midshelf to surfzone coupled roms swan model data comparison of waves currents and temperature diagnosis of subtidal forcings and response abstracta coupled wave and circulation model that includes tide wind buoyancy and wave processes is necessary to investigate tracer exchange in the shelf region here a coupled regional ocean model system roms simulating waves nearshore swan model resolving midshelf to the surfzone region of the san pedro bay california is compared to observations from the 2006 huntington beach experiment waves are well modeled and surfzone cross and alongshore velocities are reasonably well modeled modeled and observed rotary velocity spectra compare well in subtidal and tidal bands and temperature spectra compare well in the subtidal band observed and modeled mid and inner shelf subtidal velocity ellipses and temperature variability determined from the first vertical complex eof ceof mode have similar vertical structure although the modeled subtidal velocity vertical shear and stratification are weaker than observed the ratio of stratification to shear is similar suggesting model vertical mixing i

tectonic plate generation and two phase damage void growth versus grain size reduction 1 the generation of plate tectonics from mantle convection requires shear localization in order to yield narrow weak plate boundaries separating broad strong plates a plausible shear localizing mechanism involves damage e g distributed microcracking one theoretical model of which involves two phase mechanics two phase damage theory employs a nonequilibrium relation between interfacial surface energy pressure and viscous deformation thereby providing a description of void generation and microcracking and hence weakening failure and shear localization here we examine the application of this theory to the problem of generating plate like behavior from convective type divergent convergent poloidal motion through a source sink formulation we extend the previous damage theory to consider two possible damage effects 1 growth and nucleation of voids associated with dilation of the host matrix and 2 increasing fineness i e reducing coarseness of the mixture by for example grain size reduction void generating damage is found to be poor at plate generation because of the predominance of dilational motion that is adverse to the development of plate like flow fineness generating damage is found to be very efficient at generating plate like behavior if we assume that the matrix viscosity is a simple function of grain void size as is typical for diffusion creep the implied grain size reduction mechanism is different from that of dynamic recrystallization and appears to be more capable of generating the requisite shear localization for forming tectonic plates from mantle flow

wave current interaction in willapa bay 1 this paper describes the importance of wave current interaction in an inlet estuary system the three dimensional fully coupled coupled ocean atmosphere wave sediment transport coawst modeling system was applied in willapa bay washington state from 22 to 29 october 1998 that included a large storm event to represent the interaction between waves and currents the vortex force method was used model results were compared with water elevations currents and wave measurements obtained by the u s army corp of engineers in general a good agreement between field data and computed results was achieved although some discrepancies were also observed in regard to wave peak directions in the most upstream station several numerical experiments that considered different forcing terms were run in order to identify the effects of each wind tide and wave current interaction process comparison of the horizontal momentum balances results identified that wave breaking induced acceleration is one of the leading terms in the inlet area the enhancement of the apparent bed roughness caused by waves also affected the values and distribution of the bottom shear stress the pressure gradient showed significant changes with respect to the pure tidal case during storm conditions the momentum balance in the inlet shares the characteristics of tidal dominated and wave dominated surf zone environments the changes in the momentum balance caused by waves were manifested both in water level and current variations the most relevant effect on hydrodynamics was a wave induced setup in the inner part of the estuary

stratigraphical and palaeogeographical significance of the continental sedimentary transition across the permian triassic boundary in spain abstract the permian triassic transition a time of phenomenal palaeoenvironmental and palaeogeographical change represents the largest episode of mass extinctions known to palaeontologists this episode is however very poorly understood and a lack of sediments and palaeontological data particularly in the continental record is a feature common to every basin despite compelling information on the continental permian triassic boundary ptb emerging from recent efforts evaluating vertebrate evolution fungal events and isotope curves results are still insufficient to make any valuable correlations among continental basins and are even less appropriate for relating sediments of continental to those of marine origin the present report discusses and attempts to locate the ptb in the basins of iberia and balearic islands through an analysis of the palaeontological and sedimentary record across the permian triassic transition the aim of the paper is to contribute to our present knowledge of the palaeogeographical and stratigraphical significance of the permian and triassic continental units of western europe the present day iberian ranges catalonian ranges and balearic islands hold the most complete late permian early triassic sedimentary record in iberia this record consists of alluvial sediments mainly of braided fluvial systems corresponding to the saxonian and buntsandstein facies all the units examined so far have been dated through palynological associations the two saxonian facies formations are of thuringian age although the lower one shows some palynological elements of autunian affinities the buntsandstein units range from thuringian to anisian in age there being no evidence up to now of the scythian in iberia the exact position of the ptb in iberia is up to now impossible to pinpoint with the precision of the marine series sedimentary characteristics and palynological data in the iberian ranges point that it lies at the sedimentary interval 10 to 30 m thick formed by the upper member of the la hoz del gallo formation and the lowermost beds of the canizar formation or its time equivalent the prades and eramprunya units in the catalonian ranges and the asa and b 1 in the balearic islands we compare a normalized standard late permian middle triassic column of the iberian ranges with standards from western and central europe and the southern urals using recent permian time scales a palaeogeographic essay map of the permian triassic transition is provided for the iberian plate the plate was located in a northern subtropical position 200 400 km from the westernmost tethys coast as part of the central pangean mountain range comprised of the appalachian mauretanide variscan orogenic belts of estimated altitudes 2000 4000 m based on this palaeogeographic location sedimentary characteristics and the main wind flows established for the tethys we can infer conditions of high precipitation dominated by monsoon and seasonal regimes with isolated semiarid areas for the iberian plate during the transition

