nearshore internal bores and turbulent mixing in southern monterey bay 1 we observed transient stratification and mixing events associated with nearshore internal bores in southern monterey bay using an array of instruments with high spatial and temporal resolution the arrival of the bores is characterized by surging masses of dense cold water that tend to stratify the water column the bore is followed by a gradual drop in the temperature throughout the water column over several hours defined here as the bore period until a sharp warm front relaxation followed by high frequency temperature fluctuations returns the column back to nearly its original state defined here as the mixing period mixing periods revealed increased temperature variance at high frequencies n as well as a greater percentage of events where dynamic instabilities may be present ri 0 25 suggesting active mixing of the stratified water column turbulent dissipation rates in the stratified interior during the mixing period estimated using the technique of isopycnal slope spectra revealed mean values the same order of magnitude as near bed bottom generated turbulence observations indicate that local shear produced turbulent kinetic energy by the warm front relaxations dominates mixing in the stratified interior the non canonical nature of these bore and relaxation events is also investigated with a numerical model and the dynamics are shown to depend on the internal iribarren number our results suggest that nearshore internal bores interacting with local bathymetry dramatically alter local dynamics and mixing in the nearshore with important ecological implications

a self similar scaling for cross shelf exchange driven by transient rip currents transient rip currents episodic offshore flows from the surf zone to the inner shelf present a recreational beach hazard and exchange material across the nearshore ocean the magnitude and offshore extent of transient rip current induced exchange and its relative importance to other inner shelf exchange processes are poorly understood here 120 model simulations with random normally incident directionally spread waves spanning a range of beach slopes and wave conditions show that the transient rip current exchange velocity is self similar the nondimensional exchange velocity surf zone flushing time and cross shore decay length scale are scaled by beach slope and wave properties depending strongly on wave directional spread transient rip current driven exchange can be compared to other cross shelf exchange processes for example transient rip current driven exchange is stronger than wave induced stokes drift driven exchange up to six surf zone widths from shore

scale dependent dispersion within the stratified interior on the shelf of northern monterey bay abstractautonomous underwater vehicle measurements are used to quantify lateral dispersion of a continuously released rhodamine wt dye plume within the stratified interior of shelf waters in northern monterey bay california the along shelf evolution of the plume s cross shelf lateral width provides evidence for scale dependent dispersion following the 4 3 law as previously observed in both surface and bottom layers the lateral dispersion coefficient is observed to grow to 0 5 m2 s 1 at a distance of 700 m downstream of the dye source the role of shear and associated intermittent turbulent mixing within the stratified interior is investigated as a driving mechanism for lateral dispersion using measurements of time varying temperature and horizontal velocities both an analytical shear flow dispersion model and a particle tracking model generate estimates of the lateral dispersion that agree with the field measured 4 3 law of dispersion without explicit appeal to any assumed turbulence structure

lateral dispersion over the continental shelf analysis of dye release experiments lateral dispersion over the continental shelf was examined using dye studies performed as a part of the coastal mixing and optics experiment four experiments performed at intermediate depths each lasting 2 5 5 days were examined in some cases the dye patches remained fairly homogeneous both vertically and horizontally throughout an experiment in other cases significant patchiness was observed on scales ranging from 2 to 10 m vertically and a few hundred meters to a few kilometers horizontally the observations showed that the dye distributions were significantly influenced by shearing and straining on scales of 5 10 m in the vertical and 1 10 km in the horizontal superimposed on these larger scale distortions were simultaneous increases in the horizontal second moments of the dye patches with corresponding horizontal diffusivities based on a fickian diffusion model of 0 3 4 9 m 2 s 1 analysis of the dye data in concert with shear estimates from shipboard acoustic doppler current profiler observations showed that the existing paradigms of shear dispersion and dispersion by interleaving water masses cannot account for the observed diffusive spreading of the dye patches this result suggests that some other mechanisms provided an additional diffusivity of order 0 2 4 6 m 2 s 1 an alternative mechanism dispersion by vortical motions caused by the relaxation of diapycnal mixing events may explain the observed dispersion in some cases

