use of numerical models to study land based sedimentation and subsequent nearshore morphological evolution a beach sedimentation problem is presented this problem involves assessing the impact and importance of land based sediment sources erosion from gullies during intense rainfall and directly from cliffs by wave action on morphodynamic changes at a beach the site motivating the study is la barrosa beach spain the location is described and a discussion of possible approaches presented a schematized representation of a gully and beach is used a hybrid approach is adopted in which sediment deposition by run off and to a lesser extent cliff erosion is modelled using wave resolving hydrodynamic models it is found that significant amounts of sediment can be supplied by gully run off during storms for small run offs the swash can be involved in determining the region of deposition within the gully area with longer period motions favouring increased sediment deposition at gully sides simulations also show that swash motions can erode gully sides and the presence of a cross shore jet associated with the swash and gullies can also impact on sediment movement longer term wave averaged morphodynamic modelling without a swash zone indicates that run off deposits subsequently diffuse laterally whether under normal or oblique incidence these simulations also reveal the possibility of underlying crescentic bar shedding dynamics that may pertain during changes of wave conditions

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

is the electrical conductivity of the northwestern pacific upper mantle normal 1 the normal oceanic mantle project based on ocean bottom geophysical observations has been underway since 2010 to investigate the physical state of the oceanic lithosphere and asthenosphere we have conducted electromagnetic surveys on old 130 ma seafloor in the northwestern pacific region where no active tectonic processes have been identified in order to image the electrical conductivity structure beneath the region so far data have been collected at four sites through a pilot survey conducted from june 2010 to august 2012 a one dimensional electrical conductivity model was obtained by preliminary analysis of the data by using the magnetotelluric method the model shows that the resistive 0 01 s m 1 lithospheric mantle is as thick as 80 km and that the asthenospheric mantle below has a conductivity of 0 03 s m 1 the resistive layer is slightly thicker than that beneath the philippine sea but significantly thinner than that beneath the area off the bonin trench in the pacific ocean there is a greater difference in age between the survey area and the philippine sea 0 60 ma than between the survey area and the area off the bonin trench 140 155 ma this comparison suggests that the relation between age and lithospheric thickness is not as simple as that predicted by the concept of lithospheric cooling it also suggests that the lithosphere beneath the area off the bonin trench in the pacific ocean is abnormally thick if the mantle beneath the survey area in this study is normal as expected from the plate cooling model

seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

shock capturing boussinesq model for irregular wave propagation abstract in this paper a shock capturing numerical model based on the combined solution of boussinesq and nonlinear shallow water equations is validated with respect to the transformation breaking and runup of irregular waves boussinesq equations are applied where dispersive and nonlinear effects are both relevant assuring an appropriate description of wave propagation from intermediate to shallow waters nonlinear shallow water equations are used where dispersion is negligible their shock capturing features exploited by the application of the finite volume method enable an intrinsic representation of wave breaking and swash zone oscillations no case by case calibration or tracking algorithms are required comparisons with experimental data show that the model is able to simulate wave height variations mean water level setup wave runup and the generation of nearshore currents accurately

tsunami hazards associated with the perachora fault at eastern corinth gulf greece we investigate the tsunami hazard associated with the perachora fault at eastern corinth gulf greece realistic faulting parameters are used to model expected coseismic displacements of the seafloor this study also investigates the effect that rupture complexity has on the local tsunami wave field several earthquake scenarios are used as initial conditions for tsunami stimulation either considering the numerous published constant slip models or taking into account the fault rupture complexity with the help of a realistic finite extent k 2 stochastic kinematic source model with k dependent rise time the obtained results indicate that there is sub stantially more variation in the local tsunami wave field derived from the inherent complexity of the shallow fault zone than predicted by a simple elastic dislocation model rupture complexity as represented by heterogeneous slip distribution pat terns has an important effect on near field tsunami records tsunami hazards as sessments based on only a few scenario earthquakes may not accurately account for natural variation in tsunami amplitude caused by earthquake rupture complexity

mercury as a proxy for volcanic emissions in the geologic record abstract large igneous province lip eruptions are increasingly considered to have driven mass extinction events throughout the phanerozoic however uncertainties in radiometric age dating of lip materials along with difficulty in accurate age dating of sedimentary rocks that record the environmental and biological history of our planet create inherent uncertainties in any linkage as such there is interest in using geochemical proxies to fingerprint periods of major volcanism in the sedimentary record termed here lip marks the use of sedimentary mercury hg contents has been suggested to be the best tool to accomplish this goal and recent work is reviewed here studies to date show that most extinction events ocean anoxic events and other environmental crises through the phanerozoic have an associated sedimentary hg anomaly it remains unclear though if each hg anomaly is truly a signature of massive volcanism or if it is controlled by local or regional processes as hg has a strong affinity to organic matter om normalisation with total organic carbon toc has been used to assess anomalies the measurement of toc has been fraught with error throughout many studies leaving some claimed hg toc anomalies questionable normalisation by other elements that can affect hg sequestration such as al and s are less common but warrant further investigation stable isotope systematics of hg have helped to further clarify the origin of hg spikes and clearly show that not all hg anomalies are directly related to volcanism although a promising tool the hg proxy requires more refinement to accurately understand the nuances of an hg anomaly in the rock record

on the role of shoreline boundary conditions in wave overtopping modelling with non linear shallow water equations abstract the note extends and completes the analysis carried out by briganti and dodd briganti r dodd n 2009 shoreline motion in nonlinear shallow water coastal models coastal eng 56 5 6 doi 101016 j coastaleng 2008 10 008 495 505 on the performance of a state of the art non linear shallow water equations solver in common coastal engineering applications the case of bore generated overtopping of a truncated plane beach is considered and the performance of the model is assessed by comparing with the peregrine and williams peregrine d williams s m 2001 swash overtopping a truncated beach j fluid mech 440 391 399 analytical solution in particular the influence of shoreline boundary conditions is investigated by considering the two best performing approaches discussed in briganti and dodd briganti r dodd n 2009 shoreline motion in nonlinear shallow water coastal models coastal eng 56 5 6 doi 101016 j coastaleng 2008 10 008 495 505 different distances of the edge of the beach from the bore collapse point are tested for larger distances the accuracy of the overtopping modelling decreases as a consequence of the error in modelling the tip of the swash lens and consequently the run up a sensitivity analysis using the numerical resolution is carried out this reveals that the approach in which cells shallower than a prescribed threshold are drained and wave propagation speeds for wet dry riemann problem are used at the interface between a wet and a dry cell referred as option 2ea in briganti r dodd n 2009 shoreline motion in nonlinear shallow water coastal models coastal eng 56 5 6 doi 101016 j coastaleng 2008 10 008 495 505 performs consistently better than the other

upper mantle seismic shear discontinuities of the pacific 1 shear wave impedance discontinuities are inventoried for eight paths connecting circum pacific earthquakes with seismic stations on hawaii and oahu in addition to the transition zone discontinuities we observe a consistent impedance decrease at a depth of 80 km that marks the transition from the fast seismic lid to the low velocity zone the interval over which this transition occurs is less than 30 km the requisite impedance decrease ascribed almost entirely to diminished velocities in the low velocity zone exceeds predictions for peridotite chemistries of appropriate lithospheric age in all cases the transition is better matched by lithosphere of roughly half of the true age four paths show clear evidence of the x discontinuity an impedance increase of 3 8 near 300 km depth the only viable explanations would require extensive eclogite or basalt depleted mantle in the upper mantle of the western pacific the impedance contrast of the 410 km discontinuity which depends on the modal fraction of mantle olivine does not signal the presence of either although a mixture of the two remains a possibility we find no evidence of a low velocity layer atop of the 410 km discontinuity if present it is either consistently thin 15 km highly variable in thickness topography in excess of 60 km or has little impedance contrast 2 3 with overlying mantle the apparent absence of melt atop the 410 km discontinuity an intermittent and weak 520 km discontinuity and a thinned transition zone are consistent with relatively dry conditions in the deep upper mantle of the central pacific