role of a low viscosity zone in stabilizing plate tectonics implications for comparative terrestrial planetology 1 earth s near surface layer its lithosphere is broken into quasi rigid plates that form the upper thermal boundary layer for mantle convection since the discovery of plate tectonics it has been widely conjectured but only recently demonstrated that this peculiar style of convection may be facilitated by an upper mantle low viscosity zone lvz over which the plates glide easily the lvz or asthenosphere concept dates from 19th century investigations of isostatic support of mountain belts and is supported by modern evidence for a seismic low velocity zone and by studies of postglacial rebound and dynamic compensation of the earth s gravity field here we show in both two dimensional 2 d cartesian and 3 d spherical earth models that combining a pronounced lvz and a plastic yield stress to allow localized weakening of the cold thermal boundary layer results in a distinctly plate tectonic style of convection with 30 toroidal surface motion for the 3 d case recycling of water into the upper mantle at subduction zones is a plausible cause of earth s lvz whereas venus is dry and lacks both an lvz and plate tectonics

observational estimates of entrainment and vertical salt flux in the interior of a spreading river plume 1 observational estimates of entrainment and vertical salt flux into the tidally pulsed columbia river plume are presented drifting buoys deployed in ebbing plume water downstream of the lift off region are used to make measurements of velocity salinity and horizontal divergence in the surface layer drifters released near the river mouth shoreward of the propagating ocean plume front catch up to the front consistent with classical models of plume front circulation during their offshore transit drifter streamwise velocities decrease while salinities increase assuming drifter measured quantities are representative of plume averaged quantities conservation equations evaluated between adjacent spreading drifters are used to determine the plume depth and entrainment velocity throughout the experiment this approach provides knowledge of the mixing involved between the active lift off region and the offshore ocean plume front as the flow evolves because the surface drifters do not downwell at the ocean plume front we do not estimate mixing in that region we find that entrainment and vertical salt flux are largest near the river mouth as expected with typical values of o 10 3 m s 1 and o 10 2 practical salinity units psu m s 1 respectively and that these quantities steadily decrease as the drifters move offshore profiles of water properties following the drifters provide knowledge of vertical stratification 0 5 4 psu m 1 at the plume base allowing for discrete estimates of the eddy diffusivity of salt ks typical plume values of ks are o 10 3 m2 s 1 similar to estimates made in other plume systems and 2 orders of magnitude larger than open ocean eddy diffusivity estimates

results of global atmospheric circulation experiments on an earth with a meridional pole to pole continent four general circulation models forced by mean annual insolation and having an energy balance ocean have been run for pole to pole continents 1 low relief 750 m average elevation 2 high plateau 1500 m average elevation 3 mostly low 750 m but with 3 km mountains on the west and 4 mostly low 750 m but with 3 km mountains on the east the high plateau continent emphasizes the contrast between high and low pressure systems marginal mountains on either coast enhance moisture transport from the west to the continental interior but mountains on the east eliminate the tropical wet belt and produce the most arid scenario in none of the experiments do zonal climate boundaries trend steeply equatorward from east to west all of the models produce more arid continental conditions than exist today

generation of plate like behavior and mantle heterogeneity from a spherical viscoplastic convection model 1 how plate tectonics arises from mantle convection is a question that has only very recently become feasible to address with spherical viscoplastic computations we present mainly internally heated convection results with temperature dependent viscosity and explore parts of the rayleigh number ra yield stress y phase space as well as the effects of depth dependent y bottom heating and a low viscosity asthenosphere convective planform and toroidal poloidal velocity field ratio tpr are affected by near surface viscosity variations and tpr values are close to observed values for our most plate like models at the relatively low convective vigor that is accessible at present most models favor spherical harmonic degree one convection though models with a weaker surface viscosity form degree two patterns and reproduce tomographically observed power spectra an asthenospheric viscosity reduction improves plate like nature as expected for our incompressible computations pure bottom heating produces strong plumes that tend to destroy plates at the surface this implies that significant internal heating may be required both to reduce the role of active upwellings and to form a low viscosity zone beneath the upper boundary layer

an asymptotic theory for the interaction of waves and currents in coastal waters a multi scale asymptotic theory is derived for the evolution and interaction of currents and surface gravity waves in water of finite depth under conditions typical of coastal shelf waters outside the surf zone the theory provides a practical and useful model with which wave current coupling may be explored without the necessity of resolving features of the flow on space and time scales of the primary gravity wave oscillations the essential nature of the dynamical interaction is currents modulating the slowly evolving phase of the wave field and waves providing both phase averaged forcing of long infra gravity waves and wave averaged vortex and bernoulli head forces and hydrostatic static set up for the low frequency current and sea level evolution equations analogous relations are derived for wave averaged material tracers and density stratification that include advection by horizontal stokes drift and by a vertical stokes pseudo velocity that is the incompressible companion to the horizontal stokes velocity illustrative solutions are analysed for the special case of depth independent currents and tracers associated with an incident surface wave field and a vortex with o 1 rossby number above continental shelf topography

