the effect of bathymetric filtering on nearshore process model results nearshore wave and flow model results are shown to exhibit a strong sensitivity to the resolution of the input bathymetry in this analysis bathymetric resolution was varied by applying smoothing filters to high resolution survey data to produce a number of bathymetric grid surfaces we demonstrate that the sensitivity of model predicted wave height and flow to variations in bathymetric resolution had different characteristics wave height predictions were most sensitive to resolution of cross shore variability associated with the structure of nearshore sandbars flow predictions were most sensitive to the resolution of intermediate scale alongshore variability associated with the prominent sandbar rhythmicity flow sensitivity increased in cases where a sandbar was closer to shore and shallower perhaps the most surprising implication of these results is that the interpolation and smoothing of bathymetric data could be optimized differently for the wave and flow models we show that errors between observed and modeled flow and wave heights are well predicted by comparing model simulation results using progressively filtered bathymetry to results from the highest resolution simulation the damage done by over smoothing or inadequate sampling can therefore be estimated using model simulations we conclude that the ability to quantify prediction errors will be useful for supporting future data assimilation efforts that require this information

permian and triassic greenhouse crises paleoclimatic time series from permian and triassic paleosols reveal transient episodes of unusually warm and wet conditions interrupting long periods of cool and dry conditions usual for calcareous red paleosols some of these paleoclimatic events are known from stomatal index of fossil lepidopteris leaves to have been episodes of elevated global atmospheric co2 the magnitude of 19 known permian and triassic greenhouse crises varied considerably and they offer new evidence for the relationship between paleoclimate and atmospheric co2 levels these greenhouse crises also had marked effects on global lowland vegetation introducing frost sensitive tropical lycopsids to high latitudes and drought tolerant conifers to low latitude lowlands greenhouse events punctuate phases in plant evolution ottokaria callipteris plumsteadia rufloria lidgettonia tatarina pleuromeia and dicroidium scytophyllum floras greenhouse events also punctuate the evolution of reptilian dynasties successive pelycosaur dinocephalian dicynodont rhynchosaur and dinosaur faunas and respiratory adaptations such as enlarged bony secondary palate greenhouse crises of the late and middle permian were the most severe known and suggest a role for atmospheric pollution with ch4 and co2 in those mass extinction events probably from thermogenic cracking of coals by intrusive feeder dikes of flood basalts because of formalities in boundary definition these mass extinctions are neither end permian nor end guadalupian but upper changhsingian and mid capitanian respectively

a parametric model for barred equilibrium beach profiles two dimensional implementation abstract a method is proposed for estimating approximate 2dh bathymetry including longshore variable shoreline and sand bar systems the method is based on but extends a previous 1dh model of holman et al 2014 by assuming that this 1dh equilibrium barred bathymetry can be applied for any offshore location if the corresponding mean shoreline orientation is taken to be the local average over a longshore span that is k times the offshore distance thus locations close to the beach are sensitive to shoreline and bar details while more seaward locations are steadily less sensitive the model was tested against 14 ground truth surveys collected over two years and under widely ranging environmental condition spanning a 500 by 1000 m region models inputs for the shoreline and sand bar positions were extracted from measured bathymetries for these tests but would be derived from other sources in real applications while deep water inputs were found from a single deep water survey the model yielded complete 2dh bathymetry maps that were a very good approximation of ground truth the mean bias and rms error over the full region and data set were 0 27 m and 0 49 m respectively and proxy bathymetries were visually very similar to ground truth the largest source of error was occasional cross shore misplacements of otherwise realistic looking sand bars results were only weakly dependent on the value of k when tested over a factor of four and the default value of 1 0 is recommended performance statistics using input locations for the shoreline and bar crest that were manually digitized from breaking patterns in rectified optical time exposure images were no worse than bathymetry based inputs hydrodynamic predictions using these bathymetries would be a substantial improvement over those from monotonic or even barred 1dh equilibrium proxy bathymetries

climate simulation of the latest permian implications for mass extinction life at the permian triassic boundary ca 251 ma underwent the largest disruption in earth s history paleoclimatic data indicate that earth was significantly warmer than present and that much of the ocean was anoxic or euxinic for an extended period of time we present results from the first fully coupled comprehensive climate model using paleo geography for this time period the coupled climate system model simulates warm high latitude surface air temperatures related to elevated carbon dioxide levels and a stagnate global ocean circulation in concert with paleodata indicating low oxygen levels at ocean depth this is the first climate simulation that captures these observed features of this time period

observations of nearshore circulation alongshore uniformity 1 nearshore circulation observed for 4 months on a 200 m long stretch of natural beach during the sandyduck field experiment is shown to be alongshore uniform an alongshore momentum balance between wind and wave forcing and bottom stress cross shore integrated between the shoreline and approximately 4 m water depth holds on each of five instrumented cross shore transects skill 0 87 the corresponding five best fit drag coefficients are similar consistent with the assumption that terms in the momentum balance associated with alongshore nonuniformity are negligible in addition the alongshore nonuniformity of the circulation and bathymetry were examined at five cross shore locations except near the shoreline the circulation and bathymetry were rarely strongly alongshore nonuniform and the circulation nonuniformities were usually no larger than expected from current meter noise alone near the shoreline the bathymetry was more irregular and the circulation was often detectably nonuniform although no relationship between bathymetric and circulation nonuniformities was found the closure of the alongshore momentum balances on cross shore transects and the observed alongshore uniformity of the circulation on four of five alongshore transects demonstrates that the simplified dynamics of alongshore uniform circulation are valid during the experiment

alongshore momentum balances in the nearshore the one dimensional time averaged over many wave periods along shore momentum balance between forcing by wind and breaking waves and the bottom stress is examined with field observations spanning a wide range of con ditions on a barred beach near bottom horizontal currents were measured for 2 months at 15 locations along a cross shore transect extending 750 m from the shoreline to 8 m water depth the hourly averaged bottom stress was estimated from observed currents using a quadratic drag law the wave radiation stress was estimated in 8 m depth from an array of pressure sensors and the wind stress was estimated from an anemometer at the seaward end of a nearby pier the combined wind and wave forcing integrated over the entire cross shore transect is balanced by the integrated bottom stress the wind stress contributes about one third of the forcing over the transect analysis of the momentum balances in different cross shore regions shows that in the surf zone wave forcing is much larger than wind forcing and that the bottom drag coefficient is larger in the surf zone than farther seaward consistent with earlier studies

a multi data stream assimilation framework for the assessment of volcanic unrest abstract active volcanoes pose a constant risk to populations living in their vicinity significant effort has been spent to increase monitoring and data collection campaigns to mitigate potential volcano disasters to utilize these datasets to their fullest extent a new generation of model data fusion techniques is required that combine multiple disparate observations of volcanic activity with cutting edge modeling techniques to provide efficient assessment of volcanic unrest the purpose of this paper is to develop a data assimilation framework for volcano applications specifically the ensemble kalman filter enkf is adapted to assimilate gps and insar data into viscoelastic time forward finite element models of an evolving magma system to provide model forecasts and error estimations since the goal of this investigation is to provide a methodological framework our efforts are focused on theoretical development and synthetic tests to illustrate the effectiveness of the enkf and its applicability in physical volcanology the synthetic tests provide two critical results 1 a proof of concept for using the enkf for multi dataset assimilation in investigations of volcanic activity and 2 the comparison of spatially limited but temporally dense gps data with temporally limited insar observations for evaluating magma chamber dynamics during periods of volcanic unrest results indicate that the temporally dense information provided by gps observations results in faster convergence and more accurate model predictions however most importantly the synthetic tests illustrate that the enkf is able to swiftly respond to data updates by changing the model forecast trajectory to match incoming observations the synthetic results demonstrate a great potential for utilizing the enkf model data fusion method to assess volcanic unrest and provide model forecasts the development of these new techniques provides 1 a framework for future applications of rapid data assimilation and model development during volcanic crises 2 a method for hind casting to investigate previous volcanic eruptions including potential eruption triggering mechanisms and precursors and 3 an approach for optimizing survey designs for future data collection campaigns at active volcanic systems