sea surface temperature signatures of oceanic internal waves in low winds 1 in aerial surveys conducted during the tropical ocean global atmosphere coupled ocean atmosphere response experiment and the low wind component of the coupled boundary layer air sea transfer cblast low oceanographic field programs sea surface temperature sst variability at relatively short spatial scales o 50 m to o 1 km was observed to increase with decreasing wind speed a unique set of coincident surface and subsurface oceanic temperature measurements from cblast low is used to investigate the subsurface expression of this spatially organized sst variability and the sst variability is linked to internal waves the data are used to test two previously hypothesized mechanisms for sst signatures of oceanic internal waves a modulation of the cool skin effect and a modulation of vertical mixing within the diurnal warm layer under conditions of weak winds and strong insolation which favor formation of a diurnal warm layer the data reveal a link between the spatially periodic sst fluctuations and subsurface temperature and velocity fluctuations associated with oceanic internal waves suggesting that some mechanism involving the diurnal warm layer is responsible for the observed signal internal wave signals in skin temperature very closely resemble temperature signals measured at a depth of about 20 cm indicating that the observed internal wave sst signal is not a result of modulation of the cool skin effect numerical experiments using a one dimensional upper ocean model support the notion that internal wave heaving of the warm layer base can produce alternating bands of relatively warm and cool sst through the combined effects of surface heating and modulation of wind driven vertical shear

modification of fluid inclusions in quartz by deviatoric stress ii experimentally induced changes in inclusion volume and composition fluid inclusions in quartz are known to modify their densities during shear deformation modifications of chemical composition are also suspected however such changes have not been experimentally demonstrated their mechanisms remain unexplained and no criteria are available to assess whether deformed inclusions preserve information on paleofluid properties to address these issues quartz crystals containing natural co2 h2o nacl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90 250 mpa at 700 c and 600 mpa confining pressure the resulting microcracking of the inclusions leads to expansion by up to 20 producing low fluid densities that bear no relation to physical conditions outside the sample nevertheless the chemical composition of the precursor inclusions is preserved with time the microcracks heal and form swarms of tiny satellite inclusions with a wide range of densities the highest reflecting the value of the maximum principle stress 1 these new inclusions lose h2o via diffusion thereby passively increasing their salt and gas contents and triggering plastic deformation of the surrounding quartz via h2o weakening using microstructural criteria to identify the characteristic types of modified inclusions both the pre deformation fluid composition and syn deformation maximum stress on the host mineral can be derived from microthermometric analysis and thermodynamic modelling

cross shore deformation of a surfzone released dye plume by an internal tide on the inner shelf abstractan inner shelf is dye plume that formed following a 3 84 h early morning surfzone sz dye release off of imperial beach california is analyzed with in situ and aerial remotely sensed o

the inner shelf response to wind driven upwelling and downwelling abstract a two dimensional numerical model is used to study the response to upwelling and downwelling favorable winds on a shelf with a strong pycnocline during upwelling or downwelling the pycnocline intersects the surface or bottom forming a front that moves offshore the characteristics of the front and of the inner shelf inshore of the front are quite different for upwelling and downwelling for a constant wind stress the upwelling front moves offshore at roughly a constant rate while the offshore displacement of the downwelling front scales as t because the thickness of the bottom layer increases as the front moves offshore the geostrophic alongshelf transport in the front is larger during downwelling than upwelling for the same wind stress magnitude because the geostrophic shear is near the bottom in downwelling as opposed to near the surface in upwelling during upwelling weak stratification is maintained over the inner shelf by the onshore flux of denser near bottom water this weak stratif