subduction initiation at a strike slip plate boundary the cenozoic pacific australian plate boundary south of new zealand 1 we first present a synthesis of the macquarie ridge complex mrc tectonic structures as well as paleo reconstruction models of the kinematic evolution of the pacific australia plate boundary south of new zealand since the eocene we then ascertain the geodynamical conditions that preceded subduction initiation and identify the nature and structures of the crust that first subducted at the puysegur subduction zone this synthesis is used to produce a subduction initiation model for the puysegur region concomitant to inception of the alpine fault ca 23 ma a 150 km wide transpressive relay zone developed along puysegur bank inherited structures enabling localization of compressive deformation right lateral motion at the relay zone has juxtaposed oceanic and continental crusts facilitating inception of subduction and controlling the subduction vergence subsequently the puysegur subduction zone initiated at the transpressive relay zone ca 20 ma upper and lower plate inherited structures guided and facilitated the lengthening of the subduction zone during the neogene the four individual segments of the mrc represent different stages of incipient subduction whose development depends on local geodynamical conditions and lithospheric heterogeneities the example of the mrc demonstrates that subduction can initiate from an oceanic spreading center through progressive changes in plate kinematics within a 10 15 myr time frame index terms 3040 marine geology and geophysics plate tectonics 8150 8155 8157 8158 8155 tectonophysics plate motions general 9604 information related to geologic time cenozoic keywords subduction initiation pacific australia plate motion cenezoic macquarie ridge

ebb tide dynamics and spreading of a large river plume abstract momentum balances in the near field region of a large tidally pulsed river plume are examined the authors concentrate on a single ebb tide of the columbia river plume using the regional ocean modeling system roms configured to hindcast flow conditions on the washington and oregon shelves and in the columbia river estuary during ebb plume interior streamwise balances are largely between advection pressure gradient and frictional forces stream normal balances in this region reduce to centrifugal cross stream pressure gradient and coriolis terms i e the gradient wind balance commonly assumed in river plume bulge investigations temporal derivatives are most important at the plume front and as the ebb progresses winds were light and contributed little to the force balance midebb stress and vertical salt flux were largest at a midplume depth where stratification and vertical shear were also high consistent with shear induced mixing internal stress slows the spreading plume consi

late triassic liassic paleoclimatology of the photo central north atlantic rift system abstract the photo central north atlantic rift system was a complex of grabens and half grabens trending southwest northeast sedimentological and paleontological evidence suggests increasing aridity toward the northern end of the rift system and increasing aridity from the late triassic into the liassic the entire rift system drifted slowly northward during the triassic and liassic its northern end had reached about 20 n at the end of the triassic salt deposits in the eastern and central part of the rift synchronous with coal swamps fresh water lakes and zeolitic playas in basins on the western margin of the rift system suggest that the local climatology was controlled by adiabatic processes associated with the lower eastern and higher western border mountains

observed and modeled drifters at a tidal inlet material transport and dispersion near the mouth of a tidal inlet new river inlet nc are investigated using gps tracked drifters and numerical models for ebb tide releases velocities are largest 1 m s 1 in two approximately 30 m wide channels that bisect the 1 3 m deep ebb shoal in the channels drifter and subsurface current meter velocities are similar consistent with strong vertical mixing and 2 d hydrodynamics drifters were preferentially entrained in the channelized jets where drifter cluster lateral spreading rates in were small in 0 5 m2 s 1 at the seaward edge of the ebb shoal jet velocities decrease linearly with distance to 0 2 m s 1 about 1 km from shore and cluster spreading rates are larger with out 3 m2 s 1 although the models coawst and nearcom generally reproduce the observed trajectory directions certain observed drifter properties are poorly modeled for example modeled mean drifter velocities are smaller than observed and upon exiting the inlet observed drifters turn north more than modeled drifters the model simulations do reproduce qualitatively the spreading rates observed in the inner inlet the flow deceleration and the increase in out observed in the outer inlet however model spreading rates increase only to out 1 m2 s 1 smaller modeled than observed out may result from using unstratified models noncoincident in space observations show evidence of a buoyant plume 1 kg m 3 in the outer inlet likely affecting drifter lateral spreading generally drifter based model performance is good within the inlet channels where tidal currents are strongest whereas model data differences are significant farther offshore

laboratory investigation of the impact of lateral spreading on buoyancy flux in a river plume abstractthe relationship between lateral spreading and mixing in stratified gravity currents is investigated by comparing laterally confined and unconfined currents in a series of laboratory experiments the vertical turbulent buoyancy flux is determined using a control volume approach with velocity and density fields derived from combined particle image velocimetry piv and planar laser induced fluorescence plif lateral spreading is determined in the unconfined experiments based on plan view imaging using the optical thickness method otm the authors find that lateral spreading dramatically modifies the plume structure the spreading plume layer consists of approximately linear density and velocity profiles that extend to the surface whereas the channelized plume profiles are uniform near the surface lateral spreading decreases the average plume density relative to laterally confined currents with similar inflow conditions however the local turbulent buoyancy flux in the spreading experiments i