remote sensing of breaking wave phase speeds with application to non linear depth inversions abstract a number of existing models for surface wave phase speeds linear and non linear breaking and non breaking waves are reviewed and tested against phase speed data from a large scale laboratory experiment the results of these tests are utilized in the context of assessing the potential improvement gained by incorporating wave non linearity in phase speed based depth inversions the analysis is focused on the surf zone where depth inversion accuracies are known to degrade significantly the collected data includes very high resolution remote sensing video and surface elevation records from fixed in situ wave gages wave phase speeds are extracted from the remote sensing data using a feature tracking technique and local wave amplitudes are determined from the wave gage records and used for comparisons to non linear phase speed models and for non linear depth inversions a series of five different regular wave conditions with a range of non linearity and dispersion characteristics are analyzed and results show that a composite dispersion relation which includes both non linearity and dispersion effects best matches the observed phase speeds across the domain and hence improves surf zone depth estimation via depth inversions incorporating non linearity into the phase speed model reduces errors to o 10 which is a level previously found for depth inversions with small amplitude waves in intermediate water depths using linear dispersion considering the controlled conditions and extensive ground truth this appears to be a practical limit for phase speed based depth inversions finally a phase speed sensitivity analysis is performed that indicates that typical nearshore sand bars should be resolvable using phase speed depth inversions however increasing wave steepness degrades the sensitivity of this inversion method

evidence for a fungal event methane hydrate release and soil erosion at the permian triassic boundary in southern israel abstract the transition between the permian and the triassic systems in israel is evident only in the subsurface two cores from the makhtesh qatan 2 core 9 and avedat 1 core 5 drillholes in which the permian triassic boundary was found marked by a fungal event were sampled at close intervals and analysed for palynological petrographical mineralogical chemical and isotopic properties three palynozones were recorded lueckisporites virkkia zone late permian fungal event and endosporites papillatus zone early triassic the fungul event occurs in a narrow interval of 1 m and contains almost exclusively fungal remains and recycled woody particles the two cores consist of laminated sediments mainly siliciclastic that were deposited in very shallow to restricted marine environments with a minor presence of evaporites and no bioturbation green glauconitic material and framboidal pyrite suggest suboxic conditions even in the shallow waters reddish brown particles and plant fragments derived from nearby soils now outcropping on the northeast side of the dead sea these materials as well as recycled brown glauconitic grains suggest a drop in sea level and intense erosion before sedimentation which was apparently continuous major and trace element compositions including rare earth elements do not exhibit any particular pattern that might be related to the fungul event or to other core intervals the rare earth element patterns are basically normal and their concentration correlates with the clay content reflecting the provenance of the arabo nubian massif and its sedimentary rims iridium results were mostly at the background level and therefore the two distinct anomalous values are inconclusive microspherules mainly of 2 m size and al si composition were observed in a few samples in both cores their origin could not be determined though they are considered to be natural there was no evidence for shocked quartz 13corg excursion exhibits a marked negative shift in both cores just below the fungal event the lowest values 37 and 42 are among the lowest ever recorded near the permian triassic boundary and suggest large scale release of methane hydrates

video based nearshore bathymetry estimation in macro tidal environments abstract video based depth inversion through the linear dispersion relation for free surface waves using the cross spectral correlation analysis cbathy holman et al 2013 is applied for the first time in a highly energetic macro tidal environment in the south west of england at porthtowan this application of cbathy reveals two main issues 1 inaccurate depth estimations on inter camera boundaries when multiple cameras are used and 2 significantly less accurate depth estimates over the whole domain during spring tide compared to neap tide inaccuracies of around 35 of the local depths are found during spring tide these two issues are not only important in macro tidal environments the camera boundary issue has been reported in numerous video camera sites and the deviation in accuracy during tidal levels is a function of the tidal range in combination of the vertical camera position to overcome the two issues a camera boundary solution and a floating pixel solution meaning moving pixels in a horizontal plane as function of the tidal elevation are proposed here with the modifications cbathy is capable of estimating depths in the sub tidal zone with an accuracy in the order of 10 of the local depth irrespective to the local tidal regime however for the very upper part of the beach face less accurate results are found due to the reduced validity of the linear dispersion relation in that region due to the non linear behaviour of breaking waves and wave current interactions the improvements persist across all bathymetry survey campaigns at porthtowan and when compared to other well known argus video system sites the importance of the floating pixels is apparent

intrabasin variability of the carbon isotope record across the permian triassic transition sverdrup basin arctic canada abstract a major late paleozoic depocentre the sverdrup basin canadian high arctic has been largely left out of the latest permian extinction debate as early workers presumed middle to late permian strata were absent basin scale sequence stratigraphic and chemostratigraphic correlations indicate late permian strata are only missing on the basin margins where they were removed by sub triassic erosion whereas continuous deposition is recorded in the basin centre the varying degree of sub triassic erosion has significant impact on the carbon isotope record across the latest permian extinction event where both the apparent rate and magnitude of carbon isotope shift vary as a function of basin position the intrabasin variability in apparent 13corg shift across the event is equivalent to that observed globally in contrast to the abrupt isotope shifts recorded on the basin margin similar to many records reported globally the basin centre section shows a systematic shift associated with the latest permian extinction the earth likely underwent a prolonged period of increasing environmental stress leading up to the event

observations of sand bar evolution on a natural beach waves currents and the location of the seafloor were measured on a barred beach for about 2 months at nine locations along a cross shore transect extending 255 m from 1 to 4 m water depth the seafloor location was measured nearly continuously even in the surf zone during storms with sonar altimeters mounted on fixed frames the crest of a sand bar initially located about 60 m from the shoreline moved 130 m offshore primarily when the offshore significant wave height exceeded about 2 m with 1 5 m of erosion near the initial location and 1 m of accretion at the final location an energetics type sediment transport model driven by locally measured near bottom currents predicts the observed offshore bar migration but not the slow onshore migration observed during low energy wave conditions the predicted offshore bar migration is driven primarily by cross shore gradients in predicted suspended sediment transport associated with quasi steady near bottom offshore flows these strong 50 cm s currents intensified near the bar crest by wave breaking are predicted to cause erosion on the shoreward slope of the bar and deposition on the seaward side the feedback amoung morphology waves circulation and sediment transport thus forces offshore bar migration during storms