mercury deposition through the permo triassic biotic crisis abstract a 6 7 million year record of marine sedimentation through the permo triassic biotic crisis shows notable shifts in mercury concentrations that varied over an order of magnitude 0 002 to 0 116 g g mercury concentrations correlate strongly with total organic carbon showing both parallel increasing and decreasing trends over geologic time scales results suggest that changes in bioproductivity strongly influence mercury sequestration into marine sediment this may provide insight to potential marine response to modern anthropogenic hg loading and supports models that suggest enhanced bioproductivity that due to recent climate has increased hg sequestration over time

oceanic anoxia at the precambrian cambrian boundary the precambrian cambrian pc c boundary separates fossils representing two discrete evolutionary phases the neoproterozoic soft bodied ediacarian biotas and cambrian small shelly faunas the biological discontinuity is suspected to have been a result of mass extinction however recent discoveries of the ediacarian biotas in cambrian sediments have led to an understanding that the faunal change was gradual through the pc c transition th u ratios which are high in oxidizing conditions and low in reducing conditions show a considerable positive correlation with 13c values at all studied sites of the pc c boundary this correlation indicates that reported 13c variation across the pc c boundary from numerous localities corresponds to redox variation in the depositional environment the negative 13c anomaly that occurs worldwide at the pc c boundary therefore corresponds to the widespread development of an oxygen deficient shallow marine environment this finding suggests that widespread oceanic oxygen deficiency which has been interpreted to reflect phanerozoic mass extinction events also occurred immediately before the cambrian explosion

origin of azimuthal seismic anisotropy in oceanic plates and mantle abstract seismic anisotropy is ubiquitous in the earth s mantle but strongest in its thermo mechanical boundary layers azimuthal anisotropy in the oceanic lithosphere and asthenosphere can be imaged by surface waves and should be particularly straightforward to relate to well understood plate kinematics and large scale mantle flow however previous studies have come to mixed conclusions as to the depth extent of the applicability of paleo spreading and mantle flow models of anisotropy and no simple globally valid relationships exist here we show that lattice preferred orientation lpo inferred from mantle flow computations produces a plausible global background model for asthenospheric anisotropy underneath oceanic lithosphere the same is not true for absolute plate motion apm models a 200 km thick layer where the flow model lpo matches observations from tomography lies just below the 1200 c isotherm of a half space cooling model indicating strong temperature dependence of the processes that control the development of azimuthal anisotropy we infer that the depth extent of shear and hence the thickness of a relatively strong oceanic lithosphere can be mapped this way these findings for the background model and ocean basin specific deviations from the half space cooling pattern are found in all of the three recent and independent tomographic models considered further exploration of deviations from the background model may be useful for general studies of oceanic plate formation and dynamics as well as regional scale tectonic analyses

well balanced and flexible morphological modeling of swash hydrodynamics and sediment transport abstract existing numerical models of the swash zone are relatively inflexible in dealing with sediment transport due to a high dependence of the deployed numerical schemes on empirical sediment transport relations moreover these models are usually not well balanced meaning they are unable to correctly simulate quiescent flow here a well balanced and flexible morphological model for the swash zone is presented the nonlinear shallow water equations and the exner equation are discretized by the shock capturing finite volume method in which the numerical flux and the bed slope source term are estimated by a well balanced version of the slic slope limited centered scheme that does not depend on empirical sediment transport relations the satisfaction of the well balanced property is demonstrated through simulating quiescent coastal flow the quantitative accuracy of the model in reproducing key parameters i e the notional shoreline position the swash depth the flow velocity the overtopping flow volume the beach change depth and the sediment transport rate is shown to be satisfactory through comparisons against analytical solutions experimental data as well as previous numerical solutions this work facilitates an improved modeling framework for the swash hydrodynamics and sediment transport

topographically controlled breaking wave induced macrovortices part 2 changing geometries this is the second part of a series examining the behaviour of breaking wave induced macrovortices the first part examined theoretically general behaviours during startup conditions and gave computational results for macrovortex generation and their evolution on widely spaced breakwaters in this paper we extend and test qualitatively and quantitatively some of the basic results of part 1 in particular the initial longshore vortex transport for a wide range of geometries ranging from narrow rip current topographies to isolated breakwaters accounting for the presence of a shoreline is found to be necessary for the representation of longshore vortex transport results show vortex motion ranging from strongly offshore in the case of a narrow rip current to strongly longshore in the case of an isolated breakwater even with the significant approximations inherent in the analytical predictions numerical computations using time domain boussinesq type equations and laboratory experiments confirm the trends part 3 examines the horizontal mixing features of wave induced flows over isolated single breakwater configuration or multiple ripcurrent configuration submerged structures

suspended sediment transport under seiches in circular and elliptical basins abstract enclosed bodies of water such as lakes or harbours often experience large scale oscillatory motions seiching as a simple model of such flow we investigate exact solutions to the shallow water equations which represent oscillatory flow in an elliptical basin with parabolic cross section specifically we consider two fundamental modes of oscillation in one of which the flow is parallel to the axis of the ellipse while in the other it is radial we obtain periodic analytical solutions for sediment transport including erosion deposition and advection under either mode of oscillation and present a method for obtaining such solutions for a more general class of flow fields and sediment transport models our solutions provide estimates of the morphodynamical importance of seiching motions and also reveal a characteristic pattern of net erosion and deposition associated with each mode in particular we find that a net flux of suspended sediment can be transported from the deeper to the shallower regions of the basin these transport patterns which are driven essentially by settling lag are highly robust to the formulation of the sediment transport relation and appear not to be substantially affected by the omission of frictional terms in the hydrodynamics they should thus provide considerable insight into sediment transport in less idealised systems

subduction of oceanic asthenosphere evidence from sub slab seismic anisotropy 1 the oceanic asthenosphere is characterized as a low viscosity channel down to 200 300 km depth separating the cold lithosphere from above and it is intimately linked to a layer of low seismic velocity and prominent seismic anisotropy observed globally beneath ocean basins while subduction of tectonic plates in convergent margins is well recognized the fate of oceanic asthenosphere remains enigmatic we demonstrate that subduction of the oceanic asthenosphere characterized by weak azimuthal anisotropy and strong radial anisotropy explains the essence of sub slab shear wave splitting patterns where the fast splitting direction changes from predominantly trench parallel or sub parallel under relatively steep subduction zones to frequently trench normal under shallow subduction zones to explain the observed splitting time the thickness of the subducted asthenosphere is estimated to be 100 50 km

