sensitive to the technique used for the calculation and to the distribution of field data our best estimate for the erupted volume of the majority of the climactic plinian phase is between 2 9 and 3 8 km3 and was obtained by applying a power law fitting technique with different integration limits the estimated eruption duration varies between 4 and 6 h marine core data confirm that the tephra thinning is better fitted by a power law than by an exponential trend

onshore offshore correlation of pleistocene rhyolitic eruptions from new zealand implications for tvz eruptive history and paleoenvironmental construction abstract taupo volcanic zone tvz in the north island new zealand is arguably the most active quaternary rhyolitic system in the world numerous and widespread rhyolitic tephra layers sourced from the tvz form valuable chronostratigraphic markers in onshore and offshore sedimentary sequences in deep sea cores from ocean drilling program odp leg 181 sites 1125 1124 1123 and 1122 located east of new zealand ca 100 tephra beds are recognised post dating the plio pleistocene boundary at 1 81 ma these tephras have been dated by a combination of magnetostratigraphy orbitally tuned stable isotope data and isothermal plateau fission track ages the widespread occurrence of ash offshore to the east of new zealand is favoured by the small size of new zealand the explosivity of the mainly plinian and ignimbritic eruptions and the prevailing westerly wind field although some tephras can be directly attributed to known tvz eruptions there are many more tephras represented within odp cores that have yet to be recognised in near source on land sequences this is due to proximal source area erosion and or deep burial as well as the adverse effect of vapour phase alteration and devitrification within near source welded ignimbrites despite these difficulties a number of key deep sea tephras can be reliably correlated to equivalent aged tephra exposed in uplifted marine back arc successions of wanganui basin where an excellent chronology has been developed based on magnetostratigraphy orbitally calibrated sedimentary cycles and isothermal plateau fission track ages on tephra significant pleistocene tephra markers include the kawakawa omataroa rangitawa onepuhi kaukatea kidnappers b potaka unit d ahuroa ongatiti rewa sub rewa pakihikura ototoka and table flat tephras six other tephra layers are correlated between odp core sites but have yet to be recognised within onshore records the identification of pleistocene tvz sourced tephras within the odp record and their correlation to wanganui basin and other onshore sites is a significant advance as it provides 1 an even more detailed history of the tvz than can be currently achieved from the near source record 2 a high resolution tephrochronologic framework for future onshore offshore paleoenvironmental reconstructions and 3 well dated tephra beds correlated from the offshore odp sites with astronomically tuned timescales provide an opportunity to critically evaluate the chronostratigraphic framework for onshore plio pleistocene sedimentary sequences e g wanganui basin cf naish et al 1998 quaternary science reviews 17 695 710

sizes and shapes of 10 ma distal fall pyroclasts in the ogallala group nebraska abstract size distributions of distal ashfall particles from correlated 10 ma layers in nebraska measured using laser diffraction methods are lognormal with mode diameters of 90 m this ashfall is 100 bubble wall shards of rhyolite glass and apparently represents a distal ashfall from an eruption 1400 km away measured terminal velocities of these ash particles are 0 2 18 cm s consistent with stokes law settling of spherical particles with diameters of 9 50 m surface area of the ash particles measured with gas adsorption is 20 30 times the surface area of equivalent stokes spheres these results highlight the effects of shape and atmospheric drag in distal ashfalls they also highlight atmospheric transport and fallout of distal ashfall particles because these deposits resemble many other ashfalls preserved in the great plains of north america throughout the tertiary and quaternary because the ashfalls preserve major mammalian death assemblages they demonstrate that deposits with modes of op

the demise of the last interglacial recorded in isotopically dated speleothems from the alps abstract the transition from interglacial to glacial climate has attracted much attention in paleoclimatic research partly because orbital forcing dictates that such a return to a new ice age is inescapable albeit in the distant future only the detailed series of steps that leads to glacial inceptions remains poorly understood however and studies of past glacial inceptions are often compromised by incomplete records imprecise chronological control and or uncertainties associated with proxy transfer functions here we present results from u th dated speleothems from a cave in the austrian alps entrische kirche cave which grew continuously between ca 127 and 114 ka and intermittently also during subsequent stadials and interstadials the alpine setting of this cave is prone to periglacial and glacial processes as well as temperature and precipitation changes which are recorded in these cave deposits we use high resolution stable isotope data to constrain paleoenvironmental changes associated with the demise of the last interglacial unprecedented in detail for central europe peak interglacial conditions are characterized by high 18 o values and high growth rates from ca 127 to 124 ka a major drop in 18 o by 3 occurred at ca 118 ka which coincided with cold event c26 in the north atlantic this isotopic shift which occurred at or close to isotopic equilibrium cannot be explained by simple uniform cooling modelling suggests that enhanced seasonality dominated by significant changes in winter precipitation are required to reconcile the isotope data with the fact that calcite deposition continued across the mis 5e d transition i e no cave freezing this period of enhanced seasonality lasted for several millennia during which the catchment area of the cave remained geomorphologically stable and ice free eventually speleothem growth terminated at ca 114 ka which is in line with widespread ice rafting in the north atlantic cold event c24 and the onset of fully stadial conditions during mis 5d

dynamics of saturn s polar regions we analyze data retrieved by the imaging science system onboard the cassini spacecraft to study the horizontal velocity and vorticity fields of saturn s polar regions latitudes 60 90 n in june december 2013 and 60 90 s in october 2006 and july december 2008 including the northern region where the hexagonal wave is prominent with the aid of an automated two dimensional correlation algorithm we determine two dimensional maps of zonal and meridional winds and deduce vorticity maps we extract zonal averages of zonal winds providing wind profiles that reach latitudes as high as 89 5 in the south and 89 9 in the north wind measurements cover the intense polar cyclonic vortices that reach similar peak velocities of 150 m s 1 at 88 5 the hexagonal wave lies in the core of an intense eastward jet at planetocentric latitude 75 8 n with motions that become nonzonal at the hexagonal feature in the south hemisphere the peak of the eastward jet is located at planetocentric latitude 70 4 s a large anticyclone the south polar spot sps similar to the north polar spot nps observed at the voyager times 1980 1981 has been observed in images from april 2008 to january 2009 in the south polar region at latitude 66 1 close to the eastward jet the sps does not apparently excite a wave on the jet we analyze the stability of the zonal jets finding potential instabilities at the flanks of the eastward jets around 70 and we measure the eddy wind components suggesting momentum transfer from eddy motion to the westward jets closer to the poles