nearshore subtidal bathymetry from time exposure video images time averaged over many wave periods nearshore video observations show the process of wave breaking as one or more white alongshore bands of high intensity across a known depth profile similar bands of dissipation can be predicted with a model describing the time averaged cross shore evolution of organized wave and roller energy this close correspondence between observed and modeled dissipation proxies is used to develop a new remote sensing technique termed subtidal beach mapper sbm to estimate nearshore bathymetry sbm operates on a time series of cross shore intensity profiles to resolve the pattern in depth change on a morphological timescale including overall gain or loss of sediment rather than to focus on the particular change induced by a single intensity profile from each intensity profile the breaking induced component is isolated by removing the contribution of background illumination and persistent foam the depth profile is updated based on a comparison between this video derived dissipation proxy and a cross shore profile of the dissipation of the roller energy this updating is implemented through time dependent mass balance equations for the seabed and a buffer layer above the bed sbm was tested using 1 year of hourly video data collected at egmond aan zee netherlands the dominant morphological changes observed from ground truth data were reproduced reasonably well including the shoreward migration of the outer bar and the net sediment gain in the profile root mean square differences between surveyed and sbm derived depth after 1 year of video based depth updating with an average of about 70 intensity profiles per month were smallest 0 2 m on the inner bar and largest 0 6 m in the outer bar trough with a profile average value of about 0 4 m despite the many processes included in sbm the implementation of a heuristic scaling function in the mass balance equations to spatially adjust morphological growth rates was essential to these results in particular near the shoreline where otherwise the profile is prone to an unrealistic deepening

beach wizard nearshore bathymetry estimation through assimilation of model computations and remote observations article i nfo a data model assimilation method called beach wizard is presented with which the nearshore subtidal bathymetry can be accurately estimated based on video derived observations of wave roller dissipation and variation of the intertidal shoreline and or radar derived observations of wave celerity using many consecutive images these observed properties are compared with numerical model results and through a simple optimal least squares estimator approach the estimated bathymetry is adjusted gradually for each image in order to improve the fit between model output and observations the key advantages of the technique are that it is based on multiple sources of information i e different remote sensors and or data products depends on only a few free parameters to which the model results are insensitive and shows good skill herein the technique is applied to a synthetic case and two sets of field data from sites at duck nc usa and egmond the netherlands the method which may be extended with observations of other properties from other sources than the three described in this paper can deliver coastal state information i e simultaneous updates of bathymetry waves and currents with high temporal and spatial resolution and can be used in conjunction with or instead of in situ measured data

development of a largely anoxic stratified ocean and its temporary massive mixing at the permian triassic boundary supported by the sulfur isotopic record systematic sulfur isotope data for whole rock sulfides have been obtained from the chert dominated continuous pelagic sedimentary sequences spanning the permian triassic p tr boundary at tenjinmaru in the chichibu terrane and at sasayama in the tanba terrane in japan the p tr boundary is characterized by the occurrence of siliceous shales in association with a carbonaceous black mudstone which is similar in appearance to the worldwide distributed cretaceous tertiary k t boundary claystone the observed data clearly demonstrate a significant bimodalism the 34s 32s ratios with respect to cdt are generally low throughout the middle permian ca 39 to 25 0 and show a remarkable increase beginning in the lower upper permian and persisting into the lower triassic ca 20 to 2 0 with a temporary and drastic negative shift down to roughly the same isotopic level as in the middle permian just at the suspected p tr boundary ca 41 to 23 0 interestingly the mode of isotopic excursion across the p tr boundary is in striking contrast to that across the k t boundary which was recently described at kawaruppu in hokkado japan the apparent extent of fractionation with respect to contemporaneous seawater sulfate in the high 34s 32s group lies within the range of 25 10 0 which is quantitatively equivalent to the currently confirmed range of kinetic isotope effect during bacterial dissimilatory sulfate reduction and that in the low 34s 32s group mostly exceeds this range giving the values typically in the range of 45 10 0 which is similar to what is generally observed in the present day oceanic sediments the present data would provide strong evidence for the development of a largely stagnant anoxic stratified ocean which presumably began to form in the lower upper permian and persisted into the lower triassic and for a brief episode of its temporary massive mixing just at the suspected p tr boundary such an oceanic oxic anoxic history may account to some extent for the relatively high enrichments of chalcophile elements in basal triassic sediments in the world and add a significant constraint to the current arguments on the cause and consequence of the terminal permian mass extinction

sequencing events across the permian triassic boundary guryul ravine kashmir india abstract the permian triassic boundary ptb section at guryul ravine kashmir india comprises a 100 m thick apparently conformable succession of mixed siliciclastic carbonate sediments deposited in a deep shelf or ramp setting this section although long important in debates concerning placement of the ptb has not previously been the focus of an integrated chemostratigraphic study in the present study samples from a 20 m thick interval straddling the ptb were analyzed for major and trace element concentrations toc tic rees and organic 13c 15n to investigate contemporaneous environmental changes the guryul ravine section exhibits a sequence of discrete events that provide potentially important information about the character and cause s of the ptb two transient negative c isotopic excursions within the upper changxingensis zone predate the late permian event horizon lpeh i e the global mass extinction event by 200 400 kyr and are associated with the onset of a major eustatic rise and with secondary extinction peaks these excursions may record minor environmental disturbances prior to the main end permian crisis supporting an intrinsic mechanism such as volcanism and climate change rather than an extrinsic mechanism such as a bolide impact the onset of a large 4 0 to 4 5 sustained negative c isotope shift marks the lpeh which is located at the zewan khunamuh formation contact 260 cm below the biostratigraphically defined ptb the guryul ravine section exhibits a stepwise extinction pattern with the largest peak between the lpeh and ptb and a secondary peak just above the ptb a pattern similar to that observed in the meishan d gssp

modeling the alongshore current on barred beaches mean alongshore currents observed on two barred beaches are compared with predictions based on the one dimensional time and depth averaged alongshore momentum balance between forcing by breaking waves wind and 10 100 km scale alongshore surface slopes bottom stress and lateral mixing the observations span 500 hours at egmond netherlands and 1000 hours at duck north carolina and include a wide range of conditions with maximum mean currents of 1 4 m s including rollers in the wave forcing results in improved predictions of the observed alongshore current structure by shifting the predicted velocity maxima shoreward and increasing the velocity in the bar trough compared with model predictions without rollers for these data wave forcing balances the bottom stress within the surfzone with the other terms of secondary importance the good agreement between observations and predictions implies that the one dimensional assumption holds for the range of conditions examined despite the presence of small alongshore bathymetric nonuniformities with stronger bathymetric variations the model skill deteriorates particularly in the bar trough consistent with earlier modeling and laboratory studies

nonlinear shear instabilities of alongshore currents over barred beaches the nonlinear dynamics of finite amplitude shear instabilities of alongshore currents in the nearshore surf zone over barred beach topography are studied using numerical experiments these experiments extend the recent study of allen et al 1996 which utilized plane beach constant slope topography by including shore parallel sandbars the model involves finite difference solutions to the nonlinear shallow water equations for forced dissipative initial value problems and employs periodic boundary conditions in the alongshore direction effects of dissipation are modeled by linear bottom friction forcing for the alongshore currents is specified using a model formulated by thornton and guza 1986 t g distinct classes of flows develop depending on the dimensionless parameter q the ratio of an advective to a frictional timescale for q greater than a critical value qc the flows are linearly stable for q qc q 0 the flow is unstable for small values of q equilibrated shear waves develop that propagate alongshore at phase speeds and wavelengths that are in agreement with predictions from linear theory for the most unstable mode at intermediate values of q unsteady vortices form and exhibit nonlinear interactions as they propagate alongshore occasionally merging pairing or being shed seaward of the sandbar at the largest values of q examined the resulting flow field resembles a turbulent shear flow a net effect of the instabilities at large aq is to distribute the time averaged alongshore momentum from local maxima of the t g forcing located over the sandbar and near the shore into the region of the trough the across shore structure of the time averaged alongshore current is in substantially better qualitative agreement with observations than that given by a steady frictional balance with t g forcing the results point to the possible existence in the nearshore surf zone of an energetic eddy field associated with instabilities of the alongshore current