efficient computation of surf zone waves using the nonlinear shallow water equations with non hydrostatic pressure abstract a numerical method for non hydrostatic free surface irrotational flow governed by the nonlinear shallow water equations including the effects of vertical acceleration is presented at the aim of studying surf zone phenomena a vertical boundary fitted grid is used with the water depth divided into a number of layers a compact finite difference scheme is employed for accurate computation of frequency dispersion requiring a limited vertical resolution and hence capable of predicting the onset of wave breaking a novel wet dry algorithm is applied for a proper handling of moving shoreline mass and momentum are strictly conserved at discrete level while the method only dissipates energy in the case of wave breaking the numerical results are verified with a number of tests and show that the proposed model using two layers without ad hoc assumptions enables to resolve propagating nonlinear shoaling breaking waves and wave run up within the surf and swash zones in an efficient manner

advances in numerical modelling of swash zone dynamics we present a comprehensive and critical review of work on the numerical modelling of swash zone processes between 2005 and 2015 a wide range of numerical models has been employed for the study of this region and hence only phase resolving approaches i e depth averaged and depth resolving models are analyzed the current advances in the modelling of swash zone processes are illustrated by comparing different numerical models against laboratory experiments of a dam break driven swash event depth averaged and depth resolving models describe well the swash flow for both coarse sand and gravel impermeable beach cases depth averaged models provides a practical tool for engineering use whereas depth resolving models improve the flow description especially for the backwash phase with a significantly higher computational cost the evolution and magnitude of bed shear stresses predicted by all models is reasonable when compared with laboratory estimates based on the log law however differences between modelling approaches cannot be rigorously evaluated owing to the uncertainty in shear stress estimates while employing such approximation furthermore small scale processes such as turbulence evolution are investigated with depth resolving models finding differences between the two dimensional and three dimensional approaches numerical models allow us to investigate other processes such as beach morphology changes the evolution of the turbulence coherent structures and the infiltration exfiltration effects on the swash flow a discussion on the advantages and limitations of each model is presented the future of swash zone modelling depends on the increase of the computational power and more importantly on the improvement of the current capability to obtain intra wave measurements for model validation calibration and greater resolution of physical processes

mercury isotope fractionation in waters and sediments of the murray brook mine watershed new brunswick canada tracing mercury contamination and transformation abstract mercury isotope fractionation was investigated in different environmental compartments of a mining impacted ecosystem the watershed of the murray brook deposit in northern new brunswick canada mercury contaminated ground water surface water as well as sediment and samples of suspended particulate matter were collected alongside gossan creek downstream of mine tailings and analyzed for mercury isotopic composition while leachates from the tailings and ground water samples showed a uniform and similar mercury isotopic signature confirming the predominant role of the mining residues in the contamination of the surrounding environment samples collected from the surface flow system provided evidence of significant mass dependent fractionation of mercury with distance from the source as dissolved mercury contents steadily decreased from 31 1 to 1 4 g hg l 1 with distance from the headwaters of the stream 202hg in the creek water progressively increased resulting in a fractionation of 0 9 over 1 6 km as a result mercury isotopic ratios in the creek appeared to closely follow a rayleigh model assuming a constant fractionation factor reactant product of 1 00038 stream bed sediments also demonstrated an enrichment of heavy isotopes along the creek with an isotopic shift of 1 over the distance of gossan creek 3100 m although mercury losses from the water column result partly from partitioning to the sediments measured mercury isotopic ratios differences between dissolved and solid phases were likely small and this study did not observe significant fractionation due to partitioning processes results rather suggested that fractionation observed in the surface water system of gossan creek is most likely the result of a combined effect of reduction and volatilisation processes the lighter isotopes being preferentially reduced and evaporated from the water column additional sediment samples collected along reaches of eighteen mile brook and the upsalquitch river that receive water from gossan creek and from tributaries unaffected by the mine contamination were analyzed for mercury isotopic composition data obtained from those sediments clearly demonstrated that mercury derived from mining activities is isotopically different from mercury naturally present in the area measured isotopic differences can ultimately be employed to trace sources of mercury notwithstanding potential fractionation caused by natural transformation processes

on the application of a boussinesq model to river flows including shocks serr 1d is a 4th order finite volume 1d boussinesq model including wave breaking energy dissipation through extra diffusive like terms this model has been primarily conceived to compute wave propagation in coastal areas and has been validated for breaking and non breaking waves propagating over uneven bathymetries cienfuegos et al 2005 2006a b 2007 the present paper aims at investigating the ability of serr 1d to simulate challenging fluvial hydraulic applications such as sudden gate operation in open channels generating short waves dam break flows and a steady hydraulic jump over a bump the performance of the absorbing generating boundary condition implemented in serr 1d is first analysed in the context of fluvial applications where relatively short waves must be evacuated from the computational domain without producing spurious reflection next by comparing numerical results to analytical and experimental dam break test cases we show that the model is able to reproduce the overall features of these flows but that additional care should be paid to the representation of energy dissipation and front speed in order to accurately represent bore dynamics

integral flow properties of the swash zone and averaging the swash zone is that part of a beach over which the instantaneous shoreline moves back and forth as waves meet the shore this zone is discussed using the nonlinear shallow water equations which are appropriate for gently sloping beaches a weakly three dimensional extension of the two dimensional solution by carrier greenspan 1958 of the shallow water equations for a wave reflecting on an inclined plane beach is developed and used to illustrate the ideas thereafter attention is given to integrated and averaged quantities the mean shoreline might be defined in several ways but for modelling purposes we find the lower boundary of the swash zone to be more useful a set of equations obtained by integrating across the swash zone is investigated as a model for use as an alternative boundary condition for wave resolving studies comparison with sample numerical computations illustrates that they are effective in modelling the dynamics of the swash zone and that a reasonable representation of swash zone flows may be obtained from the integrated variables the longshore flow of water in the swash zone is in many ways similar to the stokes drift of propagating water waves further averaging is made over short waves to obtain results suitable as boundary conditions for longer period motions including the effect of incident short waves in order to clearly present the work a few simplifications are made the main result is that in addition to the kinematic type of boundary condition that occurs on a simple e g rigid boundary two further conditions are found in order that both the changing position of the swash zone boundary and the longshore flow in the swash zone may be determined models of the short waves both outside and inside the swash zone are needed to complete a full wave averaged model only brief indication is given of such modelling

extreme enrichment of polymetallic ni mo pge au in lower cambrian black shales of south china an os isotope and pge geochemical investigation extreme metal enrichments occur in the lower cambrian niutitang formation a thick black shale sequence deposited on the yangtze platform of south china and form a regionally distributed conformable polymetallic ni mo pge au sulfide horizon the origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of re os isotopes and platinum group elements the black shales of the lower cambrian niutitang formation in guizhou province yielded an re os isochron age of 535 11 ma with an initial 187 os 188 os ratio of 0 80 0 04 which is similar to the initial 187 os 188 os ratio 0 78 0 19 of the ni mo sulfide ores but slightly lower than the initial 187 os 188 os ratio 1 18 0 02 of lower cambrian black shales from the lesser himalaya india a comparison of os isotope data among the chinese ni mo sulfide ores the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits the pge concentrations pt anomaly pt pt pt pd ir pd au pd ratios of the chinese ni mo sulfide ores are similar to those metal rich black shales of submarine volcanogenic hydrothermal origin from czech republic namibia and canada but are different from those data of the ocean floor fe mn crusts that have scavenged their pge and other metals directly from seawater it is therefore suggested that the ni mo sulfide ores from the niutitang black shale sequence in south china had a submarine hydrothermal origin the anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments the discharge of hydrothermal fluids into the cambrian ocean may have had a great effect on life during the cambrian explosion 2007 elsevier b v all rights reserved