holocene climate change and prehistoric settlement in the lower danube valley abstract an analysis of the summed probability distributions of 293 radiocarbon dates from late glacial to mid holocene sites in the danubian iron gates highlights the existence of well marked 14c discontinuities at c 9 5 9 0 ka 8 65 8 0 ka and after 7 8 ka cal bp these coincide with climate anomalies recorded in greenland ice cores and palaeoclimate archives from the danube catchment four possible explanations are considered dwindling fish resources changes in the social environment flood induced settlement relocations and taphonomic effects on present evidence the last two factors are thought to be the most likely cause of the discontinuities observed in the iron gates mesolithic early neolithic radiocarbon record

alkalic marine tephra layers at odp site 1241 major explosive eruptions from an oceanic volcano in a pre shield stage highlights subplinian to plinian eruptions from cocos island tectonically controlled melt ascent ocean island evolution without passing typical growth stages abstract we report a series of fourteen marine tephra layers that are the products of large explosive eruptions of subplinian to plinian intensities and magnitudes vei 4 from cocos island costa rica cocos island is a volcanic island in the eastern central pacific ocean 500 km offshore costa rica and is situated on the northwestern flank of the aseismic cocos ridge geochemical fingerprinting of pleistocene 2 4 1 4 ma marine tephra layers from ocean drilling project odp leg 202 site 1241 using major and trace element compositions of volcanic glass shards demonstrates unequivocally their origin from cocos island rather than the galapagos archipelago or the central american volcanic arc cava cocos island and the adjacent seamounts of the cocos island province have alkalic compositions and formed on young 3 ma oceanic crust from an extinct spreading ridge bounded by a transform fault against the older and thicker crust of the aseismic cocos ridge cocos island has six times the average volume of the adjacent seamounts although all appear to have formed during the 3 1 4 ma time period cocos island lies closest to the transform fault and we explain its excessive growth by melts rising from garnet bearing mantle being deflected from the thick cocos ridge lithosphere toward the thinner lithosphere on the other side of the transform thus enlarging the melt catchment area for cocos island compared to the seamounts farther away from the transform this special setting favored growth above sea level and subaerial explosive eruptions even though the absence of appropriate compositions suggests that the entirely alkalic cocos island and seamounts never evolved through the productive tholeiitic shield stage typical of other pacific ocean islands possibly because melt production rates remained too small conditions of magma generation and ascent resembled hawaiian pre shield volcanoes but persisted for much longer 1 m y and formed evolved trachytic magmas therefore cocos island may be a unique example for a volcanic ocean island that did not pass through the typical growth stages

influence of convective sedimentation on the formation of widespread tephra fall layers in the deep sea the formation of widespread volcanic ash fall layers in deep sea sediments was investigated experimentally to examine the settling behavior of tephra 20 180 m diameter as it travels from the atmosphere into water using a fallout mass flux rate that was constrained by measurements of distal fallout from the 1980 eruption of mount st helens 0 2 g cm 2 hr the experiments show that particle settling in the water column is dramatically accelerated by the formation of diffuse vertical gravity currents the currents form as a result of convective instabilities that develop in a surface boundary layer when the local particle concentration becomes large at the air water interface the settling velocity of particles drops abruptly and the concentration of particles increases because of the differential in mass flux above and below the fluid surface the implication of the experiments is that deposition of distal tephra fall layers in deep sea sediments may be dominantly controlled by diffuse vertical gravity currents as opposed to passive settling of individual particles through the water column this process greatly reduces the residence time of fine ash in the ocean and diminishes the role of ocean currents in influencing the distribution patterns of individual tephra layers support for this mechanism comes from observations of greatly accelerated tephra settling rates in the south china sea following the 1991 eruption of mount pinatubo in the philippines

early eocene volcanic ashes on greifswalder oie and their depositional environment with an overview of coeval ash bearing deposits in northern germany and denmark unconsolidated bentonites and carbonate cemented volcanic ashes occur in northern germany within the clay sequence of the lamstedt and schlieven formations documented by several wells ash bearing carbonate concretions so called cementstones are also known from glacially transported rafts and erratic boulders on the baltic sea island greifswalder oie representing the easternmost exposures of early eocene sediments in the north sea basin the ashes can be correlated with water lain ashes of the danish fur and olst formations mo clay generated during the opening of the north atlantic ocean about 55 ma ago two types of cementstones can be distinguished on the basis of the mineralogical composition sedimentary features and fossil content greifswalder oie type i contains a black up to 12 cm thick ash deposit that follows above two distinct thin grey ash layers the major ash unit has a rather homogeneous lower part only a very weak normal grading and faint lamination are discernible in the upper part however intercalations with light mudstone in part intensively bioturbated together with parallel and cross lamination suggest reworking of the ash in a shallow marine environment major and trace element compositions are used to correlate type i ashes with those of the danish positive series which represent rather uniform ferrobasalts of the danish stage 4 probably related to the emergence of proto iceland in contrast type ii ash comprises a single normally graded about 5 cm thick layer of water lain air fall tuff which is embedded in fine grained sandstone to muddy siltstone type ii ash is characterised by very high tio2 but low mgo contents exceptional ree patterns with a pronounced positive eu anomaly suggest intense leaching of the glass that hampers exact correlation with pyroclastic deposits within the north atlantic igneous province

tephrostratigraphy study for the last 18 000 14 c years in a deep sea sediment sequence for the south adriatic abstract a detailed tephrostratigraphy supported by accelerator mass spectrometry ams 14c dating and isotopic and geochemical analyses has been carried out for a deep sea core collected from the southern adriatic sea which spans the last 18 14c kyr fourteen ash layers have been recognized in the marine core and the origin was determined by comparing their age and geochemistry with tephra detected in terrestrial deposits the geochemical signatures of marine ash layers indicate a prevailing campanian and subordinate etnean and eolian provenances collectively they are attributed to sources in the phlegraean fields lam lagno amendolare ln1 ln2 gm1 c 2 nyt neapolitan yellow tuff c 1 agnano pomici principali ams pf agnano monte spina ast astroni somma vesuvius l9 pomici di base l8 greenish mount etna et1 y1 biancavilla ignimbrite lipari e 1 gabellotto fiumebianco and palinuro seamount pal 1 some of these eruptions have been detected for the first time in marine cores astroni lam l9 l8 and three were detected and dated by marine tephra ln1 ln2 and pal 1 providing new more precise stratigraphic markers for the last 18 kyr in the south adriatic marine record