warming the fuel for the fire evidence for the thermal dissociation of methane hydrate during the paleocene eocene thermal maximum dramatic warming and upheaval of the carbon system at the end of the paleocene epoch have been linked to massive dissociation of sedimentary methane hydrate however testing the paleocene eocene thermal maximum hydrate dissociation hypothesis has been hindered by the inability of available proxy records to resolve the initial sequence of events the cause of the paleocene eocene thermal maximum carbon isotope excursion remains speculative primarily due to uncertainties in the timing and duration of the paleocene eocene thermal maximum we present new high resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from ocean drilling program site 690 weddell sea southern ocean demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface water warming both of these findings support the thermal dissociation of methane hydrate as the cause of the paleocene eocene thermal maximum carbon isotope excursion furthermore the data reveal that the methane derived carbon was mixed from the surface ocean downward suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

analysis of the scale of errors in nearshore bathymetric data most studies of nearshore hydrodynamics sediment transport and morphology focus on bathymetric variability within a narrow band of spatial and temporal scales typically these studies rely on bathymetry estimates derived from field observations consisting of discrete samples in space and time with varying degrees of measurement error sampling limitations which result in aliasing and measurement errors can significantly contaminate variability at resolved scales and may lead to large errors in the representation of the scales of interest using a spectral analysis interpolation errors were analyzed for three different nearshore bathymetric data sets each of which targeted a different range of spatial scales bathymetric features that were unresolved or poorly resolved e g beach cusps introduced the potential for contamination in two of the data sets this contamination was significantly reduced using an appropriate scale controlled interpolation method leading to more accurate representations of the actual bathymetry an additional benefit of using scale controlled interpolation is that interpolation errors may be estimated independently of actual observations which allows one to design bathymetric sampling strategies that ensure that dominant scales are either resolved or largely removed finally interpolation errors corresponding to a particular sample design can be used to determine which interpolated values contribute usefully to a band limited analysis of bathymetric variability

global climate perturbations during the permo triassic mass extinctions recorded by continental tetrapods from south africa several studies of the marine sedimentary record have documented the evolution of global climate during the permo triassic mass extinction by contrast the continental records have been less exploited due to the scarcity of continuous sections from the latest permian into the early triassic the south african karoo basin exposes one of the most continuous geological successions of this time interval thus offering the possibility to reconstruct climate variations in southern laurasia from the middle permian to middle triassic interval both air temperature and humidity variations were estimated using stable oxygen 18op and carbon 13cc isotope compositions of vertebrate apatite significant fluctuations in both 18op and 13cc values mimic those of marine records and suggest that stable isotope compositions recorded in vertebrate apatite reflect global climate evolution in terms of air temperature oxygen isotopes show an abrupt increase of about 8 c toward the end of the wuchiapingian this occurred during a slight cooling trend from the capitanian to the permo triassic boundary ptb at the end of the permian an intense and fast warming of 16 c occurred and kept increasing during the olenekian these thermal fluctuations may be related to the emeishan south china and siberian volcanic paroxysms that took place at the end of the capitanian and at the end of the permian respectively vertebrate apatite 13cc partly reflects the important fluctuations of the atmospheric 13c values the differences with marine curves being likely due to the evolution of local humidity both the oxygen and carbon isotope compositions indicate that the ptb was followed by a warm and arid phase that lasted 6 ma before temperatures decreased during the late anisian toward that of the end permian environmental fluctuations occurring around the ptb that affected both continental and marine realms with similar magnitude likely originated from volcanism and methane release

high resolution carbon isotope changes in the permian triassic boundary interval chongqing south china implications for control and growth of earliest triassic microbialites abstract high resolution 13 c carb analysis of the permian triassic boundary ptb interval at the laolongdong section beibei near the city of chongqing south china encompasses the latest permian and earliest triassic major facies changes in the south china block scb microbialites form a distinctive unit in the lowermost 190 cm above the top of the changhsing formation latest permian at laolongdong comparable to a range of earliest triassic sites in low latitudes in the tethyan area the data show that declining values of 13 c carb well known globally began at the base of the microbialite high positive values 3 to 4 ppt of 13 c carb in the late permian are interpreted to indicate storage of 12 c in the deep waters of a stratified ocean that was released during ocean overturn in the earliest triassic contributing to the distinctive fall in isotope values this interpretation has been stated by other authors and is followed here the 13 c carb curve shows fluctuations within the microbialite unit which are not reflected in the microbialite structure comparisons between microbialite branches and adjacent micritic sediment show little difference in 13 c carb demonstrating that the microbialite grew in equilibrium with surrounding seawater the early triassic microbialites are interpreted to be a response to upwelling of bicarbonate rich poorly oxygenated water in low latitudes of tethys ocean consistent with current ocean models for the ptb interval however the decline of 13 c carb may be due to a combination of processes including productivity collapse resulting from mass extinction return of deep water to ocean surface oxidation of methane released from methane hydrate destabilisation and atmospheric deterioration nevertheless build up of bicarbonate rich anoxic deep waters may be expected as a result of the partial isolation of tethys due to continental geography release of bicarbonate rich deep water by ocean upwelling in the earliest triassic may have been an inevitable consequence of this combination of circumstances

methane driven oceanic eruptions and mass extinctions focusing on the permian triassic boundary ca 251 ma i explore the possibility that mass extinction can be caused by an extremely fast explosive release of dissolved methane and other dissolved gases such as carbon dioxide and hydrogen sulfide that accumulated in the oceanic water masses prone to stagnation and anoxia e g in silled basins the mechanism of the explosive release is the same as in the lake nyos disaster of 1986 i e a water column eruption caused by the interplay of buoyancy forces and exsolution of dissolved gas the eruption brings to the surface deep anoxic waters that cause extinctions in the marine realm terrestrial extinctions are caused by explosions and conflagrations that follow the massive release of methane the air methane mixture is explosive at methane concentrations between 5 and 15 and by the eruption triggered floods this scenario accounts well for the available data and may be relevant to other phenomena

altered river morphology in south africa related to the permian triassic extinction the permian triassic transition in the karoo basin of south africa was characterized by a rapid and apparently basin wide change from meandering to braided river systems as evidenced by preserved sedimentary facies this radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die off of rooted plant life in the basin evidence from correlative nonmarine strata elsewhere in the world containing fluvial permian triassic boundary sections suggests that a catastrophic terrestrial die off of vegetation was a global event producing a marked increase in sediment yield as well as contributing to the global 13 c excursion across the permian triassic boundary

methane driven oceanic eruptions and mass extinctions comment and reply comment brief intervals of profound global environmental change have punctuated earth s history during some of these times including the permian triassic boundary the 13c 12c ratio of carbonate and organic matter at numerous widespread locations decreased significantly 2 these negative 13c