mercury as a proxy for volcanic activity during extreme environmental turnover the cretaceous paleogene transition abstract the usually low geological background concentrations of hg makes this trace element suitable for identifying accumulation pulses in sediments that can be tentatively related to weathering processes and thus to climatic changes intense volcanism has witnessed the cretaceous paleogene transition ktb and was perhaps responsible for dramatic climatic changes and decrease in biodiversity and mass extinction we have used hg concentrations as a proxy for volcanic activity and atmospheric hg and co2 buildup across the ktb at three localities in the salta basin argentina hg contents display several spikes across the ktb with a maximum value of 250 ng g 1 in three drill cores across the ktb in the paraiba basin northeastern brazil hg contents increase from the late maastrichtian to early danian and hg spikes predate the ktb perhaps as a record of volcanic activity before but very close to this transition at stevns klint denmark hg contents reached almost 250 ng g 1 within a 5 cm thick clay layer the fiskeler member fish clay that comprises the ktb some co variation between hg and al2o3 contents has been observed in all of the studied sections across the ktb suggesting that hg is probably adsorbed onto clays thermo desorption experiments in selected samples from the yacoraite formation showed hg 2 as the major species present which is in agreement with a volcanic origin combined hg and c isotope chemostratigraphy may become a powerful tool for the eventual assessment of the role of volcanic activity during extreme climatic and biotic events such as those during the ktb

mercury isotopic composition of hydrothermal systems in the yellowstone plateau volcanic field and guaymas basin sea floor rift abstract to characterize mercury hg isotopes and isotopic fractionation in hydrothermal systems we analyzed fluid and precipitate samples from hot springs in the yellowstone plateau volcanic field and vent chimney samples from the guaymas basin sea floor rift these samples provide an initial indication of the variability in hg isotopic composition among marine and continental hydrothermal systems that are controlled predominantly by mantle derived magmas fluid samples from ojo caliente hot spring in yellowstone range in 202hg from 1 02 to 0 58 0 11 2sd and solid precipitate samples from guaymas basin range in 202hg from 0 37 to 0 01 0 14 2sd fluid samples from ojo caliente display mass dependent fractionation mdf of hg from the vent 202hg 0 10 0 11 2sd to the end of the outflow channel 202hg 0 58 0 11 2sd in conjunction with a decrease in hg concentration from 46 6 pg g to 20 0 pg g although a small amount of hg is lost from the fluids due to co precipitation with siliceous sinter we infer that the majority of the observed mdf and hg loss from waters in ojo caliente is due to volatilization of hg0 aq to hg0 g and the preferential loss of hg with a lower 202hg value to the atmosphere a small amount of mass independent fractionation mif was observed in all samples from ojo caliente 199hg 0 13 1 0 06 2sd but no significant mif was measured in the sea floor rift samples from guaymas basin this study demonstrates that several different hydrothermal processes fractionate hg isotopes and that hg isotopes may be used to better understand these processes

a shoreline boundary condition for a highly nonlinear boussinesq model for breaking waves abstract a physically based strategy was used to model swash zone hydrodynamics forced by breaking waves within a boussinesq type of model the position and the velocity of the shoreline were determined continuously in space by solving the physically based equations of the shoreline motion moreover a fixed grid method with a wet dry interface was adopted for integrating the boussinesq model the numerical stability of the model was improved by means of an extrapolation method to validate the proposed methodology the classical analytical solution for the shoreline motion of a monochromatic wave train over a plane beach was considered the comparison between the analytical and numerical horizontal shoreline movements provided a very good agreement several other tests on the run up of non breaking and breaking waves were performed as well these tests showed that the proposed model was always in fairly good agreement with the experimental data even in complex hydrodynamic situations like those forced by breaking solitary waves in particular in comparison with other state of the art shoreline models in all the analyzed cases the proposed model allowed much better predictions of the shoreline velocity to be obtained

subsidence of normal oceanic lithosphere apparent thermal expansivity and seafloor flattening abstract seafloor topography has been a key observational constraint on the thermal evolution of oceanic lithosphere which is the top boundary layer of convection in earth s mantle at least for the first 70 myr the age progression of seafloor depth is known to follow the prediction of half space cooling and the subsidence rate is commonly believed to be 350 m ma 1 2 here we show that based on a new statistical analysis of global bathymetry the average subsidence rate of normal oceanic lithosphere is likely to be 320 m ma 1 2 i e 10 lower than the conventional value we define the normal seafloor as regions uncorrelated with anomalous crust such as hotspots and oceanic plateaus but the lower subsidence rate appears to be a stable estimate not depending on how exactly we define the normal seafloor this low subsidence rate can still be explained by half space cooling with realistic mantle properties if the effective thermal expansivity of a viscoelastic mantle is taken into account in light of a revised model of half space cooling the normal seafloor unperturbed by the emplacement of anomalous crust exists for all ages and the so called seafloor flattening seems to be mostly caused by hotspots and oceanic plateaus

sublithospheric small scale convection and its implications for the residual topography at old ocean basins and the plate model 1 the seafloor topography and heat flux differ significantly from the predictions of the half space cooling hsc model at old ocean basins understanding the deviations has important implications for thermal evolution of oceanic lithosphere and large scale mantle dynamics a widely used model that explains significant fraction of the deviations is the plate model but the dynamical feasibility of the plate model has never been demonstrated in this study we investigated the effects of sublithospheric small scale convection ssc and of internal heating on seafloor heat flux and topography and mantle thermal structure and we examined the dynamic feasibility of the plate model by formulating high resolution two dimensional numerical models of mantle convection with strongly temperature and depth dependent rheology we found that mantle convection with tectonic plates often leads to formation of a broad thermal anomaly below old lithosphere where the mantle is not cooled by subducted slabs and heat transfer is less efficient because of thick lithosphere especially when significant internal heating is present this trapped heat may exist in the middle mantle when the ssc is absent and it may also be redistributed by the ssc to shallow depths to reheat the lithosphere and to homogenize mantle temperature when internal heating accounts for 60 of the total heat output the trapped heat may provide sufficient heat supply to preferentially reheat old lithosphere via ssc while maintaining uniform mantle temperature we suggest that the trapped heat and the ssc are responsible for the residual heat flux and topography at old ocean basins relative to the hsc model predictions our models also show that for the plate model to be dynamically viable both the ssc and significant internal heating 60 are necessary this is because only the ssc in a mantle with significant internal heating can erode and reheat the lithosphere while maintaining a nearly constant mantle temperature below lithosphere which is the basic assumption of the plate model with the viscosity structure and internal heating rate for the present day mantle we think that the plate model is dynamically viable

terrestrial sources as the primary delivery mechanism of mercury to the oceans across the toarcian oceanic anoxic event early jurassic abstract this study evaluates the utility of sedimentary mercury hg contents as a proxy for fingerprinting ancient massive volcanism which is often associated with biogeochemical perturbations herein we present new hg geochemical data from anoxic marine basins across the toarcian oceanic anoxic event t oae 183 ma as a test of the complex hg cycle the t oae was likely initiated by the main eruptive phase of the karoo ferrar large igneous province which caused a subsequent cascade of environmental perturbations and resulting mass extinction at present the leading interpretation of sedimentary hg anomalies has been volcanogenic outgassing as the primary source our study and compilation results suggest however that hg toc anomalies were restricted to shallow water and or proximal environments while deep water more distal depositional settings document no significant hg related anomalies furthermore asynchronous stratigraphic deviations in hg enrichments favor terrestrially sourced materials and local redox variability rather than direct volcanogenic emissions as a primary control mechanism additionally hg isotope signatures from our only study site documenting an hg anomaly are also consistent with a terrestrial hg origin during the t oae therefore our results suggest that hg anomalies in the geological record need to be re evaluated as a smoking gun proxy that only infers volcanogenic inputs