the immediate environmental effects of tephra emission the earth s history is punctuated by large explosive eruptions that eject large quantities of magma and silicate rock fragments into the atmosphere these tephra particles can sometimes be dispersed across millions of square kilometres or even entire continents the interaction of tephra with or in receiving environments may induce an array of physical chemical and biological effects the consequences for affected systems and any dependent communities may be chronic and localised in the event of frequent small eruptions while larger and rarer events may have acute regional scale impacts it is therefore necessary to document the range of possible impacts that tephra may induce in receiving environments and any resulting effects in interconnected systems we collate results from many studies to offer a detailed multidisciplinary and interdisciplinary review of the immediate post eruptive effects of tephra emission into the atmosphere onto vegetation soil or ice snow surfaces and in aquatic systems we further consider the repercussions that may be induced in the weeks to years afterwards in the atmosphere tephra can influence cloud properties and air chemistry by acting as ice nuclei in or by offering sites for heterogeneous reactions respectively tephra on vegetation causes physical damage and sustained coverage may elicit longer term physiological responses tephra deposits on soils may alter their capacity to exchange gas water and heat with the atmosphere or may have a specific chemical effect such as nutrient input or acidification on sensitive soils tephra deposition onto snow or ice may affect ablation rates rivers and lakes may experience turbidity increases and changes in their morphology as a result of fallout and prolonged months or years erosion from the tephra covered catchment in the first weeks after deposition tephra leaching may affect river chemistry the abundance and speciation of phytoplankton populations in lakes may be altered by tephra induced changes in water chemistry or sediment water nutrient cycling in the oceans tephra deposition may fertilise fe limited waters with potential impacts on the global carbon cycle embracing the full complexity of environmental effects caused by tephra fall demands a renewed investigative effort drawing on interdisciplinary field and laboratory studies combined with consideration of the interconnectivity of induced impacts within and between different receiving environments

latest pleistocene glacier advances and post younger dryas rock glacier stabilization in the mt krivaň group high tatra mountains slovakia abstract the timing of glacier disappearance and rock glacier stabilization in the highest massifs of the carpathians is still poorly documented in this paper we establish the extent and chronology of the final stages of glaciation and timing of stabilization of the uppermost rock glaciers in the tatra mountains which are the highest 2654 m a s l northernmost n 49 12 and coldest range in the carpathians on the base of morphostratigraphic principles schmidt hammer tests and glacier equilibrium line altitude ela estimation we assigned moraines and rock glaciers in the mt kriva massif sw part of high tatras to a threefold stratigraphic sequence with glacial stages advances from older to younger popradske pleso pp sucha va ecka i sv i and sucha va ecka ii sv ii landforms attributed to two younger advances sv i and sv ii were sampled for the purpose of cosmogenic 10be surface exposure dating our data show that pp and sv i glacial advances occurred during the oldest dryas climatic downturn the younger advance sv i occurred just before the bolling allerod b a warming at 14 9 0 4 ka at this time small glaciers occupied lower glacial cirques in the study area the youngest sv ii advance was characterized by rock glaciers and small debris covered glaciers confined to the highest cirques the mean exposure age of four relict rock glaciers of this stage is 11 1 0 9 ka but individual rock glacier mean ages spanned between 11 8 and 10 4 ka our research results show that the youngest moraines and rock glaciers in the tatra mountains were formed during the younger dryas yd but the final permafrost melting and rock glacier stabilization period was delayed until the early holocene but no later than 10 4 ka in high elevation cirque bottoms up to 2120 m a s l the yd glaciers and rock glaciers readvanced across land which was ice free as early as 14 8 14 2 ka thus it is likely that during the b a interphase glaciers completely disappeared in the tatra mountains the yd was the last period of glacial periglacial activity in the massif as we investigated one of the highest situated rock glaciers in the tatras up to 2220 m a s l we conclude that all rock glaciers in this massif are relict landforms which developed in response to severe lateglacial climate conditions the lateglacial climate of the tatra mountains is discussed herein on the basis of glacier equilibrium line altitude ela estimation and the vertical distribution of rock glacier belts we argue that paleoclimate significance of the presented geomorphological record may match paleobotanical proxy reconstructions and the results of climate simulations but only if the impact of enhanced temperature seasonality on glacier mass balance and rock glacier activity is taken into account

enhanced sedimentation beneath particle laden flows in lakes and the ocean due to double diffusive convection the transport rate of particles beneath sediment laden overflows and interflows in lakes and in the ocean can be enhanced by double diffusive and settling driven convection in previous experiments with sediment laden fluid overlaying a saline layer visual measurements could only be made in the optically clear lower layer hence there was difficulty distinguishing the two processes hindering predictions of when enhanced sedimentation occurs we used an acoustic doppler velocimeter adv to measure velocities and turbulence above and below the initial sediment salt interface the velocity of the sediment fingers in the lower layer were always larger than the stokes settling velocity of the particles leading to an asymmetry in the flow field of the two convective layers sediment fingers only dominated when there were marginal density differences between the two layers we conclude that double diffusive sediment fingers control sedimentation beneath interflows in most lakes whereas settling driven convection is dominant in most oceanic overflows

u th age constraints on the absence of ice in the central inn valley eastern alps austria during marine isotope stages 5c to 5a abstract calcitic flowstones are present in fractures of a pleistocene breccia near innsbruck austria and record periods of carbonate precipitation in the unsaturated zone between 101 500 1500 and 70 300 1800 yr constrained by u series disequilibrium dates the occurrence of these speleothems their low carbon isotopic composition and the lack of infiltrated siliciclastic material demonstrate that the central inn valley which harbored one of the most extensive valley glaciers during the last glacial maximum was ice free during marine isotope stages 5c to 5a climatically warm periods are separated by distinct drops in the oxygen isotopic composition of the speleothem calcite attributed to strong and possibly seasonally biased atmospheric cooling during these intervening stadials which mirror those identified in the greenland ice cores and marine sea surface temperature records calcite deposition apparently came to a halt but the inn valley remained ice free the youngest calcite layer formed between 74 000 and 70 000 yr and places a maximum age limit on the likely expansion of alpine glaciers during the marine isotope stage 5 4 transition consistent with other speleothem records