bathymetry estimation from single frame images of nearshore waves existing methods for determining bathymetry from remotely sensed images of nearshore waves exploit only information on the magnitude of wavenumber k 2pi l ignoring spatial changes in wave direction thetas that can provide information about bathymetry gradients these methods also require wave period information so they can only be used when time series imagery is available we present an algorithm where changes in direction of refracting waves are used to determine underlying bathymetry gradients based on the irrotationality of wavenumber condition depth dependences are explicitly introduced through the linear dispersion relationship the final form of the model is independent of wave period so that all necessary input measurements can be derived from a single aerial snapshot taken from a plane unmanned aerial vehicle or satellite three different methods were tested for extracting wavenumber and angle from images i e two based on spatial gradients of wave phase and one based on integrated travel times between sample locations a tomographic approach synthetic testing using monochromatic and bichromatic waves with and without noise showed that while all three methods work well under ideal wave conditions gradient methods were overly sensitive to data imperfections the tomographic approach yielded robust wave measurements and provided confidence limits to objectively identify unusable areas further tests of this method using monochromatic waves on three synthetic bathymetries of increasing complexity showed a mean bathymetry bias of 0 01 m and a mean rms error of 0 17 m while not always applicable the model provides an alternative form of bathymetry estimation when celerity information is not available

bathymetry correction using an adjoint component of a coupled nearshore wave circulation model tests with synthetic velocity data 1 the impact of assimilation of wave averaged flow velocities on the bathymetric correction is studied in tests with synthetic model generated data using tangent linear and adjoint components of a one way coupled nearshore wave circulation model weakly and strongly nonlinear regimes are considered featuring energetic unsteady along beach flows responding to time independent wave averaged forcing due to breaking waves it is found that assimilation of time averaged velocities on a regular grid mimicking an array of remotely sensed data provides sensible corrections to bathymetry even though the wave data are not assimilated flow velocity assimilation utilizes adjoint components of both the circulation and wave models the representer formalism allows separating contributions of these two components to the bathymetric correction in a test case considered involving a beach with an alongshore varying bar the adjoint wave model contribution was mainly to determine the cross shore position of the bar crest the adjoint circulation model provided an additional contribution mostly adding to alongshore variability in the shape of the bar the array mode analysis reveals that there are very few modes that can be effectively corrected given the assumed data error level bathymetry perturbations associated with these modes are a mixture of near coast intensified modes as well as modes extending their influence to deep water along the background wave characteristics additional tests show the utility of different observational arrays in providing the bathymetric correction

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

rapid and synchronous collapse of marine and terrestrial ecosystems during the end permian biotic crisis a newly studied permian triassic p tr boundary section in jameson land east greenland contains an abundant and well preserved marine fauna as well as terrestrial palynomorphs for the first time it is possible to compare the biotic crises of the marine and terrestrial realms using the same samples from the same section the sediments record a negative excursion in 13 c carb values of 8 9 and in 13 c org values of 10 11 the presence of the conodont hindeodus parvus combined with the 13 c carb record enables correlation with the proposed global stratotype section at meishan this shows that the greenland section is the most expanded p tr section known collapse of the marine and terrestrial ecosystems took between 10 and 60 k y it took a further few hundred thousand years for the final disappearance of permian floral elements collapse of the terrestrial and marine ecosystems began at the same stratigraphic level and preceded the sharp negative excursion in the 13 c record

ocean stagnation and end permian anoxia ocean stagnation has been invoked to explain the widespread occurrence of organic carbon rich laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end permian mass extinction however to a first approximation stagnation would severely reduce the upwelling supply of nutrients to the photic zone reducing productivity moreover it is not obvious that ocean stagnation can be achieved numerical experiments performed with a three dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the late permian ocean we find that polar warming and tropical cooling of sea surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization buildup of quantities of h2s and co2 in the late permian ocean sufficient to directly cause a mass extinction however would have required large increases in the oceanic nutrient inventory

magnetostratigraphic correlations of permian triassic marine to terrestrial sections from china abstract we have studied three permian triassic pt localities from china as part of a combined magnetostratigraphic 40ar 39ar and u pb radioisotopic and biostratigraphic study aimed at resolving the temporal relations between terrestrial and marine records across the permo triassic boundary as well as the rate of the biotic recovery in the early triassic the studied sections from shangsi sichuan province langdai guihzou province and the junggar basin xinjiang province span marine paralic and terrestrial pt environments respectively each of these sections was logged in detail in order to place geochronologic paleomagnetic geochemical conodont and palynologic samples within a common stratigraphic context here we present rock magnetic paleomagnetic and magnetostratigraphic results from the three localities at shangsi northern sichuan province we sampled three sections spanning permo triassic marine carbonates magnetostratigraphic results from the three sections indicate that the composite section contains at least eight polarity chrons and that the pt boundary occurs within a normal polarity chron a short distance above the mass extinction level and a reversed to normal r n polarity reversal furthermore the onset of the illawarra mixed interval lies below the sampled section indicating that the uppermost permian changhsingian and at least part of the wuchiapingian stages postdate the end of the kiaman permo carboniferous reversed superchron at langdai guizhou province we studied magnetostratigraphy of pt paralic mudstone and carbonate sediments in two sections the composite section spans an r n polarity sequence section mean directions pass a fold test at the 95 confidence level and the section mean poles are close to the mean pt pole for the south china block based on biostratigraphic constraints the r n transition recorded at langdai is consistent with that at shangsi and demonstrates that the pt boundary occurred within a normal polarity chron a short distance above the mass extinction level in the southern junggar basin xinjiang province in northwest china we determined the magnetostratigraphy of three sections of a terrestrial sequence normal and reversed polarity directions are roughly antipodal and magnetostratigraphies from the three sections are highly consistent combined bio and magneto stratigraphy used to correlate this sequence to other pt sequences suggests that the previously proposed biostratigraphic pt boundary in the junggar sections was most likely misplaced by earlier workers suggesting that further work is necessary to confidently place the pt boundary there

macroforms large bedforms and rhythmic sedimentary sequences in subglacial eskers south central ontario implications for esker genesis and meltwater regime abstract eskers of south central ontario were deposited in closed subglacial conduits which were continuous main conduits this interpretation is supported by the intimate association of eskers with an anastomosing network of tunnel channels relatively continuous esker ridges minimal post formational disturbance of esker sediments intercalation of till and stratified sand and gravel diapiric folding at an esker core low variability in palaeocurrent direction and upslope flow paths down esker trends in clast lithology roundness and sphericity indicate continuous conduits with sediment supply by subglacial deformation of adjacent material into the conduits melt out of sediment from the conduit walls and fluvial resedimentation esker ridge morphology is attributed to synchronous erosion transportation and deposition along the main conduits such that ridge discontinuities are primarily explained as zones of non deposition during esker formation composite pseudoanticlinal and oblique accretion avalanche bed macroforms are identified gravel facies within these macroforms were deposited from fluidal flows or hyperconcentrated dispersions progradation of macroforms or migration of constituent large bedforms through the main conduits may have temporarily blocked constricted portions of those conduits and acted as possible internal autogenic controls on sediment availability and flow resistance the location of macroforms within conduits was primarily controlled by conduit geometry and sediment availability and later by feedback between macroform and conduit geometries sand and gravel units alternate rhythmically in vertical section rhythmicity is interpreted as a response to episodic flood flows controlled by seasonal changes in water supply but not necessarily representing annual events fans beads anabranched reaches and extended hummocky deposits are intimately associated with the main esker ridges they are interpreted in terms of subglacial cavities and localized flotation zones connected to the main conduits during flood events in phase wave structures are the products of hydraulic jumps in hyperconcentrated flood flows at flow expansions into swells within the main conduits into cavities connected to the main conduits or at a grounding line esker ridges record only the most powerful flood events whereas fans and beads record flow events in finer detail being primarily depositional reservoirs laterally fining deposits record the waning stages of conduit operation