an isotopic record of mercury in san francisco bay sediment article i nfo we analyzed eight sediment cores from wetland and subtidal locations around san francisco sf bay terrace sediment from the yuba river ca and precipitation from the sf bay region we defined the hg isotopic com position of uncontaminated sf bay sediment two contributing endmember sediments contaminated by dis tinct hg sources and regional precipitation deep subtidal sediments with pre mining thg concentrations less than 60 ng g have 202

early cambrian ocean mixing recorded by phosphorite successions in the nanhua basin south china abstract phosphorite successions in the nearshore meishucun section and the offshore gezhongwu section of the nanhua basin south china were investigated to decipher the circulation pattern of the early cambrian ocean the 539 535 ma phosphorites from the meishucun section contain authigenic phosphorus rich mineral aggregates collophanite grains with much lower bio limiting elements zn cd and ni than those from the gezhongwu section in contrast collophanite grains in the 535 526 ma phosphorites from both sections have similar concentrations of these elements this change indicates that the ocean likely transformed from a chemically stratified state to a homogeneous state at 535 ma phosphorites from both sections have constant 87sr 86sr ratios and end t values supporting the interpretation of a relatively constant terrestrial input into the nanhua basin between 539 ma and 526 ma instead negative 13c excursions and similar 208pb 204pb ratios of the 535 526 ma phosphorites are indicative of an extensive upwelling of the deep oceanic water in combination with previous studies of deep ocean oxygenation our work provides evidence for the vertical mixing of the ocean between 535 ma and 526 ma which introduced o2 rich water at the ocean bottom to promote early cambrian biodiversity

global geochemical cycles of carbon sulfur and oxygen time resolved data on the carbon isotopic composition of carbonate minerals and the sulfur isotopic composition or sulfate minerals show a strong negative correlation during the cretaceous carbonate minerals are isotopically heavy during this period while sulfate minerals are isotopically light the implication is that carbon is being transferred from the oxidized carbonate reservoir to the reservoir of isotopically light reduced organic carbon in sedimentary rocks while sulfur is being transferred from the reservoir of isotopically light sedimentary sulfide to the oxidized sulfate reservoir these apparently oppositely directed changes in the oxidation state of average sedimentary carbon and sulfur are surprising because of a well established and easy to understand correlation between the concentrations of reduced organic carbon and sulfide minerals in sedimentary rocks rocks rich in reduced carbon are also rich in reduced sulfur the isotopic and concentration data can be reconciled by a model which invokes a significant flux of hydrothermal sulfide to the deep sea at least during the cretaceous

shoreline motion in nonlinear shallow water coastal models abstract different shoreline boundary conditions for numerical models of the non linear shallow water equations based on godunov type schemes are compared the study focuses on the peregrine and williams peregrine d h williams s m 2001 swash overtopping a truncated plane beach journal of fluid mechanics 440 391 399 problem of a single bore collapsing on a slope this is considered the best test to assess performances of the shoreline boundary treatments in terms of all the parameters of interest in swash zone modelling emphasis is given to the shoreline trajectory and flow velocity modelling a mismatch of the velocity at the early stage of the motion is highlighted most of the tested techniques perform similarly in terms of maximum run up the backwash phase is critical in all cases starting from the brocchini et al brocchini m bernetti r mancinelli a albertini g 2001 an efficient solver for nearshore flows based on the waf method coastal engineering 43 2 105 129 shoreline boundary treatment a simple technique that improves the accuracy of velocity predictions is also developed a sensitivity analysis of the domain resolution and the threshold value of the water depth that defines a wet cell is also presented

radially anisotropic 3 d shear wave structure of the australian lithosphere and asthenosphere from multi mode surface waves abstract a new radially anisotropic shear wave speed model for the australasian region is constructed from multi mode phase dispersion of love and rayleigh waves an automated waveform fitting technique based on a global optimization with the neighbourhood algorithm allows the exploitation of large numbers of three component broad band seismograms to extract path specific dispersion curves covering the entire continent a 3 d shear wave model is constructed including radial anisotropy from a set of multi mode phase speed maps for both love and rayleigh waves these maps are derived from an iterative inversion scheme incorporating the effects of ray path bending due to lateral heterogeneity as well as the finite frequency of the surface waves for each mode the new s wave speed model exhibits major tectonic features of this region that are in good agreement with earlier shear wave models derived primarily from rayleigh waves the lateral variations of depth and thickness of the lithosphere asthenosphere transition lat are estimated from the isotropic voigt average s wave speed model and its vertical gradient which reveals correlations between the lateral variations of the lat and radial anisotropy the thickness of the lat is very large beneath the archean cratons in western australia whereas that in south australia is thinner the radial anisotropy model shows faster sh wave speed than sv beneath eastern australia and the coral sea at the lithospheric depth the faster sh anomaly in the lithosphere is also seen in the suture zone between the three cratonic blocks of australia one of the most conspicuous features of fast sh anisotropy is found in the asthenosphere beneath the central australia suggesting anisotropy induced by shear flow in the asthenosphere beneath the fast drifting australian continent

integral properties of the swash zone and averaging part 3 longshore shoreline boundary conditions for wave averaged nearshore circulation models the aim of the present work final of a three part series is to analyse in detail flow motions within the swash zone and define suitable shoreline boundary conditions for the longshore flow for wave averaged circulation models the analyses of parts 1 and 2 are extended to cover horizontally two dimensional flows an analytical solution for the longshore motion representing the drift velocity of the whole swash zone water mass is found this is seen to be approximated well by the ratio between the time integral of the longshore momentum flux crossing the swash lower boundary and the swash zone net water volume further a complete set of shoreline boundary conditions taking into account wave wave interactions is obtained on the basis of fully numerical solutions of the nonlinear shallow water equations the main focus of the work is to clarify the structure of the shoreline boundary conditions for the longshore flow but attention has also been paid to their derivation and assessment from the numerical solutions the latter have been obtained on the basis of a fairly broad range of input wave conditions which though biased towards those typical of reflective beaches are believed to cover conditions also typical of moderate dissipative beaches two main terms are found to contribute to the longshore drift velocity i a term proportional to the shallow water velocity accounting for short wave interactions frictional swash zone forces and continuous forcing due to non breaking wave nonlinearities and ii a drift type term representing the momentum transfer due to wave breaking

an efficient solver for nearshore flows based on the waf method abstract we describe an efficient and robust flow solver for the integration of the classic nonlinear shallow water equations nswe on a beach of arbitrary topography on the basis of the shock capturing weighted average flux waf method a numerical code is implemented which employs a space splitting technique to integrate the nswe over a horizontally two dimensional domain 2dh special care is put in handling the moving shoreline and a new efficient formulation of the shoreline boundary conditions is presented this is based on the hydrodynamic equivalent of the cavitation condition used in gas dynamics model capabilities are illustrated by means of a number of tests both 1dh and 2dh these reveal that though primarily conceived for modelling nearshore hydrodynamics the solver can be successfully adopted even for studying the run up of large tsunami waves