generation of plate tectonics with two phase grain damage and pinning source sink model and toroidal flow abstract the grain damage and pinning mechanism of bercovici and ricard 2012 for lithospheric shear localization is employed in two dimensional flow calculations to test its ability to generate toroidal strike slip motion and influence plate evolution this mechanism posits that damage to the interface between phases in a polycrystalline material like peridotite composed primarily of olivine and pyroxene increases the number of small zener pinning surfaces which then constrain mineral grains to ever smaller sizes regardless of creep mechanism this effect allows a self softening feedback in which damage and grain reduction can co exist with a grain size dependent diffusion creep rheology moreover grain growth and weak zone healing are greatly impeded by zener pinning thereby leading to long lived relic weak zones the fluid dynamical calculations employ source sink driven flow as a proxy for convective poloidal flow upwelling downwelling and divergent convergent motion and the coupling of this flow with non linear rheological mechanisms excites toroidal or strike slip motion the numerical experiments show that pure dislocation creep rheology and grain damage without zener pinning as occurs in a single phase assemblages permit only weak localization and toroidal flow however the full grain damage with pinning readily allows focussed localization and intense plate like toroidal motion and strike slip deformation rapid plate motion changes are also tested with abrupt rotations of the source sink field after a plate like configuration is developed the post rotation flow and material property fields retain memory of the original configuration for extensive periods leading to suboptimally aligned plate boundaries e g strike slip margins non parallel to plate motion oblique subduction and highly localized weak and long lived acute plate boundary junctions such as at what is observed at the aleutian kurile intersection the grain damage and pinning theory therefore readily satisfies key plate tectonic metrics of localized toroidal motion and plate boundary inheritance and thus provides a predictive theory for the generation of plate tectonics on earth and other planets

tropical mountains and coal formation a climate model study of the westphalian 306 ma a global climate model has been used to study the seasonal sensitivity of tropical rainfall and soil moisture to the presence of himalayan scale mountains at tropical latitudes during the westphalian these mountains act to retard the northward progression of the intertropical convergence zone in their vicinity during the northern hemisphere summer such that there is converging low level flow from both the eastern and western panthalassa ocean and an eight fold enhancement of precipitation over the mountains the computed annual cycle of soil moisture for these tropical regions concurs with geologic evidence of extensive coal deposits formed in a broad area at tropical latitudes and only small seasonality in either temperature or precipitation in these areas

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

toward reconciliation of late ordovician 440 ma glaciation with very high co2 levels although phanerozoic glaciations usually coincided with times of estimated low atmospheric co2 the late ordovician 440 ma glaciation is a significant exception co2 levels during that time may have been as much as 10 times greater than present in an earlier paper we suggested that the unique geographic configuration of gondwanaland may explain such a response as the edge of the supercontinent was essentially tangent to the south pole and the moderating effect of the nearby ocean may have suppressed the magnitude of summer warming on the landmass thereby allowing glacial inception one limitation to the earlier study was that it used a linear energy balance model ebm in this paper we further test the above hypothesis in a suite of experiments with a nonlinear ebm that allows for snow albedo feedback we also utilize updated estimates for co2 levels decreases in solar luminosity and variations in orbital forcing baseline experiments with no changes in luminosity or co2 resulted in an ice covered area of 6 3 106 km2 53 of the estimated area covered by the ordovician ice sheet additional experiments for different combinations of orbital forcing 7x 13x co2 and 3 5 5 0 luminosity yielded 0 35 of the estimated ice area in the late ordovician a crude estimate of possible topographic influences increased these numbers to7 47 of total estimated ice area additional factors related to ice sheet growth should increase these values somewhat these results provide additional support for the high co2 glaciation explanation with the caveat that even the partial success occurs only when parameters are at the extreme end of their permissible range the estimated duration of ordovician glaciation is also consistent with the migration of gondwanaland across the south pole with a centrally located pole yielding ice free conditions in the summer thus identical levels of external forcing yield either glaciated or ice free conditions with the solution dependent on location of the landmass although more work is required on this topic our experiments suggest that there may be a relatively parsimonious explanation for this perplexing paleoclimate paradox the results lend further support to the proposition that paleogeography significantly modifies the role of co2 in the long term evolution of climate

numerical climate modeling a frontier in petroleum source rock prediction results based on cretaceous simulations organic productivity and preservation are primary controls of the distribution of petroleum source beds both organic productivity and preservation are in part a function of geographic setting and climate therefore the prediction of paleoclimates is a major frontier in petroleum source rock prediction a climate model based on the fundamental laws thought to govern atmospheric circulation is applied here to the prediction of upwelling regions associated with very high productivity and bottom conditions that may become anoxic despite a high oxygen supply the potential and limitations of climate modeling in the prediction of upwelling regions are examined by 1 demonstrating the ability of the model to predict present day winds and upwelling regions 2 demonstrating t at the model and the location of upwelling regions is sensitive to geography continental positions sea level and topography and 3 investigating whether the model sensitivity to past geographies is realistic i e if predicted upwelling regions for the cretaceous period correspond to source rock localities the model predictions of ocean and coastal upwelling compare very favorably with present day observations and with estimates of primary productivity the location of middle latitude and high latitude upwelling locations are sensitive to model specified geography the location of low latitude upwelling is less sensitive to changes in global geography if coastlines are oriented appropriately despite some limitations a comparison of source rock localities with model predictions is promising the results of these studies suggest that numerical climate modeling is a potential tool in petroleum source rock prediction