a laboratory study of longshore currents over barred and non barred beaches abstract a detailed description is given of the results of laboratory experiments on wave driven longshore currents on both barred and non barred beaches the objective is to examine the cross shore distribution of the longshore current velocities for purely wave driven currents with emphasis on the position of maximum current velocity with respect to areas where wave energy is dissipated unidirectional obliquely incident waves both regular and random were used the measurements were performed in a large wave basin with a pump recirculation system to create spatially homogeneous longshore currents the experiments yielded information on wave transformation set up of the mean water level and the cross shore distribution of wave driven longshore current velocity a number of cases are presented and compared with each other the measurements show that in the case of purely wave driven longshore currents the maximum current velocities occur close to areas where wave breaking is most intense the effect of mixing bottom friction and wave rollers on the longshore current velocity profile are examined in more detail with help of numerical modelling existing model equations based on the assumption of alongshore uniformity are used the results for the mean longshore current profile on a barred beach are in close agreement with the measurements

gas hydrate destabilization enhanced dewatering benthic material turnover and large methane plumes at the cascadia convergent margin mixed methane sulfide hydrates and carbonates are exposed as a pavement at the seafloor along the crest of one of the accretionary ridges of the cascadia convergent margin vent fields from which methane charged low salinity fluids containing sulfide ammonia 4he and isotopically light co2 escape are associated with these exposures they characterize a newly recognized mechanism of dewatering at convergent margins where freshening of pore waters from hydrate destabilization at depth and free gas drives fluids upward this process augments the convergence generated overpressure and leads to local dewatering rates that are much higher than at other margins in the absence of hydrate discharge of fluids stimulates benthic oxygen consumption which is orders of magnitude higher than is normally found at comparable ocean depths the enhanced turnover results from the oxidation of methane hydrogen sulfide and ammonia by vent biota the injection of hydrate methane from the ridge generates a plume hundreds of meters high and several kilometers wide a large fraction of the methane is oxidized within the water column and generates 13c anomalies of the dissolved inorganic carbon pool

video based depth inversion techniques a method comparison with synthetic cases abstract applications of video based depth inversion in the near shore coastal environment are growing in numbers video based capabilities in nearshore monitoring are improving and coastal monitoring programs are expanding due to greater availability and reduced costs video derived beach state indicators such as beach width bar position and wave and current parameters are supplemented by accurate depth estimations through inversion video based depth inversion knows two main approaches a spectral and temporal method of celerity estimation the two methods have so far never been compared as video systems are often tailored for the chosen celerity estimation method here a spectral and temporal method are compared using controlled synthetic datasets obtained using the serre1d boussinesq model to estimate celerity and invert depth the assessment is carried out on a set of wave boundary conditions with over linear and barred bottom profile both methods invert depth with a similar accuracy for the most realistic jonswap cases an evident correlation is found between wave skewness non linearity and depth estimation error linked to the limits of the linear dispersion relation a residual sensing error is linked to method based parameters and a changing wave shape as incident waves propagate inshore the inversion error can be reduced significantly including a wave height dependent non linear correction importantly a method based error is introduced for the temporal method to increase the suitability for data assimilation likewise the spectral method has its own existing depth error estimation to feed into the kalman filter however these method based error estimates show very weakly or no relation to the observed error between estimated cross shore profile and bottom profile used for the model input

data assimilation and bathymetric inversion in a two dimensional horizontal surf zone model 1 a methodology is described for assimilating observations in a steady state two dimensional horizontal 2 dh model of nearshore hydrodynamics waves and currents using an ensemble based statistical estimator in this application we treat bathymetry as a model parameter which is subject to a specified prior uncertainty the statistical estimator uses state augmentation to produce posterior inverse updated estimates of bathymetry wave height and currents as well as their posterior uncertainties a case study is presented using data from a 2 d array of in situ sensors on a natural beach duck nc the prior bathymetry is obtained by interpolation from recent bathymetric surveys however the resulting prior circulation is not in agreement with measurements after assimilating data significant wave height and alongshore current the accuracy of modeled fields is improved and this is quantified by comparing with observations both assimilated and unassimilated hence for the present data 2 dh bathymetric uncertainty is an important source of error in the model and can be quantified and corrected using data assimilation here the bathymetric uncertainty is ascribed to inadequate temporal sampling bathymetric surveys were conducted on a daily basis but bathymetric change occurred on hourly timescales during storms such that hydrodynamic model skill was significantly degraded further tests are performed to analyze the model sensitivities used in the assimilation and to determine the influence of different observation types and sampling schemes

relative timing of deglacial climate events in antarctica and greenland the last deglaciation was marked by large hemispheric millennial scale climate variations the bolling allerod and younger dryas periods in the north and the antarctic cold reversal in the south a chronology from the high accumulation law dome east antarctic ice core constrains the relative timing of these two events and provides strong evidence that the cooling at the start of the antarctic cold reversal did not follow the abrupt warming during the northern bolling transition around 14 500 years ago this result suggests that southern changes are not a direct response to abrupt changes in north atlantic thermohaline circulation as is assumed in the conventional picture of a hemispheric temperature seesaw

spectral evolution of shoaling and breaking waves on a barred beach field observations and numerical model predictions are used to investigate the effects of nonlinear interactions reflection and dissipation on the evolution of surface gravity waves propagating across a barred beach nonlinear interactions resulted in a doubling of the number of wave crests when moderately energetic about 0 8 m significant wave height narrowband swell propagated without breaking across an 80 m wide nearly flat 2 m depth section of beach between a small offshore sand bar and a steep slope 0 1 beach face where the waves finally broke these nonlinear energy transfers are accurately predicted by a model based on the nondissipative unidirectional i e reflection is neglected boussinesq equations for a lower energy wave height about 0 4 m bimodal wave field high frequency seas dissipated in the surf zone but lower frequency swell partially reflected from the steep beach face resulting in significant cross shore modulation of swell energy the combined effects of reflection from the beach face and dissipation across the sand bar and near the shoreline are described well by a bore propagation model based on the nondispersive nonlinear shallow water equations boussinesq model predictions on the flat section where dissipation is weak are improved by decomposing the wave field into seaward and shoreward propagating components in more energetic wave heights greater than 1 m conditions reflection is negligible and the region of significant dissipation can extend well seaward of the sand bar differences between observed decreases in spectral levels and boussinesq model predictions of nonlinear energy transfers are used to infer the spectrum of breaking wave induced dissipation between adjacent measurement locations the inferred dissipation rates typically increase with increasing frequency and are comparable in magnitude to the nonlinear energy transfer rates