isotopic signatures of mercury contamination in latest permian oceans sedimentary records from the northwest margin of pangea and the tethys show anomalously high hg levels at the latest permian extinction boundary background 202 hg values are consistent with normal marine conditions but exhibit negative shifts coincident with increased hg concentrations hg isotope mass independent fractionation 199 hg trends are consistent with volcanic input in deep water marine environments in contrast nearshore environments have 199 hg signatures consistent with enhanced soil and or biomass input we hypothesize that the deep water signature represents an overall global increase in volcanic hg input and that this isotope signature is overwhelmed in nearshore locations due to hg from terrestrial sources high productivity nearshore regions may have experienced stressed marine ecosystems due to enhanced hg loading

mercury and in situ sulfur isotopes as constraints on the metal and sulfur sources for the world s largest sb deposit at xikuangshan southern china it has been well established that metal and sulfur sources in mineral deposits can be very difficult to identify especially for ore deposits hosted in sedimentary rocks using the world s largest sb deposit at xikuangshan in southern china as a case study this study combined hg isotopes and in situ sulfur isotope measurements to constrain the sources of sb and sulfur a variation of 1 1 in 202hg 0 04 to 1 15 was observed in stibnite ore samples suggesting that mass dependent fractionation of hg isotopes occurred during the formation of the deposit significant mass independent fractionation of hg isotopes with 199hg ranging from 0 03 to 0 17 was also observed in the ore samples suggesting that hg transported by the ore fluids was inherited from proterozoic basement metamorphic rocks as these rocks show similar 199hg signatures 0 03 to 0 07 in situ sulfur isotope measurements yielded 34s values that cluster in the range of 6 8 to 10 2 providing evidence that sulfur contained in ore fluids may also have been dominantly derived from underlying proterozoic basement metamorphic rocks 34s 5 6 to 11 5 using the new results from hg and s isotopes we proposed that deep circulated meteoric water mobilized sb hg and s from the proterozoic metamorphic basement ascended along deep faults and subsequently deposited sb at favorable structural zones as a result of boiling of the hydrothermal fluids generating the world class xikuangshan sb deposit this study also highlights the combined use of hg s isotopes as a novel method to provide new and additional insights into the source regions of ore materials for sedimentary hosted sb deposits

geochemical investigation of the lower cambrian mineralised black shales of south china and the late devonian nick deposit canada abstract lower cambrian tommotian black shales of the niutitang formation south china host a thin accumulation 5 20 cm of ni mo platinum group elements pge au ni as zn cu v and rare earth elements ree of all known deposits the late devonian ni mo pge sulphide horizon in black shales of the nick deposit selwyn basin in canadian yukon presents the strongest similarity with the niutitang formation polymetallic layer in the present study samples of the mineralised layer and host shales in south china from two mine sites zunyi and sancha were investigated in order to further characterise the prevailing redox conditions and mechanisms involved in the metal concentration process at both sites additional comparison with the nick deposit mineralised layer was also undertaken bulk geochemical analysis including pge analysis were conducted on all samples along with m scale investigation of metal distributions and associations by x ray fluorescence xrf mapping and synchrotron xrf mapping the comparison of the two sites from south china highlights strong similarities in metal enrichment factors pge and ree distribution patterns are also highly similar and suggest a source from seawater strong variations in elemental distributions at m scale were observed at both sites most likely related to intense variations in redox conditions in the sediment the comparison with the nick deposit highlights a stronger enrichment in ni and zn in the nick deposit and a greater variety of minerals in the niutitang shales the pge and ree distributions of both the nick deposit and the niutitang shales however present highly similar patterns and support an origin from seawater the present study provides further insight into mineralisation style and processes in these mineralised black shales highlighting the importance of redox conditions and re emphasizing the role of organic matter in the formation of these mineralised layers

spatio temporal evolution of ocean redox and nitrogen cycling in the early cambrian yangtze ocean abstract the early cambrian was a critical interval for the earth system during which a rise in oceanic and atmospheric oxygen levels coincided with the rapid diversification of metazoans a variety of contrasting models have been proposed for the spatiotemporal redox evolution of the early cambrian ocean these include the development of a well oxygenated deep ocean at the base of cambrian stage 3 commencing at 521 ma or alternatively persistent and widespread anoxic ferruginous conditions throughout the early cambrian ocean here we present redox sensitive trace element rste fe speciation and n and c isotope 15nsed and 13corg data for samples from a section zhongnancun of the early cambrian niutitang formation which was deposited on the outer shelf of the yangtze block south china the fe speciation and rste data provide evidence of a transition from euxinic through ferruginous to oxic conditions during deposition of the niutitang formation the combination of these new data with existing data from the inner shelf to basin environment implies regional redox stratification across the yangtze block during cambrian stages 2 and 3 with oxic shallow waters above ferruginous deep waters and spatial variability in the degree of mid depth euxinia oxygenation of deeper waters may have occurred by early cambrian stage 4 514 ma a compilation of 15n values from multiple early cambrian sections of the yangtze block indicate that n2 fixation dominated the nitrogen cycle during late cambrian stage 2 low 15n values

imaging the seismic lithosphere asthenosphere boundary of the oceanic plate 1 the seismic lithosphere asthenosphere boundary lab or g discontinuity a seismologically characterized abrupt drop in wave speed in the uppermost mantle is one of the key issues in current geodynamics although plate tectonics started as a theory for the ocean reports on lab for normal oceanic regions are scarce due to paucity of seismic data and whether or not the oceanic lab grows with age is the key issue to be resolved we conduct a systematic survey for the oceanic lab using s to p converted seismic waves along three margins of oceanic plates whose crustal age ranges from 10 myr to 130 myr and we observe laterally continuous oceanic lab images the thickness of the oceanic plate estimated from labs increases with the plate age though scattered suggesting that the evolution of oceanic lithosphere is predominantly governed by temperature and that the oceanic seismic lab represents a boundary that grows with age

latest permian mercury anomalies a sedimentary record from the buchanan lake section canadian high arctic shows anomalous high levels of mercury hg during the latest permian extinction lpe on northwest pangea significant influx of hg progressively overwhelmed the marine system major disruption of the organic matter mediated hg drawdown process resulted in accumulation of dissolved hg to maximum levels at the lpe boundary affecting an already stressed global ecosystem a switch to euxinic marine conditions at the lpe boundary led to chemical drawdown of hg sulfides as marked by progressive hg mitigation this allowed self recovery from toxic hg conditions and ultimately led to reestablishment of the internal hg organic matter drawdown process we hypothesize that anomalous hg levels may be attributed to the significant natural atmospheric emissions caused by catastrophic siberian traps volcanic eruptions