cretaceous climate a comparison of atmospheric simulations with the geologic record abstract atmospheric simulations using realistic cretaceous geography 100 million years ago suggest that paleography is an important factor governing the nature of the circulation the simulated cretaceous atmospheric circulations are markedly different both from the present day atmospheric circulation and from the classical hypotheses of a weaker circulation and poleward displacement of circulation features e g the subtropical high therefore they pose specific questions which can be tested against the geologic record aspects of the cretaceous simulations are verified in comparisons with the geologic record the simulations serve to guide areas of future paleoclimatic research and to formulate better the nature of the problem of warm equable climates

high resolution bathymetry estimates via x band marine radar 2 effects of currents at tidal inlets abstract in this second of two papers the high spatial resolution cbathy depth estimate algorithm is extended to account for the existence of currents aligned with the wave directions the extended algorithm is applied using x band radar image time series collected at two hydrodynamically and morphologically complex environments an ebb tidal shoal new river inlet nc and an estuarine river mouth columbia river or wa even without accounting for doppler effects the depth estimates are capable of discerning the location of channels and shoals over domain sizes of 4 km2 at the ebb tidal shoal and 25 km2 at the estuary mouth however the tidal currents at these sites are shown to strongly modulate depth estimate accuracy when only the intrinsic linear wave dispersion relation neglecting doppler shift effects is inverted low pass filtering of the depth estimate time series via an uncertainty weighted tidal average explicitly attenuates the error oscillations beyond that of the uncertainty weighted kalman filter this post hoc method of compensating for the unmodeled doppler term achieves 0 35 m rmse and 0 02 m shallow bias at the shallow ebb tidal shoal as compared to a concurrent sounding survey but substantial bias remains at the estuary mouth due to asymmetric doppler effects for large following or opposing currents at large relative water depths simultaneous estimation of depth and currents via inversion of the dispersion relation including doppler shifts is more effective at the deep estuary mouth where currents more strongly affect the incident wave field in the estuary channel with locations as deep as 27 m kalman filtered depths achieve 0 92 m rmse and 0 38 m deep bias as compared to a concurrent sounding survey 95 of estimates are within 10 of those surveyed independent of the doppler compensation technique kalman filtered depths can be used to more tightly constrain high resolution current velocity estimates

swell dominated carbonates on a mississippian ramp in the canadian rocky mountain front ranges abstract the livingstone formation and the middle opal member of the mount head formation of western canada are mississippian carbonate deposits tens to hundreds of meters thick that are interpreted to have accumulated in a mid ramp wave dominated sub thermocline environment at water depths up to 100 m or more the rocks are predominantly pelmatozoan grainstones and packstones that contain abundant physical sedimentary structures the most common sedimentary structures are planar lamination swaly and hummocky cross stratification and normally graded event beds that are interpreted as having been formed by oscillatory wave currents or oscillatory dominated combined flows the abundant oscillatory currents are interpreted to have been generated by swell waves and to a lesser extent by local storms high angle planar tabular cross bedding is also present in rare discrete beds produced by unidirectional offshore directed currents the unidirectional currents that produced the dunes are interpreted to have been generated by coastal set up that produced downwelling storm currents during the rare storms that occurred along the mississippian coastline it is hypothesized that local storms were not common due to the west coast location and the tropical latitude of the study area instead it is postulated that swell waves approaching from the broad panthalassa ocean to the west were responsible for most sediment remobilization and deposition across the mid and outer ramp swell waves are believed to have resuspended sediment to greater depths than short period less organized storm waves these mississippian deposits suggest that in situ grain production on the ramp without need for the offshore transport of sediment from the shoreface resulted in two major differences from siliciclastic wave dominated settings 1 swaly cross stratification was not restricted to environments shallower than hummocky cross stratification on the upper shoreface because sand size sediment was generated across a large portion of the ramp and 2 aggradation by means other than sediment supply from shallower water caused preservation of deep water swell dominated deposits

the cause of the late cenozoic northern hemisphere glaciations a climate change enigma the ultimate cause of the onset of glaciations remains elusive but in the case of northem hemisphere glaciation it is probable that several factors acted in combination general global cooling resulted from reduction of atmospheric c02 by weathering of silicate rocks exposed by erosion of late cenozoic uplifts uplifts in south asia southwestern north america and scandinavia occurred at distances appropriate for the generation of quasi permanent rossby waves in the atmosphere the resulting winds given suitable moisture sources were favourable for causing large scale precipitation at mid latitudes on the northern continents moisture sources were provided by the closure of the central american isthmus gulf stream flow increased carrying warm subtropical waters to high latitudes the denmark strait deepened permitting greater outflow of deep water from the norwegian greenland sea the relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity studies