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

dynamics of lake eruptions and possible ocean eruptions dissolved gas in liquid is able to power violent eruptions two kinds of such gas driven eruptions are known in nature explosive volcanic eruptions driven by dissolved h2o in magma at high temperatures and lake eruptions driven by dissolved co2 in water at low temperatures there are two known occurrences of lake eruptions one in 1984 lake monoun and one in 1986 lake nyos both in cameroon africa the erupted co2 gas asphyxiated 1700 people in the lake nyos eruption and 37 people at lake monoun here we review experimental simulations of co2 driven water eruptions and dynamic models of such eruptions and a bubble plume theory is applied to the dynamics of lake eruptions field evidence experimental results and theoretical models show that lake eruptions can be violent and theoretical calculations are consistent with the high exit velocities and eruption columns inferred from observations furthermore the dynamics of lake degassing experiments are consistent with theoretical models other kinds of gas driven eruptions are possible and may have occurred in nature in the past a concentrated and large release of methane gas or hydrate from marine sediment may result in an ocean eruption furthermore injection of liquid co2 into oceans might also lead to ocean eruptions if care is not taken the various kinetic and dynamic processes involved are examined and quantified

fullerenes found in the permo triassic mass extinction period fullerenes have been identified by high performance liquid chromatography with uv visible spectroscopic analysis of toluene extracts of deep sea claystones from permo triassic p t boundary sections in the inuyama area central japan the analysis reveals the presence of 10 20 parts per trillion of c60 only in the dark colored rock samples suggesting the anoxia at the time of the p t boundary 250 million years ago when the greatest phanerozoic mass extinction occurred the fullerenes were likely synthesized within locally anoxic zone in the extensive wildfires on the supercontinent pangea and deposited on an anoxic deep sea floor of the superocean panthalassa

quasi three dimensional modeling of rip current systems 1 the focus of the paper is the analysis of the flow in rip current systems generated by channels in longshore bars on a beach the horizontal variations of rip current systems are described through the use of the quasi three dimensional nearshore circulation model shorecirc model predictions are compared to laboratory measurements of waves and current velocities throughout the entire rip current system and show reasonable agreement the rips in the two channels are found to behave differently because of the depth variation across the basin it is found that higher bottom stress leads to more stable flow where the rip current meanders less and fewer eddies are generated the wave current interaction creates forcing which reduces the distance rip currents flow offshore and can lead to a slow pulsation of the rip current this pulsation is in addition to the instabilities of a jet which can also be present in rip currents the three dimensionality of the rip current system is found to have a significant effect on the overall circulation patterns index terms 4255 oceanography general numerical modeling 4512 oceanography physical currents 4546 oceanography physical nearshore processes keywords rip currents nearshore circulation numerical modeling waves

simultaneous mapping of coastal topography and bathymetry from a lightweight multicamera uas a low cost multicamera unmanned aircraft system uas is used to simultaneously estimate open coast topography and bathymetry from a single longitudinal coastal flight the uas combines nadir and oblique imagery to create a wide field of view fov which enables collection of mobile long dwell timeseries of the littoral zone suitable for structure from motion sfm and wave speed inversion algorithms resultant digital surface models dsms compare well with terrestrial topographic lidar and bathymetric survey data at duck nc usa with roor mean square error rmse bias of 0 26 0 05 and 0 34 0 05 m respectively bathymetric data from another flight at virginia beach va usa demonstrates successful comparison rmse bias of 0 17 0 06 m in a secondary environment uas derived engineering data products total volume profiles and shoreline position were congruent with those calculated from traditional topo bathymetric surveys at duck capturing both topography and bathymetry within a single flight the presented multicamera system is more efficient than data acquisition with a single camera uas this advantage grows for longer stretches of coastline 10 km efficiency increases further with an on board global navigation satellite system inertial navigation system gnss ins to eliminate ground control point gcp placement the appendix reprocesses the virginia beach flight with the gnss ins input and no gcps the resultant dsm products are comparable root mean squared difference rmsd bias of 0 62 0 09 m and processing time is significantly reduced

evaluation of video based linear depth inversion performance and applications using altimeters and hydrographic surveys in a wide range of environmental conditions abstract the performance of a linear depth inversion algorithm cbathy applied to coastal video imagery was assessed using observations of water depth from vessel based hydrographic surveys and in situ altimeters for a wide range of wave conditions 0 3

surf zone longshore currents and random waves field data and models abstract analytic and numerical models for longshore currents generated by obliquely incident random waves am compared with field observations five days of observations were selected during which the waves were narrow banded in both frequency and direction in keeping with model assumptions the extensive measurements included radiation stress and wave directional spectra in 9 m depth and a closely spaced array of current and pressure sensors on a line perpendicular to shore the longshore current models are based on balancing the gradient of the radiation stress with the alongshore bed shear and reynold s stresses assuming stationary wave conditions and straight and parallel bottom contours the spatial variation of wave height required to determine the gradient of the radiation stress is modeled using linear random wave theory given hrms in 9 m depth the model predicts hrms at shoreward locations with an average error of less than 9 using a nonlinear bottom shear stress formulation and the meas

catastrophic soil erosion during the end permian biotic crisis organic geochemical analyses of sedimentary organic matter from a marine permian triassic transition sequence in northeastern italy reveal a significant influx of land derived diagenetic products of polysaccharides this unique event reflects massive soil erosion resulting from destruction of land vegetation due to volcanogenic disturbance of atmospheric chemistry the excessive supply of soil materials to the oceans provides a direct link between terrestrial and marine ecological crises suggesting that ecosystem collapse on land could have contributed to the end permian marine extinctions

high resolution bathymetry estimates via x band marine radar 1 beaches abstract in this paired study we apply a recently developed high resolution bathymetry estimation algorithm cbathy to x band marine radar observations at two nearshore field sites the algorithm exploits observations of the spatial structure of wave phase to attain wavenumber estimates inverts the linear water wave dispersion relation for depth and then applies a kalman filter to objectively update the bathymetry estimates previously performance has only been tested using optical video observations in this first of two papers performance of the algorithm using x band radar image time series is tested at two disparate barred beach environments duck nc usa and benson beach wa usa each of the test beaches is either co located with duck nc or geographically close to benson beach wa those utilized in the original algorithm verification concurrent echosounder surveys are used as ground truth the bulk performance of the radar derived bathymetry estimate at duck nc achieves 0 49 m root mean square error rmse with 0 26 m bias deep this compares well with the bulk performance of the concurrent estimate derived using optical video 0 44 m rmse and 0 23 m bias deep the radar derived bathymetry estimate performance at benson beach is similar 0 35 m rmse and 0 11 m bias shallow and is comparable to that of an optical video derived estimate at a similar pacific northwest beach 0 56 m rmse and 0 41 m bias shallow at both beaches significantly higher performance is achieved at locations deeper than 2 m offshore of the surfzone than at locations shallower than 2 m surfzone where errors are often a large fraction of the total depth lastly several weeks of observations are utilized to assess the sensitivity of algorithm quality control to environmental conditions thresholds based on the shoreward component of wind stress and offshore wave steepness are identified and shown to impact the areal coverage of radar derived bathymetric estimates overall these results demonstrate the viability of marine radar observations as input to the cbathy algorithm and delineate some environmental constraints on algorithm performance in the companion paper the algorithm is extended to areas where tidal currents are important including an ebb tidal shoal and an estuary mouth

permian triassic boundary in the central transantarctic mountains antarctica the permian triassic boundary occurs within a relatively complete terrestrial sequence in the shackleton glacier area of the central transantarctic mountains the boundary is within a 7 to 10 m thick interval between the permian glossopteris flora and the lower triassic lystrosaurus fauna this interval representing on the order of 200 k y records some of the events that occurred in the transition from the permian to triassic in the best documented section at graphite peak in the beardmore glacier region protohaploxypinus microcorpus zone palynomorphs which we assign to the latest permian record the declining glossopteris flora and occur near the top of the buckley coal measures just below a previously reported major negative 13c excursion in the shackleton glacier area the permian glossopteris flora including fossil wood roots and leaves occurs within the lower part of the fremouw formation the antarctic lystrosaurus assemblage of early triassic age has several species in common with the south african fauna that lived 20 to 35 closer to the equator the migration of vertebrates from southern africa into antarctica in the early triassic supports hypotheses of runaway greenhouse warming possibly related to co2 emissions from siberian flood basalts and large methane gas releases changes in flora bracketing the first of the major negative 13c anomalies near the boundary in antarctica and in east greenland support the hypothesis that a global event perhaps through mutations caused by enhanced ultraviolet radiation may have played a role in the destruction of floras