a c mos2 mixed layer phase mosc occurring in metalliferous black shales from southern china and new data on jordisite a new phase composed mainly of mo s and c and referred to herein as mosc occurs widely in organic rich metalliferous cambrian black shales in south china mosc which has previously been referred to as jordisite has been studied by scanning electron microscopy sem electron microprobe analysis empa transmission electron microscopy tem powder x ray diffraction xrd extended x ray absorption fine structure exafs and catalytic activity tem data show mosc to have a layered structure with packets resembling molybdenite and graphite like carbon that average five layers in thickness analytical data are consistent with an idealized formula of mo3s6c10 but it commonly contains 1 3 wt each of fe ni and as so that its composition may be better approximated by the formula mo fe ni 3 s as 6c10 selected area electron diffraction saed patterns show a small number of broad inhomogeneous rings corresponding to randomly oriented layers arranged in subspherical cells a single broad weak peak corresponds to a 10 11 a layer spacing in powder xrd diffraction patterns pseudomorphism after fossil bacteria implies an origin by replacement of sedimentary organic material in its chemical properties and structure mosc resembles synthetic compounds used as catalysts for hydrodesulfurization hds in the petrochemical industry the large surface to volume ratio for mosc may be an important factor in its relatively strong hds catalytic activity cotype samples of jordisite from germany previously thought to be amorphous mos2 were also studied by sem and tem jordisite occurs as sequences of a few curved layers that form sub spherical units with an appearance remarkably like that of mosc however the layer spacing is 6 a like that of molybdenite the ratio of mo s is 1 2 and no carbon was detected although it coexists with kerogen jordisite is thus confirmed to be a form of mos2 but because powder diffraction like saed patterns were obtained it is not amorphous

surface water oxygenation and bioproductivity a link provided by combined chromium and cadmium isotopes in early cambrian metalliferous black shales nanhua basin south china abstract the intrinsic link between atmospheric oxygenation surface seawater redox and bioproductivity in the upper water column of oceans offers to combine cadmium with chromium isotopes in marine archives to deduce information on past controls of biological metal and nutrient cycling we here use a novel approach in combining chromium and cadmium isotope signatures in metalliferous and organic matter om rich shales from the early cambrian niutitang formation south china to reconstruct the surface water redox and cycling of bioessential metals in a period directly following the cambrian animal evolution the inventory of authigenic cd in the black shales is controlled by their sulfide abundance whereas authigenic cr is dominantly controlled by iron oxy hydroxides and om cadmium isotopes measured on bulk sediments and 3 n hno3 leachates exhibit e114cd values from 1 5 to 4 5 with mo ni rich sulfidic shales revealing elevated values 2 5 chromium isotopes define 53cr values from 0 4 to 1 7 with v rich non sulfidic shales yielding more positively fractionated signatures than mo ni rich sulfidic shales the negative 53cr e114cd correlation trend recorded in the black shales suggests a high e114cd sulfide endmember of authigenic cd preserved in anoxic bottom conditions the other endmember is constituted by om with the isotopically heavy cr and light cd signals reflecting efficient phytoplankton uptake in the photic zone the endmembers constrain the cd and cr isotope signatures of surface waters in the early cambrian nanhua basin to e114cd of 7 to 17 and to 53cr of 0 7 to 1 9 these values are compatible with those of modern ocean surface waters and attest to a cambrian surface ocean water sustaining elevated primary bioproductivity in the aftermath of late ediacaran snowball earth glaciations our study emphasizes the potential of the cr cd double tracer in studies aimed at the reconstruction of paleoproductivity and bio geochemical metal cycling in marine paleo basins

new u pb age from the basal niutitang formation in south china implications for diachronous development and condensation of stratigraphic units across the yangtze platform at the ediacaran cambrian transition abstract the black shale dominated niutitang formation covers a large portion of the early cambrian yangtze platform in south china the base of this unit has been traditionally taken as the ediacaran cambrian boundary ca 542 ma recent radiometric ages from the basal niutitang formation and its correlative units however are significantly younger than 542 ma and raise questions about the diachrony of stratigraphic units across the yangtze platform at the ediacaran cambrian transition here we report a new u pb sensitive high resolution ion microprobe shrimp age of 522 7 4 9 ma from a tuffaceous bed of the basal niutitang formation in a deep water section in taoying guizhou province of south china this age in combination with existing ages and biostratigraphic data suggests that the base of the niutitang formation is of tommotian or upper meishucunian age and the ediacaran cambrian boundary is most likely within the liuchapo formation the depositional age of the unusual metal enriched ni mo pge sulfide deposits which are approximately 1 m above the ca 523 ma tuffaceous bed should be early tommotian upper meishucunian rather than early nemakit daldynian lower meishucunian regional correlation confirms the diachronous development and condensation of stratigraphic units across the early cambrian yangtze platform and provides important information for understanding the paleogeography and paleoceanographic events at the ediacaran cambrian transition in south china

the runup of solitary waves this is a study of the runup of solitary waves on plane beaches an approximate theory is presented for non breaking waves and an asymptotic result is derived for the maximum runup of solitary waves a series of laboratory experiments is described to support the theory it is shown that the linear theory predicts the maximum runup satisfactorily and that the nonlinear theory describes the climb of solitary waves equally well different runup regimes are found to exist for the runup of breaking and non breaking waves a breaking criterion is derived for determining whether a solitary wave will break as it climbs up a sloping beach and a different criterion is shown to apply for determining whether a wave will break during rundown these results are used to explain some of the existing empirical runup relationships

magnetic lineations within shatsky rise northwest pacific ocean implications for hot spot triple junction interaction and oceanic plateau formation oceanic plateaus are major ocean features yet their origins and development are poorly understood many are huge piles of basalt and it is widely accepted that mantle plumes are their source perhaps from eruptions of the voluminous head of an emerging plume shatsky rise is a basaltic plateau that formed during a period of geomagnetic reversals unlike many mid cretaceous plateaus so magnetic data can help us understand its tectonic history in this study we analyzed magnetic anomaly data from 131 cruises over and around shatsky rise and constructed a magnetic lineation chart for tectonic interpretation a significant finding is that magnetic lineations are traceable through low parts of the rise between volcanic massifs indicating nearly normal lithosphere and between large volcanic edifices many lineations form bights near the rise axis and show former locations of the pacific izanagi farallon triple junction they indicate that the junction was in a ridge ridge ridge rrr configuration and closely followed the rise axis from chron m20 146 ma to chron m4 127 ma lineation and bight geometries indicate that the triple junction jumped northeastward at least nine times often apparently in response to volcanic activity from the mantle plume some jumps however appear related to ridge reorientations numerous features within the rise are parallel to lineations or lineation offsets implying that the plateau formed near the triple junction and was modified by ridge faulting most of our observations support the hypothesis that shatsky rise was formed by a mantle plume that captured a triple junction

a 2d numerical model of wave run up and overtopping a two dimensional 2d numerical model of wave run up and overtopping is presented the model called ott 2d is based on the 2d nonlinear shallow water nlsw equations on a sloping bed including bed shear stress these equations are solved using an upwind finite volume technique and a hierarchical cartesian adaptive mesh refinement amr algorithm the 2d nature of the model means that it can be used to simulate wave transformation run up overtopping and regeneration by obliquely incident and multi directional waves over alongshore inhomogeneous sea walls and complex submerged or surface piercing features the numerical technique used includes accurate shock modeling and uses no special shoreline tracking algorithm or shoreline coordinate transformation which means that noncontiguous flows and multiple shorelines can easily be simulated the adaptivity of the model ensures that only those parts of the flow that require higher resolution such as the region of the moving shoreline receive it resulting in a model with a high level of efficiency the model is shown to accurately reproduce analytical and benchmark numerical solutions existing wave flume and wave basin datasets are used to test the ability of the model to approximate 1d and 2d wave transformation run up and overtopping finally we study a 2d dataset of overtopping of random waves at off normal incidence to investigate overtopping of a sea wall by long crested waves the data set is interesting as it has not been studied in detail before and suggests that in some instances overtopping at an angle can lead to more flooding than at normal incidence