horizontal dispersion of a near bed coastal plume the transport of scalars in the coastal ocean is considered through the analysis of a vertically constrained plume which disperses laterally observations of the plume are made using an autonomous underwater vehicle auv operating in two modes i repeated transects of the plume at a fixed distance from the source and ii a large scale mapping of the plume development together these measurements define both the variability in the plume centreline i e the meandering and the growth of the plume around the centreline i e the relative dispersion the analysis of the measurements suggests that the meandering is well described by a spatially uniform but temporally variable velocity field indicating that large scale flow structures dominate the centreline variability the growth of the plume downstream is seen to follow a scale dependent dispersion law most likely of a compound structure a 4 3 law in the near field and a scale squared law in the far field this transition between dispersion laws is consistent with the transition from three dimensional turbulence structures to two dimensional eddies which is due to the constraints imposed on the vertical dimension at the site comparing the two dispersion processes the effective dispersion created by meandering is found to be comparable with or larger than the relative dispersion in the near field but in the far field the relative dispersion is found to dominate considerations of overall dispersion

direct evidence of deep water intrusions onto the continental shelf via surging internal tides 1 near bottom diurnal thermocline shoaling and diurnal baroclinic currents were observed from time series data of water temperature salinity pressure and velocity collected from august 2006 to january 2007 in the nearshore zone off the huntington beach where the local inertial frequency is higher than the diurnal frequency poleward of the diurnal critical latitude during the stratified season the deep offshore cold dense water when shoaled into shallow water along the bottom was often trapped for a few hours and dissipated in the nearshore region water depth of 10 20 m during the ebb phase of the diurnal surface tide it appears that perturbations propagating onshore along the shoaled isopycnals can form an upslope surging front and an internal bolus our data allow the application of theoretical lab criteria for internal hydraulic jumps internal bolus formation and internal wave breaking and all criteria are fulfilled during a part of the tidal shoaling cycle nonlinear advection associated with the internal boluses causes higher close to 3 spectral falloff rate of near bottom temperature with frequency than the canonical garret munk spectra 2 in the range of 0 1 1 0 cph implying strong scattering of tidal energy toward smaller scales we are able to directly calculate the offshore eddy heat flux by cold water intrusion onto the shelf resulting from this process similar impacts and implications are expected for the biogeochemical quantities as well as for the role of subinertial internal waves on turbulent mixing in the immediate proximity of the generating region i e sloping bottom

physical and biological processes underlying the sudden surface appearance of a red tide in the nearshore the sudden appearance at the surface of an alongshore parallel band of red tide near huntington beach california is described in high spatial and temporal resolution using novel instrumentation including a global positioning system tracked jet ski the scale of the surface chlorophyll a chl a band was small 200 m crossshore and ephemeral 3 h compared with the subsurface extent of the red tide 2 km 7 d the red tide was dominated by the regionally common dinoflagellate lingulodinium polyedrum f stein and had developed as a subsurface chl a layer during the 7 d prior to the surface appearance a few hours before the surface appearance a subsurface patch of elevated chl a chl a 30 m gl 21 was observed in 13 m total depth in the trough of a shoreward propagating internal wave consistent with dinoflagellate vertical swimming interacting with the internal wave driven convergence internal wave breaking induced vertical mixing in 8 m water depth vertically spread the chl a patch to the surface creating the alongshore surface band 500 m from shore both the subsurface chl a patch and the surface chl a band were prevented from entering the surf zone by a density barrier of warm water adjacent to the beach these high resolution observations emphasize the role of nearshore physical dynamics in controlling the duration and intensity of red tide exposure to coastal habitats