climate change on tectonic time scales abstract observational and modeling studies relevant to climate change on tectonic time scales are reviewed probably the most significant climate result from this time scale involves inferences about nearly ice free conditions for some intervals of earth history some additional results suggest relatively rapid transitions between climate states modeling studies indicate that although tectonic changes significantly modify the atmosphere and ocean circulation in most cases such modifications do not appear to be sufficient to explain ice free climates increased atmospheric co2 levels 5 10 presentvalues may be needed to completely reconcile models and data although the co2 paradigm has received widespread attention in the last few years the results summarized herein indicate that co2 is only one of several important factors influencing climate i believe the time is appropriate for contemplating climate change on tectonic time scales in terms of a post co2 synthesis in which direct tectonic factors are approximately equal in importance to co2 fluctuations in the last few years modeling studies have progressed from a state of virtually no work on the topic to one where the models are in some respect ahead of the observations in the sense that data have not been compiled to test even some of the most basic model predictions in particular information is needed on past atmospheric co2 levels tropical sea surface temperatures seasonality of continental interiors and locations and production rates of deep waters initial steps are being taken to integrate observational and modeling activities on tectonic time scales and some of these shortcomings may be rectified over the next few years

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

relation of selected mineral deposits to the mass age distribution of phanerozoic sediments the global mass age distribution of phanerozoic sediment shows maxima in the middle paleozoic at the paleozoic mesozoic boundary and in the late mesozoic all of these total sediment mass maxima are also maxima of masses of volcanogenic sediment and non marine sediment and represent times of maximum sediment flux on the surface of the earth the middle paleozoic and late mesozoic maxima correspond to the great marine inundations of the continents and the late paleozoic early mesozoic maximum to the time of transfer of a large number of terranes across the tethys from gondwanaland to eurasia all three maxima of sedimentary mass correspond to times of rapid sea floor spreading and orogeny

transient tidal circulation and momentum balances at a shallow inlet an analysis of transient momentum balances is carried out to elucidate circulation dynamics and exchange mechanisms at shallow barotropic tidal inlets circulation is computed using a depth integrated fully nonlinear time stepping finite element model with variably spaced grids having horizontal resolution down to 50 m velocity and elevation fields from the model are used to directly evaluate the contribution of each term in the momentum equations to the overall momentum balance a transformation of the x y momentum terms into an s n coordinate system is used to simplify the interpretation of the dynamics and provide vivid illustrations of the forces and resulting accelerations in the flow the analysis is conducted for an idealized inlet and contrasted with a highly detailed model of beaufort inlet north carolina results show that momentum balances in the immediate vicinity of these inlets vary significantly in time and space and oscillate between two dynamical states near maximum ebb or flood the alongstream momentum balances are dominated by advective acceleration pressure gradient and bottom friction cross stream balances are dominated by centrifugal acceleration and pressure gradients near slack balances more closely follow linear wave dynamics with local accelerations balancing pressure gradients and to a lesser degree coriolis comparisons between the idealized inlet and beaufort inlet show broad similarities in these momentum balances however natural inlet geometry and bottom topography as well as the tidal transmission characteristics of the sounds behind beaufort inlet produce strong asymmetries moreover momentum balances are highly localized often with subkilometer length scales the dynamics are used to explain the physical mechanisms for inlet exchange in particular the results indicate that the cross stream dynamics generate a wall along the length of an inlet during the stronger phases of the tide the wall is established by opposing cross inlet pressure gradients and centrifugal forces and it poses a significant barrier to cross inlet exchange during the stronger phases of the tide but is absent near slack

lateral spreading of a near field river plume observations and numerical simulations 1 data collected from the near field region of the merrimack river massachusetts plume were analyzed to examine plume spreading estimates of the plume spreading rate were derived from a direct assessment of the spreading of clustered surface drifters and from density and velocity data along a cross plume arc additionally plume spreading rates were also derived from highly resolved numerical model output roms these three distinct observational and numerical approaches have reasonable agreement and are compared favorably with observations using a control volume approach in a previous study it is demonstrated that these three methods are valid to estimate the plume spreading rate the observations and numerical simulations also allowed estimation of terms in the lateral momentum balance along streamline normals perpendicular to surface layer streamlines one principal finding of this study is that the dominant terms in the lateral momentum balance are the centrifugal force term associated with streamline curvature the buoyancy term the coriolis term and the interfacial stress term furthermore the lateral momentum balance shows that the lateral spreading process is significantly affected by interfacial stress within the first 1 to 2 km but thereafter is locally inviscid however turbulent mixing continues to play an important role in modifying the spreading rate by adjusting the internal wave speed

observations of the frontal region of a buoyant river plume using an autonomous underwater vehicle to characterize the transitional region from the near field to far field of a river plume entering coastal waters we conducted four surveys using an autonomous underwater vehicle auv to target the outflow of the new river inlet north carolina during maximum ebb tide the utilization of a mobile sensor to synoptically observe current velocity data in tandem with natural river plume tracers e g colored dissolved organic matter salinity was essential in understanding the mechanisms driving the observed circulation and mixing patterns within these waters we find that this region is regularly impacted by two primary processes 1 the interaction of an old dredged channel plume with the main discharge and 2 the recirculation of the discharge plume by an eddy that persistently forms between the old channel and main discharge location wind driven processes in the nearshore can enhance the interaction of these two plumes resulting in unstable regions where mixing of the merged plume with the receiving waters is accelerated we also conduct comparisons between auv velocity observations from two surveys and their corresponding velocity outputs from a parallelized quasi 3 d model we conclude that the ability to observe the estuarine outflow transitional region at near synoptic temporal scales and resolutions discussed in this paper is key in providing the mechanisms driving local circulation which is essential for proper parameterization of high resolution numerical coastal models