sediment transport and morphodynamics generated by a dam break swash uprush coupled vs uncoupled modeling the present work analyzes the hydro morphodynamics characterizing the swash region during the uprush stage a comparison is illustrated between the sediment transport measured in a series of dam break experiments and that predicted by the numerical hydro morphodynamic model of postacchini et al 2012 the primary aim is to investigate the differences arising between the weakly coupled or uncoupled model and the measurements in terms of hydrodynamics tip celerity and sediment transport the hydrodynamics are well described by the model and results have been used to calibrate both friction factor and subgrid turbulent viscosity comparison of numerically computed tip celerity with experimental data reveals a fairly good agreement i e a mean error of about 10 while modeled sediment transport differs by about 40 from the available data no evident differences are found between results obtained from the coupled and uncoupled model runs 2 for the celerity and 11 for the sediment transport rate at the tip suggesting that for the specific flow under investigation at the leading edge of the swash front hydro morphological coupling is not an issue of fundamental importance however for the special case here of a swash forced by a dam break scour occurs at the dam location and in this case the erosion of the bed is significantly larger in the uncoupled model

numerical simulation of wave overtopping of coastal structures using the non linear shallow water equations a one dimensional high resolution finite volume model capable of simulating storm waves propagating in the coastal surf zone and overtopping a sea wall is presented the model amazon is based on solving the non linear shallow water nlsw equations a modern upwind scheme of the godunov type using an hll approximate riemann solver is described which captures bore waves in both transcritical and supercritical flows by employing a finite volume formulation the method can be implemented on an irregular structured boundary fitted computational mesh the use of the nlsw equations to model wave overtopping is computationally efficient and practically flexible though the detailed structure of wave breaking is of course ignored it is shown that wave overtopping at a vertical wall may also be approximately modelled by representing the wall as a steep bed slope the amazon model solutions have been compared with analytical solutions and laboratory data for wave overtopping at sloping and vertical seawalls and good agreement has been found the model requires more verification tests for irregular waves before its application as a generic design tool

anomalous mercury enrichment in early cambrian black shales of south china mercury isotopes indicate a seawater source abstract extremely elevated hg levels up to the g g 1 range were found in sulfide rich black shale and phosphorite in the lowermost part of the early cambrian black shale sequences on the yangtze platform in south china in this study mercury isotopes were used to help resolve the origin of this anomalous hg enrichment mass independent fractionation signatures of hg isotopes with positive 199 hg values of 0 13 to 0 24 and positive 200 hg values of 0 05 to 0 10 were observed indicating seawater is an important source of hg we hypothesize that upwelling of nutrient rich waters from the open ocean resulted in high bioproductivity in the photic zone with concomitant scavenging of hg from seawater advanced decay of biomass and remineralization under anoxic to euxinic conditions combined with very low clastic input led to enrichment of hg and a broad spectrum of other redox sensitive and biogenic metals up to 10 7 compared to modern seawater such spectacular hydrogenous metal enrichment has previously been observed in the oxic deep sea environment only i e manganese crusts nodules

surf zone dynamics simulated by a boussinesq type model part i model description and cross shore motion of regular waves abstract this is the first of three papers on the modelling of various types of surf zone phenomena in this first paper part i the model is presented and its basic features are studied for the case of regular waves the model is based on two dimensional equations of the boussinesq type and it features improved linear dispersion characteristics possibility of wave breaking and a moving boundary at the shoreline the moving shoreline is treated numerically by replacing the solid beach by a permeable beach characterized by an extremely small porosity run up of nonbreaking waves is verified against the analytical solution for nonlinear shallow water waves the inclusion of wave breaking is based on the surface roller concept for spilling breakers using a geometrical determination of the instantaneous roller thickness at each point and modelling the effect of wave breaking by an additional convective momentum term this is a function of the local wave celerity which is determined interactively the model is applied to cross shore motions of regular waves including various types of breaking on plane sloping beaches and over submerged bars model results comprise time series of surface elevations and the spatial variation of phase averaged quantities such as the wave height the crest and trough elevations the mean water level and the depth averaged undertow comparisons with physical experiments are presented the phaseaveraged balance of the individual terms in the momentum and energy equation is determined by time integration and quantities such as the cross sectional roller area the radiation stress the energy flux and the energy dissipation are studied and discussed with reference to conventional phase averaged wave models the companion papers present cross shore motions of breaking irregular waves swash oscillations and surf beats part ii and nearshore circulations induced by breaking of unidirectional and multidirectional waves part iii

the geochemical behavior and isotopic composition of hg in a mid pleistocene western mediterranean sapropel abstract the concentrations of mercury hg and other trace metals ni cu zn mo ba re u and the hg isotopic composition were examined across a dramatic redox and productivity transition in a mid pleistocene mediterranean sea sapropel sequence characteristic trace metal enrichment in organic rich layers was observed with organic rich sapropel layers ranging in hg concentration from 314 to 488 ng g avg 385 with an average enrichment in hg by a factor of 5 9 compared to organic poor background sediments which range from 39 to 94 ng g hg avg 66 comparison of seawater concentrations and sapropel accumulations of trace metals suggests that organic matter quantitatively delivers hg to the seafloor near complete scavenging of hg from the water column renders the sapropel hg isotopic composition representative of mid pleistocene mediterranean seawater sapropels have an average 202hg value of 0 91 0 15 n 5 1 sd and 199hg value of 0 11 0 03 n 5 1 sd background sediments have an average 202hg of 0 76 0 16 n 5 1 sd and 199hg of 0 05 0 01 n 5 1 sd which is indistinguishable from the sapropel values we suggest that the sapropel isotopic composition is most representative of the mid pleistocene tyrrhenian sea

a boussinesq model for waves breaking in shallow water abstract a simple description of wave breaking in shallow water is incorporated in the boussinesq equations by using the concept of surface rollers the roller is considered as a volume of water being carried by the wave with the wave celerity the effect of the roller is included in the vertical distribution of the horizontal velocity which leads to an additional convective momentum term the breaking criterion is related to the local slope of water surface and the thickness of the roller is determined from simple geometrical considerations although the model is simple it is capable of representing a variety of processes such as the initiation and cessation of wave breaking the evolution of wave profiles before during and after wave breaking the initial conversion of potential energy into forward momentum flux and the associated horizontal shift between the break point and the point where the setup in mean water level is initiated results are presented for regular and irregular wave trains and comparison with measurements shows good agreement

sources and cycling of mercury in the paleo arctic ocean from hg stable isotope variations in eocene and quaternary sediments abstract mercury stable isotopic compositions were determined for marine sediments from eight locations in the arctic ocean basin mass dependent fractionation mdf and mass independent fractionation mif of hg stable isotopes were recorded across a variety of depositional environments water depths and stratigraphic ages 202hg mdf ranges from 2 34 to 0 78 199hg mif from 0 18 to 0 12 and 201hg mif from 0 29 to 0 05 for the complete data set n 33 holocene sediments from the chukchi sea and morris jesup rise record the most negative 199hg values while pleistocene sediments from the central arctic ocean record the most positive 199hg values the most negative 202hg values are recorded in pleistocene sediments eocene sediments lomonosov ridge show some overlap in their hg isotopic compositions with quaternary sediments with a sample of the arctic ocean petm 56 ma most closely matching the average hg isotopic composition of holocene arctic marine sediments collectively these data support a terrestrially dominated hg source input for arctic ocean sediment through time although other sources as well as influences of sea ice atmospheric mercury depletion events amdes and anthropogenic hg in core top samples on hg isotopic signatures must also be considered