characteristics of submarine pumice rich density current deposits sourced from turbulent mixing of subaerial pyroclastic flows at the shoreline field and experimental assessment this study investigates the types of subaqueous deposits that occur when hot pyroclastic flows turbulently mix with water at the shoreline through field studies of the znp marine tephra in japan and flume experiments where hot tephra sample interacted with water the znp is a very thick pumice rich density current deposit that was sourced from subaerial pyroclastic flows entering the japan sea in the pliocene notable characteristics are well developed grain size and density grading lithic rich base pumice rich middle and ash rich top preponderance of sedimentary lithic clasts picked up from the seafloor during transport fine ash depletion in coarse facies and presence of curviplanar pumice clasts flume experiments provide a framework for interpreting the origin and proximity to source of the znp tephra on contact of hot tephra sample with water steam explosions produced a gas supported pyroclastic density current that advanced over the water while a water supported density current was produced on the tank floor from the base of a turbulent mixing zone experimental deposits comprise proximal lithic breccia medial pumice breccia and distal fine ash experiments undertaken with cold water saturated slurries of tephra sample and water did not produce proximal lithic breccias but a medial basal lithic breccia beneath an upper pumice breccia results suggest the characteristics and variations in znp facies were strongly controlled by turbulent mixing and quenching proximity to the shoreline and depositional setting within the basin presence of abundant curviplanar pumice clasts in submarine breccias reflects brittle fracture and dismembering that can occur during fragmentation at the vent or during quenching subsequent transport in water supported pumiceous density currents preserves the fragmental textures careful study is needed to distinguish the products of subaerial versus subaqueous eruptions

post last glacial alluvial fan and talus slope associations northern calcareous alps austria a proxy for late pleistocene to holocene climate change abstract near innsbruck city austria eastern alps following the last glacial maximum lgm an alluvial fan to talus slope succession was supplied from a carbonate rock cliff more than 1000 m in height 234u 230th ages of 9 5 to 9 37 isotope kyrs of diagenetic cements in the alluvial fan succession suggest that the fan talus deposit accumulated mainly during late glacial to perhaps early holocene times the deepest exposed interval of the fan succession contains cracked lithoclasts probably fractured by overburden from late glacial ice this interval is topped by an intra sequence unconformity following final glacial retreat and rapid aggradation of the alluvial fan and talus slope the geomorphic regime changed to erosion as recorded by fanhead trenching and cutting of fluvial terraces abandonment and vegetating of scree slopes and excavation of talus flatirons the changeover from the accumulation of fan and talus to abandonment and dissection probably took place during the terminal late glacial interval to perhaps the early holocene this erosional regime persists until present a record of rapid late glacial to early holocene accumulation of an alluvial fan talus deposit followed by i abandonment and vegetation growth combined with ii cutting of intra sequence unconformities of limited lateral extent is typical of alpine mountain flank deposystems situated at comparatively low altitudes this record consists of a an autocyclic component that is progressive lowering of sediment input due to onlap and burial of freshly deglaciated mountain flanks supplying alluvial fans and talus slopes and b an allocyclic component that is deglacial climatic warming and upward rise of an altitudinal range with a maximum number of freeze thaw cycles talus window also leading to progressive vegetation induced hillslope stabilization and lowering of scree production

high resolution isotope records of early holocene rapid climate change from two coeval stalagmites of katerloch cave austria abstract two coeval stalagmites from katerloch cave show pronounced intervals of low 18o values around 8 2 9 1 and 10 0 kyr all ages are reported before the year 2000 ad and represent an inorganic u th dated climate archive from the southeast of the european alps a region where only very few well dated climate records exist the o isotope curves providing near annual resolution allow a direct comparison to the greenland ice core records as temperature was the primary factor controlling the o isotopic composition of katerloch speleothems the 8 2 kyr climate anomaly lasted about one century from 8196 to 8100 yr with a maximum amplitude of 1 1 at 8175 yr the event is characterized by a rapid onset and a more gradual demise and u th data as well as annual lamina counting support a rapid climate change towards cooler conditions within 10 20 yr there is no strong evidence that the 8 2 kyr anomaly was superimposed on a pronounced longer term cooling episode nor do the new data support two separate cooling events within the 8 2 kyr event as reported by other studies our record also shows a distinct climate anomaly around 9 1 kyr which lasted 70 110 yr and showed a maximum amplitude of 1 0 i e it had a similar duration and amplitude as the central 8 2 kyr event compared to the 8 2 kyr event the 9 1 kyr anomaly shows a more symmetrical structure but onset and demise still occurred within a few decades only the different progression of the 8 2 asymmetrical and 9 1 kyr anomaly symmetrical suggests a fundamental difference in the trigger and or the response of the climate system moreover both stalagmites show evidence of a climate anomaly around 10 0 kyr which was of comparable magnitude to the two subsequent events using a well constrained modern calibration between air temperature and 18o of precipitation for the study area and cave monitoring data confirming speleothem deposition in katerloch reflecting cave air temperature a maximum cooling by ca 3 c can be inferred at 8 2 and 9 1 kyr which is similar to other estimates e g from lake ammersee north of the alps the o isotopic composition of meteoric precipitation however is a complex tracer of the hydrological cycle and these temperature estimates do not take into account additional effects such as changes in the source area or synoptic shifts apart from that the relative thickness of the seasonally controlled lamina types in the katerloch stalagmites remains rather constant across the intervals comprising the isotopic anomalies i e the stalagmite petrography argues against major shifts in seasonality during the early holocene climate excursions

quantifying kinetic fractionation in bunker cave speleothems using δ47 abstract isotopic signals in speleothems are used for investigating paleoclimate variability on land and are useful to constrain the dating of prominent climate events a quantitative use however is limited by an incomplete understanding of parameters contributing to the carbon and oxygen isotope signals these include external and environmental parameters such as 18 o of cave drip waters as well as internal parameters associated with speleothem formation such as the presence of non equilibrium effects and especially the magnitude of their isotopic shifts we explore the use of clumped isotopes as a new tool for investigating the kinetic isotope effect in speleothems holocene and modern speleothems from bunker cave germany as well as modern material from the adjacent dechen cave are all offset from the equilibrium relationship due to kinetic fractionation this kinetic offset in clumped isotopes is observed in a stalagmite despite mostly negative hendy tests providing a sensitive indicator for kinetic fractionation in cave carbonates the temperature dependence of the clumped isotope values 0 005 per c is low compared to the observed magnitude of kinetic offsets between 0 021 and 0 075 so that the mean offsets in apparent temperatures due to kinetic isotope effects are on the order of 10 c as a result clumped isotopes are useful in identifying temporal variations in the kinetic fractionation in a stalagmite when the temperatures during the speleothem growth period are either relatively constant variations the variations in the kinetic isotope fractionation in bunker cave are associated with changing drip water super saturation with periods of stronger prior calcite precipitation associated with lower kinetic offsets in the speleothem calcite in contrast stalagmite growth rates show no direct correlation with the degree of kinetic fractionation in the investigated range 13 1500 m a