transient rip currents and nearshore circulation on a swell dominated beach 1 eulerian and lagrangian measurements of nearshore circulation on a longshore uniform beach with perpendicularly incident swell waves are described both the eulerian and lagrangian data show a variable rotational part of the current field that is distinct from but coexists with that due to infragravity waves a well defined feature of the flow field includes transient rip currents which occur in varying locations and are not topographically controlled drifter trajectories show that the rips behave like a shallow plane jet consisting of a constrained neck region that flows into a spreading head region there is continuous modulation of the flow within the rip neck estimates of the length scale across the rip neck using two particle statistics are 20 30 m well defined discrete vortex features are observed at the initiation point of one of the necks and in one of the rip heads estimated dispersion values suggest that mixing is greatly enhanced outside the surf zone by the intermittent presence of the rip heads the dispersion calculated from both inside and outside the surf zone appears to show scale dependence with a power law close to 4 3 in a similar way to oceanic turbulence at much larger scales

field observations of surf zone inner shelf exchange on a rip channeled beach cross shore exchange between the surf zone and the inner shelf is investigated using lagrangian and eulerian field measurements of rip current flows on a rip channeled beach in sand city california surface drifters released on the inner shelf during weak wind conditions moved seaward due to rip current pulses and then returned shoreward in an arcing pattern reentering the surf zone over shoals the cross shore velocities of the seaward and shoreward moving drifters were approximately equal in magnitude and decreased as a function of distance offshore the drifters carried seaward by the rip current had maximum cross shore velocities as they exited the surf zone and then decelerated as they moved offshore the drifters moving shoreward accelerated as they approached the surfzone boundary with maximum cross shore velocities as they reentered the surf zone over shoals it was found that stokes drift was not solely responsible for the onshore transport across the surfzone boundary the cross shore diffusivity on the inner shelf was greatest during observations of locally contained cross shore exchange these field observations provide evidence that the cross shore exchange between the surf zone and inner shelf on a rip channeled beach is due to wave driven rip current circulations and results in surface material being contained within the nearshore region

scaling surf zone turbulence 1 turbulence in the surf zone the shallow region adjacent to the shoreline has a key role in beach erosion fertilization dispersal and larval settlement of marine invertebrates and microbial contamination dilution in beach waters breaking wave generated the dominant source surf zone turbulence is understood poorly a new surf zone turbulent dissipation rate scaling is derived that collapses new field surf zone observations with relatively high skill compared to other scalings the vertically uniform length scale is 1 6 the water depth and 15 of the wave energy flux gradient is dissipated below the mean surface field and laboratory surf zone turbulence observations are shown to be consistent using the scaling the non dimensional surf zone diffusivity and suspended sediment profile can be applied to sediment transport and a range of biological processes including microbial pathogen contamination of beach waters

inner shelf response to cross shelf wind stress the importance of the cross shelf density gradient in an idealized numerical model and field observations this study investigates the effects of horizontal and vertical density gradients on the inner shelf response to cross shelf wind stress by using an idealizednumericalmodel and observations from a mooredarray deployed south of martha s vineyard massachusetts in two dimensional no along shelf variation numerical model runs of an initially stratified shelf a cross shelf wind stress drives vertical mixing that results in a nearly wellmixed inner shelf with a cross shelf density gradient because of the sloping bottom the cross shelf density gradient causes an asymmetric response to on and offshore wind stresses for density increasing offshore an offshore wind stress drives a near surface offshore flow and near bottom onshore flow that slightly enhances the vertical stratification and the cross shelf circulation an onshore wind stress drives the reverse cross shelf circulation reducing the vertical stratification and the cross shelf circulation a horizontal richardson number is shown to be the nondimensional parameter that controls the dependence of the wind driven nondimensional cross shelf transport on the cross shelf density gradient field observations show the same empirical relationship between the horizontal richardson number and transport fraction as the model predicts these results show that it is the cross shelf rather than vertical density gradient that is critical to predicting the inner shelf cross shelf transport driven by a cross shelf wind stress

infrared imagery of ocean internal waves 1 infrared imaging provides a new way to detect internal waves under conditions where techniques that rely on backscatter from the sea surface may not be effective and it provides a new means to investigate the spatial variability associated with internal waves this is illustrated with imagery collected in a bay under light winds using an airborne infrared camera the internal waves appear as groups of dark and bright bands corresponding to surface temperature fluctuations of about 0 05 c a signal of this size is shown to be plausible based on straining of the water s surface thermal boundary layer cool skin by internal waves having a strain rate of the order of 10 2 s 1 in addition fine scale temperature structure was detected that we speculate may indicate instabilities induced by the internal waves