palaeoclimatic significance of changes in clay mineralogy across the jurassic cretaceous boundary in england and france abstract clay mineralogical changes across the jurassic cretaceous boundary from the northern to the southern part of western europe show similar patterns in the mudrocks exposed on the yorkshire coast the paralic sediments of the dorset wessex basin and the jura and vocontian trough of s e france this comprises a change from smectite poor sediments in the jurassic with correspondingly abundant illite and kaolinite to sediments with abundant smectite in the jurassic cretaceous boundary beds depleted in kaolinite this change occurs in the oxfordian in the south to latest volgian in the north of the study area kaolinite reappears in abundance in the late ryazanian or stratigraphic equivalent in all the locations studied comparison with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest jurassic earliest cretaceous aridity the onset of which appears to be diachronous across w europe possible causes for the climatic change towards aridity are examined the orographic effect of mountains or plateaus to the east of the study area is considered most likely

observations and modeling of a tidal inlet dye tracer plume a 9 km long tracer plume was created by continuously releasing rhodamine wt dye for 2 2 h during ebb tide within the southern edge of the main tidal channel at new river inlet nc on 7 may 2012 with highly obliquely incident waves and alongshore winds over 6 h from release coawst coupled roms and swan including wave wind and tidal forcing modeled dye compares well with aerial hyperspectral and in situ observed dye concentration dye first was transported rapidly seaward along the main channel and partially advected across the ebb tidal shoal until reaching the offshore edge of the shoal dye did not eject offshore in an ebb tidal jet because the obliquely incident breaking waves retarded the inlet mouth ebb tidal flow and forced currents along the ebb shoal the dye plume largely was confined to 4 m depth dye was then transported downcoast in the narrow few 100 m wide surfzone of the beach bordering the inlet at 0 3 m s 1 driven by wave breaking over 6 h the dye plume is not significantly affected by buoyancy observed dye mass balances close indicating all released dye is accounted for modeled and observed dye behaviors are qualitatively similar the model simulates well the evolution of the dye center of mass lateral spreading surface area and maximum concentration as well as regional inlet and ocean dye mass balances this indicates that the model represents well the dynamics of the ebb tidal dye plume details of the dye transport pathways across the ebb shoal are modeled poorly perhaps owing to low resolution and smoothed model bathymetry wave forcing effects have a large impact on the dye transport

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

continental drift and the global pattern of sedimentation the breakup of pangaea through rifting and separation of the continents has special implications for the global pattern of sedimentation the important initial conditions of pangaea are area elevation the nature of the drainage and climate the development of interior uplifts associated with rifting caused significant reorganization of drainage systems rifting and continental breakup result in unique sediment sequences on passive margins

wave driven along channel subtidal flows in a well mixed ocean inlet observations of waves flows and water levels collected for a month in and near a long narrow shallow 3000 m long 1000 m wide and 5 m deep well mixed ocean inlet are used to evaluate the subtidal periods 30 h along inlet momentum balance maximum tidal flows in the inlet were about 1 5 m s and offshore significant wave heights ranged from about 0 5 to 2 5 m the dominant terms in the local across the km wide ebb shoal along inlet momentum balance are the along inlet pressure gradient the bottom stress and the wave radiation stress gradient estimated nonlinear advective acceleration terms roughly balance in the channel onshore radiation stress gradients owing to breaking waves enhance the flood flows into the inlet especially during storms

comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the mesozoic of nw europe this paper reviews the opportunities and pitfalls associated with using clay mineralogical analysis in palaeoclimatic reconstructions following this conjunctive methods of improving the reliability of clay mineralogical analysis are reviewed the mesozoic succession of nw europe is employed as a case study this demonstrates the relationship between clay mineralogy and palaeoclimate proxy analyses may be integrated with clay mineralogical analysis to provide an assessment of aridity humidity contrasts in the hinterland climate as an example the abundance of kaolinite through the mesozoic shows that while interpretations may be difficult the mesozoic climate of nw europe was subject to great changes in rates of continental precipitation we may compare sedimentological facies mineralogy geochemistry indicators of palaeoprecipitation with palaeotemperature estimates the integration of clay mineralogical analyses with other sedimentological proxy indicators of palaeoclimate allows differentiation of palaeoclimatic effects from those of sea level and tectonic change we may also observe how widespread palaeoclimate changes were whether they were diachronous or synchronous how climate sea level and tectonics interact to control sedimentary facies and what palaeoclimate indicators are reliable