saturn s northern hemisphere ribbon simulations and comparison with the meandering gulf stream voyager observations of saturn in 1980 81 discovered a wavy feature engirdling the planet at 47 n planetographic latitude its latitude coincides with that of an eastward jet stream which is the second fastest on saturn after the equatorial jet the 47 n jet s wavy morphology is unique among the known atmospheric jets on the gas giant planets since the voyagers it has been seen in every high resolution image of this latitude for over 25 years and has been termed the ribbon the ribbon has been interpreted as a dynamic instability in the jet stream this study tests this interpretation and uses forward modeling to explore the observed zonal wind profile s stability properties unforced initial value numerical experiments are performed to examine the nonlinear evolution of the jet stream parameter variations show that an instability occurs when the 47 n jet causes reversals in the potential vorticity pv gradient which constitutes a violation of the charney stern stability criterion after the initial instability development the simulations demonstrate that the instability s amplitude nonlinearly saturates to a constant when the eddy generation by the instability is balanced by the destruction of the eddies when the instability saturates the zonal wind profile approaches neutral stability according to arnol d s second criterion and the jet s path meanders in a ribbon like manner it is demonstrated that the meandering of the 47 n jet occurs over a range of tropospheric static stability and background wind speed the results here show that a nonlinearly saturated shear instability in the 47 n jet is a viable mechanism to produce the ribbon morphology observations do not yet have the temporal coverage to confirm the creation and destruction of eddies but these simulations predict that this is actively occurring in the ribbon region similarities exist between the behaviors found in this model and the dynamics of pv fronts studied in the context of meandering western boundary currents in earth s oceans in addition the simulations capture the nonlinear aspects of a new feature discovered by the cassini visual and infrared mapping spectrometer vims the string of pearls which resides in the equatorward tip of the 47 n jet the explicit planetary isentropic coordinate epic model is used herein

the younger dryas and holocene climate record of a stalagmite from holloch cave bavarian alps germany stable isotope analyses and seven u th dates of a stalagmite from the alpine holloch cave germany have yielded a palaeoclimate record for the past 14 300 yr the 18o record is positively correlated with relative temperature variations the late glacial part of this record including the younger dryas exhibits a striking correlation with records from ice cores lake sediments and marine sediments in addition this record suggests relatively high temperatures and distinct temperature fluctuations from 9000 4200 yr bp if compared with the 4200 0 yr bp period matching the regional soil formation erosion and timberline patterns the 13c record appears to have been controlled mainly by soil formation 14 300 9000 yr bp and by humidity variations 9000 0 yr bp copyright 2004 john wiley sons ltd

physics of crustal fracturing and chert dike formation triggered by asteroid impact 3 26 ga barberton greenstone belt south africa archean asteroid impacts reflected in the presence of spherule beds in the 3 2 3 5 ga barberton greenstone belt bgb south africa generated extreme seismic waves spherule bed s2 provides a field example it locally lies at the contact between the onverwacht and fig tree groups in the bgb which formed as a result of the impact of asteroid possibly 50 km diameter scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site where they widely damaged onverwacht rocks over much of the bgb lithified sediments near the top of the onverwacht group failed with opening mode fractures the underlying volcanic sequence then failed with normal faults and opening mode fractures surficial unlithified sediments liquefied and behaved as a fluid these liquefied sediments and some impact produced spherules filled near surface fractures today represented by swarms of chert dikes strong impact related tsunamis then swept the seafloor p waves and rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves the duration of extreme shaking was also far longer probably hundreds of seconds than that from strong earthquakes dynamic strains of 10 3 occurred from the surface and downward throughout the lithosphere shaking weakened the onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open mode fractures coast parallel opening mode fractures on the fore arc coast of chile formed as a result of megathrust events are the closest modern analogs it is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the onverwacht rocks

the eyjafjallajokull ad 2010 eruption and the preservation of medium sized eruptions in marine surface sediment offshore southern iceland the recent volcanic eruptions of eyjafjallajokull 2010 and grimsvotn 2011 demonstrated the risks that mediumsized explosive icelandic eruptions pose to the north atlantic region using the eyjafjallajokull 2010 eruption as a case study we assess how traceable such eruptions are in the marine sedimentary record at medial distances from the source and investigate which factors have affected the particle transport to the marine sedimentary archive during r v poseidon cruise 457 we recovered 13 box cores at 100 1600 m water depths and distances of 18 180 km southwest south and east of iceland volcanic glass shards from the uppermost surface sediment were analyzed for their major element composition by electron microprobe and assigned to their eruptive source by geochemical fingerprinting the predominantly basaltic particles are mostly derived from the katla grimsvotn lakagigar and bar arbunga vei ivotn volcanic systems we also identified rhyolitic particles from the askja 1875 and oraefajokull 1362 eruptions only three out of almost 900 analyzed glass shards are derived from the recent eyjafjallajokull 2010 eruption suggesting that medium sized eruptions are only poorly preserved in marine sediments located at medial distances southwest to east of iceland we conclude that the frequency of past medium sized eruptions is likely higher than detectable in this archive

vertical density currents a review of their potential role in the deposition and interpretation of deep sea ash layers marine tephra layers form important chronostratigraphic markers and may also provide information on eruption dynamics and chronology recent experiments and field data from the 1991 pinatubo eruption challenge tacit assumptions that following atmospheric fallout on the ocean surface marine sedimentation of ash grade material occurs by stokes law settling of individual grains laboratory experiments have demonstrated that vertical density currents can be initiated at representative mass flux rates further experiments described herein involving sustained particle fluxes entering stratified environments demonstrate that ash particles can decouple from the transporting fluid whose vertical motions are limited by the stable density gradient in the ocean vertical density currents generated by ash loading and gravitational destabilization of the water column can overcome the strong stable density gradients in the ocean and transport ash particles vertically 1 3 orders of magnitude faster than possible by stokesian settling greatly reducing their residence time sea bed sedimentation is inferred to involve settling of individual coarse or dense grains through the entire water column plus suspension fallout from the polydisperse turbid layer delivered by convective plumes yielding normal distribution grading the turbid layer may continue laterally as a nepheloid current under the influence of bottom slopes and or geostrophic forces either mechanism possibly modifying the grain size distribution of the suspension and hence the resulting ash layer by transporting selected fractions into different depositional locations consequently and regardless of any subsequent reworking deep sea ash isopachs may not directly reflect an eruptive signal and the ash layers may not directly record the order rate or location of arrival of ash particles at the ocean surface

saturn s zonal wind profile in 2004 2009 from cassini iss images and its long term variability abstract five years of cassini imaging science subsystem images from 2004 to 2009 are analyzed in this work to retrieve global zonal wind profiles of saturn s northern and southern hemispheres in the methane absorbing bands at 890 and 727 nm and in their respective adjacent continuum wavelengths of 939 and 752 nm a complete view of saturn s global circulation including the equator at two pressure levels in the tropopause 60 mbar to 250 mbar with the mt filters and in the upper troposphere from 350 mbar to 500 mbar with the cb filter set is presented both zonal wind profiles available at the supplementary material section show the same structure but with significant differences in the peak of the eastward jets and the equatorial region including a region of positive vertical shear symmetrically located around the equator between the 10 c