mechanisms of thrust faulting in the gran sasso chain central apennines italy abstract the gran sasso chain in central italy is made up of an imbricate stack of eight thrust sheets which were emplaced over the upper miocene lower pliocene laga flysch the thrust sheets are numbered from 1 to 8 in order of their decreasing elevation in the tectonic stack and their basal thrusts are numbered from t 1 to t 8 accordingly on the basis of their different deformation features the major thrust faults fall into three groups 1 thrust faults marked by thick belts of incoherent gouges and breccia zones t 1 t 2 t 3 2 thrust faults characterized by a sharp plane which truncates folds that had developed in the footwall rocks t 5 t 6 and 3 thrust faults truncating folds developed in both the hangingwall and footwall units and bordered by foliated fault rocks t 7 the deformation features observed for the different faults seem to vary because of two combined factors 1 lithologic changes in the footwall and hangingwall units separated by the thrust faults and 2 increasing amounts of deformation in the deepest portions of the imbricate stack the upper thrust sheets from 1 to 6 are characterized by massive calcareous and dolomitic rocks they maintain a homoclinal setting and are truncated up section by the cataclastic thrust faults the lowermost thrust sheets 7 and 8 are characterized by a multilayer with competence contrasts which undergoes shear induced folding prior to the final emplacement of the thrust sheets bedding and axial planes of folds rotate progressively towards the t 5 t 6 t 7 and t 8 thrust boundaries and are subsequently truncated by propagation of the brittle thrust faults the maximum deformation is observed along the t 7 thrust fault consistent with horizontal displacement that increases progressively from the uppermost to the lowermost thrust sheet in the tectonic stack the axial planes of the folds developed in the hangingwall and footwall units are parallel to the t 7 thrust fault and foliated fault rocks have developed field data and petrographic analysis indicate that cleavage fabrics in the fault rocks form by a combination of cataclasis cataclastic flow and pressure solution slip associated with pervasive shearing along subtly distributed slip zones parallel to the t 7 thrust fault the development of such fabrics at upper crustal levels creates easy slip conditions in progressively thinner domains which are regions of localized flow during the thrust sheet emplacement

cross shore surfzone tracer dispersion in an alongshore current 1 cross shore surfzone tracer dispersion in a wave driven alongshore current is examined over a range of wave and current conditions with 6 continuous dye releases each roughly 1 2 hours in duration at huntington beach california fluorescent dye tracer released near the shoreline formed shore parallel plumes that were sampled on repeated cross shore transects with a jet ski mounted fluorometer ensemble averaged cross shore tracer concentration profiles are generally shoreline attached maximum at or near the shoreline with increasing cross shore widths and decreasing peak values with downstream distance more than a few 100 m from the source tracer is often well mixed across the surfzone i e saturated with decreasing tracer concentrations farther seaward for each release cross shore surfzone absolute diffusivities are estimated using a simple fickian diffusion solution with a no flux boundary at the shoreline and range from 0 5 2 5 m2 s 1 surfzone diffusivity scalings based on cross shore bore dispersion surfzone eddy mixing length and undertow driven shear dispersion are examined the mixing length scaling has correlation r2 0 59 and the expected best fit slope 1 indicating that horizontal rotational motions are important for cross shore tracer dispersion in the surfzone