data assimilation strategies for volcano geodesy abstract ground deformation observed using near real time geodetic methods such as insar and gps can provide critical information about the evolution of a magma chamber prior to volcanic eruption rapid advancement in numerical modeling capabilities has resulted in a number of finite element models targeted at better understanding the connection between surface uplift associated with magma chamber pressurization and the potential for volcanic eruption robust model data fusion techniques are necessary to take full advantage of the numerical models and the volcano monitoring observations currently available in this study we develop a 3d data assimilation framework using the ensemble kalman filter enkf approach in order to combine geodetic observations of surface deformation with geodynamic models to investigate volcanic unrest the enkf sequential assimilation method utilizes disparate data sets as they become available to update geodynamic models of magma reservoir evolution while the enkf has been widely applied in hydrologic and climate modeling the adaptation for volcano monitoring is in its initial stages as such our investigation focuses on conducting a series of sensitivity tests to optimize the enkf for volcano applications and on developing specific strategies for assimilation of geodetic data our numerical experiments illustrate that the enkf is able to adapt well to the spatial limitations posed by gps data and the temporal limitations of insar and that specific strategies can be adopted to enhance enkf performance to improve model forecasts specifically our numerical experiments indicate that 1 incorporating additional iterations of the enkf analysis step is more efficient than increasing the number of ensemble members 2 the accuracy of the enkf results are not affected by initial parameter assumptions 3 gps observations near the center of uplift improve the quality of model forecasts 4 occasionally shifting continuous gps stations to provide variability in the locations of observations results in better model predictions than utilizing fixed locations when the number of available instruments is limited 5 spotty insar data coverage on the flanks of a volcano due to topographic shadows and or atmospheric interference does not adversely impact the effectiveness of enkf if the available coverage is 50 and 6 snow or glacial obstruction in the center of uplift can adversely impact enkf forecasts by utilizing these strategies we conclude that the enkf is an effective sequential model data fusion technique for assimilating multiple geodetic observations to forecast volcanic activity at restless volcanoes

estimation of wave phase speed and nearshore bathymetry from video imagery a new remote sensing technique based on video image processing has been developed for the estimation of nearshore bathymetry the shoreward propagation of waves is measured using pixel intensity time series collected at a cross shore array of locations using remotely operated video cameras the incident band is identified and the cross spectral matrix is calculated for this band the cross shore component of wavenumber is found as the gradient in phase of the first complex empirical orthogonal function of this matrix water depth is then inferred from linear wave theory s dispersion relationship full bathymetry maps may be measured by collecting data in a large array composed of both cross shore and longshore lines data are collected hourly throughout the day and a stable daily estimate of bathymetry is calculated from the median of the hourly estimates the technique was tested using 30 days of hourly data collected at the sandyduck experiment in duck north carolina in october 1997 errors calculated as the difference between estimated depth and ground truth data show a mean bias of 35 cm rms error 91 cm expressed as a fraction of the true water depth the mean percent error was 13 rms error 34 excluding the region of known wave nonlinearities over the bar crest the accuracy of the technique improved and the mean rms error was 20 cm 75 cm additionally under low amplitude swells wave height h 1 m the performance of the technique across the entire profile improved to 6 29 of the true water depth with a mean rms error of 12 cm 71 cm

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

stable carbon isotope stratigraphy across the permian triassic boundary in shallow marine carbonate platforms nanpanjiang basin south china a distinct negative 13c excursion is documented in two permian triassic sections heping and taiping in shallow marine carbonate platform deposits in the nanpanjiang basin south china these sections span from the changhsingian to the dienerian and are characterized by a distinct marine boundary facies change from massive skeletal lime packstone in the changhsingian to distinctive calcimicrobial framestone in the griesbachian hindeodus parvus zone the 13corg and 13ccarb excursions occur directly after the onset of the calcimicrobial framestone herein termed the permian triassic boundary event and before the first occurrence of h parvus the isotope shifts are associated with a sharp drop in species abundance and diversity and coincide with a decrease in total organic carbon toc content the shift towards depleted values in 13corg and 13ccarb at the permian triassic boundary event together with low toc contents persists throughout the griesbachian h parvus zone these data document a corresponding negative shift of 13corg and 13ccarb values and low toc contents with the onset of growth of calcified microbial framestones a postextinction disaster facies immediately below the base of the griesbachian h parvus zone based on paleontological evidence the first occurrence of the disaster facies follows the extinction event which implies that the 13c depleted values above this facies postdate the event this suggests that two separate events had to account for the initiation of the extinction and the 13c excursion however the consequences that led to the negative isotopic shift might be linked to the intriguing recovery lag of early triassic ecosystems based on data from ptb sections worldwide of a greater 13c offset in high compared with low latitudes we propose that methane eruptions from thermal destabilization of high latitude clathrate deposits may have led to the negative 13c shift and may have caused long term adverse ecological conditions

bathymetric error estimation for the calibration and validation of estuarine hydrodynamic models abstract this paper investigates the impact of uncertainty in the definition of bathymetry on the performance of estuarine shallow water models a depth averaged hydrodynamic model is used to simulate tidal flows in a meso tidal estuary simulations are performed for a range of bathymetric and bed roughness scenarios which encompass the uncertainties typically encountered in the specification of estuarine and shallow coastal models the relative sensitivity of model output to uncertainty in bathymetry and bed friction is analysed using monte carlo methods and a new generalised error model is presented that allows various sources of error in bathymetry to be treated as a calibration parameter numerical results are compared with observed current speed and water level time series at multiple locations it is shown that calibration that incorporates bathymetric uncertainty can be significantly more efficient than a classic calibration based only on adjustment of a bed friction coefficient these findings have wide ranging implications for the calibration and validation of estuarine and shallow coastal hydrodynamic models importantly our proposed bathymetry calibration framework offers the prospect of significantly improved performance from the current generation of numerical models

dynamics of co2 driven lake eruptions on 21 august 1986 a massive release of carbon dioxide from lake nyos in cameroon killed about 1 700 people a similar event occurred on 15 august 1984 at lake monoun also in cameroon it was suggested1 5 that the co2 released was initially dissolved in the hypolimnion dense lower layer of the lake and was released by eruptive outgassing because of its violence the nyos outburst was at first thought6 to have been volcanic but undisturbed sediments and other evidence indicate that no large volcanic eruption occurred7 9 recent experiments10 11 have shown that decompression of co2 saturated water is able to power explosive eruptions here i analyse the dynamics of co2 driven lake water eruptions by deriving an equation of state for gas liquid mixtures and using it to integrate the bernoulli equation which describes the dynamics of the bubbly flow i find that under certain conditions these eruptions can be violent the lake surface exit velocity of an initially gas saturated water parcel may reach 89m s 1 for lake nyos and 51m s 1 for lake monoun the dynamics are similar to those of water driven volcanic eruptions which are also powered by gas exsolution from a liquid