a facies model for a submarine volcaniclastic apron the miocene manukau subgroup new zealand submarine volcaniclastic aprons of emergent volcanoes provide a long term record of their history and are preserved long after the source has been eroded following the cessation of volcanism a facies model for submarine volcaniclastic aprons is necessary to guide interpretation of ancient uplifted successions and to understand the sedimentary and volcanic processes associated with apron formation the manukau subgroup new zealand includes a well exposed miocene submarine apron consisting of the products eroded and erupted from a basaltic andesite volcanic island complex the depositional environment setting and stratigraphy of the volcaniclastic apron are well constrained allowing us to conduct a detailed facies analysis and to assess the apron architecture lateral downslope and vertical progradational sequences reflect erosion of the subaerial edifice and the direct and subsequent products of contemporaneous volcanism the volcaniclastic facies vary largely as a function of proximity to source and the types of rock resedimented the dominant transport method was high density turbidity currents with lesser contributions from debris avalanches debris flows and dilute turbidity currents in addition eruptions from volcanic vents located within the apron are recorded as interbedded water settled and resedimented pumice and scoria deposits explosive eruptions lavas hyaloclastite and crosscutting dikes effusive eruptions the proximal apron is largely composed of coarse breccia conglomerate that is locally chaotically disrupted due to the instability promoted by steep depositional slopes and rapid sedimentation rates the subangular cobbles and boulders originated from nearby probably coastal variably vesicular and variably oxidized lavas and were deposited as lithic lags in this highly energetic environment very little sandstone was deposited or preserved and freshly erupted pumice deposits were quickly resedimented in the medial apron poorly sorted conglomerate and thickly bedded sandstone which includes pumice lapilli built up over the distal apron sequence of thinly bedded fine grained volcaniclastic mudstone sandstone the presence of pumice lapilli suggests that progradation was a response to voluminous explosive eruptions due to their low densities and easy entrainment pumice lapilli largely bypassed deposition on the steep proximal apron and were sedimented onto the more gently sloping medial apron hence coarse pumice clasts were transported much farther from their source than their dense lithic counterparts the apron records a shallowing upward sequence and the final submarine volcaniclastic facies was deposited within channels that incised the medial and distal apron the channels record an initial eruption hiatus and erosion of the edifice well rounded clasts recycled from the uplifted breccia conglomerate were initially deposited followed by pumiceous and scoriaceous pebbly sandstone from renewed explosive eruptions submarine volcaniclastic aprons involve rapid and prolific sedimentation from multiple source locations clasts of different densities and origins and can include the direct products of contemporaneous volcanism the facies architecture however can be clearly divided into proximal medial and distal volcaniclastic apron environments the proximal apron is dominated by the coarsest clasts steep slopes rapid sedimentation rates and seismic activity in the steep proximal apron promote slumping the medial and distal aprons are more likely to record explosive activity debrisflow events and eruption hiatuses due to the gentler slopes and depositional rather than erosional setting

dynamics of saturn s great storm of 2010 2011 from cassini iss and rpws saturn s quasi periodic planet encircling storms are the largest convecting cumulus outbursts in the solar system the last eruption was in 1990 sanchez lavega a 1994 chaos 4 341 353 a new eruption started in december 2010 and presented the first ever opportunity to observe such episodic storms from a spacecraft in orbit around saturn fischer g et al 2011 nature 475 75 77 sanchez lavega a et al 2011 nature 475 71 74 fletcher l n et al 2011 science 332 1413 here we analyze images acquired with the cassini imaging science subsystem iss which captured the storm s birth evolution and demise in studying the end of the convective activity we also analyze the saturn electrostatic discharge sed signals detected by the radio and plasma wave science rpws instrument the storm s initial position coincided with that of a previously known feature called the string of pearls sops at 33 n planetocentric latitude intense cumulus convection at the westernmost point of the storm formed a particularly bright head that drifted at 26 9 0 8 m s 1 negative denotes westward motion on january 11 2011 the size of the head was 9200 km and up to 34 000 km in the north south and east west dimensions respectively rpws measurements show that the longitudinal extent of the lightning source expanded with the storm s growth the storm spawned the largest tropospheric vortex ever seen on saturn on january 11 2011 the anticyclone was sized 11 000 km by 12 000 km in the north south and east west directions respectively between january and september 2011 the vortex drifted at an average speed of 8 4 m s 1 we detect anticyclonic circulation in the new vortex the vortex s size gradually decreased after its formation and its central latitude shifted to the north the storm s head moved westward and encountered the new anticyclone from the east in june 2011 after the head vortex collision the rpws instrument detected that the sed activities became intermittent and declined over 40 days until the signals became undetectable in early august in late august the sed radio signals resurged for 9 days the storm left a vast dark area between 32 n and 38 n latitudes surrounded by a highly disturbed region that resembles the mid latitudes of jupiter using iss images we also made cloud tracking wind measurements that reveal differences in the cloud level zonal wind profiles before and after the storm

saturn atmospheric dynamics one year after cassini long lived features and time variations in the drift of the hexagon abstract we examine saturn s atmospheric dynamics with observations in the visible range from ground based telescopes and hubble space telescope hst we present a detailed analysis of observations acquired during 2018 obtaining drift rates of major meteorological systems from the equator to the north polar hexagon a system of polar storms that appeared in the planet in march 2018 and remained active with a complex phenomenology at least until september is analyzed elsewhere sanchez lavega et al 2019 many of the regular cloud features visible in 2018 are long lived and can be identified in saturn images in 2017 and in some cases for up to a decade using also cassini iss images without considering the polar storms the most interesting long lived cloud systems are i a bright white spot in the equatorial zone that can be tracked continuously since 2014 with minimal changes in its zonal velocity which was 444 3 3 1 m s 1 in 2014 and 452 4 1 7 m s 1 in 2018 this velocity is remarkably different from the zonal winds at the cloud level at its latitude during the cassini mission and is closer to zonal winds obtained at the time of the voyagers flybys and to zonal winds from cassini vims infrared images of the lower atmosphere ii a large long lived anticyclone vortex here av that formed after the great white spot of 2010 2011 this vortex has changed significantly in visual contrast drift rate and latitude with minor changes in size over the last years iii a system of subpolar vortices at latitudes 60 65 n present at least since 2011 these vortices and additional atmospheric features here studied follow drift rates consistent with zonal winds obtained by cassini we also present a study of the positions of the vertices of saturn s north polar hexagon from 2015 to 2018 these measurements are compared with previous analyses during the cassini mission 2007 2014 observations with hst in the 90s and data from the voyagers in 1980 1981 to explore the long term variability of the hexagon s drift rate we find variations in the drift rate of the hexagon through these epochs that can not be fit by seasonal changes in the polar area instead the different drift rates reinforce the role of the north polar spot that was present in the voyager epoch and in the early 90s to cause a faster drift rate of the hexagon at that time compared with the current slower one