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

wave current interactions in a wave dominated tidal inlet 1 wave current interactions play a major role in the dynamics of shallow tidal inlets this study investigates these interactions at a natural inlet with a strong focus on current induced changes on wave propagation the analysis of hydrodynamic data collected at the albufeira lagoon portugal revealed spatiotemporal variations of water levels and wave heights along the inlet attributed to wave current interaction processes we compared the simulations of a coupled wave circulation modeling system computed with and without waves and propagated with and without current feedback the wave induced setup inside the lagoon represented 7 15 of the offshore significant wave height the accuracy of the wave s predictions improved when current feedback was included during ebb the currents increased the wave height at the mouth of the inlet up to 20 and decreased the wave height in the inlet up to 40 due to current induced refraction steepness dissipation and partial blocking during flood the currents decreased the wave height in the inlet up to 10 and increased the wave height at the exterior parts of the ebb shoal up to 10 due to current induced refraction these effects significantly attenuate seaward sediment fluxes during ebb and contribute to the sediment accretion in the inlet

hydrodynamic and sediment transport modeling of new river inlet nc under the interaction of tides and waves the interactions between waves tidal currents and bathymetry near new river inlet nc usa are investigated to understand the effects on the resulting hydrodynamics and sediment transport a quasi 3 d nearshore community model nearcom tvd is used in this integrated observational and modeling study the model is validated with observations of waves and currents at 30 locations including in a recently dredged navigation channel and a shallower channel and on the ebb tidal delta for a range of flow and offshore wave conditions during may 2012 in the channels model skills for flow velocity and wave height are high near the ebb tidal delta the model reproduces the observed rapid onshore offshore decay of wave heights current velocities model results reveal that this sharp transition coincides with the location of the breaker zone over the ebb tidal delta which is modulated by semidiurnal tides and by wave intensity the modulation of wave heights is primarily owing to depth changes rather than direct wave current interaction the modeled tidally averaged residual flow patterns show that waves play an important role in generating vortices and landward directed currents near the inlet entrance numerical experiments suggest that these flow patterns are associated with the channel shoal bathymetry near the inlet similar to the generation of rip currents consistent with other inlet studies model results suggest that tidal currents drive sediment fluxes in the channels but that sediment fluxes on the ebb tidal delta are driven primarily by waves

global atmospheric circulation experiments on an earth with polar and tropical continents two general circulation models forced by mean annual insolation and having an energy balance ocean have been run on an earth with polar continents and a tropical continent polar continents produce strong meridional temperature gradients and a maximum hydrological cycle a tropical continent produces the warmest planet and a minimal hydrological cycle both models produce more arid continents than exist today

the role of morphology and wave current interaction at tidal inlets an idealized modeling analysis the outflowing currents from tidal inlets are influenced both by the morphology of the ebb tide shoal and interaction with incident surface gravity waves likewise the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current the 3 d coupled ocean atmosphere wave sediment transport coawst modeling system is applied to numerically analyze the interaction between currents waves and bathymetry in idealized inlet configurations the bathymetry is found to be a dominant controlling variable in the absence of an ebb shoal and with weak wave forcing a narrow outflow jet extends seaward with little lateral spreading the presence of an ebb tide shoal produces significant pressure gradients in the region of the outflow resulting in enhanced lateral spreading of the jet incident waves cause lateral spreading and limit the seaward extent of the jet due both to conversion of wave momentum flux and enhanced bottom friction the interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume for weak outflows the outflow jet is actually enhanced by strong waves when there is a channel across the bar due to the return current effect for both strong and weak outflows waves increase the alongshore transport in both directions from the inlet due to the wave induced setup over the ebb shoal wave breaking is more influenced by the topography of the ebb shoal than by wave current interaction although strong outflows show intensified breaking at the head of the main channel

self consistent generation of tectonic plates in time dependent three dimensional mantle convection simulations 2 strain weakening and asthenosphere 1 in a previous paper tackley 2000b it was shown that a combination of temperature dependent viscosity and viscoplastic yielding is sufficient to give rudimentary plate tectonic like behavior in three dimensional models of mantle convection here the calculations are extended to include two complexities that have been suggested as being important in localizing deformation at plate boundaries strain weakening and the presence of a low viscosity asthenosphere introducing an asthenosphere by reducing the viscosity by a factor of 10 where material reaches a solidus 1 dramatically improves plate quality even if the asthenosphere is restricted to regions around spreading centers 2 gives good smoothly evolving platelike behavior over a wide range of yield stress values spanning an order of magnitude and 3 gives bimodal stable solutions over a range of yield stresses either immobile lid or plate behavior may be obtained depending on initial condition by contrast introducing an asthenosphere by using depth dependent viscosity has a much smaller effect on system behavior increasing strain weakening 1 improves localization at spreading centers but leads to an increasingly complex network of spreading centers fragmenting the plates 2 weakens convergent zones and can make downwellings highly episodic and 3 does not lead to pure transform boundaries in these calculations time dependent damage evolution and instantaneous strain rate weakening give very similar results all cases that display platelike behavior have very long wavelength mantle heterogeneity consistent with earth s

atmospheric circulation during warm geologic periods is the equator to pole surface temperature gradient the controlling factor paleoclimatologists have hypothesized that the equator to pole surface temperature gradient is a dominant control on the paleocirculation of the oceans and the atmosphere atmospheric simulations using realistic cretaceous 100 m y ago geography are used to examine quantitatively the relationships between paleogeography surface temperature gradients and the nature of the atmospheric circulation these results raise questions concerning the classical theories and interpretations of warm paleoclimates and suggest that paleogeography is an important factor governing the nature of the circulation