circulation and larval distribution in internal tidal bore warm fronts internal tidal bore warm fronts were observed during the summer of 1996 off the coast of southern california warm bore fronts had concentrating currents resulting from high frequency internal motions and from a larger two way flow the two way flow featured surface currents onshore and bottom currents offshore a sharp thermocline depression and high frequency large amplitude internal motions followed the leading edge of the bore with downwelling currents on the trailing side of the crest of the nonlinear internal waves and upwelling currents in front of the crest warm bores propagated onshore with a propagation speed c that ranged from 10 6 to 19 6 cm s 1 while time averaged frontal currents varied from 11 2 to 17 6 cm s 1 in the shallowest bin in one out of three cases c which implied that there were faster currents than the rate of advance of the front and which implied that the origin of surface frontal material is behind the front not in front of it three invertebrate larval taxa were found at all sites across fronts but only two intertidal barnacles pollicipes polymerus and chthamalus spp were concentrated at the front s surface while the subtidal bryozoan membranipora spp was not frontal pollicipes were more concentrated than were chthamalus the frontal downwelling currents observed suggested that concentrated larvae would have to swim upward in order to maintain depth pollicipes were abundant on the offshore warm side of the fronts but were absent or rare on the onshore colder side suggesting that the origin of frontal pollicipes was behind the front although an alternative cannot be ruled out conclusively chthamalus were more abundant at depth than at the surface at all sites except at the front where this pattern was reversed the origin of frontal chthamalus is uncertain membranipora were more abundant on the onshore colder side of the fronts and abundances were usually higher at depth than at surface lack of accumulation in this species may be due to its limited swimming capability

observations and modeling of coastal internal waves driven by a diurnal sea breeze during the internal waves on the continental margin iwaves field experi ments of 1996 and 1997 off of mission beach california 32 75on we observed energetic diurnal band motions across the entire study site in water depths ranging from 15 to 500 rn and spanning a cross shore distance of 15 km the spectral peak of the currents was at the diurnal frequency av 1 cpd and was sufficiently well resolved to be clearly separated from the slightly higher local inertial frequency f 1 08 cpd these motions were surface enhanced and clockwise circularly polarized and had an upward phase propagation speed of 68 m d l suggesting that the motions were driven predominantly by the diurnal sea breeze however the downward energy upward phase propagation seems irrecon cilable with the subinertial diurnal period and moreover the intermittent diurnal current events were not obviously associated with diurnal sea breeze events we rationalize these features using a flat bottomed linear modal sum internal wave model that includes advection and refraction due to subtidal alongshore flow v z t fluctuations in v at the observing site can change the effective local coriolis parameter f vz by as much as 50 thus making the diurnal motions at different times effectively either subinertial or superinertial the model is integrated numerically for 200 days at a latitude of 32 75on under different wind and subtidal flow conditions purely diurnal winds and no v purely diurnal winds and a time independent v narrow band diurnal winds and no v and narrow band diurnal winds and subtidal time dependent v model diurnal currents forced by narrow band diurnal winds and subtidal v show complex offshore structure with realistic intermittency and spectral broadening this study suggests that continental margins in the vicinity of the 30 o latitude where av f are regions that could potentially produce energetic sea breeze driven baroclinic motions and that these motions could be regulated by the vorticity of the local subtidal currents

on the response of a reservoir sidearm to diurnal heating and cooling during the day the shallower regions of a reservoir sidearm absorb more heat per unit volume than the deeper parts leading to a horizontal pressure gradient that drives a circulation in the sidearm at night the shallow regions cool more rapidly leading to a circulation in the opposite direction since the spin up time of a typical sidearm is at least of the same order as a day the flow within a diurnally forced sidearm is principally an inertia buoyancy balance in this paper a diurnally forced sidearm is modelled by periodically forced natural convection in a triangular cavity the periodic forcing enters the model via an internal heating cooling term in the temperature equation reservoir sidearms typically have small bottom slopes and this fact can be exploited to obtain asymptotic solutions of the resulting equations these solutions clearly demonstrate the transition from the viscous dominated flow in the shallows to the inertia dominated flow in the deeper parts in the inertia dominated region the flow response significantly lags the forcing numerical solutions of the full nonlinear problem are consistent with the asymptotic solutions