construction of volcanic records from marine sediment cores a review and case study montserrat west indies detailed knowledge of the past history of an active volcano is crucial for the prediction of the timing frequency and style of future eruptions and for the identification of potentially at risk areas subaerial volcanic stratigraphies are often incomplete due to a lack of exposure or burial and erosion from subsequent eruptions however many volcanic eruptions produce widely dispersed explosive products that are frequently deposited as tephra layers in the sea cores of marine sediment therefore have the potential to provide more complete volcanic stratigraphies at least for explosive eruptions nevertheless problems such as bioturbation and dispersal by currents affect the preservation and subsequent detection of marine tephra deposits consequently cryptotephras in which tephra grains are not sufficiently concentrated to form layers that are visible to the naked eye may be the only record of many explosive eruptions additionally thin reworked deposits of volcanic clasts transported by floods and landslides or during pyroclastic density currents may be incorrectly interpreted as tephra fallout layers leading to the construction of inaccurate records of volcanism this work uses samples from the volcanic island of montserrat as a case study to test different techniques for generating volcanic eruption records from marine sediment cores with a particular relevance to cores sampled in relatively proximal settings i e tens of kilometres from the volcanic source where volcaniclastic material may form a pervasive component of the sedimentary sequence visible volcaniclastic deposits identified by sedimentological logging were used to test the effectiveness of potential alternative volcaniclastic deposit detection techniques including point counting of grain types component analysis glass or mineral chemistry colour spectrophotometry grain size measurements xrf core scanning magnetic susceptibility and x radiography this study demonstrates that a set of time efficient non destructive and high spatial resolution analyses e g xrf core scanning and magnetic susceptibility can be used effectively to detect potential cryptotephra horizons in marine sediment cores once these horizons have been sampled microscope image analysis of volcaniclastic grains can be used successfully to discriminate between tephra fallout deposits and other volcaniclastic deposits by using specific criteria related to clast morphology and sorting standard practice should be employed when analysing marine sediment cores to accurately identify both visible tephra and cryptotephra deposits and to distinguish fallout deposits from other volcaniclastic deposits

tephra sedimentation during the 2010 eyjafjallajokull eruption iceland from deposit radar and satellite observations the april may 2010 eruption of eyjafjallajokull volcano iceland was characterized by a nearly continuous injection of tephra in the atmosphere that affected various economic sectors in iceland and caused a global wide interruption of air traffic eruptive activity during 4 8 may 2010 was characterized based on short duration physical parameters in order to capture transient eruptive behavior of a long lasting eruption i e total grainsize distribution erupted mass and mass eruption rate averaged over 30 minute activity resulting 30 minute total grainsize distribution based on both ground and msg seviri satellite measurements is characterized by mdphi of about 2 phi and a fine ash content of about 30wt accumulation rate varied by two orders of magnitude with an exponential decay away from the vent whereas mdphi shows a linear increase until about 18 km from vent reaching a plateau of about 4 5 phi between 20 56 km associated mass eruption rate is in between 0 6 1 2 x 10 5 kg s 1 in situ sampling showed how fine ash mainly fell as aggregates of various typologies about 5 to 9 wt of the erupted mass remained in the cloud up to 1000 km from the vent suggesting that nearly half of the ash 7 phi settled as aggregates within the first 60 km particle sphericity and shape factor varied between 0 4 and 1 with no clear correlation with size and distance from vent our experiments also demonstrate how satellite retrievals and doppler radar grainsize detection can provide real time description of the source term but for a limited particle size range

limited global change due to the largest known quaternary eruption toba 74 kyr bp abstract the 74 kyr bp super eruption of toba volcano in sumatra is the largest known quaternary eruption on the basis of preserved deposits the eruption magnitude has been estimated at 7 10 15 kg 2800 km 3 of dense magma the largest sulphate anomaly in the greenland ice sheet project 2 core has been identified as fallout from toba s stratospheric aerosol veil correlation of the sulphate and oxygen isotope stratigraphy of the ice core suggests that the toba eruption might have played a role in triggering a millennium of cool climate prior to dansgaard oeschger event 19 although a comparable stadial preceded event 20 a possible 6 yr duration volcanic winter immediately following the eruption has also been proposed as the cause of a putative bottleneck in human population supporting in a general way the garden of eden model for the origin of modern humans however along with counter arguments regarding the timing of any demographic crash there remain major gaps in our understanding of the 74 kyr bp toba eruption that hinder attempts to model its global atmospheric and climatic and hence human consequences the tephra record reveals basic aspects of the eruption style but calculations of the duration and hence intensity and plume height of the event are poorly constrained furthermore estimates of the sulphur yield of the erupting magma central to predictions of its atmospheric and climatic impacts vary by two orders of magnitude 3 5 330 10 10 kg previous estimates of globally averaged surface cooling of 3 5 c after the eruption are probably too high a figure closer to 1 c appears more realistic the volcanological uncertainties need to be appreciated before accepting arguments for catastrophic consequences of the toba super eruption

the 26 5 ka oruanui eruption new zealand an introduction and overview abstract the 26 5 ka oruanui eruption from taupo volcano in the central north island of new zealand is the largest known wet eruption generating 430 km3 of fall deposits 320 km3 of pyroclastic density current pdc deposits mostly ignimbrite and 420 km3 of primary intracaldera material equivalent to 530 km3 of magma erupted magma is 99 rhyolite and 90 pdc deposits range from mm to cm thick ultra thin veneers enclosed within fall material to 200 m thick ignimbrite in proximal areas the farthest travelled 90 km most energetic pdcs velocities 100 m s 1 occurred during phase 8 but the most voluminous pdc deposits were emplaced during phase 10 grain size variations in the pdc deposits are complex with changes seen vertically in thick proximal accumulations being greater than those seen laterally from near source to most distal deposits modern lake taupo partly infills the caldera generated during this eruption a 140 km2 structural collapse area is concealed beneath the lake while the lake outline reflects coeval peripheral and volcano tectonic collapse early eruption phases saw shifting vent positions development of the caldera to its maximum extent indicated by lithic lag breccias occurred during phase 10 the oruanui eruption shows many unusual features its episodic nature wide range of depositional conditions in fall deposits of very wide dispersal and complex interplay of fall and pdc activity

saturn s cloud structure inferred from cassini iss abstract using high resolution cassini iss images with wavelengths ranging from the ultraviolet to the near infrared we have retrieved saturn s atmospheric aerosol structure and properties for a broad range of latitudes in the southern hemisphere the observations are consistent with two distinct layers of haze above a scattered cloud each layer is characterized by a vertical location an optical thickness and an effective mean particle size all of which vary with latitude the tropospheric haze is optically thickest and extends to the greatest heights 40 mbar over the equator its top surface is at significantly greater depths 150 mbar at mid latitudes the height of the haze correlates well with position of the tropopause as indicated by the temperature field beneath this haze we find a scattered denser cloud responsible for small scale contrasts at an average depth of 1 75 0 4 bar with some features as deep as 2 5 bar or greater

an upper pliocene coarse pumice breccia generated by a shallow submarine explosive eruption milos greece the filakopi pumice breccia fpb is a very well exposed pliocene volcaniclastic unit on milos greece and has a minimum bulk volume of 1 km3 it consists of three main units a basal lithic breccia 4 8 m mainly composed of angular to subangular andesitic and dacitic clasts up to 2 6 m in diameter b very thickly bedded poorly sorted pumice breccia 16 17 m and c very thick reversely graded grain supported coarse pumice breccia 6 5 20 m at the top the depositional setting is well constrained as shallow marine up to a few hundred metres by overlying fossiliferous and bioturbated mudstone this large volume of fine pumice clasts is interpreted to be the product of an explosive eruption from a submarine vent because 1 pumice clasts are the dominant component 2 the coarse pumice clasts 64 mm have complete quenched margins 3 very large 1 m pumice clasts are common 4 overall the formation shows good hydraulic sorting and 5 a significant volume of ash was deposited together with the coarsest pyroclasts

sediment laden fresh water above salt water nonlinear simulations when a layer of particle laden fresh water is placed above clear saline water both double diffusive and rayleigh taylor instabilities may arise the present investigation extends the linear stability analysis of burns meiburg j fluid mech vol 691 2012 pp 279 314 into the nonlinear regime by means of two and three dimensional direct numerical simulations dns the initial instability growth in the dns is seen to be consistent with the dominant modes predicted by the linear stability analysis the subsequent vigorous growth of individual fingers gives rise to a secondary instability and eventually to the formation of intense plumes that become detached from the interfacial region the simulations show that the presence of particles with a stokes settling velocity modifies the traditional double diffusive fingering by creating an unstable nose region in the horizontally averaged profiles located between the upward moving salinity and the downward moving sediment interface the effective thickness l s l c of the salinity sediment interface grows diffusively as does the height h of the nose region the ratio h l s initially grows and then plateaus at a value that is determined by the balance between the flux of sediment into the rose region from above the double diffusive rayleigh taylor flux out of the nose region below and the rate of sediment accumulation within the nose region for small values of h l s leqslant o 0 1 double diffusive fingering dominates while for larger values h l s geqslant o 0 1 the sediment and salinity interfaces become increasingly separated in space and the dominant instability mode becomes rayleigh taylor like a scaling analysis based on the results of a parametric study indicates that h l s is a linear function of a single dimensionless grouping that can be interpreted as the ratio of inflow and outflow of sediment into the nose region the simulation results furthermore indicate that double diffusive and rayleigh taylor instability mechanisms cause the effective settling velocity of the sediment to scale with the overall buoyancy velocity of the system which can be orders of magnitude larger than the stokes settling velocity while the power spectra of double diffusive and rayleigh taylor dominated flows are qualitatively similar the difference between flows dominated by fingering and leaking is clearly seen when analysing the spectral phase shift for leaking dominated flows a phase locking mechanism is observed which intensifies with time hence the leaking mode can be interpreted as a fingering mode which has become phase locked due to large scale overturning events in the nose region as a result of a rayleigh taylor instability

climatic reconstruction for the younger dryas early holocene transition and the little ice age based on paleo extents of argentiere glacier french alps abstract investigation of holocene extents of mountain glaciers along with the related naturally driven climate conditions helps improve our understanding of glacier sensitivity to ongoing climate change here we present the first holocene glacial chronology in the mont blanc massif argentiere glacier in the french alps based on 25 in situ produced cosmogenic 10be dates of moraines and glacial bedrocks the obtained ages from mapped sequences of moraines at three locations reveal that the glacier retreated from its lateglacial extent and oscillated several times between 11 7 ka and 10 4 ka i e during the younger dryas early holocene yd eh transition before substantially retreating at 10 4 ka climate conditions corresponding to the past extents of argentiere glacier during the yd eh transition 11 ka and the little ice age lia were modelled with two different approaches by determining summer temperature differences from reconstructed ela rises and by using a positive degree day pdd mass balance model the ela rise reconstructions yield a possible range of temperatures for the yd eh transition that were lower by between 3 0 and 4 8 c compared to the year 2008 depending on the choice of the ela sensitivity to temperature the results from the pdd model indicate temperatures lower by 3 6 5 5 c during the yd eh transition than during the 1979 2002 period for the lia our findings highlight the role of local precipitation changes superimposed on the dominant temperature signal in the detailed evolution of the glacier overall this study highlights the challenge that remains in accurately inferring paleoclimate conditions from past glacier extents

rock glacier development in the northern calcareous alps at the pleistocene holocene boundary abstract relict rock glaciers provide information on past discontinuous permafrost and former mean annual air temperatures a lack of records showing former permafrost distribution along the northern alpine fringe prompted the investigation and numerical dating of a belt of relict rock glaciers in the karwendel mountains of the northern calcareous austrian alps in two neighbouring cirques that were still glaciated during the early younger dryas eleven 36cl exposure ages from boulder surfaces were obtained the ages imply the onset of rock glacier activity around 12 3 ka with subsequent stabilization and permafrost melt out no later than 10 1 ka hence rock glacier formation coincided with glacier retreat in the cirques around the mid younger dryas and continued into the early holocene as permafrost induced features the rock glacier termini indicate the local past lower limit of discontinuous permafrost in open cirque floors at 2000 m asl which is around 400 m lower than during the mid twentieth century at comparable locations in the karwendel mountains thus a mean annual air temperature reduction of 2 6 to 3 8 c relative to the mid twentieth century is inferred based on a minimum glacier equilibrium line altitude in the cirques a summer temperature reduction of less than 2 6 to 1 8 c is shown suggesting an increased seasonality at the time of rock glacier activity